EP260603a
GCN Circular 44846
Subject
EP260603a: COLIBRÍ optical upper limit
Date
2026-06-05T22:08:07Z (a minute ago)
From
Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra@astro.unam.mx>
Via
Web form
Enrique Moreno Méndez (UNAM), Dalya Akl (NYUAD), Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (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), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), 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 EP260603a (Liang et al., GCN Circ. 44814) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-06-04 06:09 to 06:25 UTC (from 12.30 to 12.58 hours after the trigger) and obtained 14 minutes of simultaneous exposure in the r/z filters.
The data were reduced, coadded and analysed with the ASU COLIBRÍ 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 any new source within the WXT source region (Liang et al., GCN Circ. 44814) down to the following 5-sigma limit:
r > 22.5
z > 21.3
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 44815
Subject
EP260603a: Global MASTER-Net observations report
Date
2026-06-04T06:18:16Z (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),
M. Segura, 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-OAGH robotic telescope [1] located in Mexico (OAGH National Institute for Astrophysics, Optics and Electronics) was pointed to the EP260603a ( EP Team at NAOC/CAS <ep_ta@bao.ac.cn> et al., GCN 44814) errorbox 436 sec after notice time and 43770 sec after trigger time at 2026-06-04 06:00:42 UT, with upper limit up to 17.9 mag. The observations began at zenith distance = 58 deg. The sun altitude is -33.4 deg.
The galactic latitude b = 25 deg., longitude l = 340 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3359661
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
43860 | 2026-06-04 06:00:42 | MASTER-OAGH | (15h 18m 40.19s , -26d 59m 12.9s) | C | 180 | 17.9 |
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 44814
Subject
EP260603a: Einstein Probe detection of a fast X-ray transient
Date
2026-06-04T05:48:48Z (2 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Y. F. Liang (PMO), J. W. Hu, Y. L. Wang, Z. X. Ling(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 EP260603a. The ground analysis of the WXT data shows that the event started at 2026-06-03T17:51:12 (UTC) and lasted for about 350 s. The WXT position of the source is R.A. = 229.721 deg, DEC = -26.940 deg (J2000) with an uncertainty of 2.8 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 1.56 × 10^21 cm^-2, and a photon index of 1.11 (-0.77, +0.80). The derived average unabsorbed 0.5-4 keV flux is 1.2 (-0.4, +0.6)×10^(-10) erg/s/cm^2. The peak flux is about 9.5×10^(-10) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
A Target-of-Opportunity observation with the Follow-up X-ray Telescope (FXT) has been scheduled. Further information will be updated when the telemetry data is received.
Further multi-wavelength observations are encouraged to determine the nature of this source.
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).