EDP Sciences
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Volume 399, Number 3, March I 2003
Page(s) 1151 - 1157
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20021881

A&A 399, 1151-1157 (2003)
DOI: 10.1051/0004-6361:20021881

Spectral fits to the 1999 Aql X-1 outburst data

T. J. Maccarone1 and P. S. Coppi2

1  Astrophysics Sector, SISSA/ISAS, via Beirut No. 2-4, 34014, Trieste, Italy
2  Department of Astronomy, Yale University, PO Box 208101, New Haven CT 06520-8101, USA
    e-mail: coppi@astro.yale.edu

(Received 13 June 2002 / Accepted 16 December 2002 )

We present analysis and spectral fits of the RXTE data from the May/June 1999 outburst of Aql X-1. These data include observations in the rising portion of the hard state, in the soft state, and in the falling portion of the hard state. We show that the data can be fit by a purely thermal Comptonization model for all the observations, but that more complicated models cannot be ruled out. Up to 60% of the corona's power in the soft state may be injected into non-thermal electrons. The soft state data show approximately constant optical depth and coronal temperatures over a range of ~ 10 in luminosity, while they show evidence for a reduction of seed photon temperature with reduced luminosity and indicate that the characteristic size of the seed photon emitting region is roughly constant throughout the soft state. The hard state before the soft state shows a higher luminosity, higher optical depth, and lower electron temperature than the hard state after the soft state. We find a reduction of the hard (30-60 keV) X-ray flux during a type I burst and show that it requires a total corona energy reservoir of less than ~ 1038 ergs.

Key words: accretion, accretion disks -- radiation mechanisms: non-thermal -- X-rays: individual: Aql X-1 -- X-rays: bursts

Offprint request: T. Maccarone, maccarone@ap.sissa.it

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