Optimizing multitelescope observations of gravitational-wave counterparts

Abstract

The ever-increasing sensitivity of the network of gravitational-wave detectors has resulted in the accelerated rate of detections from compact binary coalescence systems in the third observing run of Advanced LIGO and Advanced Virgo. Not only has the event rate increased, but also the distances to which phenomena can be detected, leading to a rise in the required sky volume coverage to search for counterparts. Additionally, the improvement of the detectors has resulted in the discovery of more compact binary mergers involving neutron stars, revitalizing dedicated follow-up campaigns. While significant effort has been made by the community to optimize single telescope observations, using both synoptic and galaxy-targeting methods, less effort has been paid to coordinated observations in a network. This is becoming crucial, as the advent of gravitational-wave astronomy has garnered interest around the globe, resulting in abundant networks of telescopes available to search for counterparts. In this paper, we extend some of the techniques developed for single telescopes to a telescope network. We describe simple modifications to these algorithms and demonstrate them on existing network examples. These algorithms are implemented in the opensource software gwemopt, used by some follow-up teams, for ease of use by the broader community.

Optical follow-up of the neutron star–black hole mergers S200105ae and S200115j

“…The length of the exposures was chosen to balance both the depth required for a relatively distant event and the sky area requiring coverage; specifically, we optimize the exposure times to be as long as possible while covering the 90% sky area consistent with the GW event observable from Palomar and in two filters within the night. We used gwemopt 39,40 , a codebase designed to optimize telescope scheduling for GW follow-up, to schedule the observations. The schedule is designed such that fields have reference images available to facilitate image subtraction, as well as a 30 minute gap between the observations in gand r-bands to identify and remove moving objects.…”

GROWTH on S190425z: Searching Thousands of Square Degrees to Identify an Optical or Infrared Counterpart to a Binary Neutron Star Merger with the Zwicky Transient Facility and Palomar Gattini-IR

“…We provide a brief description of each instrument in Table 1. Triggering ToO observations for survey instruments like ZTF and Palomar Gattini-IR halts their ongoing survey observations and redirects them to observe only certain fields as directed by an observation plan. The observation plan generated by the ToO marshal relies on gwemopt (Coughlin et al 2018a(Coughlin et al , 2019c, a code that optimizes the telescope scheduling process for GW follow-up. gwemopt handles both synoptic and galaxy-targeted search strategies; we employed the former to conduct observations with some of our facilities, Palomar Gattini-IR, GROWTH-India and ZTF, and the latter for scheduling observations with KPED.…”

Reanalysis of the binary neutron star mergers GW170817 and GW190425 using numerical-relativity calibrated waveform models

“…[28] for an updated analyses stating the bound on the tidal deformability in 323 ˜ 776 and Ref. [29], stating the similar bound to be in 302 ˜ 860), later systematic investigations reveal that this argument is premature [5].…”