5,894 research outputs found
An Estimation of the Gamma-Ray Burst Afterglow Apparent Optical Brightness Distribution Function
By using recent publicly available observational data obtained in conjunction
with the NASA Swift gamma-ray burst mission and a novel data analysis
technique, we have been able to make some rough estimates of the GRB afterglow
apparent optical brightness distribution function. The results suggest that 71%
of all burst afterglows have optical magnitudes with mR < 22.1 at 1000 seconds
after the burst onset, the dimmest detected object in the data sample. There is
a strong indication that the apparent optical magnitude distribution function
peaks at mR ~ 19.5. Such estimates may prove useful in guiding future plans to
improve GRB counterpart observation programs. The employed numerical techniques
might find application in a variety of other data analysis problems in which
the intrinsic distributions must be inferred from a heterogeneous sample.Comment: 15 pages including 2 tables and 7 figures, accepted for publication
in Ap
Multi-wavelength analysis of the field of the dark burst GRB 031220
We have collected and analyzed data taken in different spectral bands (from
X-ray to optical and infrared) of the field of GRB031220 and we present results
of such multiband observations. Comparison between images taken at different
epochs in the same filters did not reveal any strong variable source in the
field of this burst. X-ray analysis shows that only two of the seven Chandra
sources have a significant flux decrease and seem to be the most likely
afterglow candidates. Both sources do not show the typical values of the R-K
colour but they appear to be redder. However, only one source has an X-ray
decay index (1.3 +/- 0.1) that is typical for observed afterglows. We assume
that this source is the best afterglow candidate and we estimate a redshift of
1.90 +/- 0.30. Photometric analysis and redshift estimation for this object
suggest that this GRB can be classified as a Dark Burst and that the
obscuration is the result of dust extinction in the circum burst medium or
inside the host galaxy.Comment: 7 pages, 5 figures, accepted for publication on A&
Overall time evolution in phase-ordering kinetics
The phenomenology from the time of the quench to the asymptotic behavior in
the phase-ordering kinetics of a system with conserved order parameter is
investigated in the Bray-Humayun model and in the Cahn-Hilliard-Cook model.
From the comparison of the structure factor in the two models the generic
pattern of the overall time evolution, based on the sequence ``early linear -
intermediate mean field - late asymptotic regime'' is extracted. It is found
that the time duration of each of these regimes is strongly dependent on the
wave vector and on the parameters of the quench, such as the amplitude of the
initial fluctuations and the final equilibrium temperature. The rich and
complex crossover phenomenology arising as these parameters are varied can be
accounted for in a simple way through the structure of the solution of the
Bray-Humayun model.Comment: RevTeX, 14 pages, 18 figures, to appear in Phys. Rev.
The ultra-long GRB 111209A - II. Prompt to afterglow and afterglow properties
The "ultra-long" Gamma Ray Burst GRB 111209A at redshift z=0.677, is so far
the longest GRB ever observed, with rest frame prompt emission duration of ~4
hours. In order to explain the bursts exceptional longevity, a low metallicity
blue supergiant progenitor has been invoked. In this work, we further
investigate this peculiar burst by performing a multi-band temporal and
spectral analysis of both the prompt and the afterglow emission. We use
proprietary and publicly available data from Swift, Konus Wind, XMM-Newton,
TAROT as well as from other ground based optical and radio telescopes. We find
some peculiar properties that are possibly connected to the exceptional nature
of this burst, namely: i) an unprecedented large optical delay of 410+/-50 s is
measured between the peak epochs of a marked flare observed also in gamma-rays
after about 2 ks from the first Swift/BAT trigger; ii) if the optical and
X-ray/gamma-ray photons during the prompt emission share a common origin, as
suggested by their similar temporal behavior, a certain amount of dust in the
circumburst environment should be introduced, with rest frame visual dust
extinction of AV=0.3-1.5 mag; iii) at the end of the X-ray "steep decay phase"
and before the start of the X-ray afterglow, we detect the presence of a hard
spectral extra power law component never revealed so far. On the contrary, the
optical afterglow since the end of the prompt emission shows more common
properties, with a flux power law decay with index alpha=1.6+/-0.1 and a late
re-brightening feature at 1.1 day. We discuss our findings in the context of
several possible interpretations given so far to the complex multi-band GRB
phenomenology. We also attempt to exploit our results to further constrain the
progenitor nature properties of this exceptionally long GRB, suggesting a
binary channel formation for the proposed blue supergiant progenitor.Comment: ApJ accepted. Revised version with substantial adjustments, the main
results remain unchange
High-Pressure Phase Diagram in the Manganites: a Two-site Model Study
The pressure dependence of the Curie temperature in manganites,
recently studied over a wide pressure range, is not quantitatively accounted
for by the quenching of Jahn-Teller distortions, and suggests the occurrence of
a new pressure-activated localizing processes. We present a theoretical
calculation of based on a two-site double-exchange model with
electron-phonon coupling interaction and direct superexchange between the core spins. We calculate the pressure dependence of and compare
it with the experimental phase diagram. Our results describe the experimental
behavior quite well if a pressure-activated enhancement of the
antiferromagnetic superexchange interaction is assumed
GRB 081029: Understanding Multiple Afterglow Components
We present an analysis of the unusual optical light curve of the gamma-ray
burst GRB~081029, which occurred at a redshift of z = 3.8479$. We combine X-ray
and optical observations from the Swift X-Ray Telescope and the Swift
UltraViolet/Optical Telescope with optical and infrared data obtained using the
REM and ROTSE telescopes to construct a detailed data set extending from 86 s
to approximately 100,000 s after the BAT trigger. Our data also cover a wide
energy range, from 10 keV to 0.77 eV (1.24 Angstrom to 16,000 Angstrom). The
X-ray afterglow shows a shallow initial decay followed by a rapid decay
starting at about 18,000s. The optical and infrared afterglow, however, shows
an uncharacteristic rise at about 5000 s that does not correspond to any
feature in the X-ray light curve. Our data are not consistent with synchrotron
radiation from a single-component jet interacting with an external medium. We
do, however, find that the observed light curve can be explained using
multi-component model for the jet.Comment: 4 pages, 3 figures, to appear in the AIP Conference Proceedings for
the Gamma-Ray Burst 2010 Conference, Annapolis, MD, USA, November 201
Coarsening and Pinning in the Self-consistent Solution of Polymer Blends Phase-Separation Kinetics
We study analytically a continuum model for phase-separation in binary
polymer blends based on the Flory-Huggins-De Gennes free energy, by means of
the self-consistent large- limit approach. The model is solved for values of
the parameters corresponding to the weak and strong segregation limits. For
deep quenches we identify a complex structure of intermediate regimes and
crossovers characterized by the existence of a time domain such that phase
separation is pinned, followed by a preasymptotic regime which in the scalar
case corresponds to surface diffusion. The duration of the pinning is
analytically computed and diverges in the strong segregation limit. Eventually
a late stage dynamics sets in, described by scaling laws and exponents
analogous to those of the corresponding small molecule systems.Comment: 16 pages, 5 figures. Submitted to Phys. Rev.
The use and calibration of read-out streaks to increase the dynamic range of the Swift Ultraviolet/Optical Telescope
The dynamic range of photon counting micro-channel-plate (MCP) intensified
charged-coupled device (CCD) instruments such as the Swift Ultraviolet/Optical
Telescope (UVOT) and the XMM-Newton Optical Monitor (XMM-OM) is limited at the
bright end by coincidence loss, the superposition of multiple photons in the
individual frames recorded by the CCD. Photons which arrive during the brief
period in which the image frame is transferred for read out of the CCD are
displaced in the transfer direction in the recorded images. For sufficiently
bright sources, these displaced counts form read-out streaks. Using UVOT
observations of Tycho-2 stars, we investigate the use of these read-out streaks
to obtain photometry for sources which are too bright (and hence have too much
coincidence loss) for normal aperture photometry to be reliable. For
read-out-streak photometry, the bright-source limiting factor is coincidence
loss within the MCPs rather than the CCD. We find that photometric measurements
can be obtained for stars up to 2.4 magnitudes brighter than the usual
full-frame coincidence-loss limit by using the read-out streaks. The resulting
bright-limit Vega magnitudes in the UVOT passbands are UVW2=8.80, UVM2=8.27,
UVW1=8.86, u=9.76, b=10.53, v=9.31 and White=11.71; these limits are
independent of the windowing mode of the camera. We find that a photometric
precision of 0.1 mag can be achieved through read-out streak measurements. A
suitable method for the measurement of read-out streaks is described and all
necessary calibration factors are given.Comment: 11 pages, accepted for publication in MNRAS. Code available from the
calibration link at http://www.mssl.ucl.ac.uk/www_astro/uvo
A Large Catalog of Homogeneous Ultra-Violet/Optical GRB Afterglows: Temporal and Spectral Evolution
We present the second Swift Ultra-Violet/Optical Telescope (UVOT) gamma-ray
burst (GRB) afterglow catalog, greatly expanding on the first Swift UVOT GRB
afterglow catalog. The second catalog is constructed from a database containing
over 120,000 independent UVOT observations of 538 GRBs first detected by Swift,
the High Energy Transient Explorer 2 (HETE2), the INTErnational Gamma-Ray
Astrophysics Laboratory (INTEGRAL), the Interplanetary Network (IPN), Fermi,
and Astro-rivelatore Gamma a Immagini Leggero (AGILE). The catalog covers GRBs
discovered from 2005 Jan 17 to 2010 Dec 25. Using photometric information in
three UV bands, three optical bands, and a `white' or open filter, the data are
optimally co-added to maximize the number of detections and normalized to one
band to provide a detailed light curve. The catalog provides positional,
temporal, and photometric information for each burst, as well as Swift Burst
Alert Telescope (BAT) and X-Ray Telescope (XRT) GRB parameters. Temporal slopes
are provided for each UVOT filter. The temporal slope per filter of almost half
the GRBs are fit with a single power-law, but one to three breaks are required
in the remaining bursts. Morphological comparisons with the X-ray reveal that
approximately 75% of the UVOT light curves are similar to one of the four
morphologies identified by Evans et al. (2009). The remaining approximately 25%
have a newly identified morphology. For many bursts, redshift and extinction
corrected UV/optical spectral slopes are also provided at 2000, 20,000, and
200,000 seconds.Comment: 44 pages, 14 figures, to be published in Astrophysical Journal
Supplementa
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