The capability of the Australian Square Kilometre Array Pathfinder to detect prompt radio bursts from neutron star mergers

Abstract

We discuss observational strategies to detect prompt bursts associated with gravitational wave (GW) events using the Australian Square Kilometre Array Pathfinder (ASKAP). Many theoretical models of binary neutron stars mergers predict that bright, prompt radio emission would accompany the merger. The detection of such prompt emission would greatly improve our knowledge of the physical conditions, environment, and location of the merger. However, searches for prompt emission are complicated by the relatively poor localisation for GW events, with the 90% credible region reaching hundreds or even thousands of square degrees. Operating in fly’s eye mode, the ASKAP field of view can reach $\sim1\,000$ deg $^2$ at $\sim$ $888\,{\rm MHz}$ . This potentially allows observers to cover most of the 90% credible region quickly enough to detect prompt emission. We use skymaps for GW170817 and GW190814 from LIGO/Virgo’s third observing run to simulate the probability of detecting prompt emission for GW events in the upcoming fourth observing run. With only alerts released after merger, we find it difficult to slew the telescope sufficiently quickly as to capture any prompt emission. However, with the addition of alerts released before merger by negative-latency pipelines, we find that it should be possible to search for nearby, bright prompt fast radio burst-like emission from GW events. Nonetheless, the rates are low: we would expect to observe $\sim$ 0.012 events during the fourth observing run, assuming that the prompt emission is emitted microseconds around the merger.

Electromagnetic Precursors to Black Hole–Neutron Star Gravitational Wave Events: Flares and Reconnection-powered Fast Radio Transients from the Late Inspiral

“…Even more so, sky localization of GW events currently suffers from large uncertainties impeding swift follow-up observations. If radio transients were sourced by the merger, this would potentially enable fast localization by means of all-sky radio observations (Sachdev et al 2020;Wang et al 2020;Yu et al 2021).…”

“…In fact, prior to the merger, the orbiting NS can feature a strong exterior magnetic field, whose dynamics could be relevant in sourcing additional EM transients (Hansen & Lyutikov 2001;Lyutikov 2019). Indeed, this possibility was investigated for previous GW events (Callister et al 2019;Broderick et al 2020; see also Stachie et al 2021Stachie et al , 2022, with further efforts being proposed for future searches (James et al 2019;Gourdji et al 2020;Sachdev et al 2020;Wang et al 2020;Yu et al 2021;Cooper et al 2023). In the context of BH-NS GW events (Abbott et al 2021), the nondetection of such precursor counterparts was used to constrain the magnetic field strength present in the stars before merger (D'Orazio et al 2022).…”

Electromagnetic precursor flares from the late inspiral of neutron star binaries

“…Assuming a near-equal mass binary, q ≈ 1, with canonical neutron star masses m 1 = m 2 = 1.4 M , we find We can see that the number of potentially observable flares will strongly depend on the magnetic field strength and the emission mechanism. More specifically (40) implies, that for magnetic field strengths 10 11 G no flares will be observable. Effects such as unequal magnetization would further decrease the number of flares, as the luminosity can be suppressed by a factor of a few, see Fig.…”

“…As such, precursors are also potential candidates for powerful radio signals (e.g., [33,36]). The prospects for creating early warning systems for electromagnetic follow-up observations of precursor emission has recently been investigated [37][38][39], crucial for their potential future detection [40]. For the event GW170817 attempts have even been made to detect precursor emission [30,41], see also [42,43].…”

MWA rapid follow-up of gravitational wave transients: Prospects for detecting prompt radio counterparts

“…The colour scale corresponds to the probability of detecting a GW event at a particular sky position with respect to the Earth. The highest sensitivity region in the Southern Hemisphere (marked by a red plus) is at an elevation of 58.5 • in the MWA field (also discussed in Wang et al 2020). The red star marks the location of MWA, the red contour shows the full sky coverage of MWA down to an elevation of 30 • , and the grey contour shows the FoV of a standard MWA pointing centred on the highest sensitivity region down to 20% of the primary beam at 120 MHz.…”