Observations of X-ray Flares from GRBs Falcone, A D; Morris, D; Racusin, J ...
Gamma-Ray Bursts 2007: Proceedings of the Santa Fe Conference (AIP Conference Proceedings Volume 1000),
01/2008, Volume:
1000
Journal Article
Peer reviewed
Swift-XRT observations of the X-ray emission from gamma ray bursts (GRBs) and during the GRB afterglow have led to many new results during the past two years. One of these exciting results is that ...~1/3-1/2 of GRBs contain detectable X-ray flares. The mean fluence of the X-ray flares is ~10X less than that of the initial prompt emission, but in some cases the flare is as energetic as the prompt emission itself. The flares display fast rises and decays, and they sometimes occur at very late times relative to the prompt emission (sometimes as late as 105 s after T0) with very high peak fluxes relative to the underlying afterglow decay that has clearly begun prior to some flares. The temporal and spectral properties of the flares are found to favor models in which flares arise due to the same GRB internal engine processes that spawned the prompt GRB emission. Therefore, both long and short GRB internal engine models must be capable of producing high fluences in the X-ray band at very late times.
We present an optical (gri) study during quiescence of the accreting millisecond X-ray pulsar IGRJ00291+5934 performed with the 10.4 m Gran Telescopio Canarias (GTC) in August 2014. Although the ...source was in quiescence at the time of our observations, it showed a strong optical flaring activity, more pronounced in bluer filters (i.e. the g-band). After subtracting the flares, we tentatively recovered a sinusoidal modulation at the system orbital period in all bands, even when a significant phase shift with respect to an irradiated star, typical of accreting millisecond X-ray pulsars, was detected. We conclude that the observed flaring could be a manifestation of the presence of an accretion disc in the system. The observed light curve variability could be explained by the presence of a superhump, which might be another proof of the formation of an accretion disc. In particular, the disc at the time of our observations was probably preparing the new outburst of the source, which occurred a few months later, in 2015.
We test the correlation between temporal variability and peak luminosity of the gamma-ray profile on a homogeneous sample of 36 Swift/BAT GRBs with firm redshift determination. This is the first time ...that this correlation can be tested on a homogeneous data sample. The correlation is confirmed, as long as the 6 GRBs with low luminosity ( < 5X1050 erg s-1 in the rest-frame 100-1000 keV energy band) are ignored. We confirm that the considerable scatter of the correlation already known is not due to the combination of data from different instruments with different energy bands, but it is intrinsic to the correlation itself. Thanks to the unprecedented sensitivity of Swift/BKT, the variability/peak luminosity correlation is tested on low-luminosity GRBs. Our results show that these GRBs are outliers.
We investigated the ability of simple spectral models to describe the early afterglow emission of GRBs. We found that four spectra, belonging to the GRB060502A, GRB060729, GRB060904B, GRB061H0A ...prompt-afterglow transition phase, can be modeled neither by a single power-law nor by the Band model. Instead we find that the data present high-energy ( > 3 keV, in the observer frame) statistically significant excesses with respect to these models In all four cases, the deviations can be modeled well by adding either a second power law or a blackbody component to the usual synchrotron power law spectrum. Although the data do not allow an unequivocal physical interpretation, the importance of this analysis consists in showing that a simple power-law model or a Band model is insufficient to describe the X-ray spectra of a small homogeneous sample of GRBs at the end of their prompt phase 1.
The INTEGRAL satellite extensively observed XTE J1817-330 and XTE J1818-245 which underwent X-ray outbursts from, respectively, Jan. 2006 and Feb. 2005 to Nov. 2006, during the INTEGRAL Core Program ...and Target of Opportunity observations, dedicated to new X-ray novae, and during Galactic Bulge observations. We report some results of simultaneous multiwavelength observations of these black holes candidates performed with INTEGRAL, RXTE and with REM and ATCA for XTE J1817-330 and Swift, VLA, REM and EMMI for XTE J1818-245. Both sources are active up to 250 keV. Component evolutions occur in the accretion disk and in the hot medium (well fitted by Comptonization), with spectral changes in the hard and soft components correlated with puzzling changes in the radio and excess over a black body disk in the optical.
Trace elements incorporated into the growing surface of the fish otolith (ear stone) reflect the physical and chemical characteristics of the ambient water, although not necessarily in a simplistic ...manner. Since otoliths grow continuously without resorption throughout the life of the fish, fish populations growing up in different water masses should produce otoliths of different elemental composition. The otolith elemental composition ('fingerprint') determined with isotope dilution - inductively coupled plasma mass spectroscopy (ID-ICPMS) proved to be an effective discriminator of adjacent populations of Atlantic cod Gadus morhua off the coast of eastern Canada, with sufficient accuracy as a natural tag to determine population identity in a mixed population fishery. Classification of samples collected from the winter cod fishery on the eastern Scotian Shelf indicated that the annual winter migration out of the Gulf of St. Lawrence is more extensive than was previously believed.
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