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GCN Circular 1387

XRF020427: Chandra Observations and Candidate X-ray Counterparts
2002-05-10T02:58:17Z (22 years ago)
Derek Fox at CIT <>
D. W. Fox (Caltech) reports on behalf of the Caltech-NRAO-CARA GRB

"We have observed the error region of the X-ray flash XRF020427 (GCN
1383, 1384, 1386) with the Chandra X-ray Observatory for 13.8 ksec
beginning May 6.2456 UT.  Reduction of the data using standard Ciao
procedures yields the following source catalog (listed in decreasing
order of significance) for the most recent BeppoSAX/MECS localization
region (GCN 1386):

    ID        IAU Name          Sig    Cts       HR
     1  CXOU J220928.2-651932  26.8  57.6(78)  0.34(11)
     2  CXOU J220925.9-651855  11.9  15.8(41)  0.13(9)
     3  CXOU J220925.0-651919   7.3  20.0(46)  0.07(7)

where "Sig" is the wavdetect-quoted significance of the source in the
0.3 to 7.0 keV band, "Cts" is the counts in this band over the 13.8 ks
exposure, "HR" is the hardness ratio of 2.1-7.0 keV counts to 0.3-2.1
keV counts, and uncertainties in the trailing digits are indicated in
parentheses.  J2000 coordinates of the sources are implicit in their
IAU names.

Source CXOU J220925.0-651919 (ID 3) is coincident with a weak source
(not a USNO star) from the Digitized Sky Survey (DSS/SES).  

Identification of the brightest source, CXOU J220928.2-651932 (ID 1),
with the afterglow of XRF020427 would imply an average power-law decay
index of approximately 1.8 from the epoch of the second BeppoSAX MECS
observation (Apr 29.4439 UT) when referenced to the time of the burst
(Apr 27.1588 UT).  We therefore consider this source to be the most
likely candidate counterpart."
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