9,534 research outputs found
INTEGRAL and Swift/XRT observations of IGR J19405-3016
IGR J19405-3016 is reported in the 3rd IBIS catalog as being one of its
lowest significance sources (~4.6 sigma under an exposure of about 371 ks).
This leads to a caveat in multi-wavelength study although the source was
identified in optical as a Seyfert 1. The currently increased INTEGRAL data
stimulate us to investigate the reality of this source. We analyze all
available observations carried out by INTEGRAL and Swift on IGR J19405-3016. We
find that IGR J19405-3016 has a detection significance of ~ 9.4 sigma in the
20-60 keV band during the observational period between March 2003 and March
2008. Thus confirms a real source detection reported previously. The source
position and error location are therefore updated. The source is found to be
constant over years at the hard X-rays. Over the three XRT observations, the
source flux varied by up to 39% from the average, and the spectrum is generally
soft. The combined XRT/ISGRI spectrum is well fitted with a simple power law
model (photon index 2.11+-0.03). Such a photon index is well consistent with
the mean value 1.98 (dispersion 0.27) as obtained from Swift/BAT AGN samples at
14-195 keV. The spectral slope of IGR J19405-3016 is larger than the average
spectral slope found by Molina et al. (2009). A similar discrepancy is found
with the results of Beckmann et al. (2009) regarding Seyfert 1 AGNs. A possible
explanation of this simple spectral description may be that the low level of
the column density allows for the `true' spectrum to appear at soft X-rays as
well.Comment: Astronomy and Astrophysics, in pres
The Near Infrared and Multiwavelength Afterglow of GRB 000301c
We present near-infrared observations of the counterpart of GRB 000301c. The
K' filter (2.1 micron) light curve shows a well-sampled break in the decay
slope at t=3.5 days post-burst. The early time slope is very shallow (~ -0.1),
while the late time slope is steep (-2.2). Comparison with the optical (R band)
light curve shows marginally significant differences, especially in the early
time decay slope (which is steeper in the optical) and the break time (which
occurs later in the optical). This is contrary to the general expectation that
light curve breaks should either be achromatic (e.g., for breaks due to
collimation effects) or should occur later at longer wavelengths (for most
other breaks). The observed color variations might be intrinsic to the
afterglow, or might indicate systematic errors of > 0.08 magnitude in all
fluxes. Even if the break is achromatic, we argue that its sharpness poses
difficulties for explanations that depend on collimated ejecta. The R light
curve shows further signs of fairly rapid variability (a bump, steep drop, and
plateau) that are not apparent in the K' light curve. In addition, by combining
the IR-optical-UV data with millimeter and radio fluxes, we are able to
constrain the locations of the self-absorption break and cooling break and to
infer the location of the spectral peak at t=3 days: f_nu = 3.4 mJy at nu=1e12
Hz. Using the multiwavelength spectral energy distribution, we are able to
constrain the blast wave energy, which was E > 3e53 erg if the explosion was
isotropic. This implies a maximum gamma ray production efficiency of ~ 0.15 for
GRB 000301C.Comment: Accepted to The Astrophysical Journal. 24 pages, 4 figures, 3 tables;
uses AASTeX 5 macros. This version includes a new figure (R-K' color vs.
time), a better sampled R band light curve, and more extensive discussion of
the optical data and error analysi
The prompt optical/near-infrared flare of GRB 050904: the most luminous transient ever detected
With a redshift of z=6.295, GRB 050904 is the most distant gamma-ray burst
ever discovered. It was an energetic event at all wavelengths and the afterglow
was observed in detail in the near-infrared bands. We gathered all available
optical and NIR afterglow photometry of this GRB to construct a composite NIR
light curve spanning several decades in time and flux density. Transforming the
NIR light curve into the optical, we find that the afterglow of GRB 050904 was
more luminous at early times than any other GRB afterglow in the
pre-\emph{Swift} era, making it at these wavelengths the most luminous
transient ever detected. Given the intrinsic properties of GRB 050904 and its
afterglow, we discuss if this burst is markedly different from other GRBs at
lower redshifts.Comment: The Astronomical Journal, in press; revised version, including the
comments of the referee (one figure added, text restructured, all conclusions
unchanged), 7 pages, 3 figure
Simultaneous Heavy Ion Dissociation at Ultrarelativistic Energies
We study the simultaneous dissociation of heavy ultrarelativistic nuclei
followed by the forward-backward neutron emission in peripheral collisions at
colliders. The main contribution to this particular heavy-ion dissociation
process, which can be used as a beam luminosity monitor, is expected to be due
to the electromagnetic interaction. The Weizsacker-Williams method is extended
to the case of simultaneous excitation of collision partners which is simulated
by the RELDIS code. A contribution to the dissociation cross section due to
grazing nuclear interactions is estimated within the abrasion model and found
to be relatively small.Comment: Talk given at Bologna 2000 Conference - Structure of the Nucleus at
the Dawn of the Century, May 29 - June 3, 2000, 4 pages, 2 figure
GRB Afterglows from Anisotropic Jets
Some progenitor models of gamma-ray bursts (GRBs) (e.g., collapsars) may
produce anisotropic jets in which the energy per unit solid angle is a
power-law function of the angle (). We calculate light
curves and spectra for GRB afterglows when such jets expand either in the
interstellar medium or in the wind medium. In particular, we take into account
two kinds of wind: one () possibly from a typical red
supergiant star and another () possibly from a Wolf-Rayet
star. We find that in each type of medium, one break appears in the late-time
afterglow light curve for small but becomes weaker and smoother as
increases. When , the break seems to disappear but the afterglow decays
rapidly. Thus, one expects that the emission from expanding, highly anisotropic
jets provides a plausible explanation for some rapidly fading afteglows whose
light curves have no break. We also present good fits to the optical afterglow
light curve of GRB 991208. Finally, we argue that this burst might arise from a
highly anisotropic jet expanding in the wind () from a red
supergiant to interpret the observed radio-to-optical-band afterglow data
(spectrum and light curve).Comment: 12 pages + 10 figures, accepted by Ap
IGR J11215-5952: a hard X-ray transient displaying recurrent outbursts
The hard X-ray source IGRJ11215-5952 has been discovered with INTEGRAL during
a short outburst in 2005 and proposed as a new member of the class of
supergiant fast X-ray transients. We analysed INTEGRAL public observations of
the source field in order to search for previous outbursts from this transient,
not reported in literature.Our results are based on a systematic re-analysis of
INTEGRAL archival observations, using the latest analysis software and
instrument calibrations. We report the discovery of two previously unnoticed
outbursts, spaced by intervals of ~330 days, that occurred in July 2003 and May
2004. The 5-100keV spectrum is well described by a cut-off power law, with a
photon index of 0.5, and a cut-off energy ~15-20keV, typical of High Mass X-ray
Binaries hosting a neutron star. A 5-100keV luminosity of 3E36 erg/s has been
derived (assuming 6.2kpc, the distance of the likely optical counterpart). The
5-100keV spectral properties, the recurrent nature of the outbursts,together
with the reduced error region containing the blue supergiant star
HD306414,support the hypothesis that IGRJ11215-5952 is a member of the class of
the Supergiant Fast X-ray Transients.Comment: 4 pages, 4 figures, accepted for publication in Astronomy and
Astrophysics Letter
INTEGRAL/IBIS nine-year Galactic Hard X-Ray Survey
Context. The INTEGRAL observatory operating in a hard X-ray/gamma domain has
gathered a large observational data set over nine years starting in 2003. Most
of the observing time was dedicated to the Galactic source population study,
making possible the deepest Galactic survey in hard X-rays ever compiled. Aims.
We aim to perform a Galactic survey that can be used as the basis of Galactic
source population studies, and perform mapping of the Milky Way in hard X-rays
over the maximum exposure available at |b|<17.5 deg. Methods. We used sky
reconstruction algorithms especially developed for the high quality imaging of
INTEGRAL/IBIS data. Results. We present sky images, sensitivity maps, and
catalogs of detected sources in the three energy bands 17-60, 17-35, and 35-80
keV in the Galactic plane at |b|<17.5 deg. The total number of sources in the
reference 17-60 keV band includes 402 objects exceeding a 4.7 sigma detection
threshold on the nine-year time-averaged map. Among the identified sources with
known and tentatively identified natures, 253 are Galactic objects (108
low-mass X-ray binaries, 82 high-mass X-ray binaries, 36 cataclysmic variables,
and 27 are of other types), and 115 are extragalactic objects, including 112
active galactic nuclei (AGNs) and 3 galaxy clusters. The sample of Galactic
sources with S/N>4.7 sigma has an identification completeness of ~92%, which is
valuable for population studies. Since the survey is based on the nine-year sky
maps, it is optimized for persistent sources and may be biased against finding
transients.Comment: 18 pages, 7 figures, long table, Astronomy and Astrophysics 545, A2
GRB Energetics and the GRB Hubble Diagram: Promises and Limitations
We present a complete sample of 29 GRBs for which it has been possible to
determine temporal breaks (or limits) from their afterglow light curves. We
interpret these breaks within the framework of the uniform conical jet model,
incorporating realistic estimates of the ambient density and propagating error
estimates on the measured quantities. In agreement with our previous analysis
of a smaller sample, the derived jet opening angles of those 16 bursts with
redshifts result in a narrow clustering of geometrically-corrected gamma-ray
energies about E_gamma = 1.33e51 erg; the burst-to-burst variance about this
value is a factor of 2.2. Despite this rather small scatter, we demonstrate in
a series of GRB Hubble diagrams, that the current sample cannot place
meaningful constraints upon the fundamental parameters of the Universe. Indeed
for GRBs to ever be useful in cosmographic measurements we argue the necessity
of two directions. First, GRB Hubble diagrams should be based upon fundamental
physical quantities such as energy, rather than empirically-derived and
physically ill-understood distance indicators. Second, a more homogeneous set
should be constructed by culling sub-classes from the larger sample. These
sub-classes, though now first recognizable by deviant energies, ultimately must
be identifiable by properties other than those directly related to energy. We
identify a new sub-class of GRBs (``f-GRBs'') which appear both underluminous
by factors of at least 10 and exhibit a rapid fading at early times. About
10-20% of observed long-duration bursts appear to be f-GRBs.Comment: Accepted to the Astrophysical Journal (20 May 2003). 19 pages, 3
Postscript figure
X-ray, optical and infrared investigation of the candidate Supergiant Fast X-ray Transient IGR J18462-0223
We report on a broad-band X-ray study (0.5-60 keV) of the poorly known
candidate Supergiant Fast X-ray Transient (SFXT) IGR J18462-0223, and on
optical and near-infrared (NIR) followup observations of field objects. The
out-of-outburst X-ray state has been investigated for the first time with
archival INTEGRAL/IBIS, ASCA, Chandra and Swift/XRT observations. This allowed
us to place stringent 3 sigma upper limits on the soft (0.5-10 keV) and hard
(18-60 keV) X-ray emission of 2.9x10^-13 erg cm^-2 s^-1 and 8x10^-12 erg cm^-2
s^-1, respectively; the source was also detected during an intermediate soft
X-ray state with flux equal to 1.6x10^-11 erg cm^-2 s^-1 (0.5-10 keV). In
addition, we report on the INTEGRAL/IBIS discovery of three fast hard X-ray
flares (18-60 keV) having a duration in the range 1-12 hours: the flaring
behavior was also investigated in soft X-rays (3-10 keV) with archival
INTEGRAL/JEM-X observations. The duty cycle (1.2%) and the dynamic ranges (>
1,380 and > 190 in the energy bands 0.5-10 keV and 18-60 keV, respectively)
were measured for the first time. Archival UKIDSS JHK NIR data, together with
our deep R-band imaging of the field, unveiled a single, very red object inside
the intersection of the Swift/XRT and XMM-Newton error circles: this source has
optical/NIR photometric properties compatible with a very heavily absorbed blue
supergiant located at about 11 kpc, thus being a strong candidate counterpart
for IGR J18462-0223. NIR spectroscopy is advised to confirm the association.
Finally, a hint of a possible orbital period was found at about 2.13 days. If
confirmed by further studies, this would make IGR J18462-0223 the SFXT with the
shortest orbital period among the currently known systems.Comment: accepted for publication in A&A, 9 pages, 7 figures, 2 table
Unveiling the nature of the unidentified gamma-ray sources III: gamma-ray blazar-like counterparts at low radio frequencies
About one third of the gamma-ray sources listed in the second Fermi LAT
catalog (2FGL) have no firmly established counterpart at lower energies so
being classified as unidentified gamma-ray sources (UGSs). Here we propose a
new approach to find candidate counterparts for the UGSs based on the 325 MHz
radio survey performed with Westerbork Synthesis Radio Telescope (WSRT) in the
northern hemisphere. First we investigate the low-frequency radio properties of
blazars, the largest known population of gamma-ray sources; then we search for
sources with similar radio properties combining the information derived from
the Westerbork Northern Sky Survey (WENSS) with those of the NRAO VLA Sky
survey (NVSS). We present a list of candidate counterparts for 32 UGSs with at
least one counterpart in the WENSS. We also performed an extensive research in
literature to look for infrared and optical counterparts of the gamma-ray
blazar candidates selected with the low-frequency radio observations to confirm
their nature. On the basis of our multifrequency research we identify 23 new
gamma-ray blazar candidates out of 32 UGSs investigated. Comparison with
previous results on the UGSs are also presented. Finally, we speculate on the
advantages on the use of the low-frequency radio observations to associate UGSs
and to search for gamma-ray pulsar candidates.Comment: 15 pages, 13 figures, 3 tables, ApJS accepted for publication
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