XMM-Newton observations of PSR J0726-2612, a radio-loud XDINS

Abstract

We present the results of an XMM-Newton observation of the slowly rotating ($P=3.4$ s), highly magnetized ($B\approx 3\times 10^{13}$ G) radio pulsar PSR J0726-2612. A previous X-ray observation with the Chandra satellite showed that some of the properties of PSR J0726-2612 are similar to those of the X-ray Dim Isolated Neutron Stars (XDINSs), a small class of nearby slow pulsars characterized by purely thermal X-ray spectra and undetected in the radio band. We confirm the thermal nature of the X-ray emission of PSR J0726-2612, which can be fit by the sum of two blackbodies with temperatures $k{T}_1=0.074_{-0.011}^{+0.006}$ keV and $k{T}_2=0.14_{-0.02}^{+0.04}$ keV and emitting radii $R_1=10.4_{-2.8}^{+10.8}$ km and $R_2=0.5_{-0.3}^{+0.9}$ km, respectively (assuming a distance of 1 kpc). A broad absorption line modeled with a Gaussian profile centred at $0.39_{-0.03}^{+0.02}$ keV is required in the fit. The pulse profile of PSR J0726-2612 is characterized by two peaks with similar intensity separated by two unequal minima, a shape and pulsed fraction that cannot be reproduced without invoking magnetic beaming of the X-ray emission. The presence of a single radio pulse suggests that in PSR J0726-2612 the angles that the dipole axis and the line of sight make with the rotation axis, $\xi$ and $\chi$ respectively, are similar. This geometry differs from that of the two radio-silent XDINSs with a double peaked pulse profile similar to that of PSR J0726-2612, for which $\xi \sim 90^{\circ }$ and $\chi \sim 45^{\circ }$ have been recently estimated. These results strengthen the similarity between PSR J0726-2612 and the XDINSs and support the possibility that the lack of radio emission from the latter might simply be due to an unfavourable viewing geometry.

Accepted for publication in A&A, 10 pages, 10 figures

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