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GCN Circular 17829

Subject
GRB 150518A: Xinglong2.16m optical afterglow detection
Date
2015-05-19T23:26:00Z (9 years ago)
From
Dong Xu at NAOC/CAS <dong.dark@gmail.com>
Dong Xu (NAOC/CAS), Xue-Bing Wu, Qian Yang (PKU) report

We observed the field of the XRT transient (Sbarufatti et al., GCN
17827), which is very likely the X-ray counterpart of GRB 150518A
(Kawamuro et al., GCN 17825) , using the 2.16m telescope located at
Xinglong, Hebei, China. Observations started at 14:23:06 UT (i.e.,
16.68 hr after the burst) in a rather poor seeing of 3", and 4x300s
R-band frames were obtained.

At the XRT-UVOT enhanced position (R.A. = 15:36:48.25, Dec. =
+16:19:47.3 , Err. Rad: = 2.2������), an optical source is well detected
at m(R) = 20.3 +/- 0.2 mag, calibrated with nearby SDSS stars. The
source largely looks round in our stacked image.

We note that there exists a source at the XRT-UVOT position that is
already detected and classified as a galaxy by SDSS (u=22.88, g=22.14,
r=21.43, i=21.24, z=20.74), with a photometric redshift of z_ph=0.35
+/- 0.11. The Xinglong detection is brighter than the SDSS detection
by about 1 magnitude in the R/r filters, and we thus think that it is
the optical afterglow of the GRB. If the afterglow is indeed
associated with the galaxy at such a redshift, it would be doable to
search for a GRB-associated supernova.

We thank Junjun Jia for carrying out these observations.
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