Toward Robust Detections of Nanohertz Gravitational Waves
The recent observation of a common red-noise process in pulsar timing arrays (PTAs) suggests that the detection of nanohertz gravitational waves might be around the corner. However, in order to confidently attribute this red process to gravitational waves, one must observe the Hellings–Downs curve—t...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
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IOP Publishing
2023-01-01
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| Series: | The Astrophysical Journal |
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| Online Access: | https://doi.org/10.3847/1538-4357/acee71 |
| _version_ | 1827800315823390720 |
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| author | Valentina Di Marco Andrew Zic Matthew T. Miles Daniel J. Reardon Eric Thrane Ryan M. Shannon |
| author_facet | Valentina Di Marco Andrew Zic Matthew T. Miles Daniel J. Reardon Eric Thrane Ryan M. Shannon |
| author_sort | Valentina Di Marco |
| collection | DOAJ |
| description | The recent observation of a common red-noise process in pulsar timing arrays (PTAs) suggests that the detection of nanohertz gravitational waves might be around the corner. However, in order to confidently attribute this red process to gravitational waves, one must observe the Hellings–Downs curve—the telltale angular correlation function associated with a gravitational-wave background. This effort is complicated by the complex modeling of pulsar noise. Without proper care, misspecified noise models can lead to false-positive detections. Background estimation using “quasi-resampling” methods such as sky scrambles and phase shifts, which use the data to characterize the noise, are therefore important tools for assessing significance. We investigate the ability of current PTA experiments to estimate their background with “quasi-independent” scrambles—characterized by a statistical “match” below the fiducial value: ∣ M ∣ < 0.1. We show that sky scrambling is affected by “saturation” after ${ \mathcal O }(10)$ quasi-independent realizations; subsequent scrambles are no longer quasi-independent. We show that phase scrambling saturates after ${ \mathcal O }(100)$ quasi-independent realizations. With so few independent scrambles, it is difficult to make reliable statements about the ≳5 σ tail of the null distribution of the detection statistic. We sketch out various methods by which one may increase the number of independent scrambles. We also consider an alternative approach, wherein one reframes the background estimation problem so that the significance is calculated using statistically dependent scrambles. The resulting p -value is in principle well defined, but may be susceptible to failure if assumptions about the data are incorrect. |
| first_indexed | 2024-03-11T20:06:36Z |
| format | Article |
| id | doaj.art-8ae441d835134ffca00494012d12671d |
| institution | Directory Open Access Journal |
| issn | 1538-4357 |
| language | English |
| last_indexed | 2024-03-11T20:06:36Z |
| publishDate | 2023-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj.art-8ae441d835134ffca00494012d12671d2023-10-03T15:47:49ZengIOP PublishingThe Astrophysical Journal1538-43572023-01-0195611410.3847/1538-4357/acee71Toward Robust Detections of Nanohertz Gravitational WavesValentina Di Marco0https://orcid.org/0000-0003-3432-0494Andrew Zic1https://orcid.org/0000-0002-9583-2947Matthew T. Miles2https://orcid.org/0000-0002-5455-3474Daniel J. Reardon3https://orcid.org/0000-0002-2035-4688Eric Thrane4https://orcid.org/0000-0002-4418-3895Ryan M. Shannon5https://orcid.org/0000-0002-7285-6348School of Physics and Astronomy, Monash University , Clayton VIC 3800, Australia ; valentina.dimarco@monash.edu; OzGrav: The ARC Centre of Excellence for Gravitational Wave Discovery , Clayton VIC 3800, Australia; CSIRO , Space and Astronomy, PO Box 76, Epping, NSW 1710, AustraliaCSIRO , Space and Astronomy, PO Box 76, Epping, NSW 1710, AustraliaCentre for Astrophysics and Supercomputing, Swinburne University of Technology , Hawthorn VIC 3122, Australia; OzGrav: The ARC Centre of Excellence for Gravitational Wave Discovery , Hawthorn VIC 3122, AustraliaCentre for Astrophysics and Supercomputing, Swinburne University of Technology , Hawthorn VIC 3122, Australia; OzGrav: The ARC Centre of Excellence for Gravitational Wave Discovery , Hawthorn VIC 3122, AustraliaSchool of Physics and Astronomy, Monash University , Clayton VIC 3800, Australia ; valentina.dimarco@monash.edu; OzGrav: The ARC Centre of Excellence for Gravitational Wave Discovery , Clayton VIC 3800, AustraliaCentre for Astrophysics and Supercomputing, Swinburne University of Technology , Hawthorn VIC 3122, Australia; OzGrav: The ARC Centre of Excellence for Gravitational Wave Discovery , Hawthorn VIC 3122, AustraliaThe recent observation of a common red-noise process in pulsar timing arrays (PTAs) suggests that the detection of nanohertz gravitational waves might be around the corner. However, in order to confidently attribute this red process to gravitational waves, one must observe the Hellings–Downs curve—the telltale angular correlation function associated with a gravitational-wave background. This effort is complicated by the complex modeling of pulsar noise. Without proper care, misspecified noise models can lead to false-positive detections. Background estimation using “quasi-resampling” methods such as sky scrambles and phase shifts, which use the data to characterize the noise, are therefore important tools for assessing significance. We investigate the ability of current PTA experiments to estimate their background with “quasi-independent” scrambles—characterized by a statistical “match” below the fiducial value: ∣ M ∣ < 0.1. We show that sky scrambling is affected by “saturation” after ${ \mathcal O }(10)$ quasi-independent realizations; subsequent scrambles are no longer quasi-independent. We show that phase scrambling saturates after ${ \mathcal O }(100)$ quasi-independent realizations. With so few independent scrambles, it is difficult to make reliable statements about the ≳5 σ tail of the null distribution of the detection statistic. We sketch out various methods by which one may increase the number of independent scrambles. We also consider an alternative approach, wherein one reframes the background estimation problem so that the significance is calculated using statistically dependent scrambles. The resulting p -value is in principle well defined, but may be susceptible to failure if assumptions about the data are incorrect.https://doi.org/10.3847/1538-4357/acee71Astronomy data analysisMillisecond pulsarsGravitational waves |
| spellingShingle | Valentina Di Marco Andrew Zic Matthew T. Miles Daniel J. Reardon Eric Thrane Ryan M. Shannon Toward Robust Detections of Nanohertz Gravitational Waves The Astrophysical Journal Astronomy data analysis Millisecond pulsars Gravitational waves |
| title | Toward Robust Detections of Nanohertz Gravitational Waves |
| title_full | Toward Robust Detections of Nanohertz Gravitational Waves |
| title_fullStr | Toward Robust Detections of Nanohertz Gravitational Waves |
| title_full_unstemmed | Toward Robust Detections of Nanohertz Gravitational Waves |
| title_short | Toward Robust Detections of Nanohertz Gravitational Waves |
| title_sort | toward robust detections of nanohertz gravitational waves |
| topic | Astronomy data analysis Millisecond pulsars Gravitational waves |
| url | https://doi.org/10.3847/1538-4357/acee71 |
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