Discovery and timing of the first 8gr8 Cygnus survey pulsars

Since 2004 we have been carrying out a pulsar survey of the Cygnus region with the Westerbork Synthesis Radio Telescope (WSRT) at a frequency of 328 MHz. The survey pioneered a novel interferometric observing mode, termed 8gr8 (eight-grate), whereby multiple simultaneous digital beams provide high sensitivity over a large field of view. Since the Cygnus region is known to contain OB associations, it is likely that pulsars are formed here. Simulations have shown that this survey could detect 70 pulsars, which would increase our understanding of the radio pulsar population in this region. We also aim to expand the known population of intermittent and rotating radio transient (RRAT)-like pulsars. In this paper we describe our methods of observation, processing and data analysis, and we present the first results. Our observing method exploits the way a regularly spaced, linear array of telescopes yields a corresponding regularly spaced series of so-called ``grating beams on the sky. By simultaneously forming a modest number (eight) of offset digital beams, we can utilize the entire field of view of each WSRT dish, but retain the coherently summed sensitivity of the entire array. For the processing we performed a large number of trial combinations of period and dispersion measure (DM) using a computer cluster. In the first processing cycle of the WSRT 8gr8 Cygnus Survey, we have discovered three radio pulsars, with spin periods of 1.657, 1.099 and 0.445 seconds. These pulsars have been observed on a regular basis since their discovery, both in a special follow-up programme as well as in the regular timing programme. The timing solutions are presented in this paper. We also discuss this survey method in the context of the SKA and its pathfinders.

Multi-telescope timing of PSR J1518+4904

PSR J1518+4904 is one of only 9 known double neutron star systems. These systems are highly valuable for measuring the masses of neutron stars, measuring the effects of gravity, and testing gravitational theories. We determine an improved timing solution for a mildly relativistic double neutron star system, combining data from multiple telescopes. We set better constraints on relativistic parameters and the separate masses of the system, and discuss the evolution of PSR J1518+4904 in the context of other double neutron star systems. PSR J1518+4904 has been regularly observed for more than 10 years by the European Pulsar Timing Array (EPTA) network using the Westerbork, Jodrell Bank, Effelsberg and Nancay radio telescopes. The data were analysed using the updated timing software Tempo2. We have improved the timing solution for this double neutron star system. The periastron advance has been refined and a significant detection of proper motion is presented. It is not likely that more post-Keplerian parameters, with which the individual neutron star masses and the inclination angle of the system can be determined separately, can be measured in the near future. Using a combination of the high-quality data sets present in the EPTA collaboration, extended with the original GBT data, we have constrained the masses in the system to m_p<1.17 msun and m_c>1.55 msun (95.4% confidence), and the inclination angle of the orbit to be less than 47 degrees (99%). From this we derive that the pulsar in this system possibly has one of the lowest neutron star masses measured to date. From evolutionary considerations it seems likely that the companion star, despite its high mass, was formed in an electron-capture supernova.

A Strong Upper Limit on the Pulsed Radio Luminosity of the Compact Object 1RXS J141256.0+792204

The ROSAT X-ray source 1RXS J141256.0+792204 has recently been identified as a likely compact object whose properties suggest it could be a very nearby radio millisecond pulsar at d = 80 - 260pc. We investigated this hypothesis by searching for radio pulsations using the Westerbork Synthesis Radio Telescope. We observed 1RXS J141256.0+792204 at 385 and 1380MHz, recording at high time and frequency resolution in order to maintain sensitivity to millisecond pulsations. These data were searched both for dispersed single pulses and using Fourier techniques sensitive to constant and orbitally modulated periodicities. No radio pulsations were detected in these observations, resulting in pulsed radio luminosity limits of L_400 ~ 0.3 (d/250pc)^2 mJy kpc^2 and L_1400 ~ 0.03 (d/250pc)^2 mJy kpc^2 at 400 and 1400MHz respectively. The lack of detectable radio pulsations from 1RXS J141256.0+792204 brings into question its identification as a nearby radio pulsar, though, because the pulsar could be beamed away from us, this hypothesis cannot be strictly ruled out.