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EP260514a

GCN Circular 44641

Subject
EP260514a: refined analysis of the EP-WXT and follow-up EP-FXT observations
Date
2026-05-16T08:08:24Z (14 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Y.-H. Cheng (SWIFAR, YNU), K.R. Ni (CCNU), R.-Z. Li (YNAO, CAS) and W.-D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team:

The X-ray transient EP260514a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Cheng et al., GCN 44613) at 2026-05-14T16:56:06 (UTC). The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 1.49 × 10^20 cm^-2, and a photon index of 1.32 (+/-0.22). The derived average unabsorbed 0.5-4 keV flux is 4.24 (+0.70/-0.60) × 10^(-10) erg/s/cm^2.

Follow-up observation by the Follow-up X-ray Telescope (FXT) on board EP was performed at 2026-05-15 08:20:00(UTC), ~15.5 hours after the WXT detection. The exposure time of the observation is around 5 ks. The on-ground analysis of the FXT data found an uncatalogued source at R.A. = 214.2955 deg, DEC = 49.3733 deg (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The average FXT 0.5-10 keV spectra can be fitted with an absorbed power-law with a fixed hydrogen column density of 1.49 × 10^20 cm^-2 and a photon index of 1.28 (+0.76/-0.67). The derived average unabsorbed 0.5-10 keV flux is 2.28 (-0.55/+1.17) × 10^(-13) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. 

The optical observations of EP260514a were reported by Lipunov et al. (GCN 44614), Mohan et al. (GCN 44619), Sánchez et al. (GCN 44632) and Li et al. (GCN 44638), Liu et al.,(GCN 44639) and Liu et al.,(GCN 44640).

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 44640

Subject
EP260514a: NOT optical counterpart confirmation
Date
2026-05-16T07:51:09Z (14 days ago)
From
liuxing@nao.cas.cn
Via
Web form
X. Liu, Z.P. Zhu, J. An,  S.Q. Jiang, L.B. He, D. Xu (NAOC), S.Y. Fu (HUST), J.P.U. Fynbo (DAWN/NBI), L. Fuglsang, A. S. Martensson（NOT）report:

We observed the field of EP260514a detected by EP/WXT (Cheng et al., GCN 44613; Lipunov et al., GCN 44614; Mohan et al., GCN 44619; Sánchez et al., GCN 44632; Li et al., GCN 44638; Liu et al., GCN 44639) using the 2.56m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observation started at 2026-05-15 23:05:35 UT, i.e., about 1.26 days post-burst, and 4x300s r-band frames were obtained.

The optical counterpart candidate (Liu et al., GCN 44639) has decayed to r = 23.1 +/- 0.1 in our stacked image at a median time of 1.26 days post-trigger, calibrated with Pan-STARRS DR2 stars in the field and not corrected for Galactic extinction. Its coordinares are improved as

R.A.(J2000)= 14:17:10.49
Dec.(J2000)= +49:22:31.4
with an uncertainty of ~0.5 arcsec.

No optical source could be detected in the Legacy DR10 image at the corresponding coordinates, down to a limiting magnitude of r ~ 24.3.

We thus think the source is likely the optical counterpart of EP260514a.

GCN Circular 44639

Subject
EP260514a: TRT optical counterpart candidate
Date
2026-05-16T07:39:15Z (14 days ago)
Edited On
2026-05-17T22:41:06Z (12 days ago)
From
liuxing@nao.cas.cn
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of liuxing@nao.cas.cn
Via
Web form
X. Liu, (NAOC), S. Tinyanont, R. Anutarawiramkul, P. Butpan, K. Noysena, K. Chanchaiworawit (NARIT), S.Q. Jiang, J. An, Z.P. Zhu, L.B. He, D. Xu, Z. Fan, W.X. Li, N.C. Sun (NAOC), S.Y. Fu (HUST) report:

We observed the field of EP260514a dtected by EP/WXT (Cheng et al., GCN 44613; Lipunov et al., GCN 44614; Mohan et al., GCN 44619; Sánchez et al., GCN 44632; Li et al., GCN 44638), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Fresno, California, U.S.A (SRO). Observation started at 2026-05-15 04:25:07 UT, i.e., 0.48 day post-burst, and 6x300 s R-band frames were obtained. 

Image subtraction using Legacy-DR10 reveals an uncatalogued optical source within the EP/WXT (Cheng et al., GCN 44613) error circle at coordinates
R.A. (J2000) = 14:17:10.41
Dec. (J2000) = +49:22:30.9

with an uncertainty of ~ 1.5 arcsec. The source had R ~ 21.8 mag with SNR of ~3 at a median time of 11.74 hrs post-trigger, calibrated with Pan-STARRS DR2 converted using Lupton (2005) equations and not corrected for Galactic extinction.

The magnitude is consistent with those reported by SVOM/VT (Li et al., GCN 44638). No NEO would be at the above position at the observational time by checking MPC.

We think the source could be the optical cointerpart of EP260514a.

GCN Circular 44638

Subject
EP260514a: SVOM/VT optical candidate
Date
2026-05-16T06:59:29Z (14 days ago)
Edited On
2026-05-17T22:42:28Z (12 days ago)
From
Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>
Via
Web form
H. L. Li, Y. L. Qiu, C. Wu,  L. P. Xin, Y. N. Ma, Z. H. Yao, J. R. Xu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC) and J. Palmerio  report on behalf of the SVOM/VT team.

SVOM/VT performed ToO observations to the field of EP260514a (Lipunov et al., GCN 44614; Mohan et al., GCN 44619; Sánchez et al., GCN 44632), which was triggered by Einstein Probe (EP260514a, Cheng et al., GCN 44613). The observation started at 2026-05-15T03:03:58 UTC, 10.13 hours post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously.  

An uncatalogued optical source was detected within WXT's error box (Cheng et al., GCN 44613) in both channels, compared to the Legacy Survey. The position is at R.A., Dec. = 214.293637, 49.375378  degrees, equivalent to:
R.A. (J2000) =  14:17:10.47
Dec. (J2000) =  +49:22:31.36
with an uncertainty of 0.5 arcsec.

The following measurements are in the AB magnitude without correction for Galactic extinction:

Mid time | Band | Exposure Time | Brightness
11.96 h    VT_B     44*50 s     23.15 +/- 0.22 mag
11.97 h    VT_R     39*50 s     22.03 +/- 0.14 mag    

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 44632

Subject
EP260514a: COLIBRÍ optical upper limits
Date
2026-05-16T03:23:14Z (14 days ago)
From
freddalvarez@astro.unam.mx
Via
Web form

Fredd Sánchez Álvarez (UNAM), Noémie Globus (UNAM), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Jean-Grégoire Ducoin (CPPM), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), and Antonio de Ugarte Postigo (LAM) report:

We imaged the field of the EP260514a detected by Einstein Probe/WXT (Cheng et al., GCN Circ. 44613 ) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-05-15 03:27 to 03:44 UTC, corresponding to 10.52 to 10.80 hours after the trigger, and obtained 14 minutes of simultaneous exposure in the r and z filters.

The data were reduced and coadded with the COLIBRÍ ASU pipeline and analysed with STDWeb/STDPipe (Karpov 2025). 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 images and after performing image subtraction using templates from the DESI Legacy Survey (Dey et al. 2019), we do not detect any new sources within the WXT error region (Cheng et al., GCN Circ. 44613) down to the following 5-sigma limits:

r > 22.1.
z > 20.9.

Our upper limits are consistent with the previously reported by MASTER (Lipunov et al., GCN Circ. 44614) and GROWTH-India Telescope (Mohan et al., GCN Circ. 44619). 

We note the presence of four quasars:

SDSS J141722.46+492142.1
SDSS J141658.83+492220.9
SDSS J141720.92+492351.5
SDSS J141653.45+492109.8

within the WXT region and, considering our upper limits, we cannot rule out the possibility that the trigger is related to one of these sources.

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 44619

Subject
EP260514a: GROWTH-India Telescope optical upper limit
Date
2026-05-15T17:20:18Z (14 days ago)
From
V. Swain at IIT Bombay <vishwajeet.s@iitb.ac.in>
Via
Web form

T. Mohan (IITB), V. Vijaykumar (IITB), V. Swain (IITB), D. Eappachen (IIA), A.P. Saikia (IITB), S. Patil (IITB), V. Bhalerao (IITB), G.C. Anupama (IIA), S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team:

We observed the field of EP260514a (Cheng et al., GCN 44613

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), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2026-05-15 16:27:06 (UTC), i.e., 0.98 days after the trigger, and obtained single exposure in the r' filter. We did not detect any transient in our image within the WXT localization region. The photometric upper limit is as follows:

MJD (mid)Filtertmid-t0 (hour)Exposure Time (sec)Upper limit (AB)
61175.68756r'23.5736020.5

The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction.

Our results are consistent with other optical observation (Lipunov et al., GCN 44614

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).

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 44614

Subject
EP260514a: Global MASTER-Net observations report
Date
2026-05-15T03:27:20Z (15 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-OAFA robotic telescope  [1]  located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP260514a ( EP Team et al., GCN 44613) errorbox 35348 sec after trigger time at 2026-05-15 02:45:14 UT, with upper limit up to  18.6 mag. The observations began at zenith distance = 81 deg. The sun  altitude  is -63.2 deg. 

The galactic latitude b = 62 deg., longitude l = 91 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=3315353

We obtain a following upper limits.  

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

   35378 | 2026-05-15 02:45:14 |         MASTER-OAFA | (14h 15m 58.14s , +49d 22m 48.5s) |   C |    60 | 18.0 |        
   35443 | 2026-05-15 02:46:19 |         MASTER-OAFA | (14h 15m 57.12s , +49d 22m 52.2s) |   C |    60 | 18.0 |        
   35509 | 2026-05-15 02:47:24 |         MASTER-OAFA | (14h 15m 56.10s , +49d 22m 55.1s) |   C |    60 | 18.3 |        
   35575 | 2026-05-15 02:48:31 |         MASTER-OAFA | (14h 15m 54.95s , +49d 22m 57.3s) |   C |    60 | 18.2 |        
   35641 | 2026-05-15 02:49:37 |         MASTER-OAFA | (14h 15m 54.43s , +49d 23m 01.2s) |   C |    60 | 18.3 |        
   35701 | 2026-05-15 02:49:37 |         MASTER-OAFA | (14h 15m 54.41s , +49d 23m 01.1s) |   C |   180 | 18.6 |  Coadd 
   35707 | 2026-05-15 02:50:42 |         MASTER-OAFA | (14h 15m 54.22s , +49d 23m 03.8s) |   C |    60 | 18.2 |        
   35773 | 2026-05-15 02:51:49 |         MASTER-OAFA | (14h 15m 54.02s , +49d 23m 06.1s) |   C |    60 | 17.9 |        
   35838 | 2026-05-15 02:52:54 |         MASTER-OAFA | (14h 15m 53.77s , +49d 23m 08.7s) |   C |    60 | 18.0 |        
   35904 | 2026-05-15 02:53:59 |         MASTER-OAFA | (14h 15m 53.54s , +49d 23m 11.4s) |   C |    60 | 18.1 |        
   35970 | 2026-05-15 02:55:05 |         MASTER-OAFA | (14h 15m 53.30s , +49d 23m 11.7s) |   C |    60 | 18.2 |        
   36035 | 2026-05-15 02:56:11 |         MASTER-OAFA | (14h 15m 53.06s , +49d 23m 14.8s) |   C |    60 | 18.4 |        
   36101 | 2026-05-15 02:57:16 |         MASTER-OAFA | (14h 15m 52.80s , +49d 23m 16.2s) |   C |    60 | 18.4 |        
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 44613

Subject
EP260514a: Einstein Probe detection of a fast X-ray transient
Date
2026-05-15T03:20:32Z (15 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Y.-H. Cheng (SWIFAR, YNU), K.R. Ni (CCNU), R.-Z. Li (YNAO, CAS) and W.-D. Zhang (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 EP260514a. The ground analysis of the WXT data shows that the event started at T0 = 2026-05-14T16:56:06 (UTC) and lasted for around 500 s. The WXT position of the source is R.A. = 214.297 deg, DEC = 49.365 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) on board EP has been scheduled. 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).
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