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Issue A&A
Volume 460, Number 2, December III 2006
Page(s) L1 - L4
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20066154



A&A 460, L1-L4 (2006)
DOI: 10.1051/0004-6361:20066154

Letter

A new symbiotic low mass X-ray binary system: 4U 1954+319

F. Mattana1, 2, D. Götz3, M. Falanga3, F. Senziani1, 4, 5, A. De Luca1, P. Esposito1, 4, and P. A. Caraveo1

1  INAF - Istituto di Astrofisica Spaziale e Fisica Cosmica, via Bassini 15, 20133 Milano, Italy
    e-mail: mattana@iasf-milano.inaf.it
2  Università di Milano Bicocca, Dipartimento di Fisica G. Occhialini, P.za della Scienza 3, 20126 Milano, Italy
3  CEA Saclay, DSM/DAPNIA/Service d'Astrophysique (CNRS FRE 2591), 91191 Gif-sur-Yvette, France
4  Università di Pavia, Dipartimento di Fisica Nucleare e Teorica and INFN-Pavia, via Bassi 6, 27100 Pavia, Italy
5  Université Paul Sabatier, 31062 Toulouse, France

(Received 31 July 2006 / Accepted 24 September 2006)

Abstract
Aims.4U 1954+319 was discovered 25 years ago, but only recently has a clear picture of its nature begun to emerge. We present for the first time a broad-band spectrum of the source and a detailed timing study using more than one year of monitoring data.
Methods.The timing and spectral analysis was done using publicly available Swift, INTEGRAL, BeppoSAX, and RXTE/ASM data in the 0.7 to 150 keV energy band.
Results.The source spectrum is described well by a highly absorbed ($N_{\rm H} \sim 10^{23}$ cm-2) power law with a high-energy exponential cutoff around 15 keV. An additional black body component is needed below 3 keV to account for a soft excess. The derived ~5 h periodicity, with a spin-up timescale of ~25 years, could be identified as the neutron star spin period. The spectral and timing characteristics indicate that we are dealing both with the slowest established wind-accreting X-ray pulsar and with the second confirmed member of the emerging class dubbed "symbiotic low mass X-ray binaries" to host a neutron star.


Key words: binaries: close -- pulsars: individual: 4U 1954+319 -- stars: neutron -- X-rays: binaries



© ESO 2006


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