EP260214b
GCN Circular 44088
Subject
EP260214b: ATCA 6 GHz detection
Date
2026-03-23T15:25:11Z (7 months ago)
From
Aishwarya L Thakur at INAF-IAPS, Rome <aishth@outlook.com>
Via
Web form
G. Gianfagna, G. Bruni, A. L. Thakur, M. Fanelli, L. Piro (INAF-IAPS) report:
We re-observed the Fast X-ray Transient EP260214b (J Yang et al., GCN 43744, H Yang et al., GCN 43779) with the Australian Telescope Compact Array (ATCA) radio telescope using the 4-cm receiver. Observations were performed on March 20 2026 (at a mean epoch of ~34 days after the EP trigger and 17 days after our last observation; see Gianfagna et al., GCN 43924) for a total of 5 hours.
Data were reduced and imaged with standard CASA procedures. The final 6 GHz image has an RMS of 12 uJy/beam.
We detect radio emission at a flux density of ~0.04 mJy at a position consistent with the optical counterpart (He et al.). GCN 43745, Watson et al. GCN 43747, Le Floch et al. GCN 43749, Pérez-Fournon et al. GCN 43750, Russeil et al. 43752,Li et al. GCN 43755, Vijayjumar et al. GCN 43757, Becerra et al. GCN 43758, Yang et al. GCN 43760, Aaryan et al. GCN 43762, Bochenek et al. GCN 43764, Kar et al. GCN 43774, Volnova et al. GCN 43775).
Further ATCA observations are planned.
The Australia Telescope Compact Array is part of the Australia Telescope National Facility (grid.421683.a), which is funded by the Australian Government for operation as a National Facility managed by CSIRO. We acknowledge the Gomeroi people as the traditional owners of the Observatory site.
GCN Circular 43924
Subject
EP260214b: ATCA 6 GHz observations
Date
2026-03-05T15:31:04Z (8 months ago)
From
Giulia Gianfagna at INAF-IAPS <giulia.gianfagna@inaf.it>
Via
Web form
G. Gianfagna, G. Bruni, A. L. Thakur, L. Piro (INAF-IAPS) report:
We observed the Fast X-ray Transient EP260214b (J Yang et al., GCN 43744, H Yang et al., GCN 43779) with the Australian Telescope Compact Array radio telescope using the 4-cm receiver. Observations were performed on March 3 2026 (at a mean epoch of ~17 days after the EP trigger) for a total of 6 hours.
Data were reduced and imaged with standard CASA procedures. The final 6 GHz image has an RMS of ~15 uJy/beam.
No radio emission is apparent at the position of the optical counterpart (He et al. GCN 43745, Watson et al. GCN 43747, Le Floch et al. GCN 43749, Pérez-Fournon et al. GCN 43750, Russeil et al. 43752,Li et al. GCN 43755, Vijayjumar et al. GCN 43757, Becerra et al. GCN 43758, Yang et al. GCN 43760, Aaryan et al. GCN 43762, Bochenek et al. GCN 43764, Kar et al. GCN 43774, Volnova et al. GCN 43775).
The corresponding 3-sigma upper limit is thus ~50 uJy.
Further ATCA observations are planned.
The Australia Telescope Compact Array is part of the Australia Telescope National Facility (grid.421683.a), which is funded by the Australian Government for operation as a National Facility managed by CSIRO. We acknowledge the Gomeroi people as the traditional owners of the Observatory site.
GCN Circular 43775
Subject
EP260214b: Mondy optical observations
Date
2026-02-17T17:29:43Z (8 months ago)
From
Alina Volnova at IKI RAS <alinusss@gmail.com>
Via
Web form
A. Volnova (IKI), A. Pozanenko (IKI), E. Klunko (ISTP), N. Pankov (IKI) report on behalf of IKI-GRB-FuN:
We observed the field of the fast X-ray transient EP260214b (Yang et al., GCNs 43744, 43760) with the AZT-33IK 1.5m telescope of the Mondy observatory starting on 2026-02-16 (UT) 19:44:56 and taking several 120-seconds frames in the R band. The optical counterpart (He et al., GCN 43745; Watson et al., GCN 43747; Pérez-Fournon et al., GCN 43750; Russeil et al., GCN 43752; Li et al., GCN 43755; Vijaykumar et al., GCN 43757; Becerra et al., GCN 43758; Aryan et al., GCN 43762; Bochenek & Perley, GCN 43764; Kar et al., GCN 43774) at a redshift z = 1.208 (Le Floch et al., GCN 43749) is detected in the stacked frame.
Preliminary photometry and observational details are the following:
Date UT start t-T0 Exp. Filter Obj. Err. UL Site/Telescope
(mid,days) (n*s) (3sigma)
2026-02-16 19:44:56 1.93455 45*120 R 21.67 0.16 23.0 Mondy/AZT-33IK
The photometry is based on nearby SDSS stars (R-magnitudes obtained using the 2005 Lupton transformation equations) and is not corrected for Galactic extinction.
GCN Circular 43774
Subject
EP260214b: 1.3m DFOT optical upper limit
Date
2026-02-17T17:26:03Z (8 months ago)
From
Debalina Kar at ARIES <kardebalina2000@gmail.com>
Via
Web form
Debalina Kar, Pankaj Pawar, Anshika Gupta, Dhruv Jain and Kuntal Misra (ARIES) report:
We observed the field of EP260214b detected by EP/WXT (Yang et al., GCN 43744) with the 1.3m Devasthal Fast Optical Telescope (DFOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations began on 2026-02-17 at 00:15:22 UT, approximately 50.82 hours after the trigger. We obtained multiple exposures of 300 s each in the R filter. A total of 15 frames were aligned and stacked to improve the signal-to-noise ratio. In the stacked frame we do not detect any optical counterpart within the error box of EP/WXT (Yang et al., GCN 43760) as reported by He et al. (GCN 43745). This is consistent with the non-detection reported by Aryan et al. (GCN 43762). We derive the following 3-sigma upper limit from the stacked image:
Date (UT) Start Time T_start–T0 (hr) Filter Exposure Magnitude
----------------------------------------------------------------------------------
2026-02-17 00:15:22 ~50.82 R 300 s × 15 > 22.40
The non-detection is consistent with the detection and fading behavior reported by Watson et al. (GCN 43747), Floch et al. (GCN 43749), Pérez-Fournon et al. (GCN 43750), Russeil et al. (GCN 43752), Li et al. (GCN 43755), Becerra et al. (GCN 43758), as well as with the upper limit reported by Vijaykumar et al. (GCN 43757).
The reported magnitude is not corrected for Galactic extinction. Photometric calibration was performed using standard stars from the Pan-Starrs catalogue.
GCN Circular 43764
Subject
EP260214b: Liverpool Telescope optical observations
Date
2026-02-16T14:12:34Z (8 months ago)
From
A. Bochenek at Liverpool John Moores University <a.m.bochenek@2023.ljmu.ac.uk>
Via
Web form
A. Bochenek, D. A. Perley (LJMU) report:
We observed the field of EP 260214b (Yang et al., GCN 43744; Yang et al., GCN 43760) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 5x100s exposures in SDSS g filter and 6x100s in SDSS r and i, starting at 2026-02-16 02:51:39.908 UT, approximately 28.8 hours after trigger.
Some exposures were discarded prior to stacking due to poor seeing. They were subtracted from PanSTARRS reference images using PSF matching with the use of PSFEx. We report detections in stacked images in all filters at the position first reported by He et al., GCN 43745 and Watson et al., GCN 43747.
MJD (mid) T_mid-T_0 Filter Mag. (AB)
61087.12195 28.86 h g 22.45 ± 0.27
61087.13116 29.08 h r 22.22 ± 0.33
61087.13913 29.27 h i 21.75 ± 0.24
The photometry was obtained using nearby PanSTARRS secondary standards and was not corrected for extinction.
GCN Circular 43762
Subject
EP260214b: Optical upper limit with Kinder observations
Date
2026-02-16T10:28:20Z (8 months ago)
From
Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941@gmail.com>
Via
Web form
A. Aryan, C.-S. Lin, T.-W. Chen (all NCU), A. K. H. Kong (NTHU), J. H. Gillanders, S. J. Smartt (both Oxford), Y. J. Yang (NYUAD), Y.-H. Lee, A. Sankar.K, M.-H. Lee, C.-H. Lai, Y.-C. Pan, C.-C. Ngeow, W.-J. Hou, H.-Y. Hsiao, H.-C. Lin, J.-K. Guo (all NCU), S. Yang, Z. N. Wang, L. L. Fan, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz, and M. Huber (both IfA, Hawaii) report:
We observed the field of the fast X-ray transient EP260214b (Yang et al., GCN 43744 & GCN 43760) using the 1m LOT at the Lulin observatory, as part of the Kinder collaboration (Chen & Yang et al. 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). The first LOT epoch of observations in r-band started at 14:34 UTC on the 15th of February 2026 (MJD 61086.607), 16.50 hr after the EP-WXT trigger.
We utilized the astroalign (Beroiz et al. 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al. 2022, ApJ, 935, 167) packages to align and stack the individual frames. We used the Python-based AutoPhOT package (Brennan & Fraser 2022, A&A, 667, A62) to perform template subtraction with the DESI Legacy Survey (Dey et al. 2019, AJ 157, 168) DR10 image using the 'SFFT' (Hu et al. 2022, ApJ, 936, 157) algorithm. In the stacked frame or the difference image, we did not detect the proposed optical counterpart reported by He et al. (GCN 43745).
Moreover, we used AutoPhOT to perform PSF photometry. The details of the observations and the measured 3-sigma upper limits (in the AB system) are as follows:
Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass
LOT | r | 61086.607 | 16.50 | 300 * 6 | >22.2 | 1".76 | 1.85
The non-detection in our observations is consistent with (detection) reports by Watson et al. (GCN 43747), Floch et al. (GCN 43749), Pérez-Fournon et al. (GCN 43750), Russeil et al. (GCN 43752), Li et al. (GCN 43755), Becerra et al. (GCN 43758), and also with the upper limit reported by Vijaykumar et al. (GCN 43757).
The presented magnitude is calibrated using the field stars from the Pan-Starrs catalog and is not corrected for the expected Galactic foreground extinction of A_r = 0.04 mag in the direction of the transient (Schlafly & Finkbeiner 2011). The methodology, details on the Lulin observatory telescopes, and a compilation of our optical follow-up campaign for FXTs discovered within the first year of operation of the Einstein-Probe mission are presented in Aryan et al. 2025, ApJS, 281, 20, doi:10.3847/1538-4365/adfc69.
GCN Circular 43760
Subject
EP260214b: EP-FXT follow-up observation
Date
2026-02-16T05:59:28Z (8 months ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
J. Yang (ZZU), A. Li (BNU), Y. H. Jiang (NJU), Y. Liu (NAOC) on behalf of the Einstein Probe (EP) team:
The fast X-ray transient EP260214b was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Yang et al., GCN 43744), whose optical counterpart was detected by several optical telescopes (He et al., GCN 43745, Watson et al., GCN 43747, Pérez-Fournon et al., GCN 43750, Russeil et al., GCN 43752, Li et al., GCN 43755, Becerra et al., GCN 43758) at a resdhift z = 1.208 (Le Floch et al., GCN 43749). EP-FXT performed a follow-up observation of EP260214b about 5.8 hours after the WXT detection, with an exposure time of 2.8 ks. The FXT telemetry data shows that an uncatalogued source was detected within the WXT error circle at R.A. = 191.2581, DEC = 23.8529 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The FXT X-ray spectrum of this uncatalogued source can be fitted with an absorbed powerlaw with a hydrogen column density fixed at the Galactic value of 1.57 x 10^20 cm^-2 and a photon index of 2.2 (+0.3/-0.3). The derived unabsorbed 0.5-10 keV flux is approximately 2.8 (+0.7/-0.5) x 10^-13 erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
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 43758
Subject
EP260214b: DDOTI Optical Detection
Date
2026-02-15T20:17:14Z (8 months ago)
From
Rosa L. Becerra at Instituto de Astronomía, UNAM <rbecerra@astro.unam.mx>
Via
Web form
Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), Camila Angulo Valdez (UNAM), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM), Margarita Pereyra (UNAM) and Eleonora Troja (U Roma) report:
We observe the field of EP260214b (Yang et al., GCN Circ. 43744) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir (http://ddoti.astroscu.unam.mx) on the night of 2026-02-15 UTC. DDOTI observed from 05:32 UTC to 13:08 UTC (T+8.9 h to T+16.5 h after the trigger), with a total exposure time of 3.7 hours. These observations were interleaved with other scientific programs.
Comparing our observations to the USNO-B1 and Pan-STARRS PS1 DR2 catalogues, we detect the optical counterpart reported by He et al. (GCN Circ. 43745), at preliminary AB magnitude of:
w = 21.08 +/- 0.23.
This value is consistent with previous observations reported (He et al., GCN Circ. 43745; Watson et al., GCN Circ. 43747; Pérez-Fournon et al., GCN Circ. 43750; Russeil et al., GCN Circ. 43752; Li et al., GCN Circ. 43755; Vijaykumar et al., GCN Circ. 43757) and is not corrected for the Galactic extinction.
We thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir.
GCN Circular 43757
Subject
EP260214b: GROWTH-India Telescope optical upper limit
Date
2026-02-15T18:57:19Z (8 months ago)
From
V. Swain at IIT Bombay <vishwajeet.s@iitb.ac.in>
Via
Web form
V. Vijaykumar, A. Khade, V. Swain, S. Patil, A.P. Saikia, T. Mohan, V. Bhalerao (IITB), G.C. Anupama, S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team:
We observed the field of EP260214b detected by the Einstein Probe (EP) mission (EP mission, GCN 43744), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2026-02-15 16:28:03 (UTC), i.e., 18.40 hours after the trigger and obtained a single exposure in r' filter. We did not detect any transient in our image. The photometric upper limit is as follows:
| MJD (mid) | Filter | tmid-t0 (hours) | Exposure Time (sec) | Upper limit (AB) |
|---|---|---|---|---|
| 61086.68614 | r' | 18.40 | 650 | 20.9 |
The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction.
Our magnitude is consistent with other optical observations (He. et al., GCN 43745; Watson et.al., GCN 43747; Pérez-Fournon et.al GCN 43750; Russeil et.al GCN 43752; Li et.al GCN 43755).
The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/.
GCN Circular 43755
Subject
EP260214b: SVOM/VT optical observation
Date
2026-02-15T16:46:31Z (8 months ago)
From
Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>
Via
Web form
H. L. Li, Y. N. Ma, L. P. Xin, Y. L. Qiu, C. Wu, Z. H. Yao, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. R. Xu, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team.
SVOM/VT performed a Target of Opportunity observation of EP260214b detected by Einstein Probe (Yang et al., GCN 43744). The observation started on 2026-02-15T03:52:22 UTC, i.e. 5.81 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
The optical counterpart (He et al., GCN 43745; Watson et al., GCN 43747; Le Floch et al., GCN 43749; Pérez-Fournon et al., GCN 43750; Russeil et al., GCN 43752) were detected in both channels. The measurements in AB magnitude are derived as follows:
Mid time | Band | Exposure Time | 3 sigma limit magnitude
6.93 hours VT_B 80*50 sec 21.29 +/-0.08 mag
6.94 hours VT_R 67*50 sec 20.84 +/- 0.07 mag
The counterpart show no significant variation during our observation from 5.81 hours to 8.08 hours.
Our photometry was not corrected for Galactic extinction.
The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS.
GCN Circular 43752
Subject
EP260214b: OHP/T120 optical observations
Date
2026-02-15T14:06:52Z (8 months ago)
From
Christophe Adami at LAM <christophe.adami@lam.fr>
Via
Web form
D. Russeil (LAM/AMU), C. Adami (LAM/Pytheas/AMU), N.A. Rakotondrainibe (LAM), B. Schneider (LAM), J. Balcaen (Pytheas/OHP), Y. Degot-Longhi (Pytheas/OHP), S. Basa (LAM/OHP/Pytheas/AMU), E. Le Floc'h (CEA/Irfu), P. Araigi-hayek (AMU), J. Bourges (AMU), N. Hatchodourian (AMU), E. Lefevre-forjan (AMU), O. Maegey (AMU), P. Montaigne (AMU), C. Rey (AMU), M. Rousse (AMU), B. Sevilla (AMU), H. Subra (AMU), L. Valliccioni (AMU), H. LeCoroller (LAM), M. Ould-elhkim (LAM) report on behalf of a larger collaboration:
We observed the field of the EP260214b (Yang et al., GCN 43744) using the T120cm telescope at Observatoire de Haute-Provence (France). We obtained 40 minutes of exposure in the r-band starting at 01:37:37.6 UT on 2026-02-15 (~3.6 hr after the trigger).
In the stacked image, the optical counterpart detected by He et al.(GCN 43745), Watson et al. (GCN 43747), and Perez-Fournon et al. (GCN 43750), and measured at a redshift of 1.208 (LeFloch et al., GCN 43749) is visible with a preliminar magnitude of:
r = 21.22 +/- 0.13 mag (AB)
The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the STDWeb/STDPipe tools (Karpov 2025), is in the AB system, and is not corrected for Galactic extinction.
We acknowledge the excellent support from Observatoire de Haute-Provence.
GCN Circular 43750
Subject
EP260214b: LCO optical counterpart detection
Date
2026-02-15T11:37:27Z (8 months ago)
From
Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>
Via
Web form
I. Pérez-Fournon (IAC and ULL), F. Poidevin (IAC and ULL), D. Cano-Morales, A.E. Hernández-Díaz,
I. Correa-Plasencia, E. Lekaroz-Urriza, M. Quintana-Ansaldo (all ULL), A. López-Oramas (IAC and ULL), and D. Aguado (IAC and ULL)
Following the detection of the fast X-ray transient EP260214b (Yang et al., GCN #43744), we observed the field with one of the two Las Cumbres Observatory (LCO) 1-m telescopes located at the LCO node at
McDonald Observatory, Texas. The observation consisted of a single exposure of 500 sec in the SDSS r' filter, that started on 2026-02-15 at 09:24:15 UT, about 11.34 hours after the EP trigger. The optical counterpart detected by He et al. (GCN #43745) and Watson et al. (GCN #43747) at a resdhift z = 1.208 (Le Floch et al., GCN #43749) is clearly detected in our image with an AB magnitude of r' = 21.28 +/- 0.09, calibrated against PanSTARRS-1 DR2 stars and not corrected for Galactic extinction.
This work makes use of observations from the Las Cumbres Observatory global telescope network (LCO program IAC2026A-011, SGLF and Superluminous Supernovae surveys).
This work made use of the Astro-COLIBRI platform (P. Reichherzer et al. 2021, ApJS, 256, 5).
GCN Circular 43749
Subject
EP260214b: VLT/X-shooter spectroscopic redshift z = 1.208
Date
2026-02-15T10:06:03Z (8 months ago)
From
Aishwarya L Thakur at INAF-IAPS, Rome <aishth@outlook.com>
Via
Web form
E. Le Floch (CEA/Irfu), J. An (NAOC), A. Saccardi (CEA/Irfu), A. L. Thakur (INAF-IAPS), D. Xu (NAOC), L. Cotter (UCD), D. Malesani (DAWN/NBI and Radboud), N. R. Tanvir (U. Leicester) report on behalf of the Stargate collaboration
We observed the optical counterpart (He et al. GCN 43745; Watson et al. GCN 43747) of EP260214b (Yang et al. GCN 43744) using the ESO/VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000-21000 Å and consist of 4 exposures of 600 s each. Observations started on 2026 February 15 at 06:24:46 UT (at 8.35 hr post-trigger).
In a preliminary reduction of the spectra, we detect continuum over the entire wavelength range. From the detection of multiple absorption lines, which we interpret as the Al II, Fe II, Mg II, we infer a redshift of z = 1.208. Additionally, at a consistent redshift (z = 1.207) we note the presence of several emission lines due to the [O II] doublet, Ne III, the [O III] doublet, and the Balmer lines from the GRB host galaxy.
We acknowledge the excellent support of the ESO observing staff in Paranal, in particular Celia Desgrange, Mar Carretero Castrillo, Diego Parraguez and Fuyan Bian. The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495).
GCN Circular 43747
Subject
EP260214b: COLIBRÍ optical observations
Date
2026-02-15T06:40:56Z (8 months ago)
From
Alan Watson at UNAM <alan@astro.unam.mx>
Via
Web form
Alan M. Watson (UNAM), Damien Dornic (CPPM), Rosa L. Becerra (UNAM), Noémie Globus (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Asuka Kuwata (UNAM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), and Antonio de Ugarte Postigo (LAM) report:
We imaged the field of EP260214b (Yang et al., GCN Circ. 43744) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-02-15 05:49 to 06:12 UTC (from 7.76 to 8.13 hours after the trigger) and obtained 3, 7, 2, and 12 minutes of exposure, respectively, in the g, r, i, and z filters.
The data were reduced, calibrated, and analyzed with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.
We detect the optical counterpart reported by He et al. (GCN Circ. 43745), at preliminary magnitudes of:
g = 21.30 +/- 0.09,
r = 21.11 +/- 0.07,
i = 21.08 +/- 0.14, and
z = 21.29 +/- 0.18.
Comparing our r-band magnitude to the one reported by He et al. (GCN Circ. 43745) at about 2.2 hours, the source has faded only slowly with a temporal power law index of about alpha ≈ -0.15, which suggests the presence of a plateau. We also notice that the optical counterpart has blue colors, which are consistent with a nearby event and also consistent with the high X-ray flux reported by Yang et al. (GCN Circ. 43744).
Further observations and analysis are ongoing.
We encourage spectroscopic observations of this source to confirm its redshift.
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 43745
Subject
EP260214b: NOT optical counterpart detection
Date
2026-02-15T05:27:38Z (8 months ago)
From
L. B. He at NAOC <helb@bao.ac.cn>
Via
Web form
L.B. He, Z.P. Zhu, J. An, X. Liu, S.Q. Jiang, D. Xu (NAOC), S.Y. Fu (HUST), J.P.U. Fynbo (DAWN/NBI), K. Valeckas (NOT) report on behalf of a large collaboration:
We observed the field of EP260214b detected by EP/WXT (Yang et al., GCN 43744) using the 2.56-m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera.
In a single of 220 s Sloan r-band exposure we detect a brightened source within the EP/FXT error circle (Yang et al., GCN 43744) at coordinates:
R.A.(J2000) = 12:45:01.96 = 191.2582
Dec.(J2000) = 23:51:13.10 = 23.8536
with an uncertainty of ~0.5 arcsec. We measure r' = 20.90 +/- 0.04 at ~2.22 hrs post-trigger, calibrated with Pan-STARRS1-dr2 catalog and not corrected for Galactic extinction. The source is brighter than its underlying host galaxy by ~2.0 mag, and the galaxy has a photometric redshift z ~ 1.04 from Legacy Survey dr9.
We suggest the source is the optical counterpart of EP260214b.
GCN Circular 43744
Subject
EP260214b: Einstein Probe detection of a fast X-ray transient
Date
2026-02-15T05:11:36Z (8 months ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
J. Yang (ZZU), A. Li (BNU), Y. H. Jiang (NJU) and Y. Liu (NAOC) 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 EP260214b. The transient triggered EP-WXT (ID: 01709258389) at 2026-02-14T22:04:12 (UTC). The WXT position of the source is R.A. = 191.260 deg, DEC = 23.857 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). The preliminary analysis of the WXT data shows that the event started at T0=2026-02-14T22:03:34 (UTC), and lasted for approximately 50 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 1.57 × 10^20 cm^-2 and a photon index of 0.7 (+/-0.4). The derived average unabsorbed 0.5-4 keV flux is 2.1 (-0.5/+0.7) × 10^(-9) erg/s/cm^2.
As the EP was performing another autonomous follow-up observation, no follow-up observation was performed automatically for this source. A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed at 2026-02-15T03:59:57 (UTC), about 6 hours after T0. Within the WXT error circle, the FXT on-board alert indicated an uncatalogued X-ray source at R.A. = 191.2598 deg, DEC = 23.8533 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic).
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).