GCN Circular 37494

S.Y. Fu (NAOC), J.P.U. Fynbo (DAWN/NBI), L. Izzo (INAF/OAC and DARK/ NBI), D. B. Malesani (DAWN/NBI and Radboud Univ.), D. Xu (NAOC), N. Koivisto (NOT and UTU) report on behalf of a large collaboration:

We observed again the field of GRB 240905E detected by Swift/BAT (Dichiara et al., GCN 37397
Not found
 
 
), and SVOM/GRM (Zhang et al., GCN 37404
Not found
 
 
), using the 2.56-m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. We obtained 8 x 300 s frames in the Sloan r-band, starting at 2024-09-12T04:39:24.2, i.e., 6.43 days after the Swift/BAT trigger.

No new optical transient is detected in our stacked images within the refined Swift/XRT error circle (Ferro et al., GCN 37406
Not found
 
 
), consistent with previous optical upper limits (Lipunov et al., GCN 37398
Not found
 
 
; An et al., GCN 37399
Not found
 
 
; Moskvitin & Spiridonova, GCN 37401
Not found
 
 
; Shilling et al., GCN 37402
Not found
 
 
; Strausbaugh et al., GCN 37403
Not found
 
 
; Brivio et al., GCN 37408
Not found
 
 
; Fu et al., GCN 37409
Not found
 
 
; Adami et al., GCN 37412
Not found
 
 
; Wu et al., GCN 37413
Not found
 
 
; Odeh et al., GCN 37414
Not found
 
 
; Belkin et al., GCN 37415
Not found
 
 
;  Mo et al., GCN 37416
Not found
 
 
; Maksut et al., GCN 37419
Not found
 
 
; Fu et al., GCN 37420
Not found
 
 
; Mohan et al., GCN 37422
Not found
 
 
; Qiu et al., GCN 37453
Not found
 
 
). The 5-sigma limiting magnitude is r ~ 23.5 mag, calibrated against nearby Pan-STARRS stars, and not corrected for Galactic extinction.

The optical source report by CrAO (Belkin et al., GCN 37415
Not found
 
 
) is detected in our two epochs at the NOT (Fu et al., GCN 37409
Not found
 
 
). The photometric results are as follow:

Tmid time | T-T0 (days) | Filter | Magnitude (AB)
---------------------------------------
2024-09-05T20:51:11.5 | 0.10 | r |23.09 +- 0.12
2024-09-12T05:15:23.6 | 6.45 | r |23.10 +- 0.15

There is no variability between the two epochs. And the NOT magnitude is also consistent with r = 23.37 +/- 0.27 that we measure from the Pan-STARRS-DR1 r-band image. Also considering the large offset from the refined X-ray position (Ferro et al., GCN 37406
Not found
 
 
), we conclude that this source is unrelated to the GRB.