Timing Measurements of the Relativistic Binary Pulsar PSR B1913+16

We present results of more than three decades of timing measurements of the first known binary pulsar, PSR B1913+16. Like most other pulsars, its rotational behavior over such long time scales is significantly affected by small-scale irregularities not explicitly accounted for in a deterministic model. Nevertheless, the physically important astrometric, spin, and orbital parameters are well determined and well decoupled from the timing noise. We have determined a significant result for proper motion, $\mu_{\alpha} = -1.43\pm0.13$, $\mu_{\delta}=-0.70\pm0.13$ mas yr$^{-1}$. The pulsar exhibited a small timing glitch in May 2003, with ${\Delta f}/f=3.7\times10^{-11}$, and a smaller timing peculiarity in mid-1992. A relativistic solution for orbital parameters yields improved mass estimates for the pulsar and its companion, m_1=1.4398\pm0.0002 \ M_{\sun} and m_2=1.3886\pm0.0002 \ M_{\sun}. The system's orbital period has been decreasing at a rate $0.997\pm0.002$ times that predicted as a result of gravitational radiation damping in general relativity. As we have shown before, this result provides conclusive evidence for the existence of gravitational radiation as predicted by Einstein's theory.Comment: Published in APJ, 722, 1030 (2010

Two High-Sensitivity Pulsar Searches

We have undertaken a program of two searches at radio wavelengths for pulsars using the Arecibo Observatory. One search covered 70 square degrees of sky along the Galactic plane with sensitivity to pulsars with periods as short as 1 ms. The second search covered 170 square degrees between Galactic latitudes -50° and -30° with sensitivity to pulsars with periods of 0.5 ms or more. The sensitivity to long-period pulsars in both surveys was of order 1 mJy, with reduced sensitivity at the shortest periods. Twenty-five pulsars were detected between the two surveys. Ten of these had previously been discovered. Of the remaining fifteen new pulsars, thirteen are relatively young, slow pulsars, with periods between 0.212 s and 5.094 s. The latter period is the longest of any known radio pulsar; this pulsar also has an extraordinarily short duty cycle of 0.4%. Two millisecond pulsars were found. PSR J2019+2425 has a period of 3.934 ms and is at a distance of 1 kpc. It is in a 76.5-day binary orbit with a 0.3 M companion. Its orbital eccentricity is 1.1 x 10^-4. The spin-down rate of this pulsar is extremely small, and its evolutionary timescale of 9 x 10^9 yr is the longest of any known pulsar. Both the low eccentricity and the long evolutionary timescale put limits on violations of the strong equivalence principle which are competitive with the best previous limits. The second newly found millisecond pulsar, PSR J2322+2057, has a period of 4.808 ms and a distance of 0.8 kpc. It is the second isolated millisecond pulsar found outside of globular clusters. Its distance of nearly 0.5 kpc from the Galactic plane suggests that millisecond pulsars have a large scale height

Radio Pulses along the Galactic Plane

We have surveyed 68 deg^2 along the Galactic Plane for single, dispersed radio pulses. Each of 3027 independent pointings was observed for 68 s using the Arecibo telescope at 430 MHz. Spectra were collected at intervals of 0.5 ms and examined for pulses with duration 0.5 to 8 ms. Such single pulse analysis is the most sensitive method of detecting highly scattered or highly dispersed signals from pulsars with large pulse-to-pulse intensity variations. A total of 36 individual pulses from five previously known pulsars were detected, along with a single pulse not associated with a previously known source. Follow-up observations discovered a pulsar, PSR J1918+08, from which the pulse originated. This pulsar has period 2.130 s and dispersion measure 30 pc cm^-3, and has been seen to emit single pulses with strength up to 8 times the average.Comment: 14 pages, 5 figures, AASTeX, accepted by the Astrophysical Journa

On the Mass and Inclination of the PSR J2019+2425 Binary System

We report on nine years of timing observations of PSR J2019+2425, a millisecond pulsar in a wide 76.5 day orbit with a white dwarf. We measure a significant change over time of the projected semi-major axis of the orbit, x-dot/x=(1.3+-0.2)x10^-15 s^-1, where x=(a sin i)/c. We attribute this to the proper motion of the binary. This constrains the inclination angle to i<72 degrees, with a median likelihood value of 63 degrees. A similar limit on inclination angle arises from the lack of a detectable Shapiro delay signal. These limits on inclination angle, combined with a model of the evolution of the system, imply that the neutron star mass is at most 1.51 solar masses; the median likelihood value is 1.33 solar masses. In addition to these timing results, we present a polarization profile of this source. Fits of the linear polarization position angle to the rotating vector model indicate the magnetic axis is close to alignment with the rotation axis, alpha<30 degrees.Comment: Accepted by Ap