4U 1909+07: a well-hidden pearl (Conf. Proc.)

TL;DR

This paper presents the first detailed spectral and timing analysis of the HMXB 4U 1909+07, revealing energy-dependent pulse profiles, erratic pulse period changes, and phase-resolved spectral variations using INTEGRAL and RXTE data.

Contribution

It provides the first comprehensive spectral and timing characterization of 4U 1909+07, highlighting energy-dependent pulse profiles and spectral changes across pulse phases.

Findings

Pulse period of 605s with erratic variations.

Energy-dependent pulse profile evolution.

Phase-resolved spectral changes requiring cutoff energy variation.

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 with an average of 2.4cps in ISGRI, but shows flares up to ~50cps. The system shows a pulse period of 605s, but we found that the period changes erratically around this value. The pulse profile is extremely energy dependent: while it shows a double peaked structure at low energies, the secondary pulse decreases rapidly with increasing energy and above 20keV only the primary pulse is visible. This evolution is consistent between PCA, HEXTE and ISGRI. We find that the phase averaged spectrum can be well fitted with a photoabsorbed power law with a cutoff at high energies and a blackbody component. To investigate the peculiar pulse profile, we performed phase resolved spectral analysis. We find that a change in the cutoff energy is required to fit the changing spectrum of the different pulse phases.