Joseph Lazio

The International Pulsar Timing Array project: using pulsars as a gravitational wave detector

The International Pulsar Timing Array project combines observations of pulsars from both northern and southern hemisphere observatories with the main aim of detecting ultra-low frequency (similar to 10(-9)-10(-8) Hz) gravitational waves. Here we introduce the project, review the methods used to search for gravitational waves emitted from coalescing supermassive binary black-hole systems in the centres of merging galaxies and discuss the status of the project.

An Eccentric Binary Millisecond Pulsar in the Galactic Plane

Binary pulsar systems are superb probes of stellar and binary evolution and the physics of extreme environments. In a survey with the Arecibo telescope, we have found PSR J1903+0327, a radio pulsar with a rotational period of 2.15 milliseconds in a highly eccentric (e = 0.44) 95-day orbit around a solar mass (\batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{M}_{{\odot}}\) \end{document}) companion. Infrared observations identify a possible main-sequence companion star. Conventional binary stellar evolution models predict neither large orbital eccentricities nor main-sequence companions around millisecond pulsars. Alternative formation scenarios involve recycling a neutron star in a globular cluster, then ejecting it into the Galactic disk, or membership in a hierarchical triple system. A relativistic analysis of timing observations of the pulsar finds its mass to be 1.74 ± 0.04 \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{M}_{{\odot}}\) \end{document}, an unusually high value.

The lunar radio array (LRA)

The Lunar Radio Array (LRA) is a concept for a telescope sited on the farside of the Moon with a prime mission of making precision cosmological measurements via observations of neutral hydrogen.

Millimeter wave interferometric radiometry for passive imaging and the detection of low-power manmade signals

Millimeter wave detection and imaging is becoming increasingly important with the proliferation of hostile, mobile millimeter wave threats from both weapons systems and communication links. Improved force protection, surveillance, and targeting will rely increasingly on the interception, detection, geo-sorting, and the identification of sources, such as point-to point communication systems, missile seekers, precision guided munitions, and fire control radar systems. This paper describes the Naval Research Laboratorys (NRL) demonstration broadband passive millimeter wave (mmW) interferometric imaging system. In addition to limited active signal detection, the Ka-band system will provide the potential for detecting the passive signature of non-transmitting hostile systems along with a capability for meter-precision geolocation for imaged objects. The interferometer uses a distributed array of 12 antenna elements to synthesize a large aperture. Each antenna is packaged into an individual receiver, from which a baseband signal is recorded. The correlator is software-based, utilizing signal processing techniques for visibilities, and image formation via beamforming methods.

Gravitational-wave detection via radio-pulsar timing

The observation of gravitational waves will offer astronomers a new view of the cosmos. One promising approach for detecting those spacetime perturbations relies on the precise timing of signals from radio pulsars.

The Square Kilometer Array

The Square Kilometer Array is intended to be the centimeter‐ and meter‐wavelength telescope for the 21st century. Originally proposed as the “hydrogen telescope,” the 21‐cm hyperfine transition of neutral hydrogen continues to play a significant role in the Key Science Projects envisioned for the SKA. The 21‐cm emission from galaxies will be used both as a means of tracking galaxy evolution over a significant era in the Universes history as well as a tracer of mass for cosmological studies. The 21‐cm emission and absorption from the intergalactic medium itself at the time of the Epoch of Reionization will be traced to follow the evolution of this crucial phase of the Universes history. A number of telescopes both those currently in operation and under construction, and notably including Arecibo, will provide crucial pathfinding developments, technically, algorithmically, and scientifically.

DIVISION B COMMISSION 40: RADIO ASTRONOMY

IAU Commission 40 for Radio Astronomy (hereafter C40) brought together scientists and engineers who carry out observational and theoretical research in radio astronomy and who develop and operate the ground and space-based radio astronomy facilities and instrumentation. As of June 2015, the Commission had approximately 1,100 members from 49 countries, corresponding to nearly 10 per cent of the total IAU membership.

The Deep Space Network at 50

From rovers on the surface of Mars to Voyager 1 near the edge of the solar system, spacecraft regularly call home to Earth. For five decades, the Deep Space Network has been at the other end of the line.

A Bursting Radio Transient in the Direction of the Galactic Center

The radio sky is poorly sampled for rapidly varying transients because of the narrow field-of-view of most imaging radio telescopes at cm and shorter wavelengths. The emergence of sensitive long wavelength observations with intrinsically larger fields-of-view are changing this situation, as partly illustrated by our ongoing meter-wavelength monitoring observations and archival studies of the Galactic Center. In this search, we discovered a transient, bursting, radio source in the direction of the Galactic Center, GCRT J1745−3009, with extremely unusual properties. Its flux and rapid variability imply a brightness temperature > 1012 K if it is at a distance > 70 pc, implying that it is a coherent emitter. I will discuss the discovery of the source and the subsequent re-detections, as well as searches for counterparts at other wavelengths, and several proposed models.

Radio pulsars and transients in the Galactic center

Radio pulsars and transients provide powerful probes of the star formation history, interstellar medium, and gravitational potential of the Galactic center. Historical radio observations of the Galactic center have not emphasized the time domain aspect of observing this region. We summarize a series of recent searches for and observations of radio transients and pulsars that make use of two advances in technology. The first is the formation of large fields of view ( 1°) at relatively longer wavelengths (λ > 1 m), and the second is the construction of receivers and instruments capable of collecting data on microsecond time scales at relatively short wavelengths (≈ 3 cm).