EP260430a
GCN Circular 44436
Subject
EP260430a: refined analysis of the EP-WXT and follow-up EP-FXT observations
Date
2026-05-01T07:13:34Z (a day ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Y. Wang (PMO, CAS; UCB), Y. L. Wang (NAO, CAS; ICE, CSIC), G. J. Yang, C.C Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team:
The X-ray transient EP260430a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Wang et al., GCN 44427) at 2026-04-30T02:32:47 (UTC). The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 0.3× 10^21 cm^-2, and a photon index of 0.84 (+0.19/-0.18). The derived average unabsorbed 0.5-4 keV flux is 4.63 (+2.54/-1.56) × 10^(-10) erg/s/cm^2.
Follow-up observation by the Follow-up X-ray Telescope (FXT) on board EP was performed at 2026-04-30T02:34:41 (UTC). The exposure time of the observation is around 3 ks. The on-ground analysis of the FXT data found an uncatalogued source at R.A. = 178.3355, DEC = -10.2146 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The FXT light curve shows a raipd decay. The average FXT 0.5-10 keV spectra can be fitted with an absorbed power-law with a fixed Galactic hydrogen column density of 0.3× 10^21 cm^-2, and a photon index of 4.61 (+/-0.20). The derived average unabsorbed 0.5-10 keV flux is 1.27 (-0.16/+0.17) × 10^(-11) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
We note that follow-up observations were carried out by Lipunov et al. (GCN 44428), Fortin et al. (GCN 44431) and Chácon et al. (GCN 44432), but no optical counterpart was detected in these observation.
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 44432
Subject
EP260430a: LCO optical upper limits
Date
2026-04-30T10:50:21Z (2 days ago)
From
Jonathan Quirola at Radboud University <jaquirola1990@gmail.com>
Via
Web form
J. A. Chácon (PUC), F. E. Bauer (SSI and UTA), D. B. Malesani (DAWN/NBI and Radboud), J. Quirola-Vasquez (Radboud), A. J. Levan (Radboud & Warwick), P. G. Jonker (Radboud), R. A. J. Eyles-Ferris (Leicester), report on behalf of a larger collaboration:
We observed the field of the fast X-ray transient EP260430a (Wang et al., GCN 44427) using LCO 1m telescopes located at the Cerro Tololo Inter-American Observatory (Chile) equipped with the SINISTRO instrument. A series of 6x300 s exposures was taken using the SDSS-r filter, starting at 2026-04-30 03:32:35 UT (~1 hr after the trigger).
No new source is detected within or at the border of the EP/FXT uncertainty region (Wang et al., GCN 44427). From the stacked images, we obtain the following 3-sigma upper limit:
r > 22.1
This upper limit is in AB magnitudes, calibrated using nearby stars from the Pan-STARRS catalog, and is not corrected for Galactic extinction.
GCN Circular 44428
Subject
EP260430a: Global MASTER-Net observations report
Date
2026-04-30T04:09:48Z (2 days 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-OAFA robotic telescope [1] located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP260430a ( EP Team et al., GCN 44427) errorbox 320 sec after trigger time at 2026-04-30 02:38:07 UT, with upper limit up to 19.0 mag. The observations began at zenith distance = 23 deg. The sun altitude is -59.3 deg.
The galactic latitude b = 50 deg., longitude l = 281 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3281929
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
350 | 2026-04-30 02:38:07 | MASTER-OAFA | (11h 53m 04.26s , -09d 58m 33.8s) | C | 60 | 18.5 |
420 | 2026-04-30 02:38:07 | MASTER-OAFA | (11h 53m 04.26s , -09d 58m 33.8s) | C | 200 | 18.8 | Coadd
426 | 2026-04-30 02:39:13 | MASTER-OAFA | (11h 53m 04.09s , -09d 58m 36.3s) | C | 80 | 15.7 |
1038 | 2026-04-30 02:49:35 | MASTER-OAFA | (11h 53m 02.59s , -09d 59m 04.2s) | C | 60 | 18.5 |
1104 | 2026-04-30 02:50:40 | MASTER-OAFA | (11h 53m 02.42s , -09d 59m 07.3s) | C | 60 | 18.5 |
1164 | 2026-04-30 02:50:40 | MASTER-OAFA | (11h 53m 02.42s , -09d 59m 07.3s) | C | 180 | 18.9 | Coadd
1170 | 2026-04-30 02:51:46 | MASTER-OAFA | (11h 53m 02.26s , -09d 59m 10.5s) | C | 60 | 18.5 |
1236 | 2026-04-30 02:52:52 | MASTER-OAFA | (11h 53m 02.09s , -09d 59m 13.9s) | C | 60 | 18.4 |
1301 | 2026-04-30 02:53:57 | MASTER-OAFA | (11h 53m 01.92s , -09d 59m 17.1s) | C | 60 | 18.5 |
1361 | 2026-04-30 02:53:57 | MASTER-OAFA | (11h 53m 01.92s , -09d 59m 17.1s) | C | 180 | 19.0 | Coadd
1366 | 2026-04-30 02:55:03 | MASTER-OAFA | (11h 53m 01.76s , -09d 59m 20.5s) | C | 60 | 18.5 |
1432 | 2026-04-30 02:56:09 | MASTER-OAFA | (11h 53m 01.60s , -09d 59m 24.0s) | C | 60 | 18.5 |
1498 | 2026-04-30 02:57:14 | MASTER-OAFA | (11h 53m 01.42s , -09d 59m 27.3s) | C | 60 | 18.4 |
1558 | 2026-04-30 02:57:14 | MASTER-OAFA | (11h 53m 01.42s , -09d 59m 27.4s) | C | 180 | 19.0 | Coadd
1564 | 2026-04-30 02:58:20 | MASTER-OAFA | (11h 53m 01.25s , -09d 59m 30.6s) | C | 60 | 18.4 |
1630 | 2026-04-30 02:59:27 | MASTER-OAFA | (11h 53m 01.08s , -09d 59m 34.3s) | C | 60 | 18.5 |
1696 | 2026-04-30 03:00:32 | MASTER-OAFA | (11h 53m 00.91s , -09d 59m 37.8s) | C | 60 | 18.5 |
1761 | 2026-04-30 03:01:38 | MASTER-OAFA | (11h 53m 00.74s , -09d 59m 41.3s) | C | 60 | 18.5 |
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
GCN Circular 44427
Subject
EP260430a: Einstein Probe detection of an X-ray transient
Date
2026-04-30T03:45:21Z (2 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Y. L. Wang (NAO, CAS; ICE, CSIC), Y. Wang (PMO), G. J. Yang, C.C Jin (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 EP260430a. The transient triggered EP-WXT (ID: 01709261081) at 2026-04-30T02:32:47 (UTC).
A follow-up observation with the Follow-up X-ray Telescope (FXT) on board EP was performed automatically following the WXT trigger. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 178.3341 deg, DEC = -10.2136 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.
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).