EP261015c
GCN Circular 45968
Subject
EP261015c: J-band upper limit with WINTER
Date
2026-10-16T23:37:46Z (a day ago)
From
tanishk.mohan@iitb.ac.in
Via
Web form
Tanishk Mohan (IITB), Geoffrey Mo (Caltech/Carnegie), Viraj Karambelkar (Columbia), Benjamin Schneider (LAM), Tomas Ahumada (NOIRLab), Robert Stein (UMD), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report:
We observed the field of EP261015c (Huang et al., GCN 45959) in the near-infrared J band with the Palomar 1-m telescope, equipped with the 1.2-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024).
Observations began on 2026-10-16 at 03:42:19.088 UTC in the J band (10.2 hr after the WXT observation), consisting of 20*120 sec exposures. The images were processed using the WINTER data reduction pipeline implemented with mirar (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565).
We do not detect any new source in the WXT localization in our stacked image, and obtain the following 5-sigma upper limit: J = 18.35 mag (AB).
WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research.
GCN Circular 45959
Subject
EP261015c: Einstein Probe detection of a fast X-ray transient
Date
2026-10-16T07:54:27Z (2 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
G. -L. Huang, Z.-X. Li (IHEP), R.-Z. Li, M. Nie (YNAO) and H. Sun (NAOC) on behalf of the Einstein Probe (EP) team:
We report the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP261015c. The EP-WXT observation (ID: 11900946826) started at 2026-10-15 17:29:32 (UTC), with an exposure time of 1200 s. The WXT light curve of the transient began at 2026-10-15T17:37:52 UTC lasted for 700 s. The WXT position of the source is R.A. = 21.920 deg, DEC = 66.601 deg (J2000) (l=126.526 deg, b=3.983 deg) with an uncertainty of 2.695 arcmin in radius (90% C.L. statistical and systematic).
We fitted the WXT spectrum with an absorbed power-law model, fixing nH at 0.581e22 cm-2. We obtained a spectral index of 4.3 (-1.8/+1.9) and an unabsorbed flux of 1.5 (-0.6/+1.2) e-10 erg/cm2/s during the flare. Over the entire observation, the spectral index was 4.4 (-1.8/+1.9), with an unabsorbed flux of 9.0 (-3.7/+6.9) e-11 erg/cm2/s.
A follow-up observation by EP-FXT have been scheduled. Multi-wavelength observations are strongly encouraged.
Launched on January 9, 2024, EP is a space X-ray observatory designed to monitor the soft X-ray sky with rapid X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). EP is a mission of the Chinese Academy of Sciences in collaboration with ESA, MPE, and CNES.