Pulsar Polar Cap Heating and Surface Thermal X-Ray Emission. II. Inverse Compton Radiation Pair Fronts

By A. Harding, A. Muslimov. 2001

186 citations recorded by the source corpus.

We investigate the production of electron-positron pairs by inverse Compton scattered (ICS) photons above a pulsar polar cap (PC) and calculate surface heating by returning positrons. This paper is a continuation of our self-consistent treatment of acceleration, pair dynamics, and electric field screening above pulsar PCs. We calculate the altitude of the inverse Compton pair-formation fronts, the flux of returning positrons, and present the heating efficiencies and X-ray luminosities. We revise pulsar death lines implying cessation of pair formation, and present them in surface magnetic field-period space. We find that virtually all known radio pulsars are capable of producing pairs by resonant and nonresonant ICS photons radiated by particles accelerated above the PC in a pure star-centered dipole field, so that our ICS pair death line coincides with empirical radio pulsar death. Our calculations show that ICS pairs are able to screen the accelerating electric field only for high PC surface temperatures and magnetic fields. We argue that such screening at ICS pair fronts occurs locally, slowing but not turning off acceleration of particles until screening can occur at a curvature radiation (CR) pair front at higher altitude. In the case where no screening occurs above the PC surface, we anticipate that the pulsar γ-ray luminosity will be a substantial fraction of its spin-down luminosity. The X-ray luminosity resulting from PC heating by ICS pair fronts is significantly lower than the PC heating luminosity from CR pair fronts, which dominates for most pulsars. PC heating from ICS pair fronts is highest in millisecond pulsars, which cannot produce CR pairs, and may account for observed thermal X-ray components in the spectra of these old pulsars.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/239794ee4e334bccfad1d574ffa576b07b5c697b

How researchers see this paper

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In Astronomy and Astrophysics

1. A. Harding
2. J. Lattimer
3. J. Arons
4. Bing Zhang
5. Michael Kramer
6. E. Orlando
7. A. Strong
8. Simon Johnston

In Nuclear and High Energy Physics

1. A. Strong
2. E. Orlando
3. I. Grenier
4. J. Arons
5. A. Schwenk
6. K. Hebeler
7. A. Harding
8. Igor V. Moskalenko

Citations in the corpus

• A NICER View of PSR J0030+0451: Implications for the Dense Matter Equation of State (2019, background): “The magnetic polar caps of MSPs, thought to be heated by (return) currents in the pulsar magnetosphere, produce thermal emission in the soft X-ray band (Harding & Muslimov 2002).”
• THE FIRST FERMI LARGE AREA TELESCOPE CATALOG OF GAMMA-RAY PULSARS (2009, background): “However, as argued by Arons (2006) (see also Harding & Muslimov 2002), it is natural in many models for the gamma-ray emitting gap to maintain a fixed voltage drop.”
• Corona of Magnetars (2006, background): “Pair creation in the polar cap regions of a radio pulsar is thought to trigger a stochastic return current (Harding & Muslimov 2002).”
• Pulsar Wind Nebulae as Cosmic Pevatrons: A Current Sheet’s Tale (2012, background): “This has consequences for radio polarization structure, and for polar cap areas and dipole offsets inferred from soft X-ray emission from polar caps (Bogdanov et al. 2007), thought to be heated by magnetospheric particle bombardment (Arons 1981b; Zavlin and Pavlov 1998; Harding and Muslimov 2002).”
• Physics of strongly magnetized neutron stars (2006, background): “However, the ICS-initiated cascades have much lower multiplicity, since the emission rate decreases as the particles’ energy increases (in constrast to the CR emission rate which increases as with energy) and are not robust enough to screen the E‖ (Harding and Muslimov 2002).”
• Time-dependent pair cascades in magnetospheres of neutron stars - I. Dynamics of the polar cap cascade with no particle supply from the neutron star surface (2010, background): “…previously proposed models for polar cap cascades (and almost all quantitative models) assumed stationary unidirectional outflow of a charge separated particle beam (e.g. Arons & Scharlemann 1979; Daugherty & Harding 1982; Muslimov & Tsygan 1992; Harding & Muslimov 2002; Hibschman & Arons 2001a).”
• On the Polar Caps of the Three Musketeers (2004, background): “The former two cases are in broad agreement with the theoretical expectations of Harding & Muslimov (2002) for polar cap heating due to downstreaming of e + / generated by curvature radiation photons.”
• Extended Acceleration in Slot Gaps and Pulsar High-Energy Emission (2003, background): “In the last few years, a self-consistent model of PC acceleration has been developed, which includes effects of general relativity (Harding & Muslimov 1998, hereafter HM98) and screening by pairs (Harding & Muslimov 2001, hereafter HM01; Harding & Muslimov 2002, hereafter HM02).”