Simultaneous observations of γ-ray bursts with Phebus/Granat and ULYSSES GRB.
Hurley, K.; Sunyaev, R.; Sommer, M.; Boer, M.; Niel, M.; Kuznetsov, A.; Vedrenne, G.; Atteia, J. -L.; Dezalay, J. -P.; Barat, C.; Talon, R.; Terekhov, O.
France, Germany
Abstract
We compare the characteristics of 35 gamma-ray bursts (GRBs) detected simultaneously by Phebus aboard Granat and the Ulysses GRB experiment. Phebus observes a medium to high energy range (100 keV - 100 MeV), while the Ulysses GRB detector is sensitive to lower energy photons (25-150 keV). Comparison of the peak counts recorded by these two instruments shows that the variation in burst intensities is more extended for Phebus (above ~150 keV) than for Ulysses GRB. This result confirms similar observations from other instruments (Atteia et al. 1991; Mitrofanov et al. 1992; Belli 1992). We discuss the consequences of this behavior for the statistical properties of GRBs, and for the searches for a possible cosmological redshift.