Hours-long Near-UV/Optical Emission from Mildly Relativistic Outflows in Black Hole–Neutron Star Mergers

Journal Article · Mon Aug 14 00:00:00 EDT 2023 · The Astrophysical Journal. Letters

DOI:https://doi.org/10.3847/2041-8213/acec4a· OSTI ID:2281850

Gottlieb, Ore ^[1]; Issa, Danat ^[1]; Jacquemin-Ide, Jonatan ^[1]; Liska, Matthew ^[2]; Tchekhovskoy, Alexander ^[1]; Foucart, Francois ^[3]; Kasen, Daniel ^[4]; Perna, Rosalba ^[5]; Quataert, Eliot ^[6]; Metzger, Brian D. ^[7]

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1. Northwestern Univ., Evanston, IL (United States)
2. Harvard Univ., Cambridge, MA (United States)
3. Univ. of New Hampshire, Durham, NH (United States)
4. Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
5. Stony Brook Univ., NY (United States); Flatiron Institute, New York, NY (United States)
6. Princeton Univ., NJ (United States)
7. Flatiron Institute, New York, NY (United States); Columbia Univ., New York, NY (United States)

The ongoing LIGO–Virgo–KAGRA observing run O4 provides an opportunity to discover new multimessenger events, including binary neutron star (BNS) mergers such as GW170817 and the highly anticipated first detection of a multimessenger black hole–neutron star (BH–NS) merger. While BNS mergers were predicted to exhibit early optical emission from mildly relativistic outflows, it has remained uncertain whether the BH–NS merger ejecta provides the conditions for similar signals to emerge. We present the first modeling of early near-ultraviolet/optical emission from mildly relativistic outflows in BH–NS mergers. Adopting optimal binary properties, a mass ratio of q = 2, and a rapidly rotating BH, we utilize numerical relativity and general relativistic magnetohydrodynamic (GRMHD) simulations to follow the binary's evolution from premerger to homologous expansion. We use an M1 neutrino transport GRMHD simulation to self-consistently estimate the opacity distribution in the outflows and find a bright near-ultraviolet/optical signal that emerges due to jet-powered cocoon cooling emission, outshining the kilonova emission at early time. The signal peaks at an absolute magnitude of ~–15 a few hours after the merger, longer than previous estimates, which did not consider the first principles–based jet launching. By late 2024, the Rubin Observatory will have the capability to track the entire signal evolution or detect its peak up to distances of ≳1 Gpc. In 2026, ULTRASAT will conduct all-sky surveys within minutes, detecting some of these events within ~200 Mpc. The BH–NS mergers with higher mass ratios or lower BH spins would produce shorter and fainter signals.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC); Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Oak Ridge Leadership Computing Facility (OLCF)
• Sponsoring Organization: National Science Foundation (NSF); USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities (SUF); USDOE Office of Science (SC), High Energy Physics (HEP)
• Grant/Contract Number: AC02-05CH11231; AC05-00OR22725
• OSTI ID: 2281850
• Journal Information: The Astrophysical Journal. Letters, Journal Name: The Astrophysical Journal. Letters Journal Issue: 1 Vol. 953; ISSN 2041-8205
• Publisher: IOP Publishing
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
astrophysical black holes
compact binary stars
compact objects
gamma-ray bursts
hydrodynamical simulations
jets
near ultraviolet astronomy
optical astronomy
relativistic jets
transient sources
ultraviolet astronomy
ultraviolet transient sources