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Astron. Astrophys. 335, L101-L105 (1998)

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Letter to the Editor

RXTE observations of Proxima Centauri

Bernhard Haisch 1, Vinay Kashyap 2, Jeremy J. Drake 2 and Peter Freeman 3

1 Solar and Astrophysics Laboratory, Lockheed Martin, H1-12, B252, 3251 Hanover St., Palo Alto, CA 94304, USA
2 Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA
3 Department of Astronomy & Astrophysics and Enrico Fermi Institute, University of Chicago, Chicago, IL 60637, USA

Received 1 April 1998 / Accepted 14 May 1998


We report on Rossi X-ray Timing Explorer (RXTE) observations of the dM5e flare star Proxima Centauri. These were carried out using the Proportional Counter Array (PCA) in three segments totaling 50.87 ks on 1996 February 20, 23 and 25. The star was detected in the three lowest-energy channels (1.75-3.9 keV, 3.9-5.75 keV, 5.75-8.7 keV) with a mean X-ray luminosity of [FORMULA] ergs s-1. This is an order of magnitude higher than the mean non-flaring ASCA detection in a similar passband in March 1994. Previous Einstein Observatory , EXOSAT and ROSAT detections yielded similar [FORMULA] ([FORMULA] ergs s-1) but at lower energies. After compensating for passband differences the RXTE-PCA mean level of activity is found to be similarly enhanced with respect to these observations. The star appears to be in a higher activity state, but no major flares were detected. Owing to the high RXTE background we cannot address the issue of solar-like, M-class flaring previously measured on Proxima by ASCA. Searches were carried out for short-duration bursts - as on the Sun during the flare impulsive phase - at all PCA energies (1.75-65 keV) using statistical tests for any significant clustering of 15, 25, 50 or 100 photons. Such events would be relatively insensitive to fluctuations and modeling limitations of the background. The number of photon clusters found was consistent with statistical fluctuations.

Key words: stars: coronae – stars: individual (Proxima Centauri) – X-rays: stars – stars: flare

Send offprint requests to: B. Haisch (e-mail: haisch@starspot.com)

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© European Southern Observatory (ESO) 1998

Online publication: June 26, 1998