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the magellanic stream and its leading arm form a massive, filamentary system of gas clouds surrounding the large and small magellanic clouds. here we present a new component-level analysis of the stream's ultraviolet (uv) kinematic properties using a sample of 39 sightlines through the magellanic system observed with the cosmic origins spectrograph on the hubble space telescope. using voigt profile fits to uv metal-line absorption, we quantify the kinematic differences between the low-ion (si ii), intermediate-ion (si iii), and high-ion (si iv) absorption lines and thereby investigate the phase structure of the stream. unexpectedly, we find that in the stream the si ii, si iii and si iv all show indistinguishable b-value distributions, being dominated by narrow (b<25 km/s) components. however, the leading arm shows very different kinematic properties, with the high ions tending to be much broader than the low ions. these results support a single-phase model for the stream but require a multi-phase model for the leading arm. this provides further evidence for the galactic center flare model of bland-hawthorn et al. (2013, 2019), in which a burst of ionizing radiation photoionized the stream up to c iv as it passed below the south galactic pole where the flux of escaping ionizing radiation is high, but not the leading arm, which is shielded from the flare's ionization cone. the galactic center flare scenario can explain the origin of the giant x-ray/gamma-ray fermi bubbles at the galactic center, and is now supported by several independent lines of evidence, including the stream's observed h-alpha emission, uv line ratios, and uv kinematics. | kinematics of the magellanic stream and the imprint of a galactic center flare |
supernovae (sne) of type ib/c are believed to mark the deaths of massive stars that are stripped of their hydrogen (type ib), and possibly helium (type ic), envelope before explosion. this proposal focuses on a particular sub-class of ib/c sne called broad-line (bl) type ic, that provide us with a special window into the rarer-still engine-driven explosions known as long duration gamma-ray bursts (grbs). we propose to observe with chandra the 3 radio luminous bl-ic sne that we expect to discover with the zwicky transient facility (ztf) and the karl g. jansky very large array (vla) during chandra cycle 19. with ztf+chandra+vla, we can diagnose the fundamental physics of particle acceleration in sn shocks, and probe the cosmic-ray-dominated shock scenario. | unraveling the physics of engine-driven sne with ztf+chandra |
the calorimetric electron telescope (calet) is a payload on the international space station (iss). calet has been observing cosmic rays and gamma-rays since october 2015. the calorimeter (cal), the primary instrument of calet to observe cosmic rays and gamma-rays directly in space, has collected gamma-ray data for more than five years, and bright gamma-ray sources can be seen in cal data. the calet gamma-ray burst monitor (cgbm), a secondary instrument for gamma-ray bursts (grb) observation, has detected more than 230 grbs in five years of observation. in this work, we present calet results of gamma-ray observations, including grb observations, from five years of operation. | five years of gamma-ray observation with calet |
magnetic field plays an essential role in the plasma dynamics and particle acceleration in high-energy astrophysical systems. polarization offers a direct view of the magnetic field morphology and evolution in these systems. a regime yet to be explored is the high-energy polarimetry. mev polarimetry offers unique insights into the origin of extragalactic cosmic rays and neutrinos, as well as extreme particle acceleration processes therein. in this presentation, i will talk about scientific potentials for mev polarimetry, focusing on blazars, gamma-ray bursts, and pulsars. future gamma-ray mission with polarimetry capability, such as the newly selected gamma-ray small explorer cosi, and the amego-x that is under proposal phase, will open up this new window, bringing unprecedented scientific discoveries. | scientific potentials for mev polarimetry |
this technology advancement proposal will develop already mature silicon (si) technologies in ground-based detectors for use on space-based instruments. the particle physics community is developing monolithic (combined readout and detector medium) cmos (complementary metal-oxide-semiconductor) si pixel detectors with improved spatial resolution and lower power requirements per channel. we plan to leverage the expertise in the ground-based development of these high-spatial-resolution pixel detectors and optimize them for space-based future gamma-ray and cosmic-ray missions. the goal is to increase the technical readiness level (trl) of monolithic cmos si pixel sensors from 4 to 5 enabling their use on future space-based gamma-ray and cosmic-ray missions supported by the astro2020 decadal survey. the goals of this proposal are: 1) acquire monolithic silicon pixel detectors designed for the ground-based atlas experiment. for the first time, we will use these detectors to observe gamma-rays in the kev range to measure their performance. 2) leverage our team's expertise to design a silicon pixel detector (astropix) based on the technology developed for the atlas experiment, but optimized for a medium energy gamma-ray telescope. the same technology will be suitable for multiple space-based applications. 3) characterize, package and integrate the detectors for a beam-line test to demonstrate the ability to reconstruct gamma-ray events. 4) this technology will enable a suite of future missions from smallsats to probe scale. the science drivers encompass extreme astrophysics such as: 511 kev emission at the galactic center, nuclear lines in the galaxy, and the prompt emission (gamma-ray bursts) from neutron star mergers | astropix: developing silicon pixel detectors for gamma-ray and cosmic-ray astrophysics |
we describe glowbug, a gamma-ray telescope for bursts and other transients in the 30 kev to 2 mev band. it was recently funded by the nasa astrophysics research and analysis program, with an expected launch in the early 2020s. similar in concept to the fermi gamma burst monitor (gbm) and with similar sensitivity, glowbug will join and enhance future networks of high-energy telescopes to increase sky coverage and detection efficiency for cosmic gamma ray bursts. from its platform on the international space station, glowbug will also have significant sensitivity to terrestrial gamma-ray flashes (tgfs), the sub-millisecond bursts of gamma rays and relativistic electrons from thunderstorms. we describe the instrument and its capabilities to study these energetic transients. | glowbug, a gamma-ray telescope for bursts and other transients (including tgfs!) |
the new field of multi-messenger astrophysics adds gravitational waves to the detection of electromagnetic signals, enabling us to gain previously unavailable insights about our universe. it started with the detection in multiple wavelengths of the neutron star merger (gw/grb 170817a), and proved its extraordinary potential in answering fundamental questions about the characteristics of neutron stars. the promise of mma can be realized only with accurate theoretical models to decode the many unknown mechanisms leading to powerful electromagnetic signals such as fast radio bursts, cosmic jets, and gamma ray bursts that might be present during the merger. this work seeks to discern the role played by the magnetic field geometry and strength, equation of state and mass ratio during the chaotic dynamics of the merger, in generating or shutting off detectable multi-messenger signals from binary neutron star collisions. specifically, we carry out numerical simulations of realistic binary neutron stars, to investigate the key factors responsible for steering the production of detectable electromagnetic counterparts to the gravitational wave signals. this work addresses also the reproducibility of results by using publicly available, open-source software and documenting the workflow, which will enable researchers and students to regenerate the same findings and produce new results. this research was supported in part by the national science foundation under grant no. nsf phy-1748958 and by the national science foundation award no. iia-1458952.. | numerical simulations of realistic binary neutron stars |
hurley was known for his discovery of transient repeating gamma ray bursts, which are now identified as magnetars. he also was the principal investigator for the solar and cosmic gamma-ray burst experiment aboard nasa's ulysses mission. | obituary: kevin c. hurley (1942-2021) |
the nuclear spectroscopic telescope array (nustar) has enabled studies of the local active galactic nuclei (agn) to extend into the spectral window above 10 kev with unprecedented spatial resolution and two orders of magnitude better sensitivity than any other instrument operating in that energy range. as a part of its long-term extragalactic program nustar is surveying the nearby population of agn detected at hard x-ray energies by the swift burst alert telescope (swift/bat). i will present spectroscopic results based on nustar and swift observations of ~150 swift/bat agn surveyed in the first three years of nustar operation. this sample forms an atlas of the highest quality hard x-ray spectra available to date for a large number of agn, providing unprecedented insight into the variety agn spectra in the hard x-ray band. in addition to phenomenology, which is an essential ingredient of cosmic x-ray background studies, it is possible to use new fitting models to directly probe the geometry of the toroidal obscurer (torus). its main spectral features lie within the nustar bandpass, making it possible to test the common assumption that a similar compton-thick torus exists around essentially every seyfert-type agn. i will discuss torus geometry constraints based on the x-ray spectra in relation to those from other wavelengths, the effects on interpretation of high-redshift agn observations, and the limitations of the current results. | obscuring torus geometry from the nustar survey of swift/bat agn |
superconducting qubits suffer from decoherence caused by phonons in the substrate with energies higher than the superconducting bandgap. while radiation backgrounds and cosmic rays produce large bursts of athermal phonons that causes catastrophic whole-chip failures, other sources, such as stress in films and chip packaging, produce lower energy phonon bursts more frequently. cryogenic calorimetric sensors have achieved similar sensitivities to these phonon events. specifically, in transition edge sensor (tes) based dark matter detectors, these events are the limiting background for low-mass dark matter searches. there is a strong synergy between detector r&d and quantum computing. i will discuss our efforts to reduce the phonon background by reducing stress in our detectors. the same ideas apply to quantum computing; in addition, qubits can be cloaked from phonons with suspending structures and phonon-reflective coatings. we use superconducting resonators to study the effectiveness of these methods. | reducing phonon backgrounds for quantum computing and cryogenic calorimeters |
terrestrial gamma ray flashes (tgfs) are bursts of high-energy photons lasting less than 100 μs [fishman et al., jgr, 116, a07304, 2011]. they are produced in common thunderstorms [e.g., chronis et al., bams, 97, 639, 2016 ; splitt et al., jgr, 115, a00e38, 2010] and briggs et al. [jgr, 118, 3805-3830, 2013] estimated in 2013 that more than 400,000 fermi-gbm detectable tgfs are produced each year on earth. with a typical production altitude between 10 and 15 km [cummer et al., grl, 38, l14810, 2011; grl, 41, 8586-8593, 2014; grl, 42, 7792-7798, 2015], tgf sources are close to commercial flight altitudes, and therefore these high-energy events could represent an additional exposure to ionizing radiation for aircraft passengers and aircrews [dwyer et al., jgr, 115, d09206, 2010]. in a recent work, we showed that doses delivered by gamma rays have been seemed to be relatively low, whereas extremely high doses have been estimated to be delivered in the electron acceleration region although in compact areas (hundreds of meters of radius) [pallu et al., jgr, 126, e2020jd033907, 2021]. currently, in most of the countries, the monitoring of aircrews exposure, mainly driven by cosmic rays, is performed by software, but these systems ignore the possible tgf contribution. therefore, the need for a thorough risk assessment associated with tgfs for aircraft passengers and aircrews is called for by the predicted doses. in this work, we present a statistical study using tgf data from the first fermi-gbm tgf catalog [roberts et al., jgr, 123, 4381-4401, 2018] and both simulated and real commercial flight routes, in order to estimate an upper bound of the probability for a commercial flight to find itself in a tgf electron acceleration region and draw conclusions about the overall risk incurred by aircrews. | radiation risk assessment associated with tgfs for aircraft passengers: estimations of the probability for a commercial flight to be hit by a tgf |
one of the goals of nuclear astrophysics is to understand the various astrophysical events occurring in the cosmos. the most common stellar explosions observed in our galaxy are typei x-ray bursts (xrb1). the isotopic abundances obtained from the astrophysical models of xrb1 depend strongly on a number of nuclear reaction rates, occurring both on the surface and inside the crust by the buried ashes. the nuclear burning that creates these ashes is called the rapid proton (rp) capture process. investigating the rp process enhances our understanding of the dynamics of neutron stars and features of xrb1 spectra. the nuclear reaction flow of the rp process is sensitive to the β+ decay properties of the nuclei involved, and the experimental study of such properties is of significant importance. in this study, total absorption spectroscopy (tas) analysis was performed for the 60ga(β+)60zn decay. this experiment was performed at the national superconducting cyclotron laboratory (nscl). in this presentation, the extracted beta feeding intensity will be discussed, along with a comparison to theoretical shell model and qrpa calculations. | study of the 60ga(β+)60zn decay of for the astrophysical rp process |
gamma-ray bursts (grbs) are some of the most energetic explosions in the universe, releasing energies on the order of 1052 ergs, within a fraction of a second to minutes in the form of gamma rays. to understand the intrinsic properties of these bursts we must first determine the distance at which these bursts occur using what is known as the cosmological redshift. here we present a purely probabilistic approach to estimating the redshifts of 1366 long-duration grbs (lgrbs) as observed by the burst and transient source experiment (batse). this is accomplished through a careful selection and modeling of the 5-dimensional space of redshift and the four intrinsic prompt gamma-ray emission properties: the isotropic 1024ms peak luminosity (liso) , the total isotropic emission (eiso) , the spectral peak energy (epz) , as well as the intrinsic duration (t90z) , while simultaneously taking into account the affects of the detector mechanism of batse and sample incompleteness in our dataset. we make two fundamental assumptions in our work: 1. lgrbs trace, either exactly or closely, the cosmic star formation rate and 2. the joint 4-dimensional distribution of the aforementioned prompt gamma-ray emission properties are well-described by a multivariate log-normal distribution. the results of our work are vastly different from those of other works, likely due to the affects of the detector threshold and sample-incompleteness on shaping the previous phenomenologically-proposed high-energy correlations in the literature. | a probabilistic approach to estimating the unknown redshifts of batse catalog long-duration gamma-ray bursts |
our sample includes only the redshift-known long grbs observed with swift/bat from 2005 january to 2015 april. low-luminosity grbs are excluded since they may belong to another distinct population (e.g., chapman et al. 2007mnras.382l..21c; liang et al. 2007apj...662.1111l; lu et al. 2010apj...725.1965l). although the durations of some grbs, such as grb 050724 and grb 060614, are larger than 2s, we do not include them in our sample since they may be from merger of compact stars (berger et al. 2005natur.438..988b; gehrels et al. 2006natur.444.1044g; zhang et al. 2007apj...655l..25z, 2009apj...703.1696z). the afterglow and host galaxy observations of the high-z sgrb grb 090426 (t90=1.2s) show that it may be from the collapse of a massive star (antonelli et al. 2009a&a...507l..45a; xin et al. 2011mnras.410...27x). we thus include this grb in our sample. we finally obtain a sample of 258 grbs. they are reported in table 1. (1 data file). | vizier online data catalog: cosmic evolution of long gamma-ray burst luminosity (deng+, 2016) |
the largest amount of antineutrinos detected about the earth is emitted by the natural radioactive decays of 232th and 238u chains isotopes and of 40k. other flux components are yielded by cosmic rays interactions in the atmosphere or by possible extra-terrestrial sources such as supernovae explosions, gamma ray bursts, gw events and solar flares. this contribution is aimed to summarise the results obtained by the borexino experiment about antineutrinos from the earth and from extraterrestrial sources. | study of antineutrinos from the earth and the cosmos with the borexino detector |
using the texas petawatt laser (tpw) to irradiate thick au and pt targets at 1021 w.cm-2 and above, we have created high-density, short-pulse (100 fs) electron, positron and gamma-ray jets with in-situ physical parameters comparable to those found in cosmic gamma-ray bursts. for cm-sized targets, we discover that the hot electron emission is suppressed near the target normal direction, while the positron emission is not. this leads to the creation of angle-selected positron-dominated jets, which have many applications. we will present the results from both experiments and computer simulations, and discuss potential future applications. | creating laboratory gamma-ray bursts with 1021 w.cm-2 laser |
gamma-ray bursts (grbs) are detected in a broad redshift range. the cosmic evolution of grb luminosity is essential for revealing the grb physics and using grbs as cosmological probes. we characterize the intrinsic cosmological evolution of long grb luminosity as l=l0 (1+z)^k, and measure the k value with the non-parameterized tau statistics using a large and uniform sample of 231 redshift-known grbs observed with swift/bat in 10 operation years. we find that the observed correlation between l and (1+z) is due to the observational selection effect and do not find robust evidence for intrinsic relation between l and (1+z) derived from current sample. in addition, we also confirm this result with simulations by assuming that the long grb rate follows the star formation rate incorporating with cosmic metallicity history. | cosmic evolution of long gamma-ray burst luminosity |
γ-ray astronomy in the energy range from mev to gev can provide a unique detection window for γ-ray bursts and other transient sources, fundamental information on particle acceleration mechanisms, mev-blazar population studies up to z ~ 4.5, and a full overview of line emission from cosmic-ray interaction. silicon-based pair tracking telescopes rely on γ-ray conversion into an electron-positron pair and its tracking using a stack of silicon strips. the method presented in this work is based on a rauch-tung-striebel smoother. its internal kalman filter enables keeping multiple hypotheses about particle tracks and implementing statistically meaningful measurement selection among hits on different planes of the tracker. the algorithm can be easily configured to work with different tracker geometries and mass models. it can be used for the exploitation of data from past and current γ-ray missions as well as to assess the performances of new pair-tracking telescopes. the proposed method has been validated on astrorivelatore gamma a immagini leggero data and then used to investigate the performances of both e-astrogam and all-sky-astrogam telescopes. the algorithm efficiency and its accuracy in estimating both the photon direction and energy were evaluated on γ-ray events simulated at different energies in the range between 30 mev and 3 gev. the point-spread function of each tracker was then compared with its angular resolution limit showing both the expected performances of the instrument and the margin of improvement that could be obtained by optimizing the reconstruction method. | a multimission method for the reconstruction of gamma-ray events on silicon tracker pair telescopes |
mhd turbulence describes dynamics of astrophysical plasmas on large scale. it is characterized by energy transfer between different scales and the exchange of energy with nonthermal population - typically cosmic rays. recent progress in theory regarding almost all basic regimes of turbulence - from the dynamo to the decaying case and the asymptotic scaling laws, allowed us to proceed with more observationally motivated questions. one of them is why almost all strongly magnetized environments are indeed observable, e.g. why such environments are infused with high-energy particles, their distributions stretching to energies orders of magnitude higher than thermal. it turns out that there are generic mechanisms of acceleration in turbulence, both second and first order in v/c, the latter was somehow unnoticed. these generic mechanisms may explain the ubiquity of non-thermal tails in various magnetized astrophysical environments, e.g. solar chromosphere, pulsar magnetospheres, jets from supermassive black holes, gamma-ray bursts, etc. | particle acceleration in mhd turbulence |
short-duration gamma-ray bursts are supposed to be stellar explosions having t_{90} duration less than 2 sec. the duration t_{90} is defined as he time over which a burst emits from 5% of its total measured counts to 95%. these bursts were observed so far at comparatively lower redshifts (z < 1.5) and lower energies (e{_γ},iso < few ×10^{51} erg) than those observed in case of long-duration gamma-ray bursts in general. due to lack of associations of these bursts with the supernova collapse, studies were conducted to probe their origins and a new model called compact binary merger model was proposed with higher acceptance as compared to several other models. study about these energetic cosmic events have far-reaching astrophysical implications recently. considering the longitudinal advantage of india, the upcoming 3.6 m telescope at devasthal is an unique facility to study these events in great detail. | short-duration gamma-ray bursts |
studying the components of the universe has been a mesmerizing topic of study for many years. with constant evolvement to the knowledge humans possess today, it is important to continue discovering and revising what is known about the universe. cosmic rays are energized subatomic particles that persistently burst through earth's atmosphere from all directions at nearly the speed of light. to further elaborate not only are there few definite conclusions as to where cosmic rays originate, it is suspected that cosmic rays may have an influence on earth's temperature and possibly release radiation . hence, how it is important to investigate the mystery surrounding cosmic rays to better understand their influence. the method of study to this research is unique not because it used data collected from neutron monitors, but because data was also used to analyze correlations in earth's environment; such as temperature and weather. if there is an overall increase or decrease in scale value of cosmic rays then there will be a change in earth's environment because of the increase or reduction of cosmic rays. accordingly, the purpose of this experiment is to identify how cosmic rays have influenced earth's environment. | measuring cosmic rays and their effect on the atmosphere |
until the discovery of gamma-ray bursts, supernovae were the most powerful explosions known in the universe. supernovae have a long history in the astronomy community with both detailed observational and theoretical studies focused on pinning down the engines to these cosmic explosions. gamma-ray bursts are more exotic (associated with a short burst of gamma-rays) and rare (1,000-10,000 times less frequent than supernovae) than supernovae. discovered in the late 1970s, the exotic nature of these bursts led to a rapidly growing list of proposed models (in the hundreds) to explain the engine powering them. how do we determine which of these engines is correct? here we take lessons learned from the search for the supernova engine and apply them to the gamma-ray bursts phenomenon. | understanding the engines behind cosmic explosions: advice from willem of occam and t.h. white |
gamma-ray bursts represent unique tools to study the early phases of cosmic evolution, the formation of the first stars and galaxies. absorption line spectra of these sources located in the epoch of reionization might provide us with key information about these remote, and yet fundamental, stages of cosmic history. i will briefly review these issues, highlighting the immense leap that the theseus mission could represent for finding answers to the many fundamental open questions. | first stars, reionization and gamma-ray bursts |
long -ray bursts (grbs) have been found in association with supernovae (sne) since the emblematic case of the grb 980425/sn 1998bw. the grb emission can be detected up to and their sn counterpart has been observed up to . correlations between grb-sn observables could be useful, e. g. in determining extragalactic distances and intrinsic luminosities, if it was not for the large diversity of grb-sn observations. with a sample of 30 grb-associated sne from the literature, i selected those having observations in at least two filters. i developed a novel methodology to derive an accurate rest-frame sn brightness. using parameters of the grb emission and the sn itself, i evaluated different correlations. i found that using the grb peak spectral energy and the sn light-curve width proves promising to standardize the sn luminosity. i demonstrated that grb-sne can determine distances with 11 -15 precision. these results unfold new opportunities to exploit grb-sne to probe the cosmic expansion of the universe. | correlations for cosmology from the homogenization of grb-associated supernova observations |
the relec scientific instrumentation onboard the vernov spacecraft launched on july 8, 2014, included the drge gamma-ray and electron spectrometer. this instrument incorporates a set of scintillation phoswich detectors, including four identical x-ray and gamma-ray detectors in the energy range from 10 kev to 3 mev with a total area of 500 cm2 directed toward the nadir, and an electron spectrometer containing three mutually orthogonal detector units with a geometry factor of 2 cm2 sr, which is also sensitive to x-rays and gamma-rays. the goal of the space experiment with the drge instrument was to investigate phenomena with fast temporal variability, in particular, terrestrial gammaray flashes (tgfs) and magnetospheric electron precipitations. however, the detectors of the drge instrument could record cosmic gamma-ray bursts (grbs) and allowed one not only to perform a detailed analysis of the gamma-ray variability but also to compare the time profiles with the measurements made by other instruments of the relec scientific instrumentation (the detectors of optical and ultraviolet flashes, the radio-frequency and low-frequency analyzers of electromagnetic field parameters). we present the results of our observations of cosmicgrb 141011a and grb 141104a, compare the parameters obtained in the gbm/fermi and konus-wind experiments, and estimate the redshifts and e iso for the sources of these grbs. the detectability of grbs and good agreement between the independent estimates of their parameters obtained in various experiments are important factors of the successful operation of similar detectors onboard the lomonosov spacecraft. | cosmic gamma-ray bursts detected in the relec experiment onboard the vernov satellite |
photoionization fronts play an important role in many astrophysical environments, including the development of galactic structure at the end of the cosmic dark ages and the formation of stellar-wind bubbles around o-type stars. despite their importance, predictions of photoionization front behaviour have yet to be tested in laboratory experiments. we present designs for a new experimental platform for studying photoionization fronts using the magpie pulsed-power facility (1 ma, 500 ns). a wire array z-pinch will be used to produce an intense burst of x-rays (104 j in 20ns) which will drive a photoionization front through a target. the target, a vaporised al wire expanded to 1018 - 1019 cm-3, will be driven by a separate generator (10ka, 20ns). front properties will be diagnosed using 2-color laser interferometry, thomson scattering and x-ray absorption spectroscopy. supported by epsrc grant no. ep/n013379/1, and by the us doe awards no. de-f03-02na00057, de-sc-0001063, and de-na-0003764 and first light fusion ltd. | design of a pulsed-power driven platform to study photoionization fronts in the laboratory |
several factors contribute to the emergence and development of life on planets. in addition to local factors (e.g. intrinsic planetary properties and host-star characteristics), planetary habitability can be influenced by the larger scale radiation environment of the galaxy. powerful astrophysical transient sources of high energy radiation, like gamma ray bursts (grbs) and supernovae (sne), can be life-threatening and potential cause of mass extinctions. a typical grb at one kiloparsec distance from a planet with an earth like atmosphere would destroy most of the ozone layer, expose the biota to harmful uvb radiation from the parent star, and trigger global cooling (due to the increase of the no2 atmospheric concentration). indeed, the late ordovician mass extinction event (~440 million years ago) may have been caused by a grb. grbs are approximately 106 times more energetic than sne but their rate is ~10,000 times lower. both classes of transients share a stellar origin, either from the core collapse of very massive stars or from binaries of compact objects. the rate of both classes is higher in environments characterized by intense star formation. however, long grbs prefer relatively low metallicity star forming sites. moderately metal polluted regions seem to be the preferred sites for the formation of earth-like planets potentially suited to harbour lifeforms. therefore, the threats posed by grbs and sne to the emergence and development of life in the milky way depend in a not obvious way on the past 12 billion years of evolution of the star formation rate (fig. 1), and relative metal pollution of the interstellar medium (fig. 2). on these grounds, we identify where and when, in the galaxy, life had the best chances of success against lethal cosmic explosions. we model the lethal effect of grbs and sne by scaling their cosmic rates to the mw. grbs and all sne rates are proportional to the gas to stars conversion rate within galaxies. in the galaxy the conversion of gas into stars increased over the past 12 billion years from the center towards the outskirts. metallicity of newly born stars followed a similar inside-out evolution (fig. 1 and 2). at different epochs, the number of lethal events as a function of the distance from the center of the galaxy (fig. 3) is computed by scaling the cosmic rate to the mw evolving properties (i.e. star formation and metallicity). in the early stages of the mw evolution (from its formation up to 6 billion years ago) the largest portion of the galaxy out to 10 kpc from the center was unsuitable to life growth due to the high frequency of lethal events (i.e. > 30 every 500 million years). although the mw outskirts appear as a safer place to live (green contours in fig.3), the low density (<0.1 pc2 ) of terrestrial planets around stars of spectral type fgk and m (dashed and solid blue contours in fig.1) makes life emergence comparatively unlikely. starting around 6 gyrs ago, owing to their energetics, long grbs became the dominant lethal sources for life within the mw, with an increasing number of lethal events towards the galaxy periphery (red-to-orange contours in fig. 3). this is due to the increased conversion rate of relatively low metal polluted gas into massive stars in the outer regions of the mw. such a global trend determined the formation of an increasingly larger, safer region of the mw centered around 3 kpc (green contours in fig. 3) where biological complexes could possibly develop on the large population of terrestrial planets present there. the role of grbs and sne in the evolution of life within the last 500 myrs in our galaxy is shown in fig. 4. up to 2.5 kpc from the center the inhabitability of the mw is due to the high rate of short grbs and sne. long grbs make the outskirts of the galaxy similarly unsafe, leaving a region between 2.5 and 8 kpc as the best place where biological systems had time to develop. we estimate ~1 long grbs occurred in the last 0.5 gyrs within a few kpc from the sun, an event possibly associated with the late ordovidcian mass extinction. search for exoplanets harbouring lifeforms should have more chances of success looking in the direction of the galactic center, within 5.5 kpc from the sun, due to the combined effect of high density of terrestrial planets and of low occurrence of lethal transients. | the best place and time to live in the milky way |
cosmological models with different equations of state from the λ cold dark matter (λcdm) are at the center of the debate between the data of sne type ia and the planck data from the cosmic microwave background. thus, adding cosmological probes observed at high redshift is desired. gamma-ray bursts (grbs) are ideal candidates for investigating the expansion of the universe at high redshift, due to their high luminosities. however, it is challenging using grb correlations between luminosities and a cosmological independent variable, because grb luminosities vary widely. we corrected a tight correlation between the rest-frame end time of the plateau, its corresponding x-ray luminosity, and the peak prompt luminosity, the so-called fundamental plane relation, for the jet opening angle. its dispersion is 0.02 ± 0.04 dex, 94.12% less than the isotropic fundamental plane relation. this is the smallest scatter compared to any current grb correlation. this shows that grbs can be used as standard candles. our results on the universe matter content and the equation of state using grbs are in 1 σ with the values obtained with sne ia only, but at much larger redshift (up to z=5). | gamma-ray bursts cosmology with the x-ray fundamental plane relation |
we present summary results from the first catalog of terrestrial gamma-ray flashes (tgfs) detected with the gamma-ray burst monitor (gbm) on the fermi space telescope. the catalog reports parameters for over 2700 tgfs. since the launch of fermi in 2008 the tgf detection sensitivity of gbm has been improved several times, both in the flight software and in ground analysis. starting in 2010 july individual photons were downloaded for portions of the orbits, enabling an off-line search that found weaker and shorter tgfs. since 2012 november 26 this telemetry mode has been extended to continuous coverage. the tgf sample is reliable, with cosmic rays rejected using data both from fermi gbm and from the large area telescope on fermi. the online catalog include times (utc and solar), spacecraft geographic positions, durations, count intensities and bayesian block durations. the catalog includes separate tables for bright tgfs detected by the flight software and for terrestrial electron beams (tebs). | the first fermi gamma-ray burst monitor (gbm) terrestrial gamma-ray flash (tgf) catalog |
a particularly impressive far-ultraviolet flare (corresponding to a goes x25,000-class event: 50 is largest ever recorded on the sun) was captured serendipitously by hubble's cosmic origins spectrograph, during a campaign on young (~50 myr) solar analog ek draconis. the large outburst was like a classical solar 2-ribbon flare: it lasted several hours and all the atmospheric temperature regimes -- from c ii (30,000 k) through c iv (100,000 k), and up to fe xxi (10 mk) -- were affected simultaneously. scaling laws suggest that the ek dra event was in the upper echelons of the historical sample of stellar high-energy outbursts, but the first to be captured in the fuv with the unprecedented sensitivity, spectral resolution, and high time cadence of an instrument like cos. remarkably, time-resolved line profiles of hot species like si iv and c iv displayed strong, highly redshifted components during the event; contrary to the blueshifts one might naively anticipate from an isotropic stellar explosion. instead, the conspicuous redshifts probably are signatures of a post-flare cooling process, analogous to "coronal rain" or "super-arcade downflows" associated with large solar events. flares of this magnitude probably are common on young hyperactive sunlike stars, occurring perhaps twice a day on ek dra itself. the transient doses of fuv radiation probably are not a significant impediment to planetary habitability, compared with the "quiescent" fuv output of the star (if you can call an object with 1000 times the x-ray luminosity of the sun "quiet"), but the associated very hard x-ray and γ-ray fluences could have a much larger impact on the ionization of a primitive planetary atmosphere, boosting its exposure to gas-stripping by stellar winds or coronal mass ejections. | a giant far-ultraviolet flare on young solar analog ek draconis |
episodic eruptions of accretion disks of agns (and blazars) due to the magneto-rotational-instability are related to the excitation of intense alfven waves and their subsequently mode converted em pulses. these intense pulses are related to the emission of bursts of gamma rays and extreme high energy cosmic ray (ehecr) genesis in agn and blazars. wakefield acceleration and pondermotive acceleration of electrons give rise to gamma ray emissions of the above through synchrotron radiation which can undergo inverse-compton scattering to attain high x-ray energies. we study additional emissions of gamma rays by the betatron oscillations and qed radiative processes in the intense accelerating fields. supported by the norman rostoker fund. | high energy photon emission from wakefields and its signatures in astrophysical blazars |
gamma-ray bursts constitute one of the most fascinating and relevant phenomena in modern science, with strong implications for several fields of astrophysics, cosmology and fundamental physics. in this short review, i focus on the prospective key-role of grbs for cosmology. indeed, the huge luminosity, the redshift distribution extending at least up to z <" 10 and the association with the explosive death of very massive stars make long grbs (i.e., those lasting up to a few minutes) potentially extremely powerful probes for shedding light on main open issues in our understanding of the early universe: star formation rate evolution up to the first generation of stars (popiii), cosmic reionization, luminosity function and metallicity evolution of primordial galaxies up to the cosmic dawn . at the same time, interesting correlations between luminosity/radiated energy and spectral photon peak energy are the subject of intensive investigations for standardizing grbs and using them for measuring cosmological parameters, investigating the nature and evolution of dark energy and testing non-standard cosmological models. i will also report on the status, concepts and expected performances of space mission projects aiming at fully exploiting these potentialities of the grb phenomenon, thus providing an ideal sinergy with the large e.m. facilities of the future like lsst, elt, tmt, ska, cta, athena. | cosmology wirh gamma-ray bursts |
discovery of two giant structures seen in gamma-rays and radio, located above and below the galactic center, known as fermi bubbles, can be considered as one of the most interesting phenomena observed by fermi-lat. their position and total energy content suggest a very strong energy outburst happened in the galactic center in the past. we point out some limitations of theoretical models of fermi bubbles. we also discuss interconnection between fermi bubbles and galactic cosmic rays. in particular, we point out that gamma-ray emitting electrons in the bubbles are most likely originated from cosmic ray electrons. in addition we show that fermi bubbles may be responsible for the formation of the spectrum of cosmic rays above the “knee”. | fermi bubbles, their origin and possible connection to cosmic rays near the earth |
uffo burst alert and trigger telescope (ubat) is the x-ray trigger telescope of uffo/lomonosov to localize x-ray source with coded mask method and x-ray detector. its xray detector is made up of 36 8×8 pixels yttrium oxyorthosilicate (y2sio5:ce, yso) scintillation crystal arrays and 36 64-channel multi-anode photomultiplier tubes (mapmts) for space mission. its effective detection area is 161cm^2 and energy range is several kev to 150 kev. it was successfully launched in april 28, 2016. in several calibration run, we got several x-ray background data. we already knew x-ray background flux is 2-3 counts/cm^2/sec in space.however our x-ray background data shows approximately 7-8 times higher than what we know. there are many candidates to explain high x-ray background count in space. one of candidates is cosmic ray. we will report cosmic ray effect on the x-ray detector using yso scintillation crystal arrays in space. | cosmic ray effect on the x-ray trigger telescope of uffo/lomonosov using yso scintillation crystal array in space |
various 14c excursions apparently caused by an increase of incoming cosmic rays on a short time-scale found in the late holocene have generated widespread interest and have been reproduced in many different tree-ring records (miyake et al. 2012, 2013 2017; büntgen et al. 2018). the excursions at ad 774-775ad 993-994 are well-documented but with an increasing number of studies using annual 14c analysis a range of new structures are being revealed. this includes rapid increase events such as at 660bc (park et al. 2017) and 3372bc (wang et al. 2018) likely due to extreme solar proton events (spe). however, other types of change in 14c production seem more likely the result of other solar processes, such as around 5480bc (miyake et al. 2017),and in the sixteenth century bc (pearson et al. 2018) and 815bc (jull et al. 2018). a diverse range of processes have the potential to effect cosmic-ray flux, including solar events, gamma-ray bursts, geomagnetic shifts and supernova. while research on the latter has proved inconclusive (dee et al. 2017), such studies are providing a wealth of new information through which to characterize new 'events' in 14c structure and to begin to understand the processes behind them. this research has much modern relevance in terms of understanding solar-climate forcing as well as the potential damages to technology brought about by events such as solar flares. these effects are also highly relevance to dating using the current international radiocarbon calibration curve based on decadal data. the difference in the shape of a calibration curve based on annual data (see pearson et al. 2018) demonstrates potential to improve the calibration process using annually-derived data but also indicates that error ranges will likely be increased with a more undulating curve which features the range of structural variability. finally, a large amount of new annual data provides exciting new opportunities to explore aspects of accuracy and precision between labs and to explore the complex issue of regional 14c variability in greater detail than ever before. we highlight the importance of these annual data to improve the international radiocarbon calibration, and how these improvements may affect evaluation of radiocarbon data. such an effort requires a broad-based international collaboration to address this complex issue. | annual carbon-14 variability in tree-rings: causes and implications for the calibration curve |
the gamma-400 project will be the new generation of satellite gamma-observatory. gamma-400 space-based gamma-ray telescope represents the core of the scientific complex intended to perform a search for signatures of dark matter in the cosmic gamma-emission, measurements of diffuse gamma-emission characteristics, investigation of extended and point gamma-ray sources, studying of high energy component of gamma-ray bursts and solar flares emission. four fast plastic sub-detectors of the gamma-ray telescope are included in fast trigger logic in the main telescope aperture. this aperture expected angular and energy resolution are ∼0.01° and ∼1-2% respectively for gammas with the energy >100 gev and electron/protons rejection factor ∼5-105. prototype of anticoincidence detector based on long bc-408 scintillators with sipm readout for gamma-ray telescope was tested on a 300 mev secondary positron beam of synchrotron c-25p «pakhra» of lebedev physical institute in russia. the measurement setup, design concepts for the prototype detector and chosen solutions together with some test results are discussed. two other apertures (additional and lateral) allow analyzing transient events not required precision angular resolution, for examples, grbs and solar flares. similar plastics sub-detectors included in their fast trigger logic. using of all three apertures allows making more effective observations of grbs (better signal to noise ratio), more detailed study of its high energy afterglow due long term measurements (because of high apogee orbit provides low background variations with time) and detailed analysis of the sources luminosity variability (spectral, angular and temporal). | the beam test of anticoincidence scintillation detector prototype with sipm readout and perspectives of grbs studies for space-based gamma-ray telescope gamma-400 |
point sources that produce high energy neutrinos remain elusive. while multiple studies have focused on high energy cosmological phenomenon such as gamma ray bursts, few have looked for correlation with local superstructures like the supergalactic plane that can produce these neutrinos not only directly but also through secondary cosmic ray interactions. interaction within galactic media can produce neutrinos that can be observed in icecube, a cherenkov detector buried at the south pole in one and a half kilometers of glacial ice. the density of local galaxies in the sky, as surveyed by the two micron all sky survey (2mass) provide a spacial template for the supergalactic plane. the 2mass survey is an infrared survey of over 300 million astrophysical objects and contains over 45,000 local galaxies' position and redshift. spacial templates for the supergalactic plane are tested with one year of event data from icecube. this analysis will aid in the understanding of the methods of production of high energy neutrinos and cosmic rays. | search for neutrinos from the supergalactic plane |
los alamos national laboratory (lanl) has a long history of discovery in gamma-ray astronomy, from the first detection of gamma-ray bursts by the vela satellites to extensive involvement in nasa's highly successful swift and fermi missions. looking to the future, several exciting new opportunities are being pursued, leveraging lanl's unique expertise in space-based gamma-ray detector development and data analysis. we describe current experimental efforts at lanl, including: 1) a concept for a cubesat mission, mambo, to measure the cosmic diffuse gamma-ray background in the mev band; 2) development of an advanced compton telescope based on diamond detectors and fast scintillators; 3) a high-altitude ballooning program to test advanced detector technologies in a near-space environment; and 4) contributions to amego, a concept for nasa's next large-scale gamma-ray astronomy mission. | experimental gamma-ray astronomy at los alamos national laboratory |
with ratan-600 radio telescope we can conduct studies of pulsed radiation of events associated with fast radio bursts (frb), giant pulses (gp) of pulsars and flare activity of magnetars at high frequencies. now the telescope has been equipped with full-power radiometers with the highest possible time resolution and band division at a frequency of 4.7 ghz into four narrow channels (150 mhz), which needed for detection of pulse shifts due to cosmic dispersion. as the main aim, the search for frb in the blind 24h-surveys of sky regions has been conducted for more than four years on four radiometers (beams). in the sky regions at declinations of 33, 22, 5 and 11 degrees, no frb with a flux greater than 5 jy were detected. however, in the crab nebula, we registered seven gp from its 33-millisecond pulsar. the maximum pulse was above 100 jy. measurements of radio pulses from the x-ray magnetar xte j1810−197 were carried out from 19 december 2018, when, after ten years on december 8, 2018 a bright x-ray flare occurred and weak radio pulses were detected with a pulsar rotation period of 5.54 seconds. based on the arrival times of pulses in narrow channels, we confirmed the measure of dispersion dm=178 pc/cm3. the pulses themselves, with a total duration of about 200 ms, included up to 15 sub-pulses with a width of 10 to 50 ms with a flux density of up to 5 jy. during three months xtej1809−197 remained the brightest radio pulsar in the milky way. | fastly varying objects: fast radio bursts, magnetars, and pulsars with ratan-600 |
a future medium-energy gamma-ray (mev) mission will address many questions posed in the recent astro2020 decadal survey in both the new messengers and new physics and the cosmic ecosystems themes. gamma-ray observations were critical to understanding the underlying physical phenomena driving extremely energetic sources, and discoveries are only expected to grow in the new era of advanced multimessenger observatories. the compton pair (compair) telescope project was funded through the apra program in 2015 (pi: mcenery) and 2021 (pi: kierans) to develop an mev telescope prototype and fly it on a balloon platform. the team has designed and built an instrument that consists of 4 detector subsystems: a double-sided silicon strip detector (dssd) tracker, a frisch-grid cadmium zinc telluride (czt) calorimeter, and a high-energy hodoscopic cesium iodide (csi) calorimeter (pi: grove, pi: woolf), all of which are surrounded by a plastic scintillator anti-coincidence detector (acd). in the past 7 years, the team has also sought-out advancements for the detector designs. the next generation of compair will be upgraded to target a gamma-ray mission concept proposed in the 2021 midex announcement of opportunity called the all-sky medium energy gamma-ray observatory explorer (amego-x) (pi: caputo). this concept implements developments in silicon detector technology enabled by the 2018 apra, astropix (pi: caputo), replacing the dssd detectors with higher sensitivity, low-noise and lower-cost pixel detectors and descoping the czt calorimeter. to reduce risk and address the technical readiness, the goals of compair will be to raise the trl of a prototype amego-x instrument to 6, including complicated i&t, novel carbon-fiber mechanical structure, and full astropix tracker layer readout. furthermore, compair will provide a test-bed for mev mission software for improved event identification in the compton/pair regime developed through a 2017 apra (pi: zoglauer), and real-time transient localization of gamma-ray bursts in the compton regime. the goddard space flight center (gsfc)-led team has a strong heritage in designing and building gamma-ray telescopes; therefore, maintaining that capability is an important aspect of this program. in addition to trl advancement, this proposed research provides valuable experience and necessary hands-on training to the early-career compair management, postdocs, graduate students, and early-career engineers at gsfc and naval research laboratory (nrl). | compair: a next generation medium energy gamma-ray telescope prototype |
skyhopper is a proposed cubesat mission to simultaneously observe 4 bands in the wavelength range from 0.8 to 1.7 micron. the light is captured by a telescope with a 100 mm × 200 mm primary and a field of view of 0.6° × 2.6°. a preliminary definition (phase b) of the optical telescope assembly for the mission is now completed. it is designed to make high precision intensity measurements of every object in the field of view. this brought a series of constraints to avoid stray light. different optical designs were studied. a kösters prism is used to split the light into 4 bands on a 2k x 2k detector. the telescope design is based on a 3 mirror anastigmat with additional lenses to provide good image quality in the final focal plane for all bands and also in the intermediate focal plane and the pupil plane where cold stops are needed. aberrations and vignetting of the prism had to be removed. science applications include exoplanet transits in front of low-mass stars, rapid infrared follow-up of gamma ray bursts and exploring the cosmic infrared background. | skyhopper cubesat: a multi-band nir telescope for precise intensity measurements |
mergers of two compact objects, either two neutron stars (nss) or a ns and a stellar mass black hole (bh), are astrophysical sources of great interest. their observations enable for multi-disciplinary studies encompassing several key fields of modern astronomy: from the cosmic production of heavy metals to the formation and acceleration of relativistic outflows, and to the behavior of dense matter in extreme physical conditions. future gravitational wave (gw) detections will probe these systems in the local universe, while gamma-ray bursts (grbs) offer a unique route to study their evolution across cosmic time and assess the role of these systems in shaping the cosmic chemical evolution. we propose rapid hst too observations of newly discovered short grbs to pin down the fingerprints of heavy elements in their light, the so-called kilonova, and search for evidence of magnetar formation. these measurements will be leveraged with a multi-wavelength (from radio to x-rays) observing campaign, and represent a natural stepping stone for the james webb telescope. even a single new event observed through the combined power of these facilities will push the frontier of our knowledge a step further and provide us with a benchmark dataset to constrain the nucleosynthetic yields of ns mergers. | mapping the diversity of kilonovae through rapid hubble observations of a short gamma-ray burst |
the gamma ray polarimeter experiment (grape) is designed to investigate one of the most exotic phenomena in the universe - gamma-ray bursts (grb). there has been intense observational and theoretical research in recent years, but research in this area has been largely focused on studies of time histories, spectra, and spatial distributions. theoretical models show that a more complete understanding of the inner structure of grbs, including the geometry and physical processes close to the central engine, requires the exploitation of gamma-ray polarimetry. over the past several years, we have developed the grape instrument to measure the polarization of gamma-rays from grbs over the energy range of 50 to 500 kev. grape is a large fov instrument with a sensitive energy range covering the peak energy distribution of grbs. the design is based on an array of independent modules, each of which consists of an array of (high-z and low-z) scintillator elements read out by a multi-anode pmt (mapmt). our eventual goal is to fly grape on a long duration balloon (ldb) platform or an orbiting platform to collect data on a significant sample of grbs, allowing us to place constraints on fundmental grb models. our experience with two balloon flights (in 2011 and 2014), coupled with further design efforts focused on orbital payloads, has led to an improved polarimeter design. the new design employs a large number of optically-isolated scintillator cubes, with independent silicon photomultiplier readout, arranged in a threedimensional array. the resulting three-dimensional location data provides a moderate level of compton imaging capability (1 sigma angular resolution of 10-15 degrees). the imaging can not only be used to determine the grb location (albeit with limited accuracy), it can also be used to significantly reduce the instrumental background by limiting the impact of the cosmic diffuse flux, improving the polarization sensitivity. it is the background reduction that is most important in this case. we have already evaluated some components of this design and are now prepared to embark on an effort to fabricate a prototype to be validated on a high altitude balloon flight. the proposed four year program covers the fabrication of a prototype instrument and an engineering balloon flight palestine in the summer of 2021. | the development of a low energy compton imager for grb polarization studies |
the position of the jwst in space—close to the l2 point at a distance of 1.5 million kilometers from earth—allows us a unique chance to measure the speed of cosmic photons through a double detection in two different telescopes. the speed of cosmic photons has been considered constant as a matter of principle, but in the same way, the energy lost by these photons could have a contribution due to a different nature such as dark matter. in this work, an experiment to measure the speed of photons is proposed based on the detection on two different telescopes located at a considerable distance. some of the most important results of this experiment could be variations of the speed of light as it passes through dark matter and, as a consequence, the ability to map dark matter in the universe. although jwst is not in the direction to measure the difference in time of 5 seconds, the fact that it can move up to a 50 arc degree angle will allow us to measure a difference in detection between 3 to 4.5 seconds. the observations needed to do this experiment should come from the detection of gamma ray bursts and then, the simultaneous detection by the sudden pointing of jwst plus a secondary telescope—on ground or in space—to catch the afterglow of the grb in longer wavelengths. the new technology in telescopes will allow us to catch a difference in magnitude between both telescopes or even to measure single photon detection in time in order to accomplish the purpose of the experiment. | measuring the velocity of cosmic photons |
x-ray quasi-periodic eruptions (qpes) are a new kind of cosmic signal, detected for the first time in the nucleus of the galaxy gsn 069 (miniutti et al. 2019, nature 573, 381), and then observed by multiple x-ray telescopes in the nuclei of other four low-mass galaxies. x-ray qpes appear as rapid bursts of soft x-ray emission (e < 2 kev) which repeat every few hours, carrying each time a few 1042 erg/s. while the energetics and the time scales involved imply a link to non-stationary accretion onto low-mass black holes (m_{bh} =: {a: few}: 105-6 m_{⊙}), the exact physical mechanism responsible for qpes is still far from clear. during this presentation i will review our knowledge of x-ray qpes, starting with their discovery and going through the main observational results collected during the past three years. i will conclude with a discussion of the possible theoretical interpretations for qpes, which include accretion flow instabilities, self-lensing of supermassive black hole binaries, and extreme mass ratio inspirals; and the possible implications for important astrophysical problems such as the structure of young active galactic nuclei (agn), the connection between tidal disruption events and the agn activity, the measurement of the black hole spin, the detection of gravitational waves from space. | unexpected signals in the x-ray sky: quasi-periodic eruptions from galactic nuclei |
we use a sample of 22 swift and fermi short gamma-ray bursts (sgrbs) to test the validity of the amati and yonetoku correlations, which were originally found for long bursts. the first relationship is between e_{p,i}, the intrinsic peak energy of the grb prompt emission, and e_{iso}, the equivalent isotropic energy. the second relationship is between e_{p,i} and l_{iso}, the peak isotropic luminosity. to determine these energy and luminosity quantities, one needs grb flux and spectral quantities as well as the redshifts of the bursts, hence the small size of the sample (17 swift and 5 fermi sgrbs); in fact, this is the largest sample of such short bursts to ever be used for an investigation of the amati and yonetoku correlations. the uncertainties (error bars) on the values of the calculated energy flux p, of the energy e_{iso}, and of the peak isotropic luminosity liso are estimated using a monte carlo approach. we find that sgrbs' energy and luminosity quantities (e _{p,i}, e_{iso}, and l_{iso}) can be correlated using amati- and yonetoku-like relations reasonably well (good or moderately good pearson r-values and reduced chi-squares), although the data shows large scatter and hence large error bars on the slope and the intercept of the fitting line. we also find that e_{iso} and l_{iso} evolve with redshift as (1+z)3.6 ± 1.8 and (1+z)2.41 ± 1.04, respectively, with a moderate goodness of fit, and the ratio of e_{iso} to l_{iso} scales with (1+z)1.2, which is consistent with cosmic time dilation. we compare and find our results to be consistent with other works of the same type. | testing the amati and yonetoku correlations for short gamma-ray bursts |
neutron stars with very strong magnetic fields are known as magnetars. there are multiple theories that predict magnetars may be able to emit high-energy (he) neutrinos through hadronic processes by accelerating cosmic rays to high energies. a subclass of magnetars known as soft gamma-ray repeaters (sgrs) can produce giant flares that can result in the production of he neutrinos. some magnetars also exhibit bursting activity during which they may emit he neutrinos. here we describe our time-integrated search for neutrino emission from magnetars listed in the mcgill online magnetar catalog and three newly discovered magnetars sgr 1830-0645, swift j1555.5-5402, and ngc 253. sgr 1830-0645 and swift j1555.2-5402 were discovered in 2020 and 2021 respectively by swift after emitting short bursts. a very bright short gamma-ray burst that is believed to be a magnetar giant flare has been localized to ngc 253. we use 14 years of well-reconstructed muon-neutrino candidate events collected by the icecube neutrino observatory to look for significant clustering in the direction of magnetars. | search for high-energy neutrinos from magnetars with icecube |
the eclairs instrument onboard the french-chinese svom satellite is designed to detect gamma-ray bursts, which are the main objectives of the mission scheduled for operations after 2023. this instrument, developed in france, is a coded-mask telescope operating in the energy range between 4 and 150 kev. in order to be sensitive to a large diversity of gamma-ray bursts, the software of its on-board computer embeds two different trigger algorithms. the first one is the so called count-rate trigger for the detection of gamma-ray bursts shorter than 20 s. the second one is the image trigger, which is the subject of this presentation, dedicated to the detection of long and ultra-long gamma-ray bursts. it is composed of several bricks allowing the reconstruction of sky images with exposure times ranging from 20 s to 20 min. we present the different possibilities offered by these bricks: correction of the inhomogeneity of the detection plane, subtraction of the spatial shape of the cosmic background noise (using a polynomial fit or a wavelet based algorithm), detector image deconvolution to reconstruct the sky images in which unknown sources are searched. the performances of the image trigger are evaluated with simulated data as well as with data from thermal vacuum tests and catalogues of gamma-ray bursts detected so far. | eclairs image trigger performance studies using simulated and thermal vacuum test data |
nimble is a nasa explorer class mission concept that couples a very wide-field gamma ray monitor with a multiwavelength telescope and rapid response spacecraft. the primary mission science is focused on detection and characterization of compact binary mergers (most likely binary neutron star or neutron star/black hole) through characterizing short gamma-ray bursts and kilonovae. nimble’s high-energy all-sky monitor (ham) and small uv-optical-ir (suvoir) instruments together will detect, localize, and characterize gravitational wave counterparts, and disseminate that information to the ground for additional rapid follow-up observations. in addition to detecting short gamma-ray bursts followed by their afterglow/kilonova counterparts, nimble will be able to quickly respond to external triggers from the ground-based gravitational wave network or other triggering instruments. the broad gamma-ray and uvoir observations will trace the evolution of these events and their cosmic chemical enrichment, explore the structure and origin of their emission mechanisms, and be probes of fundamental physics and cosmology. | gravitational wave counterparts with the nimble mission concept |
although batse ceased to function in 2000, its catalog of grbs remains a large and valuable collection of uniform grb data. unfortunately, only 12 batse grbs had measured spectroscopic redshifts. to help make batse data even more useful, we have computed redshift estimates for 1366 batse individual long-duration gamma-ray bursts (lgrbs) based on a monte carlo markov chain fit to other batse data and popular star formation models in a concordance universe. specifically, the presented estimated redshift tables are based on a classification and modeling of the population distribution of batse lgrbs in the 5-dimensional space of redshift as well as intrinsic prompt gamma-ray emission properties: the isotropic 1024ms peak luminosity (liso), the total isotropic emission (eiso), the spectral peak energy (epz), and the intrinsic duration (t90z), while taking into account the on-board detection mechanism of batse and sample incompleteness. the underlying assumption in our modeling approach is that lgrbs trace the cosmic star formation rate and that the joint 4-dimensional distribution of the aforementioned prompt gamma-ray emission properties follows a multivariate log-normal distribution. our modeling approach enables us to constrain the redshifts of batse lgrbs. we compare our predictions with the previous redshift estimates of batse grbs based on the proposed phenomenological high-energy relations, including lag-luminosity, spectral peak energy, luminosity, and variability-luminosity. our predictions are somewhat at odds with the previous estimates based on the high-energy phenomenological correlations, in particular with the estimates derived form the lag-luminosity and variability-luminosity relations. there is however, a weak but significant correlation of strength 0.26 between our predicted redshift estimates and those derived from the hardness-brightness relations. the discrepancies between the estimates can be explained by the strong influence of sample incompleteness in shaping the phenomenologically proposed high-energy correlations. the presented catalog here can be useful for demographic studies of lgrbs and other cosmological populations. | a catalog of estimated redshifts for 1366 batse long-duration grbs from a monte carlo fit to brightness, hardness, and duration data |
transonic plasma winds are studied under the influence of gravitational potential well in the presence of cosmic rays and self excited alfvén waves. we present interesting features of transonic winds originating from the gravitational potential well for a three-fluid system. the model is comprising of thermal plasma, cosmic rays and alfvén waves. the analysis is carried out on the hydro-dynamical basis with a particular emphasis on cosmic-ray streaming instability and damping mechanism. boundary conditions on the base of the gravitational potential well will help to explore steady-state transonic wind solutions. a critical analysis on various mass outflow rate is also presented which is applicable to know the behaviour of normal and star-burst galaxies. the dependence of the critical or sonic point is studied for different sets of physical parameters. for the graphical interpretation of the numerical results different contour plots presented to analyze impacts of different mass flow rates. we find that transonic solutions exist for a wide range of parameters. we examine the case very close to the base of the gravitational potential well and the effect of the cosmic ray diffusion is neglected in current study. | transonic plasma winds with cosmic-rays and waves |
linearly polarized optical emission from a gamma-ray burst reveals the presence of a large-scale distorted magnetic field in the heart of this powerful cosmic explosion. | anatomy of a gamma-ray burst |
the on-off problem, aka. li-ma problem, is a statistical problem where a measured rate is the sum of two parts. the first is due to a signal and the second due to a background, both of which are unknown. mostly frequentist solutions are being used that are only adequate for high count numbers. when the events are rare such an approximation is not good enough. indeed, in high-energy astrophysics this is often the rule rather than the exception. i will present a universal objective bayesian solution that depends only on the initial three parameters of the on-off problem: the number of events in the "on" region, the number of events in the "off" region, and their ratio-of-exposure. with a two-step approach it is possible to infer the signal's significance, strength, uncertainty or upper limit in a unified a way. the approach is valid without restrictions for any count number including zero and may be widely applied in particle physics, cosmic-ray physics and high-energy astrophysics. i apply the method to gamma ray burst data. | on the on-off problem: an objective bayesian analysis |
short duration gamma-ray bursts (grbs) are brief and intense flashes of gamma-ray radiation located at cosmological distances. nasa s swift mission provided the first breakthrough observations connecting these high-energy transients to the coalescence of two compact objects, either two neutron stars (nss) or a ns and a black hole (bh). short grbs are therefore prime candidate electromagnetic counterparts of gravitational wave sources detectable by advanced ligo. unfortunately, only a fraction of short grbs visible by swift is promptly identified by the on-board trigger system. a larger number of events fails to pass the on-board trigger selection and goes unnoticed. luckily, this subset of events is not lost. it is instead downlinked through a low-priority channel and then archived. the goal of this adap proposal is to harvest this rich population of gamma-ray transients buried in the data archive. we propose to 1) systematically mine this untapped resource of the swift archive in order to discover new short grbs; 2) correlate the swift untriggered dataset with signals detected by other facilities (e.g fermi, integral), at other wavelengths (e.g. fast radio bursts) or with other messengers (e.g. gravitational waves); 3) develop and release the relevant tools and documentation to the community in order to facilitate the exploitation of this valuable dataset in future years. the proposed research will significantly expand the current database of short grbs, and aid multimessenger searches of transient phenomena. by studying the behavior of matter in extreme physical conditions, the formation of new black holes, and gravity, this project directly addresses nasa strategic objective 1.6, a key science goal in the area of cosmic origins. | a missing population of short duration gamma-ray bursts |
the gamma ray polarimeter experiment (grape) is designed to investigate one of the most exotic phenomena in the universe - gamma-ray bursts (grb). there has been intense observational and theoretical research in recent years, but research in this area has been largely focused on studies of time histories, spectra, and spatial distributions. theoretical models show that a more complete understanding of the inner structure of grbs, including the geometry and physical processes close to the central engine, requires the exploitation of gamma-ray polarimetry. over the past several years, we have developed the grape instrument to measure the polarization of gamma-rays from grbs over the energy range of 50 to 500 kev. grape is a large fov instrument with a sensitive energy range covering the peak energy distribution of grbs. the design is based on an array of independent modules, each of which consists of an array of (high-z and low-z) scintillator elements read out by a multi-anode pmt (mapmt). our eventual goal is to fly grape on a long duration balloon (ldb) platform to collect data on a significant sample of grbs. our experience with two balloon flights (in 2011 and 2014), coupled with further design efforts focused on orbital payloads, has led to an improved polarimeter concept that represents a natural evolution of the current design. the new concept employs a large number of small (1 cm), optically-isolated scintillator cubes, each of which is read out by its own silicon photomultiplier (sipm). these cubes are stacked in a three-dimensional arrangement that allows the determination of event interaction locations in three dimensions within the sensitive volume. the resulting three-dimensional location data provides a moderate level of compton imaging capability (1 sigma angular resolution of 10-15°). even this level of imaging can be used to significantly reduce the instrumental background by limiting the influence of the cosmic diffuse flux, resulting in an improved polarization sensitivity. here we shall describe this concept and the expected performance for grb polarization measurements. we will also describe our efforts to develop a working prototype, which is initially focused on the testing of various scintillators (both organic and inorganic) with sipm readouts. | a low energy compton imager for grb polarization studies |
the transient high-energy sky and early universe surveyor (theseus) is a space missionconcept, developed by a large international collaboration and recently selected by esafor a phase 0/a study within the cosmic vision - m5 selection process. theseus aims atexploiting gamma-ray bursts for investigating the early universe and at providing asubstantial advancement of multi-messenger and time-domain astrophysics, also in strongsinergy with the large observing facilities of the future. these goals will be achievedthrough a unique combination of instruments allowing grbs and x-ray transients detectionover a broad fov (more than 1sr) with 0.5-1 arcmin localization, an energy band extendingfrom several mevs down to 0.3 kev and high sensitivity to transient sources in the softx-ray domain, as well as on-board prompt (few minutes) follow-up with a 0.7 m class irtelescope with both imaging and spectroscopic capabilities. theseus will address mainopen issues in cosmology such as, e.g., star formation rate and metallicity evolution ofthe inter-stellar and intra-galactic medium up to redshift 10-12, signatures of pop iiistars, sources and physics of re-ionization, and the faint end of the galaxy luminosityfunction. in addition, theseus will provide a fundamental contribution to time-domain andmulti-messenger astrophysics by detecting, localizing, and identifying theelectromagnetic counterparts to sources of gravitational radiation, which will beroutinely detected in the late '20s / early '30s by next generation facilities likealigo/avirgo, elisa, kagra, and einstein telescope and, more in general, of severalclasses of transient sources, providing an ideal sinergy also with the largemulti-wavelength observatories of the near future like lsst, elt, tmt, ska, cta, athena). | the transient high energy sky and early universe surveyor (theseus) |
monitors of x-ray emission are important instruments for observing the long-term activity of cosmic sources on the long timescales (e.g. years). we show the perspectives and possibilities of observing the selected types of x-ray binary sources with the planned satellites theseus and extp. the hardness of the x-ray spectrum largely determines the observability of a given object (or a type of objects) with a monitor operating in the specific band. we show the perspectives of detecting and observing outbursts in the soft x-ray transients with the hard x-ray monitors extp/wfm and theseus/xgis. their broad energy bands and energy resolution will enable to detect the outbursts and the complex spectral changes during these events. we also show the perspectives of observing the binary supersoft x-ray sources with the planned theseus/sxi. these sources sometimes have the luminosity close to the eddington limit but their x-ray emission is usually below the band used by the monitors. | investigation of the long-term activity of the binary x-ray sources with the planned satellites |
one of the most computationally demanding aspects of the hydrodynamical modelingof astrophysical phenomena is the transport of energy by radiation or relativistic particles. physical processes involving energy transport are ubiquitous and of capital importance in many scenarios ranging from planet formation to cosmic structure evolution, including explosive events like core collapse supernova or gamma-ray bursts. moreover, the ability to model and hence understand these processes has often been limited by the approximations and incompleteness in the treatment of radiation and relativistic particles. the diaphane project has focused on developing a portable and scalable library that handles the transport of radiation and particles (in particular neutrinos) independently of the underlying hydrodynamic code. in this work, we present the computational framework and the functionalities of the first version of the diaphane library, which has been successfully ported to three different smoothed-particle hydrodynamic codes, gadget2, gasoline and sphynx. we also present validation of different modules solving the equations of radiation and neutrino transport using different numerical schemes. | diaphane: a portable radiation transport library for astrophysical applications |
researchers searched the remains of an exploded star for signs of its one-time companion. though they found a suitable candidate, the star is in some ways an unlikely participant in a type ia supernova explosion.a companion to an exploding starillustrations of the two main type ia supernova pathways: the single-degenerate model (top) and the double-degenerate model (bottom). [both images from nasas goddard space flight center conceptual image lab]astronomers use a class of exploding stars called type ia supernovae to measure the distances to other galaxies and even determine the universes expansion rate. in theory, all type ia supernovae are equally luminous, making them useful signposts. however, research increasingly suggests that type ia supernovae are not all alike, and their varied formation mechanisms might lead to varied brightnesses as well, which complicates their role as cosmic distance markers.in general, type ia supernovae can result from two main pathways: two white dwarfs colliding (the double-degenerate scenario) or a white dwarf stealing matter from a companion star (the single-degenerate scenario). in order to determine the event that triggered a supernova, astronomers search the rubble of these cataclysmic events for signs of a companion star scurrying from the site of the explosion; neither white dwarf survives the double-degenerate scenario, while in the single-degenerate scenario the companion star might withstand the blast and live on.and yet it livesin a recent research article, a team led by pilar ruiz-lapuente (institute of fundamental physics, spanish national research council; institute of cosmos sciences of the university of barcelona) analyzed 3,082 stars in the vicinity of a nearby supernova remnant called g272.2-3.2 to search for signs of a surviving stellar companion. if present, the companion star would 1) have a high velocity, 2) be traceable back to the center of the supernova remnant when the explosion occurred about 7,500 years ago, and 3) potentially be chemically enriched by catching debris from the exploding star.an x-ray image of the supernova remnant g272.2-3.2 with the position of the fast-moving star mv-g272 as seen today (red circle) and 8,000 years ago (cyan circle). [ruiz-lapuente et al. 2023]using data from the gaia spacecraft, the team identified a single fast-moving star that was likely to have been in the right place at the right time. curiously, the star is an m dwarf the coolest, smallest type of star. and though the star didnt show the expected chemical enrichment, ruiz-lapuentes team notes that m dwarfs, unlike more massive stars, are fully convective, which means that any enriched material that falls onto the star would be mixed throughout it rather than remaining near the surface.small star, big questionsm dwarfs dont typically participate in type ia supernovae. because of their small size, they can only transfer a small amount of mass, meaning that a white dwarf with an m-dwarf companion is more likely to undergo repeated nova outburst than a one-time, cataclysmic supernova. however, researchers suspect that the strong magnetic fields of an m dwarf and a white dwarf might help funnel material between the stars, cranking up the transfer rate and triggering a supernova. if its possible for m dwarfs to facilitate type ia supernovae, we can expect to find more cases like that of g272.2-3.2, since m dwarfs are the most common stars in the universe.citationa possible surviving companion of the sn ia in the galactic snr g272.2-3.2, p. ruiz-lapuente et al 2023 apj 947 90. doi:10.3847/1538-4357/acad74the post searching for a star that survived a supernova appeared first on aas nova. | searching for a star that survived a supernova |
the cosmic gamma-ray bursts are certainly an enigma in astrophysics. the "standard fireball" scenario developed during many years has provided a possible explanation of this phenomenon. the aim of this work is simply to explore a new possible interpretation by developing a coherent scenario inside the global picture of stellar evolution. at the basis of our scenario is the fact that maybe we have not fully understood how the core of a pair instability supernovae explode. in such a way, we have proposed a new paradigm assuming that the core of such massive star, instead of doing a symmetrical explosion, is completely fragmented in hot spots of burning nuclear matter. we have tested our scenario using some observational data like grb spectrum, light curves, amati relation and grb-sn connection, and for each set of data we have proposed a possible physical interpretation. we have also suggested some possible tests of this scenario by measurement at high redshift. if this scenario is correct, it tells us simply that cosmic gamma-ray bursts are simply a missing link in stellar evolution. | gamma-ray bursts appear simpler than expected? |
over the last seven years, fermi-lat observations have convincingly found an excess in gamma-ray emission emanating from the center of the milky way galaxy. the excess has three definitive properties: (1) it has a hard spectrum that peaks at an energy of 2 gev, (2) it extends from within 0.1 degrees to more than 10 degrees from sgr a* with a three-dimensional intensity that falls roughly as r-2 , (3) it is approximately spherically symmetric. several models for this excess have been formulated, including the collective emission from a population of individually dim gamma-ray pulsars, outbursts of cosmic-ray electrons from the central molecular zone, or potentially even dark matter annihilation. in this overview, i will discuss the observational data, and the arguments for and against each theoretical model. additionally, i will discuss significant improvements in gamma-ray diffuse emission modeling that enhance our understanding of high energy astrophysics near the galactic center, and will describe the impact of these models on our understanding of the gamma-ray excess. | the gev excess in the galactic center |
arguably humans have flourished as a result of stellar explosions; we are, after all, stardust. nonetheless, rapid technology advances of the last 200 years sometimes put society and individuals on a collision course with the natural variability of stellar and solar atmospheres. human space exploration, routine satellite navigation system applications, aviation safety, and electric power grids are examples of such vulnerable endeavors. in this presentation i will outline how global society relies on ‘normal’ solar and stellar emissions, yet becomes susceptible to extremes of these emissions. the imprints of these astronomical-terrestrial interactions abound. in particular, i will highlight ways in which stellar/solar bursts link with our space-atmosphere-interaction region, producing multi-year patterns in cosmic ray detection, gorgeous aurora, and deep concern for good order and function of global community. | space weather: linking stellar explosions to the human endeavor |
during its 2-year baseline mission, the nuclear spectroscopic array (nustar) has carried out a survey of the galactic center region with total area coverage of ~0.7 deg2 and total exposure of ~2 msec. the nustar survey with ~40 ksec depth has detected over 30 point sources above 10 kev, including three known x-ray transients during their outbursts. some of the nustar point sources have remarkably hard x-ray spectra beyond 40 kev, indicating that they are either intermediate polars or x-ray binaries with neutron star or black hole. we will present our spectral and timing analysis to identify the hard x-ray sources. deep sgr a* observations with total exposure of ~400 ksec detected sgr a* flares above 10 kev, and most remarkably nustar's sub-arcminute images above 20 kev revealed previously undetected diffuse hard x-ray emission around sgr a*. hard x-ray emission above 40 kev is dominated by a point-like source that is spatially and spectroscopically consistent with the pwn candidate g359.95-0.04, a potential counterpart of the tev source hess j1745-290. in sgr a and b2 region, nustar has spatially resolved the molecular clouds for the first time above 10 kev, and broad-band x-ray spectroscopy was used to explore an origin of their x-ray emission, either due to low energy cosmic-ray heating and/or x-ray reflection of giant flares from sgr a* in the past. we will also discuss nustar detection of non-thermal x-ray filaments and implications for their emission mechanisms. | nustar galactic center survey |
the abundance of cosmogenic isotopes in natural samples is the main source of information about past variations of cosmic ray intensity, in the solar activity and in the strength of the geomagnetic field. sharp increases could originate from powerful impulsive events such as solar flares, gamma-rays from supernova explosions and gamma-ray bursts. a significant increase in the radiocarbon record has been detected recently in tree rings around ad 775 [1]. both large solar proton event (spe) [2] and gamma-ray burst (grb) in our galaxy [3] are favored as a source. however, either of the explanations faces difficulties of low event rate because of detection of a similar peak around ad993 [4], [5]. what is more, we know other similar result [6]. we carried out a statistical analysis of these three data sets. it is shown that ad 775 event differs fundamentally from ad 993 and ad 1006 events, because the last two can be explained without the assumption of the impulsive event. | impulsive event probability in the radiocarbon record in viii - xi centuries |
straw tube detector developed for the panda experiment in [1], will be used for tracking and identifcation of charged particles in the forward tracker (ft). the detector read-out will be incorporated in panda daq running in trigger-less mode by means of synchronization of data acquisition network (sodanet). sodanet is the protocol used to synchronize individual detector subsystems by providing a common clock signal and timestamps. the reconstruction of events out of many fragments is done with the burst building network. the first tests of such system have been performed with prototypes of ft and electromagnetic calorimeter modules (emc) in [1] measuring cosmic rays. those tests allow to evaluate the detectors as well as the synchronization and processing systems. the reconstruction of particle tracks has been developed and evaluated. the results on the track reconstruction, spatial resolution and energy loss via time over threshold (tot) method is described together with the daq performance. | study of the performance of prototypes of straw tube tracker by measuring cosmic rays |
for the first time since the discovery of high-energy cosmic neutrinos in icecube, a distant gamma ray blazar was identified as a high-energy neutrino source. the extraordinary brightness of the source despite its distance suggests that it may belong to a special class of sources that produce cosmic rays. moreover, the high-energy neutrino flux from the source is dominated by a neutrino burst, which implies flaring sources strongly contribute to the cosmic ray flux. in this talk, we first investigate the contribution of a subclass of flaring blazars to the high-energy neutrino flux and speculate on its connection to the very high energy cosmic ray observations. in addition, we show how this connection provides a consistent picture in the multimessenger observation of the source during the neutrino flare. | neutrino flares in the direction of txs 0506+056 |
thunderstorms emit bursts of energetic radiation. moreover, lightning stepped leader produces x-ray pulses. the phenomena, their interrelation and impact on earth's atmosphere and near space are not fully understood yet. the in-flight lightning strike damage assessment system ildas was developed in an eu fp6 project ( http://ildas.nlr.nl/ ) to provide information on threat that lightning poses to aircraft. it is intended to localize the lightning attachment points in order to reduce maintenance time and to build statics on lightning current. the system consists of 2 e-field sensors and a varying number of h-field sensors. it has recently been enhanced by two labr3 scintillation detectors inside the aircraft. the scintillation detectors are sensitive to x- and gamma-rays above 30 kev. the entire system is installed on-board of an a-350 aircraft and digitizes data with 100msamples/sec rate when triggered by lightning. a continuously monitoring channel counts the number of occurrences that the x-ray signal exceeds a set of trigger levels. in the beginning of 2014 the aircraft flew through thunderstorm cells collecting the data from the sensors. the x-rays generated by the lightning flash are measured in synchronization better than 40 ns with the lightning current information during a period of 1 second around the strike. the continuous channel stores x-ray information with very limited time and amplitude resolution during the whole flight. that channel would allow x-rays from cosmic ray background, tgfs and continuous gamma-ray glow of thundercloud outside the 1 s time window. in the egu2014 we presented the ildas system and showed that the x-ray detection works as intended. fast x-ray bursts have been detected during stepped/dart stepped leaders and during interception of lightning. data analysis of continuous channel recordings will be presented as well. | lightning x-rays inside thunderclouds, in-flight measurements on-board an a350 |
over the last seven years, fermi-lat observations have convincingly found an excess in gamma-ray emission emanating from the center of the milky way galaxy. the excess has three definitive properties: (1) it has a hard spectrum that peaks at an energy of 2 gev, (2) it extends from within 0.1 degrees to more than 10 degrees from sgr a* with a three-dimensional intensity that falls roughly as r^{-2}, (3) it is approximately spherically symmetric. several models for this excess have been formulated, including the collective emission from a population of individually dim gamma-ray pulsars, outbursts of cosmic-ray electrons from the central molecular zone, or potentially dark matter annihilation. in this talk, i will discuss the arguments for and against each model, focusing specifically on constraints from multi-wavelength observations. additionally, i will discuss the future observations that are critical for understanding the origin of the gamma-ray excess. | dark matter at the galactic center and the galactic center gamma-ray excess |
cosmic microwave background experiments make wide-area, sensitive, high- cadence maps of the sky at mm-wavelengths. discoveries will include moving (solar system objects), time-variable (stars, active galactic nuclei), or transient sources (novae, tidal disruption events, gamma-ray bursts, nearby supernovae, gravitational wave events) . | tracking the time-variable millimeter-wave sky with cmb experiments |
the merger of binary neutron star encodes rich physics of extreme states of matter. probing it through gravitational-wave observations requires the detectors to have high sensitivity above 1 khz. here we propose a detector design that pushes down the high-frequency quantum noise with an active optomechanical filter, frequency-dependent squeezing, and high optical power. the resulting noise level from 1 khz to 4 khz approaches the current facility limit, and is a factor of 20 to 30 below the design of existing advanced detectors at these frequencies. it will allow for precision measurements of (i) the post-merger signal of binary neutron star, with electromagnetic counterparts such as short gamma-ray burst and kilonovae, and possible detection of (ii) late-time inspiral, merger, and ringdown of low-mass black hole-neutron star systems, and possible detection of (iii) high frequency modes during supernovae explosions and/or magnetar giant flares. this design tries to maximize the science return of current facilities by achieving a sensitive frequency band that is complementary to proposed longer-baseline third-generation detectors: 10 km einstein telescope, and 40 km cosmic explorer. h.m. is supported by uk stfc ernest rutherford fel- lowship (grant no. st/m005844/11). h.y. is supported in part by perimeter institute for theoretical physics. d.m. acknowledge the support of the nsf and the kavli foundation. | towards the design of gravitational-wave detectors for probing neutron-star physics |
terrestrial gamma-ray flashes (tgfs) are short burst of gamma radiation originating from thunderclouds; they are currently observed by the reuven ramaty high energy solar spectroscopic imager (rhessi) [smith et al., science, 2005], the fermi gamma-ray space telescope [briggs et al., jgr, 2010], the astrorivelatore gamma a immagini leggero (agile) satellite [marisaldi et al., jgr, 2010], and the atmosphere-space interaction monitor (asim). since the theory behind them is still partly debated, the selection of tgfs from other short transients (e.g. cosmic ray showers, electronic noise, statistical fluctuations) has always been based on empirical criteria; here we present a new set of criteria for the agile mission that, for the first time, is based on a more refined analysis of characteristics of tgfs and takes into account all of them at the same time. the analysis of a sample of known tgfs with lightning association detected by the same mission during april - june 2015 provided us with a set of parameters to analyze, but also showed that tgfs are difficult to distinguish from other types of events, hence the need for a more sophisticated approach. these new criteria have also been shown to significantly increase the rate of tgf detection, thus paving the way to the 3rd agile tgf catalog. | new design of agile selection criteria for tgfs |
two 14c excursions apparently caused by an increase of incoming cosmic rays on a short time scale found in the late holocene generated widespread interest and have been reproduced in many different tree-ring records. these excursions at ad 774-775 and ad 993-994 are usually explained as due to extreme solar proton events (spe). in addition, a larger event has also been reported at 5480 bc (miyake et al. 2017), which is attributed to a special mode of a grand solar minimum, as well as another at 660 bc (park et al. 2017). other events have been reported such as at 3371-3371bc (wang et al. 2017). clearly, other events must exist, but could be the result of diverse processes affecting the cosmic-ray flux including solar events, gamma-ray bursts and geomagnetic phenomena. searches for supernova effects have so far proved inconclusive (dee et al. 2017). in order to detect more such possible events, we have identified periods when the 14c increase rate is rapid and large in the international radiocarbon calibration (intcal) data. we identify a new possible excursion starting at 814bc,which may be connected to the beginning of a solar minimum associated with the beginning of the hallstatt period, which is characterized by relatively constant 14c ages in the period from 800-400bc. we compare results of annual c14 measurements from tree rings of giant sequoia (california) and cedar (japan), and compare these results to other identified excursions, as well as geomagnetic data. we note that the structure of the increase from 814 bc is similar to the increase at 5480 bc, suggesting a related origin. we also assess whether there are different kinds of events, which may be observed that are consistent with different types of solar phenomena, or other explanations. we also highlight the potential importance of these annual data to improve the international radiocarbon calibration, as it is increasingly clear that annual data provides additional information that needs to be included in intcal. | the expanding record of rapid carbon-14 excursions in tree-rings - what do they tell us? |
the all-sky medium energy gamma-ray observatory (amego) is a wide field of view instrument (~60 deg radius) with a broad energy range (~200 kev to >10 gev) and excellent continuum sensitivity, designed to address a broad range of astrophsical topics in this under-explored region of the em-spectrum. amego will also serve as a facility in the search for gamma-ray emission associated with gravitational wave producing compact object mergers. we describe the technical capabilities of amego and discuss how it will advance our understanding of many source classes for which the peak of the power spectrum falls into the mev band. the transition from thermal to non-thermal physics is explored in this window through observations of gamma-ray burst, supernovae, novae, supernova remnants, diffuse emission from radioactivities and cosmic-ray ism interactions in our galaxy, and active galaxies. dark matter studies will be addressed with observations of the galactic halo and nearby dwarf galaxies. the diffuse galactic background in the mev regime remains to be fully characterized and resolved by source class. amego aims at breakthroughs in all these arenas. | advancing the mev frontier with amego |
nimble is a nasa explorer class mission concept that couples a very wide-field gamma ray monitor with a multiwavelength telescope and rapid response spacecraft. the primary mission science is focused on detection and characterization of compact binary mergers (most likely binary neutron star or neutron star/black hole) through characterizing short gamma-ray bursts and kilonovae. nimble's high-energy all-sky monitor (ham) and small uv-optical-ir (suvoir) instruments together will detect, localize, and characterize gravitational wave counterparts, and disseminate that information to the ground for additional rapid follow-up observations. in addition to detecting short gamma-ray bursts followed by their afterglow/kilonova counterparts, nimble will be able to quickly respond to external triggers from the ground-based gravitational wave network or other triggering instruments. the broad gamma-ray and uvoir observations will trace the evolution of these events and their cosmic chemical enrichment, explore the structure and origin of their emission mechanisms, and be probes of fundamental physics and cosmology. | gravitational wave counterparts with the nimble mission concept |
argo-ybj (aielli et al. 2012nimpa.661s..50a) is an eas detector located at an altitude of 4300 m a.s.l. (atmospheric depth 606 g/cm2) at the yangbajing cosmic ray laboratory (30.11°n, 90.53°e) in tibet, p. r. china. the argo-ybj detector was completed in the spring of 2007; however, thanks to its modularity, the data collection started already in 2004 november (corresponding to the launch of the swift satellite), ending in 2013 february, when the detector was definitively switched off. in this period, a total of 223 grbs detected by satellite instruments, occurred inside the argo-ybj field of view (zenith angle θ<=45°, corresponding to 1.84 sr). the present analysis was carried out on 206 of them, since the other grbs occurred during periods when the detector was inactive or not properly working. (1 data file). | vizier online data catalog: gev gamma-ray bursts with the argo-ybj detector (bartoli+, 2014) |
we present results of the study of data of the monitoring of high-energy and thermal neutrons at tien shan at different stages of thunderstorm activity. the data of the neutron monitoring were used taking into account the barometric effect. the intensity of the neutron component of cosmic rays is recorded in seven energy ranges. the electric field has values of ~ 100 v/m under fair weather conditions. standard deviation of minute values of the neutron monitor data at the high altitude station does not exceed 0.5-0.6 %. found that the standard deviation of the data during thunderstorms always exceeds these values. we selected events during the passage of thunderstorm clouds over the high altitude station without lightning discharges or with a small number of them. it was found that the particle rate of the neutron monitor changes in antiphase with the electric field changes. atmospheric electric field of positive polarity decreases the count rate of the neutron monitor, and negative polarity - increases. change of the count rate occurs at values of electric field ≥ 10-15 kv/m and reaches 2 %. the neutron monitor at the high-altitude station has the ability to measure the energy of recorded particles through determination of their multiplicity. we experimentally established that the sensitivity of the detected particles to change in ez increases with decreasing their energy. the upper energy threshold of sensitivity of neutrons to change electric field is ~10 gev. the physical mechanism of effect is based on lead nucleus capture of soft negative muons with the subsequent generation of neutrons. it is known that 7% of the neutron monitor count rate caused by negative muons. absence of this effect in thermal neutrons data confirms the conclusion since the main difference of the thermal neutrons detector from the neutron monitor is the absence of the lead. in the active phase of a thunderstorm in the formed thundercloud the picture of distribution of charges is complex and multilayered. the field on the ground can essentially differ from the field that caused the acceleration or deceleration of negative muons. it is possible the occurrence of the nuclear processes caused by lightning, - all this complicates interpretation of the monitor data. however, together with the system of electric field detectors, the neutron monitor allows to expand possibilities for determining the structure of thunderclouds. recorded at the tine shan, as well as at other stations, bursts of both slow and fast neutrons during lightning discharges attract undoubted interest. however, their nature is still discussed. | response of thunderstorm activity in data of neutron monitoring at tien shan |
the swift active galactic nucleus (agn) and cluster survey (sacs) uses 125 deg^2 of swift x-ray telescope serendipitous fields with variable depths surrounding x-ray bursts to provide a medium depth (4 × 10^-15 erg cm^-2 s^-1) and area survey filling the gap between deep, narrow chandra/xmm-newton surveys and wide, shallow rosat surveys. here, we present the first two papers in a series of publications for sacs. in the first paper, we introduce our method and catalog of 22,563 point sources and 442 extended sources. we examine the number counts of the agn and galaxy cluster populations. sacs provides excellent constraints on the agn number counts at the bright end with negligible uncertainties due to cosmic variance, and these constraints are consistent with previous measurements. the depth and areal coverage of sacs is well suited for galaxy cluster surveys outside the local universe, reaching z ∼ 1 for massive clusters. in the second paper, we use sloan digital sky survey (sdss) dr8 data to study the 203 extended sacs sources that are located within the sdss footprint. we search for galaxy over-densities in 3-d space using sdss galaxies and their photometric redshifts near the swift galaxy cluster candidates. we find 103 swift clusters with a > 3σ over-density. the remaining targets are potentially located at higher redshifts and require deeper optical follow-up observations for confirmations as galaxy clusters. we present a series of cluster properties including the redshift, bcg magnitude, bcg-to-x-ray center offset, optical richness, x-ray luminosity and red sequences. we compare the observed redshift distribution of the sample with a theoretical model, and find that our sample is complete for z ≤ 0.3 and 80% complete for z ≤ 0.4, consistent with the survey depth of sdss. we also match our sdss confirmed swift clusters to existing cluster catalogs, and find 42, 2 and 1 matches in optical, x-ray and sz catalogs, respectively, so the majority of these clusters are new detections. these analysis results suggest that our swift cluster selection algorithm presented in our first paper has yielded a statistically well-defined cluster sample for further studying cluster evolution and cosmology. | the swift agn and cluster survey |
tidal disruption events (tdes) of stars by single or binary super-massive black holes illuminate the environment around quiescent black holes in galactic nuclei allowing to probe dorment black holes. we predict the tde rates expected to be detected by next-generation x-ray surveys. we include events sourced by both single and binary super-massive black holes assuming that 10% of tdes lead to the formation of relativistic jets and are therefore observable to higher redshifts. assigning the eddington luminosity to each event, we show that if the occupation fraction of intermediate black holes is high, more than 90% of the brightest tde might be associated with merging black holes which are potential sources for elisa. next generation telescopes with improved sensitivities should probe dim local tde events as well as bright events at high redshifts. we show that an instrument which is 50 times more sensitive than the swift burst alert telescope (bat) is expected to trigger ~10 times more events than bat. majority of these events originate at low redshifts (z<0.5) if the occupation fraction of imbhs is high and at high-redshift (z>2) if it is low. | tidal disruption events across cosmic time |
recent results revealed the simultaneous existence of multiple components in the prompt emission of gamma-ray bursts (grbs) leading to a unified spectro-temporal model for the broadband spectrum from the optical regime up to higher gamma rays. unexpectedly, we discovered a relation intrinsic to one specific component of this model: its luminosity is strongly and tightly correlated to its spectral break energy. this new luminosity-hardness relation has the same index for all grbs when fitted to a power law. in addition, this relation seems to have the same normalization for all grbs; therefore, this is a promising and physically motivated tool that may establish grbs as cosmological standard candles. during this presentation, i will introduce this new relation, which might eventually be used to (i) estimate grb distances, (ii) to support searches for gravitational waves and cosmic high-energy neutrinos, and (iii) constrain the cosmological parameters. i will give a few examples of grb redshift estimates using this relation and i will show why this new result cannot solely be explain by instrumental selection effects and/or measurement/analysis biases. | from a better understanding of grb prompt emission to a new type of standard candles? |
the surfaces of airless bodies, such as the moon and phobos (innermost martian moon), are directly exposed to the surrounding space environment, including energetic particle radiation from both the ever-present flux of galactic cosmic rays (gcrs) and episodic bursts of solar energetic particles (seps). characterizing this radiation exposure is critical to our understanding of the evolution of these bodies from space weathering processes, such as radiation damage of regolith, radiolysis of organics and volatiles, and dielectric breakdown. similarly, this also has important implications for the long-term radiation exposure of future astronauts and equipment on the surface. in this study, the focus is the influence of phobian topography on the direct exposure of phobos to space radiation. for a given point on its surface, this exposure depends on: (i) the solid angle subtended by the sky, (ii) the solid angle of the sky blocked by mars, and (iii) the energy and angular distributions of ambient energetic particle populations. the sky solid angle, determined using the elevation of the local horizon calculated from a digital elevation model (dem), can be significantly reduced around topographic lows, such as crater floors, or increased near highs like crater rims. the dem used in this study was produced using images from the mars express high resolution stereo camera (hrsc), and has the highest available spatial resolution ( 100m). the proximity of phobos to mars means the martian disk appears large in the phobian sky, but this only effects the moon's near side due its tidally locked orbit. only isotropic distributions of energetic particles are initially considered, which is typically a reasonable assumption for gcrs and sometimes for seps. observations of the radiation environments on mars by curiosity's radiation assessment detector (rad), and the cosmic ray telescope for the effects of radiation (crater) onboard the lunar reconnaissance orbiter (lro) at the moon, will be used to estimate the average, annual radiation dose at the orbit of phobos. these three elements will be combined to produce a map of radiation exposure on the surface of phobos, which will be used to assess the implications for space weathering and future human exploration. | the effect of topography on the exposure of airless bodies to space radiation: phobos case study |
breathtaking results from the planck satellite mission and hubble space telescope have highlighted the key role modern astronomy is playing for our understanding of big bang cosmology. however, not so widely publicized is the similar wealth of observational data now available on explosive stellar phenomena, such as x-ray bursts, novae and supernovae. these astronomical events are responsible for the synthesis of almost all the chemical elements we find on earth and observe in our galaxy, as well as energy generation throughout the cosmos. regrettably, understanding the latest collection of observational data is severely hindered by the current, large uncertainties in the underlying nuclear physics processes that drive such stellar scenarios. in order to resolve this issue, it is becoming increasingly clear that there is a need to explore the unknown properties and reactions of nuclei away from the line of stability. consequently, state-of-the-art radioactive beam facilities have become terrestrial laboratories for the reproduction of explosive astrophysical events. in this talk, both direct and indirect methods for studying key astrophysical reactions using radioactive beams will be discussed. | advances in explosive nuclear astrophysics |
the galactic center (gc) supermassive black hole sgr a* radiates at a level about 9 orders of magnitude lower than its eddington luminosity. but indication of its glorious past has come from x-ray observations of surrounding giant molecular clouds. their varying neutral iron lines and continuum emission could be due to reflection of sgr a* x-ray outbursts hundreds of years ago. however, such observational facts can also be explained by low energy cosmic ray electron (lecre) illumination. it has remained a long-standing question which scenario gives rise to the molecular cloud emission: x-ray reflection, lecre or both. in this talk, i present the nustar observation of sgr b2, the densest and most massive gc molecular clouds. its substructure at energies greater than 10 kev is revealed for the first time. the direct comparison with iron line emission morphology is consistent with x-ray reflection from a source in the direction of sgr a*. we also applied physical models of x-ray reflection and lecre to the broadband x-ray spectra. results show that the x-ray reflection model is preferred over the lecre model. we derived that both the iron fluorescence line emission and the compton scattered continuum emission point to a faraway primary source with photon index of 2 and a luminosity of ~10^39 erg/s, probably due to a past sgr a* outburst. though probably not a dominant process, the lecre contribution can be constrained by the data. besides sgr b2, i will also briefly talk about the nustar observation of other gc molecular clouds and the nature of their x-ray emission. | nustar observation of sgr b2: reflection of past sgr a* x-ray outburst, cosmic ray illumination or both? |
distribution of gamma-ray bursts (grbs) from catalogs of the batse and bepposax space observatories relative to the cosmic microwave background (cmb) data by planck space mission is studied. three methods were applied for data analysis: (1) a histogram of cmb signal values in grb directions, (2) mosaic correlation maps calculated for grb locations and cmb distribution, (3) calculation of an average response in the area of "average grb population" on the cmb map. a correlation between grb locations and cmb fluctuations was detected which can be interpreted as systematic effects in the process of observations. besides, in the averaged areas of cmb maps, a difference between the distributions of average fluctuations for short and long grbs was detected which can be caused by different natures of these events. | correlation between sphere distributions of gamma-ray bursts and cmb fluctuations |
heliospheric energetic particle populations of energies higher than 1 mev are studied using a 33 year long data record composed of hourly measurements, as extracted from the nasa goddard space flight center's omni data set. their periodicities are examined by means least-squares spectral analysis and wavelet analysis and found to be in good agreement with periodicities seen in sunspot numbers, which are well-known indicators of variations in solar activity. hence, the source of this energetic and positively charged gas is mainly the sun but part of it should be cosmic rays. as derived from the analyses of suprathermal "heavy" tails of the probability distribution, we assume that the gas kinetics is described by a deformed maxwell-boltzmann distribution, namely, the kappa distribution. the q-index analogue to the κ-index is computed for every hour in the data record and used to investigate how far away the gas is from being in classical thermal equilibrium (q = 1). we compare the q-index time series with that of sunspot numbers and conclude that the gas is in continously variable states away (q > 1) from the almost always assumed thermal equilibrium. during the first ∼15 years, the q-indices somewhat exceed the theoretically predicted limit but follow a pattern which is very homogeneous. however, just before 1990, the q-indices begin to fluctuate in a periodic manner, creating maxima and minima, as they continuously increase until they peak about 1996-1997, while after these years, they decrease following a similar pattern. as a result, we assume that after 1990, for a period that lasted at least 10 years, something changed in the sun's behaviour. a higher number of solar bursts could easily affect the gas but further research, for instance an analysis of solar flare timeseries from the same period, is required to draw a more robust conclusion of what may have caused the observed anomaly. | study of heliospheric particle populations far from thermal equilibrium during three solar cycles, periodicities and q-index |
in complement to spectro-imaging observations, gamma-ray polarimetry provides a unique insight into the geometry and magnetic configuration of compact gamma-ray sources, such as neutron stars or black holes. due to the unprecedented spectral and timing capabilities of integral, and thanks to its coded mask imaging technics, which efficiently suppresses most of the background contribution, we have measured linearly polarized emission from the brightest cosmic high energy sources. we were able to measure for the first time, at energies above 200 kev, a clear signal from several gamma-ray sources such as the crab pulsar and nebula, the black hole candidates cygnus x-1 and v404 cygni and gamma-ray bursts. these observations have enabled us to put strong constraints on the physical process at work in these sources. in that talk, we will review the recent integral observations of gamma-ray polarimetry and the prospectives with possible joint observations with astrosat and astro-h. | overview of recent integral polarimetric observations |
the study of cosmic gamma ray bursts (grbs) is one of the main goals of the lomonosov space mission. the main advantage of this mission is simultaneous multiwavelength observations of grbs covering the optical, x-ray and gamma-ray ranges. the mission payload includes the grb monitor bdrg, wide-field optical cameras shok, and the uffo instrument. data are recorded mainly by the event trigger provided by the bdrg instrument, which measures the spectral and temporal properties of the burst in the energy range 10-3000 kev. the bdrg instrument also provides estimation of the source coordinates by comparing the readings of three differently directed detectors with an accuracy of several degrees. wide-field shok optical cameras have a field of view of ~20° × 40°. they fix a set of images with a frequency of about five frames per second prior to the trigger and another set immediately after the trigger. the uffo instrument includes the ubat telescope with a coded mask for measurements in hard x-ray and soft gamma-ray ranges and an optical telescope with a slewing mirror (smt) that can be directed on the grb source for a time ~1 s for measuring grb prompt emission in the early stages. in response to an bdrg trigger signal, the real-time data on a detected grb are transmitted to the earth via globalstar network to the gamma-ray coordinates network (gcn) and ground-based observatories. during observations on the lomonosov satellite, 20 gamma-ray bursts were detected and catalogued. several gamma-ray bursts were also detected in the vernov satellite experiment. an example of such an event is given. | observation of cosmic gamma ray bursts in the experiments onboard lomonosov and vernov satellites |
in 1994, a new type of radiation coming from the earth's atmosphere was discovered. this radiation, now known as terrestrial gamma-ray flashes (tgfs), comes in the form of bursts of high-energy photons, lasting less than one millisecond [fishman et al., science, 264, 1313, 1994]. initially expected to be rare events, we now know that they are related to common thunderstorms [chronis et al., bams, 97, 639, 2016 ; splitt et al., jgr, 115, a00e38, 2010] and intra-cloud lightning discharges [e.g., cummer et al., grl, 42, 7792, 2015]. briggs et al. [jgr, 118, 3805, 2013] estimate 400,000 tgfs per year, as detectable by the fermi-gamma ray burst monitor (gbm). thunderstorms also produce another type of events, called gamma ray glows. these are significant elevations of the background radiation, lasting from seconds to minutes. both are explained by the same phenomena: bremsstrahlung emission and relativistic runaway electron avalanche (rrea) [e.g., kelley et al., nat. commun., 6, 7845, 2015 ; wada et al., comm. phys., 2, 67, 2019]. a conservative estimate of the occurence of gamma-ray glows is that 8% of electrified storms produce them [kelley et al., 2015]. both tgfs [e.g., cummer et al., grl, 41, 8586, 2014] and gamma ray glows [e.g., eack and beasley, jgr, 120, 6887, 2015] are produced at thunderstorm altitudes, which calls for a precise assessment of the risk encountered by aircrew and passengers on a plane that would fly near or through thunderstorms. the exposure of aircrew is usually monitored by software that estimates the dose received for each individual, within the route flight data, taking into account the galactic component (cosmic rays) and relevant solar flares. dwyer et al. [jgr, 115, a00e14, 2010] estimated the dose that a tgf could produce as a function of the diameter of the electron beam, and showed that tgfs could be an additional non negligible exposure for aircraft passengers. in this work, we will present calculations of doses produced by different parts and components of tgfs: rrea, gamma-rays and secondary particles, within the different theories of production (leader-based model [e.g., xu et al., grl, 39, l08801, 2012 ; celestin et al., jgr, 120, 10, 712, 2015] and relativistic feedback model [e.g., dwyer, jgr, 113, d10103, 2008]) that would be received by humans if an airplane were to find itself in such an event. | estimation of doses from electrons, photons, and secondary particles associated with tgfs |
when two ultra-compact objects inspiral and merge it is a rare cosmic event, resulting in ``luminous'' gravitational wave emission. it is also fleeting, staying in advanced ligo's current sensitive band only for at most a few minutes. but when there is at least one neutron star, disk formation during the merger may power a slew of bright electromagnetic counterparts, including short gamma-ray bursts (grbs) and their afterglows. here we present efforts to localize ligo signal candidates on the sky in under a minute after detection, and to identify coincidences in time with grbs from the swift and fermi satellites on a similar timescale. we also report on the population of swift and fermi grbs that occurred during advanced ligo's first observing run, and discuss follow-up observations of grb 150906b, a short-duration burst discovered by the interplanetary network of satellite observatories, which may have occurred in a galaxy within ligo's sensitive volume. this research was supported by nsf grants phy-0970074 and phy-1307429 as well as the uw-milwaukee research growth initiative. | never ignore a coincidence: rapid identification of advanced ligo sources with electromagnetic transients |
the proposed model provides: 1 a predicted cosmological distribution of galaxies that requires no dark energy; 2 an observationally confirmed prediction that the historical location for the peak number of quasars, star formation rate, and gamma ray bursts will occur at a red shift factor of z =2; 3 and other predictions. the “galactic horizon model” is described by geometrically defined sets of interacting spatial relationships. 1 “observable space” is the reference structure from which we measure the universe. 2 observable space is expanding relative to an “absolute space”. 3 the expansion of observable space does not stop at the “boundary of galaxies” but occurs incrementally at the atomic scale of observation. “running the clock backwards”, never has all the galaxies in the universe compressed into a singularity. 4 initially, the streams of matter that form galaxies are extremely dense and very close to each other. 5 gravitational interaction between the new galaxies causes randomized “peculiar” motions that results in randomized doppler effects that are added or subtracted to the cosmological red shift. 6 the intensity of gravitational interaction and the kinetic velocity of galaxies diminish over cosmological time. 7 a model predicted temporal delay defines with the entrance of galaxies into the universe, introduces a “galactic horizon” and establishes the location of the cosmic background radiation 8 an additional spatial frame of reference called “inertial space” contains the kinematically averaged position of the galaxies. it is from our perspective of inertial space that gives the appearance of an expanding universe. 9 the model results from combining the spatial-temporal field relationships defined in two previous papers (“a multidimensional geometric expansion of spacetime” [1] and “could the inertia and energy content of matter diminish over cosmological time?” [2]). the apparent spatial location of a galaxy over cosmological time is expressed as, d1 = cto (3/2 t 2/3 - .5). d1 is the observed spatial location of a galaxy over time, c is the present speed of light, and t is t1/to which is the historical location of the galaxy divided by the age of the universe. | an intriguing cosmological model |
the nasa/asi imaging x-ray polarimetry explorer (ixpe) will be launched in spring 2021, and will allow to perform for the first time, thanks to its imaging-capable detectors, spatially resolved x-ray polarimetry of faint, extended sources. one of the most challenging, yet rewarding, targets are expected to be the molecular clouds in the galactic center. x-ray polarimetry could be indeed the key to understanding the origin of the observed x-ray reflection spectra of these clouds, that is thought to be the echo of a past outburst from the supermassive black hole sgr a*. in this scenario, the x-ray emission of the molecular clouds is predicted to be strongly polarized through compton scattering, with the polarization angle carrying a memory of the direction of the external illuminating source. the clouds are however embedded in a diffuse, collisionally-ionized plasma that is expected to lower the overall observed polarization fraction. morover, due to their low luminosity, the effect of the instrumental and diffuse background must be carefully evaluated. we present simulations of ixpe observations of the molecular clouds in the galactic center. our simulations include the plasma component as well as the instrumental background and cosmic x-ray background. we obtain realistic estimates of the dilution of the polarized signal and of the necessary exposure times as well as the impact of the background on the observability of the targets by ixpe and extp. these pieces of information are crucial for designing any future x-ray polarization observations of this intriguing galactic region. | x-ray polarimetry of faint extended sources: the case of the molecular clouds in the galactic center |
the swift agn and cluster survey (sacs) uses 125 deg^2 of swift x-ray telescope serendipitous fields with variable depths surrounding gamma-ray bursts to provide a medium depth (4 × 10^-15 erg cm^-2 s^-1) and area survey filling the gap between deep, narrow chandra/xmm-newton surveys and wide, shallow rosat surveys. here, we present the first two papers in a series of publications for sacs. in the first paper, we introduce our method and catalog of 22,563 point sources and 442 extended sources. sacs provides excellent constraints on the agn and cluster number counts at the bright end with negligible uncertainties due to cosmic variance, and these constraints are consistent with previous measurements. the depth and areal coverage of sacs is well suited for galaxy cluster surveys outside the local universe, reaching z > 1 for massive clusters. in the second paper, we use sdss dr8 data to study the 203 extended sacs sources that are located within the sdss footprint. we search for galaxy over-densities in 3-d space using sdss galaxies and their photometric redshifts near the swift galaxy cluster candidates. we find 103 swift clusters with a > 3σ over-density. the remaining targets are potentially located at higher redshifts and require deeper optical follow-up observations for confirmations as galaxy clusters. we present a series of cluster properties including the redshift, bcg magnitude, bcg-to-x-ray center offset, optical richness, x-ray luminosity and red sequences. we compare the observed redshift distribution of the sample with a theoretical model, and find that our sample is complete for z ≤ 0.3 and 80% complete for z ≤ 0.4, consistent with the survey depth of sdss. these analysis results suggest that our swift cluster selection algorithm presented in our first paper has yielded a statistically well-defined cluster sample for further studying cluster evolution and cosmology. in the end, we will discuss our ongoing optical identification of z>0.5 cluster sample, using mdm, kpno, ctio, and magellan data, and discuss sacs as a pilot for erosita deep surveys. | early results from swift agn and cluster survey |
in the 15 years since its construction, the h.e.s.s. gamma-ray observatory has allowed the study of the very high energy gamma-ray sky at unprecedented resolutions and sensitivities. during this period h.e.s.s. has discovered a rich zoo of both galactic and extra galactic cosmic ray sources. recent major discoveries include the tev emission of gamma-ray burst in the afterglow phase, the first indication of pev emission in the galactic center, and extended tev emission along the jets of the nearby radio-galaxy centaurus a. some of these discoveries where made possible through very deep exposure coupled with advanced analysis and simulation techniques, which pave the road for the cta era. in this context, a formal decision on the prolongation of h.e.s.s. for a minimum of three years was made in january 2019, together with an upgrade of the camera of the large telescope, after the upgrade of the h.e.s.s.-i camera in 2017. in its current form, h.e.s.s. is using two camera concepts developed for cta, namely the nectarcam and the flashcam concepts. i will present a summary of the latest h.e.s.s. results, describing the most interesting new observations in the view of the upcoming cta observatories and their physical interpretation, what recent discoveries imply for the science case of cta. i will detail the latest and upcoming upgrades and improvements to the h.e.s.s. hardware and data analyses and the future science prospects for the experiment. | highlight from h.e.s.s. and implication for cta era |
on behalf of the rice-uta-mda positron-gamma-ray collaboration*, we report the latest results of the 2016-2018 dense gamma-ray and positron experiments. using the texas petawatt laser (tpw) to irradiate thick au and pt targets at intensities >=1021w / cm 2 , we have created high-density (1015 /cm3), short-pulse (100 fs) e+e- pair and gamma-ray jets with in-situ physical parameters comparable to those postulated for cosmic gamma-ray bursts. for large cm-sized targets, we discover that hot electron emission is suppressed in a cone between the target normal and laser forward directions, while the positron emission is not suppressed. this leads to the creation of angle-selectable positron-dominated jets, with many applications to fundamental physics and astrophysics. we will also present the gamma-ray data from a new type of gamma-ray spectrometer, and discuss potential future applications of ultra-intense multi-mev gamma-ray beams. * e. liang, w. lo, y. lu, k. yao, a. henderson, e. marchenka, f. fasanelli, a. zhang, w. fu, p. chaguine, rice university; h. hassan, a. dashko, g. glen, g. tiwari, h. quevedo, g. dyer, m. donovan, t. ditmire, ut austin; g. wong, y. zhang, md anderson cancer center. this work was supported by doe grant de-sc0016505. | creating dense gamma-rays and electron-positron pairs with 1021w . cm - 2 short-pulse laser |
icecube was built at the south pole and aims to detect high energy neutrinos from the universe mainly above 100 gev. the transparent ice media allows us to build a 1 km3 large detection volume to detect the rarely interacting particles. neutrinos are thought to be generated at astrophysical sources such as active galactic nuclei and gamma-ray bursts. nature of the rare interaction with matters and little deflection by a magnetic field makes it possible to explore such sources located at the deep universe. since the neutrinos are produced through collisions of hadronic particles, the observation can elucidate the origin of cosmic rays, which is still mystery after the discovery 100 years ago. the detector was completed at the end of 2010 and is running smoothly. recently, icecube has found the first evidence of extraterrestrial neutrinos with energies above approximately 60 tev. icecube also contributes to elementary particle physics by searching for neutrinos produced in self-annihilation of susy particles such as neutralinos and by investigating atmospheric neutrino oscillations. the latest icecube results and the corresponding implications are presented. | the latest icecube results and the implications |
the galactic center (gc) supermassive black hole sgr a* radiates at a level about 9 orders of magnitude lower than its eddington luminosity. but indication of its glorious past has come from x-ray observations of surrounding molecular clouds. their varying neutral iron lines and continuum emission could be due to reflection of sgr a* x-ray outbursts in the past few centuries. however, such observational facts can also be explained by low energy cosmic ray electron (lecre) bombardment. in this talk, i present the nustar observations of the gc molecular clouds. their substructures at energies greater than 10 kev are revealed for the first time. we applied physical models of x-ray reflection and lecre to the broadband x-ray spectra. results show that the x-ray reflection model is preferred over the lecre model for all the clouds. the x-ray emission from cloud sgr b2 points to a faraway illuminating source with photon index of 2 and a luminosity of ~1039 erg s-1, most likely due to a past giant x-ray outburst from sgr a*. the sgr a clouds requires a fainter and more recent x-ray outburst, revealing different stages of the sgr a* x-ray outbursts. | nustar observation of galactic center molecular clouds: reconstructing sgr a* x-ray outburst history |
darts is the space science data archive at jaxa. maxi, monitor of all-sky x-ray, has been operational since august 2009 on the japanese experiment module-exposed facility (jem-ef) of the international space station (iss). calet (calorimetric electron telescope) was equipped on the jem-ef in 2015, and has been carrying out observations of the cosmic-rays and the gamma-ray bursts with the main-instrument cal (calorimeter) and the sub-instrument cgbm (calet gamma-ray burst monitor), respectively. both the maxi and calet data are going to be archived at darts. in addition, the maxi data and analysis tools will be made available from heasarc at nasa/gsfc. | maxi and calet archives at darts |
the cadmium zinc telluride (czt) imager onboard astrosat, consists of pixelated czt detectors, which are sensitive to hard x-rays above 20 kev. the individual pixels are triggered by ionising events occurring in them, and the detectors operate in a self-triggered mode, recording each event separately with information about its time of incidence, detector co-ordinates, and channel that scales with the amount of ionisation. the detectors are sensitive not only to photons from astrophysical sources of interest, but also prone to a number of other events like background x-rays, cosmic rays, and noise in detectors or the electronics. in this work a detailed analysis of the effect of cosmic rays on the detectors is made and it is found that cosmic rays can trigger multiple events which are closely packed in time (called 'bunches'). higher energy cosmic rays, however, can also generate delayed emissions, a signature previously seen in the picsit detector on-board integral. an algorithm to automatically detect them based on their spatial clustering properties is presented. residual noise events are examined using examples of gamma ray bursts as target sources. | characterisation of cosmic ray induced noise events in astrosat-czt imager |
a gamma-ray burst, named grb 221009a, occurred on 9 october 2022 and is the brightest ever observed grb, whose frequency is now estimated as once in 10,000 years. this grb was reported to be observed from many space missions, vlf receivers, and ground observations in optical and radio data. additionally, a strikingly large number of very high energy (vhe) photons associated with this grb were observed by the gamma-ray and cosmic ray observatory lhaaso. though gamma rays of cosmic origin usually tend to be absorbed by the atmosphere, the high fluence of this grb, along with the observation of more than 5000 vhe photons (0.5 to 18 tev) by lhaaso from the ground, emphasises the need to explore other possible ground observations of this grb. the present paper examines the effect of this grb using gamma-ray data in a low energy range (0.2-6) mev obtained using nai (tl) detectors located at tirunelveli (geographic coordinates: 8.71°n, 77.76°e), india. with ra = 288.3° and dec = 19.8°, the exceptionally bright fluence of this grb was geographically centred on india. we report no significant change in the observations associated with grb 221009a. we discuss the extent of attenuation of gamma-rays in the atmosphere that could explain the reported observations. further, we investigate the likelihood of ground observation of gamma-rays ($<$10 mev) for a much more intense hypothetical grb, and estimate the parameters, such as distance, fluence, and isotropic energy of such a grb. | effect of the brightest gamma-ray burst (grb 221009a) on low energy gamma-ray counts at sea level |
india has been actively involved in the follow-up observations of optical afterglows of gamma-ray bursts (grbs) for more than two decades, using the country's meter-class facilities such as the 1.04 m sampurnanand telescope, 1.3 m devasthal fast optical telescope, 2.01 m himalayan chandra telescope along with many others in the country, utilizing the longitudinal advantage of the place. however, since 2016, indian astronomers have embarked on a new era of exploration by utilizing the country's largest optical telescope, the 3.6 m devasthal optical telescope (dot) at the devasthal observatory of aries nainital. this unique telescope has opened up exciting opportunities for transient study. starting from the installation itself, the dot has been actively performing the target of opportunity (too) observations, leading to many interesting discoveries. notable achievements include the contributions towards the discovery of long grb 211211a arising from a binary merger, the discovery of the most delayed optical flare from grb 210204a along with the very faint optical afterglow (fainter than 25 mag in g-band) of grb 200412b. we also successfully observed the optical counterpart of the very-high-energy (vhe) detected burst grb 201015a using dot. additionally, dot has been used for follow-up observations of dark and orphan afterglows, along with the observations of host galaxies associated with peculiar grbs. more recently, dot's near-ir follow-up capabilities helped us to detect the first near-ir counterpart (grb 230409b) using an indian telescope. in this work, we summarise the recent discoveries and observations of grbs using the 3.6 m dot, highlighting the significant contributions in revealing the mysteries of these cosmic transients. | recent observations of peculiar gamma-ray bursts using 3.6 m devasthal optical telescope (dot) |
fast radio bursts (frbs) are millisecond-duration radio signals from unknown cosmic origin. many models associate frbs with high-energy astrophysical objects such as magnetars. in this attempt to find counterparts to frbs, we explore gamma-ray bursts (grbs) from the swift and fermi missions. we first search for spatial correlations between frb and grb populations as a whole and then search for a one-by-one correlation between each of the frbs and grbs investigated. temporal coincidences are not considered. to evaluate the significance of any correlation found, we generate background realizations that take into account instrumentally induced anisotropies in the distribution of the sources. neither study yields any significant counterpart detection. we estimate that less than 4\% of the frbs are associated with grbs in the studied samples | all sky archival search for frb high energy counterparts with swift and fermi |
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