2014A&A...567A..84M -
Astronomy and Astrophysics, volume 567A, 84-84 (2014/7-1)
GRB 120711A: an intense INTEGRAL burst with long-lasting soft γ-ray emission and a powerful optical flash.
MARTIN-CARRILLO A., HANLON L., TOPINKA M., LACLUYZE A.P., SAVCHENKO V., KANN D.A., TROTTER A.S., COVINO S., KRUEHLER T., GREINER J., McGLYNN S., MURPHY D., TISDALL P., MEEHAN S., WADE C., McBREEN B., REICHART D.E., FUGAZZA D., HAISLIP J.B., ROSSI A., SCHADY P., ELLIOTT J. and KLOSE S.
Abstract (from CDS):
A long and intense γ-ray burst (GRB) was detected by INTEGRAL on 11 July 2012 with a duration of ∼115s and fluence of 2.8x10–4erg/cm2 in the 20keV-8MeV energy range. GRB120711A was at z∼1.405 and produced soft γ-ray emission (>20keV) for at least ∼10ks after the trigger. The GRB was observed by several ground-based telescopes that detected a powerful optical flash peaking at an R-band brightness of ∼11.5mag at ∼126s after the trigger, or ∼9th magnitude when corrected for the host galaxy extinction (AV∼0.85). The X-ray afterglow was monitored by the Swift, XMM-Newton, and Chandra observatories from 8ks to 7Ms and provides evidence for a jet break at ∼0.9Ms. We present a comprehensive temporal and spectral analysis of the long-lasting soft γ-ray emission detected in the 20-200keV band with INTEGRAL/IBIS, the Fermi/LAT post-GRB detection above 100MeV, 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 (Epeak∼1MeV) and yields an Eγ,iso∼1054erg (1keV-10MeV rest frame), making GRB120711A one of the most energetic GRBs detected so far. We modelled the long-lasting soft γ-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∼1.2, suggesting a massive star progenitor (i.e. Wolf-Rayet) with a mass-loss rate between ∼10–5-10–6M☉/yr depending on the value of the radiative efficiency (ηγ=0.2 or 0.5). The analysis of the reverse and forward shock emission reveals an initial Lorentz factor of ∼120-340, a jet half-opening angle of ∼2°-5°, and a baryon load of ∼10–5-10–6M☉ consistent with the expectations of the fireball model when the emission is highly relativistic. Long-lasting soft γ-ray emission from other INTEGRAL GRBs with high peak fluxes, such as GRB041219A, was not detected, suggesting that a combination of high Lorentz factor, emission above 100MeV, and possibly a powerful reverse shock are required. Similar long-lasting soft γ-ray emission has recently been observed from the nearby and extremely bright Fermi/LAT burst GRB130427A.
Abstract Copyright:
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Journal keyword(s):
gamma-ray burst: individual: GRB 120711A - gamma-ray burst: individual: GRB 041219A - gamma-ray burst: individual: GRB 130427A
Simbad objects:
19
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