Absolute timing of the Crab pulsar with the INTEGRAL/SPI telescope

Abstract

We have investigated the pulse shape evolution of the Crab pulsar emission in the hard X-ray domain of the electromagnetic spectrum. In particular, we have studied the alignment of the Crab pulsar phase profiles measured in the hard X-rays and in other wavebands. To obtain the hard X-ray pulse profiles, we have used six year (2003-2009, with a total exposure of about 4 Ms) of publicly available data of the SPI telescope on-board of the INTEGRAL observatory, folded with the pulsar time solution derived from the Jodrell Bank Crab Pulsar Monthly Ephemeris. We found that the main pulse in the hard X-ray 20-100 keV energy band is leading the radio one by $8.18\pm 0.46$ milliperiods in phase, or $275\pm 15\mu s$ in time. Quoted errors represent only statistical uncertainties.Our systematic error is estimated to be $\sim 40\mu s$ and is mainly caused by the radio measurement uncertainties. In hard X-rays, the average distance between the main pulse and interpulse on the phase plane is $0.3989\pm 0.0009$. To compare our findings in hard X-rays with the soft 2-20 keV X-ray band, we have used data of quasi-simultaneous Crab observations with the PCA monitor on-board the Rossi X-Ray Timing Explorer (RXTE) mission. The time lag and the pulses separation values measured in the 3-20 keV band are $0.00933\pm 0.00016$ (corresponding to $310\pm 6\mu s$) and $0.40016\pm 0.00028$ parts of the cycle, respectively. While the pulse separation values measured in soft X-rays and hard X-rays agree, the time lags are statistically different. Additional analysis show that the delay between the radio and X-ray signals varies with energy in the 2 - 300 keV energy range. We explain such a behaviour as due to the superposition of two independent components responsible for the Crab pulsed emission in this energy band.

References in corpus (4)

• Observation of Pulsed Gamma-rays Above 25 GeV from the Crab Pulsar with MAGIC
• Simultaneous Absolute Timing of the Crab Pulsar at Radio and Optical Wavelengths
• The optical to gamma-ray emission of the Crab pulsar: a multicomponent model
• The multicomponent model of the Crab Pulsar at energies above 25 GeV

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