X-ray and near-infrared observations of the middle-aged pulsar B1055-52, its multiwavelength spectrum, and proper motion

Abstract

Previous observations of the middle-aged ${\hat{I}}^3$-ray, X-ray, and radio pulsar B1055-52 indicated some peculiarities, such as a suspected changing of the X-ray flux and spectral parameters, a large excess of the alleged thermal component of the ultraviolet (UV) spectrum over the Rayleigh-Jeans extension of the X-ray thermal spectrum, and a possible double break in the nonthermal spectral component between the optical and X-ray bands. We observed PSR B1055-52 with the XMM-Newton observatory in X-rays and the Hubble Space Telescope in near-infrared (NIR). The analysis of the XMM-Newton observations does not support the notion of long-term changes in the X-ray flux and broad-band X-ray spectrum of the pulsar. Using an observing mode less affected by background noise than the previous XMM-Newton observations, we constrain the power-law (PL) spectral index as $\hat{I}{\pm }_X=-0.57_{-0.25}^{+0.26}$ ($F_{\hat{I}}½\propto \hat{I}{½}^{\hat{I}}\pm$) in the energy band 3-10 keV. From the NIR-optical data we obtain a PL slope $\hat{I}{\pm }_O=-0.24\pm 0.10$ for the color index $E(B-V)=0.03$ mag. The slopes and fluxes of the NIR-optical and X-ray nonthermal spectra suggest that the NIR through X-ray emission can be described by the same PL and is generated by the same mechanism, unlike the pulsar's ${\hat{I}}^3$-ray emission. The excess of the UV thermal component over the extension of the X-ray thermal component became smaller but did not disappear, indicating a non-uniformity of the bulk surface temperature. The NIR data also enable us to accurately measure the proper motion with values $\hat{I}{¼}_{\hat{I}}\pm =47.5\pm 0.7{\mathrm{mas}\mathrm{yr}}^{-1}$ and $\hat{I}{¼}_{\hat{I}}´=-8.7\pm 0.7{\mathrm{mas}\mathrm{yr}}^{-1}$.

ApJ accepted; 19 pages, 10 Figures, 5 Tables