Article

Luminous Millimeter, Radio, and X-Ray Emission from ZTF 20acigmel (AT 2020xnd)

A. Y. Q. HoMiller Institute for Basic Research in Science, 468 Donner Lab, Berkeley, CA 94720, USABen MargalitAstronomy Department and Theoretical Astrophysics Center, University of California, Berkeley, Berkeley, CA 94720, USAMichael BremerInstitut de Radio Astronomie Millimétrique (IRAM), 300 rue de la Piscine, F-38406 Saint Martin d'Hères, FranceD. A. PerleyAstrophysics Research Institute, Liverpool John Moores University, IC2, Liverpool Science Park, 146 Brownlow Hill, Liverpool L3 5RF, UKYuhan YaoCahill Center for Astrophysics, California Institute of Technology, MC 249-17, 1200 E California Boulevard, Pasadena, CA, 91125, USAD. DobieCentre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, Victoria, AustraliaD. L. KaplanDepartment of Physics, University of Wisconsin-Milwaukee, P.O. Box 413, Milwaukee, WI 53201, USAAndrew O’BrienDepartment of Physics, University of Wisconsin-Milwaukee, P.O. Box 413, Milwaukee, WI 53201, USAG. PetitpasHarvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USAAndrew ZicDepartment of Physics and Astronomy, and Research Centre in Astronomy, Astrophysics and Astrophotonics, Macquarie University, NSW 2109, Australia

2022en

ABI

Abstract

Abstract Observations of the extragalactic ( z = 0.0141) transient AT 2018cow established a new class of energetic explosions shocking a dense medium, producing luminous emission at millimeter and submillimeter wavelengths. Here we present detailed millimeter- through centimeter-wave observations of a similar transient, ZTF 20acigmel (AT 2020xnd), at z = 0.2433. Using observations from the NOrthern Extended Millimeter Array and the Very Large Array, we model the unusual millimeter and radio emission from AT 2020xnd under several different assumptions and ultimately favor synchrotron radiation from a thermal electron population (relativistic Maxwellian). The thermal electron model implies a fast but subrelativistic ( v ≈ 0.3 c ) shock and a high ambient density ( n e ≈ 4 × 10 3 cm −3 ) at Δ t ≈ 40 days. The X-ray luminosity of L X ≈ 10 43 erg s −1 exceeds simple predictions from the radio and UVOIR luminosity and likely has a separate physical origin, such as a central engine. Using the fact that month-long luminous ( L ν ≈ 2 × 10 30 erg s −1 Hz −1 at 100 GHz) millimeter emission appears to be a generic feature of transients with fast ( t 1/2 ≈ 3 days) and luminous ( M peak ≈ −21 mag) optical light curves, we estimate the rate at which transients like AT 2018cow and AT 2020xnd will be detected by future wide-field millimeter transient surveys such as CMB-S4 and conclude that energetic explosions in dense environments may represent a significant population of extragalactic transients in the 100 GHz sky.

Identifiers

DOI: 10.3847/1538-4357/ac4e97

Citations and references

Cited by 10 references

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