The NANOGrav 15-year Data Set: Observations and Timing of 68 Millisecond Pulsars

We present observations and timing analyses of 68 millisecond pulsars (MSPs) comprising the 15-year 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. 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 three years, now spanning nearly 16 years 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 gravitational-wave background.Comment: 90 pages, 74 figures, 6 tables; published in Astrophysical Journal Letters as part of Focus on NANOGrav's 15-year Data Set and the Gravitational Wave Background. For questions or comments, please email [email protected]

ARCC@UWM: The Search for Pulsars

Pulsars are dense, evolved stars, called neutron stars, that rotate with an extremely reliable period and emit an intense beam of radiation that can be seen from Earth in radio frequencies, appearing similar to a lighthouse pulse. This unique signal allows for novel ways to observe the universe, the most exciting of which is the potential to detect previously undiscovered gravitational waves, giving further evidence to Einstein’s theory of relativity. We currently know of over 2000 pulsars, of which around 10% have frequencies of ~500 Hz and are known as millisecond pulsars. However, methods for using pulsars to detect gravitational waves become more sensitive with every additional millisecond pulsar, so active searches for new pulsars are very important. By remotely observing from UWM with two of the world’s largest radio telescopes, the Arecibo telescope in Puerto Rico and the Green Bank telescope in West Virginia, students discover, confirm, and study these incredible neutron stars while collaborating with scientists around the globe

Searching and Solving Pulsar Puzzles

Pulsars are a type of evolved star that are extremely dense and rotate with an extremely reliable period producing an intense beam of radiation, similar to a lighthouse pulse. This unique pulse allows for novel ways to study the universe, the most exciting of which being the potential to detect low frequency gravitational waves. The Arecibo Remote Command Center (ARCC) was formed as a way for undergraduate students to be involved in the search for new pulsars. Students remotely observe from UWM with two of the world’s largest radio telescopes, the Arecibo Observatory in Puerto Rico, and the Green Bank Telescope in West Virginia, and analyze the resulting data to discover and study these incredible neutron stars. Once a pulsar is discovered, it must be timed regularly in order to determine various parameters describing the system with astounding precision. These timing proposals can require ~1000 hours per year of observing, which undergraduates can easily do in the place of faculty and senior researchers. Students are also learning to “solve” pulsars themselves, an effort which will likely lead to authorship on a refereed journal paper. UWM students collaborate with students at a number of other US institutions, including the University of Texas - Rio Grande Valley, and Franklin & Marshall College, and with researchers across the globe

ARCC@UWM: Searching and Solving Pulsar Puzzles

Pulsars are a type of evolved star that are extremely dense and rotate with an extremely reliable period producing an intense beam of radiation, similar to a lighthouse pulse. This unique pulse allows for novel ways to study the universe, the most exciting of which being the potential to detect previously undiscovered gravitational waves giving further evidence to Einstein\u27s theory of relativity. The Arecibo Remote Command Center (ARCC) was formed as a way for undergraduate students to be involved in the search for new pulsars. Students remotely observe from UWM with two of the world\u27s largest radio telescopes, Arecibo Observatory in Puerto Rico, and the Green Bank Telescope in West Virginia, and analyze the resulting data to discover and study these incredible neutron stars. Students at UWM also collaborate with students at a number of other US institutions, including the University of Texas - Rio Grande Valley, Kenyon College, Hillsdale College, Franklin & Marshall College, Swarthmore College, and with researchers across the globe

The NANOGrav 12.5 yr Data Set: Observations and narrowband timing of 47 millisecond pulsars

We present time-of-arrival (TOA) measurements and timing models of 47 millisecond pulsars observed from 2004 to 2017 at the Arecibo Observatory and the Green Bank Telescope by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). The observing cadence was three to four weeks for most pulsars over most of this time span, with weekly observations of six sources. These data were collected for use in low-frequency gravitational wave searches and for other astrophysical purposes. We detail our observational methods and present a set of TOA measurements, based on "narrowband"analysis, in which many TOAs are calculated within narrow radio-frequency bands for data collected simultaneously across a wide bandwidth. A separate set of "wideband"TOAs will be presented in a companion paper. We detail a number of methodological changes, compared to our previous work, which yield a cleaner and more uniformly processed data set. Our timing models include several new astrometric and binary pulsar measurements, including previously unpublished values for the parallaxes of PSRs J1832-0836 and J2322+2057, the secular derivatives of the projected semimajor orbital axes of PSRs J0613-0200 and J2229+2643, and the first detection of the Shapiro delay in PSR J2145-0750. We report detectable levels of red noise in the time series for 14 pulsars. As a check on timing model reliability, we investigate the stability of astrometric parameters across data sets of different lengths. We also report flux density measurements for all pulsars observed. Searches for stochastic and continuous gravitational waves using these data will be subjects of forthcoming publications

The NANOGrav 12.5 yr Data Set: Wideband Timing of 47 Millisecond Pulsars

We present a new analysis of the profile data from the 47 millisecond pulsars comprising the 12.5 yr data set of the North American Nanohertz Observatory for Gravitational Waves, which is presented in a parallel paper (Alam et al., hereafter NG12.5). Our reprocessing is performed using "wideband"timing methods, which use frequency-dependent template profiles, simultaneous time-of-arrival (TOA) and dispersion measure (DM) measurements from broadband observations, and novel analysis techniques. In particular, the wideband DM measurements are used to constrain the DM portion of the timing model. We compare the ensemble timing results to those in NG12.5 by examining the timing residuals, timing models, and noise-model components. There is a remarkable level of agreement across all metrics considered. Our best-timed pulsars produce encouragingly similar results to those from NG12.5. In certain cases, such as high-DM pulsars with profile broadening or sources that are weak and scintillating, wideband timing techniques prove to be beneficial, leading to more precise timing model parameters by 10%-15%. The high-precision, multiband measurements of several pulsars indicate frequency-dependent DMs. Compared to the narrowband analysis in NG12.5, the TOA volume is reduced by a factor of 33, which may ultimately facilitate computational speed-ups for complex pulsar timing array analyses. This first wideband pulsar timing data set is a stepping stone, and its consistent results with NG12.5 assure us that such data sets are appropriate for gravitational wave analyses