GRB 120711A - a bright gamma-ray burst with an unusually long, hard tail
At 02:44:48 UT on July 11th 2012, an extremely bright and long GRB was triggered by INTEGRAL (GCN 13434).
It had a T90 duration of 113 seconds as measured by SPI in the 20-200 keV band, and it was detected by SPI up to 8 MeV.
The IBIS/ISGRI lightcurve of the prompt emission was strongly affected by telemetry gaps.
The burst consisted of a hard precursor followed by a long multi-peaked pulse with a peak flux of ~32 ph/cm2/s in the 20-8000 keV band,
slightly less intense than INTEGRAL's brightest burst to date, GRB041219A.
Most unusually, the burst also showed a long tail of emission, lasting at least up to ~1200 sec after the trigger time and
detected by both IBIS (GCN 13435) and SPI (GCN 13468) in the 20-50 keV energy range. There is no evidence for periodicity in the tail.
The burst was rapidly followed up by other telescopes.
Fermi/LAT detected tail emission up to 2 GeV (GCN13444, GCN 13452), while robotic optical telescopes detected a rapidly brightening and
decaying optical counterpart, peaking at magnitude ~12 (R and V bands, GCN 13430) while the burst was still in progress.
A tentative spectroscopic redshift of 1.405 has been made using Gemini-S (GCN 13441),
while a photometric determination of z~3 has been made by GROND (GCN 13438).
XMM-Newton has carried out 2 follow-up observations of the source.
The INTEGRAL/IBIS images in the upper panel show the region around the GRB before, during and after the prompt emission,
in the 20-200 keV energy range. The lower panel shows the energy resolved SPI lightcurve, with the inset displaying the `tail' emission in more detail.
This burst provides us with a perfect storm of characteristics such as intensity, spectral hardness,
exceptionally long-lived tail, prompt and bright optical emission and GeV detection of the tail, to enable a rich analysis and interpretation.
