EP260101a

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 EP260101a ( EP Team et al., GCN 43288
Loading...
 
 ) errorbox  1 days 27579 sec after notice time and 1 days 29347 sec after trigger time at 2026-01-02 14:44:49 UT, with upper limit up to  15.3 mag. Observations started at twilight.  The observations began at zenith distance = 30 deg. The sun  altitude  is -10.3 deg. 

The galactic latitude b = -16 deg., longitude l = 150 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=3092541

We obtain a following upper limits.  

Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

  115778 | 2026-01-02 14:44:49 |   MASTER-Kislovodsk | (03h 03m 11.45s , +39d 18m 40.8s) |   C |    60 | 15.3 |        
  116532 | 2026-01-02 14:57:23 |   MASTER-Kislovodsk | (03h 03m 11.69s , +39d 19m 18.4s) |   C |    60 | 14.7 |        
  116631 | 2026-01-02 14:59:03 |   MASTER-Kislovodsk | (03h 03m 05.44s , +39d 18m 20.6s) |   C |    60 | 14.5 |        
  116730 | 2026-01-02 15:00:41 |   MASTER-Kislovodsk | (03h 03m 10.27s , +39d 18m 43.9s) |   C |    60 | 15.0 |        
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

M.-H. Zhang, Y.-L. Wang, W. Chen, H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team:

The fast X-ray transient EP260101a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Zhang et al., GCN 43288
Loading...
 
 ). The refined analysis of the WXT data shows that the event started at T0=2026-01-01T06:31:46 (UTC) and lasted for 200 seconds before the observation was interrupted by the autonomous follow-up. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 1.3 x 10^21 cm^-2 and a photon index of 1.7 (-0.7/+0.7). The derived average unabsorbed 0.5-4 keV flux is 6.6 (-2.0/+3.2) x 10^(-11) erg/s/cm^2. 
 
The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously at 2026-01-01T06:38:27 (UTC), about 7 minutes after T0. The exposure time of this observation is 4674s. On-ground analysis of the FXT data found an uncatalogued source at R.A. = 46.0631, DEC = 39.4376 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), which is consistent with the WXT position. A significant decay was detected in the light curve during the initial phase of FXT observation. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 1.3 x 10^21 cm^-2 and a photon index of 2.9 (-0.3/+0.4). The derived average unabsorbed 0.5-10 keV flux is 8.4 (-1.2/+1.3) x 10^(-13) erg/s/cm^2. 

We performed another ToO observation with EP-FXT, starting at 2026-01-01T11:08:28 (UTC), with an exposure time of 6950 s. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with the same fixed Galactic hydrogen column density and a photon index of 3.5 (-1.0/+1.1). The derived average unabsorbed 0.5-10 keV flux is 8.6 (-2.9/+4.1) x 10^(-14) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.


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).

M.-H. Zhang, Y.-L. Wang, W. Chen, 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 EP260101a. The transient triggered EP-WXT (ID: 01709250882) at 2026-01-01T06:35:42 (UTC). The WXT position of the source is R.A. = 46.057 deg, DEC = 39.410 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. = 46.0605 deg, DEC = 39.4380 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.

Happy 2026!!!

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).