The Astrophysical Journal (Jan 2025)
The NANOGrav 15 Yr Data Set: Removing Pulsars One by One from the Pulsar Timing Array
- Gabriella Agazie,
- Akash Anumarlapudi,
- Anne M. Archibald,
- Zaven Arzoumanian,
- Jeremy G. Baier,
- Paul T. Baker,
- Bence Bécsy,
- Laura Blecha,
- Adam Brazier,
- Paul R. Brook,
- Sarah Burke-Spolaor,
- J. Andrew Casey-Clyde,
- Maria Charisi,
- Shami Chatterjee,
- Tyler Cohen,
- James M. Cordes,
- Neil J. Cornish,
- Fronefield Crawford,
- H. Thankful Cromartie,
- Kathryn Crowter,
- Megan E. DeCesar,
- Paul B. Demorest,
- Heling Deng,
- Lankeswar Dey,
- Timothy Dolch,
- Elizabeth C. Ferrara,
- William Fiore,
- Emmanuel Fonseca,
- Gabriel E. Freedman,
- Emiko C. Gardiner,
- Nate Garver-Daniels,
- Peter A. Gentile,
- Kyle A. Gersbach,
- Joseph Glaser,
- Deborah C. Good,
- Lydia Guertin,
- Kayhan Gültekin,
- Jeffrey S. Hazboun,
- Ross J. Jennings,
- Aaron D. Johnson,
- Megan L. Jones,
- Andrew R. Kaiser,
- David L. Kaplan,
- Luke Zoltan Kelley,
- Matthew Kerr,
- Joey S. Key,
- Nima Laal,
- Michael T. Lam,
- William G. Lamb,
- Bjorn Larsen,
- T. Joseph W. Lazio,
- Natalia Lewandowska,
- Tingting Liu,
- Duncan R. Lorimer,
- Jing Luo,
- Ryan S. Lynch,
- Chung-Pei Ma,
- Dustin R. Madison,
- Alexander McEwen,
- James W. McKee,
- Maura A. McLaughlin,
- Natasha McMann,
- Bradley W. Meyers,
- Patrick M. Meyers,
- Hannah Middleton,
- Chiara M. F. Mingarelli,
- Andrea Mitridate,
- Christopher J. Moore,
- Cherry Ng,
- David J. Nice,
- Stella Koch Ocker,
- Ken D. Olum,
- Timothy T. Pennucci,
- Benetge B. P. Perera,
- Nihan S. Pol,
- Henri A. Radovan,
- Scott M. Ransom,
- Paul S. Ray,
- Joseph D. Romano,
- Jessie C. Runnoe,
- Alexander Saffer,
- Shashwat C. Sardesai,
- Ann Schmiedekamp,
- Carl Schmiedekamp,
- Kai Schmitz,
- Brent J. Shapiro-Albert,
- Xavier Siemens,
- Joseph Simon,
- Magdalena S. Siwek,
- Sophia V. Sosa Fiscella,
- Ingrid H. Stairs,
- Daniel R. Stinebring,
- Kevin Stovall,
- Abhimanyu Susobhanan,
- Joseph K. Swiggum,
- Stephen R. Taylor,
- Jacob E. Turner,
- Caner Unal,
- Michele Vallisneri,
- Alberto Vecchio,
- Sarah J. Vigeland,
- Haley M. Wahl,
- Caitlin A. Witt,
- David Wright,
- Olivia Young
Affiliations
- Gabriella Agazie
- ORCiD
- Center for Gravitation, Cosmology and Astrophysics, Department of Physics, University of Wisconsin-Milwaukee , P.O. Box 413, Milwaukee, WI 53201, USA
- Akash Anumarlapudi
- ORCiD
- Center for Gravitation, Cosmology and Astrophysics, Department of Physics, University of Wisconsin-Milwaukee , P.O. Box 413, Milwaukee, WI 53201, USA
- Anne M. Archibald
- ORCiD
- School of Mathematics, Statistics, and Physics, Newcastle University , Newcastle upon Tyne, NE1 7RU, UK
- Zaven Arzoumanian
- X-Ray Astrophysics Laboratory , NASA Goddard Space Flight Center, Code 662, Greenbelt, MD 20771, USA
- Jeremy G. Baier
- ORCiD
- Department of Physics, Oregon State University , Corvallis, OR 97331, USA
- Paul T. Baker
- ORCiD
- Department of Physics and Astronomy, Widener University , One University Place, Chester, PA 19013, USA
- Bence Bécsy
- ORCiD
- Department of Physics, Oregon State University , Corvallis, OR 97331, USA
- Laura Blecha
- ORCiD
- Physics Department, University of Florida , Gainesville, FL 32611, USA
- Adam Brazier
- ORCiD
- Cornell Center for Astrophysics and Planetary Science and Department of Astronomy, Cornell University , Ithaca, NY 14853, USA; Cornell Center for Advanced Computing, Cornell University , Ithaca, NY 14853, USA
- Paul R. Brook
- ORCiD
- Institute for Gravitational Wave Astronomy and School of Physics and Astronomy, University of Birmingham , Edgbaston, Birmingham, B15 2TT, UK ; [email protected]
- Sarah Burke-Spolaor
- ORCiD
- Department of Physics and Astronomy, West Virginia University , P.O. Box 6315, Morgantown, WV 26506, USA; Center for Gravitational Waves and Cosmology, West Virginia University , Chestnut Ridge Research Building, Morgantown, WV 26505, USA
- J. Andrew Casey-Clyde
- ORCiD
- Department of Physics, University of Connecticut , 196 Auditorium Road, U-3046, Storrs, CT 06269-3046, USA
- Maria Charisi
- ORCiD
- Department of Physics and Astronomy, Vanderbilt University , 2301 Vanderbilt Place, Nashville, TN 37235, USA
- Shami Chatterjee
- ORCiD
- Cornell Center for Astrophysics and Planetary Science and Department of Astronomy, Cornell University , Ithaca, NY 14853, USA
- Tyler Cohen
- ORCiD
- Department of Physics, New Mexico Institute of Mining and Technology , 801 Leroy Place, Socorro, NM 87801, USA
- James M. Cordes
- ORCiD
- Cornell Center for Astrophysics and Planetary Science and Department of Astronomy, Cornell University , Ithaca, NY 14853, USA
- Neil J. Cornish
- ORCiD
- Department of Physics, Montana State University , Bozeman, MT 59717, USA
- Fronefield Crawford
- ORCiD
- Department of Physics and Astronomy, Franklin & Marshall College , P.O. Box 3003, Lancaster, PA 17604, USA
- H. Thankful Cromartie
- ORCiD
- National Research Council Research Associate, National Academy of Sciences, Washington , DC 20001, USA resident at Naval Research Laboratory, Washington, DC 20375, USA
- Kathryn Crowter
- ORCiD
- Department of Physics and Astronomy, University of British Columbia , 6224 Agricultural Road, Vancouver, BC V6T 1Z1, Canada
- Megan E. DeCesar
- ORCiD
- George Mason University , Fairfax, VA 22030, resident at the U.S. Naval Research Laboratory, Washington, DC 20375, USA
- Paul B. Demorest
- ORCiD
- National Radio Astronomy Observatory , 1003 Lopezville Rd., Socorro, NM 87801, USA
- Heling Deng
- Department of Physics, Oregon State University , Corvallis, OR 97331, USA
- Lankeswar Dey
- ORCiD
- Department of Physics and Astronomy, West Virginia University , P.O. Box 6315, Morgantown, WV 26506, USA; Center for Gravitational Waves and Cosmology, West Virginia University , Chestnut Ridge Research Building, Morgantown, WV 26505, USA
- Timothy Dolch
- ORCiD
- Department of Physics, Hillsdale College , 33 E. College Street, Hillsdale, MI 49242, USA; Eureka Scientific , 2452 Delmer Street, Suite 100, Oakland, CA 94602-3017, USA
- Elizabeth C. Ferrara
- ORCiD
- Department of Astronomy, University of Maryland , College Park, MD 20742, USA; Center for Research and Exploration in Space Science and Technology , NASA/GSFC, Greenbelt, MD 20771, USA; NASA Goddard Space Flight Center , Greenbelt, MD 20771, USA
- William Fiore
- ORCiD
- Department of Physics and Astronomy, West Virginia University , P.O. Box 6315, Morgantown, WV 26506, USA; Center for Gravitational Waves and Cosmology, West Virginia University , Chestnut Ridge Research Building, Morgantown, WV 26505, USA
- Emmanuel Fonseca
- ORCiD
- Department of Physics and Astronomy, West Virginia University , P.O. Box 6315, Morgantown, WV 26506, USA; Center for Gravitational Waves and Cosmology, West Virginia University , Chestnut Ridge Research Building, Morgantown, WV 26505, USA
- Gabriel E. Freedman
- ORCiD
- Center for Gravitation, Cosmology and Astrophysics, Department of Physics, University of Wisconsin-Milwaukee , P.O. Box 413, Milwaukee, WI 53201, USA
- Emiko C. Gardiner
- ORCiD
- Department of Astronomy, University of California , Berkeley, 501 Campbell Hall #3411, Berkeley, CA 94720, USA
- Nate Garver-Daniels
- ORCiD
- Department of Physics and Astronomy, West Virginia University , P.O. Box 6315, Morgantown, WV 26506, USA; Center for Gravitational Waves and Cosmology, West Virginia University , Chestnut Ridge Research Building, Morgantown, WV 26505, USA
- Peter A. Gentile
- ORCiD
- Department of Physics and Astronomy, West Virginia University , P.O. Box 6315, Morgantown, WV 26506, USA; Center for Gravitational Waves and Cosmology, West Virginia University , Chestnut Ridge Research Building, Morgantown, WV 26505, USA
- Kyle A. Gersbach
- Department of Physics and Astronomy, Vanderbilt University , 2301 Vanderbilt Place, Nashville, TN 37235, USA
- Joseph Glaser
- ORCiD
- Department of Physics and Astronomy, West Virginia University , P.O. Box 6315, Morgantown, WV 26506, USA; Center for Gravitational Waves and Cosmology, West Virginia University , Chestnut Ridge Research Building, Morgantown, WV 26505, USA
- Deborah C. Good
- ORCiD
- Department of Physics and Astronomy, University of Montana , 32 Campus Drive, Missoula, MT 59812, USA
- Lydia Guertin
- Department of Physics and Astronomy, Haverford College , Haverford, PA 19041, USA
- Kayhan Gültekin
- ORCiD
- Department of Astronomy and Astrophysics, University of Michigan , Ann Arbor, MI 48109, USA
- Jeffrey S. Hazboun
- ORCiD
- Department of Physics, Oregon State University , Corvallis, OR 97331, USA
- Ross J. Jennings
- ORCiD
- Department of Physics and Astronomy, West Virginia University , P.O. Box 6315, Morgantown, WV 26506, USA; Center for Gravitational Waves and Cosmology, West Virginia University , Chestnut Ridge Research Building, Morgantown, WV 26505, USA
- Aaron D. Johnson
- ORCiD
- Center for Gravitation, Cosmology and Astrophysics, Department of Physics, University of Wisconsin-Milwaukee , P.O. Box 413, Milwaukee, WI 53201, USA; Division of Physics, Mathematics, and Astronomy, California Institute of Technology , Pasadena, CA 91125, USA
- Megan L. Jones
- ORCiD
- Center for Gravitation, Cosmology and Astrophysics, Department of Physics, University of Wisconsin-Milwaukee , P.O. Box 413, Milwaukee, WI 53201, USA
- Andrew R. Kaiser
- ORCiD
- Department of Physics and Astronomy, West Virginia University , P.O. Box 6315, Morgantown, WV 26506, USA; Center for Gravitational Waves and Cosmology, West Virginia University , Chestnut Ridge Research Building, Morgantown, WV 26505, USA
- David L. Kaplan
- ORCiD
- Center for Gravitation, Cosmology and Astrophysics, Department of Physics, University of Wisconsin-Milwaukee , P.O. Box 413, Milwaukee, WI 53201, USA
- Luke Zoltan Kelley
- ORCiD
- Department of Astronomy, University of California , Berkeley, 501 Campbell Hall #3411, Berkeley, CA 94720, USA
- Matthew Kerr
- ORCiD
- Space Science Division, Naval Research Laboratory , Washington, DC 20375-5352, USA
- Joey S. Key
- ORCiD
- University of Washington Bothell , 18115 Campus Way NE, Bothell, WA 98011, USA
- Nima Laal
- ORCiD
- Department of Physics, Oregon State University , Corvallis, OR 97331, USA
- Michael T. Lam
- ORCiD
- SETI Institute , 339 N Bernardo Ave Suite 200, Mountain View, CA 94043, USA; School of Physics and Astronomy, Rochester Institute of Technology , Rochester, NY 14623, USA; Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology , Rochester, NY 14623, USA
- William G. Lamb
- ORCiD
- Department of Physics and Astronomy, Vanderbilt University , 2301 Vanderbilt Place, Nashville, TN 37235, USA
- Bjorn Larsen
- Department of Physics, Yale University , New Haven, CT 06520, USA
- T. Joseph W. Lazio
- Jet Propulsion Laboratory, California Institute of Technology , 4800 Oak Grove Drive, Pasadena, CA 91109, USA
- Natalia Lewandowska
- ORCiD
- Department of Physics and Astronomy, State University of New York at Oswego , Oswego, NY 13126, USA
- Tingting Liu
- ORCiD
- Department of Physics and Astronomy, West Virginia University , P.O. Box 6315, Morgantown, WV 26506, USA; Center for Gravitational Waves and Cosmology, West Virginia University , Chestnut Ridge Research Building, Morgantown, WV 26505, USA
- Duncan R. Lorimer
- ORCiD
- Department of Physics and Astronomy, West Virginia University , P.O. Box 6315, Morgantown, WV 26506, USA; Center for Gravitational Waves and Cosmology, West Virginia University , Chestnut Ridge Research Building, Morgantown, WV 26505, USA
- Jing Luo
- ORCiD
- Department of Astronomy & Astrophysics, University of Toronto , 50 Saint George Street, Toronto, ON M5S 3H4, Canada
- Ryan S. Lynch
- ORCiD
- Green Bank Observatory , P.O. Box 2, Green Bank, WV 24944, USA
- Chung-Pei Ma
- ORCiD
- Department of Astronomy, University of California , Berkeley, 501 Campbell Hall #3411, Berkeley, CA 94720, USA; Department of Physics, University of California , Berkeley, CA 94720, USA
- Dustin R. Madison
- ORCiD
- Department of Physics, University of the Pacific , 3601 Pacific Avenue, Stockton, CA 95211, USA
- Alexander McEwen
- ORCiD
- Center for Gravitation, Cosmology and Astrophysics, Department of Physics, University of Wisconsin-Milwaukee , P.O. Box 413, Milwaukee, WI 53201, USA
- James W. McKee
- ORCiD
- Department of Physics and Astronomy, Union College , Schenectady, NY 12308, USA
- Maura A. McLaughlin
- ORCiD
- Department of Physics and Astronomy, West Virginia University , P.O. Box 6315, Morgantown, WV 26506, USA; Center for Gravitational Waves and Cosmology, West Virginia University , Chestnut Ridge Research Building, Morgantown, WV 26505, USA
- Natasha McMann
- ORCiD
- Department of Physics and Astronomy, Vanderbilt University , 2301 Vanderbilt Place, Nashville, TN 37235, USA
- Bradley W. Meyers
- ORCiD
- Department of Physics and Astronomy, University of British Columbia , 6224 Agricultural Road, Vancouver, BC V6T 1Z1, Canada; International Centre for Radio Astronomy Research, Curtin University , Bentley, WA 6102, Australia
- Patrick M. Meyers
- ORCiD
- Division of Physics, Mathematics, and Astronomy, California Institute of Technology , Pasadena, CA 91125, USA
- Hannah Middleton
- ORCiD
- Institute for Gravitational Wave Astronomy and School of Physics and Astronomy, University of Birmingham , Edgbaston, Birmingham, B15 2TT, UK ; [email protected]
- Chiara M. F. Mingarelli
- ORCiD
- Department of Physics, Yale University , New Haven, CT 06520, USA
- Andrea Mitridate
- ORCiD
- Deutsches Elektronen-Synchrotron DESY , Notkestr. 85, 22607 Hamburg, Germany
- Christopher J. Moore
- ORCiD
- Institute of Astronomy, University of Cambridge , Madingley Road, Cambridge, CB3 0HA, UK; Kavli Institute for Cosmology, University of Cambridge , Madingley Road, Cambridge, CB3 0HA, UK; Department of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences, University of Cambridge , Wilberforce Road, Cambridge, CB3 0WA, UK
- Cherry Ng
- ORCiD
- Dunlap Institute for Astronomy and Astrophysics, University of Toronto , 50 St. George St., Toronto, ON M5S 3H4, Canada
- David J. Nice
- ORCiD
- Department of Physics, Lafayette College , Easton, PA 18042, USA
- Stella Koch Ocker
- ORCiD
- Division of Physics, Mathematics, and Astronomy, California Institute of Technology , Pasadena, CA 91125, USA; The Observatories of the Carnegie Institution for Science , Pasadena, CA 91101, USA
- Ken D. Olum
- ORCiD
- Institute of Cosmology, Department of Physics and Astronomy, Tufts University , Medford, MA 02155, USA
- Timothy T. Pennucci
- ORCiD
- Institute of Physics and Astronomy, Eötvös Loránd University , Pázmány P. s. 1/A, 1117 Budapest, Hungary
- Benetge B. P. Perera
- ORCiD
- Arecibo Observatory , HC3 Box 53995, Arecibo, PR 00612, USA
- Nihan S. Pol
- ORCiD
- Department of Physics and Astronomy, Vanderbilt University , 2301 Vanderbilt Place, Nashville, TN 37235, USA
- Henri A. Radovan
- ORCiD
- Department of Physics, University of Puerto Rico , Mayagüez, PR 00681, USA
- Scott M. Ransom
- ORCiD
- National Radio Astronomy Observatory , 520 Edgemont Road, Charlottesville, VA 22903, USA
- Paul S. Ray
- ORCiD
- Space Science Division, Naval Research Laboratory , Washington, DC 20375-5352, USA
- Joseph D. Romano
- ORCiD
- Department of Physics, Texas Tech University , Box 41051, Lubbock, TX 79409, USA
- Jessie C. Runnoe
- ORCiD
- Department of Physics and Astronomy, Vanderbilt University , 2301 Vanderbilt Place, Nashville, TN 37235, USA
- Alexander Saffer
- Department of Physics and Astronomy, West Virginia University , P.O. Box 6315, Morgantown, WV 26506, USA; Center for Gravitational Waves and Cosmology, West Virginia University , Chestnut Ridge Research Building, Morgantown, WV 26505, USA
- Shashwat C. Sardesai
- ORCiD
- Center for Gravitation, Cosmology and Astrophysics, Department of Physics, University of Wisconsin-Milwaukee , P.O. Box 413, Milwaukee, WI 53201, USA
- Ann Schmiedekamp
- ORCiD
- Department of Physics, Penn State Abington , Abington, PA 19001, USA
- Carl Schmiedekamp
- ORCiD
- Department of Physics, Penn State Abington , Abington, PA 19001, USA
- Kai Schmitz
- ORCiD
- Institute for Theoretical Physics, University of Münster , 48149 Münster, Germany
- Brent J. Shapiro-Albert
- ORCiD
- Department of Physics and Astronomy, West Virginia University , P.O. Box 6315, Morgantown, WV 26506, USA; Center for Gravitational Waves and Cosmology, West Virginia University , Chestnut Ridge Research Building, Morgantown, WV 26505, USA; Giant Army , 915A 17th Ave, Seattle WA 98122, USA
- Xavier Siemens
- ORCiD
- Center for Gravitation, Cosmology and Astrophysics, Department of Physics, University of Wisconsin-Milwaukee , P.O. Box 413, Milwaukee, WI 53201, USA; Department of Physics, Oregon State University , Corvallis, OR 97331, USA
- Joseph Simon
- ORCiD
- Department of Astrophysical and Planetary Sciences, University of Colorado , Boulder, CO 80309, USA
- Magdalena S. Siwek
- ORCiD
- Center for Astrophysics, Harvard University , 60 Garden St, Cambridge, MA 02138, USA
- Sophia V. Sosa Fiscella
- ORCiD
- School of Physics and Astronomy, Rochester Institute of Technology , Rochester, NY 14623, USA; Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology , Rochester, NY 14623, USA
- Ingrid H. Stairs
- ORCiD
- Department of Physics and Astronomy, University of British Columbia , 6224 Agricultural Road, Vancouver, BC V6T 1Z1, Canada
- Daniel R. Stinebring
- ORCiD
- Department of Physics and Astronomy, Oberlin College , Oberlin, OH 44074, USA
- Kevin Stovall
- ORCiD
- National Radio Astronomy Observatory , 1003 Lopezville Rd., Socorro, NM 87801, USA
- Abhimanyu Susobhanan
- ORCiD
- Max-Planck-Institut für Gravitationsphysik (Albert-Einstein-Institut) , Callinstrasse 38, D-30167, Hannover, Germany
- Joseph K. Swiggum
- ORCiD
- Department of Physics, Lafayette College , Easton, PA 18042, USA
- Stephen R. Taylor
- ORCiD
- Department of Physics and Astronomy, Vanderbilt University , 2301 Vanderbilt Place, Nashville, TN 37235, USA
- Jacob E. Turner
- ORCiD
- Green Bank Observatory , P.O. Box 2, Green Bank, WV 24944, USA
- Caner Unal
- ORCiD
- Department of Physics, Middle East Technical University , 06531 Ankara, Turkey; Department of Physics, Ben-Gurion University of the Negev , Be’er Sheva 84105, Israel; Feza Gursey Institute, Bogazici University , Kandilli, 34684, Istanbul, Turkey
- Michele Vallisneri
- ORCiD
- Division of Physics, Mathematics, and Astronomy, California Institute of Technology , Pasadena, CA 91125, USA; Jet Propulsion Laboratory, California Institute of Technology , 4800 Oak Grove Drive, Pasadena, CA 91109, USA
- Alberto Vecchio
- ORCiD
- Institute for Gravitational Wave Astronomy and School of Physics and Astronomy, University of Birmingham , Edgbaston, Birmingham, B15 2TT, UK ; [email protected]
- Sarah J. Vigeland
- ORCiD
- Center for Gravitation, Cosmology and Astrophysics, Department of Physics, University of Wisconsin-Milwaukee , P.O. Box 413, Milwaukee, WI 53201, USA
- Haley M. Wahl
- ORCiD
- Department of Physics and Astronomy, West Virginia University , P.O. Box 6315, Morgantown, WV 26506, USA; Center for Gravitational Waves and Cosmology, West Virginia University , Chestnut Ridge Research Building, Morgantown, WV 26505, USA
- Caitlin A. Witt
- ORCiD
- Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), Northwestern University , Evanston, IL 60208, USA; Adler Planetarium , 1300 S. DuSable Lake Shore Dr., Chicago, IL 60605, USA
- David Wright
- ORCiD
- Department of Physics, Oregon State University , Corvallis, OR 97331, USA
- Olivia Young
- ORCiD
- School of Physics and Astronomy, Rochester Institute of Technology , Rochester, NY 14623, USA; Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology , Rochester, NY 14623, USA
- DOI
- https://doi.org/10.3847/1538-4357/ad93aa
- Journal volume & issue
-
Vol. 978,
no. 2
p. 168
Abstract
Evidence has emerged for a stochastic signal correlated among 67 pulsars within the 15 yr pulsar-timing data set compiled by the NANOGrav collaboration. Similar signals have been found in data from the European, Indian, Parkes, and Chinese pulsar timing arrays. This signal has been interpreted as indicative of the presence of a nanohertz stochastic gravitational-wave background (GWB). To explore the internal consistency of this result, we investigate how the recovered signal strength changes as we remove the pulsars one by one from the data set. We calculate the signal strength using the (noise-marginalized) optimal statistic, a frequentist metric designed to measure the correlated excess power in the residuals of the arrival times of the radio pulses. We identify several features emerging from this analysis that were initially unexpected. The significance of these features, however, can only be assessed by comparing the real data to synthetic data sets. After conducting identical analyses on simulated data sets, we do not find anything inconsistent with the presence of a stochastic GWB in the NANOGrav 15 yr data. The methodologies developed here can offer additional tools for application to future, more sensitive data sets. While this analysis provides an internal consistency check of the NANOGrav results, it does not eliminate the necessity for additional investigations that could identify potential systematics or uncover unmodeled physical phenomena in the data.
Keywords
- Gravitational waves
- Gravitational wave astronomy
- Millisecond pulsars
- Radio pulsars
- Supermassive black holes
