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Register a new userGRB 071003: Broadband Follow-up Observations of a Very Bright Gamma-Ray Burst in a Galactic Halo
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The optical afterglow of long-duration GRB 071003 is among the brightest yet to be detected from any GRB, with R ~ 12 mag in KAIT observations starting 42 s after the GRB trigger, including filtered detections during prompt emission. However, our high S/N ratio afterglow spectrum displays only extremely weak absorption lines at what we argue is the host redshift of z = 1.60435 - in contrast to the three other, much stronger Mg II absorption systems observed at lower redshifts. Together with Keck adaptive optics observations which fail to reveal a host galaxy coincident with the burst position, our observations suggest a halo progenitor and offer a cautionary tale about the use of Mg II for GRB redshift determination. We present early through late-time observations spanning the electromagnetic spectrum, constrain the connection between the prompt emission and early variations in the light curve (we observe no correlation), and discuss possible origins for an unusual, marked rebrightening that occurs a few hours after the burst: likely either a late-time refreshed shock or a wide-angle secondary jet. Analysis of the late-time afterglow is most consistent with a wind environment, suggesting a massive star progenitor. Together with GRB 070125, this may indicate that a small but significant portion of star formation in the early universe occurred far outside what we consider a normal galactic disk.
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The Solar Tower Atmospheric Cherenkov Effect Experiment (STACEE) is an atmospheric Cherenkov telescope (ACT) that uses a large mirror array to achieve a relatively low energy threshold. For sources with Crab-like spectra, at high elevations, the detector response peaks near 100 GeV. Gamma-ray burst (GRB) observations have been a high priority for the STACEE collaboration since the inception of the experiment. We present the results of 20 GRB follow-up observations at times ranging from 3 minutes to 15 hours after the burst triggers. Where redshift measurements are available, we place constraints on the intrinsic high-energy spectra of the bursts.
We review Gamma-Ray Burst (GRB) afterglow follow-up observations being carried out by our group in Korea. We have been performing GRB follow-up observations using the 4-m UKIRT in Hawaii, the 2.1-m telescope at the McDonald observatory in Texas, the 1.5-m telescope at Maidanak observatory in Uzbekistan, the 1.8-m telescope Mt. Bohyun Optical Astronomy Observatory (BOAO) in Korea, and the 1.0-m remotely operated telescope in Mt. Lemmon, Arizona. We outline our facilities, and present highlights of our work, including the studies of high redshift GRBs at z > 5, and several other interesting bursts.
In this letter we discuss the flux and the behavior of the bright optical flare emission detected by the 25 cm TAROT robotic telescope during the prompt high-energy emission and the early afterglow. We combine our data with simultaneous observations performed in X-rays and we analyze the broad-band spectrum. These observations lead us to emphasize the similarity of GRB 050904 with GRB 990123, a remarkable gamma-ray burst whose optical emission reached 9th magnitude. While GRB 990123 was, until now, considered as a unique event, this observation suggests the existence of a population of GRBs which have very large isotropic equivalent energies and extremely bright optical counterparts. The luminosity of these GRBs is such that they are easily detectable through the entire universe. Since we can detect them to very high redshift even with small aperture telescopes like TAROT, they will constitute powerful tools for the exploration of the high-redshift Universe and might be used to probe the first generation of stars.
There are the results of gamma-ray bursts observations obtained using the MASTER robotic telescope in 2007 - 2009. We observed 20 error-boxes of gamma-ray bursts this period.The limits on their optical brightnesses have been derived. There are 5 prompt observations among them, obtained at our very wide field cameras. Also we present the results of the earliest observations of the optical emission of the gamma-ray bursts GRB 050824 and GRB 060926.
The Swift burst GRB 110205A was a very bright burst visible in the Northern hemisphere. GRB 110205A was intrinsically long and very energetic and it occurred in a low-density interstellar medium environment, leading to delayed afterglow emission and a clear temporal separation of the main emitting components: prompt emission, reverse shock, and forward shock. Our observations show several remarkable features of GRB 110205A : the detection of prompt optical emission strongly correlated with the BAT light curve, with no temporal lag between the two ; the absence of correlation of the X-ray emission compared to the optical and high energy gamma-ray ones during the prompt phase ; and a large optical re-brightening after the end of the prompt phase, that we interpret as a signature of the reverse shock. Beyond the pedagogical value offered by the excellent multi-wavelength coverage of a GRB with temporally separated radiating components, we discuss several questions raised by our observations: the nature of the prompt optical emission and the spectral evolution of the prompt emission at high-energies (from 0.5 keV to 150 keV) ; the origin of an X-ray flare at the beginning of the forward shock; and the modeling of the afterglow, including the reverse shock, in the framework of the classical fireball model.
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