[vsnet-grb-info 18718] GRB 161104A: Chandra X-ray observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  20166
SUBJECT: GRB 161104A: Chandra X-ray observations
DATE:    16/11/10 17:27:14 GMT
FROM:    Wen-fai Fong at U of Arizona  <wfong at email.arizona.edu>

R. Margutti (Northwestern U.), E. Berger (Harvard U.), and W. Fong (U.
Arizona) report:

"We observed the location of the short GRB161104A with the Chandra X-ray
Observatory (CXO) on 2016 Nov 8th, 14:41:45 UT, 364 ks after trigger (Mingo
et al., GCN 20123) under a pre-approved guest observer program (PI Berger).
No X-ray source is detected within the enhanced XRT position (Goad et al.,
GCN 20124). In particular, we do not find evidence for statistically
significant X-ray emission at the location of the optical source reported
by Troja  et al., GCN 20137 at RA, Dec = 05:11:34.5, -51:27:33.90.   Using
19.8 ks of CXO observations we infer a 3 sigma count-rate limit of  3.0E-4
c/s in the 0.5-8 keV energy range. The neutral hydrogen absorption in the
direction of the transient is 1.4E+20 cm-2 (Kalberla et al., 2005).
Assuming the spectral parameters that best fit the Swift-XRT observations
(power-law photon index Gamma=1.36  and no evidence for intrinsic neutral
hydrogen absorption, Burrows et al., GCN 20128) the inferred absorbed
(unabsorbed) flux limit is Fx< 4.4E-15 erg/s/cm2  (Fx<4.5E-15 erg/s/cm2) in
the 0.3-10 keV energy range. Our observations indicate a steepening of the
X-ray afterglow temporal decay. Starting from 20 ks after trigger, the
X-ray afterglow decays as t^-alpha with alpha>1.3.

We thank the CXO team for rapid scheduling of our observations."