1997/08/12 by V. E. Zavlin, Zavlin, V. E., George G. Pavlov +1 · 1 citation
Earth and Planetary Sciences · Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics (astro-ph) #FOS: Physical sciences #High-pressure geophysics and materials #Pulsars and Gravitational Waves Research
paper · pdf · doi:10.48550/arxiv.astro-ph/9708101
openalex publication_date 1997/08/12 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We show that the soft X-ray spectra and light curves observed with the ROSAT and EUVE from the closest known millisecond pulsar J0437--4715 can be interpreted as thermal radiation from two hot polar caps whose emitting layers (atmospheres) are comprised of hydrogen. The simplest model yields a uniform temperature of (0.8-0.9)× 106 K within a cap radius of 0.7-0.9 km. The spectral fits indicate that the temperature may be nonuniformly distributed along the cap surface. The distribution can be approximated by a central core heated up to (1-2)× 106 K within a radius of 0.2-0.4 km, surrounded by a colder rim with temperatures (3-5)× 105 K extending out to 2-6 km. The polar cap interpretation implies low column densities, (1-3)× 1019 cm-2, and a high degree of ionization, > 20%, of the interstellar hydrogen towards the pulsar. The inferred bolometric luminosity of the polar caps, (1.0-1.6)× 1030 erg s-1, is in excellent agreement with the predictions of the slot-gap model of radio pulsars developed by Arons and his coworkers. Similar polar cap radiation should be emitted by other millisecond pulsars, although in some of them (e.~g., PSR B1821--24) the soft X-ray flux is dominated by the nonthermal radiation from pulsar magnetospheres.