[AAVSO-HEN] GRB 080822 (SGR 0501+4516): archival optical observations

[grb at aavso.org]

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TITLE:   GCN CIRCULAR
NUMBER:  8114
SUBJECT: GRB 080822 (SGR 0501+4516): archival optical observations
DATE:    08/08/22 17:49:29 GMT
FROM:    Denis Denissenko at IKI, Moscow  <denis at hea.iki.rssi.ru>

D. V. Denisenko (Space Research Institute, Moscow, Russia) reports:

Analysis of the Palomar Observatory Sky Survey plates available at
http://archive.stsci.edu/cgi-bin/dss_plate_finder has revealed a
variable object at the following position:

RA (J2000.0) = 05 01 06.47
Dec (J2000.0) = +45 16 28.0

with an uncertainty of 0.2".  This is 7" from the XRT position of GRB
080822 reported by Holland et al. (GCN 8112), thus formally outside the
reported 90% error circle with the radius of 2.6".

The above mentioned star is present in USNO-B1.0 catalogue as USNO-B1
1352-0128683 (RA = 05 01 06.42, Dec = +45 16 27.6) with the following
magnitudes:

B1=19.11, R1=15.99, B2=17.74, R2=15.97, I=16.52.

Animation of two Blue and two Red plates, as well as color-combined
(BRIR) images covering 101"x101" area around the variable star are
available at <http://hea.iki.rssi.ru/~denis/SGR0501+4516.html>.

It should be also noted that the variable object is located 16" from the
ROSAT source 1RXS J050107.9+451631 (catalog position error 13") with the
hardness ratios HR1=0.96+/-0.08, HR2=1.00+/-0.12.  These values are
typical for X-ray binaries, including X-ray transients.  Thus, the
variable star is most likely associated with the ROSAT source.  The
optical spectroscopy of this star is encouraged.  Also the follow-up
X-ray observations of SGR 0501+4846 are required to reveal its true
nature, improve the position accuracy and check the possible identification.

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