AT 2021hdr: A candidate tidal disruption of a gas cloud by a binary super massive black hole system

Year: 2024

Type: article

Abstract: With a growing number of facilities able to monitor the entire sky and produce light curves with a cadence of days, in recent years there has been an increased rate of detection of sources whose variability deviates from standard behavior, revealing a variety of exotic nuclear transients. The aim of the present study is to disentangle the nature of the transient AT 2021hdr, whose optical light curve used to be consistent with a classic Seyfert 1 nucleus, which was also confirmed by its optical spectrum and high-energy properties. From late 2021, AT 2021hdr started to present sudden brightening episodes in the form of oscillating peaks in the Zwicky Transient Facility (ZTF) alert stream, and the same shape is observed in X-rays and UV from Swift data. The oscillations occur every ∼60–90 days with amplitudes of ∼0.2 mag in the g and r bands. Very Long Baseline Array (VLBA) observations show no radio emission at milliarcseconds scale. It is argued that these findings are inconsistent with a standard tidal disruption event (TDE), a binary supermassive black hole (BSMBH), or a changing-look active galactic nucleus (AGN); neither does this object resemble previous observed AGN flares, and disk or jet instabilities are an unlikely scenario. Here, we propose that the behavior of AT 2021hdr might be due to the tidal disruption of a gas cloud by a BSMBH. In this scenario, we estimate that the putative binary has a separation of ∼0.83 mpc and would merge in ∼7 × 104 years. This galaxy is located at 9 kpc from a companion galaxy, and in this work we report this merger for the first time. The oscillations are not related to the companion galaxy.

Source: Springer Link (Chiba Institute of Technology)

DOI: 10.1051/0004-6361/202451305/pdf

Authors: L. Hernández-García, A. M. Muñoz-Arancibia, P. Lira, G. Bruni, J. Cuadra, P. Arévalo, P. Sánchez-Sáez, S. Bernal, F. E. Bauer, M. Catelan, F. Panessa, M. Pávez-Herrera, C. Ricci, I. Reyes-Jainaga, B. Ailawadhi, V. Chavushyan, R. Dastidar, A. Deconto-Machado, F. Förster, A. Gangopadhyay, A. García-Pérez, I. Márquez, J. Masegosa, K. Misra, V. M Patiño-Alvarez, M. Puig-Subirà, J. Rodi, M. Singh

Institutions: University of Chile, Millennium Institute of Astrophysics, University of Valparaíso, Adolfo Ibáñez University

Language: English

Topic: Astrophysical Phenomena and Observations

Subfield: Astronomy and Astrophysics

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: green

Funders: National Science Foundation, National Aeronautics and Space Administration, California Institute of Technology, Science and Industry Endowment Fund, Ministerio de Ciencia, Innovación y Universidades, Australian Government, European Space Agency, European Commission, Commonwealth Scientific and Industrial Research Organisation, Government of Western Australia, Agencia Nacional de Investigación y Desarrollo, Jet Propulsion Laboratory, University of California, Los Angeles, Agencia Estatal de Investigación

OpenAlex ID: W6884512685