| Autor: |
Martin-Carrillo, A., Hanlon, L., Topinka, M., LaCluyzé, A. P., Savchenko, V., Kann, D. A., Trotter, A. S., Covino, S., Krühler, 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. |
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| Zdroj: |
Astronomy & Astrophysics / Astronomie et Astrophysique; Jul2014, Vol. 567, p1-18, 18p |
| Abstrakt: |
A long and intense γ-ray burst (GRB) was detected by INTEGRAL on 11 July 2012 with a duration of ~115 s and fluence of 2.8 × 10-4 erg cm-2 in the 20 keV-8MeV energy range. GRB120711A was at z ~ 1.405 and produced soft γ-ray emission (>20 keV) for at least ~10 ks 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 ~126 s 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 8 ks 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 20-200 keV 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 ~ 1054 erg (1 keV-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 ~10-5-10-6 M⊙ yr-1 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 ~10-5-10-6 M⊙ consistent with the expectations of the fireball model when the emission is highly relativistic. Long-lasting soft γ-ray emission from other INTEGRALGRBs 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 FROM AUTHOR] |
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