High energy emission and polarisation limits for the INTEGRAL burst GRB
  061122
  (Abridged) GRB 061122 is one of the brightest GRBs detected within INTEGRAL's
field of view to date. The two gamma-ray detectors on INTEGRAL were used to
investigate the spectral characteristics of GRB 061122. A search for linear
polarisation in the prompt emission was carried out using the SPI multiple
event data in the energy range 100 keV-1 MeV.
  The prompt spectrum was best fit by a combination of a blackbody and a
power--law model (the quasithermal model), with evidence for high energy
emission continuing above 8 MeV. A pseudo-redshift value of pz = 0.95 +/- 0.18
was determined using the spectral fit parameters. The isotropic energy at this
pseudo-redshift is 8.5 x 10^{52} erg. The jet opening angle was estimated to be
smaller than 2.8 deg or larger than 11.9 deg from the X-ray lightcurve. An
upper limit of 60% polarisation was determined for the prompt emission of GRB
061122, using the multiple event data.
  The high energy emission observed in the spectrum may be due to the reverse
shock interacting with the GRB ejecta when it is decelerated by the circumburst
medium. This behaviour has been observed in a small fraction of GRBs to date,
but is expected to be more commonly observed by the Fermi Gamma-ray Space
Telescope. The conditions for polarisation are met if the jet opening angle is
less than 2.8 deg, but further constraints on the level of polarisation are not
possible.
