Spectroscopy and Timing of the Middle-aged Pulsar B1055-52

M.A. Teter(Montana State Univ.), D. Sanwal, G.G. Pavlov (Penn State), V.E. Zavlin (MPE, Garching), S. Tsuruta (Montana State Univ.), R.N. Manchester (ATNF)

Abstract

The middle-aged radio, X-ray and gamma-ray pulsar B1055-52 (P = 197 ms, $\tau = P/2 \dot{P} = 5 \times 10^{5}$ yr) was observed with Chandra using the ACIS Continuous Clocking (CC) mode. This observation, combined with the archival ROSAT data, allows us to decompose the spectrum into 3 components -- a soft thermal component with $kT_s \simeq 72$ eV and $R_s \simeq 13$ km, a hard thermal component with $kT_h \simeq 144$ eV and $R_h \simeq 780$ m, and a power-law component with a photon index $\Gamma \simeq 1.53$(the radii are given for a distance of 1 kpc). The soft and hard thermal components can be interpreted as radiation from the whole neutron star surface and the polar caps, respectively, and the power-law component as non-thermal emission from the pulsar magnetosphere. Extension of the magnetospheric component to lower and higher energies matches the $\gamma$-ray and optical spectra.

After correcting for instrumental effects, the absolute timing for the ACIS/CC mode is accurate to about 3 milliseconds. We find that the peak of the energy-resolved X-ray pulse profiles from 0.5 keV to 2 keV matches the phase of the main radio peak within the timing uncertainties. Below 0.4 keV, the phase of the X-ray peak gradually shifts so that for energy range 0.2 - 0.3 keV, it lags behind the radio peak by about 0.25 in phase, similar to that observed in the ROSAT data. Above 2.0 keV, the peak of the pulse profile leads the radio peak by about 0.1 in phase. There is some evidence for a second peak in the pulse profile for energies above 2.0 keV.

The energy-resolved light curves show variations in the shape and pulsed fraction with energy. The phase-resolved spectral analysis is presented as the phase dependence of various spectral parameters. We will discuss interpretations of the data in terms of neutron star models.

CATEGORY: SUPERNOVAE, SUPERNOVA REMNANTS AND ISOLATED NEUTRON STARS