abstract stringlengths 3 192k | title stringlengths 4 857 |
|---|---|
binary star systems composed of two white dwarfs are a natural outcome of stellar evolution. angular momentum losses from gravitational wave radiation cause the binary system's orbit to shrink until the two white dwarfs merge. the final outcome of the merger depends primarily on the masses of the white dwarfs. some potential outcomes, such as supernova explosions, may occur during or soon after the merger. other outcomes, which i will refer to as ''long-term'' outcomes, occur as the merger remnant cools and its structure adjusts to the new state created during the energetic merger. in this talk, i will focus on the merger of two carbon-oxygen wds. i will present simulations of the short-lived viscous disk initially present in these remnants and then show calculations that use the state-of-the-art mesa stellar evolution code to follow their thermal evolution. i will discuss the observational properties of these merger remnants and outline the interesting evolutionary process that leads to their final fate, which is likely collapse to a neutron star. the anticipated formation of a degenerate oxygen-neon core during this evolution necessitates an accurate treatment of the weak reactions that can drive its thermal and compositional evolution. i will discuss a series of calculations that use the mesa stellar evolution code to study degenerate oxygen-neon cores. these include previously neglected effects such as urca-process cooling and are able to reach length-scales that directly connect full-star simulations to past studies of the onset of the collapse process. | the long-term outcomes of double white dwarf mergers |
the central neutron star in cassiopeia a (cas a ns) has evidence from chandra acis data for a rapid temperature decline (2-3% per decade). if this is correct, it is a crucial constraint on understanding the cooling of young nss, and particularly on superfluidity in their cores. however, systematic uncertainties in acis data suggest the importance of a verification observation using another detector. a new hrc-s observation of cas a in 2023 would provide this crucial cross-check. | verifying the cooling of the cas a neutron star with hrc-s |
when a neutron star snares material from a stellar companion, we see a flash of x-rays called an x-ray burst. what can an analysis of 51 bursts from a single source tell us about the physics behind these events?bursting binary systemsa view of the neutron star interior composition explorer (nicer), seen at the center of this image, in its berth on the international space station. [nasa]binary systems containing a neutron star the extremely dense core of an expired massive star and a main-sequence, supergiant, or white dwarf star are called x-ray binaries for the short bursts of x-rays they emit. these outbursts are thought to arise when the neutron star accretes gas from its stellar companion, forming an accretion disk from which the neutron star siphons a stream of material that ignites in a brief flash of nuclear fusion. studying x-ray bursts allows researchers to pin down the properties of neutron stars and understand the physics that governs accreted gas.one of our best tools for studying these bursts is the neutron star interior composition explorer (nicer), which has monitored x-rays from its vantage point on the international space station since 2017. among nicers many targets is the highly active binary 4u 1636536, which was discovered just over 50 years ago. researchers have cataloged hundreds of x-ray bursts from 4u 1636536, finding that it averages one burst every four hours!an example of an x-ray burst from 4u 1636536 as seen by nicer. [adapted from gver et al. 2022]accretion increases and disk reflectionsin a recent publication, a team led by tolga gver (istanbul university) searched for evidence of additional x-ray bursts from 4u 1636536 during a monitoring campaign with nicer. gver and collaborators identified 51 x-ray bursts during 138 observations and collected spectra for 40 of them, allowing the team to characterize 4u 1636536s bursting behavior and understand how x-ray bursts affect their surroundings.gver and collaborators found that all of the bursts for which they acquired spectra had an excess of soft (i.e., low-energy) x-ray emission. modeling of this spectral feature indicated that it likely arises from either an increase in the rate at which matter is accreted onto the neutron star or from the burst scattering off the disk and/or being absorbed and re-emitted at a different wavelength, a process referred to as reflection. however, many of the bursts were fit well by models of both scenarios, and the authors pointed out that both processes likely occur simultaneously.further x-ray investigationsto learn even more about 4u 1636536s frequent outbursts, gver and collaborators analyzed data from indias multi-wavelength space telescope astrosat and the nuclear spectroscopic telescope array (nustar). using nustar data, the team searched for evidence of compton cooling, in which high-energy photons lose some of their energy through collisions with nearby electrons. the team discovered decreases in the hard (i.e., high-energy) x-ray emission shortly after the onset of several bursts, but the low count rate prevented a firm detection.comparison of reduced 2 values for best fits to the nicer spectra using the disk reflection model (blue) and the increased accretion model (red). [gver et al. 2022]the authors also used observations of several bursts made by astrosat and nustar to probe the causes of the excess soft x-ray emission further. similar to their investigations of the nicer spectra, the team found that they could fit the spectra with either a disk reflection model or an increased accretion model but simultaneously modeling both of these effects will require brighter x-ray bursts or a larger telescope.citationburstdisk interaction in 4u 1636536 as observed by nicer, tolga gver et al 2022 apj 935 154. doi:10.3847/1538-4357/ac8106the post a nicer view of a bursting x-ray binary appeared first on aas nova. | a nicer view of a bursting x-ray binary |
the "triaxial star", first proposed by s. chandrasekhar in 1969, has not yet been detected. the recently detected cosmic baby, i.e., swift j1818.0-1607 is the youngest magnetar observed so far. its characteristic age is ∼300 years, with a superfast spin period ∼1.36 s and a strong surface dipole magnetic field ∼3 ×1014g. considering the three facts in the interior of the magnetar core: i) the ambipolar diffusion, ii) negligible field decay as long as the core temperature is a few times 108 k and iii) the strong coupling between internal magnetic field decay and cooling in the early phase we estimate the ellipticity (ϵ ) and the core magnetic field (binternal) of this newly born magnetar are ∼9 ×10−3 and 8.9424 ×1017g, respectively. based on our estimated result we suggest swift j1818.0-1607 is a triaxial magnetar, i.e., simply a triaxial star. we discuss the significance of our result and encourage the gw community to search the triaxial stars through electromagnetic counterparts during their observation. | cosmic baby and the detection of a new compact star - the "triaxial star": a possibility |
i will begin this talk by briefly describing how multi-messengerobservations of neutron stars, when coupled withinformation from nuclear theory and nuclear structure,will provide new information about the equation ofstate, the composition, and the transport propertiesof dense matter. the tidal deformability of a neutron star is determinedby the equation of state of dense matter. i willpresent our earlier predictions for the tidal deformabilityconstructed from photon-based observations and show howthey were verified by gw 170817. next, i will brieflydescribe some of the thorny details of how bayesian inferenceis applied to this analysis, and showhow we can understand the prior choices we must make.observations of neutron star cooling are going beyond theequation of state to determine the composition of neutron stars. assuming no exotic matter, we find that the proton-to-neutron likely exceeds 1/9 in the core of a 2 solar mass neutron star. | multi-messenger neutron star astrophysics and determining the composition of the neutron star core |
the decay of the magnetic field in the interior of a magnetar may trigger electron captures by nuclei in the stellar crust, thus providing an internal source of heating. in turn, the onset of electron captures and the heat released are altered by the magnetic field due to the landau-rabi quantization of electron motion. the loss of magnetic pressure might also lead to pycnonuclear fusions of the lightest elements. the maximum amount of heat that can be possibly released by each reaction and their location are calculated using nuclear data from both experiments and theoretical predictions of the brussels-montreal models based on self-consistent hartree-fock-bogoliubov calculations. results are found to be consistent with those inferred empirically by comparing neutron-star cooling simulations with observed thermal luminosity of soft gamma-ray repeaters and anomalous x-ray pulsars. | heating from electron captures by nuclei in magnetar crusts |
the co-pis of this proposal are wen-fai fong and raffaella margutti. we propose joint chandra-vla-hst observations to continue our monitoring of the binary neutron star merger gw170817 at t 500-850 days since merger. our immediate objectives are: (i) to constrain the broad-band spectral evolution of the non-thermal emission from gw170817, and, in particular, the passage of the synchrotron cooling frequency within the chandra bandpass; (ii) to map the temporal evolution of the emission from gw170817 across the electromagnetic spectrum. these observations are designed to provide new insight into the current debate about the nature of the relativistic ejecta of compact- object mergers and their (now questioned) capability to successfully launch ultra-relativistic jets in their environment. | late-time monitoring of gw170817 across the electromagnetic spectrum |
maxi j1727-203 is a new transient discovered in june, 5 2018, and due to its spectral properties at the beginning of the outburst it was identified as a black hole candidate. maxi j1727 has been monitored with neutron star interior composition explorer (nicer) on almost daily basis since the beginning of the outburst. in this talk we will present the spectral and timing analysis of ~4 months of observations (more than 75 observations). preliminary results suggest a significant detection of a cool disk (~0.2 kev) and a strong hard component at the end of the outburst. we will show that maxi j1727 might have undergone the soft-to-hard transition at 0.5-10 kev luminosities ~ 1e36 erg/sec. this source is the the 3rd system in which we have detected the soft-to-hard transition at such low x-ray luminosities. | nicer observations of the 2018 outburst of the black hole candidate maxi j1727-203 |
the evolutionary paths of neutron stars post-supernova are not fullyunderstood. questions of cooling, magnetic field evolutions, spin downboth steady and via glitches, evolving emission behaviour,environmental influences and more besides are each highly complex, andat the same time intertwined. deciphering the full evolutionarypicture is thus a messy job. thankfully the discovery rate of neutronstars in comparison to that of said problems is respectable, and looksset to continue to increase so that such problems will hopefully betractable and testable with observational data. here i will present afew 'corner cases', neutron stars that one might think would be thesame that exhibit radically different behaviours. i will argue thatsome studying such cases, with tests i will describe, can give insightinto the overall evolutionary picture. | neutron star evolution |
we propose xmm-newton observations of 840 kyr old radio-quiet gamma-raypulsar j1957+5033. its short chandra observations revealed the presenceof a very soft x-ray emission in the 0.1--0.3 kev range. this suggeststhat the pulsar x-ray spectrum can have a soft thermal component from thens surface with the temperature of 27--40 ev, as is expected for the nsat the photon cooling stage. psr j1957+5033 can be the coldest isolatedneutron star at the age of 1 myr, which is important for comparison withcooling scenarios of these stars. we request for 80 ks observationsto confirm this as it is not possible with chandra due to calibrationuncertainties at low energies. | is psr j1957+5033 the coldest neutron star? |
we discuss the effect of compression on urca shells in the ocean and crust of accreting neutron stars, especially in superbursting sources. we find that urca shells may be deviated from chemical equilibrium in neutron stars which accrete at several tenths of the local eddington accretion rate. the deviation depends on the energy threshold of the parent and daughter nuclei, the transition strength, the temperature, and the local accretion rate. in a typical crust model of accreting neutron stars, the chemical departures range from a few tenths of kbt to tens of kbt for various urca pairs. if the urca shell can exist in crusts of accreting neutron stars, compression may enhance the net neutrino cooling rate by a factor of about 1-2 relative to the neutrino emissivity in chemical equilibrium. for some cases, such as urca pairs with small energy thresholds and/or weak transition strength, the large chemical departure may result in net heating rather than cooling, although the released heat can be small. strong urca pairs in the deep crust are hard to be deviated even in neutron stars accreting at the local eddington accretion rate. | net reaction rate and neutrino cooling rate for the urca process in departure from chemical equilibrium in the crust of fast-accreting neutron stars |
ultra luminous x-ray (ulx) sources are among the most intriguing binary systems, that have long been thought to host the elusive intermediate mass black holes. remarkably, within the last years there has been undisputed evidence that at least a few of these systems are powered by accreting neutron stars (ns) that are rotating with spin periods close to 1 s. in light of these recent discoveries and recently introduced models placing neutron stars as the engines of ulxs, we revisit the spectra of eighteen well-known ulxs, in search of indications that favor or reject this hypothesis. we find that the notable (>6kev) spectral curvature observed in most ulxs, is commensurate with the wien tail of a hot (t>1kev) multicolor black-body component and confirm that a double thermal model (comprised of a ”cool” and ”hot” thermal component) with the addition of a faint non-thermal tail describes all ulx spectra in our list. more importantly, we offer a new physical interpretation for the dual thermal spectrum, where it is the result of accretion onto high magnetized nss rather than black holes, in agreement with theoretical predictions. we estimate the magnetic-field strength and demonstrate that it correlates strongly with the source luminosity and the temperature of the hot component. we also discuss the application of our model on the most recent pulsating ulx "ngc 300 ulx1", casting doubts on the claimed presence of a cyclotron scattering feature in its spectrum. our findings offer an additional and compelling argument in favor of nss as prime candidates for powering ulxs, as has been also postulated by theory. | ulx spectra revisited: observational evidence of accreting envelopes around magnetized neutron stars |
we have investigated the x-ray luminosity and the rotational evolutions of the so-called "high-magnetic-field neutron stars" (hbrps) in the frame of the fallback disk model that was also applied earlier to anomalous x-ray pulsars/soft gamma repeaters (axps/sgrs), and dim isolated neutron stars (xdins). the estimated supernova ages and the measured braking indices of the three hbrps, namely psr j1734-3333, psr j1119-6127 and psr b1509-58, provide significant constraints on the models. we have shown that the individual source properties (period, period derivative, braking index and x-ray luminosity) can be reproduced simultaneously in the fallback disk model, consistently with the estimated supernova ages. our results indicate that hbrps are currently spinning down in the propeller phase without any accretion onto the star, while the x-ray luminosities are produced by the intrinsic cooling of the neutron star. this is in agreement with the observed pulsed radio emission of the sources. the strength of the dipole fields of hbrps indicated by our simulations are one or two orders of magnitude smaller than the fields inferred from the dipole-torque formula. furthermore, our results imply evolutionary connections of hbrps with axps/sgrs and normal radio pulsars. we also discuss the initial conditions responsible for the evolutions producing these different neutron star populations. | evolution of high-b radio pulsars in the fallback disk model |
x-ray bursts (type i) are produced by thermonuclear flashes in the accreted surface layers of some neutron stars in low mass x-ray binaries (lmxbs). high frequency oscillations are observed during some of these bursts. these "burst oscillations" result from rotational modulation of an inhomogeneous temperature distribution on the neutron star surface induced by ignition and subsequent spreading of the thermonuclear flash. they provide a means to measure the spin rates of accreting neutron stars and since the burst emission arises from the neutron star surface, a unique probe of neutron star structure. to date, virtually all observations of such oscillations have been made with nasa's rossi x-ray timing explorer (rxte). we have developed a burst model employing the schwarzschild + doppler approximation for surface emission coupled with realistic flame spreading geometries and burst cooling to compute light curves and oscillation amplitudes for both the rising and cooling phases of x-ray bursts. we use this model to explore the capabilities for the neutron star interior composition explorer (nicer) to detect and study burst oscillations, particularly in the energy band below 3 kev. nicer is an international space station attached payload (x-ray telescope) with capabilities optimized for fast timing of neutron stars in the 0.2-10 kev band. it has large collecting area (twice that of the xmm-newton epic-pn camera), ccd-quality spectral resolution, and high-precision time tagging referenced to utc through an onboard gps receiver. nicer will begin its 18-month prime mission around the end of 2016. we will present results of simulated x-ray bursts with nicer that explore its burst oscillation detection capabilities and prospects for inferring neutron star properties from phase-resolved spectra. | x-ray bursts and oscillations: prospects with nicer |
stars freeze. as they age and cool white dwarfs and neutron stars crystallize, with remarkable materials forming in their interiors. these `astromaterials' have structures similar to terrestrial crystalline solids and liquid crystals, though they are over a trillion times denser. notably, because their material properties affect the observable properties of the star, astromaterials must be understood to interpret observations of neutron stars. thus, astromaterial science can be thought of as an interdisciplinary field, using techniques from material science to study nuclear physics systems with astrophysical relevance. in this talk, i will discuss recent results from simulations of astromaterials and how we use these results to interpret observations of neutron stars in x-ray binaries. in addition, i will discuss how nuclear pasta, in neutron stars, forms structures remarkably similar to biophysical membranes seen in living organisms. | dissertation award in nuclear physics recipient: astromaterials in neutron stars |
superfluidity in the crust is a key ingredient for the cooling properties of proto-neutron stars. investigations on crust superfluidity carried out so far typically assumed that the cluster component was given by a single representative nucleus and did not consider the fact that at finite temperature a wide distribution of nuclei is expected to be populated at a given crust pressure condition. we want to assess the importance of this distribution on the calculation of the heat capacity in the inner crust, in the framework of an extended nse model. we additionally show that it is very important to consider the temperature evolution of the proton fraction, imposed by the β-equilibrium condition, for a quantitatively reliable estimation of the heat capacity. | impact of pairing on thermodynamical properties of stellar matter |
the composition and phase separation of rp-ash on accreting neutron stars determine the thermal properties of the crust which must be understood to interpret observations of crust cooling in x-ray bursts. in this work, we report on recent large scale molecular dynamics simulations of the outer crust. using the crust compositions calculated by mckinven et al. 2016, we study the structure of the crystal that forms, as well as diffusion and thermal properties of the crust. | simualting the phase separated rp-ash |
this talk focuses on the orbital inspiral of a neutron star (ns) through the envelope of its giant-branch companion during a common envelope (ce) episode. these ce episodes are necessary to produce close pairs of nss that can inspiral and merge due to gravitational wave losses in less than a hubble time. yet, as an embedded ns spirals to tighter separations within the ce, it can also accrete from the surrounding material. standard theories for the hydrodynamics of ce events predict that embedded nss may gain enough mass to force their collapse to black holes. we argue that ce structure, and in particular, the density gradient across the accretion radius of the ns leads to flow morphologies that prevent the ns from gaining much mass during its ce inspiral. the modest mass gains we predict can reconcile theories of neutrino-cooled accretion onto nss with the observed masses of nss in close double-ns binaries. | limiting the accretion-fed growth of neutron stars during common envelope |
we have followed the structure and thermal evolution of isolated, massive, uniformly rotating and highly magnetized white dwarf stars (wds). we studied the posibility that angular momentum losses driven by magnetic dipole braking developed the physical conditions inside the wd suitable to produce a thermonuclear explosion or the star gravitational collapse to a neutron star. we have assumed that the wd cools by neutrino emission processes and heats by carbon-burning reactions. in general, since the wd loses angular momentum by magnetic dipole breaking and its mass remains constant, its central density and temperature increase and its main radius decreases. for sub-chandrasekhar wds (with mass less than $\sim1.4\,\mathrm{m}_\odot$) the star spins-down, and for super-chandrasekhar wds (with mass greater than $\sim1.4\,\mathrm{m}_\odot$) it spins-up. we consider wds with surface magnetic fields from $10^6$ to $10^9\,\mathrm{g}$ and found that the wd lifetime is inversely proportional both to the magnetic field and to the wd mass. we have defined the wd lifetime as the time the wd needs to reach some instability condition, i.e. until it reaches mass-shedding, secular axisymmetric instability, inverse $\beta$ decay instability, or the carbon-ignition line (energy release from the carbon fusion equals the neutrino emissivity). | time evolution of rotating and magnetized white dwarf stars |
nuclear pasta, with non-spherical shapes, is expected near the base of the crust in neutron stars. large scale molecular dynamics simulations of pasta show long lived topological defects that could increase electron scattering and reduce both the thermal and electrical conductivities. we model a possible low conductivity pasta layer by increasing an impurity parameter qimp. predictions of light curves for the low mass x-ray binary mxb 1659-29, assuming a large qimp, find continued late time cooling that is consistent with chandra observations. the electrical and thermal conductivities are likely related. therefore observations of late time crust cooling can provide insight on the electrical conductivity and the possible decay of neutron star magnetic fields (assuming these are supported by currents in the crust). this research was supported in part by doe grants de-fg02-87er40365 (indiana university) and de-sc0008808 (nuclei scidac collaboration). | disordered nuclear pasta, magnetic field decay, and crust cooling in neutron stars |
a recent experiment at the national superconducting cyclotron laboratory has resulted in an extension of the nuclear mass surface for neutron-rich isotopes of argon through iron. the time-of-flight technique was employed to experimentally determine the masses of several nuclei for the first time. results include the identification of argon as the lowest even- z element exhibiting the n = 28 shell closure, as well the uncovering of a relatively small odd-even mass stagger between 56 ti and 56 sc. the latter result yields strong urca cooling when implemented in a state-of-the-art accreted neutron star crust reaction network. a strong 56 ti-56 sc urca neutrino cooling layer makes shallow neutrino cooling in the crust of accreting neutron stars a strong and robust effect due to the copious production of a = 56 material in thermonuclear burning processes that occur at the accreted neutron star surface. this project is funded by the nsf through grants 247 no. phy-0822648, phy-1102511, phy-1404442, and 248 no. phy-1430152. s.g. acknowledges support from 249 the dfg under contracts no. ge2183/1-1 and no. 250 ge2183/2-1. | results from the nscl tof mass measurement of neutron-rich isotopes of argon through iron |
pulsed non-thermal quiescent emission between 10 kev and around 150 kev has been observed in ~10 magnetars. for inner magnetospheric models of such hard x-ray signals, resonant compton upscattering of soft thermal photons from the neutron star surface is the most efficient radiative process. we present angle-dependent hard x-ray upscattering model spectra for uncooled monoenergetic relativistic electrons. the spectral cut-off energies are critically dependent on the observer viewing angles and electron lorentz factor. we find that electrons with energies less than around 15 mev will emit most of their radiation below 250 kev, consistent with the observed turnovers in magnetar hard x-ray tails. moreover, electrons of higher energy still emit most of the radiation below around 1 mev, except for quasi-equatorial emission locales for select pulses phases. our spectral computations use new state-of-the-art, spin-dependent formalism for the qed compton scattering cross section in strong magnetic fields. | hard spectral tails in magnetars |
we use the smoothed particle hydrodynamics (sph) method to simulate the behavior of viscous matter accreting on a neutron star. the fundamental difference between accretion onto black holes and neutron stars is the presence of a hard surface for the latter, which forces matter to stop moving in the radial direction at the surface of the star, making the flow subsonic. on the contrary, for black holes, matter is advected into the horizon supersonically. thus, apart from the immediate vicinity of the compact object, the flow should be similar for both the objects. we show that for an advective flow with nominal viscosity and angular momentum, the solution allows two shocks in the flow. the outer one, forms due to strong centrifugal barrier and is called centrifugal pressure dominated boundary layer or cenbol, which is a common feature for both neutron stars and black holes. the inner shock forms very close to the surface of a neutron star, due to the presence of the physical boundary. we use different viscosity prescriptions to study the behavior of the shock wave. the cases we study show a significant deviation from the ones studied in the context of black holes. we show how the angular momentum distribution deviates from a keplerian distribution when 1) the spin of the neutron star is varied, 2) the radiative pressure effect from nbol is added. the behavior of shock wave with the variation of viscosity parameter is also studied to determine the critical value of the viscosity parameter, up to which shocks are allowed in the flow. we study 1) the time evolution of such a viscous flow, 2) the oscillation of the post-shock region with viscous time-scale for intermediate viscosity. when cooling effects are added, the cenbol cools down and the outer shock moves in towards the star and is seen to be oscillating steadily. if the viscous stress is above its critical value in the equatorial plane, angular momentum is redistributed faster and a keplerian-like disk is produced. in presence of strong cooling (blackbody emission from the optically thick region), a disk is formed along the equatorial plane. the two-components, disk, and halo are disaggregated out of the halo component and remains steadily oscillating through hundreds of dynamical timescales. this indicates that the tcaf is the most general flow configuration for a neutron star when the magnetic field is weak. | formation of two-component advective flows around neutron stars |
we propose a 70 ksec observation of the neutron-star transient low-massx-ray binary exo 0748- 676. neutron-star crusts provide the uniqueopportunity to study the extreme conditions introduced by very highdensity matter. the density in a neutron-star crust increases by eightorders of magnitude over only ~1 km, from ~1e6 g/cm3 at the surface to~1e14 g/cm3 at the crust-core boundary. accretion outbursts can heatneutron-star crusts which cool once the outburst ceases. monitoringthis cooling evolution provides an insight into the properties ofthe neutron-star crusts. heat from deep in the crust propagates to thesurface on time scales of about a decade, thus our requested observation,~10 yr after the end of outburst, will enable us to study the propertyof very dense matter (~1e12-1e14 g/cm^3 ). | crust cooling of the neutron star in exo 0748-676 |
information about the structure and evolution of neutrons stars can be obtained from modeling their thermal evolution. i will present two studies, one of the cooling the crab pulsar, and one of the heating of accreting neutron stars as they accrete matter from a companion star. firstly, there is some circumstantial evidence that the crab pulsar was formed in an electron-capture supernova, which is one way stars about 8-10 solar masses die. in this type of supernova, the star's core collapses at the onemg stage, and produces a relatively low mass neutron star of around 1.25 solar masses. i calculate the cooling of low mass neutron stars and compare with measured upper limits on the crab's temperature. secondly, i consistently model the accretion of matter onto a population of neutron stars and the subsequent heating caused by nuclear reactions as the accreted matter is buried. the distribution of crustal heating as a function of initial period, magnetic field, and equation of state is presented. | the heating and cooling of neutron stars |
cooling of neutron stars has long been recognized as a way to investigate the physics of dense matter in neutron star interiors. because cooling depends on the heat capacity and neutrino emissivity of the matter, it is sensitive to both the particle content, for example the proton fraction, and state of matter, for example whether the particles are paired to form a superfluid. the traditional way to study neutron star cooling is to compare theoretical models with the observed population, either the population of young isolated neutron stars with detected x-ray emission, or with neutron stars accreting from a companion in binary systems. however, there are significant uncertainties in this comparison and degeneracies in the inferred neutron star properties.in this talk, i will focus on the new opportunity to probe neutron star interiors that comes from the ability to follow cooling of individual neutron stars on timescales of months to decades using long term monitoring with x-ray observatories. this has primarily been done for accreting neutron stars which are heated by nuclear reactions in their crust during accretion outbursts, and then cool afterwards. models of the cooling allow us to determine how much energy was deposited and then observe the response of the core to the energy input (they also provide a way to determine the envelope composition, a significant uncertainty in population studies). i will describe how this has provided the first independent constraints on heat capacity and the neutrino emissivity of neutron star cores, and the implications for the physics of the interior: how it provides a way to break the degeneracies in the models and begin to untangle the different contributions such as the dependence of pairing gap with depth. these studies are very much continuing, so i will emphasize the future constraints that we expect to obtain, and discuss how they relate to other information about neutron stars coming up (e.g. radius or moment of inertia measurements). | a new perspective on neutron star cooling |
thermal states of neutron stars in soft x-ray transients (sxrts) are thought to be governed by ``deep crustal heating'' in the accreted matter and cooling via emission of photons at the surface and neutrinos from the interior. previous studies have shown that within nucleons-only model it is difficult to explain the quiescent luminosity and mean accretion rate observed for several sxrts altogether, in particular the coldest (sax j1808.4-3658) and the hottest (aql x-1) neutron stars. we propose to examine the potential effects of exotic matter (i.e. hyperons, pion/kaon condensates and quark matter) on the thermal states of transiently accretion neutron stars, and provide a statistical analysis to quantify uncertainties in the constituents of matter at supranuclear densities. | effect of exotic matter on thermal states of transiently accreting neutron stars |
type-i x-ray bursts are thermonuclear explosions on the surface of weakly magnetized accreting neutron stars (ns) in low-mass x-ray binary (lmxb) systems where the mass donor is typically an evolved star. observationally, x-ray bursts can show a large variety in profiles, but generally they exhibit a fast rise and a longer, usually power-law like, decay. burst rise times vary from less than a second to 10 s, and decay times are in the range of seconds to minutes. bursts radiate x-ray spectra with blackbody shapes, (kt _ 3 kev) that cool during the burst decay.the joint european monitor for x-rays (jem-x) onboard integral is a coded-mask instrument operating in the 3-35 kev energy range, where the bulk of the x-ray burst energy is released. jem-x provides a fully-coded field of view of 4.8 _ 4.8 degrees, which allows concurrent monitoring of several x-ray bursters in one pointing. in this talk i will provide an overview of the results of 14 years of integral observations of the population of galactic x-ray bursters. | the population of galactic x-ray bursters as seen by integral over 14 years in space |
one of the most interesting kind of neutron stars are the pulsars, which are highly magnetized neutron stars with fields up to 1014 g at the surface. the strength of magnetic field in the center of a neutron star remains unknown. according to the scalar virial theorem, magnetic field in the core could be as large as 1018 g. in this work we study the influence of strong magnetic fields on the cooling of neutron stars coming from direct urca process. direct urca process is an extremely efficient mechanism for cooling a neutron star after its formation. the matter is described using a relativistic mean-field model at zero temperature with eight baryons (baryon octet), electrons and muons. we obtain the relative population of each species of particles as function of baryon density for different magnetic fields. we calculate numerically the cooling of neutron stars for a parametrized magnetic field and compare the results for the case without a magnetic field. | effects of neutrino emissivity on the cooling of neutron stars in the presence of a strong magnetic field |
the features of a first-order phase transition at variable pressure in mixed matter, which indicated the non-linear phase structure, have been discussed. the non-linear phase structure leads to the imbalance of the two phases during the phase transition under certain conditions. this novel non-equilibrium process is very analogous to the nuclear reactions that nuclei emit neutrons and absorb them under appropriate conditions. we present self-consistent thermodynamics in description and identify the microphysics responsible for the processes. the microphysics is an inevitable consequence of non-linear phase structure instead of the effect of an additional dissipation force. moreover, we apply our findings to the neutron star containing mixed hadron-quark matter; it is found that this newly discovered energy release strongly change the thermal evolution behavior of the star, especially for the delayed cooling of isolated neutron stars and the old neutron stars with high thermal luminosity. | novel non-equilibrium phase transition caused by non-linear hadronic-quark phase structure |
we evolve a binary system of two, equal-mass neutron stars in a quasi-circular orbit through and past merger. we consider different nuclear equations of state, which vary from soft to quite stiff, and allow for magnetization of the system and neutrino cooling via a leakage scheme. here, i focus on potential observables, other than gravitational waves, produced mainly by the hot, strongly magnetized matter resulting from the merger and study their dependence on both the equation of state and the initial magnetic field strength. | binary neutron star mergers: prospects for multimessenger observations |
we are developing a concept for a new canadian-led x-ray observatory — colibrì. the main objective of the colibrì mission is to study the structure of accretion flows in the near vicinity of black holes and neutron stars and the study of emission from the surfaces of neutron stars. the colibrì mission will look for answers to the questions: how do accretion disks transport material? how are relativistic jets launched? what is the structure of the spacetime surrounding black holes? what are the masses and radii of neutron stars? with high spectral and time resolution, and high throughput, colibrì will allow the study of accretion disks and coronae, including reflection and re-emission of radiation by the disk, and observations of isolated and accreting neutron stars.the colibrì concept concept is based on multiple aperture non-imaging x-ray collectors similar to nicer but with cryogenically cooled transition edge detectors for high energy resolution and sensitivity. colibrì aims to achieve an energy resolution finer than 1ev at 2kev, and count rates up to 10khz, in an energy range of 0.5-10 kev. the timing of colibrì aims to be better than 1 micro-sec, matching the innermost orbit period for a 10 solar-mass black hole. the total effective area of colibrì is to be at least 2000 cm2 at 6.4 kev. this concept study is being funded by the canadian space agency. | colibrì: taking the pulse of black holes and neutron stars |
quasi-spherical accreion onto magnetized neutron stars from stellar winds in high-mass x-ray binaries is discussed. depending on the x-ray luminosity of the neutron star, the accretion can proceed in two regimes (modes): at l_x ≳ 4× 10^{36} erg/s, compton cooling of accreting matter near magnetosphere leads to a supersonic (bondi) accretion, while at smaller x-ray luminosity the compton cooling is ineffective, and subsonic settling accretion regime sets in. in this regime, a hot convective shell is formed around the magnetosphere, and the plasma entry rate into magnetosphere is controlled by less effective radiative plasma cooling. the shell mediates the angular momentum transfer from/to the neutron star magnetosphere. observational evidences for the different accretion regimes in slowly rotating x-ray pulsars with moderate and low x-ray luminosity, as well as possible manifestations of non-stationary quasi-spherical settling accretion due to the magnetospheric shell instability in supergiant fast x-ray transients will be presented. | quasi-spherical accretion in high mass x-ray binaries |
we propose a 70 ks xmm-newton observation of the neutron star in 1rxsj180408.9-342058 (1rxs j1804), a transient lmxb which underwent a ~4.5month accretion outburst in 2015. the neutron star in transient lmxbs mayexperience crust heating during the outburst and subsequent cooling inquiescence. tracking the thermal evolution of the crust over time helpsindicate the properties of neutron star matter. 1rxs j1804 has alreadybeen monitored for ~480 days into quiescence and observations haveindicated crust cooling. by observing the source further in quiescencemore constraints on the neutron star crust physics can be obtained,in particular at deeper layers in the crust than currently possible forthis source. | crust cooling of the neutron star in 1rxs j180408.9 342058 |
we study the merger of unequal-mass neutron stars in a quasi-circular orbit with different nuclear equations of state ranging from from soft to stiff with a neutrino cooling scheme. | mergers of unequal mass binary neutron stars |
during a black hole-neutron star merger, baryonic material can be dynamically ejected. because this ejecta is extremely neutron-rich, the r-process rapidly synthesizes heavy nuclides as the material expands and cools. this can contribute to galactic chemical evolution of the r-process elements and lead to a short-lived optical transient, called a kilonova, powered by the radioactive decay of the heavy nuclides. we use the nuclear reaction network skynet to model r-process nucleosynthesis under varying levels of neutrino irradiation by post-processing tracer particles in the ejecta of a full numerical relativity simulation of a black hole-neutron star merger. we find the ejected material robustly produces the second and third r-process peaks, whose abundances remain unchanged even for very high neutrino luminosities, due to the rapid velocities of the outflow. nonetheless, we find that neutrinos can have an impact on the detailed abundance pattern by significantly enhancing the amount of material produced in the first peak around a ~ 78 . electron neutrinos are captured by neutrons to produce protons while neutron capture is occurring. these protons rapidly form low-mass seed nuclei, a fraction of which eventually ends up in the first peak after neutron capture ceases. partially supported by nasa and nsf under ast-1205732, ast-1313091, ast-1333520, pf3-140114, pf4-150122, and phy-1151197. | influence of neutrinos on r-process nucleosynthesis in black hole-neutron star mergers |
neutron stars are born with high temperatures and during a few seconds suffer rapid cooling by emission of neutrinos. the direct urca process is the main mechanism to explain this loss of energy. in this work we study the influence of a strong magnetic field on the composition of nuclear matter at high densities and zero temperature. we describe the matter through a relativistic mean-field model with eight light baryons (baryon octet), electrons, muons magnetic field. as output of the numerical calculations, we obtain the relative population for a parametrized magnetic field. we calculate the cooling of neutron stars with different mass and magnetic fields due to direct urca process. | cooling of neutron stars and emissivity of neutrinos by the direct urca process under influence of a strong magnetic field |
core-collapse supernovae lead to the formation of neutron stars, and both are sensitive to the dense matter equation of state. hans bethe first recognized that the matter in the collapsing core of a massive star has a relatively low entropy which prevents nuclear dissociation until nuclei merge near the nuclear saturation density. this recognition means that collapse continues until the core exceeds the saturation density. this prediction forms the foundation for modern simulations of supernovae. these supernovae sample matter up to about twice nuclear saturation density, but neutron stars are sensitive to the equation of state both near the saturation density and at several times higher densities. two important recent developments are the discovery of two-solar mass neutron stars and refined experimental determinations of the behavior of the symmetry energy of nuclear matter near the saturation density. combined with the assumption of causality, they imply that the radii of observed neutron stars are largely independent of their mass, and that this radius is in the range of 11 to 13 km. these theoretical results are not only consistent with expectations from theoretical studies of pure neutron matter, but also accumulated observations of both bursting and cooling neutron stars. in the near future, new pulsar timing data, which could lead to larger measured masses as well as measurements of moments of inertia, x-ray observations, such as from nicer, of bursting and other sources, and gravitational wave observations of neutron stars in merging compact binaries, will provide important new constraints on neutron stars and the dense matter equation of state. doe de-fg02-87er-40317. | hans a. bethe prize: neutron stars and core-collapse supernovae |
we present the results of chandra observations of two non-accreting millisecond pulsars psrs j1640+2224 (j1640) and j1709+2313(j1709), with low inferred magnetic fields in order to constrain their surface temperatures, obtain limits on the amplitude of unstable r-modes in them and make comparisons with similar limits obtained for a sample of accreting lmxb neutron stars (nss). we detect both pulsars in the x-ray band for the first time. we found upper limits on the global surface temperature of these pulsars that are ~ 3.3 - 4.7 × 105 k. these sources are several gyr old. in all standard cooling models nss cool to surface temperatures less than 104 k in less than 107 yr. while we derived upper limits on the surface temperatures of these sources, they appear to be consistent with the values measured for psr j0437-4715 and j2124-3358. taken together these results suggest that the surface temperatures of at least some msps are significantly higher, given their ages, than standard cooling models would suggest. for pulsars that are inside the r-mode instability window, r-mode dissipation can provide a potential source of reheating. | where are the r-modes? chandra observations of millisecond pulsars |
in core-collapse supernovae, the neutron rich matter is believed to have complex structures, such as spherical, slablike, and rodlike shapes. they are collectively called ``nuclear pasta''. supernovae neutrinos may scatter coherently on the ``nuclear pasta'' since the wavelength of the supernovae neutrinos are comparable to the nuclear pasta scale. consequently, the neutrino pasta scattering is important to understand the neutrino opacity in the supernovae. in this work we simulated the ``nuclear pasta'' at different temperatures and densities using our semi-classical molecular dynamics and calculated the corresponding static structure factor that describes ν-pasta scattering. we found the neutrino opacities are greatly modified when the ``pasta'' exist and may have influence on the supernovae neutrino flux and average energy. our neutrino-pasta scattering effect can finally be involved in the current supernovae simulations and we present preliminary proto neutron star cooling simulations including our pasta opacities. | supernovae neutrino pasta interaction |
the use of smoothed particle magneto hydrodynamics (spmhd) is getting nowadays more and more common in astrophysics. from galaxy clusters to neutron starts, there are multiple applications already existing in the literature. i will review some of the common methods used and highlight the successful approach of using vector potentials to describe the evolution of the magnetic fields. the latter have some interesting advantages, and their results challenge previous findings, being the magnetic divergence problem naturally vanished. we select a few examples to discuss some areas of interest. first, we show some galaxy clusters from the music project. these cosmological simulations are done with the usual sub-grid recipes, as radiative cooling and star formation, being the first ones obtained with an sph code in a self consistent way. this demonstrates the robustness of the new method in a variety of astrophysical scenarios. | the magnetic universe through vector potential spmhd simulations |
we propose to continue our successful program to use the observed cooling of the crusts in accreting neutron star systems to probe the properties of ultra-dense matter. those crusts are heated due to the accretion of matter onto neutron stars during the x-ray outburst and after the outbursts are over the crusts should cool down until they are in equilibrium with the core again. following this cooling processes in several systems has already given us new insights in the structure of neutron stars (i.e., the crust but also the core and hence in ultra dense matter), but many uncertainties remain. therefore it is needed to enlarge our sample of well studied sources to obtain better insights in the behavior of how neutron stars react to the accretion of matter. | crust cooling of accretion-heated neutron stars |
new-generation x-ray polarimeters currently under development promise to open a new window in the study of high-energy astrophysical sources. among them, neutron stars (nss) appear particularly suited for polarization measurements. radiation from the (cooling) surface of an ns is expected to exhibit a large intrinsic polarization degree due to the star strong magnetic field (≈ 10 ^{12}-10 ^{15} g). we present an efficient method for computing the observed polarization fraction and polarization angle in the case of radiation coming from the entire surface of an ns, accounting for both vacuum polarization and geometrical effects due to the extended emitting region. our approach is fairly general and is illustrated in the case of blackbody emission from an ns with either a dipolar or a (globally) twisted magnetic field. | polarization of neutron star surface emission: a systematic analysis |
the cooling of the central compact object (cco) in the cassiopeia a snr is of great importance to neutron star and fundamental physics. different setups and modes of the acis instrument (graded mode full frame and faint mode subbarray) resulted in different results for the measured temperature decay. in april 2015, there will be three observations of the cas a cco, including a dedicated calibration observation. in this proposal the two teams using different instrument modes have joined and propose a cross-calibration study with the goals (i) to derive a general calibration of the acis-graded mode, (ii) to re-calibrate the previous 12 relevant archival cco graded mode observations in order to quantify the temperature decay of the cco in a comparative study. | neutron star cooling and the calibration of the acis graded mode |
black hole-neutron star (bh-ns) mergers are exciting events to model, as they are a source of gravitational waves, like those discovered for the first time by advanced ligo earlier this year. these mergers are also the source of gamma-ray bursts and radioactively powered transients. we present here an outline of our entire research process. we first display results of general relativistic-hydrodynamic simulations using the spectral einstein code (spec). we ran a set of bh-ns merger simulations varying three of the initial parameters of the black hole: mass, spin magnitude, and spin inclination (relative to the orbital angular momentum of the binary system). the code factors in neutrino cooling and use a temperature dependent, nuclear theory based equation of state, as opposed to simpler equations of state previously used. though systems which treat precession and neutrino cooling have been simulated individually, the systems we analyzed are the first to take both into account. once a disk has formed and settled down, we take data from the gr simulations and input it into the particle evolution code, which reads in the positions/velocities and further evolves the system in a newtonian potential. we then present the fallback rate of bound particles throughout this period of evolution, the approximate density evolution, and the spatial distribution of ejecta. | black hole - neutron star merger simulations: precessing binaries with neutrino treatment |
in this work we present new observational data for hafnium (72). hf is an important element that is between the lightest rare-earth elements (e.g., la, z = 57) with elements of the third r-process peak (os, ir, pt, z =76-78). hafnium is the heaviest (z = 72) stable element represented by low-excitation (< 1:5 ev) ionized lines in the spectra of the cool stars (lawler et al., 2007). this element is important as a stable reference element for nucleocosmochronometry, and also to study of the sources of its production and enrichment with n (neutron)-capture elements of galactic disc. we provide the analysis of the spectra of 126 fgk dwarfs in metallicity range from -1.0 < [fe/h] < +0.3 that were taken from our starting sample of 276 stars (mishenina et al. 2013). the observed stars belong to the substructures of the galaxy disc. the observations were conducted using the 1.93 m telescope at observatoire de haute-provence (ohp, france) equipped with the echelle type spectrographs elodie and sophie. the results are based on analyses of spectra that have a typical s/n ∼ 100-300 and a resolution of 42 000 (elodie) and 75 000(sophie). the hafnium abundance was derived by comparing the observed and synthetic spectra in the region of two hf ii line (λ4080.437 å and λ4093.155 å), making use of the lte approximation. the obtained hafnium abundance decrease with increasing metallicity in both discs, and have a big scatter at all metallicities. the dependence of our hf abundance on metallicity and their comparison with those of other authors is presented. it corresponds to typical behavior of the elements behind the iron peak, the elements formed in the processes of neutron capture. the sources of the hf enrichment of galactic disc are considered. | hafnium abundances in fgk dwarf of galaxtic disk |
colibrì is canada's flagship x-ray observatory, proposed to have multiple aperture x-ray optics with cryogenically cooled transition-edge detectors for achieving high-energy and high-time resolution, as well as high throughput and sensitivity in the 0.1-15 kev range. colibrì is designed to probe the physics of matter under extreme conditions. we present the prospects for colibrì studies of the zoo of neutron stars, with focus on the fast-rotating pulsars and highly magnetized neutron stars. key science questions that colibrì will address include: what is the equation of state of neutron star material? can we diagnose the physics of accretion and neutron stars environment? what are the properties of material and light in strong magnetic fields? funded by the canadian space agency. | colibrì's eyes on neutron stars |
in astrophysical conditions prevalent during the late times of stellar evolution, lepton (e- and e+) emission processes compete with the corresponding lepton capture processes. prior to the collapse, lepton emissions significantly affect the cooling of the core and reduce its entropy. therefore the lepton emission rates for fe-group nuclei serve as an important input for core-collapse simulations of high-mass stars. from earlier simulation studies, isotopes of vanadium (v) have great astrophysical significance in regard to their weak-decay rates which substantially affect ye (fraction of lepton to baryon number) during the final developmental stages of massive stars. the current study involves the computation of the weak lepton emission (le) rates for v-isotopes by employing the improved deformed proton-neutron quasi-particle random phase approximation (pn-qrpa) model. the mass numbers of the selected isotopes range from 43 to 64. the le rates on these isotopes have been estimated for a broad spectrum of density and temperature under astrophysical conditions. the ranges considered for density and temperature are 101 to 1011 (g/cm3) and 107 to 3 × 1011 (k), respectively. the lepton emission rates from the present study were also compared to the rates previously estimated by using the independent-particle model (ipm) and large-scale shell model (lssm). ipm rates are generally bigger than qrpa rates, while lssm rates are overall in good comparison with the reported rates. we attribute these differences to correct placement of gt centroid in lssm and qrpa models. | lepton emission rates of 43-64v isotopes under stellar conditions |
neutron stars are a valuable asset to modern nuclear astrophysics in that they provide a unique environment to study matter under extreme conditions. much of the observational data obtained from neutron stars contains information about the structure and dynamics of the crust. using such observations to measure crust properties requires understanding the uncertainty range from models of the thickness of the different layers of the crust. these uncertainties arise from uncertainties in the properties of nuclear matter. i will use a comprehensive ensemble of nuclear matter equations of state, spanning the current uncertainty in the nuclear interaction, to examine the correlations between the crust thickness, mass distribution, and nuclear matter parameters. i will compare the results of a number of different ways to calculate the crust thickness and mass distribution, and use them to estimate the uncertainty in estimates of crust oscillation frequencies and the crust cooling time. | depth and mass of a neutron star crust |
in this talk we would discuss two-temperature accretion solution onto compact objects. it has been known that, in the two temperature regime, the number of flow variables are more than the number of governing equations. the system of equations are not complete and it admits degenrate solutions for the same set of constants of motion of the flow. we have used the second law of thermodynamics in addition to the equations of motion and the equation of state to obtain the unique accretion solution around black holes. using this technique we have obtained accretion solutions in presence of magnetic dissipative heating and cooling processes like, bremsstrahlung and synchrotron emission. the synchrotron and bremsstrahlung photons further interact with the flow electrons and cools via inverse-comptonization or heats through comptonization, depending on the relative energies of the electrons and the seed photons. although the overall spectra is dominated by leptonic processes as discussed above, but one may conjecure if there can be any weak but qualitatively different feature due to baryonic processes. we also compare the basic differences in these processes around a black hole and a neutron star. | two temperature solution and emergent spectra from compact objects |
pairing in asymmetric nuclear matter has been studied incorporating the effect of finite total momentum. we employ the generalized cooper eigenvalue equation, which can be used to demonstrate the pairing instability and also generates reasonable pairing gaps compared to the traditional bardeen-cooper-schrieffer (bcs) gap equation. from phase space arguments and the resulting strength of the pairing gap, we learn that the larkin-ovchinnikov-fulde-ferrell phase with a finite total momentum is favored over the conventional phase in asymmetric nuclear matter, but not in symmetric nuclear matter. to address open questions in neutron star cooling, neutron matter pairing gaps of the 1s0 and the 3p2 - 3f2 channels in a wide range of densities have been calculated using three different realistic interactions. instead of the mean-field bcs procedure, we incorporate the influence of short- and long-range correlations in calculating the pairing gaps. short-range correlations are treated to include the fragmentation of single-particle states, suppressing the gaps substantially. long-range correlations dress the pairing interaction via density and spin modes, and provide a smaller correction. the results provide input for neutron-star cooling scenarios and are parametrized in a user friendly way. the results are of particular relevance in view of the recent observational data on cassiopeia a. to study the nucleon-nucleus scattering problem in an ab-initio way, the optical potential in the momentum vector basis beyond the mean-field has been calculated employing the t x rho folding as the first step of the self-consistent green's function method. the deuteron pole structure of t- matrix has been properly avoided using the spectral functions from the dispersive optical model. a comparison of the resulting real and imaginary part of the self-energy at 100 mev with the corresponding dispersive-optical-model potentials shows reasonable agreement. | green's function application for pairing correlations and the optical potential |
a neutron star harbors of order $10^{56}$ electrons in its core, and almost the same number of muons, with muon decay prohibited by pauli blocking. however, as macroscopic properties of the star such as its mass, rotational velocity, or magnetic field evolve over time, the equilibrium lepton abundances (dictated by the weak interactions) change as well. scenarios where this can happen include spin-down, accretion, magnetic field decay, and tidal deformation. we discuss the mechanisms by which a star disrupted in one of these ways re-establishes lepton chemical equilibrium. in most cases, the dominant processes are out-of-equilibrium urca reactions, the rates of which we compute for the first time. if, however, the equilibrium muon abundance decreases, while the equilibrium electron abundance increases (or decreases less than the equilibrium muon abundance), outward diffusion of muons plays a crucial role as well. this is true in particular for stars older than about 10,000 yrs whose core has cooled to $\lesssim 20$ kev. the muons decay in a region where pauli blocking is lifted, and we argue that these decays lead to a flux of $\mathcal{o}$(10 mev) neutrinos. realistically, however, this flux will remain undetectable for the foreseeable future. | electron and muon dynamics in neutron stars beyond chemical equilibrium |
neutrino-cooled accretion flow around a black hole, produced by a compact binary merger, is a promising scenario for a short duration gamma ray burst central engine. the turbulence caused by magneto-rotational instability is expected to play an important role in driving accretion and thermal equilibrium of the disk. we study the magnetically-driven post-merger evolution of a black hole-neutron star binary system using results from a previous simulation and einstein's spectral code's mhd module. we mostly focus on studying the effects of neutrino cooling and magnetic filed on the structure of the disk and neutrino emission and neutrino-antineutrino energy deposition of the disk. | accretion of the magnetized neutrino-cooled torus on a rotating black hole |
we propose and experimentally demonstrate the generation of enhanced optical springs using the optical kerr effect. a nonlinear optical crystal is inserted into a fabry-perot cavity with a movable mirror, and a chain of second-order nonlinear optical effects in the phase-mismatched condition induces the kerr effect. the optical spring constant is enhanced by a factor of $1.6\pm0.1$ over linear theory. to our knowledge, this is the first realization of optomechanical coupling enhancement using a nonlinear optical effect, which has been theoretically investigated to overcome the performance limitations of linear optomechanical systems. the tunable nonlinearity of demonstrated system has a wide range of potential applications, from observing gravitational waves emitted by binary neutron star post-merger remnants to cooling macroscopic oscillators to their quantum ground state. | kerr-enhanced optical spring |
the discrepancy between expected and observed cooling rates of x-ray emitting gas has led to the cooling-flow problem at the cores of clusters of galaxies. a variety of models have been proposed to model the observed x-ray spectra and resolve the cooling-flow problem, which involves heating the cold gas through different mechanisms. as a result, realistic models of x-ray spectra of galaxy clusters need to involve both heating and cooling mechanisms. in this paper, we argue that the heating timescale is set by the magnetohydrodynamic (mhd) turbulent viscous heating for the intracluster plasma, parameterized by the shakura-sunyaev viscosity parameter, α. using a cooling+heating flow model, we show that a value of α ≃ 0.05 (with 10% scatter) provides improved fits to the x-ray spectra of cooling flow, while at the same time, predicting reasonable cooling efficiency, {ɛ }cool}={0.33}-0.15+0.63. our inferred values for α based on x-ray spectra are also in line with direct measurements of turbulent pressure in simulations and observations of galaxy clusters. this simple picture unifies astrophysical accretion, as a balance of mhd turbulent heating and cooling, across more than 16 orders of magnitudes in scale, from neutron stars to galaxy clusters. | cooling+heating flows in galaxy clusters: turbulent heating, spectral modeling, and cooling efficiency |
recent evidence for high masses ($\sim 2~ m_\odot$) pulsars psr j1614-2230 and psr j0348-0432 requires neutron star matter to have a stiff equation of state (eos). the thermal evolution of compact stars (cs) with stiff hadronic eos necessitates the application of the "nuclear medium cooling" scenario with a selection of appropriate proton gap profiles together with in-medium effects (like pion softening) on cooling mechanisms in order to achieve a satisfactory explanation of all existing observational data for the temperature-age relation of cs. here we focus on two examples from \cite{grigorian:2016leu} for a stiff hadronic eos without (dd2 eos) and with (dd2vex) excluded volume correction. | cooling of neutron stars with stiff stellar matter |
the cardinal focus of the present review is to explore the role of neutrinos originating from the ultra-dense core of neutron stars composed of quark gluon plasma in the astrophysical scenario. the collective excitations of the quarks involving the neutrinos through the different kinematical processes have been studied. the cooling of the neutron stars as well as pulsar kicks due to asymmetric neutrino emission have been discussed in detail. results involving calculation of relevant physical quantities like neutrino mean free path and emissivity have been presented in the framework of non-fermi liquid behavior as applicable to ultra-degenerate plasma. | astrophysical aspects of neutrino dynamics in ultra-degenerate quark gluon plasma |
the interpretation of observations of cooling neutron star crusts in quasi-persistent x-ray transients is affected by predictions of the strength of neutrino cooling via crust urca processes. the strength of crust urca neutrino cooling depends sensitively on the electron-capture and $\beta$-decay ground-state to ground-state transition strengths of neutron-rich rare isotopes. nuclei with mass number $a=61$ are predicted to be among the most abundant in accreted crusts, and the last remaining experimentally undetermined ground-state to ground-state transition strength was the $\beta$-decay of $^{61}$v. this work reports the first experimental determination of this transition strength, a ground-state branching of 8.1$^{+2.2}_{-2.0} \%$, corresponding to a log $ft$ value of 5.5$^{+0.2}_{-0.2}$. this result was achieved through the measurement of the $\beta$-delayed $\gamma$ rays using the total absorption spectrometer sun and the measurement of the $\beta$-delayed neutron branch using the neutron long counter system nero at the national superconducting cyclotron laboratory at michigan state university. this method helps to mitigate the impact of the pandemonium effect in extremely neutron-rich nuclei on experimental results. the result implies that $a=61$ nuclei do not provide the strongest cooling in accreted neutron star crusts as expected by some predictions, but that their cooling is still larger compared to most other mass numbers. only nuclei with mass numbers 31, 33, and 55 are predicted to be cooling more strongly. however, the theoretical predictions for the transition strengths of these nuclei are not consistently accurate enough to draw conclusions on crust cooling. with the experimental approach developed in this work all relevant transitions are within reach to be studied in the future. | $\\beta$-decay of $^{61}$v and its role in cooling accreted neutron star crusts |
proto-neutron stars forming a few seconds after core-collapse supernovae are hot and dense environments where hyperons can be efficiently produced by weak processes. by making use of various state-of-the-art supernova simulations combined with the proper extensions of the equations of state including λ hyperons, we calculate the cooling of the star induced by the emission of dark particles x0 through the decay λ → nx 0. comparing this novel energy-loss process to the neutrino cooling of sn 1987a allows us to set a stringent upper limit on the branching fraction, br(λ → nx 0) ≤ 8 × 10-9, that we apply to massless dark photons and axions with flavor-violating couplings to quarks. we find that the new supernova bound can be orders of magnitude stronger than other limits in dark-sector models. | supernova constraints on dark flavored sectors |
we present, for the first time, a detailed abundance analysis of the carbon star he 1104$-$0957 based on high resolution (r${\sim}$ 50\,000) spectra. our analysis shows that the object is an extremely metal-poor star with [fe/h] $\sim$ $-$2.96. we find that the object shows enhancement of carbon with [c/fe] $\sim$ 1.82. however, it does not fall into any of the sub-groups of carbon-enhanced metal-poor (cemp) stars based on the characteristic elemental abundance ratios used for the classification of various cemp sub-groups. he 1104$-$0957 is also found to exhibit an enhancement of oxygen and nitrogen with [o/fe], and [n/fe] $\sim$ 1.54, and 2.54 respectively. in he 1104$-$0957, $\alpha$-elements are found to be slightly enhanced with [$\alpha$/fe] $\sim$ 0.46. fe-peak elements are also moderately enhanced in he 1104$-$0957 with a value 0.63 with respect to fe. our analysis shows that he 1104$-$0957 exhibits enhancement of neutron-capture elements, particularly r-process elements. the low-resolution spectra of this object shows the spectral features characteristics of a typical c-r star. however, we find that the surface chemical compositions of this object is contradictory to that expected for a c-r star. it requires a detailed analysis to better understand the abundance anomalies exhibited by this object. | peculiar abundances of the cool carbon star he 1104-0957 |
observing the cooling of neutron stars reheated by accretion provides unique insights into neutron star structure. using chandra and xmm-newton we have followed in great detail the cooling of the neutron star transient xte j1701-462, which accreted at near/super-eddington rates for 1.6 years before returning to quiescence. our recent observations suggest that the source is currently in a phase of relatively rapid cooling that is the result of a non-steady-state crust temperature profile at the start of quiescence. we propose to continue our successful monitoring of the source with a 100 ks acis-s observation in cycle 17, extending our coverage of the source from 6.5 to 9 years into quiescence. this will serve to provide new constraints on the properties of the deep inner crust. | late-time cooling of the neutron star crust in the super-eddington accretor xte j1701-462 |
the sn1987a in the giant magellanic cloud was an amazing and extraordinary event because it was detected in real time for different neutrinos experiments (νs) around the world. approximate ∼ 25 events were observed in three different experiments: kamiokande ii (kii) ∼ 12, irvine-michigan-brookhaven (imb) ∼ 8 e baksan ∼ 5, plus a contrived burst at mont blanc (liquid scintillator detector - lsd) later dismissed because of energetic requirements (aglietta et al. 1988). the neutrinos have an important play role into the neutron star newborn: at the moment when the supernova explodes the compact object remnant is freezing by neutrinos ( ∼ 99% energy is lost in the few seconds of the explosion). the work is motivated by neutrinos’ event in relation arrival times where there is a temporal gap between set of events ( ∼ 6s). the first part of dataset came from the ordinary mechanism of freezing and the second part suggests different mechanism of neutrinos production. we tested two models of cooling for neutrinos from sn1987a: 1st an exponential cooling is an ordinary model of cooling and 2nd a two-step temperature model that it considers two bursts separated with temporal gap. our analysis was done with bayesian tools (bayesian information criterion - bic) the result showed strong evidence in favor of a two-step model against one single exponential cooling (ln bij > 5.0), and suggests the existence of two neutrino bursts at the moment the neutron star was born. | evidence for two neutrino bursts from sn1987a |
the relativistic neutrino emissivity of the nucleonic direct urca processes in neutron star matter are investigated within the relativistic hartree-fock approximation. we study particularly the influences of the tensor couplings of vector mesons $\omega$ and $\rho$ on the nucleonic direct urca processes. it is found that the inclusion of the tensor couplings of vector mesons $\omega$ and $\rho$ can slightly increase the maximum mass of neutron stars. in addition, the results indicate that the tensor couplings of vector mesons $\omega$ and $\rho$ lead to obvious enhancement of the total neutrino emissivity for the nucleonic direct urca processes, which must accelerate the cooling rate of the non-superfluid neutron star matter. however, when considering only the tensor coupling of vector meson $\rho$, the neutrino emissivity for the nucleonic direct urca processes slightly declines at low densities and significantly increases at high densities.that is to say that the tensor coupling of vector meson $\rho$ leads to the slow cooling rate of a low-mass neutron star and rapid cooling rate of a massive neutron star. | effects of the tensor couplings on the nucleonic direct urca processes in neutron star matter |
in 1t-tas2‑xsex, the charge density wave (cdw) state features a star of david lattice that expands across layers as the system becomes commensurate upon cooling. the layers can also order along the c-axis, and different stacking orders have been proposed. using neutron scattering on powder samples, we compared the stacking order previously observed in 1t-tas2 when the system is doped with se. while at low temperature, a 13c layer sequence stacking was observed in tas2; this type of ordering was not evident with doping. doping with se results in a metallic state in which the mott transition is suppressed, which may be linked to the absence of layer stacking. | suppression of stacking order with doping in 1t-tas2‑xsex |
symbiotic stars are a type of interacting stellar binary system consisting of a hot compact object (typically a white dwarf or sometimes a neutron star) and a cool companion (typically a cool giant star) orbiting around their common center of mass. these objects are generally characterized by orbital periods of 100s to 1000s of days and are surrounded by an optically thick dense circumstellar medium. understanding the process of mass transfer in this type of binary system can improve our understanding of accretion processes and these systems potential evolution to type ia supernovae, by measuring the angular diameter and shape of the cool star using optical interferometry, it is possible to determine the star's roche-filing factor and thereby study whether mass-transfer is driven by winds or roche-lobe overflow. here, we use h-band interferometric observations from the center for higher angular resolution astronomy (chara) array to determine the angular diameter and shape of the secondary component of eg and system using oitools, a julia package for working with and simulating optical interferometric data. in addition to this, we present reconstructed images for the symbiotic binary system from select epochs. we discuss the implications of these results on the nature of mass-transfer in the system and how these conclusions relate to descriptions of the system made with other observational methods including ellipsoidal variations in light curves. | interferometric modelling and imaging of the symbiotic binary system, eg andromedae |
double white dwarf (dwd) mergers are relevant astrophysical sources expected to produce massive, highly magnetized white dwarfs (wds), supernovae (sne) ia, and neutron stars (nss). although they are expected to be numerous sources in the sky, their detection has evaded the most advanced transient surveys. this article characterizes the optical transient expected from dwd mergers in which the central remnant is a stable (sub-chandrasekhar) wd. we show that the expansion and cooling of the merger's dynamical ejecta lead to an optical emission peaking at 1-10 days postmerger, with luminosities of 1040-1041 erg s-1. we present simulations of the light curves, spectra, and the color evolution of the transient. we show that these properties, together with the estimated rate of mergers, are consistent with the absence of detection, e.g., by the zwicky transient facility. more importantly, we show that the legacy survey of space and time of the vera c. rubin observatory will likely detect a few/several hundred per year, opening a new window to the physics of wds, nss, and sne ia. | on the optical transients from double white-dwarf mergers |
we present a study of weak, thermonuclear x-ray bursts from the accreting millisecond x-ray pulsar sax j1808.4-3658. we focus on a burst observed with the neutron star interior composition explorer on 2019 august 9, and describe a similar burst observed with the rossi x-ray timing explorer in 2005 june. these bursts occurred soon after outburst onset, 2.9 and 1.1 days, after the first indications of fresh accretion. we measure peak burst bolometric fluxes of 6.98 ± 0.50 × 10-9 and 1.54 ± 0.10 × 10-8 erg cm-2 s-1, respectively, which are factors of ≈30 and 15 less than the peak flux of the brightest, helium-powered bursts observed from this source. from spectral modeling we estimate the accretion rates and accreted columns at the time of each burst. for the 2019 burst we estimate an accretion rate of $\dot{m}\approx 1.4\mbox{--}1.6\times {10}^{-10}$ m ⊙ yr-1, and a column in the range 3.9-5.1 × 107 g cm-2. for the 2005 event the accretion rate was similar, but the accreted column was half of that estimated for the 2019 burst. the low accretion rates, modest columns, and evidence for a cool neutron star in quiescence, suggest these bursts are triggered by thermally unstable cno cycle hydrogen burning. the post-burst flux level in the 2019 event appears offset from the pre-burst level by an amount consistent with quasi-stable hydrogen burning due to the temperature-insensitive, hot-cno cycle, further suggesting hydrogen burning as the primary fuel source. this provides strong observational evidence for hydrogen-triggered bursts. we discuss our results in the context of previous theoretical modeling. | hydrogen-triggered x-ray bursts from sax j1808.4-3658? the onset of nuclear burning |
studying how the heated crust of a neutron star cools after an accretion outburst provides very valuable information about its structure and the nuclear reactions occurring in a neutron-rich high-density environment. we propose 3 chandra too observations (60 ks in total) and 12 ks supporting swift pointings of the frequently active transient x-ray binary aql x-1 after a bright/long outburst. our main aim is to test that crust cooling is observable in this source, which would open up an interesting opportunity in this research field: measuring multiple crust cooling curves of a single source after very different outbursts allows us to clearly separate the effects of the outburst parameters and the stellar properties on the heating and cooling of neutron star crusts. | new progress in understanding the crusts of neutron stars |
we use smoothed particle hydrodynamics to study viscous accretion flows around a weakly magnetic neutron star. we show the formation of multiple ``boundary" layers in presence of both cooling and viscosity. we find that with the introduction of a small viscosity in a sub-keplerian flow, much like the wind accretion in hmxbs such as cir x-1, only a single normal boundary layer (nbol) forms to adjust the rotational velocity component. with the increase of viscosity, the region extends radially and beyond some critical value, a radiative keplerian disk/layer (raked) forms between the sub-keplerian flow and the nbol. when viscosity is increased further only nbol and raked remain. in all such cases, the centrifugal pressure dominated boundary layer (cenbol) is formed, away from the star, as in the case of black holes. this is the first self-consistent study where such a transition from sub-keplerian flows has been reported for neutron stars. we also identify the connection between accretion and ejection of matter, following the two-component advective flow for black holes, for neutron stars. the results are crucial in the understanding of the formation of disks, boundary layers and outflows in wind dominated neutron star systems. | timing properties of shocked accretion flows around neutron stars -- ii. viscous disks and boundary layers |
4u 1608-52 is a soft x-ray transient. the analysis presented here of a particular part of its x-ray activity uses observations of rxte/asm and swift/bat. we show a time segment (mjd 54262-mjd 55090) (828 d) in which 4u 1608-52 behaved as a quasi-persistent x-ray source with a series of bumps, with a complicated relation between the evolution of fluxes in the soft (1.5-12 kev) and the hard (15-50 kev) x-ray regions. we ascribe these bumps to a series of propagations of heating and cooling fronts over the inner disk region without any transitions to the true quiescence. 4u 1608-52 oscillated around the boundary between the dominance of the comptonized component and the dominance of the multicolor accretion disk in its luminosity. only some of the bumps in this series were accompanied by a transition from the hard to the soft state; if it occurred, it displayed a strong hysteresis effect. the hard-band emission with the dominant comptonized component was present for most of this active state and showed a cycle of about 40 d. we argue that the cyclic variations of flux come from the inner disk region, not, e.g., from a jet. we also discuss the observed behavior of 4u 1608-52 in the context of other quasi-persistent low-mass x-ray binaries. | 4u 1608-52 as a quasi-persistent x-ray source |
the observation of x-rays during quiescence from transiently accreting neutron stars provides unique clues about the nature of dense matter. this, however, requires extensive modeling of the crusts and matching the results to observations. the pycnonuclear fusion reaction rates implemented in these models are theoretically calculated by extending phenomenological expressions and have large uncertainties spanning many orders of magnitude. we present the first sensitivity studies of these pycnonuclear fusion reactions in realistic network calculations. we also couple the reaction network with the thermal evolution code dstar to further study their impact on the neutron star cooling curves in quiescence. varying the pycnonuclear fusion reaction rates alters the depth at which nuclear heat is deposited although the total heating remains constant. the enhancement of the pycnonuclear fusion reaction rates leads to an overall shallower deposition of nuclear heat. the impurity factors are also altered depending on the type of ashes deposited on the crust. these total changes correspond to a variation of up to 9 ev in the modeled cooling curves. while this is not sufficient to explain the shallow heat source, it is comparable to the observational uncertainties and can still be important for modeling the neutron star crust. | impact of pycnonuclear fusion uncertainties on the cooling of accreting neutron star crusts |
the rapid neutron capture process (r-process) is responsible for the production of almost half of the natural elements heavier than iron. in order to obtain reliable calculations of r-process abundances for the models of neutron star merger and other potential astrophysical sites, precise and accurate information about neutron-rich isotopes, including their masses, is needed. in order to access the neutron-rich nuclei around the n =126 region to study the last and least explored r-process abundance peak, the future n =126 factory is under construction at argonne national laboratory (anl). the n =126 factory uses multi-nucleon transfer reactions to produce neutron-rich nuclei coming out close to the grazing angle. the products can be efficiently collected, separated and delivered to experiments for further study with the beam manipulation techniques developed for caribu, using the gas catcher, magnetic separator, rfq cooler-buncher and notre dame multi-reflection time-of-flight mass spectrometer (mr-tof). the status of the n =126 factory, commissioning results of the notre dame mr-tof before installation as well as the future mass measurement plan at the n =126 factory using canadian penning trap will be presented. this work is supported in part by the u.s. department of energy, office of nuclear physics, under contract no. de-ac02-06ch11357; by nserc (canada), application no. sappj-2018-00028; by the national science foundation under grant no. phy-2011890; by the university of notre dame; and with resources of anl's atlas facility, an office of science user facility. | accessing the last r-process abundance peak at the n=126 factory through high precision mass measurements |
we propose a new chandra epoch of the radio-quiet x-ray thermal isolated neutron star (xtins) rxj0806.4-4123 to measure its proper motion which will enable a kinematic age study. the kinematic ages of xtinss substantially deviate from their characteristic spin-down ages. since the xtinss allow to measure surface temperatures, their correct ages are a mandatory requisite to assess the general cooling behavior of neutron stars. based on previous studies, rxj0806.4-4123 seems to move slowly, but an accurate measurement is needed. it will also help to understand the unusual multiwavelength properties of this object. | proper motion of the isolated neutron star rx j0806-4123 |
the q-star structures, also called as gray holes with a radius of two times greater than the corresponding schwarzschild radius of same mass and from the compact neutron star family with a very high density, have been obtained by using a generalization of $q$-deformed fermions with two parameters $q$ and $p$ as the constituents of the star. because the interaction between particles are controlled by deformation parameters in $q,p$-fermions instead of a complicated interaction lagrangian, we consider the deformation parameters giving the maximum q-star pressure between the interacting particles of stars. the cold and hot q-stars in temperatures of $t=0$, $t=40\ \mathrm{mev}$ and $t=60\ \mathrm{mev}$ have been investigated from the numerical solutions of tov equations and it is obtained that the q-stars can reach up to $13$ solar mass and $75$ km radius. moreover, it is found that the total mass and radius of the star increase when the star gets cool down, and a much denser state is reached. | compact q-stars with q,p-deformed fermions |
neutron stars are identified as pulsars, x-ray binary components, central objects of supernovae remnants, or isolated thermally emitting sources and at distances beyond 120 pc. a population extrapolation suggests 103 objects within that boundary. potentially, neutron stars could continuously emit gravitational waves at sensitivity reach of present instrumentation. as part of our search for the nearest neutron stars ''five seasons'' project, we search for nearby resolved neutron stars. based on expected fluxes and magnitudes of thermally cooling neutron stars and pulsars, we selected sources in gaia dr3. the sources have g-band absolute magnitudes mg > 16 mag, parallax signal-to-noise ratios greater than two, and colours gbp - g < 0.78 and g - grp < 0.91 mag for power-law emitters of flux $f_{\nu } \propto \nu ^{-\alpha _{\nu }}$ with spectral indices αν < 3. the photometric region overlaps with that of white dwarfs, in confluence with most known pulsars in binaries having white dwarf companions. we looked for counterparts in gamma-ray, x-ray, ultraviolet, radio, optical, and infrared catalogues. we find about two x-ray-, 15 ultraviolet-, one radio probable counterparts, and at least four sources with power-law profiles at the ultraviolet-optical(-infrared). because the sources have g ⪆ 20 mag, we rely on gaia dr3 single-source parameters. we identify possible binaries based on photoastrometric parameters, visual companions, and flux excesses. some emission components suggest small thermal radii. source types, neutron star content, and properties require further inquiry. | search of nearby resolved neutron stars among optical sources |
some models of gamma-ray bursts (grbs) invoke nascent millisecond magnetars as the central engine and address the x-ray afterglows with the interaction of magnetar magnetospheres with fallback discs. we study the evolution of fallback discs interacting with the millisecond magnetars. initially, the accretion rate in the fallback disc is very high, well above the rate required for the eddington limit. the inner parts of such a disc, even if it is cooling by the neutrino emission, get spherical due to the radiation pressure, which regulates the mass-accretion rate within the spherization radius. such a disc can not penetrate the light cylinder radius for the typical magnetic fields, and the initial spin frequencies invoked for the magnetars. as a result of the autoregulation of the accretion flow, the fallback disc can not interact directly with the magnetar's magnetosphere within the first few days. this has implications for the fallback disc models of grb afterglows since the accretion and propeller luminosities, in the presence of radiation pressure, are too low to address the typical luminosities of x-ray afterglows. | evolution of fallback discs around millisecond magnetars: effect of supercritical accretion on grb afterglows |
the barium (ba) star phenomenon is unmissable from the study and understanding of nucleosynthetic processes occuring in agb stars. ba stars belong to binary systems, where the former agb polluted the companion, a less evolved star, which became enriched with material produced through the slow neuton capture process (s process). while the agb has evolved to a white dwarf, the currently observed ba star preserves the abundance pattern of the agb, allowing us to test the imprints of the $s$ process. comparing different agb nucleosynthetic models and ba star abundances, we are able to constrain the effect of the rotation velocity or the neutron source in the interior of the agb star. the trend in the ba star observations is predicted by non-rotating agb models where 13c is the main neutron source. the results of the comparison of models with initial agb masses from an independent source and the analysis of 28 ba giant star abundances confirm that the polluting agbs are of low mass. | probing the slow neutron capture process in agb stars using barium star abundances |
the 840-kyr-old pulsar psr j1957+5033, detected so far only in γ- and x-rays, is a nearby and rather cool neutron star with a temperature of 0.2-0.3 mk, a distance of $\lesssim 1$kpc, and a small colour reddening excess e(b - v) ≈ 0.03. these properties make it an ideal candidate to detect in the optical to get additional constraints on its parameters. we thus performed the first deep optical observations of the pulsar with the 10.4 m gran telescopio canarias in the g' band and found its possible counterpart with g' = 27.63 ± 0.26. the counterpart candidate position is consistent with the x-ray coordinates of the pulsar within the 0.5 arcsec accuracy. assuming that this is the real counterpart, we analysed the pulsar x-ray spectrum together with the derived optical flux density. as a result, we found that the thermal emission from the bulk surface of the cooling neutron star can significantly contribute to its optical flux. our multiwavelength spectral analysis favours the pulsar nature of the detected optical source, since it provides physically adequate parameters of the pulsar emission. we show that the optical data can provide new constraints on the pulsar temperature and distance. | likely optical counterpart of the cool middle-aged pulsar j1957+5033 |
novae are semi-detached binary systems in which a cool star fills its roche lobe. material from the cool star (the secondary) flows through the inner lagrangian point and is deposited onto the surface of a white dwarf (wd) via an accretion disc. in time, the base of the accreted layer becomes degenerate, and a thermonuclear runaway (tnr) occurs on the wd surface. this results in the explosive ejection of up to ∼ 10−4 m⊙ of material at several 100s to several 1000s of km s−1: a classical nova eruption has occurred. after the eruption, and the wd has returned to quiescence, mass transfer resumes and in time (of order a million years) conditions again become suitable for another nova eruption. therefore, all novae are recurrent, but there are those that repeat on a human timescale (of order < 100 yrs) and are known as recurrent novae (rne). the latter are of particular interest because the wd in these systems are thought to be close to the chandrasekhar limit. if the wd has a carbon-oxygen (co) composition, then it is potentially a progenitor of a type ia sn – a crucial tool in the determination of large-scale cosmic structure. if, on the other hand, the wd has an oxygen-neon (one) composition, then growth toward the chandrasekhar limit would drive accretion induced collapse to a neutron star and such an event should result in a low mass x-ray binary. hence, understanding rne events has wide application. here, we discuss recent optical/uv synoptic studies of the rne v3890 sgr, rs oph, and u sco and highlight derived insights into the rne phenomena. | synoptic optical/uv studies of recent recurrent novae – insights from déjá vu |
in the present work, we investigate the neutral-current neutrino-nucleon scattering in the nuclear medium using various energy-density functional models such as kids (korea-ibs-daegu-skku) and sly4, together with the quark-meson coupling model for the nucleon form factors at finite density. the differential cross-section and neutrino mean free path are computed numerically, considering the density-dependent nucleon form factors (ddff) and neutrino structural properties such as the neutrino magnetic moment (nmm) and its electric charge radius (ncr). it turns out that the ddff decreases the scattering cross-section, whereas the ncr increases it considerably. the effect of the nmm turns out to be almost negligible. we also observe that the value of the neutron effective mass is of importance in the neutron-star cooling process, indicating that for a neutron effective mass larger than the mass in free space, the neutrino can interact with matter at densities ρ ≳ 1.5ρ0 in a neutron star with radius 13 km. | neutrino propagation in the neutron star with uncertainties from nuclear, hadron, and particle physics |
it seems that the wealth of information revealed by the multi-messenger observations of the binary neutron star (ns) merger event, gw170817/grb 170817a/kilonova at2017gfo, places irreconcilable constraints to models of the prompt emission of this gamma-ray burst (grb). the observed time delay between the merger of the two nss and the trigger of the grb and the thermal tail of the prompt emission can hardly be reproduced by these models simultaneously. we argue that the merger remnant should be an ns (last for, at least, a large fraction of 1 s), and that the difficulty can be alleviated by the delayed formation of the accretion disk due to the absorption of high-energy neutrinos emitted by the ns and the delayed emergence of effective viscosity in the disk. further, we extend the consideration of the effect of the energy deposition of neutrinos emitted from the ns. if the ns is the central object of a grb with a distance and duration similar to that of grb 170817a, thermal emission of the thermal bubble inflated by the ns after the termination of accretion may be detectable. if our scenario is verified, it would be of interest to investigate the cooling of nascent nss. | revise thermal winds of remnant neutron stars in gamma-ray bursts |
the role of electron captures by nuclei in the shallow heating of magnetars is further investigated using both nuclear measurements and the theoretical atomic mass table hfb-27. starting from the composition of the outer crust in full equilibrium, we have calculated the onset of electron captures and the heat released due to the slow decay of the magnetic field. numerical results are found to be similar to those previously obtained with the hfb-24 atomic mass model and are consistent with neutron-star cooling data. | internal heating in magnetars: role of electron captures |
superbursts of neutron stars are rare but powerful events explained by the explosive burning of carbon in the deep layers of the outer envelope of the star. in this paper we perform a simulation of superbursts and propose a simple method for describing the neutrino stage of their cooling, as well as a method for describing the evolution of the burst energy on a scale of several months. we note a universal relation for the temperature distribution in the burnt layer at its neutrino cooling stage, as well as the unification of bolometric light curves and neutrino heat loss rates for deep and powerful bursts. we point out the possibility of long-term retention of the burst energy in the star's envelope. the results can be useful for interpretation of superburst observations. | neutrino emission of neutron-star superbursts |
statistical methods are frequently built upon assumptions that limit their applicability to certain problems and conditions. failure to recognize these limitations can lead to conclusions that may be inaccurate or biased. an example of such methods is the non-parametric efron-petrosian test statistic used in the studies of truncated data. we argue and show how the inappropriate use of this statistical method can lead to biased conclusions when the assumptions under which the method is valid do not hold. we do so by reinvestigating the evidence recently provided by multiple independent reports on the evolution of the luminosity/energetics distribution of cosmological long-duration gamma-ray bursts (lgrbs) with redshift. we show that the effects of detection threshold have been likely significantly underestimated in the majority of previous studies. this underestimation of detection threshold leads to severely incomplete lgrb samples that exhibit strong apparent luminosity-redshift or energetics-redshift correlations. we further confirm our findings by performing extensive monte carlo simulations of the cosmic rates and the luminosity/energy distributions of lgrbs and their detection process. | how unbiased statistical methods lead to biased scientific discoveries: a case study of the efron-petrosian statistic applied to the luminosity-redshift evolution of gamma-ray bursts |
there are still some significant and unanswered questions about the incredible very-high-energy γ -ray signatures. to help understand the mechanism, focusing on the linear and quadratic perturbation mode for the subluminal regime, we revisit the expected signature for the lorentz invariance violation (liv) effects on γ -γ absorption in the tev spectra of gamma-ray bursts (grbs). we note that there is a critical energy for the pair production process, which is sensitive to the assumed quantum gravity energy scale. we suggest that a reemergence of the energy spectrum of γ rays at several tens of tev is a rough observational diagnostic for the liv effects. the expected spectra characteristics are applied to grb 221009a. the results show that the cosmic opacity with liv effects considered here can roughly reproduce the observed γ -ray spectra for the source, which enables us to constrain the upper limit of the values of the energy scale to eqg ,1≤3.35 ×1020 gev for the linear perturbation and eqg ,2≤9.19 ×1012 gev for the quadratic perturbation. these scenarios lead to updated bounds on the liv coefficient, with ξ1'≥3.62 ×10-2 for the linear perturbation and ξ2'≥1.33 ×106 for the quadratic perturbation, in the standard model extension framework. | expected signature for the lorentz invariance violation effects on γ -γ absorption |
this manuscript presents a diagnostic analysis of three dark energy models resulting from the parametrization of the deceleration parameter. these models exhibit intriguing features, including late-time acceleration and a cosmological phase transition from early deceleration to late acceleration. the analysis utilizes parametrizations of the deceleration parameter, $q(z)$, and employs cosmic chronometers (cc), type ia supernovae (snia), gamma ray bursts (grb), quasar (q) and baryon acoustic oscillations (bao) datasets to constrain the models and determine the best-fitting values of the model parameters. additionally, the evolution of kinematic cosmographic parameters is investigated. the study focuses on discussing the statefinder and om diagnostic analyses of the considered models, comparing them with the well-established $\lambda$cdm and scdm models. by utilizing information criteria, the viability of the models is examined, assessing their goodness of fit and their ability to explain the observed data. the results provide valuable insights into the behavior and characteristics of the dark energy models. the comparison with the standard models sheds light on the similarities and differences, while the information criteria analysis offers a quantitative assessment of their suitability. this analysis contributes to our understanding of the dynamics and evolution of the universe, furthering our knowledge of dark energy and its role in shaping the cosmos. | diagnostic and comparative analysis of dark energy models with $q(z)$ parametrizations |
we report the radiation damage results of two new types of multi-pixel photon counter (mppc) under the 200 mev proton beam, for cosmic gamma-ray observations with cubesats. the new mppcs, s13360-6050cs and s14160-6050hs, have recently become commercially available by hamamatsu photonics k.k. (hpk). after 100 rad irradiation, the dark current increased by a factor of ∼100 and the threshold energy of gamma-ray detection by csi scintillator increased, but s14160-6050hs was less degraded. we then confirmed the annealing effects of the dark current and threshold energy for both. the decrease rate of the dark current in both mppcs were similar to those in the previous works. at 20 °c, the threshold energies of both mppcs reduced by several tens of percent after irradiation, but below 0 °c, the threshold energy of s14160-6050hs was not significantly lowered. we also confirmed that annealing began before one month post-irradiation. | annealing of proton radiation damages in si-pm at room temperature |
the correlation between the peak spectra energy (ep) and the equivalent isotropic energy (eiso) of long gamma-ray bursts (grbs), the so-called amati relation, is often used to constrain the high-redshift hubble diagram. assuming lambda cold dark matter cosmology, g.-j. wang et al. [astrophys. j. 836, 103 (2017), 10.3847/1538-4357/aa5b9b] found a ≳3 σ tension in the data-calibrated amati coefficients between low and high redshift grb samples. to reduce the impact of fiducial cosmology, we use the parametrization based on cosmic age (page), an almost model-independent framework to trace the cosmological expansion history. we find that the low and high redshift tension in amati coefficients stays almost the same for the broad class of models covered by page, indicating that the cosmological assumption is not the dominant driver of the redshift evolution of grb luminosity correlation. next, we analyze the selection effect due to flux limits in observations. we find amati relation evolves much more significantly across energy scales of eiso. we debias the grb data by selectively discarding samples to match low-z and high-z eiso distributions. after debiasing, the amati coefficients agree well between low-z and high-z data groups, whereas the evidence of eiso dependence of amati relation remains to be strong. thus, the redshift evolution of grb luminosity correlation can be fully interpreted as a selection bias and does not imply cosmological evolution of grbs. | reconciling low and high redshift grb luminosity correlations |
neutron star mergers are cosmic catastrophes that produce some of the most energetic observed phenomena: short gamma-ray bursts, gravitational wave signals, and kilonovae. the latter are optical transients, powered by radioactive nuclides which are synthesized when the neutron-rich ejecta of a disrupted neutron star undergoes decompression. we model this decompression phase using data from simulations of post-merger accretion disk winds. we use smoothed particle hydrodynamics with realistic nuclear heating to model the expansion over multiple scales, from initially several thousand km to billions of km. we then render a realistic image of a kilonova ejecta as it would appear for a nearby observer. this is the first time such a visualization is performed using input from state-of-the-art accretion disk simulations, nuclear physics and atomic physics. the volume rendering in our model computes an opacity transfer function on the basis of the physical opacity, varying significantly with the inhomogeneity of the neutron richness in the ejecta. other physical quantities such as temperature or electron fraction can be visualized using an independent color transfer function. we discuss several difficulties with the paraview application that we encountered during the visualization process, and give descriptions of our solutions and workarounds which could be used for future improvements. | realistic kilonova up close |
we present a catalog of the redshift estimates and probability distributions for 1366 individual long-duration gamma-ray bursts (lgrbs) detected by the burst and transient source experiment (batse). this result is based on a careful 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: peak luminosity, total isotropic emission, the spectral peak energy, and the intrinsic duration, while taking into account the 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 to average uncertainty ranges of $0.7$ and $1.7$ at $50\%$ and $90\%$ confidence levels, respectively. our predictions are almost entirely at odds with the previous estimates of batse redshifts based on the phenomenological high-energy correlations, in particular with the estimates derived from the lag-luminosity and the variability-luminosity relations. there is, however, a weak but significant correlation of strength $\sim0.26$ 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 in the literature. the presented catalog here can be useful for demographic studies of lgrbs and studies of individual batse events. | a catalog of redshift estimates for 1366 batse long-duration gamma-ray bursts: evidence for strong selection effects on the phenomenological prompt gamma-ray correlations |
baryon acoustic oscillations (bao) datasets use very precise measurements of the spatial distribution of large-scale structures as a distance ladder to help constrain cosmological parameters. in a recent article,1 we combined 17 uncorrelated bao measurements in the effective redshift range 0.106 ≤ z ≤ 2.36 with the cosmic chronometers data, the pantheon type ia supernova and the hubble diagram of gamma ray bursts and quasars to obtain that the λcdm model fit infers for the hubble constant: 69.85 ± 1.27km/sec/mpc and for the sound horizon distance: 146.1 ± 2.15mpc. beyond the λcdm model we test ωkcdm and wcdm and we get ωk = −0.076 ± 0.012, w = − 0.989 ± 0.049 accordingly. in this proceeding we present elaborate on our findings and we compare them to other recent results in the literature. | hints for the h0 — rd tension in uncorrelated baryon acoustic oscillations dataset |
the dispersion of fast radio bursts (frbs) is a measure of the large-scale electron distribution. it enables measurements of cosmological parameters, especially of the expansion rate and the cosmic baryon fraction. the number of events is expected to increase dramatically over the coming years, and of particular interest are bursts with identified host galaxy and therefore redshift information. in this paper, we explore the covariance matrix of the dispersion measure (dm) of frbs induced by the large-scale structure, as bursts from a similar direction on the sky are correlated by long-wavelength modes of the electron distribution. we derive analytical expressions for the covariance matrix and examine the impact on parameter estimation from the frb dm-redshift relation. the covariance also contains additional information that is missed by analysing the events individually. for future samples containing over ~300 frbs with host identification over the full sky, the covariance needs to be taken into account for unbiased inference, and the effect increases dramatically for smaller patches of the sky. also, forecasts must consider these effects as they would yield too optimistic parameter constraints. our procedure can also be applied to the dm of the afterglow of gamma-ray bursts. | cosmological covariance of fast radio burst dispersions |
aims: long gamma-ray bursts (lgrbs) have been shown to be powerful probes of the universe, in particular for studying the star formation rate up to very high redshift (z ∼ 9). since lgrbs are produced by only a small fraction of massive stars, it is paramount to have a good understanding of their underlying intrinsic population in order to use them as cosmological probes without introducing any unwanted bias. the goal of this work is to constrain and characterise this intrinsic population.methods: we developed a monte carlo model where each burst is described by its redshift and its properties at the peak of the light curve. we derived the best fit parameters by comparing our synthetic populations to carefully selected observational constraints based on the cgro/batse, fermi/gbm and swift/bat samples with appropriate flux thresholds. we explored different scenarios in terms of the cosmic evolution of the luminosity function and/or of the redshift distribution as well as including or not the presence of intrinsic spectral-energetics (ep − l) correlations.results: we find that the existence of an intrinsic ep − l correlation is preferred but with a shallower slope than observed (αa ∼ 0.3) and a larger scatter (∼0.4 dex). we find a strong degeneracy between the cosmic evolution of the luminosity and of the lgrb rate, and show that a sample both larger and deeper than shoals by a factor of three is needed to lift this degeneracy.conclusions: the observed ep − l correlation cannot be explained only by selection effects although these do play a role in shaping the observed relation. the degeneracy between the cosmic evolution of the luminosity function and of the redshift distribution of lgrbs should be included in the uncertainties of star formation rate estimates; these amount to a factor of 10 at z = 6 and up to a factor of 50 at z = 9. | constraining the intrinsic population of long gamma-ray bursts: implications for spectral correlations, cosmic evolution, and their use as tracers of star formation |
in this work, we use the angular diameter distances of 38 galaxy clusters with joint x-ray/sze observation to circumvent the circularity problem in the amati relation for gamma-ray bursts (grbs). assuming the validity of cosmic-distance duality relation, we obtain the luminosity distance from the cluster angular diameter distance and use that to calculate the isotropic equivalent energy of two different grb datasets, after restricting the grb redshift range to z < 0.9. we then use these grb datasets to test the amati relation at the low redshifts using the galaxy cluster distances. our best-fit amati relation parameters are consistent with a previous estimate for the same dataset. the intrinsic scatter which we obtain for the two datasets is about 45% and 15%, and is comparable with that found by other distance anchors used to study the amati relation. | low redshift calibration of the amati relation using galaxy clusters |
in this work, we restudy the dependence of luminosity function and event rates for different gamma-ray burst samples on the criteria of sample selection and threshold effect. to compare with many previous studies, we have chosen two samples including 88 and 118 long bursts with known redshift and peak flux over 2.6 ph cm-2 s-1, from which 79 bursts are picked out to constitute our complete sample. it is found that the evolution of luminosity with redshift can be expressed by l∝(1 + z)k with a diverse k relied more on the sample selection. interestingly, the cumulative distributions of either non-evolving luminosities or redshifts are found to be also determined by the sample selection rather than the instrumental sensitivity. nevertheless, the non-evolving luminosities of our samples are similarly distributed with a comparable break luminosity of l0 ~ 1051 erg s-1. importantly, we verify with a k-s test that three cases of event rates for the two burst samples evolve with redshift similarly except a small discrepancy due to sampling differences at low-redshift of z < 1, in which all event rates show an excess of gaussian profile instead of monotonous decline no matter whether the sample is complete. most importantly, it is found that the burst rates violate the star formation rate at low redshift, while both of them are good in agreement with each other in the higher-redshift regions as many authors discovered previously. therefore, we predict that two types of long bursts are favored in terms of their associations with both the star formation and the cosmic metallicity. | a comparative study of luminosity functions and event rate densities of long grbs with non-parametric method |
in this paper, we investigate the energy function, formation rate, and environment of fast radio bursts (frbs) using parkes sample and australian square kilometer array pathfinder (askap) sample. for the first time, the metallicity effect on the formation rate is considered. if frbs are produced by the mergers of compact binaries, the formation rate of frbs should have a time delay relative to cosmic star formation rate (csfr). we get the time delay is about 3-5 gyr and the index of differential energy function γ (dn/de∝e-γ) is between 1.6 and 2.0 from redshift cumulative distribution. the value of γ is similar to that of frb 121102, which indicates single bursts may share the same physical mechanism with the repeaters. in another case, if the formation rate of frb is proportional to the sfr without time delay, the index γ is about 2.3. in both cases, we find that frbs may prefer to occur in low-metallicity environment with 12 + \log ({o/h}) ∼eq 8.40, which is similar to those of long gamma-ray bursts (grbs) and hydrogen-poor superluminous supernovae (slsne-i). | energy function, formation rate, and low-metallicity environment of fast radio bursts |
we perform zoom-in cosmological simulations of a suite of dwarf galaxies, examining the impact of cosmic rays (crs) generated by supernovae, including the effect of diffusion. we first look at the effect of varying the uncertain cr parameters by repeatedly simulating a single galaxy. then we fix the comic ray model and simulate five dwarf systems with virial masses range from 8 to 30 × 1010 m⊙. we find that including cr feedback (with diffusion) consistently leads to disc-dominated systems with relatively flat rotation curves and constant star formation rates. in contrast, our purely thermal feedback case results in a hot stellar system and bursty star formation. the cr simulations very well match the observed baryonic tully-fisher relation, but have a lower gas fraction than in real systems. we also find that the dark matter cores of the cr feedback galaxies are cuspy, while the purely thermal feedback case results in a substantial core. | cosmological simulations of dwarf galaxies with cosmic ray feedback |
the delay in arrival times between high and low energy photons from cosmic sources can be used to test the violation of the lorentz invariance (liv), predicted by some quantum gravity theories, and to constrain its characteristic energy scale eqg that is of the order of the planck energy. gamma-ray bursts (grbs) and blazars are ideal for this purpose thanks to their broad spectral energy distribution and cosmological distances: at first order approximation, the constraints on eqg are proportional to the photon energy separation and the distance of the source. however, the liv tiny contribution to the total time delay can be dominated by intrinsic delays related to the physics of the sources: long grbs typically show a delay between high and low energy photons related to their spectral evolution (spectral lag). short grbs have null intrinsic spectral lags and are therefore an ideal tool to measure any liv effect. we considered a sample of 15 short grbs with known redshift observed by swift and we estimate a limit on eqg ≳ 1.5 × 1016 gev. our estimate represents an improvement with respect to the limit obtained with a larger (double) sample of long grbs and is more robust than the estimates on single events because it accounts for the intrinsic delay in a statistical sense. | limits on quantum gravity effects from swift short gamma-ray bursts |
we investigate the possibilities of reconstructing the cosmic equation of state (eos) for high redshift. in order to obtain general results, we use two model-independent approaches. the first reconstructs the eos using comoving distance and the second makes use of the hubble parameter data. to implement the first method, we use a recent set of gamma-ray bursts (grbs) measures. to implement the second method, we generate simulated data using the sandage-loeb (sl) effect; for the fiducial model, we use the λ c d m model. in both cases, the statistical analysis is conducted through the gaussian processes (non-parametric). in general, we demonstrate that this methodology for reconstructing the eos using a non-parametric method plus a model-independent approach works appropriately due to the feasibility of calculation and the ease of introducing a priori information (h0 and ωm 0). in the near future, following this methodology with a higher number of high quality data will help obtain strong restrictions for the eos. | reconstruction of the cosmic equation of state for high redshift |
the cosmic evolution of gamma-ray burst (grb) luminosity is essential for revealing the grb physics and for using grbs as cosmological probes. we investigate the luminosity evolution of long grbs with a large sample of 258 swift/bat grbs. by describing the peak luminosity evolution of individual grbs as {l}{{p}}\propto \text{}{(1+z)}k, we get k=1.49+/- 0.19 using the nonparametric τ statistics method without considering observational biases of grb trigger and redshift measurement. by modeling these biases with the observed peak flux and characterizing the peak luminosity function of long grbs as a smoothly broken power law with a break that evolves as {l}{{b}}\propto {(1+z)}{k{{b}}}, we obtain {k}{{b}}={1.14}-0.47+0.99 through simulations based on the assumption that the long grb rate follows the star formation rate incorporating the cosmic metallicity history. the derived k and kb values are systematically smaller than those reported in previous papers. by removing the observational biases of the grb trigger and redshift measurement based on our simulation analysis, we generate mock complete samples of 258 and 1000 grbs to examine how these biases affect the τ statistics method. we get k=0.94+/- 0.14 and k=0.80+/- 0.09 for the two samples, indicating that these observational biases may lead to overestimating the k value. with the large uncertainty of kb derived from our simulation analysis, one cannot even convincingly argue for a robust evolution feature of the grb luminosity. | cosmic evolution of long gamma-ray burst luminosity |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.