Pulsar J0108-1431 Research Articles

XMM-NEWTONOBSERVATION OF THE VERY OLD PULSAR J0108–1431

We report on an X-ray observation of the 166 Myr old radio pulsar J0108-1431 with XMM-Newton. The X-ray spectrum can be described by a power-law model with a relatively steep photon index Gamma~3 or by a combination of thermal and non-thermal components, e.g., a power-law component with fixed photon index Gamma~2 plus a blackbody component with a temperature of kT=0.11 keV. The two-component model appears more reasonable considering different estimates for the hydrogen column density. The non-thermal X-ray efficiency in the single power-law model is eta^PL (1-10 keV) = L^PL (1-10 keV) / Edot ~ 0.003, higher than in most other X-ray detected pulsars. In the case of the combined model, the non-thermal and thermal X-ray efficiencies are even higher, eta^PL (1-10 keV) ~ eta^bb ~ 0.006. We detected X-ray pulsations at the radio period of P=0.808s with significance of 7sigma. The pulse shape in the folded X-ray lightcurve (0.15-2 keV) is asymmetric, with statistically significant contributions from up to 5 leading harmonics. Pulse profiles at two different energy ranges differ slightly: the profile is asymmetric at low energies, 0.15-1 keV, while at higher energies, 1-2 keV, it has a nearly sinusodial shape. The radio pulse peak leads the 0.15-2 keV X-ray pulse peak by delta phi = 0.06 +/- 0.03.

A possible optical counterpart to the old nearby pulsar J0108-1431

Context. The multi-wavelength study of old (>100 Myr) radio pulsars holds the key to understanding the long-term evolution of neutron stars, including the advanced stages of neutron star cooling and the evolution of the magnetosphere. Optical/UV observations are particularly useful for such studies because they allow one to explore both thermal and non-thermal emission processes. In particular, studying the optical/UV emission constrains the temperature of the bulk of the neutron star surface, too cold to be measured in X-ray observations. Aims. Aim of this work is to identify the optical counterpart of the very old (166 Myr) radio pulsar J0108−1431. Methods. We have re-analyzed our original Very Large Telescope (VLT) observations, where a very faint object was tentatively detected close to the radio position, near the edge of a field galaxy. Results. We found that the backward extrapolation of the PSR J0108−1431 proper motion recently measured by Chandra fits the position of this object. Based on that, we propose it as a viable candidate for the optical counterpart to PSR J0108−1431. The object fluxes (U = 26.4 ± 0.3; B ≈ 27.9; V ≥ 27.8) are consistent with a thermal spectrum with a brightness temperature of ∼9 × 10 4 K (for R = 13 km at a distance of 130 pc), emitted from the bulk of the neutron star surface. Conclusions. New optical observations are required to confirm the optical identification of PSR J0108−1431 and measure its spectrum.

Ultraviolet Emission from the Millisecond Pulsar J0437−4715

We observed PSR J0437-4715 with the FUV-MAMA detector of the Space Telescope Imaging Spectrometer (STIS) to measure the pulsar's spectrum and pulsations. For the first time, UV emission from a millisecond pulsar has been detected. The measured flux, (2.0 ? 0.2) ? 10-15 ergs s-1 cm-2 in the 1150-1700 ? range, corresponds to the luminosity LFUV = (4.7 ? 0.5) ? 1027 ergs s-1, for the distance of 140 pc and negligible interstellar extinction. The shape of the observed spectrum suggests thermal emission from the neutron star surface with a surprisingly high temperature of about 1 ? 105 K, above the upper limit on the surface temperature of the younger ordinary pulsar J0108-1431. For the few-Gigayear-old J0437-4715, such a temperature requires a heating mechanism to operate. The spectrum of J0437-4715 shows marginal evidence of an emission line at 1372 ?, which might be a gravitationally redshifted Zeeman component of the hydrogen Ly? line in a magnetic field of ~7 ? 108 G. No pulsations are detected, with a 3 ? upper limit of 50% on the pulsed fraction.