Searching for electromagnetic counterparts to gravitational-wave merger events with the prototype Gravitational-Wave Optical Transient Observer (GOTO-4)

Abstract

<jats:title>Abstract</jats:title> <jats:p>We report the results of optical follow-up observations of 29 gravitational-wave triggers during the first half of the LIGO-Virgo Collaboration (LVC) O3 run with the Gravitational-wave Optical Transient Observer (GOTO) in its prototype 4-telescope configuration (GOTO-4). While no viable electromagnetic counterpart candidate was identified, we estimate our 3D (volumetric) coverage using test light curves of on- and off-axis gamma-ray bursts and kilonovae. In cases where the source region was observable immediately, GOTO-4 was able to respond to a GW alert in less than a minute. The average time of first observation was 8.79 hours after receiving an alert (9.90 hours after trigger). A mean of 732.3 square degrees were tiled per event, representing on average 45.3 per cent of the LVC probability map, or 70.3 per cent of the observable probability. This coverage will further improve as the facility scales up alongside the localisation performance of the evolving gravitational-wave detector network. Even in its 4-telescope prototype configuration, GOTO is capable of detecting AT2017gfo-like kilonovae beyond 200 Mpc in favourable observing conditions. We cannot currently place meaningful electromagnetic limits on the population of distant ($\hat{D}_L = 1.3$ Gpc) binary black hole mergers because our test models are too faint to recover at this distance. However, as GOTO is upgraded towards its full 32-telescope, 2 node (La Palma &amp; Australia) configuration, it is expected to be sufficiently sensitive to cover the predicted O4 binary neutron star merger volume, and will be able to respond to both northern and southern triggers.</jats:p>

Evidence of Extended Emission in GRB 181123B and Other High-redshift Short GRBs

“…A variant of the selection bias above, and perhaps the simplest explanation, could be that these are regular sGRBEEs, analogous to the population identified by Norris & Bonnell (2006), and they are more likely to be localized and assigned redshift than other sGRBs at similar distances. Indeed, sGRBEEs tend to be brighter than canonical sGRBs (Troja et al 2008;Norris et al 2011;Gompertz et al 2020), which increases the chance of an accurate localization, and hence a galaxy association. If this interpretation is correct, the high fraction of sGRBEEs at z > 1 is simply a selection bias.…”

Fast-transient Searches in Real Time with ZTFReST: Identification of Three Optically Discovered Gamma-Ray Burst Afterglows and New Constraints on the Kilonova Rate

“…With the end of the third LIGO-Virgo observing run (O3), and with the entrance of KAGRA, without a viable counterpart to a binary neutron star or neutron star-black hole merger candidate (e.g., Andreoni et al 2019a;Coughlin et al 2019d;Goldstein et al 2019;Gomez et al 2019;Lundquist et al 2019;Anand et al 2020;Ackley et al 2020;Andreoni et al 2020a;Antier et al 2020;Gompertz et al 2020;Kasliwal et al 2020), it becomes particularly urgent to continue the search for such objects in optical, wide-field survey data, independently of other multi-messenger and multi-wavelength triggers. These searches also serve as unbiased surveys for optical emission, with the potential to discover, for example, collapsars with dirty fireballs (Dermer et al 2000) that do not have prompt GRB emission (Dermer et al 2000;Huang et al 2002;Rhoads 2003), or study whether optically identified kilonovae differ from those identified with gravitational-wave detections, while also enabling many of the studies of both cosmology and nuclear physics identified above.…”

Implications of the search for optical counterparts during the second part of the Advanced LIGO’s and Advanced Virgo’s third observing run: lessons learned for future follow-up observations

“…1 Amongst the wide field-of-view telescopes, ATLAS (McBrien et al 2019a;Smartt et al 2019a, b;Srivastav et al 2019), ASAS-SN (Shappee et al 2019), CNEOST (Li et al 2019;Xu et al 2019b, c), Dabancheng/HMT (Xu et al 2019d), DESGW-DECam (Soares-Santos et al 2019), DDOTI/OAN (Dichiara et al 2019;Pereyra et al 2019;Watson et al 2019b), GOTO (Ackley et al 2019a, b;Steeghs et al 2019a, b;Gompertz et al 2020), GRANDMA (Antier et al 2020a;Antier et al 2020b), GRAWITA-VST (Grado et al 2019a, b), GROWTH-DECAM (Andreoni et al 2019a;Goldstein et al 2019), GROWTH-Gattini-IR (De et al 2019;Hankins et al 2019a, b), GROWTH-INDIA (Bhalerao et al 2019), HSC (Yoshida et al 2019), J-GEM (Niino et al 2019), KMTNet (Im et al 2019;Kim et al 2019), MASTERnetwork (Lipunov et al 2019a, b, c, d, e, f, g, h), MeerLICHT (Groot et al 2019), Pan-STARRS (Smith et al 2019;Smartt et al 2019a), SAGUARO (Lundquist et al 2019), SVOM-GWAC (Wei et al 2019), Swope (Kilpatrick et al 2019), Xinglong-Schmidt (Xu et al 2019a;Zhu et al 2019), and the Zwicky Transient Facility (Anand et al 2019;Coughlin et al 2019d;Kasliwal et al 2019a, b;Kool et al 2019;Singer et al 2019;…”