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GCN Circular 39646

Subject
Liverpool Telecope observations of AT 2025dws / GRB 250309B
Date
2025-03-10T03:52:06Z (4 days ago)
From
Daniel Perley at Liverpool JMU <d.a.perley@ljmu.ac.uk>
Via
Web form
D. A. Perley (LJMU), A. Bochenek (LJMU), and A. Y. Q. Ho (Cornell) report:
 
We obtained imaging observations of AT2025dws (Stein et al., GCN 39639), a possible optical counterpart of GRB 250309B (Preis & Greiner, GCN 39629; McDermott et al., GCN 39635) with IO:O on the Liverpool Telescope on UT 2025 March 10 between 01:46:53 and 02:01:08 UT.  Two 100s exposures were acquired in each of the g, r, i, and z bands.  The source was weakly detected in all four filters.  We report the following photometry, calibrated relative to SDSS standards (dt is reported relative to the GRB 250309B GBM trigger time; McDermott et al., GCN 39642):
 
MJD         dt     filter mag    err
60744.07423 0.7558    g   20.47  0.19
60744.07708 0.7587    r   20.30  0.14
60744.07991 0.7615    i   20.07  0.19
60744.08274 0.7643    z   19.44  0.17
 
The red colours and significant fading are consistent with the interpretation of this source as the afterglow (see also Pérez-Fournon et al., GCN 39643; Stein et al., GCN 39644; Alexander et al., 39645).
 
No host galaxy subtraction or extinction correction has been performed.

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