[vsnet-grb-info 4405] GRB 070125: Chandra X-ray Confirmation of Jet Break

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6186
SUBJECT: GRB 070125: Chandra X-ray Confirmation of Jet Break
DATE:    07/03/09 21:18:41 GMT
FROM:    S. Bradley Cenko at Caltech  <cenko at srl.caltech.edu>

S. B. Cenko, A. M. Soderberg (Caltech), D. A. Frail (NRAO), and D. B. Fox
(Penn State) report on behalf of a larger collaboration:

The Chandra X-ray Observatory + ACIS observed the field of GRB070125
(Hurley et al, GCN 6024) beginning 5 March 2007 21:28 UT for a 30 ks
exposure (mean epoch ~ 39.76 days after the burst).  No source is detected
at the location of the optical afterglow (Cenko & Fox, GCN 6028).
Formally, using a circular aperture with 1" diameter, we detect 0.9 +/-
5.0 photons from 0.3-10 keV.  Using spectral properties derived from early
XRT observations (Gamma=2.0, nH=8e20; Racusin and Vetere, GCN 6030),
we estimate an upper limit on the afterglow flux of < 2e-15 erg cm^-2
s^-1.

Had the X-ray flux seen by the Swift XRT (Burrows & Racusin, GCN 6181)
continued to decay as a single power-law with index ~ -1.5, we would
expect a flux ~ 5e-15 erg cm^-2 s^-1 at the Chandra epoch (~ 20 Chandra
ACIS-S photons), more than a factor of 2 above this upper limit.  We
therefore conclude the X-ray decay has steepened since the last XRT
detection, confirming the jet break seen in the optical light curve
(Mirabal, Halpern, & Thorstensen, GCN 6096; Garnavich et al., GCN 6165).

A plot of the X-ray light curve can be found at:

   http://www.srl.caltech.edu/~cenko/public/grb070125_xray.jpg

We would like to thank the entire Chandra X-ray Center staff for their
execution of this observation and the rapid processing of the data.