EP260901a
GCN Circular 45498
Subject
EP260901a: SVOM/VT optical upper limits
Date
2026-09-03T13:17:07Z (13 days ago)
From
Yinuo Ma <mayn@bao.ac.cn>
Via
Web form
Y. N. Ma, H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu, Z. H. Yao, J. R. Xu, L. J. Chen, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team.
SVOM/VT performed a Target of Opportunity observation of EP260901a detected by EP/WXT (Liang et al., GCN 45487; Liang et al., GCN 45497). SVOM/VT began observing the field at 2026-09-02T13:45:25 UTC, 32.628 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
No credible candidate was detected in our stacked images within the error box provided by EP/WXT position (Liang et al., GCN 45487) down to 5-sigma upper limits of about 22.5 mag (AB) in both channels at the mid time of 33 hr post trigger, compared to the PanSTARRS catalogue.
Our results are consistent with MASTER (Buckley et al., GCN 45492).
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 45497
Subject
EP260901a: EP-FXT follow-up observation
Date
2026-09-02T13:58:08Z (14 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Y. F. Liang, J. Y. Liu (PMO), X. Mao, Q. H. Lao, Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team:
EP-FXT performed a follow-up observation of EP260901a (Liang et al., GCN 45487; Buckley et al., GCN 45492) starting at 2026-09-01T22:26:36 (UTC), approximately 17 hours after the WXT detection. With an exposure time of 4 ks, no significant X-ray source was detected within the 2.4 arcmin radius of the EP-WXT position. The derived 0.5-10 keV upper limit is about 1.0e-13 erg cm^-2 s^-1.
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).
Previous Circular
GCN Circular 45492
Subject
EP260901a: Global MASTER-Net observations report
Date
2026-09-01T21:45:38Z (14 days ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
D.Buckley (SAAO),
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 (Lomonosov MSU)
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity)
A.Sosnovskij (CrAO RAS)
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory)
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory)
R.Rebolo (The Instituto de Astrofisica de Canarias)
O.Gress, N.Budnev(ISU)
M. Segura, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA)
MASTER-SAAO robotic telescope [1] located in South Africa (South African Astronomical Observatory) was pointed to the EP260901a ( EP Team at NAOC/CAS <ep_ta@bao.ac.cn> et al., GCN 45487) errorbox 23673 sec after notice time and 53037 sec after trigger time at 2026-09-01 19:51:42 UT, with upper limit up to 17.8 mag. The observations began at zenith distance = 38 deg. The sun altitude is -45.1 deg.
The galactic latitude b = 9 deg., longitude l = 6 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3497756
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
53068 | 2026-09-01 19:51:42 | MASTER-SAAO | (17h 20m 52.36s , -19d 19m 12.5s) | C | 60 | 17.4 |
53162 | 2026-09-01 19:53:16 | MASTER-SAAO | (17h 20m 57.98s , -19d 20m 07.5s) | C | 60 | 17.6 |
53256 | 2026-09-01 19:54:51 | MASTER-SAAO | (17h 20m 52.19s , -19d 21m 03.2s) | C | 60 | 17.6 |
53350 | 2026-09-01 19:56:24 | MASTER-SAAO | (17h 20m 57.58s , -19d 20m 49.1s) | C | 60 | 17.7 |
53454 | 2026-09-01 19:58:08 | MASTER-SAAO | (17h 20m 54.81s , -19d 19m 14.3s) | C | 60 | 17.7 |
53973 | 2026-09-01 20:06:47 | MASTER-SAAO | (17h 20m 51.34s , -19d 19m 37.7s) | C | 60 | 17.8 |
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 45487
Subject
EP260901a: EP-WXT detection of a fast X-ray transient
Date
2026-09-01T13:16:31Z (15 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Y. F. Liang, J. Y. Liu (PMO), X. Mao, Q. H. Lao, Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team:
We report on the detection of a fast X-ray transient, designated EP260901a (notice ID: 11900871682), by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient was identified in the telemetry data. The transient started about 2026-09-01T05:07:45(UTC) and lasted for about 500s. The position of the transient is R.A. = 260.845 deg, Dec. = -19.232 (J2000), with an uncertainty radius of 2.4 arcmin in radius (90% confidence level, including both statistical and systematic uncertainties). There are no known X-ray sources in the WXT error circle.
The average WXT 0.5-4 keV spectrum can be fitted by an absorbed power-law model with a fixed Galactic hydrogen column density of 3.34 × 10^21 cm^-2 and a photon index of 1.12 (-0.07/+0.07). The derived average unabsorbed 0.5-4 keV flux is 3.96(-0.61/+0.68) x 10^(-10) erg cm^-2 s^-1. The peak flux is about 3.7 x 10^(-9) erg cm^-2 s^-1. The uncertainties are at the 90% confidence level for the above parameters.
Follow-up observations by EP-FXT will be arranged.
Launched on 2024 January 9, Einstein Probe is a space-based X-ray observatory designed to monitor the dynamic X-ray sky and perform rapid follow-up observations of newly discovered transients (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).