Suzaku observation of X-ray afterglow: Spectral and temporal behaviors

We report about early X-ray afterglow observations of GRB 060105 by Swift and Suzaku. The Suzaku team commenced a pre-planned target of opportunity observation at 5.3 h after the Swift trigger. Following the prompt emission and successive very steep decay, a shallow decay was observed from T₀ + 187 s to T₀ + 1287s by Swift. After that, an extremely early steep decay was observed in T₀ + (4 30) ks. The light curve flattened again and another steep decay from T₀ + 50 ks to the end of Suzaku observations was observed. Both steep decays exhibited almost same decay indices of 2.3-2.4. This break time, if it is caused by a jet break, is the earliest case among X-ray afterglow observations, suggesting a very narrow jet opening angle is about 0.7 degree. The unique Suzaku/XIS data allow us to set very tight upper limits on emission line in this GRB. Using the reported pseudo-redshift of z = 4.0 ± 1.3. we set the upper limit on the equivalent width of iron emission line at a few eV.