We present a spectral analysis of the Crab Nebula obtained with the Chandra X-ray observatory. The X-ray spectrum is characterized by a power law whose index varies across the nebula. The variation can be discussed in terms of the particle injection from the pulsar in two different directions: the equatorial plane containing the torus and the symmetry axis along the jet. In the equatorial plane, spectra within the torus are the hardest, with a photon index % 1:9, and are almost independent of the surface brightness. At the periphery of the torus, the spectrum gradually softens in the outer, lower surface brightness regions, up to % 3:0. This indicates that synchrotron losses become significant to X-ray-emitting particles at the outer boundary of the torus. We discuss the nature of the torus, incorporating information from observations at other wavelengths. Spectral variations are also seen within the southern jet. The core of the jet is the hardest, with % 2:0, and the outer sheath surrounding the core becomes softer with up to 2.5 at the outermost part. Based on the similarity between the spectra of the jet core and the torus, we suggest that the electron spectra of the particles injected from the pulsar are also similar in these two different directions. The brightness ratio between the near and far sides of the torus can be explained by Doppler boosting and relativistic aberration; however, the observed ratio cannot be derived from the standard weakly magnetized pulsar wind model. We also found a site where an optical filament comprising supernova ejecta is absorbing the soft X-ray emission (<2 keV).

keV) spectra of the persistent X-ray emission from 9 magnetars were obtained with Suzaku, including 3 objects in apparent outburst. The soft X-ray component was detected from all of them, with a typical blackbody temperature of kT ∼ 0.5 keV, while the hard-tail component, dominating above ∼10 keV, was detected at ∼1 mCrab intensity from 7 of them. Therefore, the spectrum composed of a soft emission and a hard-tail component may be considered to be a common property of magnetars, both in their active and quiescent states. Wide-band spectral analyses revealed that the hard-tail component has a 1-60 keV flux, F h , comparable to or even higher than that carried by the 1-60 keV soft component, F s . The hardness ratio of these objects, defined as ξ ≡ F h /F s , was found to be tightly anti-correlated with their characteristic age τ c as ξ = (3.3 ± 0.3) × (τ c /1 kyr) −0.67±0.04 with a correlation coefficient of −0.989, over the range from ξ ∼ 10 to ξ ∼ 0.1. Magnetars in outburst states were found to lie on the same correlation as relatively quiescent ones. This hardness ratio is also positively correlated with their surface magnetic fields with a correlation coefficient of 0.873. In addition, the hard-tail component becomes harder towards sources with older characteristic ages, with the photon index changing from ∼1.7 to ∼0.4.

Studies were made of the 1-70 keV persistent spectra of fifteen magnetars as a complete sample observed with Suzaku from 2006 to 2013. Combined with early NuSTAR observations of four hard X-ray emitters, nine objects showed a hard power-law emission dominating at 10 keV with the 15-60 keV flux of ∼1-11 × 10 −11 ergs s −1 cm −2 . The hard X-ray luminosity L h , relative to that of a soft-thermal surface radiation L s , tends to become higher toward younger and strongly magnetized objects. Updated from the previous study, their hardness ratio, defined as ξ = L h /L s , is correlated with the measured spin-down rateṖ as ξ = 0.62 × (Ṗ /10 −11 s s −1 ) 0.72 , corresponding with positive and negative correlations of the dipole field strength B d (ξ ∝ B d) and the characteristic age τ c (ξ ∝ τ −0.68 c ), respectively. Among our sample, five transients were observed during X-ray outbursts, and the results are compared with their long-term 1-10 keV flux decays monitored with Swift/XRT and RXTE/PCA. Fading curves of three bright outbursts are approximated by an empirical formula used in the seismology, showing a ∼10-40 d plateau phase. Transients show the maximum luminosities of L s ∼1035 erg s −1 , which is comparable to those of the persistently bright ones, and fade back to 10 32 erg s −1 . Spectral properties are discussed in a framework of the magnetar hypothesis.

No abstract

We investigate a stationary pair production cascade in the outer magnetosphere of a spinning neutron star. The charge depletion due to global flows of charged particles, causes a large electric field along the magnetic field lines. Migratory electrons and/or positrons are accelerated by this field to radiate gamma-rays via curvature and inverse-Compton processes. Some of such gamma-rays collide with the X-rays to materialize as pairs in the gap. The replenished charges partially screen the electric field, which is selfconsistently solved together with the energy distribution of particles and gamma-rays at each point along the field lines. By solving the set of Maxwell and Boltzmann equations, we demonstrate that an external injection of charged particles at nearly Goldreich-Julian rate does not quench the gap but shifts its position and that the particle energy distribution cannot be described by a power-law. The injected particles are accelerated in the gap and escape from it with large Lorentz factors. We show that such escaping particles migrating outside of the gap contribute significantly to the gamma-ray luminosity for young pulsars and that the soft gamma-ray spectrum between 100 MeV and 3 GeV observed for the Vela pulsar can be explained by this component. We also discuss that the luminosity of the gamma-rays emitted by the escaping particles is naturally proportional to the square root of the spin-down luminosity.

We present new ASCA observations covering the 0.5-10 keV X-ray range of the cooling neutron star candidates PSR 0656ϩ14 and PSR 1055Ϫ52. Previous ROSAT observations had shown that two-component models, either two blackbodies or a blackbody plus a power-law, provided the best spectral fits to their X-ray emission. The combined ASCA and ROSAT spectrum of PSR 0656ϩ14 reveals two blackbody components with T 2 8 ϫ 10 5 K and T 2 1.5 ϫ 10 6 K and shows evidence that a power-law component is needed to account for higher energy photons. This three-component fit gives a reduced 2 that is half the value of a more conventional two component fit (1.3 as compared to 2.4). The fit to the combined spectrum for PSR 1055Ϫ52 yields a two-blackbody fit with T 2 8 ϫ 10 5 K and T 2 3.7 ϫ 10 6 K. Our results favor the existence of a hot polar cap in each of these pulsars with the ratio of the polar cap area to the neutron star surface area being 7 ϫ 10 Ϫ3 and 3 ϫ 10 Ϫ5 for PSR 0656ϩ14 and PSR 1055Ϫ52, respectively. The results are compared to models that make predictions of polar cap heating processes.

No abstract

No abstract