GCN Circular 45964
Subject
GRB 261010A: Pan-STARRS z-band imaging and upper limit
Event
Date
2026-10-16T16:13:47Z (6 hours ago)
From
James Gillanders at University of Oxford <jhgillanders.astro@gmail.com>
Via
Web form
J. H. Gillanders (Oxford), M. Huber, K. C. Chambers, D. Jones, A. S. B. Schultz (IfA, Univ. Hawaii), S. J. Smartt, K. W. Smith, (Oxford/QUB), S. Srivastav (Oxford), M. Nicholl, D. Young (QUB), T.-W. Chen (NCU, Taiwan) T. de Boer, J. Fairlamb, G. Paek, C. C. Lin, T. Lowe, E. Magnier, P. Minguez, I. A. Smith, R. J. Wainscoat (IfA, Univ. Hawaii).
We observed the field of GRB 261010A, discovered by the Fermi GBM Team (GCN 45888) and also detected by Swift/BAT (Lien et al., GCN 45889), Konus-Wind (Frederiks et al., GCN 45925), GRID (Yu et al., GCN 45940) and Glowbug (Cheung et al., GCN 45950), with the Pan-STARRS1 telescope (Chambers et al., 2016, arXiv e-prints, 1612.05560) in an effort to constrain the presence of transient flux at the position of the afterglow, as discovered by O’Neill et al. (GCN 45890), and subsequently detected by Aceituno et al. (GCN 45891), Corcoran et al. (GCN 45912), Castro-Tirado et al. (GCN 45928), Marchesini et al. (GCN 45952) and Rastinejad et al. (GCN 45957).
Our observation commenced on MJD 61327.22 (exposure midpoint; corresponding to 3.41 days post-GRB) and consisted of 6x300s exposures in z-band. We processed our images with the standard Pan-STARRS pipeline, whereby the images were astrometrically and photometrically calibrated before stacking (Magnier et al., 2020a, ApJS, 251, 3; Magnier et al., 2020b, ApJS, 251, 6; Waters et al., 2020, ApJS, 251, 4). No difference imaging was applied as the PS1 3Pi reference stack is significantly shallower than this 1800s stack.
We inspected this stacked target image and no detection of a source at the position of the afterglow is visible. We estimate a z-band 3-sigma upper limit, m_z > 22.5. At the redshift of the purported nearby host galaxy (z = 0.070; Corcoran et al., GCN 45912), this corresponds to a limit of M_z = -15 (assuming a distance modulus of 37.5, and ignoring extinction effects). At 3.4 days post-burst, AT2017gfo possessed m_z = 18.74 +/- 0.02 (Smartt et al., 2017, Nature, 551, 75), which, rescaled to z = 0.070, corresponds to m_z ~ 23. Thus, we would not expect to recover a signal for an AT2017gfo-like kilonova at this redshift. Of course this is also the case for an association with the alternative proposed host galaxy at z = 0.785 (Castro-Tirado et al., GCN 45928).
The Pan-STARRS system consists of two 1.8m telescope units located at the summit of Haleakala on the Hawaiian island of Maui, employing an SDSS-like filter system denoted as grizy, and a broad w-filter, which is a composite of the gri-filters.