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A Broker Integrated Algorithm for Gravitational Wave - Electromagnetic Counterpart Searches in O4a and O4b Runs

Hemanth Bommireddy, Francisco Forster, Isaac McMahon, Manuel Pavez Herrera, Regis Cartier, Felipe Olivares Estay, Lorena Hernández García, Mary Loli Martínez Aldama, Alejandra Muñoz Arancibia

TL;DR

The search for optical counterparts of LIGO-Virgo-KAGRA (LVK) gravitational wave (GW) superevents using public Zwicky Transient Facility (ZTF) alerts processed through the ALeRCE broker demonstrates that public alert brokers can establish a robust baseline for systematic searches for electromagnetic counterparts to GW superevents in current and future observing runs.

Abstract

We present an automated framework to search for optical counterparts of LIGO-Virgo-KAGRA (LVK) gravitational wave (GW) superevents using public Zwicky Transient Facility (ZTF) alerts processed through the ALeRCE broker. The goal is to filter and identify optical transients potentially associated with binary black hole (BBH) mergers during the LVK O4a and O4b observing runs. Using the Automatic Learning for the Rapid Classification of Events (ALeRCE) infrastructure, we spatially query ZTF alerts within GW localization regions and apply machine learning classifiers, host-galaxy crossmatching, and temporal cuts within 200 days post-merger to isolate plausible candidates. Our search yielded one candidate in O4a and four in O4b, several consistent with the supernova or tidal disruption event regime. This work demonstrates that public alert brokers can establish a robust baseline for systematic searches for electromagnetic counterparts to GW superevents in current and future observing runs. Our algorithm provides a systematic approach to search for BBH counterparts for all significant LVK GW superevents using survey telescope alerts. The search, together with the accompanying analysis, demonstrates the significance of the counterpart candidates, with one candidate ultimately identified as a transient event consistent with a Bowen fluorescence flare in a now discarded active galactic nucleus (AGN).

A Broker Integrated Algorithm for Gravitational Wave - Electromagnetic Counterpart Searches in O4a and O4b Runs

TL;DR

The search for optical counterparts of LIGO-Virgo-KAGRA (LVK) gravitational wave (GW) superevents using public Zwicky Transient Facility (ZTF) alerts processed through the ALeRCE broker demonstrates that public alert brokers can establish a robust baseline for systematic searches for electromagnetic counterparts to GW superevents in current and future observing runs.

Abstract

We present an automated framework to search for optical counterparts of LIGO-Virgo-KAGRA (LVK) gravitational wave (GW) superevents using public Zwicky Transient Facility (ZTF) alerts processed through the ALeRCE broker. The goal is to filter and identify optical transients potentially associated with binary black hole (BBH) mergers during the LVK O4a and O4b observing runs. Using the Automatic Learning for the Rapid Classification of Events (ALeRCE) infrastructure, we spatially query ZTF alerts within GW localization regions and apply machine learning classifiers, host-galaxy crossmatching, and temporal cuts within 200 days post-merger to isolate plausible candidates. Our search yielded one candidate in O4a and four in O4b, several consistent with the supernova or tidal disruption event regime. This work demonstrates that public alert brokers can establish a robust baseline for systematic searches for electromagnetic counterparts to GW superevents in current and future observing runs. Our algorithm provides a systematic approach to search for BBH counterparts for all significant LVK GW superevents using survey telescope alerts. The search, together with the accompanying analysis, demonstrates the significance of the counterpart candidates, with one candidate ultimately identified as a transient event consistent with a Bowen fluorescence flare in a now discarded active galactic nucleus (AGN).
Paper Structure (31 sections, 1 equation, 19 figures, 4 tables)

This paper contains 31 sections, 1 equation, 19 figures, 4 tables.

Table of Contents

  1. Introduction
  2. Data
  3. ZTF
  4. ZTF Forced Photometry
  5. ALeRCE annotations
  6. GW alerts/skymaps
  7. Methodology
  8. Retrieving GW Skymaps
  9. Performing spatial queries within skymaps
  10. Refining Candidates
  11. Effectiveness of the stamp classifier
  12. Predicting Chirp Mass
  13. Results
  14. ZTF Candidates
  15. GW-EM Parameter inference
  16. ...and 16 more sections

Figures (19)

  • Figure 1: LIGO skymap of the GW event S240902bq with color scale representing the probability contours.
  • Figure 2: Skymap converted to bounded polygons (green boundaries) filled with ZTF pubic alerts in yellow
  • Figure 3: Distribution of classes by stamp classifier, for the events originating with 1.4" of MQUAS AGN catalog for O4a and O4b runs.
  • Figure 4: Cumulative distribution function (CDF) of the skymap areas for O4a (top) and O4b(bottom) with median area values (vertical red lines)
  • Figure 5: Total number of events for both runs including all filters
  • ...and 14 more figures