Glossary

This typically refers to the autocorrelation of the dynamic spectrum with itself.

Accumulation of material onto an object.

The group of external experts tasked with providing guidance on the directions the collaboration should take in the future.

A theory of gravitation that deviates slightly from Einstein’s General Theory of Relativity (GR).

The fraction of power lost in your receiving element due to electronic (“ohmic”) losses in the element.

Related to the system equivalent flux density, it is the K/Jy conversion.

For receiving antennas, a map or function describing the dependence of the sensitivity of a telescope on the angle of the incoming radiation.

The ratio of the effective area of a telescope to the geometric area.

Arecibo Signal Processor / Green Bank Astronomical Signal Processor, used historically.

Measurements of the position and motion of objects.

An online registry of code meant for astronomy research.

The group in charge of drawing astrophysical inferences from our gravitational wave analyses. They are also in charge of combining information from electromagnetic counterparts to gravitational waves.

The data recording system that processes the radio signal.

The size of the continuous range of frequencies over which our data are taken, calculated as the difference between the the highest and lowest frequencies.

Nyquist-sampled, band-limited data, sometimes called “voltage data”. 

Comparison of the degree of belief in two hypotheses.

Software used to statistically account for the uncertainties in the position of the Solar System Barycenter on our gravitational-wave analyses.

A result of probability theory. Posterior = Likelihood × Prior / Evidence

The component of the timing model that describes the orbit of the pulsar and its companion (e.g., a white dwarf).

Gravitational wave memory is a non-oscillatory, permanent change to spacetime caused by GWs. A burst of oscillatory GWs (for example from SMBHB merger) will produce GW memory. The louder (more energetic) the burst, the bigger the GW memory amplitude. PTAs can detect GW memory even when the accompanying oscillatory burst is outside of their sensitive frequency range.

A Canadian interferometer array based on cylindrical telescopes; science carried out there include pulsar timing and Fast Radio Burst (FRB) detections.

A small frequency range in which you measure a signal.

A modification to be made to the recorded local time to get the “true” time.

Akin to a Virtual Machine, this is a lightweight, packaged set of software which can include familiar tools such as Bash, gcc, Python as well as application code.

A single SMBHB system that produces GWs.

Cosmic strings are linear topological defects that can form in the early universe as a result of symmetry-breaking phase transitions.

A measure of the joint variability of two variables, cf: variance.

A term used to describe infrastructure managing a distributed computing environment over the internet (which is a series of tubes).

The group in charge of implementing hardware and software solutions to various NANOGrav activities.

A method of analyzing random signals in data that contain periodicities, such as is true with pulses from a pulsar.

Removing the effect dispersion on our pulses.

See Equatorial Coordinates.

The group in charge of running the various gravitational-wave detection analyses. 

The fact that the rotational velocity ω is not constant along a radial line drawn through the galactic disk.

A model for dispersion measure in which we assume that the DM is constant over very small times (e.g., a few days).

A particular containerization technology (see Container).

A document repository for NANOGrav, (NANOGrav login currently required).

A method of determining which pulsars contribute significantly to a GW search by removing individual pulsars one at a time.

A Digital Signal Processing package for pulsar astronomy. 

The pulse intensity as a function of time and frequency.

The group in charge of developing and executing outreach efforts, largely towards the public but also towards other scientists not affiliated with NANOGrav.

Enhanced Numerical Toolkit Enabling Robust PulsaR Inference SuitE.

A generic term meaning the model for the orbit of an object.

One “observation”.

For astronomical bodies, this is typically expressed in terms of how the mass of an object is related to the radius of the object (more fundamentally, the pressure and density). 

The group in charge of developing new strategies to advancing equity, diversity, and inclusion within the collaboration. 

Sometimes called Bayesian Evidence or Marginal Likelihood.

Events seen in timeseries of fluxes, arrival times, scintillation parameters (e.g., scintillation bandwidth/ scintillation timescale), etc. 

A short duration (~milliseconds), very energetic flash of radio emission.

The part of instrumentation which channels incoming radio waves to the rest of the instrument, terminating at the frontend.

A space-based telescope which observes in the gamma ray portion of the electromagnetic spectrum. 

A filter array which produces channelized data made up of frequency subbands, often called filterbank data.

The problem of how SMBHB’s separation gets smaller than about a parsec, into the separation regime of about a tenth of a parsec or smaller, where gravitational waves can drive the eventual coalescence of the binary. 

Dividing up a time series into fixed time periods (say, the period of a pulsar) and then aligning them all and adding all the signals (so that the nth sample in each period is added together.

A red noise model that makes no assumption about the shape of the red noise power spectral density.

The International Telecommunications Union helps decide which radio frequency ranges are used for what purposes. 

The instrument that receives (the “receiver”) the radio signal, and includes filters and mixer.

See Antenna Gain.

A coordinate system in the reference frame of the Galactic plane.

A method of smoothly modeling a series of data.

Einstein’s geometrical description of gravity.

An artifact in data from pulsar backends due to interleaved samplers (analog-to-digital converters, or ADCs) that are not perfectly synced and have different gains. 

In some pulsars, we see very bright, very sharp emission that is not necessarily at the usual rotational phase of the pulses we typically see.

A gravitationally-bound star cluster orbits a galaxy’s center.

The stretching and compressing of spacetime, which propagates as a wave and are caused by accelerations of very compact, massive ob jects (including SMBHs orbiting each other).

One of the main pulsar surveys performed at the Green Bank Observatory.

Green Bank Ultimate Pulsar Processing Instrument / Puerto Rican Ultimate Pulsar Processing Instrument.

Non-oscillatory GWs that cause a permanent change to spacetime as they pass by.

If the pulsars are not exactly in the same direction in the sky, but are separated by some angle, then the Hellings and Downs curve describes how correlated we expect the arrival times to be as a function of that angle.

The international consortium of other pulsar timing array consortia.

A National-Science-Foundation-funded grant to support international research opportunities for students.

The material of particles, gas, and dust, between stars.

Seen in the arrival times for PSR J1713+0747, we have detected two rapid changes in the TOAs due to some structure in the interstellar medium.

A unit of flux density equal to 10⁻²⁶ W m⁻² Hz⁻¹.

While the average pulse shape of a pulsar is very stable, each single pulse varies; this is jitter.

A time (or phase) offset between TOAs, for example between two backend recording devices or between two telescopes where the absolute time difference is not known.

The components of the binary model that describe the first-order motion of a pulsar and companion (e.g., a white dwarf) orbiting around each other.

A description of the type of turbulence seen.

A frequency range covering 1400 MHz, or more notable, 1420 MHz where atomic hydrogen is seen.

The probability that you would observe the data you did, assuming your hypothesis is true.

The group of senior personnel within NANOGrav whose task is to lead collaboration members, plan future activities for the collaboration, and more. 

Calculates samples from the posterior distribution in a way that only uses the likelihood and prior functions. 

A plot of the primary mass versus companion mass. 

To obtain the best estimate of the parameters that describe a model, we calculate the likelihood and for whatever values of the parameters that maximize the likelihood, we say that those are the best estimates.

A National-Science-Foundation-funded program to support “mid-scale” programs in astronomy within a cost range of up to tens of millions of dollars. 

A pulsar which has been “spun up” by accumulating material from a companion star. 

A representation of how the receiver alters the intrinsic Stokes parameters and thus must be corrected for.

Astronomy conducted using more than one messenger carrying information from astrophysical sources, where messengers include photons, gravitational waves and particles such as neutrinos.

A pipeline script for taking raw pulse profiles, applying calibrations, cross-correlating with templates, then outputting TOAs.

A stellar remnant left behind by higher-mass stars.

An X-ray observatory attached to the International Space Station.

The group in charge for characterizing the noise properties of each pulsar line of sight.

In addition to the timing model, we incorporate a description of all of our sources on uncertainty into our modeling.

The temperature of a hypothetical resistor that would cause an equivalent amount of noise to that which is observed.

A web-accessible interface which allows code to be written in the web page and then run through an interpreter, with the subsequent output displayed.  

Generically, this is any analysis (systematic or otherwise) in which one looks for discrepant data points.

The spin period vs spin period derivative (how quickly the pulsars spin rate is slowing due to loss of luminous energy) diagram shows the different classes of neutron stars.

A text file that contains all of the relevant parameters/values describing the pulsar’s spin, spindown, position, motion on the sky (proper motion), distance/parallax, binary Keplerian and post-Keplerian elements if relevant, etc.

The angle of the receiver feed with respect to the plane of polarization. 

A National-Science-Foundation-funded grant to support international activities and partnerships.

It is theorized that when the Universe cooled, cracks or “defects” would have happened in spacetime that should be detectable through their gravitational radiation.

A National-Science-Foundation-funded organization designated to explore hard problems at the frontiers of physics.

PINT Is Not Tempo.

A region of plasma which causes bulk refractive deflection of radiation propagating through it.

The angle of the electric field of an electromagnetic wave with respect to the incidence angle.

Polarized pulsar emission is altered as it passes through the signal path that measures it, and so we must
correct for these alterations (“calibrate”).  

The angle measured clockwise from the North Celestial Pole (see Equatorial Coordinates).

The components of the binary model that describe the second-order motion of a pulsar and companion (e.g., a white dwarf) orbiting around each other, due not from simple Newtonian gravity but from Einstein’s General Relativity.

The probability that a hypothesis is true AFTER you have made a measurement.

The power in a data series as a function of frequency.

A method of analyzing signals with very steep power spectra.

A suite of software for pulsar-searching.

The probability that a hypothesis is true before you make a measurement. 

The pulse shape looks different from one frequency to the next and thus we have to make sure to account for this when creating TOAs, and we now parameterize them with FD parameters.

The ATNF (Australia Telescope National Facility) Pulsar Catalogue.

A set of powerful tools, written in C++, for pulsar data analysis.

Data files that contain our pulse profiles as a function of time, polarization, frequency, and phase (search data are also contained within PSRFITS files).

A rapidly rotating neutron star emitting electromagnetic radiation in a beam which rotates with the neutron star, causing pulsed energy received at the earth at the rotation period of the neutron star.

A survey conducted with the seven-beam Arecibo L-Band Feed Array (ALFA) at the Arecibo Observatory, at frequencies near 1.4 GHz.

A program to involve high school students in looking at plots of pulsar candidates. 

A software package that does an end-to-end simulation of the pulse emission, the propagation of the pulses through the interstellar medium, and the reception of the emission at the telescope.

The 2D pulse template used in wideband timing, which accounts for profile evolution across the entire band.

The pulse shape, or alternatively the intensity of the pulse as a function of phase.

A canonical pulse profile for a given pulsar in a given frequency band. 

A software package written entirely in the Python programming language, using only basic packages, with overlapping functionality with PSRCHIVE so that for many applications it can be used as an alternative to, or a check against, PSRCHIVE.

The third term in a “multipole” expansion, which describes some spherical pattern as the sum of components with different angular features.

A software package built upon PyPulse that allows for a rapid look at a single PSRFITS file observation and provide some useful diagnostics to visualize.

Radio signals of terrestrial origin, which have the effect of lowering the significance of astrophysical radio frequency signals of interest.

Fluctuations that add to the pulse profile due to electronic noise.

One component of a frontend, the actual component that receives the radiation.

The bulk deflection (scattering) of pulse emission through the interstellar medium. 

GWs generated in the early universe, shortly after the Big Bang.

The observed TOA minus the expected model TOA.

See Equatorial Coordinates.

A frequency range covering 2–4 GHz.

Method for generating samples from a probability distribution, especially if you don’t know the form of the distribution a priori. 

As pulses travel through the interstellar medium, the ray paths are deflected ever so slightly by the free electrons in the interstellar medium.

The time scale over which pulse broadening due to scattering happens, roughly related to how much the width of the pulse is increased by.

An optical effect caused by light rays constructively and destructively interfering.  

A “structure” observed in a secondary spectrum that is indicative of scattering material along the line of sight.

The characteristic size scale of scintles in frequency.

The characteristic size scale of scintles in time. 

Bright patches in a dynamic spectrum where the pulsar emission is brighter due to scintillation.

A colloquial term for the act of averaging a pulse profile in time, frequency, polarization, or even phase. 

The group in charge of finding new pulsars and suggesting they be added to the array.

The 2D Fourier transform of the dynamic spectrum. 

A general relativistic effect where light takes slightly longer to travel through the local spacetime of a massive object.

A generic term used to define the ratio of the strength/amplitude of your “signal” (what you are looking for) to the strength/amplitude of the uncertainties in your measurement.

Meeting with with program National Science Foundation program officers to discuss the progress of large collaboration grants, such as the PFC.

The center of mass of our solar system.

The wind of particle blown off from the Sun.

Network of undergrad/grad students across NANOGrav institutions giving the EPO presentation “Tuning Into Einstein’s Universe” as well as hands-on activities to K-12 students in their local areas. 

The component of the system temperature due to radiation from the ground and immediate surroundings.

The coordinated team of undergraduate students distributed across NANOGrav, with an emphasis on bringing students to learn about the science together.

A binary system of two SMBHs that forms after their host galaxies merge. 

The conversion of the system temperature into units of flux density, so from Kelvin to Jansky.

The noise temperature resulting from all in the system contributions.

A red noise model consisting of a typical power-law relation between noise spectral density and frequency but with deviation parameters included for every red noise frequency bin.

To calculate TOAs, we shift an idealized pulse profile shape and maximize the correlation (area overlap) between it and a noisy data profile.

Pulsar timing software written in fortran by many people over decades.

Pulsar timing software written in TEMPO in C++.

Comparison of the degree of belief in two hypotheses. Literally a betting odds.

An erroneous noise feature in the 9-year data set that resembles a burst with memory originating in the direction of PSR J0030+0451.

Noise feature uncovered in the 9-year continuous wave search. 

Revealed when calculating the Bayes factors for continuous wave signals with various spatial correlations.

An uptick in stochastic background upper limits around 2012 uncovered during the time slice analyses which is thought to be some form of DM anomaly.

We often approximate the material in the interstellar medium as being condensed from fully filling the line of sight to existing in a two-dimensional “screen”.

A text file that contains each arrival time, the frequencies observed, the template fitting errors, and a lot of metadata such as which observation it came from, what integration number, what the flux of the pulse was, etc.

A measurement of when a pulse (or an average of pulses) arrives at our telescope.

A description of when we expect pulses to arrive at our telescopes.

The group in charge of pulsar timing analyses and preparing the data sets, from the calibration of profiles to the calculation of TOAs to the fitting of individual pulsar timing models.

This next-generation frontend will be able to receive 0.7–4.0 GHz simultaneously.

Versatile GBT Astronomical Spectrometer.

A stellar remnant left behind by lower-mass stars.

Noise that is entirely uncorrelated, meaning that every measurement is independent from every other measurement.

Wideband timing takes into account the shape of the pulse changes themselves across the band and produces a single arrival time and estimate of the DM.

A colloquial term for the act of excising (removing) RFI.

The angle between a point or line, and a line pointing directly “overhead”.