EP260104a
GCN Circular 43344
Subject
EP260104a: FTW optical observations
Date
2026-01-06T15:02:43Z (a month ago)
Edited On
2026-01-06T17:25:07Z (a month ago)
From
Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann@physik.lmu.de>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov>
Via
Web form
Malte Busmann, Jule Augustin, Mitra Maleki (LMU), Xander J. Hall, Brendan O'Connor (CMU), Daniel Gruen (LMU), and Antonella Palmese (CMU) report:
We observed the 90% WXT localization of EP260104a (Zhou et al., GCN 43330) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r and i-band simultaneously for 10 x 180 s starting at 2026-01-06T01:09:48 UT (1.6 days after the trigger). We performed difference imaging with templates from the DESI Legacy Surveys and did not detect any uncatalogued sources to a 3-sigma upper limit of
r > 21.5 AB mag.
The non-detection is consistent with the report by Lipunov et al. (GCN 43331).
The magnitude is calibrated against the PS1 catalog and not corrected for Galactic extinction.
We thank Christoph Ries from the Wendelstein Observatory for obtaining these observations.
GCN Circular 43331
Subject
EP260104a: Global MASTER-Net observations report
Date
2026-01-05T09:18:34Z (2 months 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 EP260104a ( EP Team et al., GCN 43330) errorbox 56335 sec after trigger time at 2026-01-05 02:04:39 UT, with upper limit up to 15.3 mag. The observations began at zenith distance = 28 deg. The sun altitude is -27.9 deg.
The galactic latitude b = 73 deg., longitude l = 251 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3096369
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
56366 | 2026-01-05 02:04:39 | MASTER-Kislovodsk | (11h 56m 25.18s , +14d 49m 37.7s) | C | 60 | 15.3 |
80735 | 2026-01-05 08:49:48 | MASTER- | (11h 58m 24.52s , +15d 34m 21.5s) | C | 180 | 17.0 |
81514 | 2026-01-05 09:02:47 | MASTER- | (11h 58m 27.43s , +15d 32m 44.3s) | C | 180 | 17.9 |
81514 | 2026-01-05 09:02:47 | MASTER- | (11h 59m 39.45s , +14d 59m 25.9s) | C | 180 | 17.9 |
81896 | 2026-01-05 09:09:09 | MASTER- | (11h 59m 35.99s , +14d 58m 57.1s) | C | 180 | 17.3 |
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 43330
Subject
EP260104a: Einstein Probe detection of a fast X-ray transient
Date
2026-01-05T08:41:44Z (2 months ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
H. Zhou (PMO, CAS), Z. C. Zou (NJU), J. P. Chen (SYSU), Y. J. Yi (BNU), D. Y. Li, C. L. Guo, Z. X. Ling, Y. Liu (NAO, CAS) 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 EP260104a. The transient triggered EP-WXT (ID: 01709250979) at 2026-01-04T10:25:44 (UTC). The WXT position of the source is R.A. = 178.535 deg, DEC = 16.491 deg (J2000) with an uncertainty of 2.8 arcmin in radius (90% C.L. statistical and systematic).
Since EP260104a was triggered in SAA region, no autonomous follow-up observation was performed. We analyzed the telemetry data, and the 0.5-4 keV rate light curve shows a single pulse lasting for about 150 seconds. The absorbed powerlaw model with a fixed Galactic column density of Hydrogen of 4.57 x 10^20 cm^-2 was adopted to fit the average WXT spectrum. The best-fitted photon index is 2.44(+1.26/-0.96), the average flux (0.5-4 keV) is (2.4+/-1.1) x 10^-10 erg s^-1 cm^-2, and no additional absorption is required. All uncertainties are reported in 90% C.L.
We have arranged X-ray follow-up observations and will update the information upon receiving the data.
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).