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R Wijnands - One of the best experts on this subject based on the ideXlab platform.
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the long term evolution of the spin pulse Shape and orbit of the accretion powered millisecond pulsar sax j1808 4 3658
The Astrophysical Journal, 2008Co-Authors: J M Hartman, Alessandro Patruno, Deepto Chakrabarty, David L Kaplan, Craig B Markwardt, E H Morgan, P S Ray, Michiel Van Der Klis, R WijnandsAbstract:We present a 7 yr timing study of the 2.5 ms X-ray pulsar SAX J1808.4–3658, an X-ray transient with a recurrence time of 2 yr, using data from the Rossi X-Ray Timing Explorer covering four transient outbursts (1998-2005). We verify that the 401 Hz pulsation traces the spin frequency fundamental and not a harmonic. Substantial pulse Shape Variability, both stochastic and systematic, was observed during each outburst. Analysis of the systematic pulse Shape changes suggests that, as an outburst dims, the X-ray hot spot on the pulsar surface drifts longitudinally and a second hot spot may appear. The overall pulse Shape Variability limits the ability to measure spin frequency evolution within a given X-ray outburst (and calls previous $d{ν }$ --> measurements of this source into question), with typical upper limits of || 2.5 × 10−14$v d{ν }v l 2.5 × 10−14$ --> Hz s−1 (2 σ). However, combining data from all the outbursts shows with high (6 σ) significance that the pulsar is undergoing long-term spin down at a rate = (−5.6 ± 2.0) × 10−16$d{ν } = (− 5.6 ± 2.0) × 10−16$ --> Hz s−1, with most of the spin evolution occurring during X-ray quiescence. We discuss the possible contributions of magnetic propeller torques, magnetic dipole radiation, and gravitational radiation to the measured spin down, setting an upper limit of -->B Q/I s s−1. This surprisingly large orb$d{P}orb$ --> is reminiscent of the large and quasi-cyclic orbital period variation observed in the so-called black widow millisecond radio pulsars, which further strengthens previous speculation that SAX J1808.4–3658 may turn on as a radio pulsar during quiescence. In an appendix we derive an improved ( -->0.15'') source position from optical data.
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the long term evolution of the spin pulse Shape and orbit of the accretion powered millisecond pulsar sax j1808 4 3658
arXiv: Astrophysics, 2007Co-Authors: J M Hartman, Alessandro Patruno, Deepto Chakrabarty, David L Kaplan, Craig B Markwardt, E H Morgan, P S Ray, Michiel Van Der Klis, R WijnandsAbstract:We present a 7 yr timing study of the 2.5 ms X-ray pulsar SAX J1808.4-3658, an X-ray transient with a recurrence time of ~2 yr, using data from the Rossi X-ray Timing Explorer covering 4 transient outbursts (1998-2005). We verify that the 401 Hz pulsation traces the spin frequency fundamental and not a harmonic. Substantial pulse Shape Variability, both stochastic and systematic, was observed during each outburst. Analysis of the systematic pulse Shape changes suggests that, as an outburst dims, the X-ray "hot spot" on the pulsar surface drifts longitudinally and a second hot spot may appear. The overall pulse Shape Variability limits the ability to measure spin frequency evolution within a given X-ray outburst (and calls previous nudot measurements of this source into question), with typical upper limits of |nudot| < 2.5x10^{-14} Hz/s (2 sigma). However, combining data from all the outbursts shows with high (6 sigma) significance that the pulsar is undergoing long-term spin down at a rate nudot = (-5.6+/-2.0)x10^{-16} Hz/s, with most of the spin evolution occurring during X-ray quiescence. We discuss the possible contributions of magnetic propeller torques, magnetic dipole radiation, and gravitational radiation to the measured spin down, setting an upper limit of B < 1.5x10^8 G for the pulsar's surface dipole magnetic field and and Q/I < 5x10^{-9} for the fractional mass quadrupole moment. We also measured an orbital period derivative of Pdot = (3.5+/-0.2)x10^{-12} s/s. This surprising large Pdot is reminiscent of the large and quasi-cyclic orbital period variation observed in the so-called "black widow" millisecond radio pulsars, supporting speculation that SAX J1808.4-3658 may turn on as a radio pulsar during quiescence. In an appendix we derive an improved (0.15 arcsec) source position from optical data.
Craig B Markwardt - One of the best experts on this subject based on the ideXlab platform.
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the long term evolution of the spin pulse Shape and orbit of the accretion powered millisecond pulsar sax j1808 4 3658
The Astrophysical Journal, 2008Co-Authors: J M Hartman, Alessandro Patruno, Deepto Chakrabarty, David L Kaplan, Craig B Markwardt, E H Morgan, P S Ray, Michiel Van Der Klis, R WijnandsAbstract:We present a 7 yr timing study of the 2.5 ms X-ray pulsar SAX J1808.4–3658, an X-ray transient with a recurrence time of 2 yr, using data from the Rossi X-Ray Timing Explorer covering four transient outbursts (1998-2005). We verify that the 401 Hz pulsation traces the spin frequency fundamental and not a harmonic. Substantial pulse Shape Variability, both stochastic and systematic, was observed during each outburst. Analysis of the systematic pulse Shape changes suggests that, as an outburst dims, the X-ray hot spot on the pulsar surface drifts longitudinally and a second hot spot may appear. The overall pulse Shape Variability limits the ability to measure spin frequency evolution within a given X-ray outburst (and calls previous $d{ν }$ --> measurements of this source into question), with typical upper limits of || 2.5 × 10−14$v d{ν }v l 2.5 × 10−14$ --> Hz s−1 (2 σ). However, combining data from all the outbursts shows with high (6 σ) significance that the pulsar is undergoing long-term spin down at a rate = (−5.6 ± 2.0) × 10−16$d{ν } = (− 5.6 ± 2.0) × 10−16$ --> Hz s−1, with most of the spin evolution occurring during X-ray quiescence. We discuss the possible contributions of magnetic propeller torques, magnetic dipole radiation, and gravitational radiation to the measured spin down, setting an upper limit of -->B Q/I s s−1. This surprisingly large orb$d{P}orb$ --> is reminiscent of the large and quasi-cyclic orbital period variation observed in the so-called black widow millisecond radio pulsars, which further strengthens previous speculation that SAX J1808.4–3658 may turn on as a radio pulsar during quiescence. In an appendix we derive an improved ( -->0.15'') source position from optical data.
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the long term evolution of the spin pulse Shape and orbit of the accretion powered millisecond pulsar sax j1808 4 3658
arXiv: Astrophysics, 2007Co-Authors: J M Hartman, Alessandro Patruno, Deepto Chakrabarty, David L Kaplan, Craig B Markwardt, E H Morgan, P S Ray, Michiel Van Der Klis, R WijnandsAbstract:We present a 7 yr timing study of the 2.5 ms X-ray pulsar SAX J1808.4-3658, an X-ray transient with a recurrence time of ~2 yr, using data from the Rossi X-ray Timing Explorer covering 4 transient outbursts (1998-2005). We verify that the 401 Hz pulsation traces the spin frequency fundamental and not a harmonic. Substantial pulse Shape Variability, both stochastic and systematic, was observed during each outburst. Analysis of the systematic pulse Shape changes suggests that, as an outburst dims, the X-ray "hot spot" on the pulsar surface drifts longitudinally and a second hot spot may appear. The overall pulse Shape Variability limits the ability to measure spin frequency evolution within a given X-ray outburst (and calls previous nudot measurements of this source into question), with typical upper limits of |nudot| < 2.5x10^{-14} Hz/s (2 sigma). However, combining data from all the outbursts shows with high (6 sigma) significance that the pulsar is undergoing long-term spin down at a rate nudot = (-5.6+/-2.0)x10^{-16} Hz/s, with most of the spin evolution occurring during X-ray quiescence. We discuss the possible contributions of magnetic propeller torques, magnetic dipole radiation, and gravitational radiation to the measured spin down, setting an upper limit of B < 1.5x10^8 G for the pulsar's surface dipole magnetic field and and Q/I < 5x10^{-9} for the fractional mass quadrupole moment. We also measured an orbital period derivative of Pdot = (3.5+/-0.2)x10^{-12} s/s. This surprising large Pdot is reminiscent of the large and quasi-cyclic orbital period variation observed in the so-called "black widow" millisecond radio pulsars, supporting speculation that SAX J1808.4-3658 may turn on as a radio pulsar during quiescence. In an appendix we derive an improved (0.15 arcsec) source position from optical data.
V Ravi - One of the best experts on this subject based on the ideXlab platform.
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limitations in timing precision due to single pulse Shape Variability in millisecond pulsars
Monthly Notices of the Royal Astronomical Society, 2014Co-Authors: R M Shannon, W Van Straten, Matthew Bailes, S Oslowski, C A Raithel, V RaviAbstract:High-sensitivity radio-frequency observations of millisecond pulsars usually show stochastic, broad-band, pulse-Shape variations intrinsic to the pulsar emission process. These variations induce jitter noise in pulsar timing observations; understanding the properties of this noise is of particular importance for the effort to detect gravitational waves with pulsar timing arrays. We assess the short-term profile and timing stability of 22 millisecond pulsars that are part of the Parkes Pulsar Timing Array sample by examining intraobservation arrival time Variability and single-pulse phenomenology. In 7 of the 22 pulsars, in the band centred at approximately 1400 MHz, we find that the brightest observations are limited by intrinsic jitter. We find consistent results, either detections or upper limits, for jitter noise in other frequency bands. PSR J1909−3744 shows the lowest levels of jitter noise, which we estimate to contribute ∼10 ns root mean square error to the arrival times for hour-duration observations. Larger levels of jitter noise are found in pulsars with wider pulses and distributions of pulse intensities. The jitter noise in PSR J0437−4715 decorrelates over a bandwidth of ∼2 GHz. We show that the uncertainties associated with timing pulsar models can be improved by including physically motivated jitter uncertainties. Pulse-Shape variations will limit the timing precision at future, more sensitive, telescopes; it is imperative to account for this noise when designing instrumentation and timing campaigns for these facilities.
Timothy J Doherty - One of the best experts on this subject based on the ideXlab platform.
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increased motor unit potential Shape Variability across consecutive motor unit discharges in the tibialis anterior and vastus medialis muscles of healthy older subjects
Clinical Neurophysiology, 2015Co-Authors: Maddison L Hourigan, Daniel W Stashuk, Neal B Mckinnon, Marjorie Johnson, Charles L Rice, Timothy J DohertyAbstract:Abstract Objective To study the potential utility of using near fiber (NF) jiggle as an assessment of neuromuscular transmission stability in healthy older subjects using decomposition-based quantitative electromyography (DQEMG). Methods The tibialis anterior (TA) and vastus medialis (VM) muscles were tested in 9 older men (77 ± 5 years) and 9 young male control subjects (23 ± 0.3 years). Simultaneous surface and needle-detected electromyographic (EMG) signals were collected during voluntary contractions, and then analyzed using DQEMG. Motor unit potential (MUP) and NF MUP parameters were analyzed. Results NF jiggle was significantly increased for both the TA and VM in the old age group relative to the younger controls ( P P P P Conclusions Healthy aging is associated with neuromuscular transmission instability (increased NF jiggle) and MU remodeling, which can be measured using DQEMG. Significance NF jiggle derived from DQEMG can be a useful method of identifying neuromuscular dysfunction at various stages of MU remodeling and aging.
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increased motor unit potential Shape Variability across consecutive motor unit discharges in the tibialis anterior and vastus medialis muscles of healthy older subjects
Clinical Neurophysiology, 2015Co-Authors: Maddison L Hourigan, Daniel W Stashuk, Neal B Mckinnon, Marjorie Johnson, Charles L Rice, Timothy J DohertyAbstract:Abstract Objective To study the potential utility of using near fiber (NF) jiggle as an assessment of neuromuscular transmission stability in healthy older subjects using decomposition-based quantitative electromyography (DQEMG). Methods The tibialis anterior (TA) and vastus medialis (VM) muscles were tested in 9 older men (77 ± 5 years) and 9 young male control subjects (23 ± 0.3 years). Simultaneous surface and needle-detected electromyographic (EMG) signals were collected during voluntary contractions, and then analyzed using DQEMG. Motor unit potential (MUP) and NF MUP parameters were analyzed. Results NF jiggle was significantly increased for both the TA and VM in the old age group relative to the younger controls ( P P P P Conclusions Healthy aging is associated with neuromuscular transmission instability (increased NF jiggle) and MU remodeling, which can be measured using DQEMG. Significance NF jiggle derived from DQEMG can be a useful method of identifying neuromuscular dysfunction at various stages of MU remodeling and aging.
J M Hartman - One of the best experts on this subject based on the ideXlab platform.
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the long term evolution of the spin pulse Shape and orbit of the accretion powered millisecond pulsar sax j1808 4 3658
The Astrophysical Journal, 2008Co-Authors: J M Hartman, Alessandro Patruno, Deepto Chakrabarty, David L Kaplan, Craig B Markwardt, E H Morgan, P S Ray, Michiel Van Der Klis, R WijnandsAbstract:We present a 7 yr timing study of the 2.5 ms X-ray pulsar SAX J1808.4–3658, an X-ray transient with a recurrence time of 2 yr, using data from the Rossi X-Ray Timing Explorer covering four transient outbursts (1998-2005). We verify that the 401 Hz pulsation traces the spin frequency fundamental and not a harmonic. Substantial pulse Shape Variability, both stochastic and systematic, was observed during each outburst. Analysis of the systematic pulse Shape changes suggests that, as an outburst dims, the X-ray hot spot on the pulsar surface drifts longitudinally and a second hot spot may appear. The overall pulse Shape Variability limits the ability to measure spin frequency evolution within a given X-ray outburst (and calls previous $d{ν }$ --> measurements of this source into question), with typical upper limits of || 2.5 × 10−14$v d{ν }v l 2.5 × 10−14$ --> Hz s−1 (2 σ). However, combining data from all the outbursts shows with high (6 σ) significance that the pulsar is undergoing long-term spin down at a rate = (−5.6 ± 2.0) × 10−16$d{ν } = (− 5.6 ± 2.0) × 10−16$ --> Hz s−1, with most of the spin evolution occurring during X-ray quiescence. We discuss the possible contributions of magnetic propeller torques, magnetic dipole radiation, and gravitational radiation to the measured spin down, setting an upper limit of -->B Q/I s s−1. This surprisingly large orb$d{P}orb$ --> is reminiscent of the large and quasi-cyclic orbital period variation observed in the so-called black widow millisecond radio pulsars, which further strengthens previous speculation that SAX J1808.4–3658 may turn on as a radio pulsar during quiescence. In an appendix we derive an improved ( -->0.15'') source position from optical data.
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the long term evolution of the spin pulse Shape and orbit of the accretion powered millisecond pulsar sax j1808 4 3658
arXiv: Astrophysics, 2007Co-Authors: J M Hartman, Alessandro Patruno, Deepto Chakrabarty, David L Kaplan, Craig B Markwardt, E H Morgan, P S Ray, Michiel Van Der Klis, R WijnandsAbstract:We present a 7 yr timing study of the 2.5 ms X-ray pulsar SAX J1808.4-3658, an X-ray transient with a recurrence time of ~2 yr, using data from the Rossi X-ray Timing Explorer covering 4 transient outbursts (1998-2005). We verify that the 401 Hz pulsation traces the spin frequency fundamental and not a harmonic. Substantial pulse Shape Variability, both stochastic and systematic, was observed during each outburst. Analysis of the systematic pulse Shape changes suggests that, as an outburst dims, the X-ray "hot spot" on the pulsar surface drifts longitudinally and a second hot spot may appear. The overall pulse Shape Variability limits the ability to measure spin frequency evolution within a given X-ray outburst (and calls previous nudot measurements of this source into question), with typical upper limits of |nudot| < 2.5x10^{-14} Hz/s (2 sigma). However, combining data from all the outbursts shows with high (6 sigma) significance that the pulsar is undergoing long-term spin down at a rate nudot = (-5.6+/-2.0)x10^{-16} Hz/s, with most of the spin evolution occurring during X-ray quiescence. We discuss the possible contributions of magnetic propeller torques, magnetic dipole radiation, and gravitational radiation to the measured spin down, setting an upper limit of B < 1.5x10^8 G for the pulsar's surface dipole magnetic field and and Q/I < 5x10^{-9} for the fractional mass quadrupole moment. We also measured an orbital period derivative of Pdot = (3.5+/-0.2)x10^{-12} s/s. This surprising large Pdot is reminiscent of the large and quasi-cyclic orbital period variation observed in the so-called "black widow" millisecond radio pulsars, supporting speculation that SAX J1808.4-3658 may turn on as a radio pulsar during quiescence. In an appendix we derive an improved (0.15 arcsec) source position from optical data.
