[vsnet-grb-info 8731] GRB 091117: Chandra Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  10232
SUBJECT: GRB 091117:  Chandra Observations 
DATE:    09/12/02 19:36:40 GMT
FROM:    Derek Fox at PSU  <dfox at 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."