GCN Circular 35724

Malte Busmann (LMU), Daniel Gruen (LMU),  Brendan O’Connor (CMU), Antonella Palmese (CMU), Lei Hu (CMU), Arno Riffeser (LMU/MPE) report:

We observed the position of the optical afterglow candidate (AT2024cew
Not found
 
 
 / GOTO24pw;  Belkin et al. GCN 35715
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; de Ugarte Postigo et al. GCN 35716
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) for GRB 240209A (Fermi GBM team, GCN 35712
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) with the 2.1 m Fraunhofer telescope at Wendelstein Observatory, Germany. Observations were obtained using the 3kk imager in the r, i, and J bands simultaneously, starting at 2024-02-13 at 17:42 UT, and again in the g, i and J bands, starting at 04:46 UT.

At the position of the transient (Belkin et al. GCN 35715
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), we clearly detect the source in g-band, r-band and i-band in the individual epochs. We measure a brightness of r~19.5+/-0.1 AB mag calibrated to the PS1 catalog. We marginally detect it in J-band co-adding both epochs, at J~20.2+/-0.4 calibrated to the 2MASS catalog. Compared to previous NOT r-band photometry (de Ugarte Postigo et al. GCN 35716
Not found
 
 
) this represents an increase in brightness, further suggesting that this transient is unlikely to be associated with the GRB, as does the blue color r-i~0.3 mag. 

Further observations to uncover the nature of the transient are encouraged. 

We thank the staff of the Wendelstein Observatory for obtaining these observations.