Showing papers by "Mallory S. E. Roberts published in 2007"
TL;DR: In this article, the authors investigated the mechanism by which supernova ejected stars were ejected from their parent open cluster, NGC 654, and presented the results of a radio pulsar search of these systems, as well as estimates of their predicted X-ray flux assuming that each binary contains a compact object.
Abstract: The production of runaway massive binaries offers key insights into the evolution of close binary stars and open clusters. The stars HD 14633 and HD 15137 are rare examples of such runaway systems, and in this work we investigate the mechanism by which they were ejected from their parent open cluster, NGC 654. We discuss observational characteristics that can be used to distinguish supernova ejected systems from those ejected by dynamical interactions, and we present the results of a new radio pulsar search of these systems, as well as estimates of their predicted X-ray flux assuming that each binary contains a compact object. Since neither pulsars nor X-ray emission are observed in these systems, we cannot conclude that these binaries contain compact companions. We also consider whether they may have been ejected by dynamical interactions in the dense environment where they formed, and our simulations of four-body interactions suggest that a dynamical origin is possible but unlikely. We recommend further X-ray observations that will conclusively identify whether HD 14633 or HD 15137 contain neutron stars.
16 citations
TL;DR: The PSR J1744-3922 system as mentioned in this paper is a binary pulsar exhibiting highly variable pulsed radio emission, which suggests that this phenomenon is extrinsic to the pulsar and possibly tied to the companion, although not strongly correlated with orbital phase.
Abstract: PSR J1744-3922 is a binary pulsar exhibiting highly variable pulsed radio emission. We report on a statistical multifrequency study of the pulsed radio flux variability which suggests that this phenomenon is extrinsic to the pulsar and possibly tied to the companion, although not strongly correlated with orbital phase. The pulsar has an unusual combination of characteristics compared to typical recycled pulsars: a long spin period (172 ms); a relatively high magnetic field strength (1.7 × 1010 G); a very circular, compact orbit of 4.6 hr; and a low-mass companion (0.08 M☉). These spin and orbital properties are likely inconsistent with standard evolutionary models. We find similarities between the properties of the PSR J1744-3922 system and those of several other known binary pulsar systems, motivating the identification of a new class of binary pulsars. We suggest that this new class could result from: a standard accretion scenario of a magnetar or a high magnetic field pulsar; common envelope evolution with a low-mass star and a neutron star, similar to what is expected for ultracompact X-ray binaries; or accretion induced collapse of a white dwarf. We also report the detection of a possible K' = 19.30(15) infrared counterpart at the position of the pulsar, which is relatively bright if the companion is a helium white dwarf at the nominal distance, and discuss its implications for the pulsar's companion and evolutionary history.
12 citations
Posted Content•
TL;DR: In this article, the authors present results from four instruments used to characterize the aerosol component of the atmosphere: the Central Laser Facility (CLF), which provides the air fluorescence detectors with calibrated laser shots; the scanning backscatter lidars, which operate at three FD sites; the Aerosol Phase Function monitors (APFs), which measure the spraying cross section at two FD locations; and the Horizontal Attenuation Monitor (HAM), which measures the wavelength dependence of aerosol attenuation.
Abstract: The air fluorescence detectors (FDs) of the Pierre Auger Observatory are vital for the determination of the air shower energy scale. To compensate for variations in atmospheric conditions that affect the energy measurement, the Observatory operates an array of monitoring instruments to record hourly atmospheric conditions across the detector site, an area exceeding 3,000 square km. This paper presents results from four instruments used to characterize the aerosol component of the atmosphere: the Central Laser Facility (CLF), which provides the FDs with calibrated laser shots; the scanning backscatter lidars, which operate at three FD sites; the Aerosol Phase Function monitors (APFs), which measure the aerosol scattering cross section at two FD locations; and the Horizontal Attenuation Monitor (HAM), which measures the wavelength dependence of aerosol attenuation.
9 citations
01 Jan 2007
TL;DR: In this paper, the authors present results from four instruments used to characterize the aerosol component of the atmosphere: the Central Laser Facility (CLF), which provides the air fluorescence detectors with calibrated laser shots; the scanning backscatter lidars, which operate at three FD sites; the Aerosol Phase Function monitors (APFs), which measure the spraying cross section at two FD locations; and the Horizontal Attenuation Monitor (HAM), which measures the wavelength dependence of aerosol attenuation.
Abstract: The air fluorescence detectors (FDs) of the Pierre Auger Observatory are vital for the determination of the air shower energy scale. To compensate for variations in atmospheric conditions that affect the energy measurement, the Observatory operates an array of monitoring instruments to record hourly atmospheric conditions across the detector site, an area exceeding 3,000 square km. This paper presents results from four instruments used to characterize the aerosol component of the atmosphere: the Central Laser Facility (CLF), which provides the FDs with calibrated laser shots; the scanning backscatter lidars, which operate at three FD sites; the Aerosol Phase Function monitors (APFs), which measure the aerosol scattering cross section at two FD locations; and the Horizontal Attenuation Monitor (HAM), which measures the wavelength dependence of aerosol attenuation.
8 citations
TL;DR: Using the Green Bank Telescope (GBT) and Pulsar Spigot at 350MHz, a survey of the Northern Galactic Plane for pulsars and radio transients was conducted in this paper.
Abstract: Using the Green Bank Telescope (GBT) and Pulsar Spigot at 350MHz, we have surveyed the Northern Galactic Plane for pulsars and radio transients. This survey covers roughly 1000 square degrees of sky within 75 deg < l < 165 deg and |b| < 5.5 deg, a region of the Galactic Plane inaccessible to both the Parkes and Arecibo multibeam surveys. The large gain of the GBT along with the high time and frequency resolution provided by the Spigot make this survey more sensitive by factors of about 4 to slow pulsars and more than 10 to millisecond pulsars (MSPs), compared with previous surveys of this area. In a preliminary, reduced-resolution search of all the survey data, we have discovered 33 new pulsars, almost doubling the number of known pulsars in this part of the Galaxy. While most of these sources were discovered by normal periodicity searches, 5 of these sources were first identified through single, dispersed bursts. We discuss the interesting properties of some of these new sources. Data processing using the data's full-resolution is ongoing, with the goal of uncovering MSPs missed by our first, coarse round of processing.
3 citations
16 Jul 2007
TL;DR: In this article, the authors review the current status of our knowledge of these sources based on radio, infrared, and X-ray data and identify the sources that are destined to be the first sources firmly identified by GLAST.
Abstract: At the end of the EGRET mission, only 6 Galactic sources in the 3rd EGRET catalog had firm identifications: 5 young pulsars and a solar flare. Another dozen or so had plausible counterparts. Now, at the dawn of the GLAST era, around 30 sources detected at other wavelengths have been identified as probable or plausible counterparts. These include nearly all of the sources with significant emission above 1 GeV, which will be the sources GLAST will best be able to study. I review the current status of our knowledge of these sources based on radio, infrared, and X‐ray data. These Galactic sources are destined to be the first sources firmly identified by GLAST.
2 citations
TL;DR: The PSR J1744-3922 system is a binary pulsar exhibiting highly variable pulsed radio emission as mentioned in this paper, which suggests that this phenomenon is extrinsic to the pulsar and possibly tied to the companion, although not strongly correlated with orbital phase.
Abstract: PSR J1744-3922 is a binary pulsar exhibiting highly variable pulsed radio emission. We report on a statistical multi-frequency study of the pulsed radio flux variability which suggests that this phenomenon is extrinsic to the pulsar and possibly tied to the companion, although not strongly correlated with orbital phase. The pulsar has an unusual combination of characteristics compared to typical recycled pulsars: a long spin period (172 ms); a relatively high magnetic field strength (1.7x10^10 G); a very circular, compact orbit of 4.6 hours; and a low-mass companion (0.08 Msun). These spin and orbital properties are likely inconsistent with standard evolutionary models. We find similarities between the properties of the PSR J1744-3922 system and those of several other known binary pulsar systems, motivating the identification of a new class of binary pulsars. We suggest that this new class could result from either: a standard accretion scenario of a magnetar or a high-magnetic field pulsar; common envelope evolution with a low-mass star and a neutron star, similar to what is expected for ultra-compact X-ray binaries; or, accretion induced collapse of a white dwarf. We also report the detection of a possible K'=19.30(15) infrared counterpart at the position of the pulsar, which is relatively bright if the companion is a helium white dwarf at the nominal distance, and discuss its implications for the pulsar's companion and evolutionary history.