EP261010a
GCN Circular 45893
Subject
EP261010a: refined analysis of the EP-WXT and autonomous EP-FXT observations
Date
2026-10-11T05:11:11Z (a day ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
A.Li (BNU), C.Y. Wang (THU), H.Z. Wu (HUST), C.L.Guo, H.Sun (NAO, CAS), on behalf of the Einstein Probe (EP) team:
The X-ray transient EP261010a triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission at 2026-10-10T00:18:44 (UTC, Li et al., GCN 45880). The refined analysis of the WXT data shows that the event started at T0 = 2026-10-10T00:17:40 (UTC). The transient light curve shows a rising trend and lasted around 70s before the interruption by the autonomous follow-up. Subsequent follow-up observations were reported by Buckley et al. (GCN 45881), Zhu et al. (GCN 45882) and Ma et al. (GCN 45884).
The time-averaged WXT spectrum in the 0.5–4 keV band is extremely soft and can be fitted with an absorbed blackbody model. The hydrogen column density was fixed at the Galactic value of NH = 2.11 × 10^20 cm^-2 at the source position. The best-fit temperature is 0.26 (+0.12/-0.08) keV. The average unabsorbed 0.5–4 keV flux is 1.2 (+0.7/-0.6) × 10^-10 erg s^-1 cm^-2.
The autonomous observation of the Follow-up X-ray Telescope (FXT) on board EP started at 2026-10-10T00:20:35 (UTC), around 110 s after the WXT trigger. Both FXT-A and FXT-B detected an uncatalog X-ray source within the WXT error region at R.A. = 26.2203 deg, Dec. = -34.0870 deg (J2000). We jointly fitted the FXT-A and FXT-B spectra in the 0.5–10 keV band with an blackbody model. The hydrogen column density was fixed at the Galactic value. The best-fit temperature is 0.10(+0.03/-0.04) keV. The average unabsorbed 0.5–10 keV flux is 7.6 (+3.6/-2.9) × 10^-14 erg s^-1 cm^-2. All quoted uncertainties on the spectral parameters and fluxes are at the 90% confidence level.
The soft thermal spectrum and the rapid temporal decline of the X-ray emission suggest that EP261010a could be a supernova shock breakout candidate. The follow-up observation with the EP-FXT has been scheduled to monitor its further evolution.
Launched on January 9, 2024, EP is a space-based X-ray observatory designed to monitor the soft X-ray sky and perform X-ray follow-up observations (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).
GCN Circular 45884
Subject
EP261010a: SVOM/VT optical upper limits
Date
2026-10-10T12:25:59Z (2 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 EP261010a detected by EP/WXT (Li et al., GCN 45880). SVOM/VT began observing the field at 2026-10-10T02:20:41 UTC, 2.033 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
No uncatalogued candidate was identified in our stacked images within the error box provided by EP/FXT position (Li et al., GCN 45880), compared to the Legacy Survey.
The following measurements are in AB magnitudes and are not corrected for Galactic extinction:
Mid time | Band | Exposure Time | 3-sigma upper limit
3.21 hr | VT_B | 44*50 s | > 23.4 mag
2.99 hr | VT_R | 33*50 s | > 23.1 mag
Our results are consistent with MASTER and NOT (Buckley et al., GCN 45881; Zhu et al., GCN 45882).
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 45882
Subject
EP261010a: NOT optical upper limits
Date
2026-10-10T04:48:39Z (2 days ago)
From
Zipei Zhu at NAOC <zpzhu@nao.cas.cn>
Via
Web form
Z.P. Zhu, X. Liu, D. Xu, J. An, L.B. He, S.Q. Jiang (NAOC), S.Y. Fu, L. Lei (HUST), J.P.U. Fynbo (DAWN/NBI), A.S. Zanuzzi (NOT) report:
We observed the field of EP261010a detected by the Einstein Probe (Li et al., GCN 45880), using the ALFOSC camera mounted on the Nordic Optical Telescope (NOT). We obtained 3 x 300 s frames in the SDSS r filter and 5 x 200 s in the z filter, starting on 2026-10-10 at 01:43:35 UTC, i.e., 1.4 hr after the EP trigger.
No uncatalogued optical source is detected in the stacked images within the EP/FXT error circle, down to 5-sigma limiting magnitudes of r > 23.9 and z > 21.5, calibrated with Legacy Survey stars in the field.
Near-infrared follow-up observations are encouraged.
GCN Circular 45881
Subject
EP261010a: Global MASTER-Net observations report
Date
2026-10-10T02:00:44Z (2 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 (Lomonosov MSU)
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 EP261010a ( EP Team at NAOC/CAS <ep_ta@bao.ac.cn> et al., GCN 45880) errorbox 539 sec after notice time and 4266 sec after trigger time at 2026-10-10 01:29:51 UT, with upper limit up to 16.2 mag. The observations began at zenith distance = 31 deg. The sun altitude is -30.9 deg.
The galactic latitude b = -76 deg., longitude l = 246 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3523700
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
4297 | 2026-10-10 01:29:51 | MASTER-SAAO | (01h 40m 12.54s , -34d 06m 36.9s) | C | 60 | 16.1 |
4297 | 2026-10-10 01:29:51 | MASTER-SAAO | (01h 42m 24.50s , -34d 22m 33.8s) | C | 60 | 16.2 |
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 45880
Subject
EP261010a Einstein Probe detection of an X-ray transient
Date
2026-10-10T01:35:27Z (2 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
A.Li (BNU), C.Y. Wang (THU), H.Z. Wu (HUST), C.L.Guo, H.Sun, (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 EP261010a. The transient triggered EP-WXT (ID: 01709321061) at 2026-10-10T00:18:44 (UTC). The WXT position of the source is R.A. = 26.236 deg, DEC = -34.090 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) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 26.2218 deg, DEC = -34.0893 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic).
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).