EP260512a
GCN Circular 44612
Subject
EP260512a: LCO optical upper limits
Date
2026-05-14T18:45:03Z (15 days ago)
From
Jonathan Quirola at Radboud University <jaquirola1990@gmail.com>
Via
Web form
J. Quirola-Vasquez (Radboud), R. A. J. Eyles-Ferris (Leicester), G. Corcoran (UCD), P. G. Jonker (Radboud), M. Fraser (UCD), A. J. Levan (Radboud & Warwick) and D. B. Malesani (DAWN/NBI and Radboud), J. A. Chacón (PUC), F. E. Bauer (SSI and UTA), report on behalf of a larger collaboration:
We observed the field of the X-ray transient EP260512a (Liang et al., GCN 44594) using LCO 1m telescopes located at the McDonald Observatory (USA) equipped with SINISTRO instruments. A series of 6x300 s exposures was taken using the SDSS-r filter, starting at 2026-05-13 06:54:11 UT (i.e., ~0.93 days after the first X-ray detection).
No new source is detected within or at the border of the EP/WXT (Liang et al., GCN 44594) uncertainty region compared with the Legacy Survey. From the stacked images, we obtain the following 3-sigma upper limits:
r > 22.2
These upper limits are in AB magnitudes, calibrated using nearby stars from the PanSTARRS catalogue, and are not corrected for Galactic extinction.
GCN Circular 44606
Subject
EP260512a: EP-FXT follow-up observation
Date
2026-05-14T07:08:03Z (16 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
R. D. Liang, M. J. Liu (NAO, CAS), H. Z. Wu (HUST), H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team:
EP-FXT observed the field of EP260512a (detected by EP-WXT, Liang et al., GCN 44594; and followed by COLIBRÍ, Diego et al. GCN 44595, and MASTER-Net observations, Lipunov et al., GCN 44603) for 2.6 ks starting at 2026-05-13 10:06:08, around 25.6 hours after the detection by EP-WXT. No significant X-ray source is detected within the 2.6 arcmin radius of the EP-WXT position (Liang et al., GCN 44594) to a preliminary 0.5-10 keV upper limit of 7e-14 erg/cm^2/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 44603
Subject
EP260512a: Global MASTER-Net observations report
Date
2026-05-14T00:45:25Z (16 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-Kislovodsk robotic telescope [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the EP260512a ( EP Team et al., GCN 44594) errorbox 73819 sec after notice time and 1 days 57787 sec after trigger time at 2026-05-14 00:34:39 UT, with upper limit up to 18.1 mag. Observations started at twilight. The observations began at zenith distance = 49 deg. The sun altitude is -12.2 deg.
The galactic latitude b = 62 deg., longitude l = 43 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3310827
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
144248 | 2026-05-14 00:34:39 | MASTER-Kislovodsk | (14h 54m 15.49s , +28d 52m 29.4s) | C | 120 | 18.1 |
144397 | 2026-05-14 00:37:08 | MASTER-Kislovodsk | (14h 54m 18.37s , +28d 54m 03.0s) | C | 120 | 18.1 |
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 44595
Subject
EP260512a: COLIBRÍ optical upper limits
Date
2026-05-13T06:18:56Z (17 days ago)
From
J.-G. Ducoin at CPPM <ducoin@cppm.in2p3.fr>
Via
Web form
Diego López-Cámara (UNAM), Jean-Grégoire Ducoin (CPPM), Camila Angulo (UNAM), Rosa L. Becerra (UNAM), Jean-Luc Atteia (IRAP), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), 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 the EP260312a (Liang et al., GCN Circ. 44594), using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-05-13 04:09 to 04:25 UTC (from 19.6 to 19.9 hours after the trigger and 6 minutes after the release of the GCN) 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 source within the WXT error region we do not detect any new source at the WXT error position (Liang et al., GCN Circ. 44594) down to the following 5-sigma limits:
r > 23.1
z > 21.9
We note the presence of the quasar 2MASS J14554420+282524 within the WXT region and, considering our upper limits and the low SNR reported by the Einstein Probe Team (Liang et al., GCN Circ. 44594), we cannot rule out the possibility that the trigger is related to this source.
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 44594
Subject
EP260512a: Einstein Probe detection of an X-ray transient
Date
2026-05-13T04:03:17Z (17 days ago)
Edited On
2026-05-13T12:50:33Z (16 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
R. D. Liang, M. J. Liu (NAO, CAS), H. Z. Wu (HUST), H. Sun (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 EP260512a. The transient was detected at 2026-05-12 08:31:32 (UTC) with a duration of about 200s. The signal-to-noise ratio is below the on-board trigger threshold, and hence the transient was discovered by ground-based analysis. The WXT position of the source is R.A. = 223.899 deg, DEC = 28.432 deg (J2000) with an uncertainty of 2.6 arcmin in radius (90% C.L. statistical and systematic).
A follow-up observation with the Follow-up X-ray Telescope (FXT) is 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).