The late-time light curves of GRB X-ray afterglows with Chandra
Dirk Grupe (Pennsylvania State University) , Davie Burrows (PSU)
For a brief moment in time when they occur, Gamma-Ray Bursts (GRBs) are the most energetic events in the Universe. One of the predictions of the standard fireball model of GRBs is the formation of a jet. The opening angle of this jet is the crucial parameter for the energetics of the burst. This opening angle can be inferred from the 'jet break' when the jet decelerates by interacting with the interstellar gas. Jet breaks are therefore crucial for our understanding of GRBs. We will summarize our late-time detections of GRB X-ray afterglows with Chandra. For the two soft GRBs 070524 and 071221A we were able to follow both X-ray afterglows for more than 3 weeks and found no jet break in 050724 and a jet break 4 days after the burst in GRB 051221A. As for long bursts we had three observations of the extraordinary GRB 060729 with the latest 11 month after the burst - the latest detection of an X-ray afterglow ever. GRB 060729 will still be detectable by Chandra in 2008 and has just been recommended for two Chandra observation next year by the peer review. In all these cases Chandra observations were essential to get late-time detection which are important for the interpretation of the physics involved in GRBs. The detection or non detections of a jet break in GRB X-ray light curves puts tight constraints on the energetics of a GRB. No jet break means that it requires a much larger energy injection and a continuous energy input from the central engine. Only Chandra is able to detect X-ray afterglows at very late times.