Radio Counterparts of Compact Binary Mergers Detectable in Gravitational Waves: A Simulation for an Optimized Survey

Abstract

Mergers of binary neutron stars and black hole-neutron star binaries produce gravitational-wave(GW) emission and outflows with significant kinetic energies. These outflows result in radio emissions through synchrotron radiation. We explore the detectability of these synchrotron-generated radio signals by follow-up observations of GW merger events lacking a detection of electromagnetic counterparts in other wavelengths. We model radio light curves arising from (i) sub-relativistic merger ejecta and (ii) ultra-relativistic jets. The former produce radio remnants on timescales of a few years and the latter produce γ-ray bursts in the direction of the jet and orphan-radio afterglows extending over wider angles on timescales of weeks. Based on the derived light curves, we suggest an optimized survey at 1.4 GHz with five epochs separated by a logarithmic time interval. We estimate the detectability of the radio counterparts of simulated GW-merger events to be detected by advanced LIGO and Virgo by current and future radio facilities. The detectable distances for these GW merger events could be as high as 1 Gpc. Around 20%-60% of the long-lasting radio remnants will be detectable in the case of the moderate kinetic energy of 3 10 50 · erg and a circum-merger density of -0.1 cm 3 or larger, while 5%-20% of the orphan-radio afterglows with kinetic energy of 10 48 erg will be detectable. The detection likelihood increases if one focuses on the well-localizable GW events. We discuss the background noise due to radio fluxes of host galaxies and false positives arising from extragalactic radio transients and variable activegalacticnuclei, and we show that the quiet radio transient sky is of great advantage when searching for the radio counterparts.

Modeling GW170817 based on numerical relativity and its implications

“…(4.6) because the difference between the observer time and the time in the ejecta frame is significant for the ejecta with such high velocities. The rise rate of the radio flux is shallower than ∝ t 3 due to the contribution of the shells with different velocities [110]. Depending on the ISM density and the velocity distribution, the radio signal can be detected, even far before the peak time described in Eq.…”

“…Assuming that the interstellar matter is composed primarily of hydrogens and heliums, the deceleration radius, R dec , for spherical homologous ejecta is calculated [108][109][110], and then the deceleration time defined by R dec /v ej is given by 6) where n 0 is the number density of the interstellar matter (ISM) and E 0 = M ejv 2 ej /2 is the total kinetic energy of the ejecta. For M ej = 0.03M andv ej = 0.15c,…”

Electromagnetic counterparts to structured jets from gravitational wave detected mergers

“…More isotropic EM counterparts are often discussed to localize a large sample of GW events (e.g. Metzger & Berger 2012;Nissanke et al 2013;Gao et al 2013;Metzger et al 2015;Kisaka et al 2015;Hotokezaka et al 2016).…”

Variability of Radio AGN in the CHILES Field

“…Most blind radio transient surveys have turned-up non-detections because they have not been deep enough or over a wide range of time scales (Frail et al 2012;Mooley et al 2016;Hancock et al 2016). There are many events that are expected to emit radio variability or transient behavior, including AGN, SNe, TDEs, extreme scattering events (Fiedler et al 1994), and potentially even gravitational wave creating events (binary neutron star mergers and black hole-neutron star mergers) (Hotokezaka et al 2016). Improving our understanding of the nature of radio transients and variable sources requires a deep radio continuum survey with a large range of observation cadences.…”