GCN Circular 29716
Subject
GRB 210312B: OSN Afterglow Observations
Date
2021-03-24T19:45:39Z (4 years ago)
From
Alexander Kann at IAA-CSIC <kann@iaa.es>
D. A. Kann (HETH/IAA-CSIC), M. Jelinek (ASU CAS Ondrejov), A. de Ugarte
Postigo (HETH/IAA-CSIC, DARK/NBI), C. C. Thoene, M. Blazek, J. F. Agui
Fernandez (all HETH/IAA-CSIC), A. Sota, and R. M. Eloy (both IAA-CSIC)
report:
We observed the optical afterglow of GRB 210312B (INTEGRAL detection:
Mereghetti et al., GCN #29650) with both the 1.5m T150 and the 0.9m T90
telescopes of the Observatorio de Sierra Nevada (OSN),
Granada, Spain. We obtained 5 x 90 s exposures in B, V, Rc, and 6 x 90 s
in Ic, followed by 21 x 180 s exposures in Rc with the T150 telescope,
and 18 x 180 s in Rc with the T90 telescope in parallel, starting at
2021-03-12 22:51:28.19 UT. The afterglow is detected in multiple
combined images from T150, and in the complete combined T90 image. We
furthermore obtained 10 x 500 s Rc images in the second night with the
T150. The afterglow is detected in the combined image.
From three stacked images observed from 0.09577 to 0.14106 days after
the GRB, we detect a potential plateau phase, measuring Rc ~ 21.69 mag
(AB mag, vs. a nearby Pan-STARRS star converted to Rc following the
Lupton transformations, then transformed back to AB mag; errors range
from 0.04 to 0.11 mag). Then at 1.0850 days, we find the afterglow has
significantly decayed to Rc = 23.04 +/- 0.07 mag (AB).
Using photometry from our GTC observations (Kann et al., GCNs #29653,
#29655) as well as earlier photometry from the Ondrejov D50, we find a
broken power-law decay with a late slope of alpha ~ 2.2. The second-day
OSN detection is in excess of the extrapolated decay, indicating that
the host galaxy may contribute already, or that another rebrightening
has taken place.
[GCN OPS NOTE(01apr21): The typo in the SUBJECT line "230312B" was
changed to 210312B.]