EP250407a

D. F. Hu, T. C. Zheng (PMO, CAS), X. Mao, W. X. Wang, W. D. Zhang (NAO, CAS) report on behalf of the Einstein Probe team:

We report on the detection of a fast X-ray transient EP250407a detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient started at 2025-04-07T23:27:23 (UTC) and lasted for about 70s. We apologize that an incorrect trigger date was reported in the GCN Notice (trigger ID: 11916648441). The WXT position of EP250407a is R.A.= 134.813 deg, DEC = -38.956 deg (J2000) with an uncertainty of 2.5 arcmin (radius, 90% C.L. statistical and systematic). No known X-ray sources are found within the WXT error circle. The average 0.5-4 keV spectrum can be fitted with an absorbed powerlaw with a photon index of 1.4 (+/-0.6) and a fixed Galactic hydrogen column density of 4.67 x 10^21 cm^-2. We derive an average unabsorbed flux of 4.7(-1.0/+1.2) x 10^(-9) erg/s/cm^2, and a peak flux of approximately 1.0 x 10^(-8) erg/s/cm^2 (both in 0.5-4 keV).

A follow-up observation with the Follow-up X-ray Telescope (FXT) on board the EP is planned. Further follow-up observations are encouraged to identify the nature of this X-ray transient. 

The contact TA of this source is Ding-Fang Hu, please contact him via the email dfhu@pmo.ac.cn if needed.

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. A. Williams (PSU), S. Dichiara (PSU), K.L. Page (U. Leicester) and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team:

We have analyzed 2100 s of XRT data for the recently reported transient EP250407a (GCN #40118
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 ), from T0+36.5 ks to T0+42.4 ks after detection by Einstein Probe WXT. The data are entirely in Photon Counting (PC) mode.

No X-ray sources have been detected within the estimated 90% EP-WXT error region (2.5 arcmin), with an upper limit on count rate of 5.3 × 10^-3 ct/s. For a typical GRB-like spectrum, this equates to an upper limit on flux of 2 x 10^-13 erg/s/cm^2 (0.3-10 keV).

The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/EP/EP_FIELD00033/.

V.Lipunov, E.Gorbovskoy, N.Tiurina,  P.Balanutsa, , D.Vlasenko, I.Panchenko,
A.Kuznetsov,  G.Antipov,  A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, 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. 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-OAFA robotic telescope  (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)  located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP250407a ( EP Team et al., GCN 40118
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 ) errorbox  49972 sec after notice time and 85240 sec after trigger time at 2025-04-08 23:08:03 UT, with upper limit up to  18.5 mag. Observations started at twilight.  The observations began at zenith distance = 18 deg. The sun  altitude  is -10.6 deg. 

The galactic latitude b =  5 deg., longitude l = 262 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=2836941

We obtain a following upper limits.  

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

   85271 | 2025-04-08 23:08:03 |         MASTER-OAFA | (08h 59m 01.05s , -38d 53m 39.6s) |   C |    60 | 18.2 |        
   85448 | 2025-04-08 23:11:01 |         MASTER-OAFA | (08h 59m 05.07s , -38d 53m 10.9s) |   C |    60 | 18.5 |        
Filter C is a clear (unfiltred) band. 


The observation and reduction will continue. 
The message may be cited.