TITLE:   GCN CIRCULAR
NUMBER:  46093
SUBJECT: GRB261029A: Infrared fading detected with MDM/MIRAGE
DATE:    26/10/29 15:08:32 GMT
FROM:    Kishalay De at Columbia University <kd3038@columbia.edu>

K. De (Columbia U), S. Manyan (Columbia U), G. Mo (Caltech/Carnegie), V. Karambelkar (Columbia U), D. Schiminovich (Columbia U) report:

We performed a second infrared observation of the field of GRB 261029A detected by Fermi GBM (Fermi GBM Team, GCN 46071), SVOM (Goto et al., GCN 46072), Fermi/LAT (Longo et al., GCN 46085) and AstroSat CZTI (Salunke et al., GCN 46089) in the near-infrared J and Hs band with the MDM InfraRed Astronomy inGaas Experiment (MIRAGE) instrument on the MDM 1.3m telescope.

Optical observations have been reported in O'Neill et al. GCN 46073; He et al. GCN 46078; Wang et al. GCN 46079; Cotter et al. GCN 46081; Álvarez et al., GCN 46083; Yin et al., GCN 46084; Shi et al., GCN 46088; Kang et al., GCN 46090 and Ma et al. GCN 46092.

The second epoch of infrared observations began at 2026-10-27T09:08 (7.5 hours after GRB trigger) in the J band lasting 1080 s, and in the Hs band lasting 1590 s. We clearly detect an infrared source at the reported optical position with J = 18.52 +/- 0.08 AB mag and Hs = 18.76 +/- 0.20 AB mag. Compared to our previous infrared observation at at 1.5 hours after GRB trigger (De et al. GCN 46080), our measurements indicate rapid infrared fading of ~ 2.2 mag in 6 hours.

MIRAGE is a new robotic YJHs-band near infrared imager for the MDM 1.3 m telescope. We thank the Mt Cuba astronomical foundation for supporting development of MIRAGE and MDM Observatory staff for supporting the observations.