4U 1909+07: a well-hidden pearl

TL;DR

This paper provides the first detailed spectral and timing analysis of the HMXB 4U 1909+07, revealing energy-dependent pulse profiles, spectral variability, and insights into its accretion geometry using INTEGRAL and RXTE data.

Contribution

It offers the first comprehensive spectral and timing characterization of 4U 1909+07, including pulse profile evolution and phase-resolved spectral analysis.

Findings

Pulse period of ~604 sec is erratic over years.

Pulse profile is energy-dependent, with a double peak at low energies.

Spectral analysis shows a cutoff power law with blackbody component.

Abstract

We present the first detailed spectral and timing analysis of the High Mass X-ray Binary (HMXB) 4U 1909+07 with INTEGRAL and RXTE. 4U 1909+07 is detected in the ISGRI 20-40 keV energy band with an average countrate of 2.6 cps. The pulse period of ~604 sec is not stable, but changing erratically on timescales of years. The pulse profile is strongly energy dependent: it shows a double peaked structure at low energies, the secondary pulse decreases rapidly with increasing energy and above 20 keV only the primary pulse is visible. This evolution is consistent between PCA, HEXTE, and ISGRI. The phase averaged spectrum can be well described by the sum of a photoabsorbed power law with a cutoff at high energies and a blackbody component. To investigate the pulse profile, we performed phase resolved spectral analysis. We find that the changing spectrum can be best described with a variation of the folding energy. We rule out a correlation between the black body component and the continuum variation and discuss possible accretion geometries.