INTEGRAL and XMM-Newton observations of AX J1845.0-0433

Aims: AX J1845.0-0433 is a transient high-mass X-ray binary discovered by ASCA. The source displays bright and short flares observed by INTEGRAL. The transient behaviour and bright and short flares are studied to understand both the accretion mechanisms and nature of the source.
Methods: Public INTEGRAL data and a pointed XMM-Newton observation are used to study in detail the flaring and quiescent phases.
Results: AX J1845.0-0433 is a persistent X-ray binary with a O9.5I supergiant companion, emitting at a low 0.2-100 keV luminosity of 10³⁵ erg s^-1 with seldom flares and reaching luminosities of 10³⁶ erg s^-1. The most accurately measured X-ray position is RA (2000)=18^h45^m01.4^s and Dec =-04°33'57.7 arcsec (2 arcsec). Variability factors of 50 are observed on timescales as short as hundreds of seconds. The broad-band spectrum is typical of wind-fed accreting pulsars with an intrinsic absorption of N_H=(2.6±0.2)× 10²² cm^-2, a hard continuum of Γ=(0.7{-}0.9)±0.1, and a high-energy cutoff at E_cut=16_-3⁺⁵ keV. An excess at low energies is also observed fitted with a black body with a temperature of kT=0.18±0.05 keV. Optically-thin and highly-ionised iron (Fe XVIII-XIX) located close to the supergiant star is detected during the quiescence phase. The spectral shape of the X-ray continuum remains unchanged. In contrast to the persistent quiescent emission, the flare characteristics suggest that clumps of mass M∼ 10²² g are formed within the stellar wind of the supergiant companion.

Based on observations with 1) INTEGRAL, an ESA project with instruments and science data centre funded by ESA member states (especially the P.I. countries: Denmark, France, Germany, Italy, Switzerland, Spain), Czech Republic and Poland, and with the participation of Russia and the USA and 2) XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA.