GRB 050713A: High Energy Observations of the GRB Prompt and Afterglow Emission

Swift discovered GRB 050713A and slewed promptly to begin observing with its narrow field instruments 72.6 seconds after the burst onset, while the prompt gamma-ray emission was still detectable in the BAT. Simultaneous emission from two flares is detected in the BAT and XRT. This burst marks just the second time that the BAT and XRT have simultaneously detected emission from a burst and the first time that both instruments have produced a well sampled, simultaneous dataset covering multiple X-ray flares. The temporal rise and decay parameters of the flares are consistent with the internal shock mechanism. In addition to the Swift coverage of GRB 050713A, we report on the Konus-Wind (K-W) detection of the prompt emission in the energy range 18-1150 keV, an upper limiting GeV measurement of the prompt emission made by the MAGIC imaging atmospheric Cherenkov telescope and XMM-Newton observations of the afterglow. Simultaneous observation between Swift XRT and XMM-Newton produce consistent results, showing a break in the lightcurve at T+~15ks. Together, these four observatories provide unusually broad spectral coverage of the prompt emission and detailed X-ray follow-up of the afterglow for two weeks after the burst trigger. Simultaneous spectral fits of K-W with BAT and BAT with XRT data indicate that an absorbed broken powerlaw is often a better fit to GRB flares than a simple absorbed powerlaw. These spectral results together with the rapid temporal rise and decay of the flares suggest that flares are produced in internal shocks due to late time central engine activity.Comment: 22 pages, 6 tables, 10 figures; Submitted to the Astrophysical Journa

Konus catalog of SGR activity to 2000

Observational data on the bursting activity of all five known Soft Gamma Repeaters are presented. This information was obtained with Konus gamma-ray burst experiments on board Venera 11-14, Wind, and Kosmos-2326 spacecraft in the period from 1978 to 2000. These data on appearance rates, time histories, and energy spectra of repeated soft bursts obtained with similar instruments and collected together in a comparable form should be useful for further studies of SGRs. (available at http://www.ioffe.rssi.ru/LEA/SGR/Catalog/).Comment: 20 pages, including 5 tables, LaTeX AASTeX5.0, with 50 PNG-files of reduced size figures. Catalog with full size figures is available at http://www.ioffe.rssi.ru/LEA/SGR/Catalog/ To be submitted to ApJ Supp

GRB 060313: A New Paradigm for Short-Hard Bursts?

We report the simultaneous observations of the prompt emission in the gamma-ray and hard X-ray bands by the Swift-BAT and the KONUS-Wind instruments of the short-hard burst, GRB 060313. The observations reveal multiple peaks in both the gamma-ray and hard X-ray bands suggesting a highly variable outflow from the central explosion. We also describe the early-time observations of the X-ray and UV/Optical afterglows by the Swift XRT and UVOT instruments. The combination of the X-ray and UV/Optical observations provide the most comprehensive lightcurves to date of a short-hard burst at such an early epoch. The afterglows exhibit complex structure with different decay indices and flaring. This behavior can be explained by the combination of a structured jet, radiative loss of energy, and decreasing microphysics parameters occurring in a circum-burst medium with densities varying by a factor of approximately two on a length scale of 10^17 cm. These density variations are normally associated with the environment of a massive star and inhomogeneities in its windy medium. However, the mean density of the observed medium (n approximately 10^−4 cm^3) is much less than that expected for a massive star. Although the collapse of a massive star as the origin of GRB 060313 is unlikely, the merger of a compact binary also poses problems for explaining the behavior of this burst. Two possible suggestions for explaining this scenario are: some short bursts may arise from a mechanism that does not invoke the conventional compact binary model, or soft late-time central engine activity is producing UV/optical but no X-ray flaring.Comment: 28 pages, 6 figures. Accepted for publication in ApJ. Clarifications made and typos correcte

Multi-Wavelength Observations of GRB 050820A: An Exceptionally Energetic Event Followed from Start to Finish

We present observations of the unusually bright and long gamma-ray burst GRB 050820A, one of the best-sampled broadband data sets in the Swift era. The gamma-ray light curve is marked by a soft precursor pulse some 200 s before the main event; the lack of any intervening emission suggests that it is due to a physical mechanism distinct from the GRB itself. The large time lag between the precursor and the main emission enabled simultaneous observations in the gamma-ray, X-ray, and optical band-passes, something only achieved for a handful of events to date. While the contemporaneous X-rays are the low-energy tail of the prompt emission, the optical does not directly track the gamma-ray flux. Instead, the early-time optical data appear mostly consistent with the forward shock synchrotron peak passing through the optical, and are therefore likely the beginning of the afterglow. On hour time scales after the burst, the X-ray and optical light curves are inconsistent with an adiabatic expansion of the shock into the surrounding region, but rather indicate that there is a period of energy injection. Observations at late times allow us to constrain the collimation angle of the relativistic outflow to theta = 6.8 - 9.3 degrees. Our estimates of both the kinetic energy of the afterglow and the prompt gamma-ray energy release make GRB 050820A one of the most energetic events for which such values could be determined.Comment: Accepted to ApJ; 18 pages, 8 figures; High resolution version available at http://www.srl.caltech.edu/~cenko/public/papers/grb050820a.p

-WIND observation of the ultra-luminous GRB 110918A

The exceptionally intense long GRB 110918A was discovered by several GRB observing missions: INTEGRAL (SPI-ACS), Konus-WIND, Mars Odyssey (HEND), and MESSENGER (GRNS) on September 18, 2011. This GRB was localized by the Interplanetary Network (IPN) and its bright X-ray counterpart was found in close vicinity of the IPN box in the Swift/XRT follow-up observations starting 1.2 days after the trigger. The optical afterglow was discovered by the Isaac Newton Telescope and its spectroscopic redshift z = 0.982 was measured with the GMOS spectrograph mounted on the Gemini-N telescope. GRB 110918A is the brightest burst detected by Konus-WIND for more than 17 years of its continuous observations. The instrument’s light curves in three energy bands covering 22–1450 keV range show an extremely bright, short, hard pulse followed by three weaker, softer, partly overlapping pulses within next 25 seconds. A spectral lag between the light-curves is determined, showing a substantial increase in the course of the burst. The emission is detected up to 12 MeV. Modeling the time-integrated energy spectrum with the Band function yields a moderate value of Epeak = 340keV, while the time-resolved spectral analysis reveals strong hardness-intensity correlation and a hard-to-soft evolution of the emission: Epeak falls from  ~ 4 MeV at the onset of the huge initial pulse to ~50 keV at the final stage of the burst. The total 20 keV–10 MeV energy fluence amounts to S = (7.8 ± 0.4) × 10-4erg cm-2 and a 64-ms peak flux Fmax = (9.2 ± 0.4) × 10-4erg cm-2s-1, which corresponds to a huge isotropic-equivalent energy release Eiso = (2.1 ± 0.1) × 1054erg and the record-breaking peak luminosity Liso;max = (4.7 ± 0.2) × 1054erg s-1