[vsnet-grb-info 4840] GRB 070621: VLT optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6574
SUBJECT: GRB 070621: VLT optical observations
DATE:    07/06/22 18:38:01 GMT
FROM:    Paolo D'Avanzo at INAF-OAB  <paolo.davanzo at brera.inaf.it>

P. D'Avanzo (INAF - OABr) V. D'Elia (INAF - OAR), D. Fugazza,  G. 
Tagliaferri (INAF - OABr) on behalf of the MISTICI collaboration and D. 
Malesani and J.P.U. Fynbo (DARK/NBI) report:

We observed the field of GRB070621 (Sbarufatti et al., GCN 6560) with 
the ESO-VLT equipped with the FORS1 camera in the R and I bands. 
Observations were carried out on Jun 22.36 and 22.38 UT (0.39 and 0.41 
days after the GRB) in the I and R filters, respectively.

We detect two extended sources near the revised XRT error box 
(Sbarufatti et al. GCN 6569), reported by different authors (Malesani et 
al. GCN 6565, Tanvir et al. GCN 6570, Bloom et al. GCN 6568 and GCN 
6572), at the following coordinates (J2000):

S1) R.A. = 21:35:10.08, Dec. = -24:49:07.5
S2) R.A. = 21:35:10.27, Dec. = -24:49:02.8

with an uncertainty of 0.4".

A comparison between the NOT (Malesani et al. GCN 6565) and VLT images 
shows that source S1 remained constant between the NOT and VLT 
observation up to 0.1 mag.

Source S2 is not visible in the NOT image, so that a direct  comparison 
is not possible. When considering the roughly simultaneous WHT I-band 
measurement by Tanvir et al. (GCN 6570), we note a small discrepancy 
(~0.5 mag) in the magnitude of source S1. After taking into account this 
uncertainty, no variability can be claimed for source S2 as well.

Source S1 appears elongated in the East/West direction, consistent with 
the superposition of two objects as resolved in the adaptive-optics Keck 
image (Bloom et al. GCN 6572).

We acknowledge the support of the ESO staff.

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