[vsnet-grb-info 23968] GRB 191024A: VLT/X-shooter optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  26067
SUBJECT: GRB 191024A: VLT/X-shooter optical observations
DATE:    19/10/24 13:48:45 GMT
FROM:    Dong Xu at NAOC/CAS  <dxu at nao.cas.cn>

D. Xu (NAOC), J.T. Palmerio (CNRS - Obs. de Paris/GEPI), D. B. Malesani 
(DTU space), K. E. Heintz (Univ. of Iceland), N. R. Tanvir (Univ. 
Leicester), J. P. U. Fynbo (DAWN/NBI), A. J. Levan (Radboud Univ.), G. 
Pugliese (Univ. Amsterdam), C. Kouveliotou (GWU, APSIS), report on 
behalf of the Stargate collaboration:

We observed the field of GRB 191024A (Page et al., GCN 26063) using the 
ESO VLT UT2 (Kueyen) equipped with the X-shooter camera. Observations 
started at 06:14:13 UT on 2019-10-14 (i.e., 1.523 hr after the BAT 
trigger) and 3x40 s, 3x30 s , 3x60 s frames were obtained in the Sloan 
g- / r- / z- bands, respectively.

No optical source is detected in our stacked image within the enhanced 
XRT error circle (Beardmore et al., GCN 26064), down to a limiting 
magnitude of r ~ 24.3 AB mag.

However, there exist two sources just outside and south of the XRT error 
circle in all the stacked g-, r-, and z-band images. Their coordinates 
and magnitudes are as follows

S1
R.A.(J2000) = 0:40:27.360
Dec.(J2000) = -67:08:44.800
Distance from the XRT center: 2.8"
m(r) ~ 24.1 AB mag

S2
R.A.(J2000) = 00:40:27.480
Dec.(J2000) = -67:08:45.800
Distance from the XRT center: 3.6"
m(r) ~ 23.7 AB mag

Due to small FOV, the magnitudes are calculated using only one DSS-2 
reference star at R.A. (J2000) = 00:40:29.68 and Dec. (J2000) = 
-67:08:43.99 with R1=19.68.  And due to only one epoch of photometry, it 
is not clear if either of the two sources is related to the burst. 
Further observations are required to check for variability.

We acknowledge excellent support from the ESO observing staff in 
Paranal, in particular Trystyn Berg.