GCN Circular 10232
Subject
GRB 091117: Chandra Observations
Event
Date
2009-12-02T19:36:40Z (16 years ago)
From
Derek Fox at PSU <dfox@astro.psu.edu>
D. B. Fox (Penn State) and E. Berger (Harvard) report:
"We observed the Swift/BAT localization region for GRB 091117
(Cummings et al., GCN 10171; Sakamoto et al., GCN 10180) with the
Chandra X-ray Observatory + ACIS, positioned at the ACIS-S3 aimpoint,
in a 20.1 ksec integration with mean epoch Nov 21.85 UT, 4.1 days
after the burst trigger.
Analysis of these data reveals the presence of nine X-ray sources
within and near the BAT localization region, including the two X-ray
sources identified in previous Swift XRT observations (Berger, GCN
10173; D'Elia et al., GCN 10177). Comparison to deep optical imaging
of the region from Magellan (Berger & Mulchaey, GCN 10174; Berger &
Momcheva, GCN 10183) reveals point-like (nuclear, stellar, or
unresolved galactic) optical counterparts to all but three of these
sources:
# CXOU J Sigma Cts Unc Comments
==========================================================
1 020353.36-165830.0 54.0 119 11 XRT-1; Nuclear
2 020356.65-165659.1 44.5 101 10 XRT-2; Nuclear
3 020353.68-165428.1 14.7 34.9 6.5 Stellar
4 020338.35-165547.3 8.7 23.0 5.0 Stellar
5 020347.45-165927.6 6.2 13.4 3.7 (not imaged)
6 020342.46-165706.7 4.8 9.7 3.2 Stellar
7 020345.74-165817.1 4.2 8.7 3.0 Near galaxy
8 020345.21-165818.2 3.8 7.7 2.8 Stellar
9 020349.61-165430.5 3.7 7.6 2.8 No counterpart
==========================================================
The table above provides source names/coordinates (J2000) as
determined from the Chandra astrometric solution, the significance of
detection in "wavdetect" analysis over the 0.3-8.0 keV bandpass, and
estimated counts and uncertainties (0.3-8.0 keV) for each source. The
nature of the optical counterpart, if any, is also provided.
We note that the two brightest X-ray sources, also observed by Swift,
are coincident to within <1 arcsec with the active nuclei of the two
brightest galaxies in the region: Chandra source #1 (XRT-1) with the
active nucleus of the face-on spiral galaxy at z=0.096 (Chornock &
Berger, GCN 10176), and Chandra source #2 (XRT-2) with the active
nucleus of 2MASX J02035665-1656585 at z=0.092. Source #1 appears
(2.8-sigma confidence) to have faded since the first epoch of Swift
observations, consistent with inferences from Swift XRT data (Fox, GCN
10179); however, the coincidence of sources #1 and #2 with AGN
suggests that neither of these objects is associated with GRB 091117.
Chandra source #7 is notable for being located 2.4 arcsec from the
center of an edge-on galaxy that is resolved in our Magellan imaging."