Gamma-ray Burst 260314B = EP260314a

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN Circular #44009
Wenxiong Li, Runduo Liang (NAOC), Iair Arcavi, Ido Keinan (TAU), David Sand (U of Arizona)
We observed the position of the EP-WXT trigger 01709258851 with a Las Cumbres 1m telescope at Sutherland Observatory, South Africa, 50 mins after the Einstein Probe WXT trigger. We took 4x300s exposures in the broad optical w band. We didn’t detect any uncataloged source within the EP-WXT error circle down to a limiting r-band mag of 21.5 mag.
GCN Circular #44010
Yaqi Zhao (USTC, PRIC), Yue Wu (NJU), Rui-Zhi Li (YNAO, CAS) and Hai-Wu Pan (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 EP260314a. The transient triggered EP-WXT (ID: 01709258851) at 2026-03-14T22:51:36 (UTC). The WXT position of the source is R.A. = 211.845 deg, DEC = -23.445 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic).
A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 211.8437 deg, DEC = -23.4601 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic).
Further information will be updated when the telemetry data is 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).
GCN Circular #44013
H. L. Li, L. P. Xin, Y. N. Ma, C. Wu, Z. H. Yao, Y. L. Qiu, X. H. Han, J. Wang, Y. Xu, 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. T. Palmerio (CEA/Irfu) report on behalf of the SVOM/VT team.
SVOM/VT performed ToO observation of the field of EP260314a detected by Einstein Probe (Zhao et al., GCN 44010). The observation started at 2026-03-14T23:03:04 UTC, i.e., about 11.5 minutes post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously.
An uncatalogued optical source was detected in VT_R stacked image within the error box of FXT (Zhao et al., GCN 44010). The position is at R.A., Dec. = 211.842259, -23.457728 degrees, equivalent to:
```
 
    R.A. (J2000) = +14:07:22.14
    Dec. (J2000) = -23:27:27.82
```
with an uncertainty of 0.5 arcsec.
The measurements in AB magnitudes are given below:
```
    Mid_time       Band        Exposure Time     Magnitude (AB)
   1.07 hour       VT_R           29*50 sec      22.70+/-0.26 mag
   1.07 hour       VT_B           29*50 sec      > 23.0       mag
```
With the available data, we could not confirm the fading of the candidate.
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 #44014
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 EP260314a ( EP Team et al., GCN 44010) errorbox 18771 sec after notice time and 31448 sec after trigger time at 2026-03-15 07:35:44 UT, with upper limit up to 20.4 mag. The observations began at zenith distance = 10 deg. The sun altitude is -37.3 deg.
The galactic latitude b = 36 deg., longitude l = 325 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3187114
We obtain a following upper limits.

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

   31478 | 2026-03-15 07:35:44 |         MASTER-OAFA | (14h 03m 09.70s , -23d 05m 06.7s) |   C |    60 | 20.1 |        
   31538 | 2026-03-15 07:35:44 |         MASTER-OAFA | (14h 03m 09.70s , -23d 05m 06.8s) |   C |   180 | 20.4 |  Coadd 
   31555 | 2026-03-15 07:37:01 |         MASTER-OAFA | (14h 11m 52.28s , -23d 06m 44.8s) |   C |    60 | 20.0 |        
   31615 | 2026-03-15 07:37:01 |         MASTER-OAFA | (14h 11m 52.28s , -23d 06m 44.8s) |   C |   180 | 20.4 |  Coadd 
   31632 | 2026-03-15 07:38:17 |         MASTER-OAFA | (14h 03m 12.03s , -23d 05m 00.4s) |   C |    60 | 20.0 |        
   31707 | 2026-03-15 07:39:33 |         MASTER-OAFA | (14h 11m 49.57s , -23d 06m 01.9s) |   C |    60 | 20.0 |        
   31784 | 2026-03-15 07:40:49 |         MASTER-OAFA | (14h 03m 07.51s , -23d 04m 36.7s) |   C |    60 | 20.0 |        
   33575 | 2026-03-15 08:10:40 |         MASTER-OAFA | (14h 11m 51.09s , -23d 04m 19.3s) |   C |    60 | 20.0 |        
   33650 | 2026-03-15 08:11:56 |         MASTER-OAFA | (14h 11m 57.93s , -23d 05m 18.8s) |   C |    60 | 19.9 |        
   33710 | 2026-03-15 08:11:56 |         MASTER-OAFA | (14h 11m 57.94s , -23d 05m 18.8s) |   C |   180 | 20.4 |  Coadd 
   33726 | 2026-03-15 08:13:11 |         MASTER-OAFA | (14h 11m 51.16s , -23d 06m 17.7s) |   C |    60 | 19.8 |        
   33806 | 2026-03-15 08:14:32 |         MASTER-OAFA | (14h 03m 15.81s , -23d 05m 54.0s) |   C |    60 | 20.0 |        
   33866 | 2026-03-15 08:14:32 |         MASTER-OAFA | (14h 03m 15.81s , -23d 05m 54.1s) |   C |   180 | 20.4 |  Coadd 
   33886 | 2026-03-15 08:15:52 |         MASTER-OAFA | (14h 03m 12.24s , -23d 04m 20.5s) |   C |    60 | 20.1 |        
   33966 | 2026-03-15 08:17:12 |         MASTER-OAFA | (14h 03m 12.30s , -23d 05m 42.2s) |   C |    60 | 20.1 |        
   35185 | 2026-03-15 08:36:30 |             MASTER- | (14h 07m 08.18s , -23d 27m 00.1s) |   C |   180 | 19.3 |        
   35185 | 2026-03-15 08:36:30 |             MASTER- | (14h 08m 27.19s , -24d 01m 06.3s) |   C |   180 | 19.5 |        
   35377 | 2026-03-15 08:39:42 |             MASTER- | (14h 07m 13.49s , -23d 28m 05.1s) |   C |   180 | 19.6 |        
   35377 | 2026-03-15 08:39:42 |             MASTER- | (14h 08m 32.57s , -24d 02m 10.3s) |   C |   180 | 19.6 |        
   35568 | 2026-03-15 08:42:54 |             MASTER- | (14h 07m 08.52s , -23d 29m 07.4s) |   C |   180 | 19.5 |        
   35568 | 2026-03-15 08:42:54 |             MASTER- | (14h 08m 27.64s , -24d 03m 12.2s) |   C |   180 | 19.8 |        
   35534 | 2026-03-15 08:43:20 |         MASTER-OAFA | (14h 11m 56.24s , -23d 04m 00.8s) |   C |    60 | 19.9 |        
   35610 | 2026-03-15 08:44:36 |         MASTER-OAFA | (14h 11m 56.27s , -23d 05m 30.6s) |   C |    60 | 19.9 |        
   35760 | 2026-03-15 08:46:05 |             MASTER- | (14h 07m 13.91s , -23d 28m 54.9s) |   C |   180 | 19.3 |        
   35760 | 2026-03-15 08:46:05 |             MASTER- | (14h 08m 33.15s , -24d 02m 59.4s) |   C |   180 | 19.8 |        
   35891 | 2026-03-15 08:49:17 |         MASTER-OAFA | (14h 03m 17.80s , -23d 04m 26.7s) |   C |    60 | 20.0 |        
   35951 | 2026-03-15 08:49:17 |             MASTER- | (14h 07m 10.42s , -23d 27m 22.5s) |   C |   180 | 19.4 |        
   35951 | 2026-03-15 08:49:17 |             MASTER- | (14h 08m 29.74s , -24d 01m 26.6s) |   C |   180 | 19.9 |        
   36142 | 2026-03-15 08:52:28 |             MASTER- | (14h 07m 10.07s , -23d 29m 05.4s) |   C |   180 | 19.6 |        
   36142 | 2026-03-15 08:52:28 |             MASTER- | (14h 08m 29.52s , -24d 03m 08.8s) |   C |   180 | 19.8 |        
   36335 | 2026-03-15 08:55:40 |             MASTER- | (14h 07m 12.33s , -23d 27m 15.8s) |   C |   180 | 19.7 |        
   36335 | 2026-03-15 08:55:40 |             MASTER- | (14h 08m 31.87s , -24d 01m 18.8s) |   C |   180 | 19.9 |        
   36526 | 2026-03-15 08:58:52 |             MASTER- | (14h 07m 05.49s , -23d 28m 09.4s) |   C |   180 | 19.8 |        
   36526 | 2026-03-15 08:58:52 |             MASTER- | (14h 08m 25.17s , -24d 02m 11.9s) |   C |   180 | 19.8 |        
   36723 | 2026-03-15 09:02:09 |             MASTER- | (14h 07m 05.49s , -23d 27m 09.1s) |   C |   180 | 19.8 |        
   36723 | 2026-03-15 09:02:09 |             MASTER- | (14h 08m 25.25s , -24d 01m 11.3s) |   C |   180 | 19.8 |        
   36914 | 2026-03-15 09:05:20 |             MASTER- | (14h 07m 12.73s , -23d 28m 09.7s) |   C |   180 | 19.7 |        
   36914 | 2026-03-15 09:05:20 |             MASTER- | (14h 08m 32.56s , -24d 02m 11.3s) |   C |   180 | 19.8 |        
   37105 | 2026-03-15 09:08:31 |             MASTER- | (14h 07m 05.16s , -23d 29m 09.4s) |   C |   180 | 19.7 |        
   37105 | 2026-03-15 09:08:31 |             MASTER- | (14h 08m 25.09s , -24d 03m 10.6s) |   C |   180 | 19.6 |

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

GCN Circular #44015
I. Pérez-García, E. Fernández-García, M.D. Caballero-García, M. Gritsevich, S. Guziy, R. Sánchez-Ramírez, S.-Y. Wu, and A. J. Castro-Tirado (IAA-CSIC, Granada), P. J. Meintjes and H. J. van Heerden (UFS, South Africa), A. Martín-Carrillo and L. Hanlon (UCD, Ireland), Y.-D. Hu (GXU), D. R. Xiong (Yunnan Observatories of CAS) and C. J. Pérez del Pulgar (UMA, Malaga), on behalf of a larger collaboration, report:
Following the detection of EP260314a by Einstein Probe (Zhao et al., GCNC 44010), the BOOTES-6/DPRT 0.6m robotic telescope at Boyden Observatory in Maselspoort (South Africa) responded to this event starting on Mar 14, 23:00:01 UT (~ 8.5 min after trigger) with a 10s clear filter image. No new source is detected at the position of the proposed optical counterpart by SVOM/VT (Li et al., GCNC 44013) up to magnitude 16.3 using Gaia DR3 Gmag magnitude as reference on our first image. Further images were gathered and using ATLAS REFCAT2 as reference (Tonry et al. 2018) we get upper limits of: 18.5 (60s clear, at 23:03 UT), 20.9 (300s clear, at 23:06 UT) and 21.7 (600s clear, at 23:18 UT), in agreement with the upper limit reported by LCO (Li et al. GCNC 44009).
We thank the staff at Boyden Observatory for their excellent support.
GCN Circular #44016
Yue Wu (NJU), Rui-Zhi Li (YNAO, CAS), Yaqi Zhao (USTC, PRIC) and Hai-Wu Pan (NAOC) on behalf of the Einstein Probe (EP) team:
The fast X-ray transient EP260314a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Zhao et al., GCN 44010). The transient was detected immediately when WXT observation started at T0=2026-03-14T22:51:20. The WXT observation lasted for approximately 16 seconds, and was interrupted due to the autonomous follow-up observation. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a hydrogen column density of 0.54（-0.27/+0.32）×10^22 cm^-2 and a photon index of 1.81(-0.75/+0.83). The derived average unabsorbed 0.5-4 keV flux is 2.14 (-0.55/+1.13) × 10^(-8) erg/s/cm^2.
The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously at 2026-03-14T22:54:51 (UTC, T0+211 s). The exposure time of this observation is 2.9ks. On-ground analysis of the FXT data found an uncatalogued source at R.A., Dec. = 211.8426, -23.4577 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), which is consistent with the WXT position. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 0.22 (-0.07/+0.07) × 10^22 cm^-2 and a photon index of 2.21 (-0.27/+0.28). The derived average unabsorbed 0.5-10 keV flux is 5.11 (+0.46/-0.41) × 10^(-12) erg/s/cm^2.
A follow-up observation with the EP/FXT was planned, and further information will be updated when the telemetry data is received.
The optical follow-up observations were performed by Li et al. (GCN 44009), Li et al. (GCN 44013), Lipunov et al. (GCN 44014) and Pérez-García et al. (GCN 44015). We note that the SVOM/VT candidate (Li et al., GCN 44013) is located within the 10 arcsec error circle of EP/FXT. Further multi-band follow-up observations are encouraged to explore the nature of EP260314a.
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 #44019
Francis Fortin (IRAP), Edilberto Aguilar-Ruiz (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), Jean-Grégoire Ducoin (CPPM), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Missimiliano Lincetto (CPPM), 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 EP260314a (Zhao et al., GCN Circ. 44010, Wu et al., GCN Circ. 44016) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-03-15 04:49:56 to 11:14:09 UTC (from 9.1 to 12.4 hours after the trigger) and obtained 144 minutes of simultaneous exposure in the i and z filters.
The data were reduced and coadded 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.
In the stacked image, we do not detect the SVOM/VT optical counterpart candidate reported by Li et al., GCN Circ. 44013 down to the following 3-sigma limit:
```
i > 24.08
z > 23.17
```
While a direct comparison of magnitudes between the i, z filters and the VT filters is not possible, we suggest that our limits may be consistent with a fading of the VT optical candidate, which would strengthen the hypothesis that it is the true counterpart of EP260314A.
We thank the staff of the Observatorio Astronómico Nacional at Sierra de San Pedro Mártir, as well as the technical and engineering teams at CEA, CPPM, IRAP, LAM, OHP, OSU Pytheas, and UNAM.
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 #44024
C.-H. Lai, A. Aryan, Y.-H. Lee, 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), A. Sankar.K, M.-H. Lee, 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 EP260314a (Zhao et al., GCN 44010; Wu et al., GCN 44016) using the 1m LOT at the Lulin observatory, as part of the Kinder collaboration (Chen et al. 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). The first LOT epoch of observations in g-band started at 16:09 UTC on 15th of March 2026 (MJD 61114.673), 17.52 hr after the EP-WXT detection.
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 DESI Legacy Survey (Dey et al. 2019, AJ 157, 168) DR10 image using the 'SFFT' (Hu et al. 2022, ApJ, 936, 157) algorithm. Neither in the stacked nor in the difference image did we detect any signature of the optical counterpart candidate reported by Li et al., (GCN 44013).
Moreover, we further used AutoPhOT to perform PSF photometry. The details of the observations and the 3-sigma upper limit (in the AB system) are as follows:
```
Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude| avg. Seeing  | Med. Airmass               
LOT       | r      | 61114.673   | 17.52     | 300 * 6      | >22.8    | 1".31        | 1.81     
```
Our upper limit is consistent with previously reported non-detections (Lipunov et al., GCN 44014; Pérez-García et al., GCN 44015; Fortin et al., GCN 44019).
The presented magnitudes are calibrated using the field stars from the ATLAS-refcat2 catalog from MAST (Tonry J. L. et al. 2018, ApJ, 867, 105). The reported upper limit is not corrected for an expected galactic extinction of A_r = 0.16 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 #44025
Junbo-Zhang (NAOC), Junjie-Jin (NAOC), Haiyang-Mu (NAOC), Feng-Xiao (NAOC), Jie-Zheng(NAOC), Zhou-Fan (NAOC), Hong-Wu (NAOC) report on behalf of a large collaboration:
Following the detection of EP260314a by EP-WXT (Zhao et al., GCN 44010; Wu et al., GCN 44016), we observed the field of EP260314a using the 2.16-m telescope at Xinglong Observatory, NAOC. We obtained 3x600s clear-band frames with a median time of 2026-03-15 17:58:07 (UT), 19.11 hr after the EP trigger.
No uncatalogued optical transient is detected in the stacked images within the 3 arcmin EP/WXT error circle (Zhao et al., GCN 44010; Wu et al., GCN 44016), down to 3-sigma limiting magnitudes of g ~21.5, calibrated with Pan-STARRS sources in the field. Also there is no apparent brightening for the catalogued sources within the error circle.

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