EP260707a
GCN Circular 45112
Subject
EP260707a (by EP-FXT): NOT optical upper limit
Date
2026-07-08T04:41:03Z (2 days ago)
From
sqjiang at NAOC <sqjiang@bao.ac.cn>
Via
Web form
X. Liu, S.Q. Jiang, Z.P. Zhu, J. An, L.B. He, D. Xu (NAOC), S.Y. Fu (HUST), J.P.U. Fynbo (DAWN/NBI), F. Mustafaj (NOT) report:
We observed the field of the uncatalogued X-ray source detected by EP-FXT (Zhou et al., GCNs 45107 & 45111), located within the EP-WXT error circle of the very likely fake event of EP260707a, using the 2.56m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observation started at 2026-07-08 01:09:50.53 UT, i.e., 8.41 hr post-burst, and a series of r-band frames were obtained.
No new optical transient is detected in the stacked image within the EP-FXT error circle (GCN 45107), down to a 5-sigma limiting magnitude of r ~ 23.0 (AB), calibrated with Pan-STARRS DR2 stars in the field and not corrected for Galactic extinction.
GCN Circular 45111
Subject
EP260707a is not a real source
Date
2026-07-08T02:34:57Z (2 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
H. Zhou, Y. F. Liang (PMO), K. R. Ni (CCNU), C.-K. Kan (HKU), H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team:
We report on the follow-up analysis of the X-ray transient candidate EP260707a, initially triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Zhou et al. GCN 45107) also followed by optical telescopes (Liu et al. GCN 45109, Strausbaugh et al. GCN 45110)
Following the analysis of the telemetry data, we found that the EP260707a is not a real transient. The uncatalogued X-ray source subsequently detected by the Follow-up X-ray Telescope (FXT) within the WXT error circle is considered as a coincidental alignment, rather than a counterpart to a real transient.
We apologize for any inconvenience caused to the community.
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 45110
Subject
EP260707a: LCOGT Optical Upper Limit
Date
2026-07-07T21:12:22Z (2 days ago)
From
Robert Strausbaugh at Eastern Illinois University <rstrausbaugh@eiu.edu>
Via
email
R. Strausbaugh (Eastern Illinois University), A. Cucchiara (NASA) report on behalf of a larger collaboration:
We observed the EP260707a field (Zhou et al., GCN 45107) with the LCOGT 1-meter Sinistro instrument at the South African Astronomical Observatory site, on July 7, from 20:02 to 20:35 UT (corresponding to 3.28 to 3.83 hours after the trigger time) with the SDSS r and i filters.
We performed a series of 3x300s exposures in i-band and r-band. We do not detect an uncatalogued source in the FXT error region, consistent with other optical upper limits (Liu et al., GCN 45109).
The following magnitudes are calculated using the PanSTARRS catalog as reference:
r > 22.1
i > 21.6
These magnitudes are not corrected for galactic extinction.
GCN Circular 45109
Subject
EP260707a: TRT optical upper limit
Date
2026-07-07T19:33:31Z (2 days ago)
From
liuxing@nao.cas.cn
Via
Web form
X. Liu (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), S.Y. Fu (HUST), S.Q. Jiang, J. An, L.B. He, Z.P. Zhu, D. Xu (NAOC) report:
We observed the field of EP260707a detected by EP (Zhou et al., GCN 45107) using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at New South Wales, Australia (SBO). 4x300s frames in the R-band were obtained at a median time of 1.52 hr post-trigger.
No uncatalogued optical transient is detected in the stacked image within the EP/FXT error circle (Zhou et al., GCN 45107), down to a 5-sigma limiting magnitude of R ~ 21.0 (Vega), calibrated with Pan-STARRS DR2 stars in the field converted using Lupton (2005) equations and not corrected for Galactic extinction.
GCN Circular 45107
Subject
EP260707a: Einstein Probe detection of an X-ray transient
Date
2026-07-07T18:30:09Z (2 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
H. Zhou, Y. F. Liang (PMO), K. R. Ni (CCNU), C.-K. Kan (HKU), 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 EP260707a. The transient triggered EP-WXT (ID: 01709274241) at 2026-07-07T16:45:24 (UTC). The WXT position of the source is R.A. = 306.233 deg, DEC = -26.589 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. = 306.1900 deg, DEC = -26.5853 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).