GRB 260105C, EP260105b
GCN Circular 43360
Subject
EP260105b / GRB 260105C : Fermi-GBM Sub-Threshold Detection
Date
2026-01-09T17:32:30Z (a month ago)
Edited On
2026-01-09T20:00:11Z (a month ago)
From
mariaedvige.ravasio@ru.nl
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov>
Via
Web form
M. E. Ravasio (ICE-CSIC and Radboud Univ.), and P.G. Jonker (Radboud Univ.)
and
E. Burns (LSU), M. Hui (NASA MSFC), R. Hamburg and O. Mukherjee (USRA) report on behalf of the Fermi-GBM Team:
Fermi-GBM had full spatial and temporal coverage of the transient EP260105b detected by EP-WXT (Yang et al., GCN 43340, EP Team GCN 43349). There was no Fermi-GBM onboard trigger around the EP trigger time at T0=2026-01-05T18:47:36 UTC.
The GBM Targeted Search [1], the most sensitive, coherent search for GRB-like signals, was run in the time interval [-50;+500] s from the EP T0. A transient was found, with the most significant signal at T0-32 s on a 16 s timescale, with a false alarm rate of 6.5e-05 Hz. The localisation is consistent with the EP one, with a spatial association probability of 96.3%. Among the three spectral templates tested, the transient was best-fit with a “normal” spectral template (Band function with Epeak = 230 keV, alpha = -1.0, beta = -2.3) for a GRB.
[1] Goldstein et al. 2019 arXiv:1903.12597
GCN Circular 43349
Subject
EP260105b/EP-WXT trigger 01709251028: Einstein Probe detection of an X-ray transient
Date
2026-01-07T13:08:28Z (a month ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
X. X. Sun, G. J. Yang, M. J. Liu, , C. C. Jin, Y. Liu (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 EP260105b. The transient triggered EP-WXT (ID: 01709251028) at 2026-01-05T18:47:36 (UTC). The WXT position of the source is R.A. = 158.387 deg, DEC = 17.616 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic).
In a previous Circular (Yang et al. , GCN 43340) , this event was tentatively classified as a stellar flare associated with ET Leo, based on the preliminary localization and flux estimation available at that time. After refined data processing and ground analysis of the WXT and FXT observations, we find that the evnet is unlikely to be a stellar flare from ET Leo. We find a short-timescale X-ray varability in the WXT refined telemetry data, therefore classify this event as an X-ray transient.
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. = 158.3695 deg, DEC = 17.6123 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic). A significant decay was detected in the light curve during the initial phase of FXT observation. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 2.97 x 10^20 cm^-2 and a photon index of 2.18(-0.87,0.92). The derived average unabsorbed 0.5-10 keV flux is 2.6 (-0.94/+2.59) x 10^(-13) erg/s/cm^2.
Further multiwavelength follow-up observations are encouraged to clarify the physical nature of this transient.
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).