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 γ -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 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 broadband 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 ${\alpha }_{X}=-{0.57}_{-0.25}^{+0.26}$ ( F _ν ∝ ν ^α ) in the energy band 3–10 keV. From the NIR–optical data we obtain a PL slope α _O = −0.24 ± 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 γ -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 nonuniformity of the bulk surface temperature. The NIR data also enable us to measure the proper motion accurately, with values μ _α = 47.5 ± 0.7 mas yr ^−1 and μ _δ = −8.7 ± 0.7 mas yr ^−1 .

Keywords

• Pulsars
• Neutron stars