Radio&Pulse&Coincidence&...

Radio Pulse Coincidence Searches with LIGO

Brennan Hughey October 22nd 2013

2

GravitaBonal Waves: Listening to the Universe

•  Predicted by Einstein’s General Theory of Rela6vity •  When massive objects rapidly change shape or orienta6on, the curvature of space-‐6me also changes •  The change propagates as a wave traveling at the speed of light: ripples in the fabric of space •  Amplitude inversely propor6onal to distance •  2 polariza6ons: “plus” (+) and “cross” (x) (and any combina6on)

+ polarizaBon

3

How “Loud” Are They? •  Amplitude is described by dimensionless strain: stretching of

space h = ΔL/L •  Back-‐of-‐envelope calculaBon:

–  Laboratory dumbbell

4



–  Laboratory dumbbell (1 ton, 2m, 1kHz) h = 10-‐38

5



–  Laboratory dumbbell (1 ton, 2m, 1kHz) h = 10-‐38

–  Binary neutron star system (1.4 MO, 20km, 400 Hz) = 10-‐21

at a distance of 15 Mpc

•  So the search for gravitaBonal waves requires objects of astrophysical mass, and even then is a hugely difficult problem

6

So Are GravitaBonal Waves Real? Don’t take Einstein’s word for it. GravitaBonal waves haven’t been directly detected, but…. Indirect evidence from binary system including radio pulsar Shic in orbit matches GR predicBons exactly

Dantor 2007

7

The GravitaBonal Wave Spectrum

Figure credit: Hobbs 2008

Interferometers and Bars

Lisa/NGO Pulsar Timing Arrays

8

Building Ears: LIGO Laser Interferometer GravitaBonal-‐Wave Observatory Lasers split at 90 degree angle, bounced back and forth along detector arms, then recombined

Compression and contracBon of space-‐Bme due to passing GravitaBonal Waves can be reconstructed from interference pahern of the two laser beams

9

Beam tube

Vacuum System Vibra6on Isola6on

Mirror in situ The Hardware

10

Background •  There are a huge variety of Earth-‐based disturbances that cause “glitches” in the detector, so we have hundreds of internal and external sensors set up to measure non GravitaBonal wave effects

Examples of noise sources: Wind Earthquakes Waves in gulf Power Lines Anthropogenic etc…

Extreme example of an anthropogenic disturbance

So how do we look for needles in the haystack?

•  AcBvely work to characterize noise in data streams

•  Look for specific signal shapes •  Look for consistent signals across mulBple detectors

frequ

ency

time

12

The Worldwide Network of GravitaBonal Wave Interferometers

LIGO Livingston

LIGO Hanford

4 km 2 km

4 km

13

The Worldwide Network of GravitaBonal Wave Interferometers

VIRGO LIGO Livingston

LIGO Hanford

4 km 2 km

4 km 3 km

14

The Worldwide Network of GravitaBonal Wave Interferometers -‐ Someday

VIRGO LIGO Livingston

LIGO Hanford

4 km

4 km 3 km

Geo600

LIGO India

Kagra

So how do we look for needles in the haystack?

•  AcBvely work to characterize noise in data streams

•  Look for specific signal shapes •  Look for consistent signals across mulBple detectors

•  Look in the same Bme and place as an external electromagneBc trigger

ElectromagneBc Follow-‐Up Program Localize the most likely locaBon of a marginal event and send to astronomical partners for follow-‐up Prototype program in previous science run, expanded in next

Telescope Network Used in winter and autumn run autumn run only

17

The Big Dog Ø  Received alert 8 minutes after event (in middle of night)

Ø  Sent to telescopes 45 minutes after event

Ø  Visually identified as inspiral shortly after trigger generated

Ø  Demonstrates that we’re identifying “signal” with very low latency

18

Externally Triggered Searches

•  Joint emission from Gamma-‐ray Bursts, Soc Gamma Repeaters, Supernovae Use both Bme and locaBon to dramaBcally reduce the background with respect to all-‐sky searches

Joint Radio/Gravita6onal Wave Search Looking for gravitaBonal waves (GWs) in coincidence with idenBfied radio transients of unknown origin External trigger approach -‐ Increase GW detecBon confidence and learn more about astrophysical system than by a single messenger alone Radio is specifically interesBng for a number of reasons: ª  Scenarios where opBcal emission is much more strongly beamed than radio or GW emission, ª  Dispersion measure plus direcBon provide a built-‐in distance esBmate We focus here on GWs in coincidence with short duraBon radio transients idenBfied in pulsar surveys, other radio-‐coincident studies are also possible at longer duraBons and lower frequencies

GW

Radio 21

So what’s a pulsar? A pulsar is a parBcular sub-‐class of neutron star. (So what’s a neutron star?) A neutron star is a very dense remnant of an old star in which a star a bit heavier than our sun has collapsed to something with a radius of a few kilometers It’s a less extreme version of what happens when a more massive star makes a black hole

So what’s a pulsar? It’s called a neutron star because the inner layers are primarily an ultra-‐dense ball of neutrons rather than regular atomic maher However, there’s a layer of ions & electrons on the outside that produces radiaBon as a result of the star’s rapid rotaBon, leading to radio emission at the poles

So what’s a pulsar? This emission from the poles shows up at the Earth as a radio pulse every few milliseconds to seconds, depending on how fast the neutron star is spinning

If there’s a radio source with less regular emission (because it is near the end of It’s life as a pulsar or is parBally obscured from view) it is called an RRAT – A RotaBng RAdio Transient

Once you average out Bme delays from the stuff between the pulsar and the Earth, Pulsars are among the most accurate clocks in the known universe

Radio Pulsar Surveys

100 X 110 meter fully steerable scope at NRAO site in West Virginia (world’s largest of its kind) Surveys: ª  Green Bank DriV-‐scan survey: Summer 2007, telescope fixed as Earth rotates ª  Green Bank survey of northern celes6al cap: 2009-‐2012. will cover sky north of 38 declinaBon Both GBT surveys have 350 MHz central frequency

25

Radio Propaga6on Time Delay Dispersion measure (electron density integrated over distance to source) used to calculate frequency dependent Bme delay 1/f2 of radio signal with respect to GW (or light in vacuum). PropagaBon delays at most extreme dispersion measure and lowest frequency for this analysis are not more than 46 seconds.

Each of 7 ALFA beams

124 different trial DM channels

SNR determines Best DM

radio pulse From “An Arecibo Search for Pulsars and Transient Sources in M33” by N.D.R. Bhat et al., APJ 732 (2011) 14

26

Sources of Joint Emission: Single Neutron Stars

We already know that neutron stars can emit radio waves They can also emit gravitaBonal waves any Bme there’s a deviaBon from spherical symmetry

Asteroseismology: Starquakes and crustal shics can cause temporary change in shape of the neutron star These same disturbances can affect the radio emission, either bumping the pole Into our line of site or increasing amplitude

Sources of Joint Emission: Binary Neutron Star Coalescence

28 NASA

The merger of two neutron stars or a neutron star and a black hole is our most promising GravitaBonal wave source since it is “loud” enough to hear from other galaxies

There are a few (theoreBcal) ways to get short radio pulses at the same Bme as the merger ²  The pulsar emission of one of the neutron stars could get “spun up” as part Of the merger process ²  An intermediate state called a hypermassive neutron star could act as a Pulsar ²  GravitaBonal waves moving through the right medium can actually induce RadiaBon in the radio regime through magnetohydronamics

Sources of Joint Emission: Cosmic Strings

Joint sources for emission don’t have to relate directly to neutron stars at all One of the more exoBc theories comes from string theory

A cosmic string can bend and form a “cusp” or “kink”, which can lead to several Kinds of emission, including radio and gravitaBonal waves

Ken Olum

Our Search for GWs in Coincidence with Radio Pulses from Green Bank

We’ve taken 32 “single pulse” sources from Green Bank’s 2007 dric-‐scan survey And looked for gravitaBonal waves in coincidence with them We did this by starBng with an externally triggered search program designed for Gamma-‐ray Bursts and tuned it for the physics described in the last few slides ² Changed the search window size in Bme and locaBon ²  Increased the upper end of the frequency range over which we are searching ² Account for various Bming issues – for example, Green Bank supplies Bmes with respect to the center of the solar system ² Measure efficiency based on the waveforms we expect from our sources


21 of the single pulse triggers had good data in at least 2 LIGO/Virgo detectors We tuned searches for each trigger using data close to the on-‐source window and “Bme-‐shiced” between the detectors, then looked at the real data

H1

L1


21 of the single pulse triggers had good data in at least 2 LIGO/Virgo detectors We tuned searches for each trigger using data close to the on-‐source window and “Bme-‐shiced” between the detectors, then looked at the real data

H1

L1

Time-‐shics must be greater than 10s of ms travel Bme of a real GW signal


We (David SBles and I) verified results for each trigger and made correcBons We then “opened the box” and looked at real zero-‐lag results

(Technically I can’t tell you what we’ve found since the results aren’t public)

So What’s Next?

²  Hopefully we’ll soon get more data from Green Bank – northern celesBal cap ²  Working on beher ways to analyze combinaBons of two detectors (with undergraduate researcher David SBles) ²  Working on geung a memorandum of understanding with Parkes telescope to get unpublished radio triggers from 2011. ²  PublicaBon once we get more results.

Parkes Pulses The Parkes Telescope is a prolific radio telescope in New South Wales, Australia Published 4 distant radio bursts from 2011 this summer These are exciBng because they look like they are from outside our galaxy They have more unpublished triggers, and they want LIGO/Virgo to look at them (unfortunately only European detectors were on at the Bme) PresenBng science case to LIGO’s data analysis council on Friday……

Prospects for DetecBon in Advanced Era

36

Predicted Advanced Detector CBC detection rates per year at design sensitivity Low Realis6c High

NS-‐NS 0.4 40 400

NS-‐BH 0.2 10 300

BH-‐BH 0.4 20 1000

Low Realis6c High

NS-‐NS 2X10-‐4 0.02 0.2

NS-‐BH 7X10-‐5 0.004 0.1

BH-‐BH 2X10-‐4 0.007 0.5

Compared to initial detectors

Class. Quant. Grav. 27: 173001 (2010)

Order of magnitude improvement in sensitivity Order of magnitude improvement in range 3 orders of magnitude more volume

Radio&Pulse&Coincidence&...

Documents

Transcript of Radio&Pulse&Coincidence&...