The Crab pulsar in the 0.75-30 MeV range as seen by CGRO COMPTEL

Abstract

Abstract. We present the time-averaged characteristics of the Crab pulsar in the 0.75-30 MeV energy window using data from the imaging Compton Telescope COMPTEL aboard the Compton Gamma-Ray Observatory (CGRO) collected over its 9 year mission. Exploiting the exceptionally long COMPTEL exposure on the Crab allowed us to derive significantly improved COMPTEL spectra for the Crab nebula and pulsar emissions, and for the first time to accurately determine at low-energy γ-rays the pulse profile as a function of energy. These timing data, showing the well-known main pulse and second pulse at a phase separation of ∼0.4 with strong bridge emission, are studied together with data obtained at soft/hard X-ray energies from the ROSAT HRI, BeppoSAX LECS, MECS and PDS, at soft γ-rays from CGRO BATSE and at high-energy γ-rays from CGRO EGRET in order to obtain a coherent high-energy picture of the Crab pulsar from 0.1 keV up to 10 GeV. The morphology of the pulse profile of the Crab pulsar is continuously changing as a function of energy: the intensities of both the second pulse and the bridge emission increase relative to that of the first pulse for increasing energies up to ∼1 MeV. Over the COMPTEL energy range above 1 MeV an abrupt morphology change happens: the first pulse becomes again dominant over the second pulse and the bridge emission loses significance such that the pulse profile above 30 MeV is similar to the one observed at optical wavelengths. A pulse-phase-resolved spectral analysis performed in 7 narrow phase slices consistently applied over the 0.1 keV-10 GeV energy interval shows that the pulsed emission can empirically be described with 3 distinct spectral components: i) a power-law emission component (1 keV-5 GeV; photon index 2.022 ± 0.014), present in the phase intervals of the two pulses; ii) a curved spectral component required to describe soft ( < ∼ 100 keV) excess emission present in the same pulsephase intervals; iii) a broad curved spectral component reflecting the bridge emission from 0.1 keV to ∼10 MeV. This broad spectral component extends in phase over the full pulse profile in an approximately triangular shape, peaking under the second pulse. Recent model calculations for a three-dimensional pulsar magnetosphere with outer magnetospheric gap acceleration by Cheng et al. (2000) appear at present most successful in explaining the above complex high-energy characteristics of the Crab pulsar.

The Phase‐resolved X‐Ray Spectra of the Crab Pulsar

“…The observations at all wave bands show that the pulse profiles are dominated by two pulses, separated $0.4 in pulse phase (e.g., see Kuiper et al 2001). In X-ray bands, ROSAT and BeppoSAX observations provide more information to study the pulse profiles of X-rays from the Crab pulsar.…”

“…From the BeppoSAX observations, a detailed study of the changes in the pulse profile shape has been made (Massaro, Feroci, & Matt 1997;Mineo et al 1997). There are two main observed features: (1) the count rates of the second peak (P2) and bridge region (Ip) increase relative to that of the first peak (P1) for increasing energies, and (2) the shape width of the first peak increases with energy (also see Massaro et al 2000;Kuiper et al 2001). In order to quantify the variation of pulse shape with energy, the intensity ratios between the second peak and the first peak (P2/P1) and between the bridge region and the first peak (Ip/P1) in different energy ranges have been estimated (Massaro, Feroci, & Matt 1997;Mineo et al 1997).…”

PSR B1929+10 revisited in X-rays

“…Moreover, studying the Geminga pulsar (237 ms) at soft X-rays reported discrepancies in the phase alignment of different ROSAT Geminga observations, which could be traced back to leap second ignorance in the PROS software. Finally, in Kuiper et al (2001) a ROSAT HRI 0.1-2.4 keV pulse profile for the Crab pulsar (33 ms) was shown based on a 7.98 ks observation (RH400639N00) performed over the time period from 4-15 March 1995. In this observation four consecutive (ROSAT) orbital intervals could be identified yielding a stable pulse profile.…”

Multi-waveband photons and high energy neutrinos from the Crab nebula

“…4, we show the comparison of the predicted photon spectrum with the observed data for the Crab nebula. The radio data are taken from Baars & Hartsuijker (1972), millimeter and IR data from Strom & Greidanus (1992), Bandiera et al (2002), andGreen et al (2004), soft X-ray to γ-ray data from Kuiper et al (2001), and VHE γ-ray data from Aharonian et al (2004Aharonian et al ( , 2006 and Albert et al (2008). In Fig.…”

“…The proton spectrum Comparison of the calculated spectrum with observed data for the Crab nebula. The radio data are taken from Baars & Hartsuijker (1972), millimeter and IR data from Strom & Greidanus (1992), Bandiera et al (2002), and Green et al (2004), soft X-ray to γ-ray data from Kuiper et al (2001), and VHE γ-ray data from Aharonian et al (2004Aharonian et al ( , 2006 and Albert et al (2008). Dash-dotted, dot-dot dashed, and dash-dash dotted curves represent the synchrotron, bremsstrahlung, and self synchrotron Compton emission spectra of the leptons, curves 1, 2, and 3 are the spectra of the inverse Compton scattering of the leptons with the microwave background, infrared photons, and optical photons, the dashed curve represents the π 0 -decay spectrum in the pp interaction, and the solid line is total emission.…”