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1605.09398
The effect of lensing magnification on the apparent distribution of black hole mergers
Dai, Venumadhav, Sigurdson
The recent detection of GWs indicates that stellar-mass BH binaries are likely to be a key population of sources for forthcoming observations. With future upgrades, ground-based detectors could detect merging BH binaries out to cosmo distances. GW bursts from high z (z>1) can be strongly magnified by GL due to intervening galaxies along the LoS. In the absence of EM counterparts, the mergers' intrinsic mass scale and redshift are degenerate with the unknown magnification factor mu. Hence, strongly magnified low-mass mergers from high-z appear as higher-mass mergers from lower redshifts. Assess the impact of this degeneracy on the mass-z distribution of observable events for generic models for binary BH formation from normal stellar evolution, Pop III star remnants, or a primordial BH population. Find that strong magnification (mu>3) generally creates a heavy tail of apparently massive mergers in the event distribution from a given detector. For LIGO and its future upgrades, this tail may dominate the population of intrinsically massive, but unlicensed mergers in binary BH formation models involving normal stellar evolution or primordial BHs. Modeling the statistics of lensing magnification can help account for this magnification bias when testing astrophysical scenarios of BH binary formation and evolution.
1606.00233
Jackknife resampling technique on mocks: an alternative method for covariance matrix estimation
Escoffier, et al
Present a fast and robust alternative method to compute covariance matrix in case of cosmo studies. The method is based on the jackknife resampling applied on simulation from catalogues. Using a set of 600 BOSS DR11 mock catalogues as a reference, find that the JK technique gives a similar galaxy cluserig covariance matrix estimate by requiring a smaller number of mocks. A comparison of convergence rates show that ~7 times fewer simulations are needed to get a similar accuracy on variance. Expect this technique to be applied in any analysis where the number of available N-body simulations is low.
1606.00458
Arrival time differences between gravitational waves and electromagnetic signals due to gravitational lensing
Takahashi
Demonstrate that GR predicts arrival time differences between GW and EM signals caused by the wave effects in gravitational lensing. The GW signals can arrive earlier the the EM signals in some cases if the GW/EM signals have passed through a lens, even if both signals were emitted simultaneously by a source. GW wavelengths are much larger than EM wavelengths; therefore, the propagation of the GWs does not follow the laws of geometrical optics, including the Shapiro time delay, if the lens mass is less than approximately 1e5 Msun(f/Hz)^(-1), where f is the GW frequency. The arrival time difference can reach ~0.1 s (f/Hz)^(-1); therefore, it is more prominent for lower GW frequencies. Gravitational lensing imprints a characteristic modulation on a chirp waveform; therefore, we can deduce whether a measured arrival time lag arises from intrinsic source properties or gravitational lensing. Determination of arrival time differences would be extremely useful in multi messenger observations and tests of GR.
1605.09398
The effect of lensing magnification on the apparent distribution of black hole mergers
Dai, Venumadhav, Sigurdson
The recent detection of GWs indicates that stellar-mass BH binaries are likely to be a key population of sources for forthcoming observations. With future upgrades, ground-based detectors could detect merging BH binaries out to cosmo distances. GW bursts from high z (z>1) can be strongly magnified by GL due to intervening galaxies along the LoS. In the absence of EM counterparts, the mergers' intrinsic mass scale and redshift are degenerate with the unknown magnification factor mu. Hence, strongly magnified low-mass mergers from high-z appear as higher-mass mergers from lower redshifts. Assess the impact of this degeneracy on the mass-z distribution of observable events for generic models for binary BH formation from normal stellar evolution, Pop III star remnants, or a primordial BH population. Find that strong magnification (mu>3) generally creates a heavy tail of apparently massive mergers in the event distribution from a given detector. For LIGO and its future upgrades, this tail may dominate the population of intrinsically massive, but unlicensed mergers in binary BH formation models involving normal stellar evolution or primordial BHs. Modeling the statistics of lensing magnification can help account for this magnification bias when testing astrophysical scenarios of BH binary formation and evolution.
1606.00233
Jackknife resampling technique on mocks: an alternative method for covariance matrix estimation
Escoffier, et al
Present a fast and robust alternative method to compute covariance matrix in case of cosmo studies. The method is based on the jackknife resampling applied on simulation from catalogues. Using a set of 600 BOSS DR11 mock catalogues as a reference, find that the JK technique gives a similar galaxy cluserig covariance matrix estimate by requiring a smaller number of mocks. A comparison of convergence rates show that ~7 times fewer simulations are needed to get a similar accuracy on variance. Expect this technique to be applied in any analysis where the number of available N-body simulations is low.
1606.00458
Arrival time differences between gravitational waves and electromagnetic signals due to gravitational lensing
Takahashi
Demonstrate that GR predicts arrival time differences between GW and EM signals caused by the wave effects in gravitational lensing. The GW signals can arrive earlier the the EM signals in some cases if the GW/EM signals have passed through a lens, even if both signals were emitted simultaneously by a source. GW wavelengths are much larger than EM wavelengths; therefore, the propagation of the GWs does not follow the laws of geometrical optics, including the Shapiro time delay, if the lens mass is less than approximately 1e5 Msun(f/Hz)^(-1), where f is the GW frequency. The arrival time difference can reach ~0.1 s (f/Hz)^(-1); therefore, it is more prominent for lower GW frequencies. Gravitational lensing imprints a characteristic modulation on a chirp waveform; therefore, we can deduce whether a measured arrival time lag arises from intrinsic source properties or gravitational lensing. Determination of arrival time differences would be extremely useful in multi messenger observations and tests of GR.
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