Absolute timing with IBIS, SPI and JEM-X aboard INTEGRAL. Crab main-pulse arrival times in radio, X-rays and high-energy gamma -rays

Abstract

We have verified the absolute timing capabilities of the high-energy instruments aboard INTEGRAL, i.e. the imager IBIS, the spectrometer SPI and the X-ray monitor JEM-X. Calibration observations of the Crab, contemporaneous with the Rossi X-ray Timing Explorer (RXTE), have been used to measure the absolute phase of the main pulse of the Crab pulse profile using the same Jodrell Bank radio ephemeris. The three INTEGRAL instruments and RXTE give within the statistical and systematic uncertainties consistent results: The X-ray main pulse is leading the radio pulse by 280+/-40 mus . Also the shapes of the X-ray pulse profiles as measured by the different instruments are fully consistent with each other. In addition, we present the first measurement of the absolute phase of the main pulse at gamma -ray energies above 30 MeV using data from the EGRET instrument aboard the Compton Gamma-Ray Observatory: The gamma -ray main pulse is leading the radio one by 241+/-29 mus , consistent with the value for the X-ray main pulse. Comparing absolute arrival times at multiple frequencies gives important constraints to models explaining the production of non-thermal emission in magnetospheres of rotation powered neutron stars.

Based on observations with INTEGRAL, an ESA project with instruments and science data centre funded by ESA member states (especially the PI countries: Denmark, France, Germany, Italy, Switzerland, Spain), Czech Republic and Poland, and with the participation of Russia and the USA.}