EP250108A
GCN Circular 38995
Subject
EP 250108A: Late-time optical observation by LCO
Date
2025-01-20T06:12:24Z (4 months ago)
From
ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994@gmail.com>
Via
Web form
Ankur Ghosh, Soebur Razzaque (CAPP, University of Johannesburg), Rahul Gupta (NASA GSFC), Alexander Moskvitin, Yulia Sotnikova (SAO RAS), Naveen Dukiya (ARIES) on behalf of a larger collaboration.
We observed the field of the EP 250108A triggered by Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) (Li et al., GCN 38861) in V filter of the 1-meter Sinistro telescope at the Las Cumbres Observatory Global Telescope (LCOGT) node located at South African Astronomical Observatory (SAAO). The 1-m Sinistro telescope is equipped with a 4K x 4K CCD (FOV: 26 x 26 arcmin, scale: 0.39 arcsec/pixel).
Observations began on January 19, 2025, starting 11.4 days after the GRB trigger.
We clearly detect the optical transient (OT) reported by GCNs ( Zhu et al., GCN 38885; Malesani et al., GCN 38902; Kumar et al., GCN 38907; Zhu et al, GCN 38908; Levan et al., GCN 38909; Izzo, GCN 38912; Zou et al., GCN 38914; Moskvitin & Spiridonova, GCN 38925; Song et al., GCN 38972, Eyles-Ferris et al., GCN 38983) in our V, r band image. There is a confirmation of the Ic-BL supernova connection with EP 250108A (Xu et al., GCN 38984, Levan et al., GCN 38987). Observations are still ongoing in other filters.
|Date| |UTstart| |t-T0 (days)| |Exp (sec)| |Filter| |Magnitude|
2025-01-19 21:59:26.59 11.4 1 x 1200 V V = 20.37 +/- 0.04
The field was calibrated against nearby APASS stars, with magnitudes converted using Lupton (2005) equations, and has not been corrected for Galactic extinction.
GCN Circular 39108
Subject
EP250108A / SN 2025kg: Upper limits from a neutrino search with IceCube
Date
2025-01-31T15:15:59Z (4 months ago)
From
Jessie Thwaites at IceCube/U Wisc-Madison <thwaites@wisc.edu>
Via
Web form
The IceCube Collaboration (http://icecube.wisc.edu/) reports:
IceCube has performed a search for track-like muon neutrino events arriving from the direction of the FBOT EP250108A in a time window of [-600, +5000] seconds from the initial trigger reported by Einstein Probe (GCN 38861), during which time IceCube was collecting good quality data (2025-01-08 12:20:28.34 UTC to 2025-01-08 13:53:48.34 UTC). Zero track-like events are found coincident with the position of the FBOT. We accordingly derive a time-integrated muon-neutrino flux upper limit for this source of E^2 dN/ dE = 0.29 GeV cm^-2 at 90% CL, under the assumption of an E^-2 power law. 90% of events IceCube would detect from a source at this declination with an E^-2 spectrum have energies in the approximate energy range between 60 TeV and 20 PeV.
A subsequent search was performed with a time window of [-2, +12] days with respect to the initial trigger (2025-01-06 12:30:28.34 UTC to 2025-01-20 12:30:28.34 UTC). In this case, we report a p-value of 1.0, consistent with background expectation. We accordingly derive a time-integrated muon-neutrino flux upper limit for this source of E^2 dN/ dE = 0.34 GeV cm^-2 at 90% CL, under the assumption of an E^-2 power law.
The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc@icecube.wisc.edu.
[1] IceCube Collaboration, R. Abbasi et al., ApJ 910 4 (2021)
GCN Circular 39146
Subject
EP 250108A: Upper limits from Fermi-GBM Observations
Date
2025-02-04T19:53:01Z (4 months ago)
From
mariaedvige.ravasio@ru.nl
Via
Web form
M. E. Ravasio (Radboud Univ.), E. Burns (LSU), Colleen Wilson-Hodge (NASA Marshall Space Flight Center) and P.G. Jonker (Radboud Univ.) report on behalf of the Fermi-GBM Team:
The location of the EP-WXT event EP250108A (Li et al., GCN 38861) was occulted by the Earth for Fermi at the EP trigger time T0=2025-01-08T12:30:28.34 UTC. There was no Fermi-GBM onboard trigger around EP-WXT times. The location becomes visible at around ~T0+415 s.
The GBM targeted search [1], the most sensitive, coherent search for GRB-like signals, was run in the time interval [-50;+500] s centred at different times, from T0 up to T0+2500s, to cover the whole reported duration of the EP transient, seeking signals between 64 ms and 32.768 s in duration. A transient was found at ~T0+500 s, but its localization is consistent with the Crab nebula, which exited Earth occultation at that time. No signal consistent with the EP transient both temporally and spatially is identified, as confirmed by visual inspection of the data.
Assuming a “soft” spectral template (Band function with Epeak = 70 keV, alpha = -1.9, beta = -3.7), and a duration of 8.192 s, the most conservative sky-averaged upper limit is found in the time interval [T0+1450; T0+2000] s, corresponding to a flux of 2.6e-08 erg/cm2/s in the energy band 10-1000 keV.
[1] Goldstein et al. 2019 arXiv:1903.12597