A Fast-cadenced Search for Gamma-Ray Burst Orphan Afterglows with the Deeper, Wider, Faster Programme

• DOI: 10.48550/arxiv.2405.11949
• Publication Date: 2024-05-20
• Authors: James Freeburn; Jeff Cooke; A. Möller; Dougal Dobie; Jielai Zhang; O. S. Salafia; K. Siellez; Katie Auchettl; Simon Goode; T. M. C. Abbott; Igor Andreoni; Rebecca Allen; Natasha Van Bemmel; Sara Webb
• Keywords: Orphan drug

The relativistic outflows that produce Long GRBs (LGRBs) can be described by a structured jet model where prompt $\gamma$-ray emission is restricted to narrow region in the jet's core. Viewing off-axis from core, population of afterglows without an associated GRB detection predicted. In this work, we conduct archival search for these `orphan' (OAs) with minute-cadence, deep ($g\sim23$) data Dark Energy Camera (DECam) taken as part Deeper, Wider, Faster programme (DWF). We introduce method select fast-evolving OA candidates within DWF comprises machine learning model, based on realistic synthetic OAs. Using classifier, recover 51 candidates. Of candidates, 42 are likely flare events M-class stars. remaining nine possess quiescent, coincident sources angular profiles consistent star. Comparing expected LGRB host galaxies, conclude Galactic events. calculate upper limit rate OAs down $g<22$ AB mag 2.49 deg$^{-2}$yr$^{-1}$ using our criteria and constrain parameter space possible structures. also place characteristic angle between emitting half opening angle, assuming shallow structure power-law index 0.8. These values $58.3^{\circ}$ $56.6^{\circ}$ smooth core respectively.