The High Time Resolution Universe Pulsar Survey - VII. Discovery of five millisecond pulsars and the different luminosity properties of binary and isolated recycled pulsars

This paper presents the discovery and timing parameters for five millisecond pulsars (MSPs), four in binary systems with probable white dwarf companions and one isolated, found in ongoing processing of the High Time Resolution Universe Pulsar (HTRU) survey. We also present high-quality polarimetric data on four of them. These further discoveries confirm the high potential of our survey in finding pulsars with very short spin periods. At least two of these five MSPs are excellent candidates to be included in the pulsar timing array projects. Thanks to the wealth of MSP discoveries in the HTRU survey, we revisit the question of whether the luminosity distributions of isolated and binary MSPs are different. Using the Cordes and Lazio distance model and our new and catalogue flux density measurements, we find that 41 of the 42 most luminous MSPs in the Galactic disc are in binaries, and a statistical analysis suggests that the luminosity functions differ with 99.9 per cent significance. We conclude that the formation process that leads to solitary MSPs affects their luminosities, despite their period and period derivatives being similar to those of pulsars in binary systems.