TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1249
SUBJECT: GRB020127:  Comparison of Chandra Epochs and Identification of Possible Counterparts
DATE:    02/02/15 04:09:29 GMT
FROM:    Derek Fox at CIT  <derekfox@astro.caltech.edu>

Derek W. Fox (Caltech) reports on behalf of the Caltech-NRAO-CARA GRB
collaboration:

"We have made a comprehensive analysis of the data from two 10-ks
Chandra ACIS-I observations of the HETE-IPN localization region for
GRB020127 (HETE 1902; GCNs 1229, 1232, 1241).  The full source
catalogs for these observations contain 48 and 50 sources,
respectively; approximately four sources in each epoch are anticipated
to be spurious detections.  We identify three possible counterparts
based on their fading behavior between the Chandra observations (which
began at Jan 31.95 UT and Feb 11.46 UT, respectively) and the absence
of a bright stellar or galactic counterpart in archival images:

 Source        RA               Dec           Nsig     F1     F2
===================================================================
  A14=B16   08 15 01.42(1)   +36 46 33.9(1)   13.6   84(16)  19(6)
  A45       08 15 42.78(7)   +36 47 00.2(10)   5.7   28(7)  <14
   A7       08 14 47.82(3)   +36 49 35.4(3)    4.1   13(4)  <14
===================================================================

Numbers in parentheses indicate the uncertainty in the preceding
digits, and positional uncertainties do not account for the overall
Chandra aspect uncertainty of roughly one arcsec.  Nsig is the nominal
(single-trial) significance of the source detection as reported by
wavdetect.  F1 and F2 are source count rates for the first and second
epochs, respectively, in units of photons cm^(-2) ks^(-1) (0.3-7 keV);
upper limits are roughly two-sigma.  Source A14 is detected in the
second epoch as source B16, while neither source A45 nor source A7 are
detected in the second epoch.

We note explicitly that the sources above are not the only sources
within the HETE-IPN localization to show variability between the two
epochs; however, they are the only sources, not associated with bright
stellar or galactic counterparts, that show convincing evidence of a
decline in flux.  The full source catalog for the two observations is
available at the following URL:

  http://www.astro.caltech.edu/~derekfox/grb020127/chandra.html

Given the strength of source A14 (=B16) in the first observation, and
its observed fading behavior -- which is consistent with a t^(-1.2)
power-law referred to the epoch of GRB020127 -- we consider source A14
to be the most likely candidate for the afterglow of GRB020127."