EP260830a

X. Mao, Q. H. Lao (NAO, CAS), Y. F. Liang, J. Y. Liu (PMO), Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team:

EP-FXT performed a follow-up observation of EP260830a (Mao et al., GCN 45280
Loading...
 
 ; Segura et al., GCN 45481
Loading...
 
 ) starting at 2026-09-01T17:56:36 (UTC), approximately 50 hours after the WXT detection. With an exposure time of 5 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 8.8e-14 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).

M. Segura,  F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA)

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)

D.Buckley (SAAO),

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)


MASTER-OAFA robotic telescope  [1]  located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP260830a ( EP Team at NAOC/CAS <ep_ta@bao.ac.cn> et al., GCN 45480
Loading...
 
 ) errorbox  245 sec after notice time and 1 days 53772 sec after trigger time at 2026-09-01 06:26:35 UT, with upper limit up to  18.6 mag. The observations began at zenith distance = 49 deg. The sun  altitude  is -55.3 deg. 

The galactic latitude b = -45 deg., longitude l = 109 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=3497638

We obtain a following upper limits.  

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

  140203 | 2026-09-01 06:26:35 |         MASTER-OAFA | (00h 07m 26.40s , +16d 48m 31.6s) |   C |    60 | 18.5 |        
  140280 | 2026-09-01 06:27:53 |         MASTER-OAFA | (00h 07m 25.14s , +16d 49m 34.6s) |   C |    60 | 18.6 |        
  140357 | 2026-09-01 06:29:09 |         MASTER-OAFA | (00h 07m 32.14s , +16d 48m 37.1s) |   C |    60 | 18.5 |        
  140434 | 2026-09-01 06:30:27 |         MASTER-OAFA | (00h 07m 26.13s , +16d 47m 39.6s) |   C |    60 | 18.6 |        
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

X. Mao (NAO, CAS), Y. F. Liang, J. Y. Liu (PMO), 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 EP260830a (notice ID: 01709295827), 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 2026-08-30T15:30:23(UTC) and lasted for about 500s. The position of the transient is R.A. = 2.055 deg, Dec. = 16.919 (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 4.21×10^20 cm^-2 and a photon index of 1.03 (-0.92/+1.02). The derived average unabsorbed 0.5-4 keV flux is 3.69 (-1.65/+2.93) x 10^(-11) 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).