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Construction of GW waveforms and SNRs from compact objects around massive BH
Fortran Python
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README.md

README.md

Gravitational Burst Radiation from pulsars around massive BHs

This code calculates the waveforms and SNRs of gravitationa burst radiation from a pulsar orbiting a massive BH. We use a numerical kludge method where the relativistic spin-orbital dynamics are specified by the Mathsisson Papetrou Dixon formulation (see the SpinCurvature git repo).

The orbital motion is calculated by solving a set of coupled ODEs numerically and then the waveforms can be calculated. With the wavefroms constructed we can then also determine the Signal to Noise ratio, using the noise models as described in Robson 2018.

Getting Started

These instructions will get you a copy of the project up and running on your local machine for development and testing purposes.

Prerequisites

This code is written in FORTRAN with a gfortran compiler. Other compilers have not been tested. The gfortran installation binaries can be found here, although typically gfortran comes pre-installed on most Linux/Unix systems. If you have Homebew installed on OSX, you can simply run

brew install gcc

Starting steps

After cloning the repo, the first thing to do is to set the path to the output files that the code will produce.This can be found in src/parameters.f

echo 'export SCDir="/Users/tomkimpson/Data/SpinCurv/"' >> ~/.bash_profile
source ~/.bash_profile

Just change the path to some appropriate local destination

You can check the environemnt variable has been added to bash_profile by either env or vim ~/.bashprofile

Set this to point to a local direcory.

The code should then run as is, out of the box. Try

run.py

to compile and run the code. Once you have checked that everything is running OK, you can then start playing. The code structure (mdoules, subroutines etc.) is outlined below.

If making edits to the code, try to keep to the FORTRAN Style Guide

Structure

src/

parameters.f defines all the system parameters. That is, anything that needs changing (e.g. eccentricity, orbital period, BH mass) can be modified in this module

constants.f is for calculations with those parameters for use later in the code. It can effectively be ignored - no changes should be necessary to this file

main.f is where the code program is run from. After setting up the initial conditions (initial_conditions.f) it then goes on to integrate the equations and save the output (rk.f).

In turn, rk.f calls derivatives.f and tensors.f to calculate e.g. the curvature tensors, ODEs and then integrates numerically.

tools/

plot_trajectory.py. As on the tin. Can switch between 3d and 2d plotting.

plot_ds.py. Compares the spatial difference between the lamba=0 and lamba=1 cases. Useful for quickly eyeing Roemer delay. Requires interpolation.

A python wrapper has been provided to compile and run the code, run.py. We use a -O3 optimization. See the docs for discussion on the optimization flags

Numerical Method

We integrate the equations using a Runge-Kutta-Fehlberg algorithm with adaptive stepsize. See Press et al.

Authors

  • Tom Kimpson
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