[vsnet-grb-info 19286] GRB 170325A: optical observations, possible OT/host detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  20978
SUBJECT: GRB 170325A: optical observations, possible OT/host detection
DATE:    17/04/04 20:20:06 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen at iki.rssi.ru>

E. Mazaeva (IKI), A. Pozanenko (IKI), V. Rumyantsev (CrAO), P. Minaev 
(IKI),  E. Klunko (ISTP), A. Volnova (IKI), M. Eselevich (ISTP)   report 
on behalf of larger GRB follow-up collaboration:

Цe followed up the short GRB 170325A (Palmer et al., GCN  20938) with 
AZT-33IK telescope of Sayan observatory (Mondy) an ZTSh telescope of 
CrAO observatory. The burst was detected by GBM/Fermi (Bissaldi et al., 
GCN 20940) and also detected as 5.5 sigma non-triggered IBAS event of 
0.1 s duration of SPI-ACS/INTEGRAL (see 
http://grb.rssi.ru/GRB170325A/GRB170325_SPI-ACS.png).

We obtained several images in R-filter  on  March 26, March 29, and 
April 1 and cover all 90% error box of the BAT/Fermi (Palmer et al., GCN 
  20938).  We investigated variability of sources in the BAT/Fermi error 
box between the three epochs. One source exhibits marginal fading 
between first and second epochs. Preliminary photometry of the source is 
following

Date       UT start   t-T0    Filter  Exp.     OT     Err.  UL
                      (mid, days)      (s)

2017-03-26 14:10:51  1.28049  R      3600    21.94   0.15  22.2
2017-03-29 21:00:52  4.56314  R      3240    22.27   0.10  23.6
2017-04-01 15:46:59  7.35072  R      4100    22.45   0.25  22.6

the photometry is based on nearby SDSS-DR9 stars

SDSS-DR9_id         R(Lupton transformations)
J082954.53+203317.9 18.69
J083002.05+203031.2 16.74
J082950.18+203013.8 18.25
J082949.90+203106.9 16.65

Coordinates of the source are  (J2000) 08:29:57.677   +20:30:51.75 with 
uncertainty of  0.7 arcsec in both coordinates. The finding chart can be 
found in
http://grb.rssi.ru/GRB170325A/GRB170325A_Mondy_170326_2.png
http://grb.rssi.ru/GRB170325A/GRB170325A_CrAO_170329.png

The source is not presented in SDSS-DR9, but clearly visible in 
r(=22.59), i(=22.10) filters, barely visible in u-filter (23.1), and not 
detected in g and z of SDSS images.

We suggest the source is an afterglow and host candidates of the short 
GRB 170325A.