EP260223a
GCN Circular 43831
Subject
EP260223a: Liverpool Telescope upper limits
Date
2026-02-25T14:09:47Z (22 days ago)
From
Rob Eyles-Ferris at U of Leicester <raje1@leicester.ac.uk>
Via
Web form
R. A. J. Eyles-Ferris and N. Habeeb (Leicester) report on behalf of a larger collaboration:
We observed the field of EP260223a (Liu et al., GCN 43817) with the 2m Liverpool Telescope on La Palma using the IO:O instrument. We obtained 8x200s exposures in the SDSS r’ and 9x200s exposures in the SDSS z’ filters starting at 2026-02-24 21:07:44 UT, approximately 33.8 hours after the X-ray detection.
We performed image subtraction on the stacked images using reference images from Pan-STARRS and also compared the stacked and reference images manually. Within the EP/WXT localisation (Liu et al., GCN 43817), we detect no new sources in our stacked images consistent with the results of Álvarez et al. (GCN 43818) and Zhu et al. (GCN 43826). This is also consistent with the fast fading X-ray emission implied by Liu et al. (GCN 43822).
We derive 3-sigma upper limits of r’ > 22.9 and z’ > 22.6 for our stacked images.
GCN Circular 43826
Subject
EP260223a: Xinglong optical upper limit
Date
2026-02-25T06:29:12Z (22 days ago)
From
Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong@nao.cas.cn>
Via
Web form
Yinan-Zhu (NAOC), Junjie-Jin (NAOC), Haiyang-Mu (NAOC), Feng-Xiao (NAOC), Yuguang-Sun (NAOC), Pengliang-Du (NAOC), Zhou-Fan (NAOC), Hong-Wu (NAOC) report on behalf of a large collaboration:
Following the detection of EP260223a (GCN Circular 43817), we observed the field of EP260223a using the 2.16-m telescope at Xinglong Observatory, NAOC. We obtained 3x300s N-band frames by using 2.16-m with a median time of 2026-02-24 10:56:45 (UT), 4 hrs after the EP trigger and 3x300s clear-band frames by using 2.16-m with a median time of 2026-02-21T19:09:10, 8 hrs after the EP trigger.
No uncatalogued optical transient is detected in the stacked images within the 20 arcsec EP/FXT error circle (GCN Circular 43817), down to 3-sigma limiting magnitudes of N-band ~19.11 mag for 2.16-m, calibrated with Pan-STARRS sources in the field. Also there is no apparent brightening for the catalogued sources within the error circle.
GCN Circular 43822
Subject
EP260223a: EP-FXT follow-up observation
Date
2026-02-25T04:06:11Z (22 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Q. C. Liu (THU), J. W. Hu and H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team:
We performed one follow-up observation of the X-ray transient EP260223a (Liu et al., GCN 43817, and followed by Álvarez et al., GCN 43818) with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The observation started at 2026-02-24 04:45:40 (UTC), about 17.42 hours after the WXT detection, with an exposure of ~5.2 ks. No source was detected within the WXT error circle. The 0.5-10 keV flux upper limit is about 6e-14 erg/s/cm^2 (90% C. L.).
Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).
GCN Circular 43818
Subject
EP260223a: COLIBRÍ optical upper limits
Date
2026-02-24T06:15:59Z (23 days ago)
From
freddalvarez@astro.unam.mx
Via
Web form
Fredd Sánchez Álvarez (UNAM), Antonio de Ugarte Postigo (LAM), Alan M. Watson (UNAM), Rosa L. Becerra (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Edilberto Aguilar-Ruiz (UNAM), Dalya Akl (NYUAD), Camila Angulo (UNAM), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Asuka Kuwata (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Nikos Mandarakas (LAM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), and Benjamin Schneider (LAM) report:
We observed the field of the EP260223a (Liu et al., GCN Circ. 43817) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-02-24 04:07 to 05:22 UTC (from 16.79 to 18.03 hours after the trigger and 17 minutes after the GCN Circular) and obtained 57 minutes of simultaneous exposure in the r and z filters.
The data were reduced, coadded, calibrated, and analysed with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the Pan-STARRS-DR2 catalog, is in the AB system, and is not corrected for Galactic extinction. We used STDWeb (Karpov 2025) to perform image subtraction against Legacy Survey DR10 templates (Dey et al. 2019).
We do not detect any new source in the WXT uncertainty region (Liu et al., GCN Circ. 43817) down to the following 5-sigma limits:
r > 23.7
z > 22.9
We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams.
COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico.
GCN Circular 43817
Subject
EP260223a: Einstein Probe detection of an X-ray transient
Date
2026-02-24T03:53:43Z (23 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Q. C. Liu (THU), J. W. Hu and H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team:
We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260223a. The transient did not trigger the WXT onboard unit due to the limited number of counts. The WXT position of the source is R.A. = 92.774 deg, DEC = 56.577 deg (J2000) with an uncertainty of 2.7 arcmin in radius (90% C.L. statistical and systematic). The preliminary analysis of the WXT data shows that the event started at T0=2026-02-23T11:20:27 (UTC), and lasted for approximately 130 seconds. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 1.7×10^21 cm^-2 and a photon index of 2.6 (+1.1/-0.9). The derived average unabsorbed 0.5-4 keV flux is 4.1 (+1.7/-1.3) x 10^-10 erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
Further FXT follow-up observations have been arranged.
Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).