J/A+A/590/A109 Data-analysis project PSRSALSA (Weltevrede, 2016)
Investigation of the bi-drifting subpulses of radio pulsar B1839-04 using the
open-source data-analysis project PSRSALSA.
Weltevrede P.
<Astron. Astrophys. 590, A109 (2016)>
=2016A&A...590A.109W 2016A&A...590A.109W (SIMBAD/NED BibCode)
ADC_Keywords: Models
Keywords: pulsars: individual: PSR B1839-04 - pulsars: general -
methods: data analysis - methods: statistical - polarization -
radiation mechanisms: non-thermal
Abstract:
The usefulness and versatility of the PSRSALSA open-source pulsar
data-analysis project is demonstrated through an analysis of the radio
pulsar B1839-04. This study focuses on the phenomenon of
bi-drifting, an effect where the drift direction of subpulses is
systematically different in different pulse profile components.
Bi-drifting is extremely rare in the pulsar population, and the
theoretical implications are discussed after comparing B1839-04 with
the only other known bi-drifter.
Various tools in PSRSALSA, including those allowing quantification of
periodicities in the subpulse modulation, their flux distribution, and
polarization properties, are exploited to obtain a comprehensive
picture of the radio properties of PSR B1839-04. In particular, the
second harmonic in the fluctuation spectra of the subpulse modulation
is exploited to convincingly demonstrate the existence of bi-drifting
in B1839-04. Bi-drifting is confirmed with a completely independent
method allowing the average modulation cycle to be determined.
Polarization measurements were used to obtain a robust constraint on
the magnetic inclination angle.
The angle between the rotation and magnetic axis is found to be
smaller than 35°. Two distinct emission modes are discovered to be
operating, with periodic subpulse modulation being present only during
the weaker mode. Despite the variability of the modulation cycle and
interruption by mode-changes, the modulation pattern responsible for
the bi-drifting is strictly phase locked over a timescale of years
such that the variability is identical in the different components.
The phase locking implies that a single physical origin is responsible
for both drift directions. Phase locking is hard to explain for many
models, including those specifically proposed in the literature to
explain bi-drifting, and they are therefore shown to be implausible.
It is argued that within the framework of circulating beamlets,
bi-drifting could occur if the circulation were severely distorted,
possibly by distortions in the magnetic field.
Description:
PSRSALSA - A Suite of ALgorithms for Statistical Analysis of pulsar
data - code.
The functionality of the PSRSALSA package includes the following:
- Tools to analyse periodic subpulse modulation in various ways
(Weltevrede et al., 2006A&A...445..243W 2006A&A...445..243W, Cat. J/A+A/445/243,
2007A&A...469..607W 2007A&A...469..607W, Cat. J/A+A/469/607, 2012MNRAS.424..843W 2012MNRAS.424..843W;
Serylak et al., 2009A&A...506..865S 2009A&A...506..865S).
- A tool to fit the rotating vector model (RVM; Radhakrishnan & Cooke,
1969AstL....3..225R 1969AstL....3..225R) to the polarization position angle curve of
pulsars to derive viewing geometries (Rookyard et al.,
2015MNRAS.446.3367R 2015MNRAS.446.3367R).
- Tools to analyse and fit the observed flux-distribution of individual
pulses, including the possibility to remove the effect of the noise
distribution during the fitting process (e.g. Weltevrede et al.,
2006A&A...458..269W 2006A&A...458..269W).
- Plotting tools for various types of data, visualised in various
different ways, either from the command line or interactively.
- Functionality to do various standard data processing operations,
including de-dispersion, averaging, rebinning, rotating data in pulse
phase and removing the average noise level (baseline) in various ways.
There is functionality to flag and remove frequency channels and
subintegrations from a data set.
- Support of the PSRFITS (Hotan et al., 2004PASA...21..302H 2004PASA...21..302H),
SIGPROC3 (Lorimer, Astrophysics Source Code Library,
http://ascl.net/1107.016), EPN (Lorimer et al.,
1998A&AS..128..541L 1998A&AS..128..541L), and ASCII data formats.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
readme.txt 102 78 ReadMe file of the code
psrsalsa_v1.tar 5444 40300 tarball file of PSRSALSA code
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Acknowledgements:
Patrick Welevrede, patrick.weltevrede(at)manchester.ac.uk
(End) Patricia Vannier [CDS] 31-Mar-2016