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Chandra Detection of an X-Ray Flare from the Brown Dwarf LP 944-20

Rutledge, Robert E. and Basri, Gibor and Martín, Eduardo L. and Bildsten, Lars (2000) Chandra Detection of an X-Ray Flare from the Brown Dwarf LP 944-20. Astrophysical Journal, 538 (2). L141-L144. ISSN 0004-637X. doi:10.1086/312817.

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We have detected a bright X-ray flare from the nearby (d = 5.0 pc) brown dwarf LP 944-20 with the Chandra Advanced CCD Imaging Spectrometer-S. This is an old (500 Myr), rapidly rotating, lithium-bearing M9 object, with a bolometric luminosity of ≈6 × 10^(29) ergs s^(-1). It was detected only by Chandra during an X-ray flare of duration 1-2 hr near the end of a 12.1 hr observation. The peak X-ray luminosity was 1.2^(+0.5)_(-0.3) × 10^(26) ergs s^(-1) in the brightest ≈550 s, corresponding to L_X/L_(bol) ≈ 2 × 10^(-4). A total of 2 × 10^(29) ergs was released during the 43,773 s observation, giving a time-averaged L_X/L_(bol) ≈ 7 × 10^(-6). LP 944-20 was not detected before the flare, with a 3 σ upper limit on the emission at L_X/L_(bol) < 2 × 10^(-6) (L_X < 1 × 10^(24) ergs s^(-1)). This is faint for a rapidly rotating late-type star and establishes a record lower limit to the quiescent flux about an order of magnitude below the flux limit (and a factor of 5 below the L_X/L_(bol) limit) placed on quiescent X-ray emission from the M8 dwarf VB 10. The inferred flaring duty cycle is comparable to that measured via variable Hα emission for other late M-type, fully convective stars.

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Additional Information:© 2000. The American Astronomical Society. Received 2000 May 1; accepted 2000 June 14; published 2000 July 27. The authors are grateful to the Chandra Observatory team for producing this exquisite observatory. We are grateful to Andrew Cumming for his critical reading of an early version of this Letter and to the referee, Tom Fleming, for comments that dramatically improved the Letter's readability. We thank Daniel Holz for encouraging us to consider the rotational modulation of the light curve. This research was supported by NASA grant GO0-1009X and the National Science Foundation under grant PHY 94-07194. L. B. is a Cottrell Scholar of the Research Corporation.
Group:Space Radiation Laboratory
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Cottrell Scholar of Research CorporationUNSPECIFIED
Subject Keywords:stars: coronae; stars: individual (LP 944-20); stars: low-mass, brown dwarfs
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Other Numbering System NameOther Numbering System ID
Space Radiation Laboratory2000-06
Issue or Number:2
Record Number:CaltechAUTHORS:20150219-090458192
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:54992
Deposited By: Deborah Miles
Deposited On:24 Feb 2015 17:36
Last Modified:10 Nov 2021 20:40

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