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Register a new userThe Phase-resolved High Energy Spectrum of the Crab Pulsar
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Anisia Tang Pui Shan
Publication date
2007
fields
Physics
and research's language is
English
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We present a modified outer gap model to study the phase-resolved spectra of the Crab pulsar. A theoretical double peak profile of the light curve containing the whole phase is shown to be consistent with the observed light curve of the Crab pulsar by shifting the inner boundary of the outer gap inwardly to $sim 10$ stellar radii above the neutron star surface. In this model, the radial distances of the photons corresponding to different phases can be determined in the numerical calculation. Also the local electrodynamics, such as the accelerating electric field, the curvature radius of the magnetic field line and the soft photon energy, are sensitive to the radial distances to the neutron star. Using a synchrotron self-Compton mechanism, the phase-resolved spectra with the energy range from 100 eV to 3 GeV of the Crab pulsar can also be explained.
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Context{The high energy emission regions of rotation powered pulsars are studied using folded light curve (FLCs) and phase resolved spectra (PRS).} aims{This work uses the NICER observatory to obtain the highest resolution FLC and PRS of the Crab pulsar at soft X-ray energies.} methods{NICER has accumulated about 347 ksec of data on the Crab pulsar. The data are processed using the standard analysis pipeline. Stringent filtering is done for spectral analysis. The individual detectors are calibrated in terms of long time light curve (LTLC), raw spectrum and deadtime. The arrival times of the photons are referred to the solar systems barycenter and the rotation frequency $ u$ and its time derivative $dot u$ are used to derive the rotation phase of each photon.} results{The LTLCs, raw spectra and deadtimes of the individual detectors are statistically similar; the latter two show no evolution with epoch; detector deadtime is independent of photon energy. The deadtime for the Crab pulsar, taking into account the two types of deadtime, is only approx 7% to 8% larger than that obtained using the cleaned events. Detector 00 behaves slightly differently from the rest, but can be used for spectral work. The PRS of the two peaks of the Crab pulsar are obtained at a resolution of better than 1/512 in rotation phase. The FLC very close to the first peak rises slowly and falls faster. The spectral index of the PRS is almost constant very close to the first peak.} conclusions{The high resolution FLC and PRS of the {{peaks}} of the Crab pulsar provide important constraints for the formation of caustics in the emission zone.}
We investigate polarization of high-energy emissions from the Crab pulsar in the frame work of the outer gap accelerator, following previous works of Cheng and coworkers. The recent version of the outer gap, which extends from inside the null charge surface to the light cylinder, is used for examining the synchrotron radiations from the secondary and the tertiary pairs, which are produced outside the gap. We calculate the light curve, the spectrum and the polarization characteristics, simultaneously, by taking into account gyration motion of the particles. The polarization position angle curve and the polarization degree are calculated to compare with the Crab optical data. We demonstrate that the radiations from inside the null charge surface make outer-wing and off-pulse emissions in the light curve, and the tertiary pairs contribute to bridge emissions. The emissions from the secondary pairs explain the main features of the observed light curve and spectrum. On the other hand, both emissions from inside the null charge surface and from the tertiary pairs are required to explain the optical polarization behavior of the Crab pulsar. The energy dependence of the polarization features is expected by the present model. For the Crab pulsar, the polarization position angle curve indicates that the viewing angle of the observer measured from the rotational axis is greater than $90^{circ}$.
The POLAR detector is a space based Gamma-Ray Burst (GRB) polarimeter sensitive in the 15-500 keV energy range. Apart from its main scientific goal as a Gamma-Ray Burst polarimeter it is also able to detect photons from pulsars in orbit. By using the six-months in-orbit observation data, significant pulsation from the PSR B0531+21 (Crab pulsar) was obtained. In this work, we present the precise timing analysis of the Crab pulsar, together with a phase-resolved spectroscopic study using a joint-fitting method adapted for wide field of view instruments like POLAR. By using single power law fitting over the pulsed phase, we obtained spectral indices ranging from 1.718 to 2.315, and confirmed the spectral evolution in a reverse S shape which is homogenous with results from other missions over broadband. We will also show, based on the POLAR in-orbit performance and Geant4 Monte-Carlo simulation, the inferred capabilities of POLAR-2, the proposed follow-up mission of POLAR on board the China Space Station (CSS), for pulsars studies.
We use 73 h of stereoscopic data taken with the MAGIC telescopes to investigate the very high-energy (VHE) gamma-ray emission of the Crab pulsar. Our data show a highly significant pulsed signal in the energy range from 50 to 400 GeV in both the main pulse (P1) and the interpulse (P2) phase regions. We provide the widest spectra to date of the VHE components of both peaks, and these spectra extend to the energy range of satellite-borne observatories. The good resolution and background rejection of the stereoscopic MAGIC system allows us to cross-check the correctness of each spectral point of the pulsar by comparison with the corresponding (strong and well-known) Crab nebula flux. The spectra of both P1 and P2 are compatible with power laws with photon indices of 4.0 pm 0.8 (P1) and 3.42 pm 0.26 (P2), respectively, and the ratio P1/P2 between the photon counts of the two pulses is 0.54 pm 0.12. The VHE emission can be understood as an additional component produced by the inverse Compton scattering of secondary and tertiary epm pairs on IR-UV photons.
We investigate polarization of high-energy emissions from the Crab pulsar in the frame work of the outer gap accelerator. The recent version of the outer gap, which extends from inside the null charge surface to the light cylinder, is used for examining the light curve, the spectrum and the polarization characteristics, simultaneously. The polarization position angle curve and the polarization degree are calculated to compare with the Crab optical data. We show that the outer gap model explains the general features of the observed light curve, the spectrum and the polarization by taking into account the emissions from inside of the null charge surface and from tertiary pairs, which were produced by the high-energy photons from the secondary pairs. For the Crab pulsar, the polarization position angle curve indicates that the viewing angle of the observer measured from the rotational axis is greater than 90 degrees.
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