scholarly journals Very low-frequency oscillations from the 11 Hz pulsar in Terzan 5: frame dragging back on the table.

2021 ◽  
Vol 502 (4) ◽  
pp. 5472-5479
Author(s):  
L du Buisson ◽  
S Motta ◽  
R Fender
Keyword(s):  
Low Frequency ◽  
Compact Object ◽  
Compact Objects ◽  
Time Variability ◽  
Fast Time ◽  
Horizontal Branch ◽  
Frame Dragging ◽  
Very Low Frequency ◽  
Low Frequency Oscillations ◽  
Large Frequency

ABSTRACT We present a re-analysis of 47 Rossi X-ray Timing Explorer observations of the 11 Hz accreting pulsar IGR J17480-2446 in Terzan 5 during its 2010 outburst. We studied the fast-time variability properties of the source and searched for quasi-periodic oscillations (QPOs) in a large-frequency range. General relativity predicts that frame dragging occurs in the vicinity of a spinning compact object and induces the precession of matter orbiting said object. The relativistic precession model predicts that this frame dragging can be observed as QPOs with a characteristic frequency in the light curves of accreting compact objects. Such QPOs have historically been classified as horizontal branch oscillations in neutron star (NS) systems, and for a NS spinning at 11 Hz, these oscillations are expected at frequencies below 1 Hz. However, previous studies of IGR J17480-2446 have classified QPOs at 35–50 Hz as horizontal branch oscillations, thus casting doubts on the frame-dragging nature of such QPOs. Here, we report the detection of seven very low-frequency QPOs, previously undetected, with centroid frequencies below 0.3 Hz, and which can be ascribed to frame dragging. We also discuss the possible nature of the QPOs detected at 35–50 Hz in this alternative scenario.

Analysis of Very Low Frequency Oscillations in Hydro-Dominant Power Systems Using Multi-Unit Modeling

2012 ◽  
Vol 27 (4) ◽  
pp. 1906-1915 ◽  
Author(s):  
Hugo Villegas Pico ◽  
James D. McCalley ◽  
Andrea Angel ◽  
Ramon Leon ◽  
Neby J. Castrillon
Keyword(s):  
Power Systems ◽  
Low Frequency ◽  
Very Low Frequency ◽  
Low Frequency Oscillations

Very-low-frequency oscillations in heart rate and blood pressure in periodic breathing: role of the cardiovascular limb of the hypoxic chemoreflex

2000 ◽  
Vol 99 (2) ◽  
pp. 125 ◽  
Author(s):  
Darrel P. FRANCIS ◽  
L. Ceri DAVIES ◽  
Keith WILLSON ◽  
Piotr PONIKOWSKI ◽  
Andrew J.S. COATS ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Low Frequency ◽  
Periodic Breathing ◽  
Very Low Frequency ◽  
Low Frequency Oscillations

scholarly journals A review of unusual VLF bursty-patches observed in Northern Finland for Earth, Planets and Space

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Claudia Martinez-Calderon ◽  
Jyrki K. Manninen ◽  
Jemina T. Manninen ◽  
Tauno Turunen
Keyword(s):  
Low Frequency ◽  
Spectral Features ◽  
Radio Waves ◽  
Very Low Frequency ◽  
Ground Station ◽  
New Type ◽  
The Moment ◽  
Electron Gyrofrequency ◽  
Different Characteristics ◽  
Large Frequency

AbstractUsing numerical filtering techniques allowing us to reduce noise from sferics, we are able to clearly study a new type of differently structured very low frequency (VLF) radio waves above f = 4 kHz at the ground station of Kannuslehto in northern Finland (KAN, MLAT = 64.4°N, L = 5.5). These emissions are intriguing, since they are detected at frequencies above half the electron gyrofrequency in the equatorial plane (fce) for the L-shell of Kannuslehto (fce ~ 5–6 kHz). They are commonly observed at Kannuslehto, but have also been infrequently reported at other stations, sometimes under different names. Their possible common origin and manner of propagation is still under investigation. This paper unifies the nomenclature by regrouping all these waves detected at frequencies higher than the local equatorial 0.5 fce at the L-shell of observation under the name of VLF bursty-patches. While these waves have different spectral features, they appeared mostly composed of hiss bursts with durations of a few seconds to several minutes. They also show periodic features with varying periodicity and shape. They are sometimes characterized by single bursts covering very large frequency ranges of several kHz. We also give a review of the different characteristics of VLF bursty-patches observed at Kannuslehto, which at the moment, is the station with the highest observation rate. We present recent observations between 2019 and 2021.

Type I Membranes, Phase Resetting Curves, and Synchrony

1996 ◽  
Vol 8 (5) ◽  
pp. 979-1001 ◽  
Author(s):  
Bard Ermentrout
Keyword(s):  
Perturbation Methods ◽  
Low Frequency ◽  
Type I ◽  
Type Ii ◽  
Phase Resetting ◽  
Applied Current ◽  
Very Low Frequency ◽  
Low Frequency Oscillations ◽  
Singular Perturbation Methods ◽  
Membrane Models

Type I membrane oscillators such as the Connor model (Connor et al. 1977) and the Morris-Lecar model (Morris and Lecar 1981) admit very low frequency oscillations near the critical applied current. Hansel et al. (1995) have numerically shown that synchrony is difficult to achieve with these models and that the phase resetting curve is strictly positive. We use singular perturbation methods and averaging to show that this is a general property of Type I membrane models. We show in a limited sense that so called Type II resetting occurs with models that obtain rhythmicity via a Hopf bifurcation. We also show the differences between synapses that act rapidly and those that act slowly and derive a canonical form for the phase interactions.

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