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 ORCID: 0000-0001-7485-3020, Ashall, C, Tucker, MA, Williams, JP, De Jaeger, T, Do, A, Fausnaugh, M, Gruen, D et al (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

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Abstract

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
Date of acceptance:	8 March 2022
Date of first compliant Open Access:	8 November 2022
Date Deposited:	08 Nov 2022 15:39
Last Modified:	03 Jul 2025 12:31
DOI or ID number:	10.3847/1538-4357/ac5f54
URI:	https://researchonline.ljmu.ac.uk/id/eprint/18074

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