Fig 4 - uploaded by Dominique Eckert
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Chandra/ACIS-S image of the central region of the Crab nebula, with the best-fit ISGRI positions in the 20-40 (band 1), 40-100 (2) and 100-200 keV (3) bands overlayed. The red circles show the best-fit positions and 1σ error circles of the total emission, while the black (yellow) circles show the measured positions of the off-pulse (on-pulse) phase bins. The position of the Crab pulsar and of the X-ray centroid of the nebula are also displayed. The size of the blue arrow is 17.3". For comparison, the inset shows a global view of the nebula. The black rectangle represents the size of the region displayed here.
Source publication
Aims. We use the IBIS/ISGRI telescope on-board INTEGRAL to measure the position of the centroid of the 20-200 keV emission from the Crab region. Methods. We find that the astrometry of the IBIS telescope is affected by the temperature of the IBIS mask during the observation. After correcting for this effect, we show that the systematic errors in th...
Contexts in source publication
Context 1
... resulting best- fit position for the centroid lies 17.3" away from the pulsar, in the torus and along the axis of the jet. Figure 4 shows the best- fit positions with 1σ error circles shown in Tab. 1 for the total emission and the on-and off-pulse cases, superimposed on the Table 1. IBIS/ISGRI best-fit positions of the Crab in 3 energy bands. ...
Context 2
... all the measured positions lie less than 1σ away from the line joining the Crab pulsar to the X-ray centroid of the nebula, which corresponds roughly to the jet line from the pulsar. This indicates that the measured positions are a combination of the pulsar position with the position of the centroid of the nebula. Interestingly, we can see in Fig. 4 that all the measurements are found to be significantly offset from the centroid of the X- ray emission. Given that the pulsed emission accounts only for ∼ 15% of the flux, this indicates that the centroid of the emission from the nebula, i.e., its morphology, varies relative to the soft X- ray band. This statement is confirmed by the ...
Context 3
... In X-rays, the nebula is ∼ 2 times smaller than in the optical, and therefore the synchrotron emis- sion in the outer regions probably cuts off in the optical/UV. Following this picture, it is natural to expect that a similar effect is happening when we compare the hard X-ray/soft γ-ray band with the soft X-rays. In the 20-40 keV band, we see in Fig. 4 that the centroid of the emission is found to be very close to the inner ring, which corresponds to the region where the most energetic electrons are produced. This indicates that in the outer regions of the X-ray image the spectrum cuts off in the X-ray/hard X- ray range. This interpretation is supported by the presence of the ...
Context 4
... a reasonable scenario for the electron distribution in the nebula. Indeed, our results are in excellent agreement with detailed theoretical modelling of the source us- ing MHD simulations ( Volpi et al. 2008;Del Zanna et al. 2006), which predict that the jet and the external regions of the torus should disappear in hard X-rays/soft γ-rays (see Fig. 4 of Volpi et al. 2008). Therefore, our measurements qualitatively confirm the predictions of MHD ...
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Citations
We report on a detailed spectral characterization of the non-thermal X-ray emission for a large sample of gamma-ray pulsars in the second Fermi Large Area Telescope catalogue. We outline the criteria adopted for the selection of our sample, its completeness, and critically describe different approaches to estimate the spectral shape and flux of pulsars. We perform a systematic modelling of the pulsars’ X-ray spectra using archival observations with XMM–Newton, Chandra, and NuSTAR and extract the corresponding non-thermal X-ray spectral distributions. This set of data is made available online and is useful to confront with predictions of theoretical models.
We report on a detailed spectral characterization of the non-thermal X-ray emission for a large sample of gamma-ray pulsars in the second Fermi-LAT catalogue. We outline the criteria adopted for the selection of our sample, its completeness, and critically describe different approaches to estimate the spectral shape and flux of pulsars. We perform a systematic modelling of the pulsars' X-ray spectra using archival observations with XMM-Newton, Chandra, and NuSTAR and extract the corresponding non-thermal X-ray spectral distributions. This set of data is made available online and is useful to confront with predictions of theoretical models.
Context: In 6 years of operation, INTEGRAL/ISGRI revealed more than 500 sources. Many of these sources are variable. Taking into account that nearly half of INTEGRAL/ISGRI sources are new and many of them are still unidentified, the variability properties of the sources can serve as additional parameters that may help to classify and identify the unknown sources. Aims: In order to study the variability properties of the sources detected by INTEGRAL/ISGRI we develop a method to quantify the variability of a source. We describe here our techniques and compile a catalog of the sources that fit our criteria of variability. Methods: We use the natural time binning of INTEGRAL observations called Science Window ($\approx 2000$ seconds) and test the hypothesis that the detected sources are constant using a $\chi^2$ all-sky map in three energy bands (20-40, 40-100, 100-200 keV). We calculate an intrinsic variance of the flux in individual pixels and use it to define the fractional variability of a source. The method is sensitive to the source variability on time scales of one Science Window and higher. We concentrate only on the sources which were already reported to be detected by INTEGRAL. Results: We present a catalog of 202 sources which are found to be significantly variable. For the catalog sources we give the measure of variability and fluxes with corresponding errors in 20-40, 40-100, 100-200 keV energy bands, and we present some statistics about the population of variable sources. The description of the physical properties of the variable sources will be given in a forthcoming paper. Comment: 16 pages, 7 figures, Accepted to Astronomy and Astrophysics
