GCN Circular 30391
Subject
GRB 210704A: CAHA 2.2m Afterglow Detection
Event
Date
2021-07-06T12:12:22Z (4 years ago)
From
Alexander Kann at IAA-CSIC <kann@iaa.es>
D. A. Kann (HETH/IAA-CSIC), A. de Ugarte Postigo (HETH/IAA-CSIC,
DARK/NBI), C. Thoene, M. Blazek, J. F. Agui Fernandez (all
HETH/IAA-CSIC), and P. Martin-Fernandez (CAHA) report:
We observed the afterglow of GRB 210704A (BALROG localization:
Kunzweiler et al., GCN #30369; Fermi/LAT detection: Berretta et al., GCN
#30375; Fermi/GBM detection: Malacaria & Meegan, GCN #30382; AGILE/MCAL
detection: Ursi et al., GCN #30372; AstroSat/CZTI detection: Prasad et
al., GCN #30378; Konus-Wind detection: Ridnaia et al., GCN #30388;
Swift/XRT afterglow detection: D'Ai et al., GCN #30379) with CAFOS
mounted at the 2.2m Calar Alto telescope (Almeria, Spain), under good
conditions but at high airmass. We obtained 5 x 300 s images in i'.
The optical afterglow (Kim et al., GCN #30384, D'Avanzo et al., GCN
#30385) is faintly detected in the stacked image. Against four
Pan-STARRS comparison stars, we derive a preliminary measurement of i' =
21.84 +/- 0.13 mag at 1.09286 ���d after the trigger.
Compared to contemporary observations (D'Avanzo et al., GCN #30385), the
r' - i' color is unremarkable, indicating the afterglow likely does not
suffer from high extinction, and is therefore intrinsically faint. If it
is associated with the surrounding galaxy cluster (Levan et al., GCN
#30381), this would add evidence to the merger-induced ("short") nature
of the event.