The detectability of high-redshift gamma-ray bursts near-infrared afterglows with CAGIRE

TL;DR

This paper evaluates CAGIRE's ability to detect high-redshift gamma-ray burst afterglows in the near-infrared, demonstrating its potential to identify some of the most distant GRBs up to redshifts of 13.3.

Contribution

It presents an end-to-end simulation framework to assess CAGIRE's performance in detecting faint, high-redshift GRB afterglows in the near-infrared bands.

Findings

CAGIRE can detect GRB afterglows up to z=9.6 in J band and z=13.3 in H band.

Early observations within two minutes post-burst improve detection prospects.

Simulations show CAGIRE's potential to discover the most distant GRBs to date.

Abstract

Context. Transient sky astronomy is entering a new era with the advent of the SVOM mission (Space Variable Objects Monitor), which was successfully launched on the 26th of June, 2024. The primary goal of SVOM is to monitor the hard X-ray sky searching for gamma-ray bursts (GRBs). On top of its on-board follow-up capabilities, SVOM will be backed by its ground segment composed of several facilities, of which the near-infrared imager CAGIRE. Mounted on the robotic telescope COLIBRI, it will be a unique instrument, able to perform fast follow-up of GRB afterglows in J and H bands, an ideal combination to catch high-redshift (z>6) and/or obscured GRBs. Aims. This paper aims at estimating the performances of CAGIRE for GRB near-infrared afterglow detection based on the characteristics of the detector and the specificities of the COLIBRI telescope. Quickly fading GRB afterglows pose challenges that should be addressed by adapting observing strategies to the capabilities of CAGIRE. Methods. We use an end-to-end image simulator to produce realistic CAGIRE images, taking into account results from the characterization of the ALFA detector used by CAGIRE. We implemented a GRB afterglow generator that simulates infrared lightcurves and spectra based on published observation of distant GRBs (z>6). Results. We retrieved the photometry of 9 GRB afterglows in various scenarios covered by CAGIRE. Catching afterglows as early as two minutes after burst allows the identification of a nIR counterpart in the brightest 4 events. When artificially redshifted even further away, these events remain detectable by CAGIRE up to z=9.6 in J band, and z=13.3 in H band, indicating the potential of CAGIRE to be a pioneer in the identification of the most distant GRBs to date.