Astrophage of neutron stars from supersymmetric dark matter Q-balls

The gauge-mediated model of supersymmetry breaking implies that stable non-topological solitons, Q-balls, could form in the early universe and comprise the dark matter. It is shown that the inclusion of the effects from gravity-mediation set an upper limit on the size of Q-balls. When in a dense baryonic environment Q-balls grow until reaching this limiting size at which point they fragment into two equal-sized Q-balls. This Q-splitting process will rapidly destroy a neutron star that absorbs even one Q-ball. The new limits on Q-ball dark matter require an ultralight gravitino m_3/2 < keV, naturally avoiding the gravitino overclosure problem, and providing the MSSM with a dark matter candidate where gravitino dark matter is not viable.Comment: 4 pages, 1 figure, Published in Phys. Rev. D. Rapid Communication

A Search for Sub-millisecond Pulsations in Unidentified FIRST and NVSS Radio Sources

We have searched 92 unidentified sources from the FIRST and NVSS 1400 MHz radio survey catalogs for radio pulsations at 610 MHz. The selected radio sources are bright, have no identification with extragalactic objects, are point-like and are more than 5% linearly polarized. Our search was sensitive to sub-millisecond pulsations from pulsars with dispersion measures (DMs) less than 500 pc cm-3 in the absence of scattering. We have detected no pulsations from these sources and consider possible effects which might prevent detection. We conclude that as a population, these sources are unlikely to be pulsars.Comment: 8 pages, including 2 tables and 1 figure. Accepted for publication in A

Heartbeat of the Mouse: a young radio pulsar associated with the axisymmetric nebula G359.23-0.82

We report the discovery of PSR J1747-2958, a radio pulsar with period P = 98 ms and dispersion measure DM = 101 pc/cc, in a deep observation with the Parkes telescope of the axially-symmetric "Mouse" radio nebula (G359.23-0.82). Timing measurements of the newly discovered pulsar reveal a characteristic age Pdt/2dP = 25 kyr and spin-down luminosity dE/dt = 2.5e36 erg/s. The pulsar (timing) position is consistent with that of the Mouse's "head". The distance derived from the DM, ~2 kpc, is consistent with the Mouse's distance limit from HI absorption, < 5.5 kpc. Also, the X-ray energetics of the Mouse are compatible with being powered by the pulsar. Therefore we argue that PSR J1747-2958, moving at supersonic speed through the local interstellar medium, powers this unusual non-thermal nebula. The pulsar is a weak radio source, with period-averaged flux density at 1374 MHz of 0.25 mJy and luminosity ~1 mJy kpc^2.Comment: 6 pages, 2 figures, accepted for publication in ApJ Letter

Arecibo timing and single-pulse observations of 17 pulsars

We report on timing and single-pulse observations of 17 pulsars discovered at the Arecibo observatory. The highlights of our sample are the recycled pulsars J1829+2456, J1944+0907 and the drifting subpulses observed in PSR J0815+0939. For the double neutron star binary J1829+2456, in addition to improving upon our existing measurement of relativistic periastron advance, we have now measured the pulsar's spin period derivative. This new result sets an upper limit on the transverse speed of 120 km/s and a lower limit on the characteristic age of 12.4 Gyr. From our measurement of proper motion of the isolated 5.2-ms pulsar J1944+0907, we infer a transverse speed of 188 +/- 65 km/s. This is higher than that of any other isolated millisecond pulsar. An estimate of the speed, using interstellar scintillation, of 235 +/- 45 km/s indicates that the scattering medium along the line of sight is non-uniform. We discuss the drifting subpulses detected from three pulsars in the sample, in particular the remarkable drifting subpulse properties of the 645-ms pulsar J0815+0939. Drifting is observed in all four components of the pulse profile, with the sense of drift varying among the different components. This unusual `bi-drifting'' behaviour challenges standard explanations of the drifting subpulse phenomenon.Comment: 9 pages, 6 figures. Accepted for publication in MNRA

PSR J1829+2456: a relativistic binary pulsar

We report the discovery of a new binary pulsar, PSR J1829+2456, found during a mid-latitude drift-scan survey with the Arecibo telescope. Our initial timing observations show the 41-ms pulsar to be in a 28-hr, slightly eccentric, binary orbit. The advance of periastron, omegadot = 0.28 +/- 0.01 deg/yr is derived from our timing observations spanning 200 days. Assuming that the advance of periastron is purely relativistic and a reasonable range of neutron star masses for PSR J1829+2456 we constrain the companion mass to be between 1.22 Msun and 1.38 Msun, making it likely to be another neutron star. We also place a firm upper limit on the pulsar mass of 1.38 Msun. The expected coalescence time due to gravitational-wave emission is long (~60 Gyr) and this system will not significantly impact upon calculations of merger rates that are relevant to upcoming instruments such as LIGO.Comment: Accepted MNRAS, 5 pages, 3 figure

Propagation of gravitational waves in multimetric gravity

We discuss the propagation of gravitational waves in a recently discussed class of theories containing N >= 2 metric tensors and a corresponding number of standard model copies. Using the formalism of gauge-invariant linear perturbation theory we show that all gravitational waves propagate at the speed of light. We then employ the Newman-Penrose formalism to show that two to six polarizations of gravitational waves may exist, depending on the parameters entering the equations of motion. This corresponds to E(2) representations N_2, N_3, III_5 and II_6. We finally apply our general discussion to a recently presented concrete multimetric gravity model and show that it is of class N_2, i.e., it allows only two tensor polarizations, as it is the case for general relativity. Our results provide the theoretical background for tests of multimetric gravity theories using the upcoming gravitational wave experiments.Comment: 21 pages, no figures, journal versio

Discovery of Five New Pulsars in Archival Data

Reprocessing of the Parkes Multibeam Pulsar Survey has resulted in the discovery of five previously unknown pulsars and several as-yet-unconfirmed candidates. PSR J0922-52 has a period of 9.68 ms and a DM of 122.4 pc cm^-3. PSR J1147-66 has a period of 3.72 ms and a DM of 133.8 pc cm^-3. PSR J1227-6208 has a period of 34.53 ms, a DM of 362.6 pc cm^-3, is in a 6.7 day binary orbit, and was independently detected in an ongoing high-resolution Parkes survey by Thornton et al. and also in independent processing by Einstein@Home volunteers. PSR J1546-59 has a period of 7.80 ms and a DM of 168.3 pc cm^-3. PSR J1725-3853 is an isolated 4.79-ms pulsar with a DM of 158.2 pc cm^-3. These pulsars were likely missed in earlier processing efforts due to their high DMs and short periods and the large number of candidates that needed to be looked through. These discoveries suggest that further pulsars are awaiting discovery in the multibeam survey data.Comment: 12 pages, 2 figures, 2 tables, accepted to Ap

Lutz-Kelker bias in pulsar parallax measurements

Lutz & Kelker showed that parallax measurements are systematically overestimated because they do not properly account for the larger volume of space that is sampled at smaller parallax values. We apply their analysis to neutron stars, incorporating the bias introduced by the intrinsic radio luminosity function and a realistic Galactic population model for neutron stars. We estimate the bias for all published neutron star parallax measurements and find that measurements with less than ~95% certainty, are likely to be significantly biased. Through inspection of historic parallax measurements, we confirm the described effects in optical and radio measurements, as well as in distance estimates based on interstellar dispersion measures. The potential impact on future tests of relativistic gravity through pulsar timing and on X-ray--based estimates of neutron star radii is briefly discussed.Comment: 9 pages, 3 tables, 1 figure. Accepted for publication in MNRA

Timing of pulsars found in a deep Parkes multibeam survey

We have carried out a sensitive radio pulsar survey along the northern Galactic plane ($50^{\circ} < l < 60^{\circ}$ and |b| \lapp 2^{\circ}) using the Parkes 20-cm multibeam system. We observed each position for 70-min on two separate epochs. Our analyses to date have so far resulted in the detection of 32 pulsars, of which 17 were previously unknown. Here we summarize the observations and analysis and present the timing observations of 11 pulsars and discovery parameters for a further 6 pulsars. We also present a timing solution for the 166-ms bursting pulsar, PSR~J1938+2213, previously discovered during an Arecibo drift-scan survey. Our survey data for this pulsar show that the emission can be described by a steady pulse component with bursting emission, which lasts for typically 20--25 pulse periods, superposed. Other new discoveries are the young 80.1-ms pulsar PSR~J1935+2025 which exhibits a significant amount of unmodeled low-frequency noise in its timing residuals, and the 4.2-ms pulsar PSR~J1935+1726 which is in a low-mass binary system with a 90.7-day circular orbit.Comment: 6 pages, 2 figures, accepted for publication in MNRA