EP260901a

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
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 ) 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

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).