Swift and Suzaku Observations of the X-Ray Afterglow from the GRB 060105
Maeda, Yoshitomo; Kelley, Richard L.; Yamaoka, Kazutaka; Maeno, Shouta; Murakami, Toshio; Nakagawa, Yujin E.; Nakazawa, Kazuhiro; Onda, Kaori; Sato, Goro; Sonoda, Eri; Suzuki, Motoko; Takahashi, Tadayuki; Tashiro, Makoto S.; Urata, Yuji; Yamauchi, Makoto; Yoshida, Atsumasa; Ueda, Yoshihiro; Reeves, James N.; Yonetoku, Daisuke; Angelini, Lorella; Kawai, Nobuyuki; Kohmura, Takayoshi; Murakami, Hiroshi; Tamagawa, Toru; Ricker, George; Abe, Keiichi; Gehrels, Neil; Torii, Ken'ichi; Kinugasa, Kenzo; Barthelmy, Scott; Kodaira, Hironobu; Yoshinari, Satoru; Kubota, Kaori; Nousek, John; Ishikawa, Nobuyuki; Kaluzienski, Louis J.; Okuno, Shin'ya
Japan, United States
Abstract
Results are presented of early X-ray afterglow observations of GRB 060105 by Swift and Suzaku. The bright, long gamma-ray burst GRB 060105 triggered the Swift Burst Alert Telescope at 06:49:28 on 2006 January 5 (T0). The Suzaku team commenced a pre-planned target of opportunity observation at 19ks (5.3hr) after the Swift trigger. The X-ray flux faded during observations from 6.8 × 10-9 erg s-1 cm-2 (at T0 + 87s with the Swift/XRT) to 1.5 × 10-13 erg s-1 cm-2 [at T0 + 94-101 ks with the Suzaku X-ray Imaging Spectrometer (XIS)] in the 2-10keV energy band. Following prompt emission and successive very steep decay, a shallow decay was observed from T0 + 187s to T0 + 1287s. After an observation gap during T0 + (1.5-3) ks, an extremely early steep decay was observed in T0 + (4-30) ks. The lightcurve flattened again at T0 + 30 ks, and another steep decay followed from T0 + 50 ks to the end of observations. Both steep decays exhibited decay indices of 2.3-2.4. This very early break, if it is a jet break, is the earliest case among X-ray afterglow observations, suggesting a very narrow jet whose opening angle is well below 1°. The unique Suzaku/XIS data allow us to set very tight upper limits on line emission or absorption in this GRB. For the reported pseudo-redshift of z = 4.0 ± 1.3 the upper limit on the iron line equivalent width is 50eV.