TITLE: GCN CIRCULAR NUMBER: 36713 SUBJECT: GRB 240615A: NOT optical observations DATE: 24/06/20 13:43:59 GMT FROM: Dong Xu at NAOC/CAS dxu@nao.cas.cn
S.Q. Jiang, S.Y. Fu, X. Liu (NAOC), D. B. Malesani (DAWN/NBI and Radboud Univ.), Z.P. Zhu, J. An, D. Xu (NAOC), B. Gompertz (Birmingham), M. A. Diaz Teodori (NOT), report on behalf of a large collaboration:
We observed the Swift/BAT-GUANO field of GRB 240615A detected by Fermi/GBM (Fermi GBM team, GCN 36671), Swift/BAT-GUANO (DeLaunay et al., GCN 36672), Konus-Wind (Frederiks et al., GCN 36677) and GECAM (Tan et al., GCN 36682) using the 2.56-m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera.
Observations were carried out in the r band on 2024-06-16 and in the r and z bands on 2024-06-20. A red optical source is detected in the z-band of the second NOT epoch at the Wendelstein position (Busmann et al., GCN GCN 36706), which is consistent with the XRT Source #1 position (Page et al., GCN 36683). Preliminary photometry for the optical transient is as follows:
Tmid(UT) Tmid-T0(hr) Mag MagErr UL(5-sigma) Filter 2024-06-16T03:50:07 9.98 - - >23.9 r 2024-06-20T01:23:48 103.53 - - >22.8 r 2024-06-20T01:41:45 103.83 21.95 0.14 - z
calibrated against nearby Pan-STARRS stars and not corrected for Galactic extinction.
Photometry of the Pan-STARRS archival images yields r > 23.2 (5-sigma) and z > 22.1 (5-sigma). We notice that the NOT z-band magnitude is not significantly brighter than the Pan-STARRS limit, hence our data alone do not allow to robustly claim the detection of a new source.
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