Discovery of a new supergiant fast X-ray transient MAXI J0709−159 associated with the Be star LY Canis Majoris

Creators: Sugizaki, Mutsumi; Mihara, Tatehiro; Kobayashi, Kohei; Negoro, Hitoshi; Shidatsu, Megumi; Pike, Sean N.; Iwakiri, Wataru; Urabe, Sota; Serino, Motoko; Kawai, Nobuyuki; Nakajima, Motoki; Kennea, Jamie A.; Liu, Zhu

Abstract

We report on the discovery of a new supergiant fast X-ray transient (SFXT), MAXI J0709−159, and its identification with LY CMa (also known as HD 54786). On 2022 January 25, a new flaring X-ray object, named MAXI J0709−159, was detected by the Monitor of All-sky X-ray Image (MAXI). Two flaring activities were observed in two scans ∼3 hr apart, where the 2–10 keV flux reached 5 × 10⁻⁹ erg cm⁻² s⁻¹. During the period, the source exhibited a large spectral change, suggesting that the absorption column density NH increased from 10²² to 10²³ cm⁻². A NuSTAR follow-up observation on January 29 identified a new X-ray source with a flux of 6 × 10⁻¹³ erg cm⁻² s⁻¹ at a position consistent with LY CMa, which has been identified as a B supergiant as well as a Be star, located at a 3 kpc distance. The observed X-ray activity, characterized by short (≲several hours) duration, rapid (≲ a few seconds) variabilities accompanied by spectral changes, and a large luminosity swing (1032–1037 erg s⁻¹), agree with those of SFXTs. On the other hand, optical spectroscopic observations of LY CMa reveal a broad Hα emission line, which may indicate the existence of a Be circumstellar disk. These results suggest that the optical companion, LY CMa, certainly has a complex circumstellar medium including dense clumps.

Additional Information

© The Author(s) 2022. Published by Oxford University Press on behalf of the Astronomical Society of Japan. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model) Received: 14 June 2022. Accepted: 05 July 2022. Published: 28 July 2022. The authors thank the MAXI team members for their dedicated work on the mission operation. M. Sugizaki acknowledges support from the Chinese Academy of Sciences (CAS) President's International Fellowship Initiative (PIFI) (grant No. 2020FSM004). Part of this work was financially supported by Grants-in-Aid for Scientific Research 17H06362 (TM, HN, NK), 19K14762 (M. Shidatsu), and 21K03620 (HN) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan. We thank the NuSTAR and Swift operation teams for performing the ToO observations, and Brian Grefenstette for the quick-look analysis of the NuSTAR data. This work is based on data from eROSITA, the soft X-ray instrument aboard SRG, a joint Russian–German science mission supported by the Russian Space Agency (Roskosmos), in the interests of the Russian Academy of Sciences represented by its Space Research Institute (IKI) and the Deutsches Zentrum für Luft- und Raumfahrt (DLR). The SRG spacecraft was built by the Lavochkin Association (NPOL) and its subcontractors, and is operated by NPOL with support from the Max Planck Institute for Extraterrestrial Physics (MPE). The development and construction of the eROSITA X-ray instrument was led by MPE, with contributions from the Dr Karl Remeis Observatory Bamberg and ECAP (FAU Erlangen-Nuernberg), the University of Hamburg Observatory, the Leibniz Institute for Astrophysics Potsdam (AIP), and the Institute for Astronomy and Astrophysics of the University of Tübingen, with the support of DLR and the Max Planck Society. The Argelander Institute for Astronomy of the University of Bonn and the Ludwig Maximilians Universität Munich also participated in the science preparation for eROSITA. This work has also made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. The Digitized Sky Surveys were produced at the Space Telescope Science Institute under US Government grant NAG W-2166. The images of these surveys are based on photographic data obtained using the Oschin Schmidt Telescope on Palomar Mountain and the UK Schmidt Telescope. The plates were processed into the present compressed digital form with the permission of these institutions. The National Geographic Society Palomar Observatory Sky Atlas (POSS-I) was made by the California Institute of Technology with grants from the National Geographic Society. The Second Palomar Observatory Sky Survey (POSS-II) was made by the California Institute of Technology with funds from the National Science Foundation, the National Geographic Society, the Sloan Foundation, the Samuel Oschin Foundation, and the Eastman Kodak Corporation. The Oschin Schmidt Telescope is operated by the California Institute of Technology and Palomar Observatory. The UK Schmidt Telescope was operated by the Royal Observatory Edinburgh, with funding from the UK Science and Engineering Research Council (later the UK Particle Physics and Astronomy Research Council) until 1988 June, and thereafter by the Anglo-Australian Observatory. The blue plates of the Southern Sky Atlas and its equatorial extension (together known as SERC-J), as well as the Equatorial Red (ER), and the Second Epoch [red] Survey (SES) were all taken with the UK Schmidt. Supplemental funding for sky-survey work at the ST ScI is provided by the European Southern Observatory.

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