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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.
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.
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, M Bailes, W Van Straten, 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.
Sara A Pozzi - One of the best experts on this subject based on the ideXlab platform.
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comparison of analog and digital Pulse Shape discrimination systems
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2016Co-Authors: Charles Sosa, Marek Flaska, Sara A PozziAbstract:Abstract Pulse Shape discrimination (PSD) performance of two optimized PSD systems (one digital and one analog) is compared in this work. One system uses digital charge integration, while the other system uses analog zero crossing. Measurements were conducted with each PSD system using the CAEN V1720 (250 MHz) data acquisition system. An organic-liquid scintillator, coupled to a photo-multiplier tube, was used to detect neutrons and gamma rays from a Cf-252 spontaneous-fission source. The PSD performance of both systems was optimized and quantified using a traditional figure-of-merit (FOM) approach. FOM's were found for three, 300 keVee light-output bins, spanning from 100 to 1000 keVee, and one larger bin from 100 to 1800 keVee. Digital PSD outperformed analog PSD in the lowest light-output bin by approximately 50%, and by 11% for the highest light-output bin.
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an algorithm for charge integration Pulse Shape discrimination and estimation of neutron photon misclassification in organic scintillators
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2015Co-Authors: J K Polack, Marek Flaska, Andreas Enqvist, C S Sosa, C C Lawrence, Sara A PozziAbstract:Abstract Organic scintillators are frequently used for measurements that require sensitivity to both photons and fast neutrons because of their Pulse Shape discrimination capabilities. In these measurement scenarios, particle identification is commonly handled using the charge-integration Pulse Shape discrimination method. This method works particularly well for high-energy depositions, but is prone to misclassification for relatively low-energy depositions. A novel algorithm has been developed for automatically performing charge-integration Pulse Shape discrimination in a consistent and repeatable manner. The algorithm is able to estimate the photon and neutron misclassification corresponding to the calculated discrimination parameters, and is capable of doing so using only the information measured by a single organic scintillator. This paper describes the algorithm and assesses its performance by comparing algorithm-estimated misclassification to values computed via a more traditional time-of-flight estimation. A single data set was processed using four different low-energy thresholds: 40, 60, 90, and 120 keVee. Overall, the results compared well between the two methods; in most cases, the algorithm-estimated values fell within the uncertainties of the TOF-estimated values.
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application of bayes theorem for Pulse Shape discrimination
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2015Co-Authors: Mateusz Monterial, Peter Marleau, Shaun D Clarke, Sara A PozziAbstract:A Bayesian approach is proposed for Pulse Shape discrimination of photons and neutrons in liquid organic scinitillators. Instead of drawing a decision boundary, each Pulse is assigned a photon or neutron confidence probability. In addition, this allows for photon and neutron classification on an event-by-event basis. The sum of those confidence probabilities is used to estimate the number of photon and neutron instances in the data. An iterative scheme, similar to an expectation-maximization algorithm for Gaussian mixtures, is used to infer the ratio of photons-to-neutrons in each measurement. Therefore, the probability space adapts to data with varying photon-to-neutron ratios. A time-correlated measurement of Am–Be and separate measurements of 137Cs, 60Co and 232Th photon sources were used to construct libraries of neutrons and photons. These libraries were then used to produce synthetic data sets with varying ratios of photons-to-neutrons. Probability weighted method that we implemented was found to maintain neutron acceptance rate of up to 90% up to photon-to-neutron ratio of 2000, and performed 9% better than the decision boundary approach. Furthermore, the iterative approach appropriately changed the probability space with an increasing number of photons which kept the neutron population estimate from unrealistically increasing.
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comparison between silicon photomultipliers and photomultiplier tubes for Pulse Shape discrimination with stilbene
Nuclear Science Symposium and Medical Imaging Conference, 2014Co-Authors: Marc L Ruch, Marek Flaska, Ciara B Sivels, Steven A Czyz, Sara A PozziAbstract:A stilbene crystal was coupled to a silicon photomultiplier (SiPM) to assess the performance of the detector's Pulse Shape discrimination (PSD) between fast neutrons and gamma rays. Pulses were digitized from a measurement of Cf-252 and digital charge comparison was used to perform PSD. The stilbene crystal was then coupled to a photomultiplier tube (PMT) and the measurement was repeated. The PSD performance when using the SiPM was compared to that of the system using the PMT. Both systems demonstrate efficient ability to discriminate between neutrons and gamma rays. While PMTs have long been the standard technology for light readout, SiPMs show similar capabilities while being less expensive, significantly more compact in size, significantly less sensitive to magnetic fields, and having lower power requirements. Potential drawbacks of SiPMs include elevated levels of noise and nonlinearity at high energies.
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Pulse Shape discrimination in the plastic scintillator ej 299 33
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2013Co-Authors: Sara A Pozzi, M M Bourne, Shaun D ClarkeAbstract:Abstract New advances in plastic scintillation compositions have opened the field to new, exciting instruments capable of neutron-gamma ray Pulse Shape discrimination (PSD). We present PSD figure of merit parameters and neutron time-of-flight from Cf-252 using a 5.08-cm diameter by 5.08-cm thick sample of PSD-capable plastic scintillator EJ-299-33 and compare these results to those from a same-sized EJ-309 liquid scintillator detector. An offline, digital PSD method was applied to both detectors. The results show that EJ-299-33 plastic PSD is very good, having a figure of merit of approximately 0.9 for 120 keVee threshold; however the EJ-309 liquid scintillator PSD is superior to the EJ-299-33 plastic scintillator PSD, with a figure of merit of 1.5 at the same measurement threshold. We also found that the EJ-299-33 has reduced neutron detection efficiency compared to the EJ-309. For the fission neutron spectrum measured here, the ratio of the plastic to liquid total number of measured neutrons was approximately 0.63.
