GCN Circular 24459

D. A. Kann (HETH/IAA-CSIC), C. Thoene (HETH/IAA-CSIC), C. Stachie 
(Artemis), X. Zhang (THU), Z. Vidadi (Shao), M. Blazek (HETH/IAA-CSIC), 
K. Bensch (HETH/IAA-CSIC), L. Izzo (HETH/IAA-CSIC), A. de Ugarte Postigo 
(HETH/IAA-CSIC, DARK/NBI), S. Antier (APC), S. Basa (LAM), M. Boer 
(Artemis), D. Corre (LAL), M. Coughlin (Caltech), D. Coward 
(OzGrav-UWA), J.G. Ducoin (LAL), B. Gendre (OzGrav-UWA), P. Hello (LAL), 
A. Klotz (IRAP), C. Lachaud (APC), N. Leroy (LAL), D. Turpin (NAOC), and 
X. Wang (THU)

report on behalf of the HETH group and GRANDMA collaboration:

We observed the location of the Swift UVOT transient (Breeveld et al., 
GCN #24296) discovered in the error region of the aLIGO/Virgo Binary 
Neutron Star merger event S190425z (Ligo Scientific Collaboration and
VIRGO Collaboration, GCN #24168, #24228), with 
the 2.2m CAHA telescope and CAFOS. We obtained 3 x 240 s each in U/B and 
6 x 120 s in V/Rc/Ic. The observations were performed on 2019-04-28 from 
02:11:50 to 03:52:47 UT.

At the position (Palmese et al., GCN #24312) of the likely counterpart 
(thought to be an M2 dwarf that had a powerful flare which UVOT 
detected, Lipunov et al., GCN #24326; Bloom et al., GCN #24337), we 
detect a source in Rc and Ic and derive the following upper limits and 
magnitudes:

U > 22.9 mag;
B > 23.5 mag;
V > 23.5 mag;
Rc = 22.51 +/- 0.15 mag (depth Rc > 23.8 mag);
Ic = 21.53 +/- 0.15 mag (depth Ic > 22.9 mag).

Magnitudes are given in the AB system and were obtained vs. a comparison 
star from PanSTARRS and the transformations of Lupton (2005).

Our detections are in reasonable agreement with other reports (Palmese 
et al., GCN #24312; Bloom et al., GCN #24337; Hu et al., GCN #24324) and 
indicate the source was quiescent during our observations.

GRANDMA (Global Rapid Advanced Network Devoted to the Multi-messenger 
Addicts) is a network of robotic telescopes connected all over the world 
with both photometry and spectrometry capabilities for Time-domain 
Astronomy (https://grandma.lal.in2p3.fr/).

This message may be cited.

[GCN OPS NOTE(12jun19), The second reference in the first paragraph
was changed from "Breeveld et al., #24296" to
"Ligo Scientific Collaboration and VIRGO Collaboration, GCN #24168, #24228".]