NSBH population modeling

Code to infer the neutron star-black hole merger mass and spin distributions using gwpopulation and then to calculate the multimessenger prospects for such systems using the fitting formulae from Foucart+ 2018 using the neutron star equation of state inference from Legred+ 2022. This method was originally presented in Biscoveanu+ 2022.

• fitting_formulae.py: contains the remnant mass and eqaution of state fitting formulae required for the EM-bright calculation
• pop_models_nsbh.py: contains the NSBH mass and spin distributions
• calc_embright_fraction_realistic_EOS.py: performs the calculation of the EM-bright fraction given a population inference result file
• nsbh_inference_S230529ay.py: performs hierarchical inference to infer the hyper-parameters governing the NSBH mass and spin distributions

Installation

In addition to cloning this repo, you will need to install bilby, gwpopulation, and gwpopulation_pipe in addition to standard packages like numpy, h5py, argparse, etc. All can be installed using pip.

Running the Code

usage: nsbh_inference_S230529ay.py [-h] [--S230529ay] [--outdir OUTDIR]
                                   [--runtype {gaussian,power_law}]

optional arguments:
  -h, --help            show this help message and exit
  --S230529ay           include S230529ay
  --outdir OUTDIR       output directory
  --runtype {gaussian,power_law}
                        mass ratio model

Running nsbh_inference_S230529ay.py as indicated above will produce two files, one is a corner plot in png format showing the hyperparameter posteriors, and the other is a bilby result.json file that contains the relevant meta data and posterior samples. In order to calculate the fraction of NSBH systems that may be EM bright for a given hierarchical inference result, you just need to run

>>> python calc_embright_fraction_realistic_EOS.py my_result.json

This will produce a file called {outdir}/{result_label}_embright_fraction_realistic_EOS.dat where the outdir is what was specified in the call to nsbh_inference_S230529ay.py and the result_label depends on whether or not S230529ay was included in the analysis. This file contains the fraction of GW-detectable NSBH events that result in a remnant mass left outside the black hole ISCO radius > 0 Msun, > 0.001 Msun, and > 0.01 Msun, in that order, for each hyper-parameter posterior sample in the original result.json file.