GCN Circular 45133

Pierre-Yves Lechapelain and Thierry Midavaine report on behalf of the RAPAS network:  the field of EP-0170924151 (Y.F. Liang et al. GCN 45095
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 ) was observed using a N254mm F/3 robotic telescope equiped with a CMOS FPA IMX533 at Observatoire de Bretagne Sud (Y80). The filters used were 
RAPAS filters meeting the Gaia G, Gbp, Grp photometric bands and astrometry was done with the GaiaDR3 catalogue. 

The observations began 20 minutes after the EP-WXT trigger (Jul 06,
22:18 UTC) and continued for 60 minutes with 120s exposures using a cycle of RAPAS G, Gbp and  Grp filters. A follow-up epoch was obtained 24.2 hours later (Jul 07, 22:08 UTC) with 30s exposures. We identify the optical counterpart as the high-proper-motion M-dwarf star from the Gaia DR3 catalog : EP-WXT designation RA(J2000) = 239.6790° ; Dec(J2000) = 23.873° ; ±0.0520°. Our astrometry gives RA(J2000) = 239.6871° ; Dec(J2000) = 23.8549°; ±0.0001°, which is a mean value from 11 acquisitions in G and Grp bands. The target is found close to the Gaia DR3 source J15587+2351E, PM 1218502635856444672, RA = 239,6879070°, Dec = 23,8551800°, G=12.855, BP-RP=2.89. The angular difference between the target and the above Gaia source is around 0.001°. The shift seems in agreement with the Gaia measured proper motion of this Gaia DR3 source.
Forced aperture photometry at the source position, calibrated against
Gaia DR3 with a linear color term, yields the following G, Gbp Grp magnitudes and Gbp-Grp color index :

MJD (mid)     G mag   G std  Gbp mag Grp mag Gbp-Grp
61227.92963   12.13   0.72   12.70   11.65   1.05
61227.93420   12.19   0.64   12.76   11.46   1.30
61227.93895   12.30   0.54   12.86   11.57   1.29
61227.94359   12.38   0.46   13.02   11.61   1.41
61227.94815   12.46   0.37   13.19   11.59   1.60
61227.95297   12.59   0.25   13.29   11.71   1.58
61227.95763   12.61   0.23   13.37   11.76   1.61
61227.96211   12.67   0.17   13.50   11.78   1.72
61227.96678   12.67   0.19   13.47   11.80   1.67
61227.97132   12.71   0.13   13.52   11.82   1.70
61228.92248   13.14   0.29					

We conclude that EP 01709274151 is a stellar flare from the nearby M-dwarf
PM J15587+2351E. Further multi-band monitoring and SED are encouraged to characterize the recovery timescale. All the FITS files are available on request and are on the way to be archived in PADC facility for RAPAS at Paris Observatory.

Acknowledgements :
RAPAS ( https://gemini.obspm.fr/20220101-rapas/ ) is a ProAm collaboration created by T. Midavaine (SAF), W. Thuillot (LTE, Obs. de Paris-PSL) and M. Dennefeld (IAP/CNRS and Sorbonne Univ.) and funded by the Paris Observatory under API ProAm of the Scientific Council. It aims at homogenizing observing procedures and filters, and is delivering to a network of french amateur observatories a set of 3 filters which have been chosen to meet the Gaia G, Gbp and Grp spectral bands. This network produces data on  astrophysical alerts delivered by various Alert systems (Gaia Alerts, Atlas, ZTF, etc…) and collected by Astro-COLIBRI ( https://astro-colibri.science ). It is similarly progressing towards an homogeneous spectroscopic equipment to deliver SED. Paris Observatory PADC which is on the way to archive all the FITS files with attached processing pipeline.