Статья

A Measurement of the Broadband Spectrum of XTE J1118+480 with<i>BeppoSAX</i>and Its Astrophysical Implications

F. FronteraDipartimento di Fisica, Università degli Studi di Ferrara, via Paradiso 12, I-44100 Ferrara, ItalyA. A. ZdziarskiNicolaus Copernicus Astronomical Center, Bartycka 18, 00-716 Warsaw, PolandL. AmatiJ. MikołajewskaNicolaus Copernicus Astronomical Center, Bartycka 18, 00-716 Warsaw, PolandT. BelloniOsservatorio Astronomico di Brera, via Bianchi, 46, I-23807 Merate, ItalyS. Del SordoIstituto di Fisica Cosmica ed Applicazioni dell’Informatica, CNR, via U. La Malfa 153, I-90146 Palermo, ItalyFrancesco HaardtUniversità dell’Insubria, Como, via Lucini 3, I-22100 Como, ItalyE. KuulkersSpace Research Organization of the Netherlands, Sorbonnelaan 2, 3584 CA Utrecht, Netherlands; and Astronomical Institute, Utrecht University, P.O. Box 80000, 3504 TA Utrecht, NetherlandsN. MasettiM. OrlandiniE. PalazziA. N. ParmarAstrophysics Division, Space Science Department, ESA, 2200 AG Noordwijk, NetherlandsRonald A. RemillardCenter for Space Research and Department of Physics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139A. SantangeloIstituto di Fisica Cosmica ed Applicazioni dell’Informatica, CNR, via U. La Malfa 153, I-90146 Palermo, ItalyL. StellaOsservatorio Astronomico di Roma, via Frascati, 33, I-00040 Monteporzio Catone, Italy

2001en

ABI

Аннотация

We report on results of a Target-of-Opportunity observation of the X-ray transient XTE J1118+480 performed on 2000 April 14-15 with the Narrow Field Instruments (0.1-200 keV) of the BeppoSAX satellite. The measured spectrum is a power law with a photon index of ~1.7 modified by an ultrasoft X-ray excess and a high-energy cutoff above ~100 keV. The soft excess is consistent with a blackbody with a temperature of ~40 eV and a low flux, while the cutoff power law is well fitted by thermal Comptonization in a plasma with an electron temperature of ~102 keV and an optical depth of order unity. Consistent with the weakness of the blackbody, Compton reflection is weak. Although the data are consistent with various geometries of the hot and cold phases of the accreting gas, we conclude that a hot accretion disk is the most plausible model. The Eddington ratio implied by recent estimates of the mass and the distance is ~10-3, which may indicate that advection is probably not the dominant cooling mechanism. We finally suggest that the reflecting medium has a low metallicity, consistent with the location of the system in the halo.

Перевод пока недоступен

Идентификаторы

DOI: 10.1086/323258

Цитирования и источники

Цитирований: 2Использованных источников: 0

Показатели — AkademScholar