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1998-08-27
|
Iron Opacity and the Pulsar of Supernova 1987A
|
Neutron stars formed in Type II supernovae are likely to be initially
obscured by late-time fallback. Although much of the late-time fallback is
quickly accreted via neutrino cooling, some material remains on the neutron
star, forming an atmosphere which slowly accretes through photon emission. In
this paper, we derive structure equations of the fallback atmosphere and
present results of one-dimensional simulations of that fallback. The atmosphere
remaining after neutrino cooling becomes unimportant (less than the Compton
Eddington limit) is only a fraction of the total mass accreted (10^-8 of the
accreted mass or 10^-9 solar masses.) Recombined iron dominates the opacity in
the outer regions leading to an opacity 1000-10,000 times higher than that of
electron scattering alone. The resultant photon emission of the remnant
atmosphere is limited to 1/1000th the Compton Eddington Luminosity. The
late-time evolution of this system leads to the formation of a photon-driven
wind from the accretion of the inner portion of the atmosphere, leaving, for
most cases, a bare neutron star on timescales shorter than a year. The
degenerate remnant of 1987a may not be a black hole. Instead, the fallback
material may have already accreted or blown off in the accretion-driven wind.
If the neutron star has either a low magnetic field or a low rotational spin
frequency, we would not expect to see the neutron star remnant of 1987a.
|
9808309v1
|
1998-10-28
|
Reprocessing and Variable Cold Absorption in the Broad-Line Radio Galaxy 3C390.3
|
A BeppoSAX observation of the BLRG 3C390.3 is reported. For the first time,
both the 6.4 keV iron line and a strong reflection hump, produced by the
illumination of the primary X-ray emission on cold matter, are detected in this
source. The 0.1-100 keV continuum is modeled by an absorbed power law (\Gamma~
1.8) reflected at high energies by material with a fairly large covering factor
(\Omega/2\pi~1). The iron line is intrinsically narrow ($\sigma=73(+207,-73)
eV) and has an equivalent width of ~140$ eV. We discuss the results in the
context of current models for AGNs and suggest that the primary X-ray power law
continuum is probably produced by a hot inner flow, while the reprocessed
radiation comes from an outer cold thin disk, and/or from a thick torus at even
larger radii. Further observations with BeppoSAX could distinguish between the
latter two cases. Beamed radiation associated to the radio jet is unlikely to
contribute significantly to the X-ray emission. Finally, an historical study of
the column density NH, also reported here, shows that the absorption along the
line of sight changes in time. The NH time variability, which is not correlated
with that of the primary continuum, seems to imply variations of the geometry
of the absorber rather than variations in the ionization state of the gas.
|
9810450v1
|
1998-11-16
|
A Comparison of Metal Enrichment Histories in Rich Clusters and Individual Luminous Elliptical Galaxies
|
Hot, X-ray emitting gaseous halos around massive elliptical galaxies are a
result of both stellar mass loss and inflow toward the overdensity from which
giant ellipticals and their associated galaxy groups formed. The metal
abundance in this gas contains important information about early star formation
and past supernova activity. We find that Type II supernovae based on a
Salpeter IMF, plus a small number of additional Type Ia supernovae, can explain
the the density, temperature and abundance profiles currently observed in
gaseous halos around massive ellipticals. Within the central, optically bright
regions of luminous ellipticals, approximately half of the interstellar iron is
produced by Type Ia supernovae and half by mass lost from evolving stars which
were originally enriched by Type II supernovae. However, iron and silicon
abundances in the intracluster gas within rich clusters suggest enrichment by a
larger number of supernovae per unit optical light than we require for massive
ellipticals, either more Type Ia or more Type II from a flatter IMF. Since the
enrichment histories of massive ellipticals and rich clusters are fundamentally
different, E and SO galaxies may not be the only sources of metal enrichment in
rich cluster gas.
|
9811258v1
|
1999-01-09
|
Constraining the Role of SN Ia and SN II in Galaxy Groups by Spatially Resolved Analysis of ROSAT and ASCA Observations
|
We present the results of modelling the distribution of gas properties in the
galaxy groups HCG51, HCG62 and NGC5044, and in the poor cluster AWM7, using
both ASCA SIS and ROSAT data. The spectral quality of the ASCA data allows the
radial distribution in the abundances of several elements to be resolved. In
all systems apart from HCG51, we see both central cooling flows, and a general
decline in metal abundances with radius. The ratio of iron to alpha-element
abundances varies significantly, and in comparison with theoretical supernova
yields, indicates a significant contribution to the metal abundance of the
intergalactic medium (IGM) from type Ia supernovae. This is seen both within
the groups, and also throughout much of the cluster AWM7. The total energy
input into the IGM from supernovae can be calculated from our results, and is
typically 20-40 per cent of the thermal energy of the gas, mostly from SNe II.
Our results support the idea that the SN II ejecta have been more widely
distributed in the IGM, probably due to the action of galaxy winds, and the
lower iron mass to light ratio in groups suggests that some of this enriched
gas has been lost altogether from the shallower potential wells of the smaller
systems.
|
9901100v1
|
1999-01-16
|
Concave Accretion Discs and X-ray Reprocessing
|
Spectra of Seyfert Is are commonly modelled as emission from an X-ray
illuminated flat accretion disc orbiting a central black hole. This provides
both a reprocessed and direct component of the X-ray emission as required by
observations of individual objects and possibly a fraction of the cosmological
X-ray background. There is some observational motivation to at least consider
the role that an effectively concave disc surface might play: (1) a reprocessed
fraction $\gsim 1/2$ in some Seyferts and possibly in the X-ray background, and
(2) the commonality of a sharp iron line peak for Seyferts at 6.4KeV despite a
dependence of peak location on inclination angle for flat disc models. Here it
is shown that a concave disc may not only provide a larger total fraction of
reprocessed photons, but can also reprocess a much larger fraction of photons
in its outer regions when compared to a flat disc. This reduces the sensitivity
of the 6.4KeV peak location to the inner disc inclination angle because the
outer regions are less affected by Doppler and gravitational effects. If the
X-ray source is isotropic, the reprocessed fraction is directly determined by
the concavity. If the X-ray source is anisotropic, the location of iron line
peak can still be determined by concavity but the total reflected fraction need
not be as large as for the isotropic emitter case. The geometric calculations
herein are applicable to general accretion disc systems illuminated from the
center.
|
9901216v2
|
1999-03-30
|
The complex 0.1-200 keV spectrum of the Seyfert 1 Galaxy NGC4593
|
We report on the first observation of the Seyfert 1 galaxy NGC4593 in the
0.1-200 keV band, performed with the BeppoSAX observatory. Its spectral
components are for the first time simultaneously measured: a power-law with
photon spectral index ~1.9; the Compton-reflection of the primary power-law; a
moderately broad (>60 eV) K-alpha fluorescent line from neutral iron; and an
absorption edge, whose threshold energy is consistent with K-shell
photoionization from OVII. The amount of reflection and the iron line
properties are consistent with both being produced in a plane-parallel, X-ray
illuminated relativistic accretion disc surrounding the nuclear black hole,
seen at an inclination of 30 degrees. Any cutoff of the intrinsic continuum is
constrained to lay above 150 keV. The claim for a strongly variable soft excess
is dismissed by our data and by a reanalysis of archival ASCA and ROSAT data.
|
9903449v1
|
1999-06-23
|
Iron line signatures in X-ray afterglows of GRB by BeppoSAX
|
We report the possible detection (99.3% of statistical significance) of
redshifted Fe iron line emission in the X-ray afterglow of Gamma-ray burst
GRB970508 observed by BeppoSAX. Its energy is consistent with the redshift of
the putative host galaxy determined from optical spectroscopy. In contrast to
the fairly clean environment expected in the merging of two neutron stars, the
observed line properties would imply that the site of the burst is embedded in
a large mass of material ($>0.5 \Ms$), consistent with pre-explosion ejecta of
a very massive star. This material could be related with the outburst observed
in the afterglow 1 day after the GRB and with the spectral variations measured
during this phase. We did not find evidence of Fe line in two other GRB with
known redshift (GB971214 and GB980613), but we note that the upper limits are
of the same order of the intensity measured in GB97508 and that none of these
afterglows shows rebursting activity.
|
9906363v1
|
1999-07-09
|
Simultaneous EUVE/ASCA/RXTE Observations of NGC 5548
|
We present simultaneous observations by EUVE, ASCA, and RXTE of the type~1
Seyfert galaxy NGC 5548. These data indicate that variations in the EUV
emission (at $\sim 0.2 $keV) appear to lead similar modulations in higher
energy ($\ga 1 $keV) X-rays by $\sim$10--30 ks. This is contrary to popular
models which attribute the correlated variability of the EUV, UV and optical
emission in type~1 Seyferts to reprocessing of higher energy radiation. This
behavior instead suggests that the variability of the optical through EUV
emission is an important driver for the variability of the harder X-rays which
are likely produced by thermal Comptonization. We also investigate the spectral
characteristics of the fluorescent iron K$\alpha$ line and Compton reflection
emission. In contrast to prior measurements of these spectral features, we find
that the iron K$\alpha$ line has a relatively small equivalent width
($W_{K\alpha} \sim 100 $eV) and that the reflection component is consistent
with a covering factor which is significantly less than unity ($\Omega/2\pi
\sim 0.4$--0.5). Notably, although the 2--10 keV X-ray flux varies by $\sim \pm
25$% and the derived reflection fraction appears to be constant throughout our
observations, the flux in the Fe~K$\alpha$ line is also constant. This behavior
is difficult to reconcile in the context of standard Compton reflection models.
|
9907114v1
|
1999-07-14
|
The properties of the relativistic iron K-line in NGC 3516
|
We present an analysis of the relativistic iron K-alpha line in the Seyfert 1
galaxy NGC 3516, based on a continuous, five-day ASCA observation. The broad
profile which has been found in several other AGN is confirmed in NGC 3516 with
unprecedented signal-to-noise ratio. Disk-line models with either a Kerr or
Schwarzschild metric fit the integrated profile, but both require emission very
strongly concentrated in the inner disk. We find tentative evidence for the
line signatures of Ni K-alpha and/or Fe K-beta. The continuum flux varied by
\~50 per cent during the observation and time-resolved analysis shows that the
line also changes. The line core seems to follow the continuum, but the blue
wing is unrelated and shows a greater amplitude (factor ~2) of variability. The
red wing is formally consistent with a constant but appears to be correlated
with the blue wing. We interpret this as evidence for independent variability
of the broadest parts of the line. There also appears to be an absorption
feature in the profile, consistent with resonance scattering in infalling
material. This variable feature may be the signature of material being accreted
by the central black hole.
|
9907193v1
|
1999-09-01
|
Evidence for Doppler-Shifted Iron Emission Lines in Black Hole Candidate 4U 1630-47
|
We report the first detection of a pair of correlated emission lines in the
X-ray spectrum of black hole candidate 4U 1630-47 during its 1996 outburst,
based on RXTE observations of the source. At the peak plateau of the outburst,
the emission lines are detected, centered mostly at $\sim$5.7 keV and $\sim$7.7
keV, respectively, while the line energies exhibit random variability $\sim$5%.
Interestingly, the lines move in a concerted manner to keep their separation
roughly constant. The lines also vary greatly in strength, but with the
lower-energy line always much stronger than the higher-energy one. The measured
equivalent width ranges from $\sim$50 eV to $\sim$270 eV for the former, and
from insignificant detection to $\sim$140 eV for the latter; the two are
reasonably correlated.
The correlation between the lines implies a causal connection --- perhaps
they share a common origin. Both lines may arise from a single $K_{\alpha}$
line of highly ionized iron that is Doppler-shifted either in a Keplerian
accretion disk or in a bi-polar outflow or even both. In both scenarios, a
change in the line energy might simply reflect a change in the ionization state
of line-emitting matter. We discuss the implication of the results and also
raise some questions about such interpretations.
|
9909023v1
|
1999-11-10
|
Nucleosynthesis and Clump Formation in a Core Collapse Supernova
|
High-resolution two-dimensional simulations were performed for the first five
minutes of the evolution of a core collapse supernova explosion in a 15 solar
mass blue supergiant progenitor. The computations start shortly after bounce
and include neutrino-matter interactions by using a light-bulb approximation
for the neutrinos, and a treatment of the nucleosynthesis due to explosive
silicon and oxygen burning. We find that newly formed iron-group elements are
distributed throughout the inner half of the helium core by Rayleigh-Taylor
instabilities at the Ni+Si/O and C+O/He interfaces, seeded by convective
overturn during the early stages of the explosion. Fast moving nickel mushrooms
with velocities up to about 4000 km/s are observed. This offers a natural
explanation for the mixing required in light curve and spectral synthesis
studies of Type Ib explosions. A continuation of the calculations to later
times, however, indicates that the iron velocities observed in SN 1987 A cannot
be reproduced because of a strong deceleration of the clumps in the dense shell
left behind by the shock at the He/H interface.
|
9911183v2
|
1999-12-07
|
BeppoSAX uncovers a type-2 QSO in the hyperluminous infrared galaxy IRAS 09104+4109
|
We studied with BeppoSAX the infrared luminous galaxy IRAS 09104+4109 over a
very wide X-ray band from 0.1 to 80 keV. Our observations indicate the
dominance of a thermal component at energies below 8 keV, which we attribute to
the free-free emission from the intracluster (IC) plasma surrounding the
source. Above 10 keV we find evidence for the existence of flux in excess with
respect to the free-free IC plasma emission. This, together with the marginal
detection of a neutral iron line at $\sim 6.4$ keV, gives a strong indication
for the presence of an AGN deeply buried within the source. This component is
best modelled by a strongly absorbed (N_H > 5 10^{24} cm^{-2}) power-law plus
unabsorbed reflection spectrum (0.15<R<0.3), which is also responsible for the
cold iron line. The unabsorbed broad-band (2-100 keV) X-ray emission of this
AGN is 2.5 10$^{46} erg/s, well within the range of quasar luminosities. Our
results indicate that IRAS 09104+4109 is indeed the prototype of a rare class
of sources, the luminous type-2 QSOs. The association of this source with a
huge cooling-flow of $\sim 1000 M_\odot$ in the cluster, as indicated by the
X-ray data, might suggest that such condition of extremely fast mass
accumulation could favour the survival of a thick obscuring envelope, which
would otherwise be quickly destroyed by the very luminous central source.
|
9912127v1
|
1999-12-25
|
Global Relationships among Physical Properties of Galaxy Cluster Cores
|
Using X-ray data, we investigate interrelations between gas density rho_0,
virial density rho_vir, core radius R, temperature T, entropy S_gas, and metal
abundance Z in the core region of clusters of galaxies. First, we confirm that
fundamental relations among rho_0, R, and T found by Fujita and Takahara are
reproduced by another data catalogue. Second, we find that, when clusters have
two components in their surface brightness distribution, the inner components
also satisfy the same fundamental relations on the assumption that the average
temperature of the inner component is the same as that of the outer component.
These results strengthen our interpretation that clusters form a two parameter
family in terms of mass and rho_vir; larger rho_vir corresponds to earlier
formation epoch. We argue that the inner components represent distinct dark
matter components which collapsed ahead of the outer components. Third, we also
find a tight relation between S_gas and rho_vir both for the outer and inner
components; S_gas is smaller for larger rho_vir but is larger than that
produced through gravitational collapse alone for larger rho_vir. Although
radiative cooling affects the thermal evolution, the tight relationship
discovered suggests the existence of stable heating sources or stable energy
transmission mechanisms. Finally, we find that the iron abundance at the
centers of clusters is correlated with rho_vir for the inner components. This
implies that iron produced by Type Ia supernovae has more accumulated for
clusters formed earlier. We briefly discuss the implications of these findings.
|
9912515v1
|
2000-01-15
|
Helium Emission in the Type Ic SN 1999cq
|
We present the first unambiguous detection of helium emission lines in
spectra of Type Ic supernovae (SNe Ic). The presence of He I lines, with full
width at half maximum ~ 2000 km/s, and the distinct absence of any other
intermediate-width emission (e.g., Halpha), implies that the ejecta of SN Ic
1999cq are interacting with dense circumstellar material composed of almost
pure helium. This strengthens the argument that the progenitors of SNe Ic are
core-collapse events in stars that have lost both their hydrogen and helium
envelopes, either through a dense wind or mass-transfer to a companion. In this
way, SN 1999cq is similar to supernovae such as SN 1987K and SN 1993J that
helped firmly establish a physical connection between Type Ib and Type II
supernovae. The light curve of SN 1999cq is very fast, with an extremely rapid
rise followed by a quick decline. SN 1999cq is also found to exhibit a high
level of emission at blue wavelengths (< 5500 A), likely resulting from either
an unusually large amount of iron and iron-group element emission or
uncharacteristically low reddening compared with other SNe Ic.
|
0001270v1
|
2000-01-18
|
WWhat Heavy Elements in Clusters of Galaxies Tell About Clusters and Galaxies
|
Clusters of galaxies allow a direct estimate of the metallicity and metal
production yield on the largest scale so far. The ratio of the total iron mass
in the ICM to the total optical luminosity of the cluster (the iron
mass-to-light-ratio) is the same for all clusters which ICM is hotter than
$\sim 2$ keV, and the elemental proportions (i.e. the [$\alpha$/Fe] ratio)
appear to be solar. The simplest interpretation of these evidences is that both
the IMF as well the relative contributions of SN types are universal. Currently
available abundances in cooler clusters and groups are much more uncertain,
possibly due to insufficiently accurate atomic physics data for multi-electron
ions, or to the ICM being multi-phase, or to a combination thereof. This
uncertainty automatically extends to the reality of radial abundance gradients
so far reported in cool clusters. It is emphasized that most metals reside in
the ICM rather than in galaxies, which demonstrates that energetic winds
operated early in the evolution of massive galaxies, the likely producers of
most metals now in the ICM. The ICM metallicity is also used to set a
semiempirical constraint of $\sim 0.1$ keV per particle to the ICM {\it
preheating} due to supernova driven galactic winds. A lower limit of the
universe global metallicity at $z=3$ is also mentioned.
|
0001312v1
|
2000-02-01
|
The relativistic iron line profile in the Seyfert 1 Galaxy IC4329a
|
We present simultaneous ASCA and RXTE data on the bright Seyfert 1 galaxy
IC4329a. The iron line is significantly broadened, but not to the extent
expected from an accretion disk which extends down to the last stable orbit
around a black hole. We marginally detect a narrow line component, presumably
from the molecular torus, but even including this gives a line profile from the
accretion disk which is significantly narrower that that seen in MCG-6-30-15,
and is much more like that seen from the low/hard state galactic black hole
candidates. This is consistent with the inner disk being truncated before the
last stable orbit, forming a hot flow at small radii as in the ADAF models.
However, we cannot rule out the presence of an inner disk which does not
contribute to the reflected spectrum, either because of extreme ionisation
suppressing the characteristic atomic features of the reflected spectrum or
because the X-ray source is intrinsically anisotropic, so it does not
illuminate the inner disk.
The source was monitored by RXTE every 2 days for 2 months, and these
snapshot spectra show that there is intrinsic spectral variability. The data
are good enough to disentangle the power law from the reflected continuum and
we see that the power law softens as the source brightens. The lack of a
corresponding increase in the observed reflected spectrum implies that either
the changes in disk inner radial extent/ionisation structure are small, or that
the variability is actually driven by changes in the seed photons which are
decoupled from the hard X-ray mechanism.
|
0002023v1
|
2000-02-02
|
Stellar Iron Abundances at the Galactic Center
|
We present measurements of [Fe/H] for six M supergiant stars and three giant
stars within 0.5 pc of the Galactic Center (GC) and one M supergiant star
within 30 pc of the GC. The results are based on high-resolution (lambda /
Delta lambda =40,000) K-band spectra, taken with CSHELL at the NASA Infrared
Telescope Facility.We determine the iron abundance by detailed abundance
analysis,performed with the spectral synthesis program MOOG.The mean [Fe/H] of
the GC stars is determined to be near solar,[Fe/H] = +0.12 $\pm$ 0.22. Our
analysis is a differential analysis, as we have observed and applied the same
analysis technique to eleven cool, luminous stars in the solar neighborhood
with similar temperatures and luminosities as the GC stars. The mean [Fe/H] of
the solar neighborhood comparison stars, [Fe/H] = +0.03 $\pm$ 0.16, is similar
to that of the GC stars. The width of the GC [Fe/H] distribution is found to be
narrower than the width of the [Fe/H] distribution of Baade's Window in the
bulge but consistent with the width of the [Fe/H] distribution of giant and
supergiant stars in the solar neighborhood.
|
0002062v1
|
2000-02-23
|
ISO spectroscopy of circumstellar dust in the Herbig Ae systems AB Aur and HD 163296
|
Using both the Short- and Long-wavelength Spectrometers on board the Infrared
Space Observatory (ISO), we have obtained infrared spectra of the Herbig Ae
systems AB Aur and HD 163296. In addition, we obtained ground-based N band
images of HD 163296. Our results can be summarized as follows: (1) The main
dust components in AB Aur are amorphous silicates, iron oxide and PAHs; (2) The
circumstellar dust in HD 163296 consists of amorphous silicates, iron oxide,
water ice and a small fraction of crystalline silicates; (3) The infrared
fluxes of HD 163296 are dominated by solid state features; (4) The colour
temperature of the underlying continuum is much cooler in HD 163296 than in AB
Aur, pointing to the existence of a population of very large (mm sized) dust
grains in HD 163296; (5) The composition and degree of crystallization of
circumstellar dust are poorly correlated with the age of the central star. The
processes of crystallization and grain growth are also not necessarily coupled.
This means that either the evolution of circumstellar dust in protoplanetary
disks happens very rapidly (within a few Myr), or that this evolution is
governed by factors other than stellar mass and age.
|
0002440v1
|
2000-06-05
|
Iron K line Variability in the Low-Luminosity AGN NGC 4579
|
We present results of new ASCA observations of the low-luminosity AGN (LLAGN)
NGC 4579 obtained on 1998 December 18 and 28, and we report on detection of
variability of an iron K emission line. The X-ray luminosities in the 2--10 keV
band for the two observations are nearly identical (LX $\approx$
2$\times10^{41}$ ergs/s), but they are $\sim$35% larger than that measured in
1995 July by Terashima et al. An Fe K emission line is detected at
$6.39\pm0.09$ keV (source rest frame) which is lower than the line energy
$6.73^{+0.13}_{-0.12}$ keV in the 1995 observation. If we fit the Fe lines with
a blend of two Gaussians centered at 6.39 keV and 6.73 keV, the intensity of
the 6.7 keV line decreases, while the intensity of the 6.4 keV line increases,
within an interval of 3.5 yr. This variability rules out thermal plasmas in the
host galaxy as the origin of the ionized Fe line in this LLAGN. The detection
and variability of the 6.4 keV line indicates that cold matter subtends a large
solid angle viewed from the nucleus and that it is located within $\sim1$ pc
from the nucleus. It could be identified with an optically thick standard
accretion disk. If this is the case, a standard accretion disk is present at
the Eddington ratio of $L_{\rm Bol}/L_{\rm Eddington} \sim 2\times10^{-3}$. A
broad disk-line profile is not clearly seen and the structure of the innermost
part of accretion disk remains unclear.
|
0006055v1
|
2000-06-30
|
Chemical abundances in seven red giants of NGC 2360 and NGC 2447
|
Chemical abundances of about fifteen elements from oxygen to europium are
measured in seven red giants of the two open clusters NGC 2360 and NGC 2447.
The effective temperatures of the giants are determined spectroscopically by
taking advantage of their known masses (~2 Mo in NGC 2360 and ~3 Mo in NGC
2447) and bolometric magnitudes.
The average iron abundances we obtain for the two clusters are [Fe/H]=0.07
for NGC 2360 and [Fe/H]=0.03 for NGC 2447.
Evolutionary stellar model calculations are performed in the mass range 1-4
Mo in order to analyze the surface Na and O abundances predicted after the
first dredge-up. The sodium abundance shows a well defined correlation with
stellar mass in the 2-3 Mo range. The agreement between our Na abundance
determinations in NGC 2360 and our model predictions at 2 Mo is very good. In
contrast, the overabundance in one of the three stars in NGC 2447 exceeds that
predicted at 3 Mo by ~0.08 dex, which is significant compared to the
observational error bars. The effects of core overshooting, convection
prescription, metallicity and nuclear reaction rates on the Na surface
predictions of our models are investigated.
An oxygen deficiency relative to iron by 0.2 dex is measured in our stars, in
disagreement with our model predictions. Assuming that the Sun is 0.1-0.3 dex
enriched in oxygen relative to neighbor stars could explain the discrepancy.
|
0006442v1
|
2000-07-24
|
Iron K line emission in AGN: observations
|
Iron K-alpha lines are key diagnostics of the central regions of AGN. Their
profiles indicate that they are formed deep in the potential well of the
central black hole, where extreme broadening and red shift occur. The profiles
are most easily reproducible in an accretion disk: the lack of significant
emission blue-ward of the rest energy is difficult produce in other geometries.
In one source an apparent (and perhaps variable) absorption feature in the red
wing of the line may represent rare evidence for inflow onto the black hole.
Sample analysis has defined the mean properties, showing a strong concentration
of the emission in the central regions and face-on accretion disks, at least in
Seyfert 1 galaxies. Surprising results have been obtained from examination of
the line variability. Strong profile changes may be accounted for by changes in
the illumination pattern of the central, relativistic part of the disk. In at
least the case of MCG-6-30-15, there is evidence for emission from within 6
R_g, possibly indicating a spinning black hole. Developing an understanding of
these complex changes has the potential to reveal the geometry and kinematics
of the inner few gravitational radii around extragalactic black holes.
|
0007356v1
|
2000-08-01
|
Atomic data from the Iron Project XLV. Relativistic transition probabilities for carbon-like Ar XIII and Fe XXI using Breit-Pauli R-matrix method
|
The Breit-Pauli R-matrix method developed under the Iron Project has been
used to obtain extensive sets of oscillator strengths and transition
probabilities for dipole allowed and intercombination fine structure
transitions in carbon like ions, Ar XIII and Fe XXI. The complete set consists
of 1274 fine structure bound energy levels and 198,259 oscillator strengths for
Ar XIII, and 1611 bound levels and 300,079 oscillator strengths for Fe XXI.
These correspond to levels of total angular momenta of 0 <= J <= 7 of even and
odd parities formed from total spin of 2S+1=5,3,1, and orbital angular momenta
0 <= L <= 9 with n <= 10, 0 <= l <= 9 for each ion. The relativistic effects
are included in the Breit-Pauli approximation. The close coupling wavefunction
expansion for each ion is represented by the lowest 15 fine structure levels of
target configuations, 2s2.2p, 2s.2p2 and 2p3. The energy levels are identified
spectroscopically using a newly developed identification procedure. The
procedure also makes a correspondence between the fine strucure energy levels
and LS terms. This provides the check for completeness of the calculated
levels. Comparison is made of the present energies and the f-values with the
available observed and theoretical values. Present transition probabilitis
agree very well with the relativistic atomic structure calculations of Mendoza
et al. for the intercombination transitions, 2s.2p3(5So)2 -
2s2.2p2(3P){1,2},(1D)2. This further indicates that the importance of the
neglected Breit interaction decreases with ion charge and constrains the
uncertainty in the present calculations to within 15% even for the weak
transitions.
|
0008032v1
|
2000-09-17
|
Reprocessed emission line profiles from dense clouds in geometrically thick accretion engines
|
The central engines of active galactic nuclei (AGN) contain cold, dense
material as well as hot X-ray emitting gas. The standard paradigm for the
engine geometry is a cold thin disc sandwiched between hot X-ray coronae.
Strong support for this geometry in Seyferts comes from the study of
fluorescent iron line profiles, although the evidence is not ubiquitously air
tight. The thin disc model of line profiles in AGN and in X-ray binaries should
be bench marked against other plausible possibilities. One proposed alternative
is an engine consisting of dense clouds embedded in an optically thin,
geometrically thick X-ray emitting engine. This model is further motivated by
studies of geometrically thick engines such as advection dominated accretion
flows (ADAFs). Here we compute the reprocessed iron line profiles from dense
clouds embedded in geometrically thick, optically thin X-ray emitting discs
near a Schwarzchild black hole. We consider a range of cloud distributions and
disc solutions, including ADAFs, pure radial infall, and bipolar outflows. We
find that such models can reproduce line profiles similar to those from
geometrically thin, optically thick discs and might help alleviate some of the
problems encountered from the latter.
|
0009263v2
|
2000-09-20
|
ASCA Observations of the Twin Supernova Remnants in the Large Magellanic Cloud, DEM L316
|
We report results from an ASCA X-ray study of DEM L316, an emission nebula in
the Large Magellanic Cloud (LMC) consisting of two closely-spaced supernova
remnants (SNRs). The SIS image shows separate X-ray sources located at the
positions of the two radio- and optically-emitting SNR shells, 0547$-$69.7A and
0547$-$69.7B (hereafter, shell A and B). The individual X-ray spectrum of each
shell is well described by optically-thin thermal emission, although the
characteristics of the emission differ in important details between them. Shell
A exhibits strong iron L emission, which we attribute to the presence of
iron-rich ejecta leading to the suggestion that this SNR originates from a Type
Ia SN, an explosion of a moderate mass progenitor. Shell B, on the other hand,
has a chemical composition similar to that of the interstellar medium of the
LMC and so its X-ray emission is dominated by swept-up matter. The different
spectral features strongly disfavor the hypothesis that the two shells are due
to one supernova explosion into an interconnected bubble. We could not obtain
the evidence which positively supports the collision between two SNRs.
|
0009318v1
|
2000-09-20
|
Matter in Strong Magnetic Fields
|
The properties of matter are significantly modified by strong magnetic
fields, $B>>2.35\times 10^9$ Gauss ($1 G =10^{-4} Tesla$), as are typically
found on the surfaces of neutron stars. In such strong magnetic fields, the
Coulomb force on an electron acts as a small perturbation compared to the
magnetic force. The strong field condition can also be mimicked in laboratory
semiconductors. Because of the strong magnetic confinement of electrons
perpendicular to the field, atoms attain a much greater binding energy compared
to the zero-field case, and various other bound states become possible,
including molecular chains and three-dimensional condensed matter. This article
reviews the electronic structure of atoms, molecules and bulk matter, as well
as the thermodynamic properties of dense plasma, in strong magnetic fields,
$10^9G << B < 10^{16}G$. The focus is on the basic physical pictures and
approximate scaling relations, although various theoretical approaches and
numerical results are also discussed. For the neutron star surface composed of
light elements such as hydrogen or helium, the outermost layer constitutes a
nondegenerate, partially ionized Coulomb plasma if $B<<10^{14}G$, and may be in
the form of a condensed liquid if the magnetic field is stronger (and
temperature $<10^6$ K). For the iron surface, the outermost layer of the
neutron star can be in a gaseous or a condensed phase depending on the cohesive
property of the iron condensate.
|
0009333v2
|
2000-10-13
|
Evidence for Rapid Iron K_alpha Line Flux Variability in MCG--6-30-15
|
This paper employs direct spectral fitting of individual orbital data in
order to measure rapid X-ray iron K_alpha line and continuum spectral slope
variations in Seyfert 1 galaxies with unprecedented temporal resolution.
Application of this technique to a long RXTE observation of MCG--6-30-15
indicates that the line flux does vary on short (~1d) timescales, but that
these variations are not correlated with changes in the continuum flux or
slope. These rapid variations indicate that the line does indeed originate
close to the black hole, confirming predictions based on its very broad
profile. However, the lack of a correlation with the continuum presents
problems for models in which the line variations are driven by those in the
continuum, modified only by light-travel time effects. Instead, it may be that
the line responds according to a physical process with a different time scale,
such as ionization instabilities in the disk, or perhaps that the geometry and
physical picture is more complex than implied by the simplest disk-corona
models.
These data also indicate that the slope of the underlying power-law continuum
(Gamma) shows strong variability and is tightly correlated with the continuum
flux in the sense that the spectrum steepens as the source brightens. All of
these results have been checked with extensive simulations, which also
indicated that a spurious correlation between Gamma and Compton reflection
fraction (R) will result if these quantities are measured from the same
spectra. This casts serious doubts on previous claims of such a Gamma-R
correlation.
|
0010274v1
|
2000-10-18
|
The first XMM-Newton spectrum of a high redshift quasar - PKS 0537-286
|
We present XMM-Newton observations of the high redshift z=3.104, radio-loud
quasar PKS 0537-286. The EPIC CCD cameras provide the highest signal-to-noise
spectrum of a high-z quasar to date. The EPIC observations show that PKS
0537-286 is extremely X-ray luminous (Lx=2x10^47 erg/s), with an unusually hard
X-ray spectrum (Gamma=1.27+/-0.02). The flat power-law emission extends over
the whole observed energy range; there is no evidence of intrinsic absorption,
which has been claimed in PKS 0537-286 and other high z quasars.
However, there is evidence for weak Compton reflection. A redshifted iron K
line, observed at 1.5 keV - corresponding to 6.15 keV in the quasar rest frame
- is detected at 95% confidence. If confirmed, this is the most distant iron K
line known. The line equivalent width is small (33eV), consistent with the
`X-ray Baldwin effect' observed in other luminous quasars. The reflected
continuum is also weak (R=0.25). We find the overall spectral energy
distribution of PKS 0537-286 is dominated by the X-ray emission, which,
together with the flat power-law and weak reflection features, suggests that
the X-radiation from PKS 0537-286 is dominated by inverse Compton emission
associated with a face-on relativistic jet.
|
0010367v1
|
2000-12-14
|
Discovery of a Transient Absorption Edge in the X-ray Spectrum of GRB 990705
|
We report the discovery of a transient equivalent hydrogen column density
with an absorption edge at ~3.8 kiloelectron volts in the spectrum of the
prompt x-ray emission of gamma-ray burst (GRB) 990705. This feature can be
satisfactorily modeled with a photoelectric absorption by a medium located at a
redshift of ~0.86 and with an iron abundance of ~75 times the solar one. The
transient behavior is attributed to the strong ionization produced in the
circumburst medium by the GRB photons. The high iron abundance points to the
existence of a burst environment enriched by a supernova along the line of
sight. The supernova explosion is estimated to have occurred about 10 years
before the burst. Our results agree with models in which GRBs originate from
the collapse of very massive stars and are preceded by a supernova event
|
0012318v1
|
2001-01-12
|
Accretion and emission processes in AGN
|
The UV-X continuum, the X-ray spectral features, and the variability in these
bands provide powerful tools for studying the innermost regions of AGNs from
which we gain an insight into the accretion process. In this chapter the
discussion focusses on luminous AGN, i.e. Seyfert galaxies and quasars. The
standard accretion disk model (a stationary geometrically thin disk) is
described, and vertically averaged solutions for the radial structure are
given. The emission of the standard disk is discussed using different
approximations, and it is compared to the observations. This leads to the
conclusion that more complex models are required, such as the irradiated disk
and the disk-corona models. The advantage of this last model is that it
explains the overall UV-X spectral distribution. In the framework of these disk
models, the profile, intensity, and variability properties of the X-ray iron
line can be explained by reprocessing at the surface of the cold disk very
close to the black hole (the "relativistic disk model"). An alternative
possibility is discussed, where the UV-X continuum is produced by a
quasi-spherical distribution of dense clouds surrounded by (or embedded in) a
hot medium. In such a model the iron line profile could be due to
Comptonization instead of relativistic effects.
|
0101203v2
|
2001-03-06
|
A Simple Model for r-Process Scatter and Halo Evolution
|
Recent observations of heavy elements produced by rapid neutron capture
(r-process) in the halo have shown a striking and unexpected behavior: within a
single star, the relative abundances of r-process elements heavier than Eu are
the same as the same as those of solar system matter, while across stars with
similar metallicity Fe/H, the r/Fe ratio varies over two orders of magnitude.
In this paper we present a simple analytic model which describes a star's
abundances in terms of its ``ancestry,'' i.e., the number of nucleosynthesis
events (e.g., supernova explosions) which contributed to the star's
composition. This model leads to a very simple analytic expression for the
abundance scatter versus Fe/H, which is in good agreement with the data and
with more sophisticated numerical models. We investigate two classes of
scenarios for r-process nucleosynthesis, one in which r-process synthesis
events occur in only \sim 4% of supernovae but iron synthesis is ubiquitous,
and one in which iron nucleosynthesis occurs in only about 9% of supernovae.
(the Wasserburg- Qian model). We find that the predictions in these scenarios
are similar for [Fe/H] \ga -2.5, but that these models can be readily
distinguished observationally by measuring the dispersion in r/Fe at [Fe/H] \la
-3.
|
0103083v1
|
2001-03-26
|
Weak Reprocessed Features in the Broad Line Radio Galaxy 3C382
|
We present a detailed X-ray study of the Broad Line Radio Galaxy 3C382,
observed with the BeppoSAX satellite in a very bright state. The continuum
emission is well modeled with a power law that steepens at high energies, with
an e-folding energy of about 120 keV. At soft energies a clear excess of
emission is detected, which can not be explained solely by the extended thermal
halo seen in a ROSAT HRI image. A second, more intense soft X-ray component,
possibly related to an accretion disk, is required by the data. Both a
reflection component (R=0.3) and an iron line (EW \sim 50) are detected, at
levels much weaker than in Seyfert galaxies, suggesting a common origin.
Combining our measurements with results from the literature we find that the
iron line has remained approximately constant over 9 years while the continuum
varied by a factor of 5. Thus the fluorescent gas does not respond promptly to
the variations of the X-ray primary source, suggesting that the reprocessing
site is located away, likely at parsec distances. While the continuum shape
indicates that X-rays derive from a thermal Comptonization process, the
weakness of other spectral features implies that either the upper layers of the
optically thick accretion disk are completely ionized or the corona above the
disk is outflowing with mildly relativistic velocity.
|
0103413v1
|
2001-03-29
|
Abundances in Stars from the Red Giant Branch Tip to the Near Main Sequence in M71: II. Iron Abundance
|
We present [Ffe/H] abundance results that involve a sample of stars with a
wide range in luminosity from luminous giants to stars near the turnoff in a
globular cluster. Our sample of 25 stars in M71 includes 10 giant stars more
luminous than the RHB, 3 horizontal branch stars, 9 giant stars less luminous
than the RHB, and 3 stars near the turnoff. We analyzed both Fe I and Fe II
lines in high dispersion spectra observed with HIRES at the W. M. Keck
Observatory. We find that the [Fe/H] abundances from both Fe I and Fe II lines
agree with each other and with earlier determinations. Also the [Fe/H] obtained
from Fe I and Fe II lines is constant within the rather small uncertainties for
this group of stars over the full range in Teff and luminosity, suggesting that
NLTE effects are negligible in our iron abundance determination. In this
globular cluster, there is no difference among the mean [Fe/H] of giant stars
located at or above the RHB, RHB stars, giant stars located below the RHB and
stars near the turnoff.
|
0103494v2
|
2001-04-04
|
X-Ray Probing of the Central Regions of Clusters of Galaxies
|
Results of ASCA X-ray study of central regions of medium-richness clusters of
galaxies are summarized, emphasizing differences between cD and non-cD
clusters. The intra-cluster medium (ICM) is likely to consist of two (hot and
cool) phases within $\sim 100$ kpc of a cD galaxy, where the ICM metallicity is
also enhanced. In contrast, the ICM in non-cD clusters appears to be isothermal
with little metallicity gradient right to the center. The gravitational
potential exhibits a hierarchical nesting around cD galaxies, while a total
mass-density profile with a central cusp is indicated for a non-cD cluster
Abell~1060. The iron-mass-to-light ratio of the ICM decreases toward the center
in both types of clusters, although it is radially constant in peripheral
regions. The silicon-to-iron abundance ratio in the ICM increases with the
cluster richness, but remains close to the solar ratio around cD galaxies.
These overall results are interpreted without appealing to the popular
cooling-flow hypothesis. Instead, an emphasis is put on the halo-in-halo
structure formed around cD galaxies.
|
0104079v1
|
2001-06-01
|
X-Ray Spectroscopy of II Pegasi: Coronal Temperature Structure, Abundances, and Variability
|
We have obtained high resolution X-ray spectra of the coronally active
binary, II Pegasi (HD 224085), covering the wavelength range of 1.5-25
Angstroms. For the first half of our 44 ksec observation, the source was in a
quiescent state with constant X-ray flux, after which it flared, reaching twice
the quiescent flux in 12 ksec, then decreasing. We analyze the emission-line
spectrum and continuum during quiescent and flaring states. The differential
emission measure derived from lines fluxes shows a hot corona with a continuous
distribution in temperature. During the non-flare state, the distribution peaks
near log T = 7.2, and when flaring, near 7.6. High-temperature lines are
enhanced slightly during the flare, but most of the change occurs in the
continuum. Coronal abundance anomalies are apparent, with iron very deficient
relative to oxygen and significantly weaker than expected from photospheric
measurements, while neon is enhanced relative to oxygen. We find no evidence of
appreciable resonant scattering optical depth in line ratios of iron and
oxygen. The flare light curve is consistent with Solar two-ribbon flare models,
but with a very long reconnection time-constant of about 65 ks. We infer loop
lengths of about 0.05 stellar radii, to about 0.25 in the flare, if the flare
emission originated from a single, low-density loop.
|
0106007v1
|
2001-06-28
|
On a possible GRB-supernova time sequence
|
The data from the Chandra satellite on the iron emission lines in the
afterglow of GRB 991216 are used to give further support for the EMBH theory,
which links the origin of the energy of GRBs to the extractable energy of
electromagnetic black holes (EMBHs), leading to an interpretation of the
GRB-supernova correlation. Following the relative space-time transformation
(RSTT) paradigm and the interpretation of the burst structure (IBS) paradigm,
we introduce a paradigm for the correlation between GRBs and supernovae. The
following sequence of events is shown as kinematically possible and consistent
with the available data: a) the GRB-progenitor star $P_1$ first collapses to an
EMBH, b) the proper GRB (P-GRB) and the peak of the afterglow (E-APE) propagate
in interstellar space until the impact on a supernova-progenitor star $P_2$ at
a distance $\le 2.69\times 10^{17}$ cm, and they induce the supernova
explosion, c) the accelerated baryonic matter (ABM) pulse, originating the
afterglow, reaches the supernova remnants 18.5 hours after the supernova
explosion and gives rise to the iron emission lines. Some considerations on the
dynamical implementation of the paradigm are presented. The concept of induced
supernova explosion introduced here specifically for the GRB-supernova
correlation may have more general application in relativistic astrophysics.
|
0106534v1
|
2001-07-09
|
BeppoSAX observations of Mrk 841 and Mrk335
|
We present and discuss BeppoSAX observations of Mrk841 and Mrk335, two
Seyfert 1 galaxies in which previous observations have established the presence
of soft excesses. We confirm the soft excess in both sources, even if for
Mrk~841 a warm absorber provides a fit almost as good as the one with a true
excess. As far as the hard X-ray continuum is concerned, a Comptonization model
provides a fit as good as a power law and a physically sound solution for
Mrk841. For Mrk335, the Comptonization model gives a result which is somewhat
better on statistical ground, but rather problematic on physical ground. The
most interesting results regard the reprocessing components. For Mrk841 we find
a very large reflection continuum but an almost normal iron line equivalent
width even if, within the errors, a solution in which both components are a
factor ~2 larger than expected for an accretion disc is still marginally
acceptable. If this is the case, an anisotropy of the primary emission seems
the best explanation. On the contrary, in Mrk335 we find a very large iron line
EW but a reflection component not accordingly large. In this case, the best
solution seems to be in terms of reflection from an ionized disc.
|
0107151v1
|
2001-07-20
|
On the GRB progenitors: possible consequences for supernovae connection with gamma-ray bursts
|
Unique data on $BVRI$ light curves of the optical transient (OT) of GRB
970508 obtained with the 6-m telescope have been interpreted in the framework
of the idea of a straightforward link between supernovae (SNe) and long
duration gamma-ray bursts (GRBs). The effect must be maximum in the $I_{c}$
band as for OT GRB 970228. The peak absolute ($M_{B}$) magnitude of the
suggested SN must be around -19.5 for the OT of GRB 970508. So, in addition to
the characteristic "shoulders" on the light curves of the OTs of GRB 970228,
GRB 980326, 990712, 991208, more evidence of the link between GRBs and Type
Ib/c SNe (or core-collapse SNe) was found, which could be an argument in favor
of the idea of massive stars as progenitors of long duration GRBs. If all or
the main part of long duration GRBs are associated with the SNe, GRB host
galaxies (for ground-based observations, at least) must be dimmer than the peak
magnitude of a SN. If some GRB/SN relation really exists, and if all or at
least the main part of long duration GRBs are associated with SNe, then as a
consequence we have a very strong $\gamma$-ray beaming with a solid angle of up
to $\Omega_{beam} \sim (10^{-5} - 10^{-6})\cdot 4\pi$. Besides, the
observations of K$_{\alpha}$ lines of iron in the X-ray afterglow spectra of
GRBs (970508, 970828, 991216, 000214) and the observation of redshifted
absorption feature of neutral iron (7.1 keV) simultaneously with GRB 990705 are
also evidence in favor of massive stars -- progenitors of GRBs.
|
0107399v1
|
2001-07-25
|
The X-ray emission of the Intermediate Polar V709 Cas
|
We present RXTE and BeppoSAX observations of the Intermediate Polar V709 Cas
acquired in 1997 and 1998 respectively. The X-ray emission from 0.1 to 30keV is
dominated by the strong pulsation at the rotational period of the white dwarf
(312.8s) with no sign of orbital or sideband periodicity, thus confirming
previous ROSAT results. However, we detect changes in the power spectra between
the two epochs. While the second harmonic of the spin period is present during
both observations, the first harmonic is absent in 1997. An increase in the
amplitude of the spin pulsation is found between 1997 and 1998 together with a
decrease in the X-ray flux. The average X-ray spectrum from 0.1 to 100keV is
well described by an isothermal plasma at ~27keV plus complex absorption and an
iron K(alpha) fluorescent line, due to reflection from the white dwarf surface.
The rotational pulsation is compatible with complex absorption dominating the
low energy range, while the high energy spin modulation can be attributed to
tall shocks above the accreting poles. The RXTE spectrum in 1997 also shows the
presence of an absorption edge from ionized iron likely located in the
pre-shock accretion flow. The variations along the spin period of the partial
covering absorber and of reflection are compatible with the classical accretion
curtain scenario. The variations in the spin pulse characteristics and X-ray
flux indicate that V709 Cas experiences changes in the mass accretion rate on
timescales from months to years.
|
0107480v1
|
2001-08-15
|
Boron Abundances in Main Sequence B-type Stars: A Test of Rotational Depletion during Main Sequence Evolution
|
Boron abundances have been derived for seven main sequence B-type stars from
HST STIS spectra around the B III 2066 A line. In two stars, boron appears to
be undepleted with respect to the presumed initial abundance. In one star,
boron is detectable but it is clearly depleted. In the other four stars, boron
is undetectable implying depletions of 1 to 2 dex. Three of these four stars
are nitrogen enriched, but the fourth shows no enrichment of nitrogen. Only
rotationally induced mixing predicts that boron depletions are unaccompanied by
nitrogen enrichments. The inferred rate of boron depletion from our
observations is in good agreement with these predictions. Other boron-depleted
nitrogen-normal stars are identified from the literature. Also, several
boron-depleted nitrogen-rich stars are identified, and while all fall on the
boron-nitrogen trend predicted by rotationally-induced mixing, a majority have
nitrogen enrichments that are not uniquely explained by rotation.
The spectra have also been used to determine iron-group (Cr, Mn, Fe, and Ni)
abundances. The seven B-type stars have near solar iron-group abundances, as
expected for young stars in the solar neighborhood. We have also analysed the
halo B-type star, PG0832+676. We find [Fe/H] = -0.88 +/- 0.10, and the absence
of the B III line gives the upper limit [B/H]<2.5. These and other published
abundances are used to infer the star's evolutionary status as a post-AGB star.
|
0108263v1
|
2001-09-20
|
An XMM-Newton observation of the extreme Narrow Line Seyfert 1 Galaxy, Mrk 359
|
We present XMM-Newton observations of Mrk 359, the first Narrow Line Seyfert
1 galaxy discovered. Even among NLS1s, Mrk 359 is an extreme case with
extraordinarily narrow optical emission lines. The XMM-Newton data show that
Mrk 359 has a significant soft X-ray excess which displays only weak absorption
and emission features. The (2-10) keV continuum, including reflection, is
flatter than the typical NLS1, with Gamma approximately 1.84. A strong emission
line of equivalent width approximately 200 eV is also observed, centred near
6.4 keV. We fit this emission with two line components of approximately equal
strength: a broad iron-line from an accretion disc and a narrow, unresolved
core. The unresolved line core has an equivalent width of approximately 120 eV
and is consistent with fluorescence from neutral iron in distant reprocessing
gas, possibly in the form of a `molecular torus'. Comparison of the narrow-line
strengths in Mrk 359 and other low-moderate luminosity Seyfert 1 galaxies with
those in QSOs suggests that the solid angle subtended by the distant
reprocessing gas decreases with increasing AGN luminosity.
|
0109346v1
|
2001-11-21
|
Detection of an Iron Emission Feature from the Lensed BAL QSO H1413+117 at z=2.56
|
We present the X-ray energy spectrum of the lensed BAL QSO H1413+117 (the
Cloverleaf) at z=2.56 observed with the Chandra X-ray observatory. We detected
293 photons in a 40 ks Advanced CCD Imaging Spectrometer (ACIS-S) observation.
The X-ray image consists of four lensed image components, thus the photons are
from the lensed QSO itself. The overall spectrum can be described with a
power-law function heavily absorbed by neutral matter at a redshift consistent
with the QSO redshift. This supports the idea that intrinsic absorption is
significant for BAL QSOs. The spectral fit significantly (99% confidence)
improves when we include an emission line. The centroid energy and intrinsic
width (Gaussian \sigma) of the line are 6.21 \pm 0.16 keV and 220
^{+270}_{-130} eV (90% errors), respectively, in the QSO rest frame, assuming
the absorbed power-law as the continuum. The equivalent width of the line in
the QSO rest frame is 960 ^{+1400}_{-480} eV. We suggest that the large
equivalent width, the centroid energy, and the line broadness can be explained
by iron K emission arising from X-ray reprocessing in the BAL flow, assuming it
has a conical thin-sheet structure.
|
0111410v1
|
2001-11-30
|
Deep inside the core of Abell 1795: the Chandra view
|
We present X-ray spatial and spectral analysis of the Chandra data from the
central 400 kpc (H0 = 50 km/s/Mpc) of the cluster of galaxies Abell 1795. The
plasma temperature rises outwards by a factor of 3, whereas the iron abundance
decreases by a factor of 4. The spatial distribution of Oxygen, Neon, Sulphur,
Silicon and Iron shows that supernovae Type Ia dominate the metal enrichment
process of the cluster plasma within the inner 150 kpc. Resolving both the gas
density and temperature in 9 radial bins, we recover the gravitational mass
density profile and show that it flattens within 100 kpc as rho_DM \propto
r^{-0.6} with a power law index flatter than -1 at >3 sigma level. The observed
motion of the central galaxy and the presence of excesses and deficits along
the North-South direction in the brightness distribution indicate that the
central cluster region is not relaxed. In the absence of any non-gravitational
heating source, the data from the inner ~200 kpc indicate the presence of a
cooling flow with an integrated mass deposition rate of about 100 Msun/yr. Over
the same cluster region, the observed rate of 74 Msun/yr is consistent with the
recent XMM Reflection Grating Spectrometer limit of 150 Msun/yr.
|
0111586v1
|
2001-12-01
|
Production of neutrons, neutrinos and gamma-rays by a very fast pulsar in the Galactic Center region
|
We consider the possibility that the excess of cosmic rays near $\sim
10^{18}$ eV, reported by the AGASA and SUGAR groups from the direction of the
Galactic Center, is caused by a young, very fast pulsar in the high density
medium. The pulsar accelerates iron nuclei to energies $\sim 10^{20}$ eV, as
postulated by the Galactic models for the origin of the highest energy cosmic
rays. The iron nuclei, after about 1 yr since pulsar formation, leave the
supernova envelope without energy losses and diffuse through the dense central
region of the Galaxy. Some of them collide with the background matter creating
neutrons (from desintegration of Fe), neutrinos and gamma-rays (in inelastic
collisions). Wse suggest that neutrons produced at a specific time after the
pulsar formation are responsible for the observed excess of cosmic rays at
$\sim 10^{18}$ eV. From normalization of the calculated neutron flux to the one
observed in the cosmic ray excess, we predict the neutrino and gamma-ray
fluxes. It has been found that the 1 km$^2$ neutrino detector of the IceCube
type should detect from a few up to several events per year from the Galactic
Center, depending on the parameters of the considered model. Also future
systems of Cherenkov telescopes (CANGAROO III, HESS, VERITAS) should be able to
observe 1 - 10 TeV $\gamma$-rays from the Galactic Center if the pulsar was
created inside a huge molecular cloud about $3-10\times 10^3$ yrs ago.
|
0112008v1
|
2001-12-02
|
Asymmetric Supernovae from Magneto-Centrifugal Jets
|
Strong toroidal magnetic fields generated in stellar collapse can generate
magneto-centrifugal jets in analogy to those found in simulations of black hole
accretion and explain why all core collapse supernovae are found to be
substantially asymmetric and predominantly bi-polar. We describe two phases:
the initial LeBlanc-Wilson jet and a subsequent protopulsar or toroidal jet
that propagates at about the core escape velocity. The jets will produce bow
shocks that tend to expel matter, including iron and silicon, into equatorial
tori, accounting for observations of the element distribution in Cas A. A
magnetic ``switch'' mechanism may apply in instances of low density and large
magnetic field with subsequent increase in the speed and collimation of the
toroidal jet, depositing relatively little momentum. The result could be enough
infall to form a black hole with a third, highly relativistic jet that could
catch up to the protopulsar jet after it has emerged from the star. The
interaction of these two jets could generate internal shocks and explain the
presence of iron lines in the afterglow. Recent estimates that typical
gamma-ray burst energy is about 3x10^50 erg imply either a very low efficiency
for conversion of rotation into jets, or a rather rapid turnoff of the jet
process even though the black hole still rotates rapidly. Magnetars and
``hypernovae'' might arise in an intermediate parameter regime of energetic
jets that yield larger magnetic fields and provide more energy than the routine
case, but that are not so tightly collimated that they yield failed supernova.
(slightly abridged)
|
0112020v1
|
2002-03-04
|
X-ray Sources and Star Formation Activity in the Sgr B2 Cloud Observed with Chandra
|
We report the X-ray population study in the giant molecular cloud Sagittarius
B2 (SgrB2). More than a dozen of X-ray cloud members (and candidates) are
discovered with Chandra. Two bright X-ray sources are located near Sgr B2 Main,
the most copious complex of the ultra compact HII sources. The X-ray spectra
are fitted with a thin thermal plasma model of 5-10 keV temperature. The
intrinsic luminosity after correcting the absorption of 5 x 10^23 H/cm^2 is
about 10^33 erg/s. Although these two X-ray sources are attributable to young
stellar objects (YSOs) in the same HII complex, they are in sharp contrast; one
at the center of the HII complex exhibits strong K-shell transition lines of
iron, while the other near the east has only weak lines. The other HII
complexes, SgrB2 North and South, also show hard and highly absorbed X-ray
emissions due possibly to the star formation activity. The composite X-ray
spectrum of the other cloud member X-ray sources is fitted with a thin thermal
plasma of about 10-keV temperature with the hydrogen column density (N_H) of
1.3 x 10^23 H/cm^2, and the individual X-ray luminosity of a few times of
10^31-32$ erg/s. These are likely to be a single or cluster of YSO(s), but
neither radio nor infrared counterpart is found. An alternative scenario of
isolated white dwarfs powered by the Bondi-Hoyle accretion from the dense cloud
gas is also discussed. The X-ray spectra exhibit an additional 6.4-keV line of
neutral or low-ionization irons, which indicates that the environment gas is
concentrated near at the sources.
|
0203035v1
|
2002-04-08
|
X-Ray Resonance Opacity of Oxygen and Iron in AGN MCG--6-30-15
|
Theoretical differential oscillator strengths related to monochromatic
opacity due to K- and L-shell absorption from oxygen and iron ions are directly
compared with the Chandra and Xmm-Newton spectra of Seyfert~1 galaxy
MCG--6-30-15. We compute the highly resolved continuum with resonances due to O
I - VI and Fe XVI. It is found that the KLn (n --> infty) resonance series
limits in O VI, and the lowest LMM resonance in Fe XVI, lie at the prominent
17.5 A break in the observed spectra. We also calculate and identify, for the
first time, the observed gap in spectral flux at 22-23 A in the Chandra spectra
due to K --> L resonant absorption features from all O-ions O I - VI,
potentially leading to abundance determination of several or all ionization
stages; similar signature gaps may be predicted due to other elements. The
precise atomic parameters are computed in the relativistic close coupling
approximation using the Breit-Pauli R-matrix method. The new X-ray opacities
might possibly distinguish between models of a dusty warm absorber, and/or
gravitational redshift and broadening due to a massive black hole in
MCG--6-30-15.
|
0204116v2
|
2002-05-02
|
History of Milky Way Dwarf Spheroidal Galaxies Imprinted on Abundance Patterns of Neutron-Capture Elements
|
Stellar abundance pattern of neutron-capture elements such as barium is used
as a powerful tool to infer how star formation proceeded in dwarf spheroidal
(dSph) galaxies. It is found that the abundance correlation of barium with iron
in stars belonging to dSph galaxies orbiting the Milky Way, i.e., Draco,
Sextans, and Ursa Minor have a feature similar to the barium-iron correlation
in Galactic metal-poor stars. The common feature of these two correlations can
be realized by our inhomogeneous chemical evolution model based on the
supernova-driven star formation scenario if dSph stars formed from gas with a
velocity dispersion of ~26 km/s. This velocity dispersion together with the
stellar luminosities strongly suggest that dark matter dominated dSph galaxies.
The tidal force of the Milky Way links this velocity dispersion with the
currently observed value <10 km/s by stripping the dark matter in dSph
galaxies. As a result, the total mass of each dSph galaxy is found to have been
originally ~25 times larger than at present. Our inhomogeneous chemical
evolution model succeeds in reproducing the stellar [Fe/H] distribution
function observed in Sextans. In this model, supernovae immediately after the
end of the star formation epoch can expel the remaining gas over the
gravitational potential of the dSph galaxy.
|
0205013v1
|
2002-06-06
|
Predicted FeII Emission-Line Strengths from Active Galactic Nuclei
|
We present theoretical FeII emission line strengths for physical conditions
typical of Active Galactic Nuclei with Broad-Line Regions. The FeII line
strengths were computed with a precise treatment of radiative transfer using
extensive and accurate atomic data from the Iron Project. Excitation mechanisms
for the FeII emission included continuum fluorescence, collisional excitation,
self-fluorescence amoung the FeII transitions, and fluorescent excitation by
Lyman-alpha and Lyman-beta. A large FeII atomic model consisting of 827 fine
structure levels (including states to E ~ 15 eV) was used to predict fluxes for
approximately 23,000 FeII transitions, covering most of the UV, optical, and IR
wavelengths of astrophysical interest. Spectral synthesis for wavelengths from
1600 Angstroms to 1.2 microns is presented. Applications of present theoretical
templates to the analysis of observations are described. In particular, we
discuss recent observations of near-IR FeII lines in the 8500 Angstrom -- 1
micron region which are predicted by the Lyman-alpha fluorescence mechanism. We
also compare our UV spectral synthesis with an empirical iron template for the
prototypical, narrow-line Seyfert galaxy I Zw 1. The theoretical FeII template
presented in this work should also applicable to a variety of objects with FeII
spectra formed under similar excitation conditions, such as supernovae and
symbiotic stars.
|
0206096v1
|
2002-07-10
|
The Iron Project and Non-LTE stellar modeling
|
Latest developments in theoretical computations since the international
Opacity Project (OP), under the new the Iron Project (IP) and extensions, are
described for applications to a variety of objects such as stellar atmospheres,
nebulae, and active galactic nuclei. The primary atomic processes are: electron
impact excitation (EIE), photoionization, electron-ion recombination, and
bound-bound transitions, all considered using the accurate and powerful
R-matrix method including relativistic effects. As an extension of the OP and
the IP, a self-consistent and unified theoretical treatment of photoionization
and recombination has been developed. Both the radiative and the dielectronic
recombination (RR and DR) processes are considered in a unified manner.
Photoionization and recombination cross sections are computed with identical
wavefunction expansions, thus ensuring self-consistency in an ab initio manner.
The new unified results differ from the sum of previous results for RR and DR
by up to a factor of 4 for the important but complex atomic systems such as Fe
I - V. The fundamental differences are due to quantum mechanical intereference
and coupling effects neglected in simpler approximations that unphysically
treat RR and DR separately, which can not be independently measured or
observed. I will also describe the electronic, web-interactive, database,
TIPTOPBASE, to archive the OP/IP data in a readily accessible manner.
TIPTOPBASE would also include electron-ion recombination data and new fine
structure transition probabilities. Efficient codes developed by M.J. Seaton to
calculate `customized' mixture opacities and radiative accelerations
('levitation') in stars will also be available.
|
0207223v1
|
2002-08-06
|
The Magnetorotational Instability in Core Collapse Supernova Explosions
|
We investigate the action of the magnetorotational instability (MRI) in the
context of iron-core collapse. Exponential growth of the field on the rotation
time scale by the MRI will dominate the linear growth process of field line
"wrapping" with the same characteristic time. We examine a variety of initial
rotation states, with solid body rotation or a gradient in rotational velocity,
that correspond to models in the literature. A relatively modest value of the
initial rotation, a period of ~ 10 s, will give a very rapidly rotating PNS and
hence strong differential rotation with respect to the infalling matter. We
assume conservation of angular momentum on spherical shells. Results are
discussed for two examples of saturation fields, a fiducial field that
corresponds to Alfven velocity = rotational velocity and a field that
corresponds to the maximum growing mode of the MRI. Modest initial rotation
velocities of the iron core result in sub-Keplerian rotation and a
sub-equipartition magnetic field that nevertheless produce substantial MHD
luminosity and hoop stresses: saturation fields of order 10^{15} - 10^{16} G
develop within 300 msec after bounce with an associated MHD luminosity of about
10^{52} erg/s. Bi-polar flows driven by this MHD power can affect or even cause
the explosions associated with core-collapse supernovae.
|
0208128v2
|
2002-09-12
|
Integrated Spectroscopy of Bulge Globular Clusters and Fields I. The Data Base and Comparison of Individual Lick Indices in Clusters and Bulge
|
We present a comprehensive spectroscopic study of the integrated light of
metal-rich Galactic globular clusters and the stellar population in the
Galactic bulge. We measure line indices which are defined by the Lick standard
system and compare index strengths of the clusters and Galactic bulge. Both
metal-rich globular clusters and the bulge are similar in most of the indices,
except for the CN index. We find a significant enhancement in the CN/<Fe> index
ratio in metal-rich globular clusters compared with the Galactic bulge. The
mean iron index <Fe> of the two metal-rich globular clusters NGC 6528 and NGC
6553 is comparable with the mean iron index of the bulge. Index ratios such as
Mgb/<Fe>, Mg2/<Fe>, Ca4227/<Fe>, and TiO/<Fe>, are comparable in both stellar
population indicating similar enhancements in individual elements which are
traced by the indices. From the globular cluster data we fully empirically
calibrate several metallicity-sensitive indices as a function of [Fe/H] and
find tightest correlations for the Mg2 index and the composite [MgFe] index. We
find that all indices show a similar behavior with galactocentric radius,
except for the Balmer series, which show a large scatter at all radii. However,
the scatter is entirely consistent with the cluster-to-cluster variations in
the horizontal branch morphology.
|
0209238v1
|
2002-09-12
|
The Spiral Structure of the Milky Way, Cosmic Rays, and Ice Age Epochs on Earth
|
The short term variability of the Galactic cosmic ray flux (CRF) reaching
Earth has been previously associated with variations in the global low altitude
cloud cover. This CRF variability arises from changes in the solar wind
strength. However, cosmic ray variability also arises intrinsically from
variable activity of and motion through the Milky Way. Thus, if indeed the CRF
climate connection is real, the increased CRF witnessed while crossing the
spiral arms could be responsible for a larger global cloud cover and a reduced
temperature, thereby facilitating the occurrences of ice ages. This picture has
been recently shown to be supported by various data (Shaviv, 2001). In
particular, the variable CRF recorded in Iron meteorites appears to vary
synchronously with the appearance ice ages.
Here we expand upon the original treatment with a more thorough analysis and
more supporting evidence. In particular, we discuss the cosmic ray diffusion
model which considers the motion of the Galactic spiral arms. We also elaborate
on the structure and dynamics of the Milky Way's spiral arms. In particular, we
bring forth new argumentation using HI observations which imply that the
galactic spiral arm pattern speed appears to be that which fits the glaciation
period and the cosmic-ray flux record extracted from Iron meteorites. In
addition, we show that apparent peaks in the star formation rate history, as
deduced by several authors, coincides with particularly icy epochs, while the
long period of 1 to 2 Gyr before present, during which no glaciations are known
to have occurred, coincides with a significant paucity in the past star
formation rate.
|
0209252v1
|
2002-11-07
|
Gamma-Ray Bursts in Pulsar Wind Bubbles: Putting the Pieces Together
|
We present the main observational features expected for GRBs that occur
inside pulsar wind bubbles (PWBs). This is the most natural outcome of
supranova model where initially a supernova explosion takes place, leaving a
supra-massive NS, which loses its rotational energy over a time t_sd and
collapses to a BH, triggering a GRB explosion. We find that the time delay t_sd
between the supernova and GRB events is the most important parameter that
determines the behavior of the system. We consider the afterglow, prompt GRB
and direct emission from the PWB. The observational signatures for different
t_sd are described and joined together into one coherent framework. Constraints
on the model are derived for a spherical PWB, from the lack of detection of the
PWB emission and afterglow observations. For very low values of t_sd<1 hr the
supranova model reduces to the collapsar model; 0.4<t_sd/1yr<1 is required to
produce the iron lines seen in some X-ray afterglows. However, we find that for
a spherical PWB, this implies no detectable radio afterglow, a small jet break
time and non-relativistic transition time, in disagreement with observations
for some of these GRBs. These discrepancies with the observations may be
reconciled by resorting to a non-spherical geometry. We find that light element
lines, recently detected in a few X-ray afterglows, are expected to dominate
over iron lines for small t_sd, while for large t_sd the situation is reversed.
Finally, we predict that external Compton scattering of the PWB photons by the
afterglow relativistic electrons, should lead to high energy emission during
the early afterglow that may explain the GeV photons detected by EGRET in some
GRBs, and should be detectable by future missions (GLAST).
|
0211136v1
|
2002-11-20
|
Magnetic Field in Supernovae
|
A relatively modest value of the initial rotation of the iron core, a period
of ~ 6-31 s, will give a very rapidly rotating protoneutron star and hence
strong differential rotation with respect to the infalling matter. Under these
conditions, a seed field is expected to be amplified by the MRI and to grow
exponentially. Exponential growth of the field on the time scale Omega^{-1} by
the magnetorotational instability (MRI) will dominate the linear growth process
of field line "wrapping" with the same characteristic time. The shear is
strongest at the boundary of the newly formed protoneutron star. Modest initial
rotation velocities of the iron core result in sub-Keplerian rotation and a
sub-equipartition magnetic field that nevertheless produce substantial MHD
luminosity and hoop stresses: saturation fields of order 10^{15} - 10^{16} G
develop ~ 300 msec after bounce with an associated MHD luminosity of ~ 10^{49}
- 10^{53} erg s^{-1}. Bi-polar flows driven by this MHD power can affect or
even cause the explosions associated with core-collapse supernovae. If the
initial rotation is too slow, then there will not be enough rotational energy
to power the supernova despite the high luminosities. The MRI should be active
and may qualitatively alter the flow if a black hole forms directly or after a
fall-back delay.
|
0211458v1
|
2002-12-27
|
Iron is not Depleted in High-Ionization Nuclear Emission-Line Regions of Active Galactic Nuclei
|
In order to examine whether or not high-ionization nuclear emission-line
regions (HINERs) in narrow-line regions of active galactic nuclei are dusty, we
focus on two high-ionization forbidden emission lines, [Fe VII]6087 and [Ne
V]3426. We perform photoionization model calculations to investigate possible
dependences of the flux ratio of [Fe VII]6087/[Ne V]3426 on various gas
properties, in order to investigate how useful this flux ratio to explore the
dust abundances in HINERs. Based on our photoionization model calculations, we
show that the observed range of the flux ratio of [Fe VII]6087/[Ne V]3426 is
consistent with the dust-free models while that is hard to be explained by the
dusty models. This suggests that iron is not depleted at HINERs, which implies
that the HINERs are not dusty. This results is consistent with the idea that
the HINERs are located closer than the dust-sublimation radius (i.e., inner
radius of dusty tori) and thus can be hidden by dusty tori when seen from a
edge-on view toward the tori, which has been also suggested by the AGN-type
dependence of the visibility of high-ionization emission lines.
|
0212546v1
|
2003-02-26
|
Atomic data from the Iron Project. LIII. Relativistic allowed and forbidden transition probabilities for Fe XVII
|
An extensive set of fine structure levels and corresponding transition
probabilities for allowed and forbidden transitions in Fe XVII is presented. A
total of 490 bound energy levels of Fe XVII of total angular momenta 0 <= J <=
7 of even and odd parities with 2 <= n <= 10, 0 <= l <= 8, 0 <= L <= 8, and
singlet and triplet multiplicities, are obtained. They translate to over 2.6 x
10^4 allowed (E1) transitions that are of dipole and intercombination type, and
about 3000 forbidden transitions that include electric quadrupole (E2),
magnetic dipole (M1), electric octopole (E3), and magnetic quadrupole (M2) type
representing the most detailed calculations to date for the ion. Oscillator
strengths f, line strengths S, and coefficients A of spontaneous emission for
the E1 type transitions are obtained in the relativistic Breit-Pauli R-matrix
approximation. A valus for the forbidden transitions are obtained from atomic
structure calculations using codes SUPERSTRUCTURE and GRASP. The energy levels
are identified in spectroscopic notation with the help of a newly developed
level identification algorithm. Nearly all 52 spectroscopically observed levels
have been identified, their binding energies agreeing within 1% with our
calculation. Computed transition probabilities are compared with other
calculations and measurement. The effect of 2-body magnetic terms and other
interactions is discussed. Present data set enhances by more than an order of
magnitude the heretofore available data for the transition probabilities of Fe
XVII.
|
0302561v1
|
2003-04-08
|
BeppoSAX average spectra of Seyfert galaxies
|
We have studied the average 3-200 keV spectra of Seyfert galaxies of type 1
and 2, using data obtained with BeppoSAX. The average Seyfert 1 spectrum is
well-fitted by a power law continuum with photon spectral index Gamma~1.9, a
Compton reflection component R~0.6-1 (depending on the inclination angle
between the line of sight and the reflecting material) and a high-energy cutoff
at around 200 keV; there is also an iron line at 6.4 keV characterized by an
equivalent width of 120 eV. Seyfert 2's on the other hand show stronger neutral
absorption (NH=3-4 x 10^{22} atoms cm-2) as expected but are also characterized
by an X-ray power law which is substantially harder (Gamma~1.75) and with a
cut-off at lower energies (E_c~130 keV); the iron line parameters are instead
substantially similar to those measured in type 1 objects. There are only two
possible solutions to this problem: to assume more reflection in Seyfert 2
galaxies than observed in Seyfert 1 or more complex absorption than estimated
in the first instance. The first possibility is ruled out by the Seyfert 2 to
Seyfert 1 ratio while the second provides an average Seyfert 2 intrinsic
spectrum very similar to that of the Seyfert 1. The extra absorber is likely an
artifact due to summing spectra with different amounts of absorption, althought
we cannot exclude its presence in at least some individual sources. Our result
argues strongly for a very similar central engine in both type of galaxies as
expected under the unified theory.
|
0304133v1
|
2003-04-26
|
Hot HB stars in globular clusters - Physical parameters and consequences for theory. VI. The second parameter pair M 3 and M 13
|
We present the results of spectroscopic analyses of hot horizontal branch
(HB) stars in M 13 and M 3, which form a famous ``second parameter'' pair. From
the spectra and Stroemgren photometry we derived -- for the first time in M 13
-- atmospheric parameters (effective temperature and surface gravity). For
stars with Stroemgren temperatures between 10,000 and 12,000 K we found
excellent agreement between the atmospheric parameters derived from Stroemgren
photometry and those derived from Balmer line profile fits. However, for cooler
stars there is a disagreement in the parameters derived by the two methods, for
which we have no satisfactory explanation. Stars hotter than 12,000 K show
evidence for helium depletion and iron enrichment, both in M 3 and M 13.
Accounting for the iron enrichment substantially improves the agreement with
canonical evolutionary models, although the derived gravities and masses are
still somewhat too low. This remaining discrepancy may be an indication that
scaled-solar metal-rich model atmospheres do not adequately represent the
highly non-solar abundance ratios found in blue HB stars affected by diffusion.
We discuss the effects of an enhancement in the envelope helium abundance on
the atmospheric parameters of the blue HB stars, as might be caused by deep
mixing on the red giant branch or primordial pollution from an earlier
generation of intermediate mass asymptotic giant branch stars.
|
0304475v1
|
2003-05-24
|
A New Population of Old Stars
|
We report the results of a coherent study of three chemically anomalous
metal-poor ([Fe/H] ~ -2) stars. These objects exhibit unusually low abundances
of Mg, Si, Ca (alpha-elements) and Sr, Y, and Ba (neutron-capture elements).
Our analyses confirm and expand upon earlier reports of atypical abundances in
BD+80~245, G4-36, and CS22966-043. We also find that the latter two stars
exhibit enhanced abundances of Cr, Mn, Ni, and Zn (iron-peak elements), along
with what appears to be large abundances of Ga, with respect to the abundance
of iron. Comparing the chemical abundances of these stars to supernova model
yields, we derive supernovae ratios of Type Ia versus Type II events in the
range of 0.6 <= (N_Ia/N_II) <= 1.3. Whereas, for the Sun, we derive supernovae
ratios in good agreement with those found in the literature: 0.18 +/- 0.01 <
(N_Ia/N_II)_sun < 0.25 +/- 0.06. Given the relatively low metallicity and high
(N_Ia/N_II) ratios of the low-alpha stars studied here, these objects may have
witnessed, or been born from material produced in the yields of the earliest
supernova Type Ia events.
|
0305479v1
|
2003-06-26
|
An intense and broad FeKalpha line observed in the X-ray luminous quasar Q0056-363 with XMM-Newton
|
We present an XMM-Newton observation of the radio-quiet quasar Q0056-363
(z=0.162). This is the first time that this quasar is observed in the hard
X-ray range (above 2 keV). We find that Q0056-363 is a powerful X-ray quasar,
with a 0.3-12 keV unabsorbed luminosity of about 1.2 x 10^45 erg s-1 with the
largest part (~67%) emitted below 2 keV. The spectrum reveals a large
featureless soft X-ray excess below 2 keV and a strong broad FeKalpha line at
6.4 keV (in the quasar frame). The FeK alpha line is due to low to moderate
ionization states of iron (i.e., < Fe XVII), with an equivalent width of about
250 eV and a velocity width of about 25,000 km s-1. Q0056-363 is presently the
most luminous AGN known to exhibit such a broad and intense FeKalpha line
profile from near neutral iron. The line can be fitted with a relativistic
profile from an accretion disc around either a Schwarzschild (non-rotating) or
a Kerr (rotating) black hole. A combination of two thermal Comptonization
components and a disc reflection model is favored to explain both the continuum
over the energy range 0.3-12 keV and the FeK alpha line. A patchy corona
covering a large part of the inner disc surface is needed in order to be
compatible with the accretion rate inferred from the spectral energy
distribution of Q0056-363, unless the mass of the black hole is much higher
than about 5 x 10^8 M_odot.
|
0306550v1
|
2003-08-05
|
The hard X-ray view of the low-luminosity blazar in the radio galaxy NGC6251
|
We present results from a BeppoSAX (July 2001) observation of the FRI radio
galaxy NGC6251, together with a re-analysis of archival ASCA (October 1994) and
Chandra (September 2000) data. The weak detection above 10 keV and the lack of
iron fluorescent K-alpha emission lines in the BeppoSAX spectrum rule out that
the bulk of the X-ray emission is due to an obscured Seyfert nucleus. The study
of the multiwavelength spectral energy distribution suggests instead that
X-rays probably originate as inverse-Compton of synchrotron seed photons in a
relativistic jet, indicating that NGC6251 hosts a low radio luminosity [L(5
GHz) ~10^40 erg/s] blazar. The BeppoSAX spectrum is flatter than in the earlier
ASCA observation. This might be due to the emergence of a different spectral
component during phases of lower X-ray flux. In this context, we discuss some
possible explanations for the intense and mildly-ionized fluorescent iron line
measured by ASCA.
|
0308076v3
|
2003-08-11
|
The XMM/BeppoSAX observation of Mkn 841
|
Mkn 841 has been observed simultaneously by XMM and BeppoSAX in January 2001.
Due to operational contingency, the 30ks XMM observation was split into two
parts, separated by about 15 hours. We first report the presence of a narrow
iron line which appears to be rapidly variable between the two pointings,
requiring a non-standard interpretation. We then focus on the analysis of the
broad band (0.3-200 keV) continuum using the XMM/EPIC, RGS and SAX/PDS data.
The Mkn 841 spectrum is well fitted by a comptonization model in a geometry
more photon-fed than a simple slab geometry above a passive disk. It presents a
relatively large reflection (R>2) which does not agree with an apparently weak
iron line. It also show the presence of a strong soft excess wellfitted by a
comptonized spectrum in a cool plasma, suggesting the presence of a
multi-temperature corona.
|
0308176v1
|
2003-09-15
|
The X-ray spectra of the flaring and quiescent states of AT Microscopii observed by XMM-Newton
|
The X-ray spectrum of the late-type M-dwarf binary AT Mic (dM4.5e+dM4.5e) is
observed in the wavelength range 1 - 40 Angstrom by means of rgs and epic-mos
on board XMM-Newton. During the exposure a flare occured. We have performed a
3-temperature fit and a DEM-modeling to the flaring and quiescent part of the
spectrum. We report the coronal temperature distribution, emission measures,
and abundances of the flaring and quiescent state of this bright X-ray source.
The temperature range stretches from about 1 to 60 MK. The total volume
emission measure in this temperature interval is ~12.2*10^51 cm^-3 for the
quiescent state and ~19.5*10^51 cm^-3 for the flare state. This difference is
due to the contribution of the hot temperature component. The high-resolution
spectrum of AT Mic, obtained by rgs, is dominated by the H- and He-like
transitions of C, N, O, and Ne and by Fe XVII lines, produced by the plasma
with temperatures from 1 to 10 MK. The epic-mos spectrum below 10 Angstrom
shows H- and He-like Ne, Si and the iron K-shell transitions. They are produced
by the hot component (30 MK). The iron K-shell is more prominent in the flare
state. The abundance pattern in the quiescent state of AT Mic shows the
depletion of low-FIP elements relative to high-FIP elements, indicating the
presence of an I(nverse)FIP effect in this active star. In the flare state,
however, some flattening of this IFIP effect is present.
|
0309383v1
|
2003-09-16
|
Timing and spectral studies of LMC X-4 in high and low states with Beppo-SAX: Detection of pulsations in the soft spectral component
|
We report here detailed timing and spectral analysis of two Beppo-SAX
observations of the binary X-ray pulsar LMC X-4 carried out during the low and
high states of its 30.5 days long super-orbital period. Timing analysis clearly
shows 13.5 s X-ray pulsations in the high state of the super-orbital period
which allows us to measure the mid-eclipse time during this observation.
Combining this with two other mid-eclipse times derived earlier with the ASCA,
we derived a new estimate of the orbital period derivative. Pulse-phase
averaged spectroscopy in the high and low states shows that the energy spectrum
in the 0.1 - 10 keV band comprises of a hard power-law, a soft excess, and a
strong iron emission line. The continuum flux is found to decrease by a factor
of ~ 60 in the low state while the decrease in the iron line flux is only by a
factor of ~ 12, suggesting a different site for the production of the line
emission. In the low state, we have not found any significant increase in the
absorption column density. The X-ray emission is found to come from a very
large region, comparable to the size of the companion star. Pulse phase
resolved spectroscopy in the high state shows a pulsating nature of the soft
spectral component with some phase offset compared to the hard X-rays, as is
known in some other binary X-ray pulsars.
|
0309431v1
|
2003-09-19
|
The photospheric abundances of active binaries II. Atmospheric parameters and abundance patterns for 6 single-lined RS CVn systems
|
Photospheric parameters and abundances are presented for a sample of
single-lined chromospherically active binaries from a differential LTE analysis
of high-resolution spectra. Abundances have been derived for 13 chemical
species, including several key elements such as Li, Mg, and Ca. Two methods
have been used. The effective temperatures, surface gravities and
microturbulent velocities were first derived from a fully self-consistent
analysis of the spectra, whereby the temperature is determined from the
excitation equilibrium of the Fe I lines. The second approach relies on
temperatures derived from the (B-V) colour index. These two methods give
broadly consistent results for the stars in our sample, suggesting that the
neutral iron lines are formed under conditions close to LTE. We discuss the
reliability in the context of chromospherically active stars of various colour
indices used as temperature indicators, and conclude that the (V-R) and (V-I)
colours are likely to be significantly affected by activity processes.
Irrespective of the method used, our results indicate that the X-ray active
binaries studied are not as metal poor as previously claimed, but are at most
mildly iron-depleted relative to the Sun (-0.41<[Fe/H]<+0.11). A significant
overabundance of several chemical species is observed (e.g., the
alpha-synthezised elements). These abundance patterns are discussed in relation
to stellar activity.
|
0309535v1
|
2003-10-09
|
BeppoSAX observations of Seyfert 1s in the Piccinotti sample I: poorly studied sources
|
In this work we present the first of two papers devoted to the study of the
X-ray spectral characteristics of Seyfert 1 galaxies in the Piccinotti sample.
In particular we analyse here the BeppoSAX broad band (0.1-100 keV) data of 4
objects which, despite their X-ray brightness, have been historically poorly
studied due to their late identification with an AGN; these are H0111-149
(MKN1152), H0235-525 (ESO198-G24), H0557-385 (IRAS F05563-3820) and H1846-786
(IRAS F18389-7834). We have assumed for all the sources a baseline model which
includes a power law with an exponential cut-off plus a reflection component
and an iron K_alpha line; we have also searched for the presence of intrinsic
absorption and/or a soft excess component. Our analysis indicates the presence
of complex absorption in two objects (H0557-385 and H0111-149) best described
by a combination of two uniform absorbers, one cold and one warm. Only in one
source, H0557-385, a soft excess component has been measured. The primary
continuum is best described by a canonical power law (Gamma=1.7-2) with a high
energy cut-off in the range 40-130 keV. A cold reflection component is likely
present in all sources with values ranging from less than 0.6 to higher than 2.
In 3 out of 4 objects we find a cold iron line having equivalent width typical
of Seyfert 1s (100-200 eV).
|
0310248v1
|
2003-10-22
|
A Method for energy estimation and mass composition determination of primary cosmic rays at Chacaltaya observation level based on atmospheric Cerenkov light technique
|
A new method for energy and mass composition estimation of primary cosmic ray
radiation based on atmospheric Cerenkov light flux in extensive air showers
(EAS) analysis is proposed. The Cerenkov light flux in EAS initiated by primary
protons and iron nuclei is simulated with CORSIKA 5.62 code for Chacaltaya
observation level (536 g/cm2) in the energy range 10 TeV - 10 PeV. An adequate
model, approximation of lateral distribution of Cerenkov light in showers is
obtained. Using the proposed model and solution of overdetermined system of
nonlinear equations based on Gauss Newton method with autoregularization, two
different array detector arrangements are compared. The detector response for
the detector sets is simulated. The accuracies in energy and shower axis
determination are studied and the corresponding selection criteria are
proposed. An approximation with nonlinear fit is obtained and the energy
dependence of the proposed model function parameters is studied. The
approximation of model parameters as function of the primary energy is carried
out. This permits, taking into account the properties of the proposed method
and model, to distinguish proton primaries from iron primaries. The detector
response for the detector sets is simulated and the accuracies in energy
determination are calculated. Moreover the accuracies in shower axis
determination are studied and criteria in shower axis position estimation are
proposed.
|
0310651v2
|
2003-11-20
|
A long, hard look at MCG-6-30-15 with XMM-Newton II: detailed EPIC analysis and modelling
|
The bright Seyfert 1 galaxy MCG-6-30-15 has provided some of the best
evidence to date for the existence of supermassive black holes in active
galactic nuclei. Observations with ASCA revealed an X-ray iron line profile
shaped by strong Doppler and gravitational effects. In this paper the shape of
the iron line, its variability characteristics and the robustness of this
spectral interpretation are examined using the long XMM-Newton observation
taken in 2001. A variety of spectral models, both including and excluding the
effects of strong gravity, are compared to the data in a uniform fashion. The
results strongly favour models in which the spectrum is shaped by emission from
a relativistic accretion disc. It is far more difficult to explain the 3-10 keV
spectrum using models dominated by absorption (either by warm or partially
covering cold matter), emission line blends, curved continua or additional
continuum components. These provide a substantially worse fit to the data and
fail to explain other observations (such as the simultaneous BeppoSAX
spectrum). This reaffirms the veracity of the relativistic `disc line'
interpretation. The short term variability in the shape of the energy spectrum
is investigated and explained in terms of a two-component emission model. Using
a combination of spectral variability analyses the spectrum is successfully
decomposed into a variable power-law component (PLC) and a reflection dominated
component (RDC). The former is highly variable while the latter is
approximately constant throughout the observation, leading to the well-known
spectral variability patterns. (Abridged)
|
0311473v1
|
2004-01-09
|
Theoretical FeI/II/III Emission-Line Strengths from Active Galactic Nuclei with Broad-Line Regions
|
We present theoretical iron emission line strengths for physical conditions
typical of Active Galactic Nuclei with Broad-Line Regions. The non-local
thermodynamic equilibrium (NLTE) models include a new and extensive treatment
of radiative transfer in the FeIII ion, complementing the FeII emission line
strengths predicted in our earlier works. We also briefly present preliminary
results for the FeI emission from AGN using a reduced atom model. We can
satisfactorily reproduce the empirical UV FeIII emission line template of
Vestergaard & Wilkes (2001) for the prototypical narrow-line Seyfert 1 galaxy I
Zw 1, both in terms of the general FeIII flux distribution and the relative
strength of the FeIII and FeII emission. However, a number of detailed features
are still not matched; the most prominent example is the strongest single FeIII
feature observed in the I Zw 1 spectrum, UV47: it is predicted to be strong
only in models suppressing Fe-H charge exchange reactions. We examine the role
of variations in cloud turbulent velocity and iron abundance and carry out
Monte Carlo simulations to demonstrate the effect of uncertainties in atomic
data on the computed spectra.
|
0401168v1
|
2004-01-20
|
Nitrogen abundances in Planet-harbouring stars
|
We present a detailed spectroscopic analysis of nitrogen abundances in 91
solar-type stars, 66 with and 25 without known planetary mass companions. All
comparison sample stars and 28 planet hosts were analysed by spectral synthesis
of the near-UV NH band at 3360 \AA observed at high resolution with the
VLT/UVES,while the near-IR NI 7468 \AA was measured in 31 objects. These two
abundance indicators are in good agreement. We found that nitrogen abundance
scales with that of iron in the metallicity range -0.6 <[Fe/H]< +0.4 with the
slope 1.08 \pm 0.05. Our results show that the bulk of nitrogen production at
high metallicities was coupled with iron. We found that the nitrogen abundance
distribution in stars with exoplanets is the high [Fe/H] extension of the curve
traced by the comparison sample of stars with no known planets. A comparison of
our nitrogen abundances with those available in the literature shows a good
agreement.
|
0401396v1
|
2004-02-09
|
The Toroidal Iron Atmosphere of a Protoneutron Star: Numerical Solution
|
A numerical method presented by Imshennik et al. (2002) is used to solve the
two dimensional axisymmetric hydrodynamic problem on the formation of a
toroidal atmosphere during the collapse of an iron stellar core and outer
stellar layers. An evolutionary model from Boyes et al. (1999) with a total
mass of $25M_{\odot}$ is used as the initial data for the distribution of
thermodynamic quantities in the outer shells of a high-mass star. We analyze in
detail the results of three calculations in which the difference mesh and the
location of the inner boundary of the computational region are varied. In the
initial data, we roughly specify an angular velocity distribution that is
actually justified by the final result - the formation of a hydrostatic
equilibrium toroidal atmosphere with reasonable total mass, $M^{tot} = (0.117
\div 0.122)M_{\odot}$, and total angular momentum, $J^{tot} = (0.445 \div
0.472) x 10^{50} erg \cdot s$, for the two main calculations. We compare the
numerical solution with our previous analytical solution in the form of
toroidal atmospheres (Imshennik and Manukovskii 2000). This comparison
indicates that they are identical if we take into account the more general and
complex equation of state with a nonzero temperature and self-gravitation
effects in the atmosphere. Our numerical calculations, first, prove the
stability of toroidal atmospheres on characteristic hydrodynamic time scales
and, second, show the possibility of sporadic fragmentation of these
atmospheres even after a hydrodynamic equilibrium is established. The
calculations were carried out under the assumption of equatorial symmetry of
the problem and up to relatively long time scales $(\approx 10s)$.
|
0402191v1
|
2004-02-10
|
Discovery of Soft Spectral Component and Transient 22.7s Quasi Periodic Oscillations of SAX J2103.5+4545
|
XMM-Newton observed SAX J2103.5+4545 on January 6, 2003, while RXTE was
monitoring the source. Using RXTE-PCA dataset between December 3, 2002 and
January 29, 2003, the spin period and average spin-up rate during the
XMM-Newton observations were found to be $354.7940\pm0.0008$ s and
$(7.4\pm0.9)\times10^{-13}$Hz s$^{-1}$ respectively. In the power spectrum of
the 0.9-11 keV EPIC-PN lightcurve, we found quasi periodic oscillations around
0.044 Hz (22.7 s) with an rms fractional amplitude $\sim $6.6 %. We interpreted
this QPO feature as the Keplerian motion of inhomogenuities through the inner
disk. In the X-ray spectrum, in addition to the power law component with high
energy cutoff and $\sim6.4$ keV fluorescent iron emission line (Baykal et al.,
2002), we discovered a soft component consistent with a blackbody emission with
${\rm{kT}}\sim1.9$keV. The pulse phase spectroscopy of the source revealed that
the blackbody flux peaked at the peak of the pulse with an emission radius
$\sim 0.3$ km, suggesting the polar cap on the neutron star surface as the
source of blackbody emission. The flux of the iron emission line at $\sim 6.42$
keV was shown to peak at the off-pulse phase, supporting the idea that this
feature arises from fluorescent emission of the circumstellar material around
the neutron star rather than the hot region in the vicinity of the neutron star
polar cap.
|
0402221v2
|
2004-02-13
|
The high energy X-ray tail of Eta Car revealed by BeppoSAX
|
We report on the June 2000 long (100 ks) BeppoSAX exposure that has unveiled
above 10 keV a new very high energy component of the X-ray spectrum of Eta Car
extending to at least 50 keV. We find that the 2-150 keV spectrum is best
reproduced by a thermal + non-thermal model. The thermal component dominates
the 2-10 keV spectral range with kT_h=5.5 +/- 0.3 keV and log NH_h=22.68 +/-
0.01. The spectrum displays a prominent iron emission line centred at 6.70 keV.
Its equivalent width of 0.94 keV, if produced by the thermal source, gives a
slightly sub-solar iron abundance ([Fe/H]=-0.15 +/- 0.02).
The high energy tail above 10 keV is best fitted by a power law with a photon
index of 2.42 +/- 0.04. The integrated 13-150 keV luminosity of ~12 L-sun is
comparable to that of the 2-10 keV thermal component. The present result can be
explained, in the Eta Car binary star scenario, by Comptonisation of low
frequency radiation by high energy electrons, probably generated in the
colliding wind shock front, or in instabilities in the wind of the S Dor
primary star. It is possible that the high energy tail had largely weakened
near the minimum of the 5.53 yr cycle. With respect to the thermal component,
it probably has a longer recovering time like that of the highest excitation
optical emission lines. Both features can be associated with the large
absorption measured by BeppoSAX at phase 0.05.
|
0402329v1
|
2004-03-03
|
XMM-Newton Observations of NGC 507: Super-solar Metal Abundances in the Hot ISM
|
We present the results of the X-ray XMM-Newton observations of NGC 507, a
dominant elliptical galaxy in a small group of galaxies, and report
'super-solar' metal abundances of both Fe and a-elements in the hot ISM of this
galaxy. We find Z_Fe = 2-3 times solar inside the D25 ellipse of NGC 507. This
is the highest Z_Fe reported so far for the hot halo of an elliptical galaxy;
this high Iron abundance is fully consistent with the predictions of stellar
evolution models, which include the yield of both type II and Ia supernovae.
The spatially resolved, high quality XMM spectra provide enough statistics to
formally require at least three emission components: two soft thermal
components indicating a range of temperatures in the hot ISM, plus a harder
component, consistent with the integrated output of low mass X-ray binaries
(LMXBs). The abundance of a-elements (most accurately determined by Si) is also
found to be super-solar. The a-elements to Fe abundance ratio is close to the
solar ratio, suggesting that ~70% of the Iron mass in the hot ISM was
originated from SNe Type Ia. The a-element to Fe abundance ratio remains
constant out to at least 100 kpc, indicating that SNe Type II and Ia ejecta are
well mixed in a scale much larger than the extent of the stellar body.
|
0403105v2
|
2004-03-10
|
Far-UV Spectroscopic Analyses of Four Central Stars of Planetary Nebulae
|
We analyze the Far-UV/UV spectra of four central stars of planetary nebulae
with strong wind features -- NGC 2371, Abell 78, IC 4776 and NGC 1535, and
derive their photospheric and wind parameters by modeling high-resolution FUSE
(Far-Ultraviolet Spectroscopic Explorer) data in the Far-UV and HST-STIS and
IUE data in the UV with spherical non-LTE line-blanketed model atmospheres.
Abell 78 is a hydrogen-deficient transitional [WR]-PG 1159 object, and we find
NGC 2371 to be in the same stage, both migrating from the constant-luminosity
phase to the white dwarf cooling sequence with Teff ~= 120 kK, Mdot ~= 5x10^-8
Msun/yr. NGC 1535 is a ``hydrogen-rich'' O(H) CSPN, and the exact nature of IC
4776 is ambiguous, although it appears to be helium burning. Both objects lie
on the constant-luminosity branch of post-AGB evolution and have Teff ~= 65 kK,
Mdot ~= 1x10^-8 Msun/yr. Thus, both the H-rich and H-deficient channels of PN
evolution are represented in our sample. We also investigate the effects of
including higher ionization stages of iron (up to FeX) in the model atmosphere
calculations of these hot objects (usually neglected in previous analyses), and
find iron to be a useful diagnostic of the stellar parameters in some cases.
The Far-UV spectra of all four objects show evidence of hot (T ~ 300 K)
molecular hydrogen in their circumstellar environments.
|
0403262v1
|
2004-04-15
|
Iron abundances from high-resolution spectroscopy of the open clusters NGC 2506, NGC 6134, and IC 4651
|
This is the first of a series of papers devoted to derive the metallicity of
old open clusters in order to study the time evolution of the chemical
abundance gradient in the Galactic disk. We present detailed iron abundances
from high resolution (R~40000) spectra of several red clump and bright giant
stars in the open clusters IC 4651, NGC 2506 and NGC 6134. We observed 4 stars
of NGC 2506, 3 stars of NGC 6134, and 5 stars of IC 4651 with the FEROS
spectrograph at the ESO 1.5 m telescope; moreover, 3 other stars of NGC 6134
were observed with the UVES spectrograph on Kueyen (VLT UT2). After excluding
the cool giants near the red giant branch tip (one in IC 4651 and one in NGC
2506), we found overall [Fe/H] values of -0.20 +/- 0.01, rms = 0.02 dex (2
stars) for NGC 2506, +0.15 +/- 0.03, rms = 0.07 dex (6 stars) for NGC 6134, and
+0.11 +/- 0.01, rms = 0.01 dex (4 stars) for IC 4651. The metal abundances
derived from line analysis for each star were extensively checked using
spectrum synthesis of about 30 to 40 Fe I lines and 6 Fe II lines. Our
spectroscopic temperatures provide reddening values in good agreement with
literature data for these clusters, strengthening the reliability of the
adopted temperature and metallicity scale. Also, gravities from the Fe
equilibrium of ionization agree quite well with expectations based on cluster
distance moduli and evolutionary masses.
|
0404298v1
|
2004-05-19
|
Where Did The Moon Come From?
|
The current standard theory of the origin of the Moon is that the Earth was
hit by a giant impactor the size of Mars causing ejection of iron poor impactor
mantle debris that coalesced to form the Moon. But where did this Mars-sized
impactor come from? Isotopic evidence suggests that it came from 1AU radius in
the solar nebula and computer simulations are consistent with it approaching
Earth on a zero-energy parabolic trajectory. But how could such a large object
form in the disk of planetesimals at 1AU without colliding with the Earth
early-on before having a chance to grow large or before its or the Earth's iron
core had formed? We propose that the giant impactor could have formed in a
stable orbit among debris at the Earth's Lagrange point $L_4$ (or $L_5$). We
show such a configuration is stable, even for a Mars-sized impactor. It could
grow gradually by accretion at $L_4$ (or $L_5$), but eventually gravitational
interactions with other growing planetesimals could kick it out into a chaotic
creeping orbit which we show would likely cause it to hit the Earth on a
zero-energy parabolic trajectory. This paper argues that this scenario is
possible and should be further studied.
|
0405372v2
|
2004-05-27
|
High resolution X-ray spectra of quasars
|
Past X-ray observations by ASCA suggest that warm absorbers (O VII and O VIII
edges) are apparently rare in high luminosity AGNs (quasars) while they are
more common in low luminosity AGNs (Seyferts). However, this could be a
selection effect if high luminosity AGNs have mostly narrow absorption lines
(with no strong bound free edges), which escaped detection by the low
resolution of ASCA. To check this hypothesis we are studying the
high-resolution X-ray spectra of quasars from grating spectrometers on board
Chandra and XMM-Newton in search for absorption lines. In this contribution we
present spectra of three quasars. The spectra show narrow (several hundred
km/s) absorption and emission X-ray lines from H-like and He-like ions of O,
Ne, Mg, and other abundant elements. We also detect absorption from iron
L-shell lines and iron M-shell unresolved transition array. We present the
analysis of MR2251-178 where we find that at least two, and probably three,
distinct warm absorbers are needed to explain the high resolution spectrum of
this object. We re-analyze the high-resolution X-ray spectrum of PG1211+143 and
suggest that an outflow velocity of about 3000 km/s provides an adequate
explanation to these data. We also present preliminary results form the
Chandra/HETGS observation of the quasar 4C74.26.
|
0405563v1
|
2004-06-11
|
Intracluster Stars and the Chemical Enrichment of the Intracluster Medium
|
We explore the contribution of intracluster stars (ICS) to the chemical
enrichment history of the intracluster medium (ICM). In contrast to scenarios
in which all the metals originate in cluster galaxies and are then transported
into the ICM, intracluster stars enrich the ICM in situ, thereby contributing
100% of their supernovae ejecta directly into the ICM. Modeling the ICS as an
ancient, single burst stellar population with a normal initial mass function,
we generate ICM iron abundances in the range of the observed values of several
tenths solar. Large observational and theoretical uncertainties preclude us
from concluding that the intracluster stars are the primary contributor of
metals to the ICM in general. However, for the two clusters in our sample, and
one from the literature, for which all of the required observational
constraints exist, we are able to reproduce between half and all of the ICM
iron. Due to the ubiquity of intracluster stars in clusters and their direct
connection with the ICM, we conclude that all models of the chemical enrichment
history and energy budget of the ICM should account for the impact of the ICS.
|
0406291v2
|
2004-07-19
|
The Origin of Fe II Emission in AGN
|
We used a very large set of models of broad emission line (BEL) clouds in AGN
to investigate the formation of the observed Fe II emission lines. We show that
photoionized BEL clouds cannot produce both the observed shape and observed
equivalent width of the 2200-2800A Fe II UV bump unless there is considerable
velocity structure corresponding to a microturbulent velocity parameter v_turb
> 100 km/s for the LOC models used here. This could be either microturbulence
in gas that is confined by some phenomenon such as MHD waves, or a velocity
shear such as in the various models of winds flowing off the surfaces of
accretion disks. The alternative way that we can find to simultaneously match
both the observed shape and equivalent width of the Fe II UV bump is for the Fe
II emission to be the result of collisional excitation in a warm, dense gas.
Such gas would emit very few lines other than Fe II. However, since the
collisionally excited gas would constitute yet another component in an already
complicated picture of the BELR, we prefer the model involving turbulence. In
either model, the strength of Fe II emission relative to the emission lines of
other ions such as Mg II depends as much on other parameters (either v_turb or
the surface area of the collisionally excited gas) as it does on the iron
abundance. Therefore, the measurement of the iron abundance from the FeII
emission in quasars becomes a more difficult problem.
|
0407404v1
|
2004-07-29
|
A Study of the Composition of Ultra High Energy Cosmic Rays Using the High Resolution Fly's Eye
|
The composition of Ultra High Energy Cosmic Rays (UHECR) is measured with the
High Resolution Fly's Eye cosmic ray observatory (HiRes) data using the Xmax
technique. Data were collected in stereo between 1999 November and 2001
September. The data are reconstructed with well-determined geometry.
Measurements of the atmospheric transmission are incorporated in the
reconstruction. The detector resolution is found to be 30 g cm^-2 in Xmax and
13% in Energy. The Xmax elongation rate between 10^18.0 eV and 10^19.4 eV is
measured to be 54.5 +/- 6.5 (stat) +/- 4.5 (sys) g cm^-2 per decade. This is
compared to predictions using the QGSJet01 and SIBYLL 2.1 hadronic interaction
models for both protons and iron nuclei. CORSIKA-generated Extensive Air
Showers (EAS) are incorporated directly into a detailed detector Monte Carlo
program. The elongation rate and the Xmax distribution widths are consistent
with a constant or slowly changing and predominantly light composition. A
simple model containing only protons and iron nuclei is compared to QGSJet and
SIBYLL. The best agreement between the model and the data is at 80% protons for
QGSJet and 60% protons for SIBYLL.
|
0407622v3
|
2004-08-27
|
The metal enrichment of the intracluster medium in hierarchical galaxy formation models
|
We investigate the metal enrichment of the intracluster medium (ICM) in the
framework of hierarchical models of galaxy formation. We calculate the
formation and evolution of galaxies and clusters using a semi-analytical model
which includes the effects of flows of gas and metals both into and out of
galaxies. For the first time in a semi-analytical model, we calculate the
production of both alpha and iron-peak elements based on theoretical models for
the lifetimes and ejecta of type Ia and type II supernovae (SNe Ia and SNe II).
It is essential to include the long lifetimes of the SNIa progenitors in order
to correctly model the evolution of the iron-peak elements. We find that if all
stars form with an IMF similar to that found in the solar neighbourhood, then
the metallicities of O, Mg, Si and Fe in the ICM are predicted to be 2-3 times
lower than observed values. In contrast, a model (also favoured on other
grounds) in which stars formed in bursts triggered by galaxy mergers have a
top-heavy IMF reproduces the observed ICM abundances of O, Mg, Si and Fe. The
same model predicts ratios of ICM mass to total stellar luminosity in clusters
which agree well with observations. According to our model, the bulk of the
metals in clusters are produced by L* and brighter galaxies. [abridged]
|
0408529v2
|
2004-09-02
|
Orbital Phase Spectroscopy of GX 301--2 with RXTE-PCA
|
We have investigated the orbital phase dependence of the X-ray spectrum of
the High Mass X-ray Binary pulsar GX 301--2. Here we present the results from a
spectral analysis of two sets of observations of GX 301--2 with the Rossi X-ray
Timing Explorer (RXTE). Of particular interest are the variations of the
absorption column density and the iron line flux along with other parameters of
the spectral model with the orbital phase. We found that the X-ray spectrum can
almost always be fitted with a partial covering absorption model. We have
detected enhanced absorption near the periastron. However, the column density
variation with orbital phase is not smooth, as is expected in a smooth stellar
wind model. We discuss the results of the column density variation in the light
of the two proposed models for GX 301-2, an equatorial disk emanating from the
companion star Wray 977 and a gas stream following the neutron star. We also
found that the iron K_alpha and K_beta line fluxes have peaks near the
periastron and are well correlated with the continuum hard X-ray flux. The line
equivalent width shows an interesting pattern with the column density,
reasonably constant for low values of the column density and increasing rapidly
beyond a certain value.
|
0409056v1
|
2004-09-17
|
Presupernova Evolution of Differentially Rotating Massive Stars Including Magnetic Fields
|
As a massive star evolves through multiple stages of nuclear burning on its
way to becoming a supernova, a complex, differentially rotating structure is
set up. Angular momentum is transported by a variety of classic instabilities,
and also by magnetic torques from fields generated by the differential
rotation. We present the first stellar evolution calculations to follow the
evolution of rotating massive stars including, at least approximately, all
these effects, magnetic and non-magnetic, from the zero-age main sequence until
the onset of iron-core collapse. The evolution and action of the magnetic
fields is as described by Spruit 2002 and a range of uncertain parameters is
explored. In general, we find that magnetic torques decrease the final rotation
rate of the collapsing iron core by about a factor of 30 to 50 when compared
with the non-magnetic counterparts. Angular momentum in that part of the
presupernova star destined to become a neutron star is an increasing function
of main sequence mass. That is, pulsars derived from more massive stars will
rotate faster and rotation will play a more dominant role in the star's
explosion. The final angular momentum of the core is determined - to within a
factor of two - by the time the star ignites carbon burning. For the lighter
stars studied, around 15 solar masses, we predict pulsar periods at birth near
15 ms, though a factor of two range is easily tolerated by the uncertainties.
Several mechanisms for additional braking in a young neutron star, especially
by fall back, are also explored.
|
0409422v1
|
2004-11-12
|
An XMM-Newton Observation of the Seyfert 2 Galaxy NGC 6300. I. The Nucleus
|
We present results from a half-day observation by XMM-Newton of the nucleus
of the nearby Seyfert 2 galaxy NGC 6300. The X-ray spectrum of the nucleus
consists of a heavily absorbed hard component dominating the 3--10 keV band and
a soft component seen in the 0.2--2 keV band. In the hard band, the spectrum is
well fitted by a power-law model with photon index of 1.83+/-0.08 attenuated by
a Compton-thin absorber (N_H \simeq 2.2 x 10^{23} cm^{-2}). A narrow iron line
is detected at 6.43_{-0.02}^{+0.01} keV with an equivalent width of ~150 eV;
the line velocity width is marginally resolved to be \sigma~60eV. The soft
emission can be modeled as a power-law and may be emission scattered by
surrounding plasma. Rapid and high-amplitude variability is observed in the
hard X-ray band, whereas both the iron line and the soft emission show no
significant variability. It is suggested that the nucleus has experienced an
overall long-term trend of decreasing hard X-ray intensity on a timescale of
years. We discuss the origins of the spectral components.
|
0411328v1
|
2004-11-18
|
An XMM-Newton view of the cluster of galaxies Abell 85
|
We have observed the cluster of galaxies Abell 85 with XMM-Newton. These data
have allowed us to confirm in a previous paper the existence of the extended 4
Mpc filament detected by the ROSAT PSPC in the neighbourhood of this cluster,
and to determine an X-ray temperature of about about 2 keV. We now present a
thorough analysis of the properties of the X-ray gas in the cluster itself,
including temperature and metallicity maps for the entire cluster. These
results show that Abell 85 had intense merging activity in the past and is not
fully relaxed, even in the central region. We have also determined the
individual abundances for some iron-group metals and alpha-elements in various
regions; the ratios of these metallicities to the iron abundance show that both
supernova types Ia and II must be involved in the intra-cluster gas enrichment.
Spectral analysis of the central region suggests a different redshift of the
X-ray emitting gas compared to the mean cluster velocity derived from galaxy
member redshifts. We discuss the implications of the difference between the cD
galaxy redshift, the mean galaxy redshift and the hot gas redshift, as well as
the possibility of several groups being accreted on to Abell 85. Finally, we
obtain the dynamical mass profile and baryon fraction taking into account the
new determined temperature profile. The dynamical mass in Abell 85 has a steep
density profile, similar to the ones found in N-body simulations.
|
0411527v1
|
2004-11-22
|
The iron $K_α$-line as a tool for an evaluation of black hole parameters
|
Recent X-ray observations of microquasars and Seyfert galaxies reveal broad
emission lines in their spectra, which can arise in the innermost parts of
accretion disks. Simulations indicate that at low inclination angle the line is
measured by a distant observer as characteristic two-peak profile. However, at
high inclination angles ($> 85^0$) two additional peaks arise. This phenomenon
was discovered by Matt et al. (1993) using the Schwarzschild black hole metric
to analyze such effect. They assumed that the effect is applicable to a Kerr
metric far beyond the range of parameters that they exploited. We check and
confirm their hypothesis about such a structure of the spectral line shape for
the Kerr metric case. We use no astrophysical assumptions about the physical
structure of the emission region except the assumption that the region should
be narrow enough.
Positions and heights of these extra peaks drastically depend on both the
radial coordinate of the emitting region (annuli) and the inclination angle. It
was found that these extra peaks arise due to gravitational lens effect in the
strong gravitational field, namely they are formed by photons with some number
of revolutions around black hole. This conclusion is based only on relativistic
calculations without any assumption about physical parameters of the accretion
disc like X-ray surface emissivity etc.
We discuss how analysis of the iron spectral line shapes could give an
information about an upper limit of magnetic field near black hole horizon.
|
0411611v1
|
2004-12-03
|
How do Uncertainties in the Surface Chemical Abundances of the Sun Affect the Predicted Solar Neutrino Fluxes?
|
We show that uncertainties in the values of the surface heavy element
abundances of the Sun are the largest source of the theoretical uncertainty in
calculating the p-p, pep, 8B, 13N, 15O, and 17F solar neutrino fluxes. We
evaluate for the first time the sensitivity (partial derivative) of each solar
neutrino flux with respect to the surface abundance of each element. We then
calculate the uncertainties in each neutrino flux using `conservative
(preferred)' and `optimistic' estimates for the uncertainties in the element
abundances. The total conservative (optimistic) composition uncertainty in the
predicted 8B neutrino flux is 11.6% (5.0%) when sensitivities to individual
element abundances are used. The traditional method that lumps all abundances
into a single quantity (total heavy element to hydrogen ratio, Z/X) yields a
larger uncertainty, 20%. The uncertainties in the carbon, oxygen, neon,
silicon, sulphur, and iron abundances all make significant contributions to the
uncertainties in calculating solar neutrino fluxes; the uncertainties of
different elements are most important for different neutrino fluxes. The
uncertainty in the iron abundance is the largest source of the estimated
composition uncertainties of the important 7Be and 8B solar neutrinos. Carbon
is the largest contributor to the uncertainty in the calculation of the p-p,
13N, and 15O neutrino fluxes. However, for all neutrino fluxes, several
elements contribute comparable amounts to the total composition uncertainty.
|
0412096v2
|
2004-12-09
|
Unusual X-ray transients in the Galactic Centre
|
We report the discovery in the Galactic Centre region of two hard X-ray
sources, designated as XMM J174457-2850.3 and XMM J174544-2913.0, which
exhibited flux variations in the 2--10 keV band in excess of a factor of 100 in
observations spanning roughly a year. In both cases the observed hydrogen
column density is consistent with a location near to the Galactic Centre,
implying peak X-ray luminosities of ~5 x 10^34 erg/s. These objects may
represent a new population of transient source with very different properties
to the much more luminous Galactic Centre transients associated with neutron
star and black-hole binary systems. Spectral analysis shows that XMM
J174457-2850.3 has relatively weak iron-line emission set against a very hard
continuum. XMM J174544-2913.0, on the other hand, has an extremely strong
K-line from helium-like iron with an equivalent width of ~2.4keV. The nature of
the latter source is of particular interest. Does it represent an entirely new
class of object or does it correspond to a known class of source in a very
extreme configuration?
|
0412236v1
|
2005-01-26
|
The XMM-Newton view of PG quasars: II. Properties of the Fe K-alpha line
|
The properties of the fluorescence Fe K-alpha emission lines of a sample of
38 quasars (QSOs) observed with XMM-Newton are studied. These objects are
included in the optically selected sample from the Palomar-Green (PG) Bright
Quasar Survey with an X-ray luminosity 1.3E43<L(2-10 keV)<5.1E45 ergs/s and
z<1.72. For each object in the sample, we investigated the presence of both
narrow and broad iron lines in detail. A total of 20 out of the 38 QSOs show
evidence of an Fe K-alpha emission line with a narrow profile. The majority of
the lines are consistent with an origin in low ionization material, which is
likely to be located in the outer parts of the accretion disk, the molecular
torus, and/or the Broad Line Region. The average properties of the narrow Fe
K-alpha emission line observed in the sample are similar to those of Seyfert
type galaxies as inferred from recent XMM-Newton and Chandra studies. A broad
line has been significantly detected in only three objects. Furthermore, we
studied the relationship between the equivalent width (EW) of the iron line and
the hard band X-ray luminosity for radio quiet quasars. The analysis indicates
that no clear correlation between the strength of the line and the hard X-ray
luminosity is present, and our results do not show compelling evidence for an
anticorrelation between these two quantities, i.e. the so-called X-ray Baldwin
effect.
|
0501587v1
|
2005-02-13
|
Neural Networks as a Composition Diagnostic for Ultra-high Energy Cosmic Rays
|
We analyze here the possibility of studying mass composition in the Auger
data sample using neural networks as a diagnostic tool. Extensive air showers
were simulated using the AIRES code, for the two hadronic interaction models in
current use: QGSJet and Sibyll. Both, photon and hadron primaries were
simulated and used to generate events. The output parameters from the ground
array were simulated for the typical instrumental and environmental conditions
at the Malarg\"ue Auger site using the code SAMPLE. Besides photons, hydrogen,
helium, carbon, oxygen, magnesium, silicon, calcium and iron nuclei were also
simulated. We show that Principal Components Analysis alone is enough to
separate individual photon from hadron events, but the same technique cannot be
applied to the classification of hadronic events. The latter requires the use
of a more robust diagnostic. We show that neural networks are potentially
powerful enough to discriminate proton from iron events almost on an
event-by-event basis. However, in the case of a more realistic multi-component
mixture of primary nuclei, only a statistical estimate of the average mass can
be reliably obtained. Although hybrid events are not explicitly simulated, we
show that, whenever hybrid information in the form of $X_{max}$ is introduced
in the training procedure of the neural networks, a considerable improvement
can be achieved in mass discrimination analysis.
|
0502255v1
|
2005-03-01
|
Nucleosynthetic signatures of the first stars
|
The chemically most primitive stars provide constraints on the nature of the
first stellar objects that formed in the Universe; elements other than
hydrogen, helium and traces of lithium within these objects were generated by
nucleosynthesis in the very first stars. The relative abundances of elements in
the surviving primitive stars reflect the masses of the first stars, because
the pathways of nucleosynthesis are quite sensitive to stellar masses. Several
models have been suggested to explain the origin of the abundance pattern of
the giant star HE 0107-5240, which hitherto exhibited the highest deficiency of
heavy elements known. Here we report the discovery of HE 1327-2326, a subgiant
or main-sequence star with an iron abundance about a factor of two lower than
that of HE 0107-5240. Both stars show extreme overabundances of carbon and
nitrogen with respect to iron, suggesting a similar origin of the abundance
patterns. The unexpectedly low Li and high Sr abundances of HE 1327-2326,
however, challenge existing theoretical understanding: none predicts the high
Sr abundance or provides a Li depletion mechanism consistent with data
available for the most metal-poor stars.
|
0503021v2
|
2005-04-14
|
Iron abundances derived from RR Lyrae light curves and low-dispersion spectroscopy
|
With the aid of the All Sky Automated Survey (ASAS) database on the Galactic
field, we compare the iron abundances of fundamental mode RR Lyrae stars
derived from the Fourier parameters with those obtained from low-dispersion
spectroscopy. We show from a set of 79 stars, distinct from the original
calibrating sample of the Fourier method and selected without quality control,
that almost all discrepant estimates are the results of some defects or
peculiarities either in the photometry or in the spectroscopy. Omitting objects
deviating by more than 0.4dex, the remaining subsample of 64 stars yields
Fourier abundances that fit the spectroscopic ones with a standard deviation of
0.20dex. Other, more stringent selection criteria and different Fourier
decompositions lead to smaller subsamples and concomitant better agreement,
down to 0.16dex standard deviation. Except perhaps for two variables among the
163 stars, comprised of the ASAS variables and those of the original
calibrating set of the Fourier method, all discrepant values can be accounted
for by observational noise and insufficient data coverage. We suggest that the
agreement can be further improved when new, more accurate spectroscopic data
become available for a test with the best photometric data. As a by-product of
this analysis, we also compute revised periods and select Blazhko variables.
|
0504327v1
|
2005-04-21
|
Sulphur abundances in Terzan 7
|
We present here the first measurements of sulphur abundances in extragalactic
stars. We make use of high resolution spectra, obtained with UVES at the ESO
8.2 m Kueyen telescope, of three giants of the Globular Cluster Terzan 7, which
belongs to the Sagittarius dwarf galaxy. We measure the sulphur abundances
using the lines of S I multiplet 1. The S/Fe ratios for all three stars are
nearly solar, thus considerably lower than what is found in Galactic stars of
comparable iron content ([Fe/H] ~ -0.50). This finding is in keeping with the
abundances of other alpha-chain elements in this cluster and in Sagittarius and
other dSphs in general. These low alpha-chain elements to iron ratios suggest
that Sagittarius and its Globular Clusters have experienced a low or bursting
star-formation rate. Our sulphur abundances imply <\log (S/O)> = -1.61 which is
comparable to what is found in many H II regions of similar oxygen content, and
is slightly lower than the solar value (log (S/O)sun = -1.51). These are also
the first measurements of sulphur abundances in a Globular Cluster, thus a
direct comparison of Terzan 7 and Galactic Globular Clusters is not possible
yet. However our analysis suggests that the lines of S I multiplet 1 should be
measurable for other Globular Clusters at least down to a metallicity ~ -1.5.
|
0504463v1
|
2005-08-02
|
Charge Exchange Spectra of Hydrogenic and He-like Iron
|
We present H-like Fe XXVI and He-like Fe XXV charge-exchange spectra
resulting from collisions of highly charged iron with N2 gas at an energy of 10
eV/amu in an electron beam ion trap. Although individual high-n emission lines
are not resolved in our measurements, we observe that the most likely level for
Fe25+ --> Fe24+ electron capture is n~9, in line with expectations, while the
most likely value for Fe26+ --> Fe25+ charge exchange is significantly higher.
In the Fe XXV spectrum, the K-alpha emission feature dominates, whether
produced via charge exchange or collisional excitation. The K-alpha centroid is
lower in energy for the former case than the latter (6666 versus 6685 eV,
respectively), as expected because of the strong enhancement of emission from
the forbidden and intercombination lines, relative to the resonance line, in
charge-exchange spectra. In contrast, the Fe XXVI high-n Lyman lines have a
summed intensity greater than that of Ly-alpha, and are substantially stronger
than predicted from theoretical calculations of charge exchange with atomic H.
We conclude that the angular momentum distribution resulting from electron
capture using a multi-electron target gas is significantly different from that
obtained with H, resulting in the observed high-n enhancement. A discussion is
presented of the relevance of our results to studies of diffuse Fe emission in
the Galactic Center and Galactic Ridge, particularly with ASTRO-E2/Suzaku.
|
0508078v1
|
2005-08-05
|
The Radiative Transport of Dust in Primordial Galaxies and Second-Generation Star Formation
|
We investigate the radiative transport of dust in primordial galaxies in the
presence of the UV radiation field from the first metal-free stars. We find
that dust created in the first supernova (SN) explosions can be driven through
the interior of the SN remnant to accumulate in the SN shells, where
second-generation stars may form from compressed cooling gas. This scenario
requires metal-free stars to form continuously over timescales of up to 10 Myr,
consistent with recent estimates. Silicate and graphite grains, as well as
iron-bearing magnetites, are transported to the shells for reasonable parameter
assumptions, but their relative yields from primordial SNe is an important
factor in the resulting abundance ratios. We compare the results of segregated
grain transport with the current nucleosynthetic data on extremely metal-poor
Galactic halo stars. Fossil signatures of this process may already have been
detected in those iron-poor stars with enhanced carbon and silicate elements
such as magnesium, silicon and oxygen. We discuss the implications of our
results for the transition from first- to second-generation star formation in
primordial galaxies, and the role played by the radiative transport of dust in
this process.
|
0508163v2
|
2005-08-24
|
XMM-Newton spectroscopy of high-redshift QSOs
|
XMM-Newton observations of 29 high redshift (z>2) quasars, including seven
radio-quiet, 16 radio-loud and six Broad Absorption Line (BAL) objects, are
presented; due to the high redshifts, the rest-frame energy bands extend up to
\~30-70 keV. Over 2-10 keV, the quasars can be well fitted in each case by a
simple power-law, with no strong evidence for iron emission lines. The lack of
iron lines is in agreement both with dilution by the radio jet emission (for
the radio-loud quasars) and the X-ray Baldwin effect. No Compton reflection
humps at higher energies (i.e., above 10 keV in the rest frame) are detected
either. Over the broad-band (0.3-10 keV), approximately half (nine out of 16)
of the radio-loud quasars are intrinsically absorbed, with the values of N_H
generally being 1-2 x 10^22 cm^-2 in the rest frames of the objects. None of
the seven radio-quiet objects shows excess absorption, while four of the six
BAL quasars are absorbed. The radio-loud quasars have flatter continuum slopes
than their radio-quiet counterparts (Gamma_RL ~ 1.55; Gamma_RQ ~ 1.98 over 2-10
keV), while, after modelling the absorption, the underlying photon index for
the six BAL quasars is formally consistent with the non-BAL radio-quiet
objects.
|
0508524v1
|
2005-09-22
|
The new record holder for the most iron-poor star: HE 1327-2326, a dwarf or subgiant with [Fe/H]=-5.4
|
We describe the discovery of HE 1327-2326, a dwarf or subgiant with
[Fe/H]}=-5.4. The star was found in a sample of bright metal-poor stars
selected from the Hamburg/ESO survey. Its abundance pattern is characterized by
very high C and N abundances. The detection of Sr which is overabundant by a
factor of 10 as compared to iron and the Sun, suggests that neutron-capture
elements had already been produced in the very early Galaxy. A puzzling Li
depletion is observed in this unevolved star which contradicts the value of the
primordial Li derived from WMAP and other Li studies. Possible scenarios for
the origin of the abundance pattern (Pop. II or Pop. III) are presented as well
as an outlook on future observations.
|
0509658v1
|
2005-10-05
|
IGR J16393-4643: a new heavily-obscured X-ray pulsar
|
An analysis of the high-energy emission from IGR J16393-4643 (=AX
J1639.0-4642) is presented using data from INTEGRAL and XMM-Newton. The source
is persistent in the 20-40 keV band at an average flux of 5.1x10^-11
ergs/cm2/s, with variations in intensity by at least an order of magnitude. A
pulse period of 912.0+/-0.1 s was discovered in the ISGRI and EPIC light
curves. The source spectrum is a strongly-absorbed (nH=(2.5+/-0.2)x10^23
atoms/cm2) power law that features a high-energy cutoff above 10 keV. Two iron
emission lines at 6.4 and 7.1 keV, an iron absorption edge >7.1 keV, and a soft
excess emission of 7x10^-15 ergs/cm2/s between 0.5-2 keV, are detected in the
EPIC spectrum. The shape of the spectrum does not change with the pulse. Its
persistence, pulsation, and spectrum place IGR J16393-4643 among the class of
heavily-absorbed HMXBs. The improved position from EPIC is R.A.
(J2000)=16:39:05.4 and Dec.=-46:42:12 (4" uncertainty) which is compatible with
that of 2MASS J16390535-4642137.
|
0510112v2
|
2006-02-03
|
On the origin of the Fe K-alpha line cores in Active Galactic Nuclei
|
X-ray observations with Chandra and XMM-Newton have shown that there are
relatively narrow cores to the iron K-alpha emission lines in active galactic
nuclei (AGN). Plausible origins for this core emission include the outer
regions of an accretion disk, a pc-scale molecular torus, and the optical
broad-line region (BLR). Using data from the literature it is shown that no
correlation exists between the Fe K-alpha core width and the BLR (specifically
H-beta) line width. This shows that in general the iron K-alpha core emission
does not arise from the BLR. There is a similar lack of correlation between the
width of the Fe K-alpha core and black hole mass. The average K-alpha width is
about a factor of two lower than the H-beta width. It therefore seems likely
that in many cases the narrow core arises in the torus. There is a very wide
range of observed Fe K-alpha core widths, however, and this argues for multiple
origins. The simplest explanation for the observed line profiles in AGN is that
they are due to a mixing of very narrow emission from the inner edge of the
torus, and broadened emission from the accretion disk, in varying proportions
from object-to-object.
|
0602081v1
|
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