1. Search for gravitational waves in coincidence with radio transients from pulsar surveys
Brennan Hughey for the LIGO and Virgo Collaborations
Amaldi 9 at Cardiff, Wales
July 14th, 2011
LIGO DCC-G

2. Joint Radio/Gravitational Wave Search
Looking for gravitational waves (GWs) in coincidence with
identified radio transients of unknown origin
Gravitational wave search externally triggered by EM
rather than initiating EM follow-up as in last few talks
Science goals are similar – increase GW detection
confidence and learn more about astrophysical system
than by a single messenger alone
Radio is specifically interesting for a number of reasons:
Scenarios where optical emission is much more
strongly beamed than radio or GW emission,
Dispersion measure plus direction provide a built-in
distance estimate
Several radio/GW collaborative efforts in progress,
We focus on GWs in coincidence with short duration
radio transients identified in pulsar surveys GW
Radio

3. Joint Radio/Gravitational Wave Search
Looking for gravitational waves (GWs) in coincidence with
identified radio transients of unknown origin
Gravitational wave search externally triggered by EM
rather than initiating EM follow-up as in last few talks
Science goals are similar – increase GW detection
confidence and learn more about astrophysical system
than by a single messenger alone
Radio is specifically interesting for a number of reasons:
Scenarios where optical emission is much more
strongly beamed than radio or GW emission,
Dispersion measure plus direction provide a built-in
distance estimate
Several radio/GW collaborative efforts in progress,
We focus on GWs in coincidence with short duration
radio transients identified in pulsar surveys GW
Radio

4. Radio Pulsar Surveys
We are negotiating MoUs with 3 pulsar survey groups at 2 observatories
Robert C. Byrd Green Bank Telescope:
100 X 110 meter fully steerable scope
at NRAO site in West Virginia
Green Bank Drift-scan survey:
Summer 2007, telescope fixed as Earth rotates
Green Bank survey of northern celestial cap:
will cover sky north of 38 declination
Both GBT surveys have 350 MHz central frequency
Arecibo Observatory:
305 meter diameter, located in Puerto Rico
Arecibo L-band Feed Array (ALFA) is a
7-beam receiver operating at 20 cm
P-ALFA: March 2005 – present
1.4 GHz central frequency,
300 MHz bandwidth

5. Radio Propagation Time Delay
Dispersion measure (electron density integrated over distance to source) used
to calculate frequency dependent time delay of radio signal with respect to GW
(or light in vacuum). Propagation delays at most extreme dispersion measure
and lowest frequency for this analysis are not more than 46 seconds.
Each of
7 ALFA beams
SNR determines
Best DM
124 different
trial DM
channels
radio pulse
From “An Arecibo Search for Pulsars and Transient Sources in M33” by N.D.R. Bhat et al., APJ 732 (2011) 14

6. Sources of Joint Emission
Binary neutron star coalescence:
Radio emission from magnetospheric interactions (e.g. astro-ph/ ),
Rapidly rotating post-merger object (arXiv: ),
Plasma excitation via relativistic MHD followed by inverse compton scattering (gr-qc/ )
Single neutron star (pulsar, RRAT): starquakes etc.
Transient GW emission would in many cases be accompanied by a “glitch” in a steady state
signal (e.g. James Clark’s talk) but beaming or other mechanisms could cause radio signal
to manifest as a transient
Cosmic strings:
Cusps in cosmic strings could nearly simultaneously emit GWs and radio pulses (arXiv: )
NASA
NASA
Ken Olum

7. Other sources
Some other scenarios for joint GW-radio emission are interesting but probably less relevant
for this specific search. For example:
GRB or SN afterglow: shortest radio afterglow scenario peaks ~20 minutes after coalescence
in short GRB scenario (astro-ph/ v2), still too broad in duration for our radio pulses
Prompt radio emission from GRBs: As discussed in astro-ph/ , simply too low frequency
for our radio partners
Primordial black hole dissipation, massive black hole tidal disruption or coalescence :
Not promising as LIGO sources
University of Warwick/Mark Galick
Dana Berry, SkyWorks Digital

8. Analysis Design (I)
Search for gravitational waves will be conducted with X-pipeline (arXiv: ),
which was used to conduct many previous externally triggered GW analyses
Resembles GRB searches (see Michal Was’s plenary talk tomorrow),
with a factor of O(2) sensitivity improvement expected relative to an all-sky search
Sample X-pipeline output from S5 GRB search:
Sensitivity curve
Background
Efficiency for an injection
Amplitude (Hz-1/2)
fraction above loudest event
frequency
significance
hrss amplitude Hz-1/2

9. Analysis Design (II)
Several parameters will be adjusted with respect to S6 GRB search:
Shorten time window
Change cut method to not require circular polarization
Expand frequency range
Add to set of injection types used
Analysis tuned on “Straw Man” data set of 5 hypothetical transients during S6/VSR2
Will analyze real triggers once cuts are finalized and radio events are available….
In summary:
Radio/GW observations are a promising avenue for multimessenger astronomy
We are developing an analysis to search for GWs in coincidence with radio
pulses of unknown origin in the few hundred MHz to GHz frequency range
Collaborative efforts between the radio and GW communities should pave the
way for further collaboration in the Advanced Detector era