TITLE: GCN CIRCULAR NUMBER: 39330 SUBJECT: EP250215a / GRB 250215A (potentially): NOT likely optical counterpart DATE: 25/02/15 04:44:25 GMT FROM: Dong Xu at NAOC/CAS dxu@nao.cas.cn
X. Liu, Z.P. Zhu, J. An, S.Y. Fu, S.Q. Jiang, D. Xu (NAOC), J.P.U. Fynbo (DAWN/NBI), N. Pyykkinen, M. A. Diaz Teodori (NOT) report on behalf of a large collaboration:
We observed the field of EP250215a (Wang et al., GCN 39329), using the ALFOSC instrument mounted on the Nordic Optical Telescope (NOT).
EP250215a is basically consistent with GRB 250215A also newly detected by Fermi/GBM (Fermi GBM team, GCN 39327) in both trigger time and position. Therefore, they seem to be an identical event.
We obtained 5 x 180 s frames in the SDSS-z band at a median time of 0.45 hr after the EP trigger. An uncatalogued optical transient (OT) is detected in the stacked image within the EP/FXT error circle (Wang et al., GCN 39329) at coordinates
R.A. (J2000) = 10:25:19.49 Dec. (J2000) = -27:41:54.37
with an uncertainty of ~ 0.5 arcsec. The OT has z ~ 20.6 mag, calibrated with Pan-STARRS DR1 and not corrected for Galactic extinction. There was no known NEO object at the above position by checking MPC. The 3-sigma limiting magnitude of the image is z ~ 21.5 (AB).
We thus conclude the OT is very likely the optical counterpart of EP250215a.
Further observations are planned.
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