arXiv subjects

Randy S. Conklin

Publications and source records attributed to Randy S. Conklin.

4 recordsLinked to original sources

arXiv2021

Boltzmann Meets Lorentz: A Surrogate Model for Black Hole Echoes

The existence of black hole horizons has not been strictly proven observationally, and indeed it may not be possible to do so. However, alternatives may be established by the observation of gravitational wave echoes that probe possible near-horizon structure. These echoes are proposed to be generated in exotic compact objects that are horizonless and feature a partially reflecting "wall" inside their light rings, creating a cavity in which gravitational perturbations may echo, while leaking out through the angular momentum barrier with each pass. The characteristic signature of echoes is a comb of nearly evenly spaced spectral resonances. While approximately true, deviations from this simple picture can lead to severe observational signal losses. In this paper, we explore such subtleties with the latest results for echo sourcing and geometry. A physically motivated echo model is then developed as a sum over Lorentzian spectral lines, parametrized by functions of the horizon frame frequency and the size of the cavity. Our final spectrum is a function of only the mass and spin of the black hole, as well as the UV scale of the near-horizon physics. We then apply this model in a search for echoes in the gravitational wave event with the loudest ringdown signal in LIGO/Virgo, i.e. GW190521. We interpret our findings as a measurement of the fractional energy in post-merger echoes equal to $E_{echoes} / E_{GR} = 8.9 \pm 4.5\%$, where the uncertainty range represents the 90% credible region. The robustness of this result is tested against noise backgrounds and simulated injections, and we find that a signal persists through modifications to the model and changes in the data search.

gr-qc↗

arXiv2019

Gravitational Wave "Echo" Spectra

Exotic compact objects may resemble black holes very closely while remaining horizonless. They may be distinguished from black holes because they effectively give rise to a resonant cavity for the propagation of low frequency gravity waves. In a Green's function approach, the resonance structure appears in a transfer function. The transfer function in turn is modulated by an initial-condition-dependent source integral to obtain the observed spectrum. We find that the source integral displays universal factors that tend to enhance low and negative frequencies, and this increases the complexity of the waveforms in the time domain. These waveforms also display a significant sensitivity to initial conditions. For these reasons a standard matched-filter search strategy is difficult. In contrast, the sharp and evenly spaced resonance spectrum presents a much more robust signal to target. It persists even in the absence of simple echoes. We also describe an additional two-component structure of this resonance pattern.

gr-qc↗

arXiv2019

Gravitational Wave Perturbations on a Kerr Background and Applications for Echoes

Gravitational wave echoes may imply physics beyond general relativity; however, several approaches to searching for echoes require fitting the data to toy templates which are not physically motivated. Here, I create a procedure which outputs a more realistic form for echoes, starting from initial conditions, by calculating the modulated transfer function.

gr-qc↗

arXiv2018

Gravitational wave echoes through new windows

There has been a striking realization that physics resolving the black hole information paradox could imply postmerger gravitational wave echoes. We here report on evidence for echoes from the LIGO compact binary merger events, GW151226, GW170104, GW170608, GW170814, as well as the neutron star merger GW170817. There is a signal for each event with a $p$-value of order 1% or sometimes significantly less. Our study begins with the comparison of echoes from a variety of horizonless exotic compact objects. Next we investigate the effects of spin. The identification of the more generic features of echoes then leads to the development of relatively simple windowing methods, in both time and frequency space, to extract a signal from noise. The time delay between echoes is inversely related to the spacing between the spectral resonances, and it is advantageous to look directly for this resonance structure. We find time delays for the first four events that are consistent with a simple model that accounts for mass and spin of the final object, while for the neutron star merger the final mass and spin are constrained.

gr-qc↗