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ASAS-SN Rates IV: Constraints on the Kilonova Rate

Dhvanil D. Desai, Benjamin J. Shappee, Christopher S. Kochanek, Krzysztof Z. Stanek, Katie Auchettl, John F. Beacom, Jeff Cooke, Subo Dong, Willem B. Hoogendam, Jose L. Prieto, Todd A. Thompson, Michael A. Tucker, Natasha Van Bemmel

Abstract

Kilonovae (KNe) are the electromagnetic signatures of neutron star mergers and are likely the dominant site of cosmic $r$-process nucleosynthesis. However, their intrinsic rate remains poorly constrained due to a paucity of confirmed events. We use the All-Sky Automated Survey for Supernovae (ASAS-SN) to place limits on the rate of bright, nearby KNe over an 11-year baseline ranging from 2014 to 2024. To evaluate the survey's completeness for KNe, we employ an injection-recovery simulation using a shock-cooling cocoon model calibrated to the early blue emission of the only well-sampled KN, SSS17a (AT 2017gfo). Finding no KNe within the survey, we calculate a $2σ$ ($\sim95\%$) upper limit on the local volumetric KN rate of $R_{\mathrm{KN}} < 4400\,\mathrm{yr}^{-1}\,\mathrm{Gpc}^{-3}$. Despite ASAS-SN's shallower limiting magnitude compared to other time-domain searches, its continuous, high-cadence, all-sky monitoring yields a constraint that is competitive with the strongest results from electromagnetic surveys but remains a factor of 18 higher than the LIGO-Virgo-KAGRA GWTC-4 estimate of the binary neutron star merger rate.

ASAS-SN Rates IV: Constraints on the Kilonova Rate

Abstract

Kilonovae (KNe) are the electromagnetic signatures of neutron star mergers and are likely the dominant site of cosmic -process nucleosynthesis. However, their intrinsic rate remains poorly constrained due to a paucity of confirmed events. We use the All-Sky Automated Survey for Supernovae (ASAS-SN) to place limits on the rate of bright, nearby KNe over an 11-year baseline ranging from 2014 to 2024. To evaluate the survey's completeness for KNe, we employ an injection-recovery simulation using a shock-cooling cocoon model calibrated to the early blue emission of the only well-sampled KN, SSS17a (AT 2017gfo). Finding no KNe within the survey, we calculate a () upper limit on the local volumetric KN rate of . Despite ASAS-SN's shallower limiting magnitude compared to other time-domain searches, its continuous, high-cadence, all-sky monitoring yields a constraint that is competitive with the strongest results from electromagnetic surveys but remains a factor of 18 higher than the LIGO-Virgo-KAGRA GWTC-4 estimate of the binary neutron star merger rate.

Paper Structure

This paper contains 5 sections, 2 equations, 4 figures.

Table of Contents

  1. Introduction
  2. Light Curve Template
  3. Rate Constraints
  4. Discussion
  5. Unclassified Transients Verification

Figures (4)

  • Figure 1: Normalized $V$- and $g$-band KN light curve templates from the shock-cooling cocoon model of piro_evidence_2018, which explain the early, blue emission from SSS17a (AT 2017gfo). The templates are shifted such that the peak is at $t=0$ days.
  • Figure 2: Completeness as a function of time and peak apparent magnitude for KNe. The dashed curve shows the $V$-band era (2014--2017), while the solid curves show individual years of the $g$-band era (2018--2024). The top axis indicates the distance corresponding to an event with a peak absolute magnitude of $M_{\mathrm{peak}}=-16$ mag, similar to SSS17a (AT 2017gfo).
  • Figure 3: Comparison of the ASAS-SN $95\%$ volumetric KN rate upper limit ($R_{\mathrm{KN}} < 4400\,\mathrm{yr}^{-1}\,\mathrm{Gpc}^{-3}$) with the $95\%$ confidence limits from other optical surveys: ATLAS smartt_kilonova_2017, PTF kasliwal_illuminating_2017, DES doctor_search_2017, DLT40 yang_empirical_2017, ZTF andreoni_fast-transient_2021, and KNTraP vanbemmel_optically_2025. The color of the point indicates the filters used for the KNe search in those surveys. The top axis illustrates the corresponding horizon distance for an SSS17a-like event with a peak absolute magnitude of $M_{\mathrm{peak}} = -16$ mag. The light and dark shaded bands show the estimate of the local ($z=0$) BNS merger rate from the LIGO-Virgo-KAGRA collaboration GWTC-3 abbott_population_2023 and GWTC-4 abac_gwtc-40_2025, respectively. The dashed and dash-dotted lines show the ASAS-SN core-collapse and Type Ia SN rates, respectively pessi_supernova_2025desai_supernova_2026. The KN rate inferred from short GRB observations ranges between $160 - 352\,\mathrm{yr}^{-1}\,\mathrm{Gpc}^{-3}$ with $>60\%$ fractional uncertainties fong_decade_2015dellavalle_gw170817_2018zhang_peculiar_2018dichiara_short_2020.
  • Figure 11: ASAS-SN light curves of the six unclassified transients rejected as KN candidates based on their photometric evolution. In the first five panels, the observed slow-evolving transients are compared to a nominal $M = -16.0$ mag KN template from piro_evidence_2018 (solid lines) placed at the distance of their respective host galaxies. The final panel shows ASASSN-14eb, a single-epoch detection. The solid line represents a forced KN template fit using the piro_evidence_2018 template.