On the detection of the electromagnetic counterparts from lensed gravitational wave events by binary neutron star mergers

Future ground-based gravitational wave (GW) detectors, i.e. Einstein telescope (ET) and Cosmic Explorer (CE), are expected to detect a significant number of lensed binary neutron star (BNS) mergers, which may provide a unique tool to probe cosmology. In this paper, we investigate the detectability of the optical/infrared electromagnetic (EM) counterparts (kilonov ae/afterglo ws) from these lensed BNS mergers by future GW detectors and EM telescopes using simple kilonov a, afterglo w, and lens models. ET and CE are expected to detect similar to 5 . 32(+26 . 1) (-5 . 10) and 67 . 3 (+ 332)( -64 . 7) lensed BNS mergers per year. We find that the EM counterparts associated with all these mergers will be detectable by an all sk y-surv e y in the H band with the limiting magnitude m(lim) (sic) 27, while the detectable fraction is (sic) 0 . 4 per cent in the g/z band if with m(lim) (sic) 24. Generally, it is more efficient to search the lensed EM counterparts by adopting the infrared bands than the optical/UV bands with the same m(lim). Future telescopes like Vera C. Rubin Observatory, China Space Station Telescope, and Euclid can hardly detect the EM counterparts of even one lensed BNS merger. Roman Space Telescope (RST) and James Webb Space Telescope (JWST) have the capability to detect about a few or more such events per year. Moreover, the time delays and separations between the lensed image pairs are typically in the ranges from minutes to months and from 0.1 to 1 arcsec, suggesting that both the GW and EM images of most lensed BNS mergers can be well resolved by not only CE/ET in the time domain but also RST /JWST spatially.

Automated summary

Future ground-based gravitational wave (GW) detectors are expected to detect lensed binary neutron star (BNS) mergers, which can provide a unique tool for cosmology. This study investigates the detectability of the optical/infrared electromagnetic counterparts (kilonovae/afterglows) from these lensed BNS mergers. It is found that future telescopes like Vera C. Rubin Observatory, China Space Station Telescope, and Euclid can hardly detect the electromagnetic counterparts, while Roman Space Telescope and James Webb Space Telescope have the capability to detect a few or more such events per year.