EP260417a
GCN Circular 44344
Subject
EP260417a: GROWTH-India Telescope optical upper limit
Date
2026-04-18T23:25:30Z (6 days ago)
From
V. Swain at IIT Bombay <vishwajeet.s@iitb.ac.in>
Via
Web form
A. Khade (IITB), A. Kumar (IITB), V. Vijaykumar (IITB), T. Mohan (IITB), V. Swain (IITB), D. Eappachen (IIA), S. Patil (IITB), A.P. Saikia (IITB), V. Bhalerao (IITB), G.C. Anupama (IIA), S. Barway (IIA) and R. Norbu (IAO) report on behalf of the GIT team:
We observed the field of EP260417a detected by Einstein Probe (Wang et al., GCN 44325), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2026-04-18 21:01:23 (UTC), i.e., 1.86 days after the trigger, and obtained multiple exposures in the r' filter. No optical counterpart is detected at the position reported by He et al. (GCN 44326) in our stacked image. The photometric upper limit is as follows:
| MJD (mid) | Filter | tmid-t0 (hours) | Exposure Time (sec) | Upper limit (AB) |
| ------------ | ------ | -------------- | ------------------- | ---------------- |
| 61148.885 | r' | 44.85 | 4x360 | 20.64 |
The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction.
Our upper limit is consistent with the reported optical measurements by He et al. (GCN 44326) and Lipunov et al. (GCN 44338).
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 44338
Subject
EP260417a: Global MASTER-Net observations report
Date
2026-04-18T09:45:27Z (6 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 EP260417a ( EP Team et al., GCN 44325) errorbox 12831 sec after trigger time at 2026-04-17 03:56:53 UT, with upper limit up to 19.9 mag. The observations began at zenith distance = 45 deg. The sun altitude is -67.6 deg.
MASTER-OAGH robotic telescope located in Mexico (OAGH National Institute for Astrophysics, Optics and Electronics) was pointed to the EP260417a errorbox 78480 sec after notice time and 1 days 33084 sec after trigger time at 2026-04-18 09:34:26 UT, with upper limit up to 19.2 mag. The observations began at zenith distance = 53 deg. The sun altitude is -36.9 deg.
The galactic latitude b = 19 deg., longitude l = 355 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3256324
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
4312 | 2026-04-17 01:34:24 | MASTER- | (16h 25m 32.78s , -22d 27m 07.0s) | C | 60 | 16.8 |
12861 | 2026-04-17 03:56:53 | MASTER-OAFA | (16h 22m 03.10s , -23d 33m 17.7s) | C | 60 | 18.9 |
12921 | 2026-04-17 03:56:53 | MASTER-OAFA | (16h 22m 03.09s , -23d 33m 17.9s) | C | 180 | 19.7 | Coadd
13013 | 2026-04-17 03:59:24 | MASTER-OAFA | (16h 22m 05.31s , -23d 31m 13.7s) | C | 60 | 19.5 |
13243 | 2026-04-17 04:03:14 | MASTER-OAFA | (16h 22m 01.68s , -23d 31m 04.9s) | C | 60 | 19.4 |
13395 | 2026-04-17 04:05:46 | MASTER-OAFA | (16h 22m 02.65s , -23d 33m 00.6s) | C | 60 | 19.5 |
13455 | 2026-04-17 04:05:46 | MASTER-OAFA | (16h 22m 02.65s , -23d 33m 00.5s) | C | 180 | 19.9 | Coadd
15146 | 2026-04-17 04:34:57 | MASTER-OAFA | (16h 22m 04.82s , -23d 30m 29.9s) | C | 60 | 19.6 |
15221 | 2026-04-17 04:36:12 | MASTER-OAFA | (16h 22m 04.76s , -23d 32m 06.6s) | C | 60 | 19.7 |
15297 | 2026-04-17 04:37:28 | MASTER-OAFA | (16h 22m 07.64s , -23d 30m 28.6s) | C | 60 | 19.6 |
15357 | 2026-04-17 04:37:28 | MASTER-OAFA | (16h 22m 07.64s , -23d 30m 28.6s) | C | 180 | 19.9 | Coadd
15613 | 2026-04-17 04:42:44 | MASTER-OAFA | (16h 22m 02.17s , -23d 31m 58.9s) | C | 60 | 19.5 |
15688 | 2026-04-17 04:43:59 | MASTER-OAFA | (16h 22m 07.18s , -23d 31m 53.2s) | C | 60 | 19.5 |
15766 | 2026-04-17 04:45:17 | MASTER-OAFA | (16h 22m 04.70s , -23d 30m 07.5s) | C | 60 | 19.4 |
15826 | 2026-04-17 04:45:17 | MASTER-OAFA | (16h 22m 04.69s , -23d 30m 07.5s) | C | 180 | 19.9 | Coadd
17894 | 2026-04-17 05:20:45 | MASTER-OAFA | (16h 22m 01.37s , -23d 29m 11.6s) | C | 60 | 19.6 |
17967 | 2026-04-17 05:21:59 | MASTER-OAFA | (16h 22m 07.83s , -23d 30m 10.7s) | C | 60 | 19.6 |
18047 | 2026-04-17 05:23:18 | MASTER-OAFA | (16h 22m 00.60s , -23d 31m 09.3s) | C | 60 | 19.6 |
18107 | 2026-04-17 05:23:18 | MASTER-OAFA | (16h 22m 00.60s , -23d 31m 09.3s) | C | 180 | 19.5 | Coadd
18354 | 2026-04-17 05:28:26 | MASTER-OAFA | (16h 22m 07.10s , -23d 29m 32.0s) | C | 60 | 19.2 |
18433 | 2026-04-17 05:29:44 | MASTER-OAFA | (16h 22m 02.40s , -23d 30m 03.3s) | C | 60 | 18.9 |
18509 | 2026-04-17 05:31:00 | MASTER-OAFA | (16h 22m 00.62s , -23d 29m 01.8s) | C | 60 | 18.9 |
18569 | 2026-04-17 05:31:00 | MASTER-OAFA | (16h 22m 00.62s , -23d 29m 01.9s) | C | 180 | 19.4 | Coadd
21141 | 2026-04-17 06:14:52 | MASTER-OAFA | (16h 22m 06.99s , -23d 29m 57.4s) | C | 60 | 19.3 |
21216 | 2026-04-17 06:16:08 | MASTER-OAFA | (16h 22m 01.94s , -23d 30m 56.8s) | C | 60 | 19.2 |
21290 | 2026-04-17 06:17:21 | MASTER-OAFA | (16h 22m 08.44s , -23d 30m 33.6s) | C | 60 | 19.3 |
21350 | 2026-04-17 06:17:21 | MASTER-OAFA | (16h 22m 08.45s , -23d 30m 33.6s) | C | 180 | 19.6 | Coadd
21365 | 2026-04-17 06:18:36 | MASTER-OAFA | (16h 22m 04.86s , -23d 29m 08.6s) | C | 60 | 19.2 |
21439 | 2026-04-17 06:19:50 | MASTER-OAFA | (16h 22m 04.87s , -23d 30m 41.6s) | C | 60 | 18.7 |
21515 | 2026-04-17 06:21:07 | MASTER-OAFA | (16h 22m 08.53s , -23d 29m 14.9s) | C | 60 | 19.4 |
74895 | 2026-04-17 21:10:46 | MASTER- | (16h 16m 30.79s , -20d 56m 12.9s) | C | 60 | 13.1 |
110797 | 2026-04-18 07:09:09 | MASTER-OAFA | (16h 17m 04.14s , -21d 44m 07.5s) | C | 60 | 19.4 |
110874 | 2026-04-18 07:10:25 | MASTER-OAFA | (16h 25m 34.38s , -21d 45m 27.4s) | C | 60 | 19.5 |
110950 | 2026-04-18 07:11:42 | MASTER-OAFA | (16h 16m 57.59s , -21d 43m 52.3s) | C | 60 | 19.5 |
111028 | 2026-04-18 07:12:59 | MASTER-OAFA | (16h 25m 40.71s , -21d 45m 23.9s) | C | 60 | 19.5 |
111103 | 2026-04-18 07:14:15 | MASTER-OAFA | (16h 16m 57.41s , -21d 45m 48.8s) | C | 60 | 19.5 |
119575 | 2026-04-18 09:34:26 | MASTER-OAGH | (16h 20m 52.34s , -22d 05m 17.1s) | C | 180 | 19.2 |
119575 | 2026-04-18 09:34:26 | MASTER-OAGH | (16h 22m 13.44s , -22d 38m 32.3s) | C | 180 | 19.2 |
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 44337
Subject
EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
Date
2026-04-18T08:34:24Z (6 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
K. R. Ni (CCNU), Y. L. Wang (NAO, CAS; ICE, CSIC), Y. Q. Zhao (USTC; PRIC) and Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team:
The X-ray transient EP260417a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Wang et al., GCN 44325) at 2026-04-17 00:23:02 (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 1.32 × 10^21 cm^-2, and a photon index of 0.78 (+/-0.27). The derived average unabsorbed 0.5-4 keV flux is 1.57 (+0.49/-0.39) × 10^(-10) erg/s/cm^2.
Follow-up observation by the Follow-up X-ray Telescope (FXT) on board EP was performed at 2026-04-17T14:24:17 (UTC), ~14 hours after the WXT detection. 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. = 245.3232, DEC = -22.0249 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The FXT light curve shows no significant variability. The average FXT 0.5-10 keV spectra can be fitted with an absorbed power-law with a free hydrogen column density of 1.54 (+/-0.4) × 10^21 cm^-2, and a photon index of 1.68 (+/-0.13). The derived average unabsorbed 0.5-10 keV flux is 7.79 (-0.76/+0.89) × 10^(-12) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
We note that the X-ray position determined from EP/FXT observation is ~6.6 degrees away from that of GRB 260417A, which is RA = 252.0, Dec = -19.8 (J2000) with a statistical uncertainty of 3.4 degrees, as reported by the Fermi GBM team (GCN 44317). The detection in X-rays by WXT was ~13 minutes later than the reported GBM detection time of GRB 260417A. Therefore it is possible that GRB 260417A is the Gamma-ray counterpart of EP260417a.
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 44326
Subject
EP260417a: TRT optical counterpart detection
Date
2026-04-17T11:48:23Z (7 days ago)
From
L. B. He at NAOC <helb@bao.ac.cn>
Via
Web form
L.B. He (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), S.Q. Jiang, X. Liu, Z.P. Zhu, J. An, D. Xu (NAOC), S.Y. Fu (HUST) report:
We observed the field of EP260417a detected by EP (Wang et. al, GCN 44325), using the 0.7-m telescope of the Thai Robotic Telescope network, located at Cerro Tololo Inter-American Observatory, Chile (TRT-CTO). We obtained a series of frames in the Sloan-r band.
An uncatalogued source is detected within the EP/WXT error circle at coordinates
R.A. (J2000) = 16:21:17.47 (245.3228),
Dec. (J2000) = -22:01:26.31 (-22.0240)
with an uncertainty of ~ 1.0 arcsec. The source had r = 20.30 +/- 0.03 mag at a median time of ~ 7.92 hr post-trigger, calibrated with Pan-STARRS1 DR2 and not corrected for Galactic extinction.
No NEO would be at the above position at the observational time by checking MPC.
We thus think the source could be the optical counterpart of EP260417a.
GCN Circular 44325
Subject
EP260417a: Einstein Probe detection of an X-ray transient
Date
2026-04-17T11:44:47Z (7 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Y. L. Wang (NAO, CAS; ICE, CSIC), Y. Q. Zhao (USTC; PRIC), K. R. Ni (CCNU) and Z. X. Ling (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 EP260417a. The source was detected at 2026-04-17 00:23:02 (UTC). The WXT light curve showed a slow decreasing trend. The WXT position of the source is R.A. = 245.324 deg, DEC = -22.023 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). Preliminary spectral analysis with an absorbed power-law model gave a best-fit photon index of 0.75 (-0.38/+0.97) and an unconstrained hydrogen column density of ~2.3e-20. The unabsorbed 0.5-4 keV flux is 1.3(-0.3/+0.4)e-10 erg/s/cm^2. Quoted uncertainties are at 90% confidence level.
A follow-up observation with the Follow-up X-ray Telescope (FXT) on board EP has been scheduled. 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).