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Jetzer Philippe - One of the best experts on this subject based on the ideXlab platform.
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Pulse redshift of pulsar timing array signals for all possible gravitational wave polarizations in modified general relativity
'American Physical Society (APS)', 2020Co-Authors: Boîtier Adrian, Tiwari Shubhanshu, Philippoz Lionel, Jetzer PhilippeAbstract:Pulsar timing arrays (PTA) have the promise to detect gravitational waves (GWs) from sources which are in a unique frequency range of 10−9−10−6 Hz. This in turn also provides an opportunity to test the theory of general relativity in the low frequency regime. The central concept of the detection of GWs with PTA lies in measuring the time of arrival difference of the pulsar signal due to the passing of GWs; i.e., the pulses get redshifted. In this paper we provide a complete derivation of the redshift computation for all six possible polarizations of GWs which arise due to the modifications to general relativity. We discuss the smoothness of the redshift and related properties at the critical point, where the GW source lies directly behind the pulsar. From our mathematical discussion we conclude that the redshift has to be split differently into polarization part (pattern functions) and interference part, to avoid discontinuities and singularities in the pattern functions. This choice of pattern functions agrees with the formula one uses for interferometers with a single Detector Arm. Finally, we provide a general expression which can in principle be used for pulsars and GWs of any frequency without invoking the low frequency assumption and using said assumption we develop the expression up to first order in the strain and find correction terms to the canonical redshift formula
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Pulse redshift of pulsar timing array signals for all possible gravitational wave polarizations in modified general relativity
'American Physical Society (APS)', 2020Co-Authors: Boîtier Adrian, Tiwari Shubhanshu, Philippoz Lionel, Jetzer PhilippeAbstract:Pulsar timing arrays (PTA) have the promise to detect gravitational waves (GWs) from sources which are in a unique frequency range of 10^-9 - 10^-6 Hz. This in turn also provides an opportunity to test the theory of general relativity in the low frequency regime. The central concept of the detection of GWs with PTA lies in measuring the time of arrival difference of the pulsar signal due to the passing of GWs i.e. the pulses get red-shifted. In this paper we provide a complete derivation of the redshift computation for all six possible polarizations of GW which arise due to the modifcations to general relativity. We discuss the smoothness of the redshift and related properties at the critical point, where the GW source lies directly behind the pulsar. From our mathematical discussion we conclude that the redshift has to be split differently into polarization part (pattern functions) and interference part, to avoid discontinuities and singularities in the pattern functions. This choice of pattern functions agrees with the formula one uses for interferometers with a single Detector Arm. Finally, we provide a general expression which can in principle be used for pulsars and GW of any frequency without invoking the low frequency assumption and using said assumption we develop the expression up to first order in the strain and find correction terms to the canonical redshift formula.Comment: Accepted for publication in PR
B Allen - One of the best experts on this subject based on the ideXlab platform.
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from einstein s general theory of relativity to gravitational wave astronomy
Annalen der Physik, 2016Co-Authors: B AllenAbstract:In his 1916 article [1] predicting the existence of gravitational waves, Einstein wrote that they were too weak to be of any consequence. A century later, the world’s attention was captured by the February 11th announcement, demonstrating how wrong this was. In a landmark publication in Physical Review Letters [2], an international team reports the first direct detection of the gravitational waves emitted by a pair of black holes (29 and 36 solar masses) during their final few orbits before merging to form a single 62 solar-mass black hole. Physicists love extremes, because pushing the limits leads to insight and understanding. This discovery, a short chirp lasting about a quarter-second (see Fig. 1, adapted from [2]), pushes the limits in many different directions. Let’s start with the human side. The first unsuccessful attempts to detect gravitational waves were smallinvestigator experiments made about fifty years ago. In contrast, the discovery paper had about 1000 authors (20% are from the Max Planck Institute for Gravitational Physics, for which I am the Managing Director). Some of these authors have worked towards the discovery for more than forty years. The Detector technology also pushes the limits. The advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) instruments are located 3000 km apart, in Hanford, Washington and Livingston, Louisiana. The effect of the gravitational waves is to distort the effective path length between pairs of mirrors hanging 4 km apart in a seismically-isolated high-vacuum system. At the peak of the signal the measured length change in each Detector Arm is about 0.002 femtometers, 1/1000 the diameter of a hydrogen nucleus. This is a fractional precision of a part in 1021; analogous to measuring the distance to the nearest star (Proxima Centuri) to an accuracy of 40 μm. I don’t know of any other measurement done with comparable precision. The binary system we observed was about one billion light years distant from earth; over some tens of milliseconds it converted about three solar masses of gravitational binding energy into gravitational waves. During that brief time, the system emitted more power than the optical luminosity of every star in every galaxy in the visible universe. My kids, jaded by generations of Star Wars movies, were unimpressed until I told them that in comparison with this, the “Death Star”, capable of vaporizing entire planets, is child’s toy, a hArmless plaything. Three solArmasses is enough energy to vaporize every planet in many galaxies! Binary black hole systems like this one could not have been detected in any other way, because (being black!) they do not emit any light or electromagnetic energy. But there are intriguing reports [3] that a team analyzing data from the Gamma-ray Burst Monitor (GBM) Detector on board NASA’s Fermi satellite observed a gammaray burst 0.4 seconds after the merger. So Nature might still surprise us. Could such systems be surrounded by clouds of gas or dust? We can’t be sure now, but within a few years, I am confident that we will know the answer to this and to many other questions. The rate at which our knowledge will now increase is breathtaking. In their first observing run the advanced LIGODetectors were a factor of three below their final design sensitivity. That doesn’t seem like much, but keep in mind that the expected number of sources/detections is proportional to the observable volume of space, which scales like the cube of the sensitivity. So the second observing run, starting this September and lasting six months, should observe about a dozen black hole mergers, and the third observing run, starting in 2017, should see about one hundred. It’s going to be quite a ride – a golden age of gravitational wave astronomy. By the end of it, we’ll know themass distribution and spatial density of these stellArmass black hole binary systems. And perhaps our catalog of observations will include new extremes, such as systemswith high spin, or neutron-star/black-hole binaries, or other surprises.
Boîtier Adrian - One of the best experts on this subject based on the ideXlab platform.
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Pulse redshift of pulsar timing array signals for all possible gravitational wave polarizations in modified general relativity
'American Physical Society (APS)', 2020Co-Authors: Boîtier Adrian, Tiwari Shubhanshu, Philippoz Lionel, Jetzer PhilippeAbstract:Pulsar timing arrays (PTA) have the promise to detect gravitational waves (GWs) from sources which are in a unique frequency range of 10−9−10−6 Hz. This in turn also provides an opportunity to test the theory of general relativity in the low frequency regime. The central concept of the detection of GWs with PTA lies in measuring the time of arrival difference of the pulsar signal due to the passing of GWs; i.e., the pulses get redshifted. In this paper we provide a complete derivation of the redshift computation for all six possible polarizations of GWs which arise due to the modifications to general relativity. We discuss the smoothness of the redshift and related properties at the critical point, where the GW source lies directly behind the pulsar. From our mathematical discussion we conclude that the redshift has to be split differently into polarization part (pattern functions) and interference part, to avoid discontinuities and singularities in the pattern functions. This choice of pattern functions agrees with the formula one uses for interferometers with a single Detector Arm. Finally, we provide a general expression which can in principle be used for pulsars and GWs of any frequency without invoking the low frequency assumption and using said assumption we develop the expression up to first order in the strain and find correction terms to the canonical redshift formula
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Pulse redshift of pulsar timing array signals for all possible gravitational wave polarizations in modified general relativity
'American Physical Society (APS)', 2020Co-Authors: Boîtier Adrian, Tiwari Shubhanshu, Philippoz Lionel, Jetzer PhilippeAbstract:Pulsar timing arrays (PTA) have the promise to detect gravitational waves (GWs) from sources which are in a unique frequency range of 10^-9 - 10^-6 Hz. This in turn also provides an opportunity to test the theory of general relativity in the low frequency regime. The central concept of the detection of GWs with PTA lies in measuring the time of arrival difference of the pulsar signal due to the passing of GWs i.e. the pulses get red-shifted. In this paper we provide a complete derivation of the redshift computation for all six possible polarizations of GW which arise due to the modifcations to general relativity. We discuss the smoothness of the redshift and related properties at the critical point, where the GW source lies directly behind the pulsar. From our mathematical discussion we conclude that the redshift has to be split differently into polarization part (pattern functions) and interference part, to avoid discontinuities and singularities in the pattern functions. This choice of pattern functions agrees with the formula one uses for interferometers with a single Detector Arm. Finally, we provide a general expression which can in principle be used for pulsars and GW of any frequency without invoking the low frequency assumption and using said assumption we develop the expression up to first order in the strain and find correction terms to the canonical redshift formula.Comment: Accepted for publication in PR
G Bushnellwye - One of the best experts on this subject based on the ideXlab platform.
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software for automatic calibration of synchrotron powder diffractometers
Journal of Synchrotron Radiation, 2003Co-Authors: D Laundy, Chiu C Tang, Mark A Roberts, Mike Miller, S P Thompson, G BushnellwyeAbstract:An automatic procedure to calibrate angular-dispersive monochromatic diffraction instruments has been developed at the Daresbury Synchrotron Radiation Source. The procedure uses a macro language to control the powder diffraction instruments to locate Bragg reflections and perform peak-centre refinement from a standard reference material. The information obtained is used to refine the wavelength of the radiation used and the angular offset of the Detector Arm. The concept and implementation of the new software are described with applications to demonstrate its viability. The results of a reliability and accuracy study are also presented.
H C Watson - One of the best experts on this subject based on the ideXlab platform.
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a paris edinburgh cell for high pressure and high temperature structure studies on silicate liquids using monochromatic synchrotron radiation
Minerals, 2019Co-Authors: Clemens Prescher, Young Jay Ryu, Feng Shi, Eran Greenberg, Vitali B Prakapenka, Peter J Eng, Joanne E Stubbs, Yoshio Kono, Guoyin Shen, H C WatsonAbstract:A Paris-Edinburgh press combined with a multi-channel collimator assembly has been commissioned at the GeoSoilEnviro Center for Advanced Radiation Sources (GSECARS) beamline for monochromatic X-ray scattering, with an emphasis on studying low-Z liquids, especially silicate liquids at high pressure. The Paris-Edinburgh press is mounted on a general-purpose diffractometer, with a pixel array Detector mounted on the Detector Arm. The incident monochromatic undulator beam with energies up to 60 keV is focused both horizontally and vertically to a beam size about 30 × 30 µm. With this setup, background scattering from the surrounding pressure media is completely removed at 2θ angles above 10° for samples larger than 1.05 mm in diameter. Thirty minutes is typically sufficient to collect robust X-ray scattering signals from a 1.6 mm diameter amorphous silicate sample. Cell assemblies for the standard Paris-Edinburgh anvils have been developed and pressures and temperatures up to 7 GPa and 2300 K, respectively, have been maintained steadily over hours. We have also developed a cupped-toroidal Drickamer anvil to further increase pressure and temperature capabilities. The cupped-toroidal Drickamer anvil combines features of a modified Drickamer anvil and the traditional Paris-Edinburgh anvil. Pressures up to 12 GPa have been generated at temperatures up to 2100 K.