K. Stovall

Fast Radio Burst Discovered in the Arecibo Pulsar ALFA Survey

Recent work has exploited pulsar survey data to identify temporally isolated, millisecond-duration radio bursts with large dispersion measures (DMs). These bursts have been interpreted as arising from a population of extragalactic sources, in which case they would provide unprecedented opportunities for probing the intergalactic medium; they may also be linked to new source classes. Until now, however, all so-called fast radio bursts (FRBs) have been detected with the Parkes radio telescope and its 13-beam receiver, casting some concern about the astrophysical nature of these signals. Here we present FRB 121102, the first FRB discovery from a geographic location other than Parkes. FRB 121102 was found in the Galactic anti-center region in the 1.4?GHz Pulsar Arecibo L-band Feed Array (ALFA) survey with the Arecibo Observatory with a DM = 557.4 ? 2.0 pc cm?3, pulse width of 3.0 ? 0.5 ms, and no evidence of interstellar scattering. The observed delay of the signal arrival time with frequency agrees precisely with the expectation of dispersion through an ionized medium. Despite its low Galactic latitude (b = ?0.?2), the burst has three times the maximum Galactic DM expected along this particular line of sight, suggesting an extragalactic origin. A peculiar aspect of the signal is an inverted spectrum; we interpret this as a consequence of being detected in a sidelobe of the ALFA receiver. FRB 121102s brightness, duration, and the inferred event rate are all consistent with the properties of the previously detected Parkes bursts.

A millisecond pulsar in a stellar triple system

Gravitationally bound three-body systems have been studied for hundreds of years and are common in our Galaxy. They show complex orbital interactions, which can constrain the compositions, masses and interior structures of the bodies and test theories of gravity, if sufficiently precise measurements are available. A triple system containing a radio pulsar could provide such measurements, but the only previously known such system, PSR B1620-26 (refs 7, 8; with a millisecond pulsar, a white dwarf, and a planetary-mass object in an orbit of several decades), shows only weak interactions. Here we report precision timing and multiwavelength observations of PSR J0337+1715, a millisecond pulsar in a hierarchical triple system with two other stars. Strong gravitational interactions are apparent and provide the masses of the pulsar (1.4378(13), where is the solar mass and the parentheses contain the uncertainty in the final decimal places) and the two white dwarf companions (0.19751(15) and 0.4101(3)), as well as the inclinations of the orbits (both about 39.2°). The unexpectedly coplanar and nearly circular orbits indicate a complex and exotic evolutionary past that differs from those of known stellar systems. The gravitational field of the outer white dwarf strongly accelerates the inner binary containing the neutron star, and the system will thus provide an ideal laboratory in which to test the strong equivalence principle of general relativity.

The NANOGrav Nine-year Data Set: Limits on the Isotropic Stochastic Gravitational Wave Background

We compute upper limits on the nanohertz-frequency isotropic stochastic gravitational wave background (GWB) using the 9 year data set from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) collaboration. Well-tested Bayesian techniques are used to set upper limits on the dimensionless strain amplitude (at a frequency of 1 yr^(−1) for a GWB from supermassive black hole binaries of A_(gw) < 1.5 x 10^(-15). We also parameterize the GWB spectrum with a broken power-law model by placing priors on the strain amplitude derived from simulations of Sesana and McWilliams et al. Using Bayesian model selection we find that the data favor a broken power law to a pure power law with odds ratios of 2.2 and 22 to one for the Sesana and McWilliams prior models, respectively. Using the broken power-law analysis we construct posterior distributions on environmental factors that drive the binary to the GW-driven regime including the stellar mass density for stellar-scattering, mass accretion rate for circumbinary disk interaction, and orbital eccentricity for eccentric binaries, marking the first time that the shape of the GWB spectrum has been used to make astrophysical inferences. Returning to a power-law model, we place stringent limits on the energy density of relic GWs, Ω_(gw)(f)h^2 < 4.2 x 10^(-10). Our limit on the cosmic string GWB, Ω_(gw)(f)h^2 < 2.2 x 10^(-10), translates to a conservative limit on the cosmic string tension with Gµ < 3.3 x 10^(-8), a factor of four better than the joint Planck and high-l cosmic microwave background data from other experiments.

THE GREEN BANK TELESCOPE 350 MHz DRIFT-SCAN SURVEY. I. SURVEY OBSERVATIONS AND THE DISCOVERY OF 13 PULSARS

Over the summer of 2007, we obtained 1191 hr of “drift-scan” pulsar search observations with the Green Bank Telescope at a radio frequency of 350 MHz. Here we describe the survey setup, search procedure, and the discovery and follow-up timing of 13 pulsars. Among the new discoveries, one (PSR J1623−0841) was discovered only through its single pulses, two (PSRs J1327−0755 and J1737−0814) are millisecond pulsars, and another (PSR J2222−0137) is a mildly recycled pulsar. PSR J1327−0755 is a 2.7 ms pulsar at a dispersion measure (DM) of 27.9 pc cm −3 in an 8.7 day orbit with a minimum companion mass of 0.22 M� . PSR J1737−0814 is a 4.2 ms pulsar at a DM of 55.3 pc cm −3 in a 79.3 day orbit with a minimum companion mass of 0.06 M� . PSR J2222−0137 is a 32.8 ms pulsar at a very low DM of 3.27 pc cm −3 in a 2.4 day orbit with a minimum companion mass of 1.11 M� . It is most likely a white-dwarf–neutron-star system or an unusual low-eccentricity double neutron star system. Ten other pulsars discovered in this survey are reported in the companion paper Lynch et al.

The Green Bank Northern Celestial Cap Pulsar Survey. I. Survey Description, Data Analysis, and Initial Results

We describe an ongoing search for pulsars and dispersed pulses of radio emission, such as those from rotating radio transients (RRATs) and fast radio bursts (FRBs), at 350 MHz using the Green Bank Telescope. With the Green Bank Ultimate Pulsar Processing Instrument, we record 100 MHz of bandwidth divided into 4,096 channels every 81.92

Gravitational Waves from Individual Supermassive Black Hole Binaries in Circular Orbits: Limits from the North American Nanohertz Observatory for Gravitational Waves

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THE GREEN BANK TELESCOPE 350 MHz DRIFT-SCAN SURVEY II: DATA ANALYSIS AND THE TIMING OF 10 NEW PULSARS, INCLUDING A RELATIVISTIC BINARY

. This survey will cover the entire sky visible to the Green Bank Telescope (

Pulsar J0453+1559: A Double Neutron Star System with a Large Mass Asymmetry

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Pulsar discovery by global volunteer computing

, or 82% of the sky) and outside of the Galactic Plane will be sensitive enough to detect slow pulsars and low dispersion measure (

GOALS, STRATEGIES AND FIRST DISCOVERIES OF AO327, THE ARECIBO ALL-SKY 327 MHz DRIFT PULSAR SURVEY

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