C. Blanchard

Context. Optical pulsations from millisecond pulsars (MSPs) have recently been detected in a transitional MSP and an accreting MSP. Evidence for optical pulsations has also been found for a rotation-powered redback MSP. Observations suggest that optical pulsed emission is produced by different mechanisms depending on whether an accretion disk is present in the system. Aims. We explored a sample of rotation-powered MSPs in close binaries (P _orb < 1 day; redbacks and black widows), searching for optical periodic signals with the SiFAP2 photometer mounted on the Telescopio Nazionale Galileo (TNG). Methods. We performed pulsation searches using the epoch-folding method with the most up-to-date (radio or gamma-ray) orbital solution for each system. These solutions were based either on previously published works or recent observations from Nançay, the Giant Metrewave Radio Telescope, the Parkes Observatory, and Fermi -LAT. Results. We update or confirm radio and gamma-ray ephemerides for five of the presented systems. No optical pulsations were detected with a significance exceeding a 3 σ confidence level in any of our searches, despite achieving sensitivities close to the instrument’s limit. This places correspondingly stringent upper limits on the systems’ optical pulsed magnitude and conversion efficiency. Our upper limits are consistent with the pulsed optical luminosity of optical pulsations from the redback PSR J2339-0533. Compared to accreting and transitional MSPs, redback and black widow systems show much lower efficiency in converting their spin-down power into pulsed optical emission. This supports the recent suggestion that the accretion disk around the neutron star plays a role in accelerating the particles responsible for producing bright optical pulsed emission.

Context. Spider binary pulsars are systems in which a millisecond pulsar (MSP) tightly orbits (P_b ≲ 1 day) a low mass (m_c ≲ 0.5 M_⊙) non-degenerate or semi-degenerate star. Spider systems often display eclipses around superior conjunction, and their orbital periods often exhibit rapid time variations. The eclipse phenomenon is currently poorly understood. However, eclipses are excellent probes of plasma physics and intrabinary shocks, and they can also be used to study MSP formation processes. Aims. In this work, we present Nançay Radio Telescope (NRT) observations of a sample of 19 spider pulsars conducted over several years. The sample includes 11 eclipsing and eight non-eclipsing systems. We aim to provide a homogeneous phenomenological study of the eclipses in order to compare spiders and study their group properties, as those eclipsing systems are often studied individually. We compare our results with those derived from other studies, mainly optical observations and analyses of the pulsar companions. Methods. We analysed eclipses via pulsar timing by using a 2D template-matching technique that allowed us to simultaneously determine radio pulse times of arrival (TOAs) and dispersion measures (DMs) along the lines of sight to the pulsars. The eclipses were then fit with a phenomenological model that gives a measurement of the duration and asymmetry of the eclipses. We then compared these parameters to other eclipse and system measurements in order to discuss the potential link between the presence of eclipses and orbital inclination, as eclipsing systems are known to have higher mass functions than non-eclipsing ones. Finally, we formed polarisation-calibrated profiles for the pulsars in our sample and derived some of their main polarisation properties. Results. We present a comprehensive review of the NRT NUPPI backend spider pulsar dataset. We also present the first review and systematic analysis of a large sample of eclipsers monitored with the NRT over several years. The phenomenological fit allowed us to derive a number of parameters to compare the eclipsers with each other, which led to the categorisation of eclipsers depending on the shape of their eclipses. We present the polarimetric properties of the 19 spiders in the sample alongside their profiles, which were previously unpublished in some cases. We compared the mass function distributions of the eclipsing and non-eclipsing systems in our sample and found (in agreement with previous studies) that eclipsing systems have higher mass functions than their non-eclipsing counterparts, suggesting that the latter have lower orbital inclinations. For the eclipsing systems, we found evidence of a positive correlation between eclipse duration and mass function, as expected if more eclipsing material crosses the line of sight in higher inclination systems. For the entire sample, we found marginal evidence for increasing pulse profile width with decreasing mass function, possibly indicating that the low mass function spiders are indeed those seen under low inclinations. Finally, we conducted a comprehensive literature review of the published inclination measurements for the pulsars in the sample and compared the inclinations to eclipse parameters, (unexpectedly) finding no clear correlations between orbital inclination and eclipse properties. Nevertheless, the small number of available orbital inclination constraints, which contradict each other in some cases, hinders such searches for correlations.