Glossary
========
.. glossary::
BBH
Binary black hole, a binary system composed of two black holes. See
:term:`BH`.
BH
Black hole.
BNS
Binary neutron star, a binary system composed of two neutron stars.
See :term:`NS`.
burst
In the context of gravitational waves, a signal candidate that is
detected without a template and without prior knowledge of the
waveform. Examples of potential sources of gravitational-wave bursts
include high mass :term:`BBH` mergers, core-collapse supernovae, and
cosmic string cusps.
chirp mass
In a binary system, the chirp mass is a symmetric combination of the
:term:`primary` and :term:`secondary` component masses :math:`m_1` and
:math:`m_2` that parameterizes the leading-order time or frequency
evolution of the gravitational-wave signal. It is usually denoted by a
script "M" symbol, :math:`\mathcal{M}`, and is defined as
:math:`\mathcal{M} = (m_1 m_2)^{3/5} (m_1 + m_2)^{-1/5}`.
CBC
Compact binary coalescence.
FAR
False alarm rate, a statistic that is used to describe the significance
of a gravitational-wave event. It is defined as the rate of accidental
events due to detector noise or glitches, in the absence of any
astrophysical sources, that are as loud as or louder than the event in
question.
FITS
Flexible Image Transport System, a format for astronomical tables,
images, and multidimensional data sets. See NASA's FITS Support Office
(https://fits.gsfc.nasa.gov) for specifications, software, and
documentation.
GCN
The Gamma-ray Coordinates Network (https://gcn.gsfc.nasa.gov), a portal
for discoveries and observations of astronomical transients.
Historically, GCN has served high-energy satellites but now also other
electromagnetic wavelengths and also gravitational-wave, cosmic ray,
and neutrino facilities.
GCN Circular
A human-readable astronomical bulletin distributed through :term:`GCN`.
GCN Notice
A machine-readable alert distributed through :term:`GCN`.
GraceDB
Gravitational Wave Candidate Event Database (https://gracedb.ligo.org),
the official public marshal portal for LIGO/Virgo candidates.
GRB
Gamma-ray burst.
HEALPix
Hierarchical Equal Area isoLatitude Pixelation, a scheme for indexing
positions on the unit sphere. See https://healpix.sourceforge.io.
HEN
High Energy Neutrino, particularly in the context of multi-messenger
GW+HEN follow-up.
KAGRA
Kamioka Gravitational Wave Detector (see `KAGRA home page
`_), an underground
gravitational-wave detector in the Kamioka mine in Japan.
LHO
LIGO Hanford Observatory (see `LHO observatory home page
`_), site of a 4 km gravitational-wave
detector in Hanford, Washington, USA.
LLO
LIGO Livingston Observatory (see `LLO observatory home page
`_), site of a 4 km gravitational-wave
detector in Livingston, Louisiana, USA.
MassGap
Compact binary systems with at least one compact object whose mass is
in the hypothetical "mass gap" between neutron stars and black holes,
defined here as 3-5 solar masses.
MCMC
Markov chain Monte Carlo. A numerical algorithm for sampling complex,
multidimensional probability distributions, or for integrating
functions of many variables. Used extensively in gravitational-wave
parameter estimation.
MOC
Multi-Order Coverage map, a format to describe the coverage of an
arbitrary region on the unit sphere. A MOC consists of a list of
:term:`HEALPix` cells at different depths. For the specification, see
the `HiPS IVOA Recommendation `_.
NS
Neutron star.
NSBH
Neutron star black hole, a binary system composed of one neutron star
and one black hole. See :term:`NS`, :term:`BH`.
O1
Advanced LIGO and Advanced Virgo's first observing run.
O2
Advanced LIGO and Advanced Virgo's second observing run.
O3
Advanced LIGO and Advanced Virgo's third observing run.
primary
When referring to the two component compact objects or the masses of
the two component compact objects in a binary, the `primary` is the
more massive one, i.e., :math:`m_1 \geq m_2`. See :term:`secondary`.
range
A figure of merit to describe the sensitivity of a gravitational-wave
detector to a given source population at cosmologically significant
distances. It is defined as the radius :math:`R` of a Euclidean sphere
with the volume equal to the :term:`sensitive volume` :math:`V_z`. It
may be written as:
.. math::
R = \left(\frac{3 V_z}{4 \pi}\right)^{1/3}.
secondary
When referring to the two component compact objects or the masses of
the two component compact objects in a binary, the `secondary` is the
less massive one, i.e., :math:`m_2 \leq m_1`. See :term:`primary`.
sensitive volume
A figure of merit for the sensitivity of a gravitational-wave detector
or a network of detectors. It is defined as the space-time volume
surveyed per unit detector time, and may be expressed as (cf.
[#DistanceMeasuresInGWCosmology]_):
.. math::
V_\mathrm{z}
= \frac{
\int_{z < z^*(\Theta)} p(\Theta) \frac{dV_C}{dz} \frac{dz}{1 + z}
}{\int p(\Theta) d\Theta}.
Here, :math:`\Theta` is the set of parameters that describe the
gravitational-wave signal (merger time, sky location, orbital elements,
masses, and spins) and :math:`p(\Theta)` is the redshift-independent
population model for those parameters. The term :math:`\frac{dV_C}{dz}`
is differential comoving volume per unit redshift. The function
:math:`z^*(\Theta)` is the *threshold redshift*, or the redshift at
which a binary with parameters :math:`\Theta` is just at the limit of
detection. The factor of :math:`{1 + z}` in the denominator accounts
for time dilation from the source frame to the detector frame.
If a population of sources occurs at a fixed rate per unit comoving
volume per unit proper time :math:`\dot{n}`, then the rate of observed
events in the detector frame is :math:`\dot{n} V_z`.
SN
Supernova.
SNR
Signal-to-noise ratio, here applied to gravitational-wave signals. It
is defined the square root of the integral over frequency of the power
spectral density of the gravitational-wave signal over the integral
over frequency of the average power spectral density of the noise.
Terrestrial
Classification for signals in gravitational-wave detectors that are of
instrumental or environmental origin. Terrestrial signals are not
astrophysical and not due to gravitational waves. Some examples of
sources of terrestrial signals are statistical noise fluctuations,
detector glitches, and ground motion.
Virgo
Virgo Observatory (see `Virgo observatory home page
`_), site of a 3 km gravitational-wave detector
in Cascina, Italy.
VOEvent
An XML format for describing astronomical transients. For the
specification, see the official `VOEvent IVOA Recommendation
`_.
VTP
VOEvent Transport Protocol, a simple TCP-based protocol for sending and
receiving VOEvents, used by :term:`GCN`. For the specification, see the
official `VTP IVOA recommendation
`_.
.. [#DistanceMeasuresInGWCosmology]
Chen, H.-Y., Holz, D. E., et al. 2017, *Distance measures in
gravitational-wave astrophysics and cosmology*. :arxiv:`1709.08079`