RMNest

RMNest is an open source python package for estimating both standard and generalised rotation measures via direct fits to Stokes Q, U and V spectra.

Installation

The latest release of RMNest can be installed from PyPi by running the following

bash pip install rmnest

Note that while a working installation of the PSRCHIVE Python-3 bindings is not necessary for using RMNest, it is strongly recommended.

Requirements

The following packages are required to running RMNest.

• numpy: Array manipulation

• matplotlib: Modules for plotting

• bilby: Inference calculations framework

• dynesty: Modules for nested sampling

Usage

RMNest can be run directly from the command line within using rmnest. As an example, the below command would run a standard rotation-measure fit on the provided test data after frequency-averaging to 128 channels within a [pulse] phase window between phase = 0.45 to 0.55

bash rmnest archive test/2020-03-16-18\:12\:00.calib.ST -o test/output/ -l testrun --window 0.45:0.55 -f 128

Alternatively, fitting for the generalised form of Faraday rotation, sometimes referred to as Faraday conversion (see e.g. Kennett & Melrose 1998), can be performed by adding the --gfr and --free_alpha flags as

bash rmnest <archive>.ar -o <outdir> -l testrun --window 0.45:0.55 --gfr --free_alpha

Omitting the --free_alpha flag will result in the spectral exponent being fixed to 3. Details of the underlying phenomenological model can be found in a technical document by Lower (2021).

The likelihood and Faraday rotation models, as well as the general RMFit class in fit_RM.py, can also be imported like any other API.

Issues and Contributing

If you encounter any issues with RMNest, or have in mind a feature that currently does not exist, then you can contribute by openning a Github Issue and outlining the feature.

Referencing RMNest

If you make use of RMNest in your research, we would greatly appreciate it if you cite both the ASCL entry (Lower et al. 2022) and the papers behind its development.

@software{2022ascl.soft04008L, author = {{Lower}, Marcus E. and {Kumar}, Pravir and {Shannon}, Ryan M.}, title = "{RMNest: Bayesian approach to measuring Faraday rotation and conversion in radio signals}", keywords = {Software}, howpublished = {Astrophysics Source Code Library, record ascl:2204.008}, year = 2022, month = apr, eid = {ascl:2204.008}, pages = {ascl:2204.008}, archivePrefix = {ascl}, eprint = {2204.008}, adsurl = {https://ui.adsabs.harvard.edu/abs/2022ascl.soft04008L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System} }

For standard rotation measure fitting, then please cite Bannister et al. (2019).

@ARTICLE{2019Sci...365..565B, author = {{Bannister}, K.~W. and {Deller}, A.~T. and {Phillips}, C. and {Macquart}, J. -P. and {Prochaska}, J.~X. and {Tejos}, N. and {Ryder}, S.~D. and {Sadler}, E.~M. and {Shannon}, R.~M. and {Simha}, S. and {Day}, C.~K. and {McQuinn}, M. and {North-Hickey}, F.~O. and {Bhandari}, S. and {Arcus}, W.~R. and {Bennert}, V.~N. and {Burchett}, J. and {Bouwhuis}, M. and {Dodson}, R. and {Ekers}, R.~D. and {Farah}, W. and {Flynn}, C. and {James}, C.~W. and {Kerr}, M. and {Lenc}, E. and {Mahony}, E.~K. and {O'Meara}, J. and {Os{\l}owski}, S. and {Qiu}, H. and {Treu}, T. and {U}, V. and {Bateman}, T.~J. and {Bock}, D.~C. -J. and {Bolton}, R.~J. and {Brown}, A. and {Bunton}, J.~D. and {Chippendale}, A.~P. and {Cooray}, F.~R. and {Cornwell}, T. and {Gupta}, N. and {Hayman}, D.~B. and {Kesteven}, M. and {Koribalski}, B.~S. and {MacLeod}, A. and {McClure-Griffiths}, N.~M. and {Neuhold}, S. and {Norris}, R.~P. and {Pilawa}, M.~A. and {Qiao}, R. -Y. and {Reynolds}, J. and {Roxby}, D.~N. and {Shimwell}, T.~W. and {Voronkov}, M.~A. and {Wilson}, C.~D.}, title = "{A single fast radio burst localized to a massive galaxy at cosmological distance}", journal = {Science}, keywords = {ASTRONOMY, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Nongalactic Astrophysics}, year = 2019, month = aug, volume = {365}, number = {6453}, pages = {565-570}, doi = {10.1126/science.aaw5903}, archivePrefix = {arXiv}, eprint = {1906.11476}, primaryClass = {astro-ph.HE}, adsurl = {https://ui.adsabs.harvard.edu/abs/2019Sci...365..565B}, adsnote = {Provided by the SAO/NASA Astrophysics Data System} }

If you used RMNest for generalised Faraday rotation measure fitting, please include a citation to Lower (2021).

@ARTICLE{2021arXiv210809429L, author = {{Lower}, Marcus E.}, title = "{A phenomenological model for measuring generalised Faraday rotation}", journal = {arXiv e-prints}, keywords = {Astrophysics - High Energy Astrophysical Phenomena}, year = 2021, month = aug, eid = {arXiv:2108.09429}, pages = {arXiv:2108.09429}, archivePrefix = {arXiv}, eprint = {2108.09429}, primaryClass = {astro-ph.HE}, adsurl = {https://ui.adsabs.harvard.edu/abs/2021arXiv210809429L}, adsnote = {Provided by the SAO/NASA Astrophysics Data System} }