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 ≈ 3×10 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 kT 1 = 0.074 +0.006 −0.011 keV and kT 2 = 0.14 +0.04 −0.02 keV and emitting radii R 1 = 10.4 +10.8 −2.8 km and R 2 = 0.5 +0.9 −0.3 km, respectively (assuming a distance of 1 kpc). A broad absorption line modeled with a Gaussian profile centred at 0.39 +0.02 −0.03 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, ξ and χ 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 ξ ∼ 90 • and χ ∼ 45 • 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.

Thermal luminosities of cooling neutron stars

“…PSR J0726−2612. The reported luminosities and temperatures correspond to the best G2BB fit of Rigoselli et al (2019a). The dispersion measure implies d = 2.9 kpc assuming the Galactic electron distribution, but it may be an overestimate, as discussed by Rigoselli et al (2019a).…”

“…The reported luminosities and temperatures correspond to the best G2BB fit of Rigoselli et al (2019a). The dispersion measure implies d = 2.9 kpc assuming the Galactic electron distribution, but it may be an overestimate, as discussed by Rigoselli et al (2019a). Speagle, Kaplan & van Kerkwijk (2011) suggested that PSR J0726−2612 could be associated with the Gould (Ng et al 2012).…”

The SUrvey for Pulsars and Extragalactic Radio Bursts – IV. Discovery and polarimetry of a 12.1-s radio pulsar

“…XINS have never been seen in the radio domain despite extensive attempts, although this could just be caused by a chance misalignment of their hypothetical radio beams with our line of sight (Kondratiev et al 2009). The fact that the radio pulsar PSR J0726−2612 was found to produce thermal emission similar to that of the XINS (Rigoselli et al 2019) supports the misalignment hypothesis. For a complete overview of the INS diversity, one can refer to a review paper such as Kaspi & Kramer (2016).…”

Candidate isolated neutron stars in the 4XMM-DR10 catalog of X-ray sources

“…Strong spectral variability is also visible in the magnetar SGR J0418+5729 (Guillot et al 2015). All the other INSs (black stars) have steady HRs: We found the central compact object 1E 1207.4−5209 (Bignami et al 2003), the high magnetic field pulsar J0726−2612 (Rigoselli et al 2019a), two thermally-emitting pulsars (McGowan et al 2006;Ng et al 2007), the INS candidate of Pires et al (2015) and, as expected, six of the seven known XDINSs (the lack of RX J0420.0−5022 is due to the fact that its spectrum is so soft that its HR 2 had error >0.1). We also found PSR J1400−1431, a binary system composed of a millisecond pulsar and a white dwarf (Swiggum et al 2017).…”