NANOGrav 15-Year Narrowband Dataset

• The NANOGrav 15-year narrowband dataset is a public release featuring sub-banded TOAs and timing models for 68 millisecond pulsars observed over up to 16 years.
• It uses a traditional PTA narrowband workflow that measures a separate TOA for each frequency channel and models dispersion effects later, forming the basis for both single-pulsar and PTA studies.
• The dataset underpins advanced research including customized chromatic-noise modeling and stochastic gravitational-wave background inference, supported by full software reproducibility.

Searching arXiv for papers on the NANOGrav 15-year narrowband dataset and closely related analyses. The NANOGrav 15-year narrowband dataset is the narrowband timing component of NANOGrav’s fifth public data release, comprising channelized or sub-banded time-of-arrival measurements and corresponding timing models for 68 millisecond pulsars observed with the Arecibo Observatory, the Green Bank Telescope, and the Very Large Array between 327 MHz and 3 GHz, with baselines reaching nearly 16 years for some sources. In this release, “narrowband” denotes the traditional PTA workflow in which a separate TOA is measured for each frequency channel or subband and dispersion-related chromaticity is modeled later in the timing analysis, rather than the wideband workflow in which a single TOA and a DM value are jointly measured for a full receiver band. Subsequent NANOGrav literature uses these narrowband products both directly, in single-pulsar timing and event searches, and indirectly, as the observational basis for 67-pulsar PTA analyses restricted to sources with timing baselines exceeding three years (Agazie et al., 2023, Dey et al., 25 Jul 2025).

1. Release definition and archival scope

The narrowband dataset is part of a release that added 21 MSPs to the previous 12.5-year data set and extended the timing baselines of the 47 previously monitored pulsars by about 2.9 additional years. It was released together with narrowband TOA files (*.tim), timing-model parameter files (*.par), configuration files (*.yaml), TOA files with excision flags applied (*excise.tim), noise-model chains and parameter files, DMX time series (*dmxparse*.[out](https://www.emergentmind.com/topics/outer-automorphism-out)), telescope clock offset measurements, and fit-parameter correlation matrices in text, NumPy (*.npz), and HDF5 (*.hdf5) formats. The release is hosted at data.nanograv.org and preserved on Zenodo at doi:10.5281/zenodo.7967585; it was accompanied, for the first time, by a full suite of software to reproduce reduction, analysis, and results, including pint_pal and the nanopipe reduction pipeline (Agazie et al., 2023).

Although the timing release contains 68 MSPs, much of the PTA stochastic-background literature built on it uses a 67-pulsar subset with baselines longer than three years. In that 67-pulsar subset, the interval between the first and last TOAs is 16.03 years. This dual usage is standard in the 15-year literature: the narrowband release is the data product, whereas the common-spectrum and correlation analyses often operate on the 67-pulsar PTA subset derived from it (Agazie et al., 2023, Agazie et al., 2024).

Property	Value
Release status	Fifth public data release
Timing-release sample	68 MSPs
Common PTA stochastic-analysis sample	67 pulsars with timing baselines $>3$ years
Observing facilities	Arecibo Observatory, Green Bank Telescope, Very Large Array
Radio-frequency range	327 MHz to 3 GHz
Final narrowband TOAs	676,465
Wideband TOAs	20,290

The release also established that the narrowband data set, not the wideband product, underpinned the reported 15-year evidence for a stochastic gravitational-wave background. The wideband data set was retained mainly for method development and some preliminary mass calculations, whereas the narrowband product remained the primary PTA-analysis data set (Agazie et al., 2023).

2. Observations, instrumentation, and construction of narrowband TOAs

The observing program used Arecibo, GBT, and VLA, with most sources observed approximately monthly: roughly every three weeks at Arecibo and every four weeks at GBT and VLA, plus higher-cadence campaigns for six especially high-precision pulsars. ASP at Arecibo and GASP at GBT were used for about the first six years with 64 MHz bandwidth; later, PUPPI at Arecibo and GUPPI at GBT increased usable bandwidths up to 800 MHz, while VLA observations used YUPPI throughout. Folded raw data consist of full-Stokes pulse profiles with 2048 phase bins, frequency resolution of 4 MHz for ASP/GASP, about 1.5 MHz for GUPPI/PUPPI, and 1 MHz for YUPPI, with subintegrations of 1 s for some PUPPI 1.4/2.1 GHz modes and 10 s otherwise (Agazie et al., 2023).

Narrowband TOA generation followed a specific reduction sequence. Known bad or corrupted files were removed first. A dedicated correction was then applied for interleaved-ADC artifacts in the UPPI backends, which otherwise appear as negatively dispersed pulses. Standard RFI excision and calibration followed, including excision of RFI from calibration files. At the start of each pulsar observation, a pulsed noise diode was injected for amplitude calibration; for GUPPI/PUPPI, the noise-diode scale was converted approximately monthly into physical flux-density units using continuum calibrators, whereas YUPPI/VLA data were left scaled relative to the noise-diode power. For narrowband timing, cleaned calibrated profiles were frequency-scrunched into channels of 1.6 to 32 MHz for UPPI data, left at native 4 MHz resolution for ASP/GASP, and time-averaged into subintegrations up to 30 minutes, or no more than 2.5% of the orbital period for very short binaries. All narrowband templates were regenerated from UPPI data by iteratively aligning, S/N-weighting, summing, and denoising profiles with wavelet decomposition and thresholding, after which all narrowband TOAs, including older ASP/GASP data, were measured against that template set (Agazie et al., 2023).

NG15 also changed how TOA uncertainties and provenance were handled. Instead of relying only on a simple approximation, the timing pipeline numerically integrated the TOA probability distribution to avoid underestimating uncertainties for low-S/N TOAs. Final TOA lines include a version tag and git hash linking each TOA to a specific git commit in the TOA-generation repository, so that the provenance of every narrowband TOA is reconstructible (Agazie et al., 2023).

The final narrowband data set contains 676,465 TOAs, with 34.6% of originally generated narrowband TOAs removed. The largest removals were the -cut snr cut, which removed 255,118 narrowband TOAs with S/N $<8$, and the -cut badrange cut, which removed 56,658 Arecibo TOAs from MJDs 57984–58447 because of a malfunctioning local oscillator whose reference frequency shifted by 5–10 MHz and sometimes wandered on sub-millisecond timescales. Additional removals included -cut dmx of 13,006 TOAs with insufficient frequency leverage, -cut eclipsing of 4,551 TOAs near superior conjunction, automated Gibbs-sampler outlier removals via enterprise_outliers, epoch-drop removals by an $F$-test, and smaller manual cuts for bad TOAs and bad files (Agazie et al., 2023).

3. Timing architecture, DMX, and narrowband noise modeling

In the narrowband paradigm, dispersion and other chromatic effects are modeled after TOA formation. The release states the distinction explicitly: in the narrowband approach, a separate TOA is measured for each frequency channel, and dispersion measure is fit to those TOAs along with other timing parameters; in the wideband approach, a single TOA and DM value are measured jointly for the full receiver band using a frequency-dependent portrait (Agazie et al., 2023).

The central chromatic timing construct in the release is DMX, a piecewise-constant model of time-variable DM. DMX windows were chosen according to observing system: 0.5-day windows for pulsars with Arecibo observations, 15-day windows for GASP-only GBT cases, and 6.5-day windows for GUPPI/YUPPI GBT/VLA data. A DMX parameter was fit only if the frequency coverage in that window satisfied $\nu_{\max}/\nu_{\min} > 1.1$; otherwise the corresponding TOAs were excised. For low-ecliptic-latitude lines of sight, a toy solar-wind model $n_e(r)=n_0(r/r_0)^{-2}$ with $n_0=5~\mathrm{cm}^{-3}$ at $r_0=1$ au was used only to decide whether DMX windows should be split more finely. If the projected solar-wind-induced timing variation across a window exceeded 100 ns, the DMX windows were split to 0.5 day. The toy solar-wind model was not included in the timing model itself; fitted DMX parameters absorb both interstellar and solar-wind contributions (Agazie et al., 2023).

Final narrowband timing models include six broad parameter classes: spin, astrometry, binary parameters, DM parameters, FD parameters, and jumps. For every pulsar, five astrometric parameters are fit. For 50 binary MSPs, one of ELL1, ELL1H, BT, DD, or DDK is adopted as appropriate. Additional parameters such as $\dot{P}_{\mathrm b}$, $\dot{\omega}$, $\dot{x}$, Shapiro-delay terms, FD terms, and higher-order orbital-frequency derivatives are included only if the nested-model $<8$0-statistic satisfies $<8$1, approximately $<8$2 (Agazie et al., 2023).

White noise is described by per-system EFAC, EQUAD, and ECORR parameters, with covariance

$<8$3

where $<8$4 is block-diagonal within observing epochs. Red noise is modeled phenomenologically as a stationary Gaussian process with a power-law spectrum. Timing and noise inference are iterated: an initial timing fit is followed by a Bayesian noise analysis with enterprise, then a refit of the timing model, and repetition until timing and noise solutions stabilize. All NG15 fits use the JPL DE440 solar-system ephemeris and the TT(BIPM2019) timescale, and the release formalized a software transition from TEMPO-centered workflows to a Python-based PINT pipeline driven by YAML configuration files and standardized notebooks (Agazie et al., 2023).

This narrowband architecture remained the reference point for later chromatic-noise studies. A six-pulsar comparison of NANOGrav and EPTA-inspired chromatic Gaussian-process models, for example, explicitly used the NANOGrav 15-year narrowband TOAs derived from many subbands of the radio observing bands and demonstrated that altered chromatic modeling can move power between chromatic and achromatic channels in a way that is directly relevant for PTA gravitational-wave inference (Larsen et al., 2024).

4. Frequency-resolved structure and “narrowband” behavior within the 15-year data

The narrowband release enabled later analyses of frequency-localized structure, but several of the most cited 15-year studies explicitly do not operate on a separate released “narrowband dataset” product. Instead, they examine narrowband behavior inside the standard 15-year PTA analysis. A prominent example is the harmonic analysis of pulsar angular correlations, which found that when Legendre multipoles with $<8$5 are included, only the quadrupole is significantly detected, with amplitude consistent with general relativity and a Bayes factor of 200 relative to $<8$6. When monopole and dipole terms are added through free-spectrum models, however, the Bayes factor evidence for quadrupole correlations decreases by more than an order of magnitude because of evidence for a monopolar signal at approximately 4 nHz, localized in the second Fourier bin $<8$7 nHz (Agazie et al., 2024).

A second line of work interprets the 15-year free-spectrum in terms of SMBHB discreteness rather than an exactly smooth $<8$8 strain law. In that framework, the PTA Fourier frequencies are $<8$9 with $F$0. The analysis identified two mild excursions: at 2 nHz the 15-year residual spectrum lies below discrete-SMBHB realizations with $F$1 to $F$2 ($F$3 to $F$4), and at 16 nHz it lies above them with $F$5 to $F$6 ($F$7 to $F$8), depending on how weak-signal posterior tails are treated. The same work found that the expected number of SMBHBs contributing to a PTA frequency bin drops by three orders of magnitude, from $F$9 at 2 nHz to $\nu_{\max}/\nu_{\min} > 1.1$0 at 20 nHz, and inferred a representative break frequency $\nu_{\max}/\nu_{\min} > 1.1$1 (Agazie et al., 2024).

Posterior predictive checks provide the complementary conclusion that the 15-year spectral structure is not extreme under the standard stochastic-background model. Using 67 pulsars timed for more than three years and a 16.03-year span, posterior predictive replications recovered Hellings–Downs correlations at significance levels consistent with those measured in the real data, gave a posterior-predictive optimal-statistic significance of $\nu_{\max}/\nu_{\min} > 1.1$2, and found no evidence that any individual frequency bin deviates significantly from the power-law model for either intrinsic pulsar noise or the GW background. The same study states that some “spikes” are evident in spectral plots, but they are not statistically significant in the replicated population (Agazie et al., 2024).

These results establish an important distinction. The release is narrowband in its TOA construction, but frequency-localized inference in the 15-year literature can refer to at least three different things: sub-banded TOA timing; free-spectrum common-process inference in Fourier bins; and model-specific interpretations of individual bins or breaks. The literature does not collapse these uses into a single standalone “narrowband file” or “narrowband likelihood” (Agazie et al., 2024, Agazie et al., 2024, Agazie et al., 2024).

5. Single-pulsar applications, event searches, and diagnostic reanalyses

The narrowband dataset has also been used directly in single-pulsar and event-based analyses. A clear example is the search for hyperbolic gravitational scattering by free-floating objects. That work uses the NANOGrav 15-year narrowband dataset as its full observational basis, describing it as a 68-MSP sample with sub-banded TOAs and best-fit timing models, a maximum data span of 15.9 years for some pulsars, observations from 327 MHz to 3 GHz, monthly cadence for most pulsars, DE440, TT(BIPM2019), and DMX corrections. No statistically significant events were detected, but the non-detection yielded the first pulsar-timing upper limits on free-floating-object number density. For Jupiter-mass objects, individual-pulsar upper limits range from $\nu_{\max}/\nu_{\min} > 1.1$3 to $\nu_{\max}/\nu_{\min} > 1.1$4, and the combined 68-pulsar upper limit is $\nu_{\max}/\nu_{\min} > 1.1$5 (Dey et al., 25 Jul 2025).

A second example is the pulsar-specific reanalysis of PSR J1455−3330. That study argues that the standard DMX treatment used for this narrowband timing analysis is over-parameterized for this pulsar. Replacing 157 piecewise-constant DM parameters with a simpler physical model consisting of a fixed solar-wind density $\nu_{\max}/\nu_{\min} > 1.1$6 plus a linear DM trend changes the timing parallax from $\nu_{\max}/\nu_{\min} > 1.1$7 to $\nu_{\max}/\nu_{\min} > 1.1$8, makes red noise significant, and renders that red noise consistent with the common signal found for other pulsars. The authors also report that the revised model improves the single-pulsar gravitational-wave sensitivity curve at all frequencies (Lam et al., 4 Jun 2025).

The profile-domain narrowband products have proved equally important. A pulse-shape analysis of nine NANOGrav pulsars used the .ff profile products, formed 100 MHz subaveraged pulse profiles, and applied principal component analysis to seven pulsars from the 15-year dataset plus two with added forthcoming-20-year data. It recovered the three known pulse-shape change events in PSR J1713+0747 and the known event in PSR J1643−1224, identified additional high-ranked candidates in J0030+0451, B1937+21, and J1600−3053, and showed that some timing anomalies or DMX anomalies can instead reflect pulse-shape variability. This suggests that the narrowband profile products, not only the TOA files, are part of the practical content of the 15-year narrowband release (Jacobson-Bell et al., 7 Apr 2026).

6. Customized chromatic noise models and downstream GW inference

The most substantial post-release reworking of the narrowband data concerns chromatic noise. A six-pulsar study comparing NANOGrav-style DM models with EPTA DR2-inspired chromatic Gaussian-process models used the NANOGrav 15-year narrowband TOAs for PSRs J0613−0200, J1012+5307, J1600−3053, J1713+0747, J1744−1134, and J1909−3744. It found that the choice of chromatic noise model noticeably affects achromatic red-noise properties, most dramatically for J1713+0747, where the achromatic red-noise amplitude changes from $\nu_{\max}/\nu_{\min} > 1.1$9 under DMX to $n_e(r)=n_0(r/r_0)^{-2}$0 under a custom model, while the spectral index changes from $n_e(r)=n_0(r/r_0)^{-2}$1 to $n_e(r)=n_0(r/r_0)^{-2}$2. The same study found that the second transient event in J1713+0747 is not a pure $n_e(r)=n_0(r/r_0)^{-2}$3 DM event, with $n_e(r)=n_0(r/r_0)^{-2}$4 in NANOGrav data (Larsen et al., 2024).

That six-pulsar result was generalized to 67 pulsars in the customized-chromatic-models study. Starting from the standard NG15 data and replacing DMX with pulsar-by-pulsar customized Gaussian processes plus deterministic DM, DM1, and DM2 terms, that analysis found evidence for non-dispersive chromatic delays in 21 out of 67 pulsars, significant impacts on achromatic-noise inference in 19 out of 67 pulsars, and significant band-dependent DM variations in five pulsars: J1012+5307, J1125+7819, J1643−1224, J1747−4036, and J1802−2124. It also inferred the solar-wind electron density over the course of $n_e(r)=n_0(r/r_0)^{-2}$5 solar cycles and concluded that refined chromatic modeling is essential to enhance the sensitivity and accuracy of low-frequency gravitational-wave searches (Larsen et al., 26 Jun 2026).

When these customized chromatic-noise models were propagated into full PTA analyses, the consequences were substantial. The reanalysis of the 15-year dataset with CNMs reported a Bayes factor of $n_e(r)=n_0(r/r_0)^{-2}$6 for Hellings–Downs correlations over a common uncorrelated red-noise process using a power-law model with 14 Fourier modes, an increase of about $n_e(r)=n_0(r/r_0)^{-2}$7 relative to the original DMX-based result. Under fixed $n_e(r)=n_0(r/r_0)^{-2}$8, the inferred power-law GWB amplitude decreased to $n_e(r)=n_0(r/r_0)^{-2}$9; in a varied-$n_0=5~\mathrm{cm}^{-3}$0 analysis, the spectral index increased to $n_0=5~\mathrm{cm}^{-3}$1. The same work reports a $n_0=5~\mathrm{cm}^{-3}$2 larger CW detection volume, reduced evidence for a scalar-transverse mode of gravity, and interprets the previously discussed 16 nHz feature as noise-model dependent rather than as a robust astrophysical excess (Agarwal et al., 26 Jun 2026).

7. Interpretive scope, robustness checks, and common misconceptions

A recurring misconception in the post-2023 literature is to equate every analysis of the 15-year common-spectrum signal with a “narrowband dataset” analysis. The leave-one-pulsar-out internal-consistency study is illustrative. It uses the 67-pulsar 15-year dataset and recomputes noise-marginalized optimal statistics as pulsars are removed one by one, but it explicitly states that it is not a narrowband analysis, does not decompose the signal frequency-bin by frequency-bin, and does not test whether the signal is concentrated in one or a few spectral bins. Its role is instead to show that visually surprising features in the removal sequence, such as the 29% drop in HD S/N when PSR J1909−3744 is removed first, are not statistically unusual relative to SGWB simulations (Agazie et al., 2024).

The same distinction applies to cosmological reinterpretations. The pre-big-bang-cosmology study asks whether the NANOGrav 15-year signal can be fit by a broadband piecewise PBB spectrum using NANOGrav-derived posterior samples for the GW energy density in 14 frequency bins spanning $n_0=5~\mathrm{cm}^{-3}$3 to $n_0=5~\mathrm{cm}^{-3}$4; it explicitly states that it does not analyze a dedicated narrowband search product. Its preferred dilaton parameter is $n_0=5~\mathrm{cm}^{-3}$5, outside the theoretically allowed range $n_0=5~\mathrm{cm}^{-3}$6, and it finds a Bayes factor of about 468 in favor of a simple power law over the PBB template (Tan et al., 2024).

Two other widely cited alternatives operate in the same broadband or peaked-spectrum register. The cosmic-superstring reinterpretation fits the PTA-band stochastic signal with $n_0=5~\mathrm{cm}^{-3}$7 and $n_0=5~\mathrm{cm}^{-3}$8, but it is not a narrowband search; it treats the 15-year result as the low-frequency segment of a broadband SGWB (Ellis et al., 2023). The ultra-slow-roll inflation analysis instead fits a peaked scalar-induced SGWB, relevant to frequency-localized interpretations but still not a line search, and reports Bayes factors $n_0=5~\mathrm{cm}^{-3}$9 for USR alone and $r_0=1$0 for USR plus SMBHBs, while also noting that with astrophysically motivated priors the USR and SMBHB models fit the 15-year data equally well (Mu et al., 2023).

This suggests a precise usage. Properly speaking, the NANOGrav 15-year narrowband dataset is the public sub-banded TOA and timing-model release, together with its associated DMX, noise, and profile-domain products. Many later papers that discuss frequency-localized behavior, free spectra, or model refits are instead using compressed stochastic-background inferences derived from that release. The distinction is methodological rather than terminological, but it is central for interpreting what any given “narrowband” statement in the 15-year literature actually denotes.