EP251214a
GCN Circular 43135
Subject
EP251214a: Optical upper limit with Kinder observations
Date
2025-12-16T04:56:08Z (18 hours ago)
From
Janet Chen at National Central University <janetstars@gmail.com>
Via
Web form
A. Aryan, T.-W. Chen, H.-Y. Hsiao, C.-S. Lin (all NCU), A. K. H. Kong (NTHU), J. Gillanders, S. J. Smartt (both Oxford), Y. J. Yang (NYUAD), Y.-H. Lee, A. Sankar.K, Y.-C. Pan, C.-C. Ngeow, M.-H. Lee, C.-H. Lai, W.-J. Hou, 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 EP251214a (Yin et al., GCN 43087; GCN 43102) using the 40 cm SLT at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). The first SLT epoch of observations started at 16:25 UTC on the 14th of December 2025 (MJD 61023.684), 13.97 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 utilized the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform template subtraction with the Pan-STARRS1 3Pi (Chambers et al., 2016 arXiv:1612.05560) image using the 'sfft' (Hu et al., 2022, ApJ, 936, 157) algorithm. We do not find any evidence of a new and uncataloged optical counterpart candidate within the 3.1 arcminute error circle of the EP-WXT localization in either the stacked or the difference image.
Moreover, we further utilized AutoPhOT to perform PSF photometry. The details of the observations and the measured upper limit (in the AB system) are as follows:
Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass
SLT | i | 61023.684 | 13.97 | 300 * 24 | >21.9 | 1".3 | 1.30
Our non-detection is consistent with Basa et al. (GCN 43092); Lipunov et al. (GCN 43099); Zheng et al. (GCN 43110). The absence of any associated optical counterpart down to 21.9 mag with the optical observations starting within 24 hours of its X-ray discovery aligns well with the 'Dark' nature of FXTs (Aryan et al., 2025, ApJS, 281, 20, doi:10.3847/1538-4365/adfc69).
The presented magnitude is calibrated using the field stars from the Pan-STARRS DR2 catalog and is not corrected for the expected Galactic foreground extinction of A_i = 0.05 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 can be found in Aryan et al. (2025).
GCN Circular 43110
Subject
EP251214a: KAIT optical upper limit
Date
2025-12-15T07:28:01Z (2 days ago)
From
Weikang Zheng at UC Berkeley <weikang@berkeley.edu>
Via
email
WeiKang Zheng (UCB), Xuhui Han (NAOC), Pinpin Zhang (NAOC) and
Alexei V. Filippenko (UCB) report on behalf of the KAIT GRB team:
The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at
Lick Observatory, observed the field of EP251214a (Yin et al.,
GCN 43087; 43102) starting at 08:58, Dec 14 UT, about 6.52 hours
after the burst. A set of 129x60s clear (roughly R) filter images
were obtained. In our coadd image, we did not detect any new source
within the EP-WXT error circle (Yin et al., GCN 43087) down to a
limiting mag of 21.6 mag (Vega) at a mid-time of 8.88 hours after
the burst. Our result is consistent with the upper limit reported
by other groups (Basa et al., GCN 43092; Lipunov et al., GCN 43099).
GCN Circular 43102
Subject
EP251214a: EP-FXT non-detection and upper limit
Date
2025-12-15T02:22:09Z (2 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Y.-H. I. Yin (HKU), Y. H. Jiang (NJU), Y. Q. Zhao (PRIC,USTC), W. F. Wen (SZTU), H. Q. Cheng, and H. Sun (NAOC) on behalf of the Einstein Probe (EP) team:
EP-FXT observed the field of EP251214a (Yin et al., GCN 43087) for 2997 seconds starting at 2025-12-14T15:14:34, around 13 hours after the detection by EP-WXT. No significant X-ray source is detected within the 3.1 arcmin radius of the EP-WXT position (Yin et al., GCN 43087) to a preliminary 0.5-10 keV upper limit of 7e-14 erg/cm2/s.
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 43099
Subject
EP251214a: Global MASTER-Net observations report
Date
2025-12-14T19:09:20Z (2 days ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko,
G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU),
O.Gress, N.Budnev (ISU),
C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A.Sosnovskij (CrAO),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity),
D.Buckley (SAAO),
R.Rebolo (The Instituto de Astrofisica de Canarias),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory)
MASTER-Tunka robotic telescope [1] located in Russia (Applied Physics Institute, Irkutsk State University) was pointed to the EP251214a ( EP Team et al., GCN 43087) errorbox 23345 sec after notice time and 44450 sec after trigger time at 2025-12-14 14:47:51 UT, with upper limit up to 20.0 mag. The observations began at zenith distance = 80 deg. The sun altitude is -52.2 deg.
The galactic latitude b = 50 deg., longitude l = 212 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3070739
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
11367 | 2025-12-14 05:35:57 | MASTER- | (09h 49m 46.34s , +21d 15m 33.3s) | C | 60 | 17.1 |
12140 | 2025-12-14 05:48:51 | MASTER- | (09h 47m 03.54s , +20d 23m 17.9s) | C | 60 | 18.1 |
12140 | 2025-12-14 05:48:51 | MASTER- | (09h 58m 23.13s , +19d 21m 03.2s) | C | 60 | 17.0 |
12427 | 2025-12-14 05:53:37 | MASTER- | (09h 54m 39.28s , +22d 17m 23.3s) | C | 60 | 18.4 |
28176 | 2025-12-14 10:15:06 | MASTER- | (09h 45m 41.72s , +21d 23m 05.5s) | C | 180 | 19.6 |
28176 | 2025-12-14 10:15:06 | MASTER- | (09h 57m 15.83s , +20d 21m 58.5s) | C | 180 | 19.3 |
44480 | 2025-12-14 14:47:51 | MASTER-Tunka | (09h 53m 14.05s , +20d 49m 09.6s) | C | 60 | 18.4 |
57811 | 2025-12-14 18:30:01 | MASTER-Tunka | (09h 50m 07.21s , +22d 38m 41.9s) | C | 60 | 20.0 |
57812 | 2025-12-14 18:30:02 | MASTER-Tunka | (09h 49m 36.25s , +22d 46m 24.5s) | C | 60 | 19.6 |
59105 | 2025-12-14 18:51:35 | MASTER-Tunka | (09h 58m 44.22s , +20d 43m 39.4s) | C | 60 | 19.6 |
59105 | 2025-12-14 18:51:35 | MASTER-Tunka | (09h 58m 13.62s , +20d 51m 19.9s) | C | 60 | 19.1 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
[1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp.
http : // www.pereplet.ru/lipunov/625.html
GCN Circular 43092
Subject
EP251214a: COLIBRÍ optical upper limit
Date
2025-12-14T11:44:06Z (2 days ago)
From
Stephane Basa at UAR Pytheas/OHP, LAM <stephane.basa@lam.fr>
Via
Web form
Stéphane Basa (UAR Pytheas), Leonardo García García (UNAM), Noémie Globus (UNAM), Benjamin Schneider (LAM), Jean-Grégoire Ducoin (CPPM), William H. Lee (UNAM), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Ramandeep Gill (UNAM), Enrique Moreno Méndez (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Nikos Mandarakas (LAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), and Antonio de Ugarte Postigo (LAM).
We imaged the field of EP251214a (Y.-H. I. Yin et al., GCN Circ. 43087) potentially associated with GRB 251214A reported by the Fermi GBM Team (GCN Circ. 43085), using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-12-14 at 09:12:10.65 to 09:56:13.15 UTC (from 6.75 to 7.49 hr after the trigger) and obtained 32 minutes of simultaneous exposure in the r and z filters.
The data were reduced, coadded and analyzed with the COLIBRÍ pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and was not corrected for Galactic extinction.
In the stacked image, we do not detect any new source at the WXT uncertainty region (Y.-H. I. Yin et al., GCN Circ. 43087) down to the following 5-sigma limit:
r > 23.1
z > 21.6
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 43087
Subject
EP251214a: EP-WXT detection of an X-ray transient possibly associated with GRB 251214A
Date
2025-12-14T08:15:25Z (3 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Y.-H. I. Yin (HKU), Y. H. Jiang (NJU), Y. Q. Zhao (PRIC, USTC), W. F. Wen (SZTU), H. Q. Cheng, and H. Sun (NAOC) on behalf of the Einstein Probe (EP) team:
We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP251214a. The source, with a signal-to-noise ratio of 6, did not trigger the WXT on-board trigger unit. The observation started at 2025-12-14T02:27:01 (UTC) and lasted for 3043 seconds. The WXT position of the source is R.A. = 148.471 deg, DEC = 21.053 deg (J2000) with an uncertainty of 3.1 arcmin in radius (90% C.L. statistical and systematic).
The average WXT 0.5 - 4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 2.82 x 10^20 cm^-2 and a photon index of 1.84 (-/+0.94). The derived average unabsorbed 0.5-4 keV flux is 1.05 (-0.42/+0.70) x 10^-11 erg/s/cm^2.
The position of EP251214a is around 4.86 deg away from GRB 251214A reported by the Fermi GBM Team (GCN 43085), and the observation was carried out around 2 hours after the GRB trigger. Given the temporal proximity and spatial consistency, we thus consider the EP-WXT detection the possible X-ray afterglow of GRB 251214A. EP-FXT follow-up observation has 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).