A flat-spectrum flare in S4 0444+63 revealed by a new implementation of multiwavelength single-dish observations
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Authors: Giroletti, M.; Righini, S.
Abstract
Relativistic amplification boosts the contribution of the jet base to the total emission in blazars, thus making single-dish observations useful and practical to characterize their physical state, particularly during episodes of enhanced multiwavelength activity. Following the detection of a new gamma-ray source by Fermi-LAT in 2017 July, we observed S4 0444+63 in order to secure its identification as a gamma-ray blazar. We conducted observations with the Medicina and Noto radio telescopes at 5, 8, and 24 GHz for a total of 12 epochs between 2017 August 1 and 2018 September 22. We carried out the observations with on-the-fly cross-scans and reduced the data with our newly developed CROSS-SCAN ANALYSIS PIPELINE, which we present here in detail for the first time. We found the source to be in an elevated state of emission at radio wavelength, compared to historical values, which lasted for several months. The maximum luminosity was reached on 2018 May 16 at 24 GHz, with L-24 = (1.7 +/- 0.3) x 10(27) W Hz(-1); the spectral index was found to evolve from slightly rising to slightly steep. Besides the new observations, which have proved to be an effective and efficient tool to secure the identification of the source, additional single dish and very long baseline interferometry data provide further insight on the physics of the source. We estimate a synchrotron peak frequency nu(peak) = 10(12.97) Hz and a Doppler factor in excess of delta similar to 5.0, with both quantities playing a role in the gamma-ray emission from the source.
Constructing a Human Atrial Fibre Atlas
ANNALS OF BIOMEDICAL ENGINEERING
Authors: Roney, Caroline H.; Bendikas, Rokas; Pashakhanloo, Farhad; Corrado, Cesare; Vigmond, Edward J.; McVeigh, Elliot R.; Trayanova, Natalia A.; Niederer, Steven A.
Abstract
Atrial anisotropy affects electrical propagation patterns, anchor locations of atrial reentrant drivers, and atrial mechanics. However, patient-specific atrial fibre fields and anisotropy measurements are not currently available, and consequently assigning fibre fields to atrial models is challenging. We aimed to construct an atrial fibre atlas from a high-resolution DTMRI dataset that optimally reproduces electrophysiology simulation predictions corresponding to patient-specific fibre fields, and to develop a methodology for automatically assigning fibres to patient-specific anatomies. We extended an atrial coordinate system to map the pulmonary veins, vena cava and appendages to standardised positions in the coordinate system corresponding to the average location across the anatomies. We then expressed each fibre field in this atrial coordinate system and calculated an average fibre field. To assess the effects of fibre field on patient-specific modelling predictions, we calculated paced activation time maps and electrical driver locations during AF. In total, 756 activation time maps were calculated (7 anatomies with 9 fibre maps and 2 pacing locations, for the endocardial, epicardial and bilayer surface models of the LA and RA). Patient-specific fibre fields had a relatively small effect on average paced activation maps (range of mean local activation time difference for LA fields: 2.67-3.60 ms, and for RA fields: 2.29-3.44 ms), but had a larger effect on maximum LAT differences (range for LA 12.7-16.6%; range for RA 11.9-15.0%). A total of 126 phase singularity density maps were calculated (7 anatomies with 9 fibre maps for the LA and RA bilayer models). The fibre field corresponding to anatomy 1 had the highest median PS density map correlation coefficient for LA bilayer simulations (0.44 compared to the other correlations, ranging from 0.14 to 0.39), while the average fibre field had the highest correlation for the RA bilayer simulations (0.61 compared to the other correlations, ranging from 0.37 to 0.56). For sinus rhythm simulations, average activation time is robust to fibre field direction; however, maximum differences can still be significant. Patient specific fibres are more important for arrhythmia simulations, particularly in the left atrium. We propose using the fibre field corresponding to DTMRI dataset 1 for LA simulations, and the average fibre field for RA simulations as these optimally predicted arrhythmia properties.