ORCID Profile
0000-0002-4843-1112
Current Organisations
KEMRI-Wellcome Trust Research Programme
,
Universität Hamburg
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Publisher: American Physical Society (APS)
Date: 19-01-2022
Publisher: American Physical Society (APS)
Date: 23-07-2021
Publisher: American Physical Society (APS)
Date: 16-06-2021
Publisher: American Physical Society (APS)
Date: 11-11-2021
Publisher: American Physical Society (APS)
Date: 31-03-2022
Publisher: American Physical Society (APS)
Date: 27-07-2021
Publisher: American Physical Society (APS)
Date: 09-05-2022
Publisher: EDP Sciences
Date: 03-2022
DOI: 10.1051/0004-6361/202141452
Abstract: Intermediate-mass black holes (IMBHs) span the approximate mass range 100−10 5 M ⊙ , between black holes (BHs) that formed by stellar collapse and the supermassive BHs at the centers of galaxies. Mergers of IMBH binaries are the most energetic gravitational-wave sources accessible by the terrestrial detector network. Searches of the first two observing runs of Advanced LIGO and Advanced Virgo did not yield any significant IMBH binary signals. In the third observing run (O3), the increased network sensitivity enabled the detection of GW190521, a signal consistent with a binary merger of mass ∼150 M ⊙ providing direct evidence of IMBH formation. Here, we report on a dedicated search of O3 data for further IMBH binary mergers, combining both modeled (matched filter) and model-independent search methods. We find some marginal candidates, but none are sufficiently significant to indicate detection of further IMBH mergers. We quantify the sensitivity of the in idual search methods and of the combined search using a suite of IMBH binary signals obtained via numerical relativity, including the effects of spins misaligned with the binary orbital axis, and present the resulting upper limits on astrophysical merger rates. Our most stringent limit is for equal mass and aligned spin BH binary of total mass 200 M ⊙ and effective aligned spin 0.8 at 0.056 Gpc −3 yr −1 (90% confidence), a factor of 3.5 more constraining than previous LIGO-Virgo limits. We also update the estimated rate of mergers similar to GW190521 to 0.08 Gpc −3 yr −1 .
Publisher: Cold Spring Harbor Laboratory
Date: 26-08-2021
DOI: 10.1101/2021.08.21.21262393
Abstract: Genomic sequencing provides critical information to track the evolution and spread of SARS-CoV-2, optimize molecular tests, treatments and vaccines, and guide public health responses. To investigate the spatiotemporal heterogeneity in the global SARS-CoV-2 genomic surveillance, we estimated the impact of sequencing intensity and turnaround times (TAT) on variant detection in 167 countries. Most countries submit genomes days after s le collection, and 77% of low and middle income countries sequenced .5% of their cases. We found that sequencing at least 0.5% of the cases, with a TAT days, could be a benchmark for SARS-CoV-2 genomic surveillance efforts. Socioeconomic inequalities substantially impact our ability to quickly detect SARS-CoV-2 variants, and undermine the global pandemic preparedness. Socioeconomic inequalities impacted the SARS-CoV-2 genomic surveillance, and undermined the global pandemic preparedness.
Publisher: American Physical Society (APS)
Date: 08-10-2021
Publisher: arXiv
Date: 2022
Publisher: American Physical Society (APS)
Date: 28-11-2022
Publisher: American Physical Society (APS)
Date: 28-04-2022
Publisher: American Physical Society (APS)
Date: 21-09-2022
Publisher: American Physical Society (APS)
Date: 12-03-2021
Publisher: American Astronomical Society
Date: 06-2022
Abstract: Isolated neutron stars that are asymmetric with respect to their spin axis are possible sources of detectable continuous gravitational waves. This paper presents a fully coherent search for such signals from eighteen pulsars in data from LIGO and Virgo’s third observing run (O3). For known pulsars, efficient and sensitive matched-filter searches can be carried out if one assumes the gravitational radiation is phase-locked to the electromagnetic emission. In the search presented here, we relax this assumption and allow both the frequency and the time derivative of the frequency of the gravitational waves to vary in a small range around those inferred from electromagnetic observations. We find no evidence for continuous gravitational waves, and set upper limits on the strain litude for each target. These limits are more constraining for seven of the targets than the spin-down limit defined by ascribing all rotational energy loss to gravitational radiation. In an additional search, we look in O3 data for long-duration (hours–months) transient gravitational waves in the aftermath of pulsar glitches for six targets with a total of nine glitches. We report two marginal outliers from this search, but find no clear evidence for such emission either. The resulting duration-dependent strain upper limits do not surpass indirect energy constraints for any of these targets.
Publisher: arXiv
Date: 2022
Publisher: American Astronomical Society
Date: 04-2022
Abstract: We search for gravitational-wave signals associated with gamma-ray bursts (GRBs) detected by the Fermi and Swift satellites during the second half of the third observing run of Advanced LIGO and Advanced Virgo (2019 November 1 15:00 UTC–2020 March 27 17:00 UTC). We conduct two independent searches: a generic gravitational-wave transients search to analyze 86 GRBs and an analysis to target binary mergers with at least one neutron star as short GRB progenitors for 17 events. We find no significant evidence for gravitational-wave signals associated with any of these GRBs. A weighted binomial test of the combined results finds no evidence for subthreshold gravitational-wave signals associated with this GRB ensemble either. We use several source types and signal morphologies during the searches, resulting in lower bounds on the estimated distance to each GRB. Finally, we constrain the population of low-luminosity short GRBs using results from the first to the third observing runs of Advanced LIGO and Advanced Virgo. The resulting population is in accordance with the local binary neutron star merger rate.
Publisher: arXiv
Date: 2021
Publisher: American Astronomical Society
Date: 29-06-2021
Abstract: We report the observation of gravitational waves from two compact binary coalescences in LIGO’s and Virgo’s third observing run with properties consistent with neutron star–black hole (NSBH) binaries. The two events are named GW200105_162426 and GW200115_042309, abbreviated as GW200105 and GW200115 the first was observed by LIGO Livingston and Virgo and the second by all three LIGO–Virgo detectors. The source of GW200105 has component masses 8 . 9 − 1 . 5 + 1. 2 and 1. 9 − 0. 2 + 0. 3 M ⊙ , whereas the source of GW200115 has component masses 5. 7 − 2 . 1 + 1. 8 and 1. 5 − 0. 3 + 0. 7 M ⊙ (all measurements quoted at the 90% credible level). The probability that the secondary’s mass is below the maximal mass of a neutron star is 89%–96% and 87%–98%, respectively, for GW200105 and GW200115, with the ranges arising from different astrophysical assumptions. The source luminosity distances are 280 − 110 + 110 and 300 − 100 + 150 Mpc , respectively. The magnitude of the primary spin of GW200105 is less than 0.23 at the 90% credible level, and its orientation is unconstrained. For GW200115, the primary spin has a negative spin projection onto the orbital angular momentum at 88% probability. We are unable to constrain the spin or tidal deformation of the secondary component for either event. We infer an NSBH merger rate density of 45 − 33 + 75 Gpc − 3 yr − 1 when assuming that GW200105 and GW200115 are representative of the NSBH population or 130 − 69 + 112 Gpc − 3 yr − 1 under the assumption of a broader distribution of component masses.
Publisher: arXiv
Date: 2021
Publisher: arXiv
Date: 2021
Publisher: American Astronomical Society
Date: 12-2022
Abstract: We present the results of a model-based search for continuous gravitational waves from the low-mass X-ray binary Scorpius X-1 using LIGO detector data from the third observing run of Advanced LIGO and Advanced Virgo. This is a semicoherent search that uses details of the signal model to coherently combine data separated by less than a specified coherence time, which can be adjusted to balance sensitivity with computing cost. The search covered a range of gravitational-wave frequencies from 25 to 1600 Hz, as well as ranges in orbital speed, frequency, and phase determined from observational constraints. No significant detection candidates were found, and upper limits were set as a function of frequency. The most stringent limits, between 100 and 200 Hz, correspond to an litude h 0 of about 10 −25 when marginalized isotropically over the unknown inclination angle of the neutron star’s rotation axis, or less than 4 × 10 −26 assuming the optimal orientation. The sensitivity of this search is now probing litudes predicted by models of torque balance equilibrium. For the usual conservative model assuming accretion at the surface of the neutron star, our isotropically marginalized upper limits are close to the predicted litude from about 70 to 100 Hz the limits assuming that the neutron star spin is aligned with the most likely orbital angular momentum are below the conservative torque balance predictions from 40 to 200 Hz. Assuming a broader range of accretion models, our direct limits on gravitational-wave litude delve into the relevant parameter space over a wide range of frequencies, to 500 Hz or more.
Publisher: American Physical Society (APS)
Date: 09-08-2022
Publisher: American Physical Society (APS)
Date: 05-08-2022
Publisher: American Physical Society (APS)
Date: 23-12-2021
Publisher: arXiv
Date: 2021
Publisher: American Physical Society (APS)
Date: 03-06-2022
Publisher: arXiv
Date: 2021
Publisher: arXiv
Date: 2021
Location: United Kingdom of Great Britain and Northern Ireland
Location: United States of America
No related grants have been discovered for Alexander Franke.