Constraints on Supermassive Black Hole Binaries from the Lack of Resolvable Sources in the NANOGrav 15-yr Dataset

@misc{gardiner2026constraints,
  title = {{Constraints on Supermassive Black Hole Binaries from the Lack of Resolvable Sources in the NANOGrav 15-yr Dataset}},
  author = {Emiko C. Gardiner and Kayhan Gültekin and Philippe Turgeon and Bence Bécsy and Laura Blecha and Nikita Agarwal and Gabriella Agazie and Akash Anumarlapudi and Anne M. Archibald and Zaven Arzoumanian and Anjana Ashok and Jeremy G. Baier and Paul T. Baker and Adam Brazier and Paul R. Brook and Sarah Burke-Spolaor and Rand Burnette and Robin Case and J. Andrew Casey-Clyde and Maria Charisi and Shami Chatterjee and Tyler Cohen and James M. Cordes and Neil J. Cornish and Fronefield Crawford and H. Thankful Cromartie and Kathryn Crowter and Megan E. DeCesar and Paul B. Demorest and Heling Deng and Lankeswar Dey and Timothy Dolch and Graham M. Doskoch and Elizabeth C. Ferrara and William Fiore and Emmanuel Fonseca and Gabriel E. Freedman and Nate Garver-Daniels and Peter A. Gentile and Kyle A. Gersbach and Joseph Glaser and Deborah C. Good and Aiden Gundersen and C. J. Harris and Jeffrey S. Hazboun and Ross J. Jennings and Aaron D. Johnson and Megan L. Jones and David L. Kaplan and Anala Kavumkandathil Sreekumar and Luke Zoltan Kelley and Matthew Kerr and Joey S. Key and Nima Laal and Michael T. Lam and William G. Lamb and Bjorn Larsen and T. Joseph W. Lazio and Natalia Lewandowska and Tingting Liu},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.32306},
  eprint = {2609.32306},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.32306},
  note = {CC BY 4.0},
}

TY  - UNPB
TI  - Constraints on Supermassive Black Hole Binaries from the Lack of Resolvable Sources in the NANOGrav 15-yr Dataset
AU  - Emiko C. Gardiner
AU  - Kayhan Gültekin
AU  - Philippe Turgeon
AU  - Bence Bécsy
AU  - Laura Blecha
AU  - Nikita Agarwal
AU  - Gabriella Agazie
AU  - Akash Anumarlapudi
AU  - Anne M. Archibald
AU  - Zaven Arzoumanian
AU  - Anjana Ashok
AU  - Jeremy G. Baier
AU  - Paul T. Baker
AU  - Adam Brazier
AU  - Paul R. Brook
AU  - Sarah Burke-Spolaor
AU  - Rand Burnette
AU  - Robin Case
AU  - J. Andrew Casey-Clyde
AU  - Maria Charisi
AU  - Shami Chatterjee
AU  - Tyler Cohen
AU  - James M. Cordes
AU  - Neil J. Cornish
AU  - Fronefield Crawford
AU  - H. Thankful Cromartie
AU  - Kathryn Crowter
AU  - Megan E. DeCesar
AU  - Paul B. Demorest
AU  - Heling Deng
AU  - Lankeswar Dey
AU  - Timothy Dolch
AU  - Graham M. Doskoch
AU  - Elizabeth C. Ferrara
AU  - William Fiore
AU  - Emmanuel Fonseca
AU  - Gabriel E. Freedman
AU  - Nate Garver-Daniels
AU  - Peter A. Gentile
AU  - Kyle A. Gersbach
AU  - Joseph Glaser
AU  - Deborah C. Good
AU  - Aiden Gundersen
AU  - C. J. Harris
AU  - Jeffrey S. Hazboun
AU  - Ross J. Jennings
AU  - Aaron D. Johnson
AU  - Megan L. Jones
AU  - David L. Kaplan
AU  - Anala Kavumkandathil Sreekumar
AU  - Luke Zoltan Kelley
AU  - Matthew Kerr
AU  - Joey S. Key
AU  - Nima Laal
AU  - Michael T. Lam
AU  - William G. Lamb
AU  - Bjorn Larsen
AU  - T. Joseph W. Lazio
AU  - Natalia Lewandowska
AU  - Tingting Liu
PY  - 2026
DA  - 2026/09/26
PB  - arXiv
DO  - 10.48550/arxiv.2609.32306
UR  - https://arxiv.org/abs/2609.32306
AB  - Pulsar timing arrays (PTAs) have found evidence of a gravitational wave background (GWB) consistent with a population of supermassive black hole binaries (SMBHBs), but have not yet resolved a continuous wave (CW) from an individual binary. We present the first SMBHB population constraints incorporating PTA upper limits on CWs, based on the NANOGrav 15-year (NG15) data. Using semi-analytic models to generate simulated populations, we calculate each sample's GWB likelihood by free spectral comparison and CW nondetection (nCW) likelihoods by (1) mapping each realization's highest CW signal-to-noise ratio (S/N) to a detection probability and (2) counting the fraction of realizations without a binary close enough that NG15 would have detected it. CW nondetection favors populations in which many lower-mass sources, rather than a few ultramassive ones, dominate the GWB. This information is complementary to that provided by the GWB amplitude, breaking the degeneracy between the masses and number of binaries required to reproduce the observed spectrum. Relative to GWB-only constraints, the joint posteriors favor higher galaxy merger rates, lower M_BH-M_bulge scatter, shorter binary lifetimes, and steeper small-separation hardening. The most detectable sources in the S/N-weighted joint posterior have chirp masses ∼ 10^9.6 M_⊙, luminosity distances ∼1300 Mpc, and frequencies ∼6 nHz, while the nCW-only constraints favor lower frequencies, coinciding with the NG15 4 nHz candidate. These constraints will tighten if CW nondetection continues.
ER  -