科研之友
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摘要
A long and intense gamma-ray burst (GRB) was detected by INTEGRAL on 11 July 2012 with a duration of similar to 115 s and fluence of 2.8 x 10(-4) erg cm(-2) in the 20 keV-8 MeV energy range. ORB 120711A was at z similar to 1.405 and produced soft gamma-ray emission (>20 keV) for at least similar to 10 ks after the trigger. The ORB was observed by several ground-based telescopes that detected a powerful optical flash peaking at an R-band brightness of similar to 11.5 mag at similar to 126 s after the trigger, or similar to 9th magnitude when corrected for the host galaxy extinction (A(V) similar to 0.85) The X-ray afterglow was monitored by the Swift, XMM-Newton, and Chandra observatories from 8 ks to 7 Ms and provides evidence for a jet break at similar to 0.9 Ms. We present a comprehensive temporal and spectral analysis of the long-lasting soft gamma-ray emission detected in the 20-200 keV band with INTEGRAL/IBIS. the Fermi/LAT post-ORB detection above 100 MeV, the soft X-ray afterglow and the optical/near-infrared detections from Watcher, Skynet/PROMPT. GROND, and REM. The prompt emission had a very hard spectrum (E-peak similar to 1 MeV) and E-gamma,E-iso similar to 10(54) erg (1 keV-10 MeV rest frame). making GRB 120711A one of the most energetic GRBs detected so far. We modelled the long-lasting soft gamma-ray emission using the standard afterglow scenario. which indicates a forward shock origin. The combination of data extending from the near-infrared to GeV energies suggest that the emission is produced by a broken power-law spectrum consistent with synchrotron radiation, The afterglow is well modelled using a stratified wind like environment with a density profile k similar to 1.2, suggesting a massive star progenitor (i.e. Wolf-Rayet) with a mass loss rate between similar to 10(-5)-10(-6) M-circle dot yr(-1) depending on the value of the radiative efficiency (eta gamma = 0.2 or 0.5), The analysis of the reverse and forward shock emission reveals an initial Lorentz factor of similar to 120-340, a jet half-opening angle of similar to 2 degrees-5 degrees, and a baryon load of similar to 10(-5)-10(-6) M-circle dot consistent with the expectations of the fireball model when the emission is highly relativistic. Long-lasting soft gamma-ray emission from other INTEGRAL GRBs with high peak fluxes such as ORB 041219A, was not detected, suggesting that a combination of high Lorentz Factor, emission above 100 MeV, and possibly a powerful reverse shock am required. Similar long-lasting soft gamma-ray emission has recently been observed from the nearby and extremely bright Fermi/LAT burst GRB 130427A.
- 出版日期2014-7
- 单位中国地震局
