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GCN Circular 9635

Subject
GRB 090709A - PAIRITEL Discovery of a Red Afterglow
Date
2009-07-09T19:03:47Z (15 years ago)
From
Adam Morgan at U.C. Berkeley <qmorgan@gmail.com>
A. N. Morgan, J. S. Bloom, C. R. Klein (UC Berkeley), report:

Using a re-reduction of the early PAIRITEL data for GRB 090709A
(Morgan et al. GCN 9628) we report a probable detection of a red
source in the H and Ks bands within the XRT circle (Morris et al. GCN
9625).  The source is located at the following J2000 position (3.15
arcsec away from the center of the current XRT position):

RA = 19:19:42.64
Dec = +60:43:39.3

The uncertainty in this position relative to the ICRS is 0.4" in each direction.

The preliminary photometry yields:

post_burst
t_mid(s) exp(s)  filt  mag
438       374     J     > 17.7 (3 sig)
438       374     H     16.7 +/- 0.2
438       374     Ks    15.3 +/- 0.2

Deeper mosaics obtained later in the night do not contain this source,
indicating that it has faded.  We thus conclude that this is the
afterglow of GRB 090709A.  Note that this is the same source 'B' as
that was just reported in Aoki et al. (GCN 9634).  Our detection in
the H band places a less stringent redshift limit on the afterglow
(although this limit is still high; z > 8.5), if indeed our
non-detection in J is due to a Lyman break and not extinction.  We
also note that source 'A' of GCN 9634, which is of comparable
brightness to 'B' 2 hours after the burst, is not detected in our
shallower image, confirming our conclusion that source 'B' has faded
and is the afterglow.

All magnitudes given in the Vega system, calibrated to 2MASS.  No
correction for Galactic extinction has been made to the above reported
values.
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