INTEGRAL OBSERVATIONS OF THE VELA REGION FOCUSING ON VELA X-1

ABSTRACT The Vela region has been observed for 1.7 Ms in November 2005 by the INTEGRAL satellite. We present preliminary spectral and temporal results of Vela X-1, an eclipsing neutron star hosted in a wind-accreting high-mass X-ray binary system. Using data from ISGRI, SPI and JEM-X, we firmly confirm the existence of cyclotron resonant scattering features (CRSF) at ~27 keV and ~54 keV, implying a neutron-star magnetic field of 3×10 12 Gauss, and the presence of an iron emission line at ~6.5 keV. During two strong flares those parameters remained unchanged. Furthermore we measure the neutron-star spin period of 283.6 s, indicating a still constant trend. 1. INTRODUCTION The Vela region has been observed by INTEGRAL [1], ESA’s gamma-ray satellite, in the frame of our accepted AO-3 open-time proposal. Data were taken from November 4 to December 4, 2005, during 1.7 Ms, from INTEGRAL revolution n°373 to 383, in 473 different pointings. The key target is the detection of γ-rays emitted by the decay of radioactive isotopes produced in stellar nucleosynthesis processes as e.g. 1809 keV emission from