Volume 615, July 2018
|Number of page(s)||10|
|Section||Stellar structure and evolution|
|Published online||17 July 2018|
A new X-ray look into four old pulsars
Istituto di Astrofisica Spaziale e Fisica Cosmica Milano,
via E. Bassini 15,
2 Dipartimento di Fisica G. Occhialini, Università degli Studi di Milano Bicocca, Piazza della Scienza 3, 20126 Milano, Italy
Accepted: 26 February 2018
We report on the X-ray properties of four rotation-powered pulsars with characteristic ages in the range 0.3–5 Myr, derived from the analysis of XMM–Newton archival observations. We found convincing evidence of thermal emission only in the phase-averaged spectrum of PSR B0114+58, which is well fitted by a blackbody with temperature kT = 0.17 ± 0.02 keV and emitting radius R = 405+110−90 m, consistent with the size of its polar cap. The three other considered pulsars, PSR B0628−28, PSR B0919+06, and PSR B1133+16, have phase-averaged spectra that can be described well by single power laws with photon index Γ ~ 3. The 3σ upper limits on the bolometric luminosity of a possible thermal component with temperatures in the range ~0.05−2 keV are Lbol ≲ 3.2 × 1028 erg s−1 and Lbol ≲ 2.4 × 1029 erg s−1, for PSR B0628−28 and PSR B0919+06, respectively. On the other hand, we found possible evidence that the pulsed emission of PSR B0628−28 is thermal. Two absorption lines at ~0.22 keV and ~0.44 keV are detected in the spectrum of PSR B1133+16. They are best interpreted as proton cyclotron features, implying the presence of multipolar components with a field of a few 1013 G at the neutron star polar caps. We discuss our results in the context of high-energy emission models of old rotation-powered pulsars.
Key words: pulsars: general / stars: neutron / pulsars: individual: PSR B0628−28 / pulsars: individual: PSR B0919+06 / pulsars: individual: PSR B0114+58 / pulsars: individual: PSR B1133+16
© ESO 2018
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