Document 
| Abstract | PDF (541.4 KB) | PS (1.017 MB) | References | HTML | Tables at CDS | Simbad Objects | NASA ADS Abstract Service |
A&A 458, 21-29 (2006)
DOI: 10.1051/0004-6361:20065297
The X-ray spectrum of the bursting atoll source 4U 1728-34 observed with INTEGRAL
M. Falanga1, 2, D. Götz1, P. Goldoni1, 2, R. Farinelli3, A. Goldwurm1, 2, S. Mereghetti4, A. Bazzano5 and L. Stella61 CEA Saclay, DSM/DAPNIA/Service d'Astrophysique (CNRS FRE 2591), 91191 Gif-sur-Yvette, France
e-mail: mfalanga@cea.fr
2 Unité mixte de recherche Astroparticule et Cosmologie, 11 place Berthelot, 75005 Paris, France
3 Dipartimento di Fisica, Università di Ferrara, via Paradiso 12, 44100 Ferrara, Italy
4 INAF - Istituto di Astrofisica Spaziale e Fisica Cosmica, Milano, via Bassini 15, 20133 Milano, Italy
5 INAF - Istituto di Astrofisica Spaziale e Fisica cosmica, via del Fosso del Cavaliere 100, 00133 Roma, Italy
6 INAF - Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone (Roma), Italy
(Received 28 March 2006 / Accepted 10 July 2006)
Abstract
We present for the first time a study of the 3-200 keV
broad band spectra of the bursting atoll source 4U 1728-34 (GX 354-0)
along its hardness intensity diagram. The analysis was done using the
INTEGRAL public and Galactic Center deep exposure data ranging from
February 2003 to October 2004. The spectra are well described by a
thermal Comptonization model with an electron temperature from 35 keV to 3 keV and Thomson optical depth,
, from 0.5 to 5 in a slab
geometry. The source undergoes a transition from an intermediate/hard
to a soft state where the source luminosity increases from 2 to 12%
of Eddington. We have also detected 36 type I X-ray bursts two of
which show photospheric radius expansion. The energetic bursts with
photospheric radius expansion occurred at an inferred low mass
accretion rate per unit area of
g cm-2 s-1, while the others at a higher one between
g m-2 s-1. For 4U 1728-34 the
bursts' total fluence, and the bursts' peak flux are anti-correlated
with the mass accretion rate.
The type I X-ray bursts involve pure helium burning either during the hard
state, or during the soft state of the source.
Key words: binaries: close -- stars: pulsars: individual 4U 1728-34 -- stars: neutron -- X-rays: bursts
© ESO 2006