Constraints on the Physical Properties of GW190814 through Simulations Based on DECam Follow-up Observations by the Dark Energy Survey

Abstract

On 2019 August 14, the LIGO and Virgo Collaborations detected gravitational waves from a black hole and a 2.6 solar mass compact object, possibly the first neutron star-black hole merger. In search of an optical counterpart, the Dark Energy Survey (DES) obtained deep imaging of the entire 90% confidence level localization area with Blanco/DECam 0, 1, 2, 3, 6, and 16 nights after the merger. Objects with varying brightness were detected by the DES Pipeline, and we systematically reduced the candidate counterparts through catalog matching, light-curve properties, host-galaxy photometric redshifts, Southern Astrophysical Research spectroscopic follow-up observations, and machine-learning-based photometric classification. All candidates were rejected as counterparts to the merger. To quantify the sensitivity of our search, we applied our selection criteria to full light-curve simulations of supernovae and kilonovae as they would appear in the DECam observations. Because the source class of the merger was uncertain, we utilized an agnostic, three-component kilonova model based on tidally disrupted neutron star (NS) ejecta properties to quantify our detection efficiency of a counterpart if the merger included an NS. We find that, if a kilonova occurred during this merger, configurations where the ejected matter is greater than 0.07 solar masses, has lanthanide abundance less than 10 −8.56 , and has a velocity between 0.18c and 0.21c are disfavored at the 2σ level. Furthermore, we estimate that our background reduction methods are capable of associating gravitational wave signals with a detected electromagnetic counterpart at the 4σ level in 95% of future follow-up observations.

Probing Kilonova Ejecta Properties Using a Catalog of Short Gamma-Ray Burst Observations

“…In addition to BNS mergers, some neutron star-black hole (NSBH) mergers are predicted to produce kilonovae. Thus far, there are only a few potential cases of an NSBH merger, including GW190426 152155 (Abbott et al 2020b) and GW190814 (Abbott et al 2020c), though none have a confirmed associated kilonova to date (e.g., Hosseinzadeh et al 2019;Gomez et al 2019;Morgan et al 2020;Vieira et al 2020;Anand et al 2020;Andreoni et al 2020;Ackley et al 2020;Paterson et al 2020a). The lack of EM emission from GW190814 is consistent with the finding that the primary BH is 23 M and thus unlikely to produce a kilonova (Foucart et al 2013;Fernández & Metzger 2016).…”

El-CID: A filter for Gravitational-wave Electromagnetic Counterpart Identification

“…This event was interesting for follow-up since it was reported to have strong chance of having a NS component (mass less than 3 M (LIGO Scientific Collaboration, Virgo Collaboration 2019). Several teams across the globe participated in the follow-up effort of this event (Antier et al 2019;Dobie et al 2019;Andreoni et al 2020;Morgan et al 2020;Vieira et al 2020;Watson et al 2020;de Wet et al 2021). AT 2019npv was discovered by Goldstein et al (2019) and confirmed by several groups (Herner et al 2019;Smartt et al 2019;T.-W. Chen et al 2019;V.…”

Target of Opportunity Observations of Gravitational Wave Events with Vera C. Rubin Observatory

“…As of the end of O3, several GW detections of NS-BH merger candidates have been reported (The LIGO Scientific Collaboration et al 2021a;Abbott et al 2021), but no EM counterpart to a NS-BH merger was found (e.g., Anand et al 2020;Dichiara et al 2021, for the most robust NS-BH GW detections). Extensive follow-up was also performed for the peculiar source GW190814 (Dobie et al 2019;Gomez et al 2019;Ackley et al 2020;Andreoni et al 2020;Morgan et al 2020;Thakur et al 2020;Vieira et al 2020;Watson et al 2020;Alexander et al 2021;de Wet et al 2021;Dobie et al 2021;Kilpatrick et al 2021;Tucker et al 2021). However, the nature of the secondary component of GW190814 unclear, as it can be either the lightest black hole or the heaviest neutron star ever discovered in a double compact-object system (Abbott et al 2020c).…”