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 ( BAT ) at 06:49:28 on 5 January 2006 .
The Swift X-Ray Telescope ( XRT ) started pointed observations 87 s after the trigger ( T _ { 0 } ) .
The Suzaku team commenced a pre-planned target of opportunity observation at 19 ks ( 5.3 hr ) after the Swift trigger as the first Suzaku attempt at a rapid response to a new gamma-ray burst .
The X-ray flux faded during the observations from 6.8 \times 10 ^ { -9 } erg s ^ { -1 } cm ^ { -2 } ( at T _ { 0 } +87 s with the Swift /XRT ) to 1.5 \times 10 ^ { -13 } erg s ^ { -1 } cm ^ { -2 } ( at T _ { 0 } +94 – 101 ks with the Suzaku X-ray Imaging Spectrometer ( XIS ) ) in the 2–10 keV energy band .
The afterglow exhibited four phases of decay consisting of different decay indices during the Swift /XRT and Suzaku /XIS observations .
The inferred flux and spectral shapes with both instruments are fully consistent within the statistics , although there are hardening in the first shallow decay phase and softening in very steep decay phases in the end of the observations .
Following the prompt emission and successive very steep decay , a shallow decay was observed from T _ { 0 } +187 s to T _ { 0 } +1287 s. After an observation gap during T _ { 0 } + ( 1.5 – 3 ) ks , an extremely early steep decay was observed in T _ { 0 } + ( 4 – 30 ) ks .
The lightcurve flattened again at T _ { 0 } +30 ks , and another steep decay followed from T _ { 0 } +50 ks to the end of observations .
Both steep decays exhibited decay indices \alpha \sim 2.3 – 2.4 .
This lightcurve behavior can be explained as a steep decay resulting from side expansion of a jet , while the two flattening portions suggest energy injection and refreshed shock passage , respectively .
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 ^ { \circ } .
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 \pm 1.3 the upper limit on the iron line equivalent width is 50 eV .