TITLE: GCN CIRCULAR NUMBER: 40405 SUBJECT: GRB 250506A: NOT optical upper limits DATE: 25/05/09 09:37:58 GMT FROM: Gregory Corcoran at University College Dublin gregory.corcoran@ucdconnect.ie
Z. P. Zhu (NAOC), B. Schneider (LAM), A. Martin-Carrillo (UCD), G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), D. Xu (NAOC), T. T. Hansen, W. M. Ali, P. H. Chan, N. Hölinger, E. Lamprou, R. Lesley, H. Lundberg, J. Pajak, L. Peschieras, and N. Valsamidis (all Stockholm University), report on behalf of a larger collaboration.
We observed the field of GRB 250506A detected by SVOM/ECLAIRs (Wang et al., GCN 40358) and Fermi/GBM (Sonawane et al., GCN 40362), using the ALFOSC camera mounted on the Nordic Optical Telescope (NOT) centered at the X-ray source detected by EP/FXT (Zhang et al. GCN 40365). We obtained exposures in the SDSS r (3x600 s) and z (4x300 s) bands starting at 23:44:29 UT on 2025-05-06 (21.35 hr after the SVOM/ECLAIRs trigger).
No new optical source is detected at a position consistent with the Swift/XRT error region (the best currently available for this event; Burrows et al., GCN 40378) in the stacked images of either band down to the 5-sigma limiting AB magnitudes of r > 23.6 and z > 22.5, calibrated against nearby Pan-STARRS stars.
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