Hard X-ray Emission from Low Mass X-ray Binaries

摘要: In this paper we review our current knowledge of the hard X-ray emission properties old accreting neutron stars in low mass binaries, with particular attention to recent results obtained for brightest sources class, so-called Z sources. While less luminous binaries often show quite spectra, sometimes extending up energies g 100 keV, spectra are always very soft, dominated by thermal components characteristic temperatures ∼ 3-6 keV. However, broad band observations revealed presence a weak (power-law) component that is present these These have strengthened analogies between spectral behavior hosting and binary systems containing black hole candidates. The physical parameters regulating unknown yet. first parameter may be accretion rate, as indicated general anticorrelation fraction luminosity X-rays rate apparent over different spanning large range luminosities well individual undergoing state changes. second, yet unknown, probably needed explain all phenomenology. high energy coverage good sensitivity INTEGRAL mission can represent an important step forward understanding origin binaries.