Rotation Measure Scatter (RMS)

✨ Code repository for Papers ✨
Frequency Dependent Polarization of Repeating Fast Radio Bursts - Implications for Their Origin
Magnetic Field Reversal around an Active Fast Radio Burst

Description

RM Scatter

In this paper, we report polarization measurements of five repeating FRBs. Combining these with archival observations, we identify trends of lower polarisation at lower frequencies. We model this behaviour as multi-path Rotation Measure Scatter (RMS).

Sources with higher RMS have higher RM magnitude and scattering timescales, indicating a complex environment near the sources, such as a supernova remnant or a pulsar wind nebula, consistent with FRBs arising from young stellar populations.

Figure 2, 3, and 4 of this paper are plotted in RMS-Figure.ipynb. Polarization-RM.ipynb contains Figure 1 and the measurements of FRBs' Rotation Measure. Data and Figures are stored in CalData and Figure, respectively.

RM Reverse

In this paper, we report direct evidence for a B-field reversal based on the observed sign change and extreme variation of FRB~20190520B's RM.

The implied short-term change of the B-field configuration in or around the FRB could be due to the vicinity of massive black holes, or a magnetized companion star in binary systems, or a young supernova remnant along the line of sight.

All figures of this paper are plotted in RMR-Figure.ipynb.

Structure

ModulePy contains two methods for measuring RM, RM Synthesis in rm_synthesis.py, and RM QU Fitting in rm_qu_fitting.py. The code usage method shows in code_usage.py.

`-- RMS
    |-- CalData
    |   |-- 210608_135610_21.rf.TSb4.txt
    |   |-- 190417-FAST.csv
    |   |-- 201124-FAST.csv
    |   |-- 201124-GBT.csv
    |   |-- RM-190303-1.txt
    |   |-- RM-190417-7.txt
    |   |-- RM-190520-437.txt
    |   |-- RM-201124-26.txt
    |   `-- RM-437.txt
    |-- Data
    |   |-- 210608_135610_21.rf.TSb4
    |   `-- Parkes-DM.csv
    |-- Figure
    |   |-- RM-Time-New.png
    |   `-- RM_Scatter_New.png
    |-- ModulePy
    |   |-- code_usage.py
    |   |-- translate_data.py
    |   |-- extract_pulse.py
    |   |-- requirements.txt
    |   |-- rm_qu_fitting.py
    |   `-- rm_synthesis.py
    |-- RMR-Figure.ipynb
    |-- RMS-Figure.ipynb
    |-- Polarization-RM.ipynb
    |-- LICENSE
    `-- README.md

Usage of rm_qu_fitting.py - For example:

from rm_qu_fitting import mcmc_fit, plot_mcmc_samp

# Q and U - 1D numpy array of a pulse, as a function of frequency.
result, RM, RM_error_left, RM_error_right = mcmc_fit(Q, U, freq, rm_left=-10000, rm_right=10000)
print('RM: {:.0f} +{:.0f} -{:.0f}'.format(RM, RM_error_right, RM_error_left))
plot_mcmc_samp(result, save=False)

Usage of rm_synthesis.py - For example:

from rm_synthesis import synthesis_rm, get_rm, plot_rm_synthesis

# I, Q and U - 2D numpy array of a pulse, as a function of frequency and time.
rm_list, Linear                   = synthesis_rm(I, Q, U, freq, rm_left=-20000, rm_right=20000)
RM, RM_error_left, RM_error_right = get_rm(rm_list, Linear, snr)
print('RM: {:.0f} +{:.0f} -{:.0f}'.format(RM, RM_error_right, RM_error_left))
plot_rm_synthesis(rm_list, Linear, save=False)

TO-DO

Optimized pulse extraction algorithm.