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Issue A&A
Volume 411, Number 1, November III 2003
Special letters issue on: first science with integral
Page(s) L31 - L36
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20031353



A&A 411, L31-L36 (2003)
DOI: 10.1051/0004-6361:20031353

Letter

Absolute timing with IBIS, SPI and JEM-X aboard INTEGRAL

Crab main-pulse arrival times in radio, X-rays and high-energy $\gamma$-rays
L. Kuiper1, W. Hermsen1, R. Walter2, 3 and L. Foschini4

1  SRON National Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
2  INTEGRAL Science Data Centre, Chemin d'Écogia 16, 1290 Versoix, Switzerland
3  Geneva Observatory, Chemin des Maillettes 51, 1290 Sauverny, Switzerland
4  IASF/CNR, sezione di Bologna, via P. Gobetti 101, 40129 Bologna, Italy

(Received 28 July 2003 / Accepted 2 September 2003 )

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 $280\pm40~\mu{\rm s}$. 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 $241\pm29~\mu{\rm s}$, 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.


Key words: stars: neutron -- pulsars: individual: PSR B0531+21 -- X-rays: stars -- gamma rays: stars

Offprint request: L. Kuiper, L.M.Kuiper@sron.nl

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