Chasing Kilonovae: How LIGO-India Multiplies Multimessenger Discoveries

In this episode, we explore the future of multimessenger astronomy as neutron star–black hole (NSBH) mergers take center stage. While binary neutron star collisions have delivered iconic multimessenger detections, finding the faint optical kilonova counterparts of NSBH mergers remains one of astrophysics' biggest challenges. We dive into how adding LIGO-India (Aundha) to the global gravitational-wave network will transform our ability to catch these elusive optical transients using the Vera C. Rubin Observatory.

Key Topics Covered:

• The LIGO-India Boost: How expanding from the three-detector LHV network (Livingston, Hanford, Virgo) to the four-detector LHVA network roughly doubles gravitational-wave detection rates and boosts joint optical counterpart discoveries by a factor of 2 to 5.
• Shrinking the Sky Maps: How LIGO-India’s long geographical baseline shrinks median 90% sky-localization areas dramatically—from ~130.7 deg² down to ~23.7 deg² for standard populations—making target search areas manageable for deep-imaging surveys.
• The Depth vs. Sky Coverage Dilemma: Why fixed telescope exposure times hit diminishing returns after a few hundred seconds, as longer exposures waste precious observing time on depth at the expense of sky coverage.
• Event-by-Event Exposure Optimization: How tailored exposure times—calculated directly from expected kilonova brightness (derived from remnant mass and distance) and sky-localization area—maximize total counterpart discoveries while keeping total time within Rubin’s 50–60 hours/year Target-of-Opportunity (ToO) budget.
• Operational Implementation: How observation planning toolkits (such as `GWEMOPT` and the `tilepy` platform accessible within Astro-COLIBRI) tessellate sky maps into tiles and schedule real-time follow-ups.

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### Referenced Article

Title: Prospects of electromagnetic follow-up of neutron star-black hole mergers in the LIGO-India era

Authors: Yogita Kumari, Kanchan Soni, and Sanjit Mitra

Identifier / Reference: arXiv:2609.09926v1 [astro-ph.HE]

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Acknowledements: Podcast prepared with Google/Gemini Notebook. Illustration credits: LIGO India