EP250304A
GCN Circular 39594
Subject
EP 250304A: Optical counterpart detection by LCO
Date
2025-03-05T09:43:20Z (3 months ago)
From
ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994@gmail.com>
Via
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Ankur Ghosh, Soebur Razzaque (CAPP, University of Johannesburg), Alexander Moskvitin, Yulia Sotnikova (SAO RAS), Naveen Dukiya (ARIES), Rahul Gupta (NASA GSFC) on behalf of a larger collaboration.
We observed the field of the EP 250304A triggered by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Chen et al., GCN 39580) in r filter of the 1-meter Sinistro telescope at the Las Cumbres Observatory Global Telescope (LCOGT) node located at South African Astronomical Observatory (SAAO), South Africa. 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 March 04, 2025, starting 19.80 hours after the GRB trigger.
We clearly detect the optical transient (OT) reported by GCNs (Xu et al, GCN 39583, Page et al., GCN 39584, Saccardi et al., GCN 39585, Shilling et al., 39587) in our r band image.
|Date| |UTstart| |t-T0 (hours)| |Exp (sec)| |Filter| |Magnitude|
--------------------------------------------------------------------------------------------------
2025-03-04 21:20:52.80 19.80 1 x 1000 r r = 20.00 +/- 0.08
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 39600
Subject
EP250304A: Upper limits from Fermi-GBM Observations
Date
2025-03-06T09:13:06Z (3 months ago)
From
mariaedvige.ravasio@ru.nl
Via
Web form
M. E. Ravasio (Radboud Univ.), E. Burns (LSU), and P.G. Jonker (Radboud Univ.) report on behalf of the Fermi-GBM Team:
At the starting time T0=2025-03-04T01:29:49 UTC of the EP-WXT event EP250304A (Zhang et al., GCN 39591), Fermi was in South Atlantic Anomaly (SAA). Fermi-GBM had exited SAA approximately 50 seconds after T0. There was no Fermi-GBM onboard trigger around EP-WXT time.
The GBM targeted search [1], the most sensitive, coherent search for GRB-like signals, was run in the time interval [T0-50;T0+500] s, seeking signals between 64 ms and 32.768 s in duration. 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, we derive a sky-averaged flux upper limit of 3.9e-08 erg/cm2/s in the energy band 10-1000 keV.
[1] Goldstein et al. 2019 arXiv:1903.12597