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EXTraS discovery of a peculiar flaring X-ray source in the Galactic globular cluster NGC 6540

Journal
Date Issued
2018
Author(s)
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Salvetti, David
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DOI
Abstract
We report the discovery of a flaring X-ray source 7″ from the center of the globular cluster NGC 6540 obtained during the EXTraS project devoted to a systematic search for variability in archival data of the XMM-Newton satellite. The source had a quiescent X-ray luminosity on the order of 1032 erg s-1 in the 0.5-10 keV range (for a distance of NGC 6540 of 4 kpc) and showed a flare lasting about 300 s. During the flare, the X-ray luminosity increased by more than a factor 40, with a total emitted energy of 1036 erg. These properties, as well as Hubble Space Telescope photometry of the possible optical counterparts, suggest the identification with a chromospherically active binary in the cluster. However, the flare luminosity is significantly higher than what is commonly observed in stellar flares of such a short duration, leaving open the possibility of other interpretations.
Volume
616
Start page
A36
Uri
Url
Issn Identifier
0004-6361
Ads BibCode
2018A&A...616A..36M
Rights
open.access
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