The ROTSE-IIIa telescope at Siding Spring Observatory, Australia, detected prompt optical emission from Swift GRB 050401. We present observations of the early optical afterglow, first detected by the ...ROTSE-IIIa telescope 33 s after the start of g-ray emission, contemporaneous with the brightest peak of this emission. This GRB was neither exceptionally long nor bright. This is the first prompt optical detection of a GRB of typical duration and luminosity. We find that the early afterglow decay does not deviate significantly from the power-law decay observable at later times and is uncorrelated with the prompt g-ray emission. We compare this detection with the other two GRBs with prompt observations, GRB 990123 and GRB 041219a. All three bursts exhibit quite different behavior at early times.
We analyze Swift gamma-ray bursts (GRBs) and X-ray afterglows for three GRBs with spectroscopic redshift determinations: GRB 050401, XRF 050416a, and GRB 050525a. We find that the relation between ...spectral peak energy and isotropic energy of prompt emissions (the Amati relation) is consistent with that for the bursts observed in the pie-Swift era. However, we find that the X-ray afterglow light curves, which extend up to 10--70 days, show no sign of the jet break that is expected in the standard framework of collimated outflows. We do so by showing that none of the X-ray afterglow light curves in our sample satisfy the relation between the spectral and temporal indices that is predicted for the phase after jet break. The jet break time can be predicted by inverting the tight empirical relation between the peak energy of the spectrum and the collimation-corrected energy of the prompt emission (the Ghirlanda relation). We find that there are no temporal breaks within the predicted time intervals in X-ray band. This requires either that the Ghirlanda relation has a larger scatter than previously thought, that the temporal break in X-rays is masked by some additional source of X-ray emission, or that it does not happen for some unknown reason.
We systematically analyze the prompt emission and the early afterglow data of a sample of 31 GRBs detected by Swift before 2005 September and estimate the GRB radiative efficiency. BAT's narrow band ...inhibits a precise determination of the GRB spectral parameters, and we have developed a method to estimate these parameters with the hardness ratio information. The shallow decay component commonly existing in early X-ray afterglows, if interpreted as continuous energy injection in the external shock, suggests that the GRB efficiencies previously derived from the late-time X-ray data were not reliable. We calculate two radiative efficiencies using the afterglow kinetic energy E sub(K) derived at the putative deceleration time (t sub(dec)) and at the break time (t sub(b)), when the energy injection phase ends, respectively. At t sub(b) XRFs appear to be less efficient than normal GRBs. However, when we analyze the data at t sub(dec), XRFs are found to be as efficient as GRBs. Short GRBs have similar radiative efficiencies to long GRBs despite of their different progenitors. Twenty-two bursts in the sample are identified to have the afterglow cooling frequency below the X-ray band. Assuming e sub(e) = 0.1, we find g(t sub(b))usually <10% and g(t sub(dec)) varying from a few percent to >90%. Nine GRBs in the sample have the afterglow cooling frequency above the X-ray band for a very long time. This suggests a very small e sub(B) and/or a very low ambient density n.
We present a comprehensive analysis of a bright, long-duration (T sub(90) ~ 257 s) GRB 110205A at redshift z = 2.22. The optical prompt emission was detected by Swift/UVOT, ROTSE-IIIb, and BOOTES ...telescopes when the gamma-ray burst (GRB) was still radiating in the gamma -ray band, with optical light curve showing correlation with gamma -ray data. Nearly 200 s of observations were obtained simultaneously from optical, X-ray, to gamma -ray (1 eV to 5 MeV), which makes it one of the exceptional cases to study the broadband spectral energy distribution during the prompt emission phase. In particular, we clearly identify, for the first time, an interesting two-break energy spectrum, roughly consistent with the standard synchrotron emission model in the fast cooling regime. Shortly after prompt emission (~1100 s), a bright (R = 14.0) optical emission hump with very steep rise ( alpha ~ 5.5) was observed, which we interpret as the reverse shock (RS) emission. It is the first time that the rising phase of an RS component has been closely observed. The full optical and X-ray afterglow light curves can be interpreted within the standard reverse shock (RS) + forward shock (FS) model. In general, the high-quality prompt and afterglow data allow us to apply the standard fireball model to extract valuable information, including the radiation mechanism (synchrotron), radius of prompt emission (R sub(GRB) ~ 3 x 10 super(13) cm), initial Lorentz factor of the outflow (Gamma sub(0) ~ 250), the composition of the ejecta (mildly magnetized), the collimation angle, and the total energy budget.
Between the launch of the Global Geospace Science Wind spacecraft in 1994 November and the end of 2010, the Konus-Wind experiment detected 296 short-duration gamma-ray bursts (including 23 bursts ...which can be classified as short bursts with extended emission). During this period, the Interplanetary Network (IPN) consisted of up to 11 spacecraft, and using triangulation, the localizations of 271 bursts were obtained. We present the most comprehensive IPN localization data on these events. The short burst detection rate, ~18 yr super(-1), exceeds that of many individual experiments.
Hard X-ray variability of active galactic nuclei Beckmann, V.; Barthelmy, S. D.; Courvoisier, T. J.-L. ...
Astronomy and astrophysics (Berlin),
12/2007, Letnik:
475, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Aims.Active Galactic Nuclei are known to be variable throughout the electromagnetic spectrum. An energy domain poorly studied in this respect is the hard X-ray range above 20 keV. Methods.The first 9 ...months of the Swift/BAT all-sky survey are used to study the 14-195 keV variability of the 44 brightest AGN. The sources have been selected due to their detection significance of >$10 \sigma$. We tested the variability using a maximum likelihood estimator and by analysing the structure function. Results.Probing different time scales, it appears that the absorbed AGN are more variable than the unabsorbed ones. The same applies for the comparison of Seyfert 2 and Seyfert 1 objects. As expected the blazars show stronger variability. 15% of the non-blazar AGN show variability of >$20\%$ compared to the average flux on time scales of 20 days, and 30% show at least $10\%$ flux variation. All the non-blazar AGN which show strong variability are low-luminosity objects with $L_{(14{-}195\,\rm~keV)} < 10^{44} \rm \, erg \, s^{-1}$ Conclusions.Concerning the variability pattern, there is a tendency of unabsorbed or type 1 galaxies being less variable than the absorbed or type 2 objects at hardest X-rays. A more solid anti-correlation is found between variability and luminosity, which has been previously observed in soft X-rays, in the UV, and in the optical domain.
We report on our serendipitous pre-discovery detection and follow-up observations of the broad-lined Type Ic supernova (SN Ic) 2010ay at z = 0.067 imaged by the Pan-STARRS1 3pi survey just ~4 days ...after explosion. The supernova (SN) had a peak luminosity, MsubR approximate -20.2 mag, significantly more luminous than known GRB-SNe and one of the most luminous SNe Ib/c ever discovered. We therefore rule out the association of a relativistic outflow like those that accompanied SN 1998bw and traditional long-duration gamma-ray bursts (GRBs), but we place less-stringent constraints on a weak afterglow like that seen from XRF 060218. If this SN did not harbor a GRB, these observations challenge the importance of progenitor metallicity for the production of relativistic ejecta and suggest that other parameters also play a key role.
We present Interplanetary Network (IPN) data for the gamma-ray bursts in the first Fermi Gamma-Ray BurstMonitor (GBM) catalog. Of the 491 bursts in that catalog, covering 2008 July 12 to 2010 July ...11, 427 wereobserved by at least one other instrument in the nine-spacecraft IPN. Of the 427, the localizations of 149 could beimproved by arrival time analysis (or triangulation). For any given burst observed by the GBM and one otherdistant spacecraft, triangulation gives an annulus of possible arrival directions whose half-width varies betweenabout 0. 4 and 32, depending on the intensity, time history, and arrival direction of the burst, as well as the distancebetween the spacecraft. We find that the IPN localizations intersect the 1 GBM error circles in only 52 of thecases, if no systematic uncertainty is assumed for the latter. If a 6 systematic uncertainty is assumed and added inquadrature, the two localization samples agree about 87 of the time, as would be expected. If we then multiply theresulting error radii by a factor of three, the two samples agree in slightly over 98 of the cases, providing a goodestimate of the GBM 3 error radius. The IPN 3 error boxes have areas between about 1 arcmin2 and 110 deg2,and are, on the average, a factor of 180 smaller than the corresponding GBM localizations. We identify two burstsin the IPNGBM sample that did not appear in the GBM catalog. In one case, the GBM triggered on a terrestrialgamma flash, and in the other, its origin was given as uncertain. We also discuss the sensitivity and calibration ofthe IPN.
The ROTSE-IIIc telescope at the HESS site, Namibia, obtained the earliest detection of optical emission from a gamma-ray burst (GRB), beginning only 21.8 s from the onset of Swift GRB 050801. The ...optical light curve does not fade or brighten significantly over the first 6250 s, after which there is an achromatic break and the light curve declines in typical power-law fashion. The Swift XRT also obtained early observations starting at 69 s after the burst onset. The X-ray light curve shows the same features as the optical light curve. These correlated variations in the early optical and X-ray emission imply a common origin in space and time. This behavior is difficult to reconcile with the standard models of early afterglow emission.
We present a multi-wavelength study of GRB 081008, at redshift 1.967, by Swift, ROTSE-III, and Gamma-Ray Burst Optical/NearInfrared Detector. Compared to other Swift GRBs, GRB 081008 has a typical ...gamma-ray isotropic equivalent energy output ({approx}10{sup 53} erg) during the prompt phase, and displayed two temporally separated clusters of pulses. The early X-ray emission seen by the Swift X-Ray Telescope was dominated by the softening tail of the prompt emission, producing multiple flares during and after the Swift Burst Alert Telescope detections. Optical observations that started shortly after the first active phase of gamma-ray emission showed two consecutive peaks. We interpret the first optical peak as the onset of the afterglow associated with the early burst activities. A second optical peak, coincident with the later gamma-ray pulses, imposes a small modification to the otherwise smooth light curve and thus suggests a minimal contribution from a probable internal component. We suggest the early optical variability may be from continuous energy injection into the forward shock front by later shells producing the second epoch of burst activities. These early observations thus provide a potential probe for the transition from the prompt phase to the afterglow phase. The later light curve of GRB 081008 displays a smooth steepening in all optical bands and X-ray. The temporal break is consistent with being achromatic at the observed wavelengths. Our broad energy coverage shortly after the break constrains a spectral break within optical. However, the evolution of the break frequency is not observed. We discuss the plausible interpretations of this behavior.
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