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GCN Circular 35375

Subject
GRB 231215A: NOT optical observations
Date
2023-12-16T16:50:36Z (2 months ago)
From
Zipei Zhu at NAOC <zpzhu@nao.cas.cn>
Via
email
Z. Zhu, J. An, D. Xu (NAOC), D. B. Malesani (DAWN/NBI), L. Izzo (INAF/Capodimonte), A. de Ugarte Postigo (CNRS/OCA and LAM), Z. Gray (NOT) report on behalf a large collaboration:

We observed the optical afterglow of GRB 231215A detected by Swift/BAT (D’Avanzo et al., GCN 35343, Evans et al., GCN 35345, Pankov et al., GCN 35349), using the 2.56-m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations started at 20:23:33 UT on 2023-12-15, i.e., 10.6 hr after the BAT trigger. We obtained 2x120 s in the Sloan r-band and then 2x1800 s spectroscopy.

The previously reported optical counterpart (e.g., Lipunov et al., GCN 35347, Pankov et al., GCN 35349, Sasada et al., GCN 35351, An et al., GCN 35353, Wagh et al., GCN 35354, Hu et al., GCN 35363, Turpin et al., GCN 35367) was clearly detected in our stacked image with m(r) = 21.21 +/- 0.03 at 10.64 hr post-burst, calibrated with nearby Pan-STARRS stars.

However, the S/N of the spectrum is quite low. The spectrum shows a rather flat and featureless continuum. No unambiguous absorption feature can be identified at the reported GTC redshift (Thoene et al., GCN 35373).

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