Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe Crab pulsar in the 0.75-30 MeV range as seen by CGRO COMPTEL
57
0
0.0
(
0
)
Authors
L. Kuiper
Ask ChatGPT about the research
No Arabic 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 gamma-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 gamma-rays from CGRO BATSE and at high-energy gamma-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.
rate research
Read More
We report on a study of the gamma-ray continuum emission from the Crab supernova nebula and on a search for nuclear de-excitation gamma-ray lines. Crab is the brightest continuum source in the 1-10 MeV gamma-ray sky, and its continuum radiation is most likely of synchrotron origin. It is a likely source of cosmic rays through shock acceleration and thus a potential candidate for gamma-ray line emission from nuclear interactions. Five years of COMPTEL observations enable a fine spectral binning to investigate the behaviour of the 0.75-30 MeV emission in detail and to search for nuclear de-excitation lines on top of the continuum. The nebular spectrum shows a break at the edge of the COMPTEL energy range and connects well to the EGRET spectrum, probably reflecting electron energy losses in the synchrotron emission scenario. Such a smooth continuum model alone may not be sufficient to explain the observations. A weak bump in the spectrum at 1-2 MeV may be present. No significant evidence for distinct line emission is seen, but the presence of a blend of line features or another synchrotron component cannot be excluded.
The COMPTEL experiment aboard the Compton Gamma-Ray Observatory (CGRO) has observed the gamma-ray blazar 3C 279 several times between April 1991 and September 1995. This paper reports on a consistent analysis of these observations using the most recent COMPTEL data analysis tools. Detections and non-detections of 3C 279 along the CGRO-mission indicate a time-variable MeV-flux. Spectral variability is indicated as well, however can not be significantly proven by spectral fitting. The average MeV-spectrum of 3C 279, as measured by COMPTEL over the four-year period, is consistent with a photon power-law slope of about -1.9. This spectrum smoothly connects to the simultaneous 30 MeV to 10 GeV spectrum obtained from an analysis of the combined EGRET observations. No spectral break is required to fit the time-averaged MeV- to GeV-spectrum of 3C 279.
Neutron stars generate powerful winds of relativistic particles that form bright synchrotron nebulae around them. Polarimetry provides a unique insight into the geometry and magnetic configuration of the wind, but high-energy measurements have failed until recently. The Integral-IBIS telescope has been used in its Compton mode to search for linearly polarized emission for energies above 200 keV from the Crab nebula. The asymmetries in the instrument response are small and we obtain evidences for a strongly polarized signal at an angle parallel to the pulsar rotation axis. This result confirms the detection recently reported by Dean et al. (2008), and extends the polarization measure for all the pulsars phases. The hard X-ray/soft $gamma$-ray observations therefore probe the inner jets or equatorial flow of the wind. The achieved sensitivity opens a new window for polarimetric studies at energies above 200 keV.
The COMPTEL observations of the blazar-type quasar PKS 0528+134 in the energy range 0.75 MeV to 30 MeV carried out between April 1991 and September 1994 have been analyzed. During the first two years PKS 0528+134 was most significantly detected at energies above 3 MeV. During the last year there is only evidence for the quasar at energies below 3 MeV indicating a spectral change. The time-averaged COMPTEL energy spectrum between 0.75 MeV and 30 MeV is well represented by a power-law shape. Spectra collected from different observational periods reveal different power-law shapes: a hard state during flaring observations reported by EGRET, and a soft state otherwise. The combined simultaneous EGRET and COMPTEL spectra indicate these two spectral states as well. During low intensisty gamma-ray phases no spectral break is obvious from the combined COMPTEL and EGRET measurements. For the gamma-ray flaring phases however, the combined COMPTEL and EGRET data require a spectral bending at MeV-energies. By fitting broken power-law functions the best-fit values for the break in photon index range between 0.6 and 1.7, and for the break energy between ~5 MeV and ~20 MeV. Because the flux values measured by COMPTEL below 3 MeV in both states are roughly equal, the observations would be consistent with an additional spectral component showing up during gamma-ray flaring phases of PKS 0528+134. Such a component could be introduced by e.g. a high-energy electron-positron population with a low-energy cutoff in their bulk Lorentz factor distribution. The multiwavelength spectrum of PKS 0528+134 for gamma-ray flaring phases shows that the major energy release across the entire electro-magnetic spectrum is measured at MeV-energies.
COMPTEL was the Compton telescope on NASAs Compton Gamma Ray Observatory CGRO launched in April 1991 and which was re-entered in June 2000. COMPTEL covered the energy range 0.75 to 30 MeV, and performed a full-sky survey which is still unique in this range, with no followup mission yet approved. This remains a major uncharted region, and the heritage data from COMPTEL are still our main source of information. Data analysis has continued at MPE however, since the data were never fully analysed during the mission or in the period following, and improvements in analysis techniques and computer power make this possible.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
