GW190521

Alexander H. Nitz^1,2, Collin D. Capano^1,2

<sub>1. Albert-Einstein-Institut, Max-Planck-Institut for Gravitationsphysik, D-30167 Hannover, Germany
2. Leibniz Universitat Hannover, D-30167 Hannover, Germany</sub>

This repository is a companion to Nitz and Capano (https://arxiv.org/abs/2010.12558). It contains posterior probability density files from the parameter estimation analysis described in the paper and the configuration files needed to run the analysis. We encourage use of these data in derivative works. If you use the material provided here, please cite the paper using the reference:

@article{Nitz:2020,
    author = "Nitz, Alexander H. and Collin D. Capano",
    title = "{GW190521 may be an intermediate mass ratio inspiral}",
    eprint = "2010.12558",
    archivePrefix = "arXiv",
    primaryClass = "gr-qc",
    month = "10",
    year = "2020"
}

Abstract for "GW190521 may be an intermediate mass ratio inspiral"

GW190521 is the first confident observation of a binary black hole merger with total mass M > 100 M. Given the lack of observational constraints at these masses, we analyze GW190521 considering two different priors for the binary’s masses: uniform in mass ratio and source-frame total mass, and uniform in source-frame component masses. For the uniform in mass-ratio prior, we find that the component masses are msrc 1 = 168+15 −61 M and msrc 2 = 16+33 −3 M. The uniform in component-mass prior yields a bimodal posterior distribution. There is a low-mass-ratio mode (q < 4) with msrc 1 = 100+17 −18 M and msrc 2 = 57+17 −16 M and a high-mass-ratio mode (q ≥ 4) with msrc 1 = 166+16 −35 M and msrc 2 = 16+14 −3 M. Although the two modes have nearly equal posterior probability, the maximumlikelihood parameters are in the high-mass ratio mode, with msrc 1 = 171 M and msrc 2 = 16 M, and a signal-to-noise ratio of 16. These results are consistent with the proposed “mass gap” produced by pair-instability in supernova. Our results are inconsistent with those published in Abbott et al. (2020b). We find that a combination of the prior used and the constraints applied may have prevented that analysis from sampling the high-mass-ratio mode. An accretion flare in AGN J124942.3+344929 was observed in possible coincidence with GW190521 by the Zwicky Transient Facility (ZTF). We report parameters assuming a common origin; however, the spatial agreement of GW190521 and the EM flare alone does not provide convincing evidence for the association (ln B & −4).

Posterior files

HDF files containing posterior samples are in the posteriors directory. Each posterior is split into 5 files (due to github file size constraints). Samples are stored as 1D arrays in the samples group in the posterior files. There is a separate dataset for each parameter that was varied in the analysis, along with a dataset for the log likelihood at that point. The parameters are:

Parameter	Description
srcmass1	The source-frame mass of the larger object, in solar masses.
srcmass2	The source-frame mass of the smaller object, in solar masses.
spin1_a	The magnitude of the dimensionless spin of the larger object.
spin2_a	"" smaller object.
spin1_azimuthal	The azimuthal angle of the dimensionless spin of the larger object.
spin2_azimuthal	"" smaller object.
spin1_polar	The polar angle of the dimensionless spin of the smaller object.
spin2_polar	"" smaller object.
ra	The right ascension of the binary, in radians.
dec	The declination of the binary, in radians.
comoving_volume	The comoving volume (in Mpc3). To convert to luminosity distance we use standard Lambda-CDM cosmology, with values from the Planck 2015 results.
inclination	The angle between the orbital angular momentum and the line of sight to the binary at the reference frequency (stored as f_ref in the file's attrs), in radians.
delta_tc	The difference between the measured coalescence time of the event and a reference GPS time, which is stored in the file's attrs as trigger_time.
loglikelihood	The log of the likelihood at the given point.
maxl_coa_phase	Phase is marginalized in the likelihood. This gives the maximum likelihood phase for each sample.
maxl_polarization	The polarization angle is marginalized in the likelihood. This gives the maximum likelihood angle for each sample.
maxl_loglr	The unmarginalized (over phase and polarization angle) maximum likelihood for each sample.

The files contain metadata about the analysis, including the parameters that were fixed. These can be found in the files' attrs. There are five file sets, the posteriors IMRPhenomXPN and NRSur7dq4 both with and without constraint on the EM flare location. There is also a reweighted set that converts the XPHM gw-only results into source-frame uniform in component mass priors.

Configuration files

The configuration files used in the analyses are in the configuration directory. These specify the prior, sampler, model used, and the data analyzed.

License

This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 United States License.