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Multiwavelength approach to classifying transient events in the direction of M31

Soraisam, Monika D. and Gilfanov, Marat and Kupfer, Thomas and Prince, Thomas A. and Masci, Frank and Laher, Russ R. and Kong, Albert K. H. (2018) Multiwavelength approach to classifying transient events in the direction of M31. Astronomy and Astrophysics, 615 . Art. No. A152. ISSN 0004-6361. doi:10.1051/0004-6361/201732068.

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Context. In the hunt for rare time-domain events, it is important to consider confusing exotic extragalactic phenomena with more common Galactic foreground events. Aims. We show how observations from multiple wavebands, in this case optical and X-ray observations, can be used to facilitate the distinction between the two. Methods. We discovered an extremely bright and rapid transient event during optical observations of the M 31 galaxy taken by the intermediate Palomar Transient Factory (iPTF). The persistent optical counterpart of this transient was previously thought to be a variable star in M 31 without any dramatic flux excursions. The iPTF event initially appeared to be an extraordinarily rapid and energetic extragalactic transient, which had a ≈3 mag positive flux excursion in less than a kilosecond; one of the exciting possibilities was this event could be a very fast nova in M 31. The nature of the source was resolved with the help of Chandraarchival data, where we found an X-ray counterpart and obtained its X-ray spectrum. Results. We find the X-ray spectrum of the quiescent emission can be described by a model of optically thin plasma emission with a temperature of ≈7 MK, typical for coronal emission from an active star. The combination of the X-ray luminosity, which is calculated assuming the source is located in M 31 (~3 × 10^(36) erg s^(−1)), and the color temperature exclude any type of known accreting compact object or active star in M 31. We argue instead that the optical transient source is an M-type main-sequence, active star located in the disk of the Milky Way at a distance of ~0.5–1 kpc. Its persistent X-ray luminosity is in the ≈1.3–5 × 10^(30)erg s^(−1) range and it has the absolute optical magnitude of 9.5–11.0 mag in the R band. The observed optical flare has the equivalent duration of ≈95 min and total energy of ≈(0.3–1) × 10^(35) erg in the R band, which places it among the brightest flares ever observed from an M-type star. This case can serve as an example for the classification of Galactic and extragalactic events in upcoming high-cadence time-domain projects, such as the Zwicky Transient Facility and the Large Synoptic Survey Telescope.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Kupfer, Thomas0000-0002-6540-1484
Prince, Thomas A.0000-0002-8850-3627
Masci, Frank0000-0002-8532-9395
Laher, Russ R.0000-0003-2451-5482
Kong, Albert K. H.0000-0002-5105-344X
Alternate Title:A multi-wavelength approach to classifying transient events in the direction of M31
Additional Information:© 2018 ESO. Article published by EDP Sciences. Received 9 October 2017; Accepted 28 March 2018; Published online 31 July 2018. This research has made use of data obtained from the Chandra Data Archive and the Chandra Source Catalog, and software provided by the Chandra X-ray Center (CXC) in the application packages CIAO, ChIPS, and Sherpa. It is also based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. MG acknowledges partial support by Russian Scientific Foundation (RNF), project 14-22-00271. This research has made use of software obtained from the High Energy Astrophysics Science Archive Research Center (HEASARC), a service of the Astrophysics Science Division at NASA/GSFC and of the Smithsonian Astrophysical Observatory’s High Energy Astrophysics Division. We also thank the anonymous referee for the many helpful comments and suggestions that helped improve this paper.
Group:Astronomy Department
Funding AgencyGrant Number
Russian Science Foundation14-22-00271
Subject Keywords:stars: general – galaxies: individual: M31 – surveys – X-rays: stars
Record Number:CaltechAUTHORS:20180816-105138658
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Official Citation:Multiwavelength approach to classifying transient events in the direction of M 31 Monika D. Soraisam, Marat Gilfanov, Thomas Kupfer, Thomas A. Prince, Frank Masci, Russ R. Laher and Albert K. H. Kong A&A, 615 (2018) A152. DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:88856
Deposited By: Tony Diaz
Deposited On:16 Aug 2018 19:53
Last Modified:16 Nov 2021 00:30

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