EP250802a
GCN Circular 41257
Subject
EP250802a: EP-FXT follow-up observation
Date
2025-08-07T08:39:07Z (3 months ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Y.-H. I. Yin (NJU), X. Mao, T. Zhao, C. C. Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team:
EP-FXT performed a follow-up observation of EP250802a (GCN 41221) at 2025-08-04T04:10:31 (UTC), about 42 hours after the WXT detection, with an exposure time of 1.5 ks. The source was also followed by several optical telescopes (GCN 41222, GCN 41223, GCN 41224, GCN 41227). Three uncatalogued sources are detected within the WXT error circle, among which Source 1 is spatially consistent with a known star TYC 2158-1481-1. Preliminary analysis on these sources are automatically conducted, and the details are listed as follows.
Source 1: EPF_J201319.4+244937
RA (J2000): 303.3308
Dec (J2000): 24.8268
Flux: 4.63 x 10^-13 erg/s/cm^2 (observed, 0.5-10 keV)
Flux_err: 1.25 x 10^-13 erg/s/cm^2 (1 sigma)
Note: This source is spatially consistent with the a known star TYC 2158-1481-1.
Source 2: EPF_J201330.2+244901
RA (J2000): 303.3759
Dec (J2000): 24.8168
Flux: 2.21 x 10^-13 erg/s/cm^2 (observed, 0.5-10 keV)
Flux_err: 6.99 x 10^-14 erg/s/cm^2 (1 sigma)
Source 3: EPF_J201318.2+245121
RA (J2000): 303.3260
Dec (J2000): 24.8559
Flux: 3.56 x 10^-13 erg/s/cm^2 (observed, 0.5-10 keV)
Flux_err: 9.84 x 10^-14 erg/s/cm^2 (1 sigma)
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).
GCN Circular 41227
Subject
EP250802a: additional Liverpool Telescope upper limits
Date
2025-08-04T12:15:11Z (3 months ago)
From
Rob Eyles-Ferris at U of Leicester <raje1@leicester.ac.uk>
Via
Web form
R. A. J. Eyles-Ferris and N. R. Tanvir (U of Leicester) report on behalf of a larger collaboration:
We observed the field of the X-ray transient EP250802a (Yin et al., GCN 41221) with the 2m Liverpool Telescope using the IO:O instrument. We obtained 8x150s exposures in each of the SDSS r’ and SDSS z’ filters starting at 2025-08-03 22:17:48 UT, approximately 35.7 hours after the X-ray detection.
We performed image subtraction on the stacked images using reference images from Pan-STARRS and also compared the stacked and reference images manually. Similarly to Bochanek et al. (GCN 41224), the bright stars in the error region affected our subtractions, however, no new sources are detected in either the subtractions or stacked images. Our results are consistent with Mohan et al. (GCN 41222), Lipunov et al. (GCN 41223) and Bochanek et al. (GCN 41224).
At the position of the X-ray source, we derive 3-sigma upper limits of r’ > 22.44 and z’ > 21.73 with photometry calibrated to Pan-STARRS and not corrected for Galactic extinction.
GCN Circular 41224
Subject
EP250802a: Liverpool Telescope optical upper limits
Date
2025-08-04T01:27:27Z (3 months ago)
From
A. Bochenek at Liverpool John Moores University <a.m.bochenek@2023.ljmu.ac.uk>
Via
Web form
A. Bochenek and D. A. Perley (LJMU) report:
We observed the field of the fast X-ray transient EP250802a (Yin et al., GCN 41221) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 4x120s exposures in the SDSS r’ and i’ filters starting at 2025-08-03 21:42:37 UT, approximately 35 hours after the trigger.
The images were stacked, and their background was subtracted relative to Pan-STARRS-1 using PSF matching with the help of PSFEx. We do not detect any new object at the EP/WXT error region of the transient: the 3-sigma limiting magnitudes on the stacked images are r > 22.67 mag and i > 22.33 mag, in line with Mohan et al. (GCN 41222) and Lipunov et al. (GCN 41223). However, we note that there are a few bright, saturated stars inside the error region on our images, impacting the image subtraction.
GCN Circular 41223
Subject
EP250802a: Global MASTER-Net observations report
Date
2025-08-04T00:09:32Z (3 months ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
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-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) was pointed to the EP250802a ( EP Team et al., GCN 41221) errorbox 39315 sec after notice time and 1 days 47045 sec after trigger time at 2025-08-03 23:41:13 UT, with upper limit up to 18.0 mag. The observations began at zenith distance = 62 deg. The sun altitude is -70.6 deg.
The galactic latitude b = -6 deg., longitude l = 65 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=2958029
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
133475 | 2025-08-03 23:41:13 | MASTER-SAAO | (20h 11m 03.23s , +24d 50m 38.4s) | C | 60 | 18.0 |
133475 | 2025-08-03 23:41:13 | MASTER-SAAO | (20h 12m 56.78s , +24d 35m 32.1s) | C | 60 | 17.3 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
GCN Circular 41222
Subject
EP250802a: GROWTH-India Telescope optical upper limit
Date
2025-08-03T19:17:03Z (3 months ago)
From
V. Swain at IIT Bombay <vishwajeet.s@iitb.ac.in>
Via
Web form
T. Mohan, V. Swain, A.P. Saikia, V. Bhalerao (IITB), D. Eappachen, G.C. Anupama, S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team:
We observed the field of EP transient EP250802a (Yin et al., GCN 41221), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2025-08-03 16:11:32 UT, i.e., ~29.5 hours after the EP trigger and obtained an exposure in r' filter. We do not detect any afterglow candidates within the uncertainty region of WXT localization. The photometric upper limit is as follows:
| MJD (mid) | Filter | tmid-t0 (day) | Exposure Time (sec) | Upper limit (AB) |
| ------------ | ------ | ------------- | ------------------- | ---------------- |
| 60890.67467 | r' | 1.23 | 300 | 20.8 |
The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction.
The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/.
GCN Circular 41221
Subject
EP250802a: Einstein Probe detection of an X-ray transient
Date
2025-08-03T12:45:12Z (3 months ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Y.-H. I. Yin (NJU), X. Mao, T. Zhao, C. C. Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team:
We report on the detection of an X-ray transient by EP-WXT through ground data analysis, designated EP250802a (ObsID:06800000790). The transient was detected at 2025-08-02 10:37:08 (UTC).
The WXT position of the source is R.A. = 303.321 deg, DEC = 24.814 deg (J2000) with an uncertainty of 3.1 arcmin (radius, 90% C.L. statistical and systematic). The transient event lasted for about 650 seconds.
The average 0.5-4 keV spectrum can be fitted with an absorbed powerlaw model, with absorption fixed at the Galactic value of 3.5 x 10^21 cm^-2 and a photon index of 2.81 (+/-0.47). The unabsorbed average 0.5-4 keV flux is estimated to be 3.81 (-0.57, +0.67) x 10^-11 erg/s/cm2. The peak flux is about 1.16 (-0.20, +0.25) x 10^-10 erg/s/cm2. The uncertainties are at the 90% confidence level for the above parameters.
Further FXT observations are scheduled.
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).