TITLE:   GCN CIRCULAR
NUMBER:  38064
SUBJECT: EP241101a: Possible detection of an optical counterpart with FTW
DATE:    24/11/03 17:56:13 GMT
FROM:    Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann@physik.lmu.de>

Malte Busmann (LMU), Daniel Gruen (LMU), Brendan O’Connor (Carnegie Mellon U.) and Antonella Palmese (Carnegie Mellon U.) report:

We observed the 90% localization area of EP241101a (Liang et al., GCN 38039) with the Three Channel Imager (3KK) at the Fraunhofer Telescope Wendelstein (FTW) for 40 x 180 s in the r, i and J band simultaneously. Observations started at 2024-11-03T01:36:19 UT (1.07 days after the EP-WXT trigger). Our observations are calibrated against the PS1 catalog and reach 24.5 AB mag in the r band and 24.0 AB mag in the i band at the 3σ limit.

We performed difference imaging in the r band with images from the DESI Legacy Survey DR10. In the difference image, we detect a source at 

RA, DEC (J2000) = 02:31:10.85, +22:44:54.75

corresponding to PSO J037.7952+22.7485 in the PS1 catalog, which is labeled as a variable source and a possible AGN/QSO. Compared to the mean magnitude in PS1 the source is brighter by ~0.5 mag in r-band and ~0.4 mag in i-band. This detection is consistent with the upper limits from Perez-Garcia et al., GCN 38047; Lipunov et al., GCN 38049 and Aryan et al., GCN 38061.

While it is difficult to explain the short duration flare of EP241101a in the context of an AGN/QSO, we do not uncover any other variable sources to depth r>24.5 AB mag and i>24.0 AB mag over the entire 90% WXT localization.

Further observations are encouraged to determine the nature of the source.

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