Gravitational-wave follow-up with CTA after the detection of GRBs in the TeV energy domain

TL;DR

This paper explores how the Cherenkov Telescope Array (CTA) can enhance gravitational-wave follow-up observations of gamma-ray bursts in the TeV energy range, leveraging recent TeV detections to improve detection strategies and coordination.

Contribution

It analyzes the implications of TeV emission for optimizing CTA's gravitational-wave follow-up strategies, including timing, telescope configuration, and network coordination.

Findings

TeV emission allows for delayed CTA observations by over an hour.

Small size telescopes with large fields of view are advantageous for follow-up.

Prioritization and network coordination are essential for effective follow-up.

Abstract

The recent discovery of TeV emission from gamma-ray bursts (GRBs) by the MAGIC and H.E.S.S. Cherenkov telescopes confirmed that emission from these transients can extend to very high energies. The TeV energy domain reaches the most sensitive band of the Cherenkov Telescope Array (CTA). This newly anticipated, improved sensitivity will enhance the prospects of gravitational-wave follow-up observations by CTA to probe particle acceleration and high-energy emission from binary black hole and neutron star mergers, and stellar core-collapse events. Here we discuss the implications of TeV emission on the most promising strategies of choice for the gravitational-wave follow-up effort for CTA and Cherenkov telescopes more broadly. We find that TeV emission (i) may allow more than an hour of delay between the gravitational-wave event and the start of CTA observations; (ii) enables the use of CTA's small size telescopes that have the largest fields of view. We characterize the number of pointings needed to find a counterpart. (iii) We compute the annual follow-up time requirements and find that prioritization will be needed. (iv) Even a few telescopes could detect sufficiently nearby counterparts, raising the possibility of adding a handful of small-size or medium-size telescopes to the network at diverse geographic locations taking into account the positions of CTA and the LIGO-Virgo-KAGRA network. (v) The continued operation of VERITAS/H.E.S.S./MAGIC would be a useful compliment to CTA's follow-up capabilities by increasing the sky area that can be rapidly covered, especially for directions above and 'below' the United States in which the present network of gravitational-wave detectors is more sensitive.