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Alexander Nitz

Publications and source records attributed to Alexander Nitz.

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Adapting the PyCBC pipeline to find and infer the properties of gravitational waves from massive black hole binaries in LISA

The Laser Interferometer Space Antenna (LISA), due for launch in the mid 2030s, is expected to observe gravitational waves (GW)s from merging massive black hole binaries (MBHB)s. These signals can last from days to months, depending on the masses of the black holes, and are expected to be observed with high signal to noise ratios (SNR)s out to high redshifts. We have adapted the PyCBC software package to enable a template bank search and inference of GWs from MBHBs. The pipeline is tested on the LISA data challenge (LDC)'s Challenge 2a (\enquote{Sangria}), which contains MBHBs and thousands of galactic binaries (GBs) in simulated instrumental LISA noise. Our search identifies all 6 MBHB signals with more than $92\%$ of the optimal SNR. The subsequent parameter inference step recovers the masses and spins within their $90\%$ confidence interval. Sky position parameters have 8 high likelihood modes which are recovered but often our posteriors favour the incorrect sky mode. We observe that the addition of GBs biases the parameter recovery of masses and spins away from the injected values, reinforcing the need for a global fit pipeline which will simultaneously fit the parameters of the GB signals before estimating the parameters of MBHBs.

astro-ph.IM

Space-based Gravitational Wave Observatories Will Be Able to Use Eccentricity to Unveil Stellar-mass Binary Black Hole Formation

The measurement of eccentricity would provide strong constraints on the formation channel of stellar-mass binary black holes. However, current ground-based gravitational wave detectors will, in most cases, not be able to measure eccentricity due to orbital circularization. Space-based observatories, in contrast, can determine binary eccentricity at 0.01Hz to $e_{0.01}\gtrsim\mathcal{O}(10^{-4}) $. Directly observing stellar-mass binary black holes with space-based observatories remains a challenging problem. However, observing such systems with ground-based detectors allows the possibility to identify the same signal in archival data from space-based observatories in the years previous. Since ground-based detectors provide little constraints on eccentricity, including eccentricity in the archival search will increase the required number of filter waveforms for the archival search by 5 orders of magnitudes [from $\sim \mathcal{O}(10^3)$ to $\sim \mathcal{O}(10^8)$], and will correspondingly need $ \sim8\times10^5 $ core hours (and $ \sim 10^5$ GB of memory), even for a mild upper limit on eccentricity of $0.1$. In this work, we have constructed the first template bank for an archival search of space-based gravitational wave detectors, including eccentricity. We have demonstrated that even though the inclusion of eccentricity brings extra computational burden, an archival search including eccentricity will be feasible in the time frame of planned space-based observatories, and will provide strong constraints on the eccentricities of stellar-mass binary black holes.

astro-ph.HE