The NANOGrav 15 yr Data Set: Observations and Timing of 68 Millisecond Pulsars
Authors: Agazie Gabriella , Alam Md Faisal , Anumarlapudi Akash , Archibald Anne M. , Arzoumanian Zaven , Baker Paul T. , Blecha Laura , Bonidie Victoria , Brazier Adam , Brook Paul R. , Burke-Spolaor Sarah , Bécsy Bence , Chapman Christopher , Charisi Maria , Chatterjee Shami , Cohen Tyler , Cordes James M. , Cornish Neil J. , Crawford Fronefield , Cromartie H. Thankful , Crowter Kathryn , DeCesar Megan E. , Demorest Paul B. , Dolch Timothy , Drachler Brendan , Ferrara Elizabeth C. , Fiore William , Fonseca Emmanuel , Freedman Gabriel E. , Garver-Daniels Nate , Gentile Peter A. , Glaser Joseph , Good Deborah C. , Gültekin Kayhan , Hazboun Jeffrey S. , Jennings Ross J. , Jessup Cody , Johnson Aaron D. , Jones Megan L. , Kaiser Andrew R. , Kaplan David L. , Kelley Luke Zoltan , Kerr Matthew , Key Joey S. , Kuske Anastasia , Laal Nima , Lam Michael T. , Lamb William G. , W. Lazio T. Joseph , Lewandowska Natalia , Lin Ye , Liu Tingting , Lorimer Duncan R. , Luo Jing , Lynch Ryan S. , Ma Chung-Pei , Madison Dustin R. , Maraccini Kaleb , McEwen Alexander , McKee James W. , McLaughlin Maura A. , McMann Natasha , Meyers Bradley W. , Mingarelli Chiara M. F. , Mitridate Andrea , Ng Cherry , Nice David J. , Ocker Stella Koch , Olum Ken D. , Panciu Elisa , Pennucci Timothy T. , Perera Benetge B. P. , Pol Nihan S. , Radovan Henri A. , Ransom Scott M. , Ray Paul S. , Romano Joseph D. , Salo Laura , Sardesai Shashwat C. , Schmiedekamp Carl , Schmiedekamp Ann , Schmitz Kai , Shapiro-Albert Brent J. , Siemens Xavier , Simon Joseph , Siwek Magdalena S. , Stairs Ingrid H. , Stinebring Daniel R. , Stovall Kevin , Susobhanan Abhimanyu , Swiggum Joseph K. , Taylor Stephen R. , Turner Jacob E. , Unal Caner , Vallisneri Michele , Vigeland Sarah J. , Wahl Haley M. , Wang Qiaohong , Witt Caitlin A. , Young Olivia ,   The NANOGrav Collaboration
Published: June 2023

Abstract
We present observations and timing analyses of 68 millisecond pulsars (MSPs) comprising the 15 yr data set of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). NANOGrav is a pulsar timing array (PTA) experiment that is sensitive to low-frequency gravitational waves (GWs). This is NANOGrav’s fifth public data release, including both “narrowband” and “wideband” time-of-arrival (TOA) measurements and corresponding pulsar timing models. We have added 21 MSPs and extended our timing baselines by 3 yr, now spanning nearly 16 yr for some of our sources. The data were collected using the Arecibo Observatory, the Green Bank Telescope, and the Very Large Array between frequencies of 327 MHz and 3 GHz, with most sources observed approximately monthly. A number of notable methodological and procedural changes were made compared to our previous data sets. These improve the overall quality of the TOA data set and are part of the transition to new pulsar timing and PTA analysis software packages. For the first time, our data products are accompanied by a full suite of software to reproduce data reduction, analysis, and results. Our timing models include a variety of newly detected astrometric and binary pulsar parameters, including several significant improvements to pulsar mass constraints. We find that the time series of 23 pulsars contain detectable levels of red noise, 10 of which are new measurements. In this data set, we find evidence for a stochastic GW background.