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The Curious Case of ASASSN-20hx: A Slowly Evolving, UV- and X-Ray-Luminous, Ambiguous Nuclear Transient

Hinkle, JT, Holoien, TWS, Shappee, BJ, Neustadt, JMM, Auchettl, K, Vallely, PJ, Shahbandeh, M, Kluge, M, Kochanek, CS, Stanek, KZ, Huber, ME, Post, RS, Bersier, D, Ashall, C, Tucker, MA, Williams, JP, De Jaeger, T, Do, A, Fausnaugh, M, Gruen, D , Hopp, U, Myles, J, Obermeier, C, Payne, AV and Thompson, TA (2022) The Curious Case of ASASSN-20hx: A Slowly Evolving, UV- and X-Ray-Luminous, Ambiguous Nuclear Transient. Astrophysical Journal, 930 (1). ISSN 0004-637X

The curious case of ASASSN-20hx a slowly evolving UV and X-ray-luminous ambiguous nuclear transient.pdf - Published Version
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We present observations of ASASSN-20hx, a nearby ambiguous nuclear transient (ANT) discovered in NGC 6297 by the All-Sky Automated Survey for Supernovae (ASAS-SN). We observed ASASSN-20hx from -30 to 275 days relative to the peak UV/optical emission using high-cadence, multiwavelength spectroscopy and photometry. From Transiting Exoplanet Survey Satellite data, we determine that the ANT began to brighten on 2020 June 22.8 with a linear rise in flux for at least the first week. ASASSN-20hx peaked in the UV/optical 30 days later on 2020 July 22.8 (MJD = 59052.8) at a bolometric luminosity of L = (3.15 ± 0.04) × 1043 erg s-1. The subsequent decline is slower than any TDE observed to date and consistent with many other ANTs. Compared to an archival X-ray detection, the X-ray luminosity of ASASSN-20hx increased by an order of magnitude to L x ∼1.5 × 1042 erg s-1 and then slowly declined over time. The X-ray emission is well fit by a power law with a photon index of "∼2.3-2.6. Both the optical and near-infrared spectra of ASASSN-20hx lack emission lines, unusual for any known class of nuclear transient. While ASASSN-20hx has some characteristics seen in both tidal disruption events and active galactic nuclei, it cannot be definitively classified with current data.

Item Type: Article
Uncontrolled Keywords: 0201 Astronomical and Space Sciences; 0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics; 0306 Physical Chemistry (incl. Structural); Astronomy & Astrophysics
Subjects: Q Science > QB Astronomy
Divisions: Astrophysics Research Institute
Publisher: American Astronomical Society
SWORD Depositor: A Symplectic
Date Deposited: 08 Nov 2022 15:39
Last Modified: 08 Nov 2022 15:45
DOI or ID number: 10.3847/1538-4357/ac5f54
URI: https://researchonline.ljmu.ac.uk/id/eprint/18074
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