Multicomponent X‐Ray Emissions from Regions near or on the Pulsar Surface

Abstract

We present a model of X-ray emission from rotation-powered pulsars, which in general consist of one nonthermal component, two hard thermal components, and one soft thermal component. The nonthermal X-rays come from synchrotron radiation of eB pairs created in the strong magnetic Ðeld near the neutron star surface by curvature photons emitted by charged particles on their way from the outer gap to the neutron star surface. The Ðrst hard thermal X-ray component results from polar-cap heating by the return current in the polar gap. The second hard thermal X-ray component results from polar-cap heating by the return particles from the outer gap. Because of cyclotron resonance scattering, most of the hard thermal X-rays will be e †ectively reÑected back to the stellar surface and eventually reemitted as soft thermal X-rays. However, some of the hard thermal X-rays can still escape along the open magnetic Ðeld lines, where the e`/e~pair density is low. Furthermore, the characteristic blackbody temperatures of the two hard X-ray components emitted from the polar-cap area inside the polar gap and the polarcap area deÐned by the footprints of the outer-gap magnetic Ðeld lines are strongly a †ected by the surface magnetic Ðeld, which can be much larger than the dipolar Ðeld. In fact, the strong surface magnetic Ðeld can explain why the e †ective blackbody radiation area is nearly 2 orders of magnitude larger than that deduced from the dipolar Ðeld for young pulsars (2 orders of magnitude less for old pulsars). Our model indicates how several possible X-ray components may be observed, depending on the magnetic inclination angle and viewing angle. Using the expected X-ray luminosity and spectra, we explain the observed X-ray spectra from pulsars such as Geminga, PSR B1055[52, PSR B0656]14, and PSR B1929]10.

Nonthermal X‐Ray Properties of Rotation‐powered Pulsars and Their Wind Nebulae

“…The X-ray luminosities in Saito (1998) and Possenti et al (2002) also include the total emission due to the pulsars plus PWNe, given the limited spatial resolutions of ASCA, RXTE, and BeppoSAX. Cheng et al (2004) divided the total X-ray emission into pulsed and nonpulsed components, and found that the X-ray luminosity of the pulsed component follows L X;pul /Ė 1:2 , which agrees with the model prediction L X /Ė 1:15 by Cheng & Zhang (1999). For nonpulsed emission, they got L X;npul /Ė 1:4 , where they supposed that the nonpulsed component comes mainly from PWNe and that the contribution of the nonpulsed component from pulsars is negligible.…”

“…The nonpulsed component originates from the cooling of the neutron star, emitted from the whole pulsar surface with a characteristic temperature of about 0.1 keV, while the pulsed component comes from hot spots ($1.0 keV) on the pulsar surface, which are heated by the bombardment of relativistic particles streaming back to the surface from the pulsar magnetosphere (Kundt & Schaaf 1993;Zavlin et al 1995;Gil & Krawczyk 1996). The pulsar's nonthermal emission arises from the pulsar magnetosphere, and it might also contain pulsed (e.g., Cheng & Zhang 1999;Zhang & Harding 2000) and nonpulsed components (e.g., Tennant et al 2001;Becker et al 2004). In some cases, a pulsar wind nebula ( PWN ) is found to surround a RPP.…”

PSR B1929+10 revisited in X-rays

“…For the double BB model a plausible explanation could be that the observed X-ray radiation originates from a heated polar cap characterized by two different thermal components (Cheng & Zhang 1999). The derived hydrogen column densities (N H ) are in both cases much larger than the value used in previous X-ray studies.…”

“…However, a plausible explanation could be that the observed X-ray radiation originates from a heated polar cap characterized by two different thermal components (see e.g. Cheng & Zhang 1999). The simultaneous double BB fit to the ROSAT and ASCA data implies emission luminosities of L 1 = (1.56 ± 0.25) × 10 30 erg s −1 and L 2 = (1.47 ± 0.25) × 10 29 erg s −1 for T 1 and T 2 components, respectively.…”

X-ray follow-up observations of the twoγ-ray pulsars PSR J1459–6053 and PSR J1614–2230

“…Becker & Trümper (1997), Cheng & Zhang (1998) and others showed that X-ray emission from rotationally powered pulsars can have thermal and non-thermal components. Thermal radiation is expected to arise from the heating of the polar caps by particles returning from the outer magnetosphere, or from the cooling neutron star surface in the case of pulsars (i.e.…”