Astron.Astrophys.462:73,2007 The short/hard GRB051210 was detected and located by the Swift-BAT instrument
and rapidly pointed towards by the narrow field instrumens. The XRT was able to
observe a ...bright X-ray afterglow, one of the few ever observed for this class
of bursts. We present the analysis of the prompt and afterglow emission of this
event The BAT spectrum is a power-law with photon index 1.1 +/-0.3. The X-ray
light curve decays with slope 2.58+/-0.11 and shows a small flare in the early
phases. The spectrum can be described with a power law with photon index
1.54+/-0.16 and absorption (7.5 (-3.2, +4.3)*10^20 cm-2 We find that the X-ray
emission is consistent with the hypothesis that we are observing the curvature
effect of a GRB occurred in a low density medium, with no detectable afterglow.
We estimate the density of the circumburst medium to be lower than 4*10^-3
cm^-3. We also discuss different hypothesis on the possible origin of the
flare.
Astron.Astrophys. 461 (2007) 95-101 We present a detailed study of the spectral and temporal properties of the
X-ray and optical emission of GRB050713a up to 0.5 day after the main GRB
event. The ...X-ray light curve exhibits large amplitude variations with several
rebrightenings superposed on the underlying three-segment broken powerlaw that
is often seen in Swift GRBs. Our time-resolved spectral analysis supports the
interpretation of a long-lived central engine, with rebrightenings consistent
with energy injection in refreshed shocks as slower shells generated in the
central engine prompt phase catch up with the afterglow shock at later times.
Our sparsely-sampled light curve of the optical afterglow can be fitted with a
single power law without large flares. The optical decay index appears flatter
than the X-ray one, especially at later times.
AIP Conf.Proc.836:386-391,2006 Observations of gamma ray bursts (GRBs) with Swift produced the initially
surprising result that many bursts have large X-ray flares superimposed on the
underlying ...afterglow. These flares were sometimes intense, rapid, and late
relative to the nominal prompt phase. The most intense of these flares was
observed by XRT with a flux >500 the afterglow. This burst then surprised
observers by flaring again after >10000 s. The intense flare can be most easily
understood within the context of the standard fireball model, if the internal
engine that powers the prompt GRB emission is still active at late times.
Recent observations indicate that X-ray flares are detected in ~1/3 of XRT
detected afterglows. By studying the properties of the varieties of flares
(such as rise/fall time, onset time, spectral variability, etc.) and relating
them to overall burst properties, models of flare production and the GRB
internal engine can be constrained.
We present H\(_\alpha\) photometry for a sample of 95 galaxies in Hickson Compact Groups obtained from observations of 31 groups. The Catalogue lists isophotal and adaptive aperture (Kron aperture) ...flux measurements for about 75% of the accordant galaxies inside the observed HCGs, 22 out of which are upper limits. Non standard data reduction procedures have been used to obtain the continuum subtracted H\(_\alpha\) images for each HCG of the target sample. Flux calibration has also been performed in order to obtain H\(_\alpha\) luminosities for the whole sample. Both the data reduction and calibration procedures are carefully described in this paper. The new data listed in this Catalogue are of great importance in understanding the star formation rate inside HCG galaxies and in giving new insights on its dependence on galaxy interactions.
AIPConf.Proc.836:467-470,2006 Understanding the reasons for the faintness of the optical/near-infrared
afterglows of the so-called dark bursts is essential to assess whether they
form a subclass of ...GRBs, and hence for the use of GRBs in cosmology. With VLT
and other ground-based telescopes, we searched for the afterglows of the
INTEGRAL bursts GRB 040223, GRB 040422 and GRB 040624 in the first hours after
the triggers. A detection of a faint afterglow and of the host galaxy in the K
band was achieved for GRB 040422, while only upper limits were obtained for GRB
040223 and GRB 040624, although in the former case the X-ray afterglow was
observed. A comparison with the magnitudes of a sample of afterglows clearly
shows the faintness of these bursts, which are good examples of a population
that an increasing usage of large diameter telescopes is beginning to unveil.
GRB 070724B is the first Gamma Ray Burst localized by SuperAGILE, the hard X-ray monitor aboard the AGILE satellite. The coordinates of the event were published \(\sim 19\) hours after the trigger. ...The Swift X-Ray Telescope pointed at the SuperAGILE location and detected the X-ray afterglow inside the SuperAGILE error circle. The AGILE gamma-ray Tracker and Minicalorimeter did not detect any significant gamma ray emission associated with GRB 070724B in the MeV and GeV range, neither prompt nor delayed. Searches of the optical afterglow were performed by the Swift UVOT and the Palomar automated 60-inch telescopes without any significant detection. Similarly the Very Large Array did not detect a radio afterglow. This is the first GRB event with a firm upper limit in the 100 MeV -- 30 GeV energy range, associated with an X-ray afterglow.
Astrophys.J.642:L103-L106,2006 We report observations of GRB 050525A, for which a Gemini North spectrum
shows its redshift to be z = 0.606. This is the third closest long GRB
discovered by Swift. We ...observed its afterglow using the VLT, Gemini and TNG
telescopes to search for an associated SN. We find that the early-time light
curve is described by a broken power law with a break at t ~ 0.3 d after the
burst. About 5 d after the burst, a flattening is apparent, followed by a
further dimming. Both the magnitude and the shape of the light curve suggest
that a supernova was emerging during the late decay of the afterglow. This
supernova, dubbed SN 2005nc, had a rise time faster than SN 1998bw and a
long-lasting maximum. A spectrum obtained about 20 d (rest-frame) after the GRB
resembles the spectrum of SN 1998bw obtained close to maximum light.
Astron.Astrophys.462:73,2007 Swift discovered the high redshift (z=6.29) GRB050904 with the Burst Alert
Telescope (BAT) and began observing with its narrow field instruments 161 s
after the burst ...onset. This gamma-ray burst is the most distant cosmic
explosion ever observed. Because of its high redshift, the X-ray Telescope
(XRT) and BAT simultaneous observations provide 4 orders of magnitude of
spectral coverage (0.2-150 keV; 1.4-1090 keV in the source rest frame) at a
very early source-frame time (22 s). GRB050904 was a long, multi-peaked, bright
GRB with strong variability during its entire evolution. The light curve
observed by the XRT is characterized by the presence of a long flaring activity
lasting up to 1-2 hours after the burst onset in the burst rest frame, with no
evidence of a smooth power-law decay following the prompt emission as seen in
other GRBs. However, the BAT tail extrapolated to the XRT band joins the XRT
early light curve and the overall behavior resembles that of a very long GRB
prompt. The spectral energy distribution softens with time, with the photon
index decreasing from -1.2 during the BAT observation to -1.9 at the end of the
XRT observation. The dips of the late X-ray flares may be consistent with an
underlying X-ray emission arising from the forward shock and with the
properties of the optical afterglow reported by Tagliaferri et al. (2005b). We
interpret the BAT and XRT data as a single continuous observation of the prompt
emission from a very long GRB. The peculiarities observed in GRB050904 could be
due to its origin within one of the first star-forming regions in the Universe;
very low metallicities of the progenitor at these epochs may provide an
explanation.
We present a comparison between two optical cluster finding methods: a matched filter algorithm using galaxy angular coordinates and magnitudes, and a percolation algorithm using also redshift ...information. We test the algorithms on two mock catalogues. The first mock catalogue is built by adding clusters to a Poissonian background, while the other is derived from N-body simulations. Choosing the physically most sensible parameters for each method, we carry out a detailed comparison and investigate advantages and limits of each algorithm, showing the possible biases on final results. We show that, combining the two methods, we are able to detect a large part of the structures, thus pointing out the need to search for clusters in different ways in order to build complete and unbiased samples of clusters, to be used for statistical and cosmological studies. In addition, our results show the importance of testing cluster finding algorithms on different kinds of mock catalogues to have a complete assessment of their behaviour.
Long duration gamma-ray bursts (GRBs) release copious amounts of energy across the entire electromagnetic spectrum, and so provide a window into the process of black hole formation from the collapse ...of a massive star. Over the last forty years, our understanding of the GRB phenomenon has progressed dramatically; nevertheless, fortuitous circumstances occasionally arise that provide access to a regime not yet probed. GRB 080319B presented such an opportunity, with extraordinarily bright prompt optical emission that peaked at a visual magnitude of 5.3, making it briefly visible with the naked eye. It was captured in exquisite detail by wide-field telescopes, imaging the burst location from before the time of the explosion. The combination of these unique optical data with simultaneous gamma-ray observations provides powerful diagnostics of the detailed physics of this explosion within seconds of its formation. Here we show that the prompt optical and gamma-ray emissions from this event likely arise from different spectral components within the same physical region located at a large distance from the source, implying an extremely relativistic outflow. The chromatic behaviour of the broadband afterglow is consistent with viewing the GRB down the very narrow inner core of a two-component jet that is expanding into a wind-like environment consistent with the massive star origin of long GRBs. These circumstances can explain the extreme properties of this GRB.
