EP251212a

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-OAFA robotic telescope  [1]  located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP251212a ( EP Team et al., GCN 43081
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 ) errorbox  7432 sec after notice time and 60333 sec after trigger time at 2025-12-13 06:29:42 UT, with upper limit up to  20.8 mag. The observations began at zenith distance = 21 deg. The sun  altitude  is -28.6 deg. 

MASTER-Tunka robotic telescope  located in Russia (Applied Physics Institute, Irkutsk State University) was pointed to the EP251212a errorbox  56042 sec after notice time and 1 days 22543 sec after trigger time at 2025-12-13 19:59:52 UT, with upper limit up to  17.4 mag. The observations began at zenith distance = 74 deg. The sun  altitude  is -45.8 deg. 

The galactic latitude b = 14 deg., longitude l = 249 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=3069779

We obtain a following upper limits.  

Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

   60363 | 2025-12-13 06:29:42 |         MASTER-OAFA | (08h 52m 06.66s , -23d 02m 09.3s) |   C |    60 | 20.0 |        
   60544 | 2025-12-13 06:32:43 |         MASTER-OAFA | (08h 52m 13.47s , -23d 02m 07.8s) |   C |    60 | 20.0 |        
   60724 | 2025-12-13 06:35:42 |         MASTER-OAFA | (08h 52m 12.36s , -23d 02m 47.2s) |   C |    60 | 19.8 |        
   60799 | 2025-12-13 06:36:58 |         MASTER-OAFA | (09h 00m 51.90s , -23d 01m 25.6s) |   C |    60 | 20.0 |        
   60949 | 2025-12-13 06:36:58 |         MASTER-OAFA | (09h 00m 51.89s , -23d 01m 25.7s) |   C |   360 | 20.8 |  Coadd 
   60878 | 2025-12-13 06:38:16 |         MASTER-OAFA | (09h 00m 52.01s , -23d 02m 51.7s) |   C |    60 | 20.0 |        
   60952 | 2025-12-13 06:39:31 |         MASTER-OAFA | (09h 00m 55.66s , -23d 01m 23.0s) |   C |    60 | 20.0 |        
   62872 | 2025-12-13 07:11:31 |         MASTER-OAFA | (09h 00m 51.73s , -23d 02m 08.7s) |   C |    60 | 20.0 |        
   62949 | 2025-12-13 07:12:47 |         MASTER-OAFA | (09h 00m 56.52s , -23d 01m 41.3s) |   C |    60 | 20.0 |        
   63023 | 2025-12-13 07:14:02 |         MASTER-OAFA | (09h 00m 54.42s , -23d 00m 05.6s) |   C |    60 | 20.1 |        
  108959 | 2025-12-13 19:59:52 |        MASTER-Tunka | (08h 56m 23.31s , -22d 50m 56.5s) |   C |    30 | 15.9 |        
  109002 | 2025-12-13 20:00:36 |        MASTER-Tunka | (08h 56m 22.49s , -22d 49m 57.8s) |   C |    30 | 15.9 |        
  109050 | 2025-12-13 20:01:24 |        MASTER-Tunka | (08h 56m 28.21s , -22d 50m 58.5s) |   C |    30 | 16.2 |        
  109094 | 2025-12-13 20:02:07 |        MASTER-Tunka | (08h 56m 21.99s , -22d 52m 00.7s) |   C |    30 | 16.6 |        
  109094 | 2025-12-13 20:02:07 |        MASTER-Tunka | (08h 56m 04.58s , -22d 45m 54.5s) |   C |    30 | 14.9 |        
  109145 | 2025-12-13 20:02:58 |        MASTER-Tunka | (08h 56m 27.67s , -22d 51m 54.9s) |   C |    30 | 16.9 |        
  109145 | 2025-12-13 20:02:58 |        MASTER-Tunka | (08h 56m 11.31s , -22d 45m 17.0s) |   C |    30 | 12.4 |        
  109186 | 2025-12-13 20:03:40 |        MASTER-Tunka | (08h 56m 25.45s , -22d 50m 22.2s) |   C |    30 | 17.3 |        
  109186 | 2025-12-13 20:03:40 |        MASTER-Tunka | (08h 56m 06.73s , -22d 43m 38.7s) |   C |    30 | 13.0 |        
  109230 | 2025-12-13 20:04:23 |        MASTER-Tunka | (08h 56m 25.51s , -22d 52m 02.9s) |   C |    30 | 17.4 |        
  109230 | 2025-12-13 20:04:23 |        MASTER-Tunka | (08h 56m 06.86s , -22d 45m 19.2s) |   C |    30 | 12.9 |        
  109273 | 2025-12-13 20:05:06 |        MASTER-Tunka | (08h 56m 13.03s , -22d 43m 50.4s) |   C |    30 | 12.6 |        
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

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 EP251212a (Yang et al.,

GCN 43076
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 ; Salunke et al., GCN 43082
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 ) starting at 11:09, Dec 12 UT,

about 4.95 hours after the burst. A set of 38x60s clear (roughly R)

filter images were obtained. In our coadd image, we did not detect

any new source within the EP-FXT error circle (Yang et al., GCN

43081
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 ) down to a limiting mag of 21.2 mag (Vega) at a mid-time of

5.57 hours after the burst. Our result is consistent with the upper

limit reported from COLIBRÍ observations (Ducoin et al., GCN 43077
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 ).

S. Salunke (IUCAA), M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), A. Arya (IITB), A. Goyal (IITB), G. Waratkar (Caltech/IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:

Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of GRB 251212A which was also detected by Konus-Wind (via IPN Notices), about 20 s after the trigger time of EP251212a detected by Einstein Probe / WXT (Yang et. al., GCN Circ. 43076
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 ).

The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-12-12 06:13:13.50 UTC. The measured peak count rate associated with the burst is 64 (+20, -21) counts/s above the background in the data of one quadrant (out of four), with a total of 136 (+55, -58) counts. The local mean background count rate was 83 (+2, -2) counts/s. Using cumulative rates, we measure a T90 of 5.6 (+0.6, -3.8) s. 

The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-12-12 06:13:13.22 UTC. The measured peak count rate associated with the burst is 475 (+72, -74) counts/s above the background in the combined data of all quadrants, with a total of 1524 (+245, -269) counts. The local mean background count rate was 1568 (+7, -9) counts/s. We measure a T90 of 5.7 (+0.9, -1.9) s from the cumulative Veto light curve.

CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project.

CZTI GRB detections are reported regularly on the payload site at:
http://astrosat.iucaa.in/czti/?q=grb

J. Yang (ZZU), Y. H. Jiang (NJU), Z. X. Li, G. L. Huang, J. Y. Cao (IHEP), S. Y. Fu (HUST), Z. X. Ling (NAOC) on behalf of the Einstein Probe (EP) team:

EP-FXT performed a follow-up observation of EP251212a (GCN 43076
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 ) at 2025-12-12T13:44:09 (UTC), about 7.5 hours after the WXT detection, with an exposure time of 2.7 ks. FXT detected an uncatalogued source within the WXT error circle at R.A. = 134.0471, DEC = -23.2992 (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 of 1.1 x 10^21 cm^-2 and a photon index of 1.7. The derived unabsorbed 0.5-10 keV flux is approximately 1.54 x 10^-12 erg/s/cm^2.

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).

Jean-Grégoire Ducoin (CPPM), Enrique Moreno Méndez (UNAM), Stéphane Basa (UAR Pytheas), 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), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (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), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM):

We imaged the field of the EP251212a (Yang et al., GCN Circ. 43076
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 ) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-12-12T11:08:54.118 to 11:27:56.049 UTC (from 4.94 to 5.25 hours after the trigger) and obtained 960 seconds 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 (Yang et al., GCN Circ. 43076
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 ) down to the following 5-sigma limit:

r > 22.59
z > 21.41

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.

J. Yang (ZZU), Y. H. Jiang (NJU), Z. X. Li, G. L. Huang, J. Y. Cao (IHEP), S. Y. Fu (HUST), Z. X. Ling (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 EP251212a. The source did not trigger the WXT on-board trigger unit. A GCN Notice was sent manually (trigger ID: 11916652735). The ground analysis of the WXT data shows that the event started at T0=2025-12-12T06:12:52 (UTC) and lasted for around 100 seconds. The WXT position of the source is R.A. = 134.041 deg, DEC = -23.279 deg (J2000) with an uncertainty of 2.4 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 hydrogen column density of 3.6 x 10^21 cm^-2 and a photon index of 1.1. The derived average unabsorbed 0.5-4 keV flux is 2.0 x 10^-9 erg/s/cm^2. 

The follow-up observation with the Follow-up X-ray Telescope (FXT) has been scheduled. Further information will be updated when the FXT telemetry data are received. 

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).