The NANOGrav 15-Year Data Set

The NANOGrav 15-Year Data Set
Public release "v2" 2023/10/09

OVERVIEW
--------

This file contains "narrowband" and "wideband" TOAs and timing
solutions for the NANOGrav 15-year data set, covering data taken from
2004 to mid-2020 using Arecibo, the Green Bank Telescope (GBT), and the
Very Large Array (VLA) with ASP/GASP and PUPPI/GUPPI/YUPPI backend
instrumentation. The observations, data reduction, and analysis
procedures used to produce these data are described in detail in the
accompanying paper, "The NANOGrav 15-year Data Set: Observations and
Timing of 68 Millisecond Pulsars" (Agazie et al., 2023, ApJL 951 L9,
DOI 10.3847/2041-8213/acda9a, arXiv:2306.16217).

This release is available at Zenodo (DOI 10.5281/zenodo.8423265).

All *.par and *.tim files are ASCII and are formatted for use with
standard pulsar timing packages such as tempo2 and PINT, except for
profile template files which are FITS format (narrowband) or python
pickle files (wideband).

Correlation matrix files are available in three formats (*.txt, *.npz,
and *.hdf5). See "description.txt" in both the narrowband and wideband
./correlations subdirectories for more details about these files.

Questions about the contents of this data set can be addressed to Joe
Swiggum ([e-mail]) or [e-mail].

DIRECTORY AND FILE STRUCTURE (FURTHER DETAILS BELOW)
---------------------------------------------------

./README
This file.
./clock
Files for tracing observatory-measured TOAs to clock standards.
./narrowband
Directory containing the narrowband data set.
Details are provided in README.narrowband in that directory.
./wideband
Directory containing the wideband data set.
Details are provided in README.wideband in that directory.
./correlations
Directory containing the correlation matrix files for both the
narrowband and wideband data. Details are provided in the
/wideband/ and /narrowband/ subdirectories' description.txt
files.

SOFTWARE
--------

This data set requires up-to-date installations of PINT or tempo2.
Our original analysis used PINT v0.9.1 and tempo2 v2022.01.1. Up to date
versions of these packages, as well as usage information and
documentation can be found at the following repositories:

PINT https://github.com/nanograv/PINT
tempo2 https://bitbucket.org/psrsoft/tempo2

Note that we do not guarantee complete/correct functionality of these
timing models in the older original tempo software package.

Please also ensure that the clock files you are using cover the full
range of the data set. Using the provided clock files (see below)
will ensure this.

All models included here are based on a generalized least squares
(GLS) fit that includes a noise model with covariance between TOAs
(ECORR/jitter parameters, if narrowband; RNAMP/RNIDX red noise
parameters, if significant), as well as "traditional" EQUAD and EFAC
parameters. Additional EFAC parameters for the wideband DM measurements
are also included. All noise model parameters are included in the par
files.

CLOCK FILES
-----------

The clock files used for our analysis are provided in the clock/
subdirectory. While the standard files distributed with tempo and
tempo2 should be consistent with the clock files provided in the current
release at the time of writing, this may be a source of inconsistent
results in the future. Please see ./clock/README.clock directory for
installation instructions.

PLANNED REVISIONS
-----------------

The initial release of the data set contained all fundamental data
products needed for pulsar timing analysis: Times of arrival (.tim
files), timing models (.par files), standard template profiles,
clock correction files, and noise modeling MCMC chains. In v2,
parameter correlation matrices were added, as well as alternate versions
of timing model parameter files ("NoRedNoise" and "predictive"). A
future release will add a number of other useful derived products as
mentioned in the paper, including post-fit timing residuals and dispersion
measure time series.

CHANGE LOG
----------
2023/09/19
Addition of "NoRedNoise" and "predictive" par files, correlation
matrices, noise modeling chains (v2).
2023/07/01
Correction to tar.gz directory structure (v1.0.1).
2023/06/28
Initial public release (v1).

北美纳赫兹引力波天文台（NANOGrav）15年数据集
2023年10月9日发布的公开版本“v2”

概述
--------

本文件包含北美纳赫兹引力波天文台15年数据集的“窄带”与“宽带”脉冲到达时间（Time of Arrival, TOA）及计时解，涵盖2004年至2020年中期使用阿雷西博天文台（Arecibo）、绿岸望远镜（Green Bank Telescope, GBT）以及甚大阵（Very Large Array, VLA），搭配ASP/GASP与PUPPI/GUPPI/YUPPI后端仪器获取的观测数据。本次数据生成所采用的观测、数据约简与分析流程，已在配套论文《北美纳赫兹引力波天文台15年数据集：68颗毫秒脉冲星的观测与计时》（Agazie等，2023，《天体物理学杂志快报》（ApJL）951 L9，DOI:10.3847/2041-8213/acda9a，arXiv:2306.16217）中详细阐述。

本版本数据集已上传至Zenodo平台，DOI为10.5281/zenodo.8423265。

所有*.par与*.tim文件均为ASCII格式，适配tempo2与PINT等标准脉冲星计时软件包，轮廓模板文件除外：窄带模板为FITS格式，宽带模板为Python pickle文件。

相关矩阵文件提供三种格式：*.txt、*.npz与*.hdf5。如需了解这些文件的详细信息，请查阅窄带与宽带./correlations子目录下的description.txt文件。

若对本数据集内容有疑问，请联系Joe Swiggum（[e-mail]）或发送邮件至[e-mail]。

目录与文件结构（详见下文）
---------------------------------------------------

./README
本说明文件。
./clock
用于将天文台测量的TOA溯源至时钟标准的文件。
./narrowband
存储窄带数据集的目录。详细信息请参见该目录下的README.narrowband文件。
./wideband
存储宽带数据集的目录。详细信息请参见该目录下的README.wideband文件。
./correlations
存储窄带与宽带数据相关矩阵文件的目录。详细信息请参见两个子目录下的description.txt文件。

软件依赖
--------

本数据集需要使用最新版本的PINT或tempo2软件。本次原始分析采用的版本为PINT v0.9.1与tempo2 v2022.01.1。上述软件包的最新版本、使用说明与文档可在以下仓库获取：
PINT https://github.com/nanograv/PINT
tempo2 https://bitbucket.org/psrsoft/tempo2

请注意，我们无法保证旧版tempo软件包中此类计时模型的完整或正确功能。

请确保您使用的时钟文件覆盖数据集的完整时间范围，使用本数据集提供的时钟文件即可满足该要求。安装说明详见./clock/README.clock文件。

本数据集包含的所有模型均基于广义最小二乘（Generalized Least Squares, GLS）拟合，其中包含考虑TOA间协方差的噪声模型：若为窄带数据则包含ECORR/抖动参数；若红噪声显著则包含RNAMP/RNIDX红噪声参数，同时包含“传统”的EQUAD与EFAC参数。宽带色散测量还额外包含EFAC参数。所有噪声模型参数均已包含在par文件中。

时钟文件
-----------

本次分析使用的时钟文件已存放于clock/子目录中。尽管在本文撰写时，tempo与tempo2官方分发的标准时钟文件与本版本提供的时钟文件保持一致，但未来可能会出现结果不一致的情况。安装说明详见./clock/README.clock文件。

计划修订内容
-----------------

本数据集的初始版本包含了脉冲星计时分析所需的全部基础数据产品：到达时间文件（.tim）、计时模型文件（.par）、标准模板轮廓、时钟校正文件以及噪声建模马尔可夫链蒙特卡洛（Markov Chain Monte Carlo, MCMC）链。在v2版本中，我们新增了参数相关矩阵，以及计时模型参数文件的两个变体：“NoRedNoise”与“predictive”版本。未来的版本还将新增论文中提及的其他多种实用衍生产品，包括拟合后计时残差与色散测量时间序列。

更新日志
----------
2023/09/19
新增“NoRedNoise”与“predictive”格式的par文件、相关矩阵以及噪声建模链（v2版本）。
2023/07/01
修正tar.gz压缩包的目录结构（v1.0.1）。
2023/06/28
首次公开发布（v1版本）。