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

Ho, Anna Y. Q. and Margalit, Ben and Bremer, Michael and Perley, Daniel A. and Yao, Yuhan and Dobie, Dougal and Kaplan, David L. and O'Brien, Andrew and Petitpas, Glen and Zic, Andrew (2022) Luminous Millimeter, Radio, and X-Ray Emission from ZTF 20acigmel (AT 2020xnd). Astrophysical Journal, 932 (2). Art. No. 116. ISSN 0004-637X. doi:10.3847/1538-4357/ac4e97.

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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 ≈ 0.3c) shock and a high ambient density (nₑ ≈ 4 × 10³ cm⁻³) at Δt ≈ 40 days. The X-ray luminosity of Lₓ ≈ 10⁴³ 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 × 10³⁰ 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.

Item Type:Article
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URLURL TypeDescription Paper
Ho, Anna Y. Q.0000-0002-9017-3567
Margalit, Ben0000-0001-8405-2649
Perley, Daniel A.0000-0001-8472-1996
Yao, Yuhan0000-0001-6747-8509
Dobie, Dougal0000-0003-0699-7019
Kaplan, David L.0000-0001-6295-2881
O'Brien, Andrew0000-0003-4609-2791
Zic, Andrew0000-0002-9583-2947
Additional Information:© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2021 October 11; revised 2022 January 21; accepted 2022 January 23; published 2022 June 22. A.Y.Q.H. would like to thank Eliot Quataert, Dan Kasen, Sterl Phinney, Anatoly Spitkovsky, and Shri Kulkarni for useful discussions about steep-spectrum radio sources and relativistic Maxwellians; Kunal Mooley for assistance with VLA calibration; Fabian Walter for advice regarding NOEMA data reduction; and Joe Bright, Greg Sivakoff, and Susan Clark for a careful reading of the manuscript. D.K. and A.O. are supported by NSF grant AST-1816492. B.M. is supported by NASA through the NASA Hubble Fellowship grant #HST-HF2-51412.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. The authors would like to thank the anonymous referee for detailed comments that greatly improved the clarity of the paper. The Submillimeter Array is a joint project between the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics and is funded by the Smithsonian Institution and the Academia Sinica. This work is based on observations carried out under project numbers D20AF and D20AG with the IRAM NOEMA Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain). The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. The Australia Telescope Compact Array is part of the Australia Telescope National Facility (grid.421683.a), which is funded by the Australian Government for operation as a National Facility managed by CSIRO. We acknowledge the Gomeroi people as the traditional owners of the Observatory site. The scientific results reported in this article are based in part on observations made by the Chandra X-ray Observatory. This research has made use of software provided by the Chandra X-ray Center (CXC) in the application package CIAO. Facilities: EVLA - Expanded Very Large Array, VLA - , IRAM:NOEMA - , SMA - . Software: CASA (McMullin et al. 2007), astropy (Astropy Collaboration et al. 2013, 2018), matplotlib (Hunter 2007), scipy (Virtanen et al. 2020), pyne2001.
Funding AgencyGrant Number
NASA Hubble FellowshipHST-HF2-51412.001-A
Smithsonian InstitutionUNSPECIFIED
Academia SinicaUNSPECIFIED
Institut national des sciences de l'Univers (INSU)UNSPECIFIED
Centre National de la Recherche Scientifique (CNRS)UNSPECIFIED
Instituto Geográfico Nacional (IGN)UNSPECIFIED
Commonwealth Scientific and Research Organization (CSIRO)UNSPECIFIED
Subject Keywords:Radio astronomy; Millimeter astronomy; Spectral index; Submillimeter astronomy; Transient sources; Core-collapse supernovae; Supernovae; Shocks
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Radio astronomy (1338); Millimeter astronomy (1061); Spectral index (1553); Submillimeter astronomy (1647); Transient sources (1851); Core-collapse supernovae (304); Supernovae (1668); Shocks (2086)
Record Number:CaltechAUTHORS:20220715-744324000
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Official Citation:Anna Y. Q. Ho et al 2022 ApJ 932 116
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:115652
Deposited By: George Porter
Deposited On:20 Jul 2022 21:45
Last Modified:27 Jul 2022 17:54

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