EP260812a
GCN Circular 45394
Subject
EP260812a: AbAO optical upper limit
Date
2026-08-18T14:36:58Z (9 days ago)
From
Nicolai Pankov at IKI <colinsergesen@gmail.com>
Via
Web form
N. Pankov (IKI), R. Ya. Inasaridze (AbAO), A. Pozanenko (IKI), M. Zhuzhunadze
(AbAO) report on behalf of IKI-GRB-FuN:
We observed the field of the Einstein Probe fast X-ray transient EP260812a
(Liu et al., GCN 45362) with the AS-32 telescope of Abastumani Observatory
(AbAO). The observations were conducted on 2026-08-13 starting at 17:12:50 UT,
i.e. ~1.267 days since trigger. The series of 66x60 sec exposures was taken in
the R-filter using CCD-photometer. No new sources was identified within the
X-ray error circle (Yang et al., GCN 45373). A faint optical source found in
the NOT and LT observations (Corcoran et al., GCN 45376) is not detected in our
observations. The observation summary and preliminary upper limit are
provided below:
Date UTstart t-T0 Exp. Filter UL
(mid, d) (n*s) (3sigma)
2026-08-13 17:12:50 1.26723 65x60 R 22.1
The photometry is based on nearby USNO-B1.0 stars (R2 magnitudes) and has not
been corrected for the Galactic extinction. Our results are consistent with the
upper limits reported by Yin et al. (GCN 45372), Corcoran et al. (GCN 45376),
and Mirzakulov et al. (GCN 45387).
GCN Circular 45387
Subject
EP260812a: AZT-22 optical upper limit
Date
2026-08-15T14:16:38Z (12 days ago)
From
Xiaofeng Wang at Tsinghua University <wang_xf@mail.tsinghua.edu.cn>
Via
Web form
D. Mirzakulov (UBAI), J. Baxtiyorov (UBAI), X.-F. Wang (THU), S. Ehgamberdiev (UBAI), A. Shaymanov (Maidanak Observatory/UBAI), and H.-W. Peng (THU) report on behalf of the UBAI and THU joint teams:
We observed the field of the Einstein Probe fast X-ray transient EP260812a (Liu et al., GCN 45362) with the AZT-22 1.5~m telescope of the Maidanak Astronomical Observatory (MAO) starting on 2026-08-12 at 15:49:06 UTC, and obtained 4x300s exposure in the B and R filters using 4kx4k CCD SNUCAM camera (Im et al., 2010).
We did not detect any optical counterpart at positions provided either by EP-WXT (Liu et al., GCN 45362) or by Corcoran et.al. (GCN 45376) in our stacked frames. We measure the following upper limits for our stacked images:
DATE-OBS t-T0(hrs) Exptime(s) Filter Upperlimit(mag) Site/Telescope
2026-08-12T15:49:06 4.468 4x300 B 23.30 MAO/AZT-22
2026-08-12T16:12:58 4.866 3x300 R 23.05 MAO/AZT-22
2026-08-12T20:29:38 9.144 4x300 B 23.92 MAO/AZT-22
2026-08-12T20:36:41 9.261 4x300 R 23.72 MAO/AZT-22
2026-08-13T16:29:13 29.137 4x300 R 23.28 MAO/AZT-22
All the data have been reduced by the data processing pipeline, STDWeb (Karpov 2025). We performed images subtraction on the stacked images using the Pan-STARRS templates. The photometry was calibrated using the Gaia DR3 Synphot catalog and was not corrected for extinction.
We thanks the MAO staff for supporting the observations.
GCN Circular 45376
Subject
EP260812a: NOT and Liverpool Telescope upper limits:
Date
2026-08-13T15:24:20Z (14 days ago)
From
Gregory Corcoran at University College Dublin <gregory.corcoran@ucdconnect.ie>
Via
Web form
G. Corcoran (UCD), R. A. J. Eyles-Ferris (Leicester), D. B. Malesani (DAWN/NBI and Radboud), P. G. Jonker (Radboud), R. L. C. Starling (Leicester), V. Vuolteenaho (NOT / University of Oulu), K. Kisielowski (ING / University of Groningen), R. Vieliute (ING / University of St Andrews) report on behalf of a larger collaboration:
We observed the field of the Einstein Probe fast X-ray transient EP260812a (Liu et al., GCN 45362) with the Nordic Optical Telescope (NOT) using the ALFOSC camera and the Liverpool Telescope (LT) using the IO:O camera. NOT observations started on 2026-08-12 at 20:52:46 UT (9.53 hr post trigger), while LT observations began on 2026-08-12 at 23:23:50 UT (12.06 hr post trigger).
We do not identify any new object brighter than our reference Pan-STARRS image sensitivity limit, however our observations are deeper. We note the presence of one possible source, detected in both the NOT and LT r-band images, located at coordinates RA, Dec = 20:45:45.28, +14:09:21.3 (J2000), for which we measure a magnitude of r = 23.87 +/- 0.24 (AB) from the NOT images. However, as our observations cannot establish if this is a new source, further follow up observations are encouraged and planned. A summary of our observations is presented below.
| Telescope | Mid time (hr) | Band | Exptime (s) | Limit mag (3 sigma) |
|---|---|---|---|---|
| NOT | 9.66 | r | 3 x 300 | 24.11 |
| NOT | 9.96 | z | 5 x 200 | 22.99 |
| LT | 12.16 | r | 4 x 150 | 23.57 |
| LT | 12.44 | z | 5 x 150 | 22.60 |
Our photometry is in the AB system, calibrated against Pan-STARRS and not corrected for Galactic extinction. These limits are consistent with those reported by Yin et al. (GCN 45372).
GCN Circular 45373
Subject
EP260812a: refined analysis of the EP-WXT and autonomous EP-FXT observation
Date
2026-08-13T11:10:34Z (14 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
G. J. Yang, H. R. Ren, Tian-Yu Liu and H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team:
The X-ray transient EP260812a triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Liu et al., GCN 45362) and followed by Yin et al., GCN 45372. The refined analysis of the WXT data shows that the event started at T0=2026-08-12T11:20:03(UTC) and lasted for 60 s before the observation was interrupted by the autonomous follow-up observation.The average WXT 0.5–4 keV spectrum can be fitted with an absorbed power-law model. The best-fit photon index is 1.54 (-0.82/+0.88), and the hydrogen column density is 3.3 (-2.6/+2.9) × 10^21 cm^-2. The derived average unabsorbed 0.5–4 keV flux is 2.72 (-0.73/+1.59) × 10^-9 erg s^-1 cm^-2.
The autonomous observation by the Follow-up X-ray Telescope (FXT) was performed at 2026-08-12 11:25:03(UTC), about 5 minutes after T0. The exposure time of this observation is 3898 s. The on-ground analysis shows that an uncatalogued source was detected at R.A., Dec. = 311.4373, 14.1577 deg (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic). The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fitted Galactic equivalent hydrogen column density of 1.0 × 10^21 cm^-2 and a photon index of 2.00 (-0.08/+0.08). The derived average unabsorbed 0.5-10 keV flux is 2.61(-0.14/+0.15)× 10^(-11) erg/s/cm^2. The uncertainties are at the 1 sigma confidence level for the above parameters.
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 45372
Subject
EP260812a: SVOM/C-GFT optical upper limit
Date
2026-08-13T06:50:14Z (14 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
S.J. Yin (GXU), Z. Kang (CHO), Y.X. Guan (GXU), C. Wu (NAOC), L.P. Xin, X.H. Han, P.P. Zhang, X.M. Lu (NAOC), Z.W. Li, Y. Lv (CHO), R.S. Zhang, Y.J. Xiao, Y.L. Qiu, J. Wang, J.S. Deng, L. Huang, J.Y. Wei (NAOC) report on behalf of the SVOM/C-GFT team:
We observed the field of EP260812a detected by EP-WXT (Liu et al., GCN 45362) with LATIOS on SVOM/C-GFT. Observations started at 2026-08-12T11:28:12 UTC, ~ 7.2 minutes after the trigger.
We obtained r-band follow-up imaging（Poor weather interrupted the observations, affecting image quality）. After preliminary analysis，no credible candidate was detected within the error box provided by EP-WXT (Liu et al., GCN 45362) in our images. We measure the following upper limit calibrated against the Pan-STARRS DR1 catalog, and not corrected for Galactic extinction:
r > 18.3 AB (3-sigma, mid-time 27.5 min after the trigger).
We thank the observation assistants B.-W. Li and H.-X. Xue at Jilin observatory for their excellent support.
The Chinese Ground Follow-up Telescope (C-GFT) for the SVOM mission is located at Jilin Station, Changchun Observatory, National Astronomical Observatories, CAS. It features two instruments: (1) CATCH at the Cassegrain focus with a 21 arcmin x 21 arcmin FOV for simultaneous g/r/i-band imaging, and (2) LATIOS, a 4k x 4k CMOS camera at the prime focus with a 1.28 deg x 1.28 deg FOV that images in g, r, and i bands via filter switching.
GCN Circular 45362
Subject
EP260812a: Einstein Probe detection of an X-ray transient
Date
2026-08-12T12:00:11Z (15 days ago)
Edited On
2026-08-12T13:07:46Z (15 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Tian-Yu Liu, H. R. Ren, G. J. Yang and H. Sun (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 EP260812a. The transient triggered EP-WXT (ID: 01709278114) at 2026-08-12T11:21:01 (UTC). The WXT position of the source is R.A. = 311.450 deg, DEC = 14.142 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic).
A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 311.4377 deg, DEC = 14.1600 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).