GCN Circular 46097
Subject
GRB 261029A: FRAM-ORM and FRAM-Auger optical afterglow light curve
Event
Date
2026-10-29T17:15:07Z (2 days ago)
From
Filip Novotný at Masaryk University <filip.novotny@talentovani.cz>
Via
Web form
Filip Novotny, Martin Jelinek and Jan Strobl
(ASU CAS Ondrejov, CZ),
Martin Masek, Sergey Karpov, Petr Janecek, Jakub Jurysek,
Jan Ebr, Ronan Cunniffe, Petr Travnicek and Michael Prouza
(Institute of Physics, Prague, CZ)
report:
The 25 cm robotic telescope FRAM-ORM at La Palma (Spain) reacted
robotically to the SVOM/ECLAIRs alert of GRB 261029A (Goto et al.,
GCN 46072; Fermi GBM Team, GCN 46071), obtaining a series of
120 x 60 s unfiltered images between 01:38:35 and 03:55:27 UT,
i.e. from ~11.5 min to ~148 min post trigger.
We clearly detect the optical afterglow (O'Neill et al., GCN 46073;
He et al., GCN 46078; Wang et al., GCN 46079; De et al., GCN 46080;
Cotter et al., GCN 46081; Sanchez Alvarez et al., GCN 46083; Yin et
al., GCN 46084; Shi et al., GCN 46088; Kang et al., GCN 46090; Ma et
al., GCN 46092) in single images up to ~T0+42 min and in combined
frames thereafter. Forced aperture photometry at the GOTO position
yields, for the first image and the last combined frame:
T-T0[mid] Images Filter Mag (AB)
12.0 min 1 x 60 s CR 13.30 +/- 0.03
138.0 min 18 x 60 s CR 17.42 +/- 0.10
CR denotes unfiltered magnitudes calibrated to the r band.
The 30 cm robotic telescope FRAM-Auger at the Pierre Auger
Observatory (Malargue, Argentina) also reacted to the alert. The
images obtained before 02:53 UT are not usable due to a technical
problem. Combining 14 x 60 s R-band images obtained between 02:57:57
and 03:15:44 UT at an elevation of ~20 deg, we detect the afterglow
with R(Vega) = 16.34 +/- 0.10 at T0+99 min.
A preliminary fit suggests a steeper decay before ~T0+50 min,
followed by a shallower power-law decline, F ~ t^-alpha, with
alpha ~ 1.3. Our late-time magnitudes are consistent with those
reported by NOT, LCO and TRT (Cotter et al., GCN 46081; Yin et al.,
GCN 46084; He et al., GCN 46078).
The photometry was reduced with the PyRT pipeline and is calibrated
against the ATLAS-REFCAT2 catalogue (Tonry et al. 2018, ApJ, 867,
105). It is not corrected for Galactic extinction.