Can Pulsar Timing Arrays Detect Gravitational Wave Bursts with Memory?

[wolram]

arXiv:1404.5682
arXiv:1404.5682 [pdf, ps, other]
Assessing Pulsar Timing Array Sensitivity to Gravitational Wave Bursts with Memory
D. R. Madison, J. M. Cordes, S. Chatterjee
Comments: Submitted to ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Highly energetic astrophysical phenomena like supermassive black hole binary (SMBHB) mergers are predicted to emit prodigious amounts of gravitational waves (GWs). An anticipated component of the gravitational waveform known as "memory" is permanent and non-oscillatory. For SMBHB mergers, the memory is created primarily during the most violent moments of the inspiral immediately preceding the final plunge and ring-down when the strongest gravitational fields are at work and the non-linearities of general relativity are most pronounced. The essentially time-domain nature of memory makes it forbiddingly difficult to detect with ground based GW detectors, leaving pulsar timing array (PTA) experiments as the most promising means by which it may be detected and studied. In this paper, we discuss how GW bursts with memory (BWMs) influence pulsar timing experiments and develop methods to assess how sensitive modern timing efforts are to such GW events. We discuss how PTA searches for BWMs can be used to constrain the rate of BWMs and how these constraints relate to information regarding the population of SMBHBs

I don't under stand this, does it mean time varies along the length of the memory wave?

 

[wolram]

Marc Favata
(Submitted on 17 Mar 2010)
The nonlinear memory effect is a slowly-growing, non-oscillatory contribution to the gravitational-wave amplitude. It originates from gravitational waves that are sourced by the previously emitted waves. In an ideal gravitational-wave interferometer a gravitational-wave with memory causes a permanent displacement of the test masses that persists after the wave has passed. Surprisingly, the nonlinear memory affects the signal amplitude starting at leading (Newtonian-quadrupole) order. Despite this fact, the nonlinear memory is not easily extracted from current numerical relativity simulations. After reviewing the linear and nonlinear memory I summarize some recent work, including: (1) computations of the memory contribution to the inspiral waveform amplitude (thus completing the waveform to third post-Newtonian order); (2) the first calculations of the nonlinear memory that include all phases of binary black hole coalescence (inspiral, merger, ringdown); and (3) realistic estimates of the detectability of the memory with LISA.
Comments: 11 pages, 2 figures; proceedings of the 8th Amaldi Conference on Gravitational Waves (New York, June 2009); accepted for publication in special issue of Classical and Quantum Gravity
Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Astrophysical Phenomena (astro-ph.HE)
Journal reference: Class. Quant. Grav.27:084036, 2010
DOI: 10.1088/0264-9381/27/8/084036
Cite as: arXiv:1003.3486 [gr-qc]
(or arXiv:1003.3486v1 [gr-qc] for this version)

 

[wolram]

I really do not understand this it seems to be saying that space time is some fabric that can be permanently deformed can anyone shed some light on this.

 

[wolram]

www.google.co.uk/search?q=gravitati..._sm=122&tbm=isch&tbo=u&source=univ&ei=rbdaU_7

Diagrams of memory wave

 

[Mordred]

There is a lot of that article I can't make heads or tails of. For the memory aspects, I'll simply think of it as perturbations of energy-mass distributions in the IGM. I don't particularly agree with the terminology use of memory, nor with the space-time fabric descriptive. Seems to me the article is describing a possible manner of detecting GW via energy-mass perturbations. Though I can't understand their Earth term reference. Just my take on it

 

[wolram]

If you google gravitational memory wave there are quite a few hits, all seem to say the same thing,
a memory wave distorts space time and the distortion is permanent, me only being a tyro can not understand as they must be referring to space time fabric.

 

[wolram]

http://journals.aps.org/prd/abstract/10.1103/PhysRevD.45.520

This paper has 6o citations ans says pretty much the same thing.

The ‘‘memory’’ of a gravitational-wave burst is the permanent relative displacement that it imposes on free test masses, or more precisely, the permanent change in the burst’s gravitational-wave field hTTjk. This memory, in general, is equal to the change, from before the burst to afterward, in the transverse-traceless (TT) part of the ‘‘1/r, Coulomb-type’’ gravitational field generated by the four-momenta of the source’s various independent pieces. Christodoulou has recently identified a contribution to a burst’s memory that arises from nonlinearities in the vacuum Einstein field equation. This paper shows that the Christodoulou memory is precisely the TT part of the ‘‘1/r, Coulomb-type’’ gravitational field produced by the burst’s gravitons, and it therefore gets built up over the same length of time τbwm as it takes for the source to emit the gravitons. The sensitivity of broad-band gravitational-wave detectors such as LIGO to the Christodoulou memory is analyzed and discussed.

 

[Mordred]

"The ‘‘memory’’ of a gravitational-wave burst is the permanent relative displacement that it imposes on free test masses"
think carefully about this terminology, its not saying space itself as a test mass, its referring to test particles contained within the volume of space. Or residing in the interstellar medium. In other words its referring to permanent distortion distributions of the intergalactic medium.
Space itself is not a fabric, its a geometric volume filled with the contents of the universe. space geometry is a measure of the relative distribution relations of the energy-mass contents.
In the wording above I would agree with its accuracy. However defining space itself as a fabric is misleading, as it implies that space itself has properties and energy-mass other than simply geometric volume. Leads to misnomers such as space stretching, growing etc.

 

[wolram]

Thanks for clearing that up Mordred, when people start citing the fabric of space time i think of cranks, its not obvious in these papers and it shows that tyro like me can be easily misled.

 

[Mordred]

no problem, after thinking about the article further, I don't have an issue with the term memory, as it refers to the alignment of particles. Much the same way as particles align in say a semi-conductor. (though with specific conditions) So that in itself is appropriate.