GCN Circular 31221
Subject
GRB 211211A: NOT optical spectroscopy
Date
2021-12-12T16:24:56Z (3 years ago)
From
Daniele B Malesani at Radboud U <d.malesani@astro.ru.nl>
D. B. Malesani (Univ. Radboud and DAWN/NBI), J. P. U. Fynbo (DAWN/NBI),
A. de Ugarte Postigo (Obs. Cote d'Azur), L. Izzo (DARK/NBI), S. Fu, D.
Xu, Z. Zhu (NAOC/CAS), N. R. Tanvir (Univ. Leicester), A. A. Djupvik
(NOT), report on behalf of a larger collaboration:
We observed the optical afterglow of GRB 211211A (D'Ai et al., GCN
31202; Zheng & Filippenko, GCN 31203) using the Nordic Optical Telescope
(NOT) equipped with the ALFOSC instrument. Images were secured in the
SDSS r, g and i filters.
At the mean time of Dec 12.24 UT (16.6 hr after the GRB), we measure a
magnitude r = 20.89 +- 0.05 AB, calibrated against nearby stars from the
Pan-STARRS survey. Our measurement is in agreement with those by
Strausbaugh & Cucchiara (GCN 31214) and de Ugarte Postigo et al. (GCN
31218), taken at a comparable epoch. Compared to the magnitudes reported
by Zheng & Filippenko (GCN 31203), Ito et al. (GCN 31217) and Jang (GCN
31213), our data confirm the unusually slow decay,
We report for the afterglow the following coordinates (0.3" uncertainty):
RA = 14:09:10.12
Dec = +27:53:18.1
A bright, extended object (r ~ 19.5) is visible about 5.5" to the N-E of
the afterglow (as already pointed out by Zheng & Filippenko, GCN 31203),
which is also visible in the SDSS, Pan-STARRS, and Legacy surveys.
A spectrum was secured covering both the afterglow and the nearby galaxy
(wavelength range 3700-9400 AA). A weak emission line is detected on top
of the host galaxy trace at 7063 AA, which could be due to Halpha at z =
0.076. This is marginally consistent with the SDSS photometric redshift
0.140 +- 0.0375, unlike other interpretations of the same line.
No clear absorption or emission features are detected in the afterglow
trace. This may be due to the modest S/N, and is also consistent with a
low redshift, as is the detection of the afterglow in all the UVOT UV
filters (Swift observation ID 1088940000).
It is not clear at the present stage whether the afterglow is physically
associated with the galaxy at z = 0.076. While the sky proximity and the
low redshift are indeed suggestive, the physical offset at z = 0.076
would be about 8 kpc (in projection), an unusually large value for long
GRBs. There is also no visible emission in the archival images down to r
~ 24 (AB) at the location of the afterglow, which would be unusual for a
long GRB at z = 0.076.
Moreover, if placed at z = 0.076, GRB 211211A would be an outlier of the
the Amati relation (e.g. Nava et al. 2012, MNRAS, 421, 1256), with E_iso
= 1.4*10^54 erg and E_peak ~ 700 keV (using the Fermi/GBM prompt
properties from Mangan et al., GCN 31210).
Overall, a moderate-redshift GRB (with z > 0.076) is consistent with the
available information. The detection of an emerging supernova could
clarify the situation. We encourage further photometric and
spectroscopic follow-up of this potentially interesting event.