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

Hinkle, Jason T.; Holoien, Thomas W.-S.; Shappee, Benjamin J.; Neustadt, Jack M. M.; Auchettl, Katie; Vallely, Patrick J.; Shahbandeh, Melissa; Kluge, Matthias; Kochanek, Christopher S.; Stanek, K. Z.; Huber, Mark E.; Post, Richard S.; Bersier, David; Ashall, Christopher; Tucker, Michael A.; Williams, Jonathan P.; de Jaeger, Thomas; Do, Aaron; Fausnaugh, Michael; Gruen, Daniel; Hopp, Ulrich; Myles, Justin; Obermeier, Christian; Payne, Anna V. und Thompson, Todd A. (2022): The Curious Case of ASASSN-20hx: A Slowly Evolving, UV- and X-Ray-Luminous, Ambiguous Nuclear Transient. In: Astrophysical Journal, Bd. 930, Nr. 1, 12

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) x 10(43) 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 ) similar to 1.5 x 10(42) 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 Gamma similar to 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.

• Dokumententyp: Zeitschriftenartikel
• Fakultät: Physik
• Themengebiete: 500 Naturwissenschaften und Mathematik > 530 Physik
• ISSN: 0004-637X
• Sprache: Englisch