NASA EM Followup of LIGO-Virgo Candidate Events

We present a strategy for a follow-up of LIGO-Virgo candidate events using offline survey data from several NASA high-energy photon instruments aboard RXTE, Swift, and Fermi. Time and sky-location information provided by the GW trigger allows for a targeted search for prompt and afterglow EM signals. In doing so, we expect to be sensitive to signals which are too weak to be publicly reported as astrophysical EM events

Open Issues in the search for gravitational wave transients

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 193-201).The LIGO-Virgo network of kilometer-scale laser interferometric gravitational-wave detectors reached a major milestone with the successful operation of LIGO's fifth (S5) and Virgo's first (VSR1) science runs during 2005-2007. This thesis presents several issues related to gravitational-wave transient detection from the perspective of the joint all-sky, un-triggered burst search over S5/VSR1 data. Existing searches for gravitational-wave bursts must deal with the presence of non-Gaussian noise transients which populate the data over the majority of sensitive signal space. These events may be confused with true signals, and are the current limiting factor in search sensitivity and detection confidence for any real event. The first part of this thesis focuses on the development of tools to identify, monitor and characterize these instrumental disturbances in LIGO and Virgo data. An automated procedure is developed and applied to the S5/VSR1 search in order to safely remove noise transients from the analysis without sacrificing sensitivity by making use of the wealth of auxiliary information recorded by the detectors. The second part of this thesis focuses on the interpretation of outlier events in the context of a non-Gaussian, non-stationary background. An extensive follow-up procedure for candidate gravitational-wave events is developed and applied to a single burst outlier from the S5/VSR1 search, later revealed to be a blind simulation injected into the instruments. While the follow-up procedure correctly finds no reason to reject the candidate as a possible gravitational wave, it highlights the difficulty in making a confident detection for signals with similar waveform morphology to common instrumental disturbances. The follow-up also deals with the problem of objectively defining the significance of a single outlier event in the context of many semi-disjoint individual searches. To address this, a likelihood-ratio based unified ranking is developed and tested against the original procedures of the S5/VSR1 burst search. The new ranking shows a factor of four improvement in the statistical significance of the outlier event, and a 12% reduction using fixed thresholds and 38% reduction using a loudest event statistic for a rate upper limit on a mock signal population.by Lindy L. BlackburnPh.D

Optimizing Vetoes for Gravitational-wave Transient Searches

Interferometric gravitational-wave detectors like LIGO, GEO600 and Virgo record a surplus of information above and beyond possible gravitational-wave events. These auxiliary channels capture information about the state of the detector and its surroundings which can be used to infer potential terrestrial noise sources of some gravitational-wave-like events. We present an algorithm addressing the ordering (or equivalently optimizing) of such information from auxiliary systems in gravitational-wave detectors to establish veto conditions in searches for gravitational-wave transients. The procedure was used to identify vetoes for searches for unmodelled transients by the LIGO and Virgo collaborations during their science runs from 2005 through 2007. In this work we present the details of the algorithm; we also use a limited amount of data from LIGO's past runs in order to examine the method, compare it with other methods, and identify its potential to characterize the instruments themselves. We examine the dependence of Receiver Operating Characteristic curves on the various parameters of the veto method and the implementation on real data. We find that the method robustly determines important auxiliary channels, ordering them by the apparent strength of their correlations to the gravitational-wave channel. This list can substantially reduce the background of noise events in the gravitational-wave data. In this way it can identify the source of glitches in the detector as well as assist in establishing confidence in the detection of gravitational-wave transients

Techniques for targeted Fermi-GBM follow-up of gravitational-wave events

The Advanced LIGO and Advanced Virgo ground-based gravitational-wave detectors are projected to come online 2015-2016, reaching a final sensitivity sufficient to observe dozens of binary neutron star mergers per year by 2018. We present a fully-automated, targeted search strategy for prompt gamma-ray counterparts in offline Fermi-GBM data. The multi-detector method makes use of a detailed model response of the instrument, and benefits from time and sky location information derived from the gravitational-wave signal.Comment: 2012 Fermi Symposium proceedings - eConf C12102

Planned search for LIGO-GBM coincidence in the first advanced LIGO data run

In the fall of 2015 the first scientific observing run (O1) of the advanced LIGO detectors will be conducted. Based on the recent commissioning progress at the LIGO Hanford and Livingston sites, the gravitational wave detector range for a neutron star binary inspiral is expected to be of order 60 Mpc. We describe here our planning for an O1 search for coincidence between a LIGO gravitational wave detection and a gamma-ray signal from the Fermi Gamma-ray Burst Monitor. Such a coincidence would constitute measurement of an electromagnetic counterpart to a gravitational wave signal, with significant corresponding scientific benefits, including revealing the central engine powering the gamma-ray burst, enhanced confidence in the event as a genuine astrophysical detection, and a determination of the relative speed of the photon and graviton.Comment: Submitted to Moriond Gravitation Conference Proceedings 201

Closure statistics in interferometric data

Interferometric visibilities, reflecting the complex correlations between signals recorded at antennas in an interferometric array, carry information about the angular structure of a distant source. While unknown antenna gains in both amplitude and phase can prevent direct interpretation of these measurements, certain combinations of visibilities called closure phases and closure amplitudes are independent of antenna gains and provide a convenient set of robust observables. However, these closure quantities have subtle noise properties and are generally both linearly and statistically dependent. These complications have obstructed the proper use of closure quantities in interferometric analysis, and they have obscured the relationship between analysis with closure quantities and other analysis techniques such as self calibration. We review the statistics of closure quantities, noting common pitfalls that arise when approaching low signal-to-noise due to the nonlinear propagation of statistical errors. We then develop a strategy for isolating and fitting to the independent degrees of freedom captured by the closure quantities through explicit construction of linearly independent sets of quantities along with their noise covariance in the Gaussian limit, valid for moderate signal-to-noise, and we demonstrate that model fits have biased posteriors when this covariance is ignored. Finally, we introduce a unified procedure for fitting to both closure information and partially calibrated visibilities, and we demonstrate both analytically and numerically the direct equivalence of inference based on closure quantities to that based on self calibration of complex visibilities with unconstrained antenna gains.Comment: 31 pages, 17 figure

X-Ray Transients in the Advanced LIGO/Virgo Horizon

Advanced LIGO and Advanced Virgo will be all-sky monitors for merging compact objects within a few hundred megaparsecs. Finding the electromagnetic counterparts to these events will require an understanding of the transient sky at low redshift (z < 0.1). We performed a systematic search for extragalactic, low redshift, transient events in the XMM-Newton Slew Survey. In a flux limited sample, we found that highly variable objects comprised 10% of the sample, and that of these, 10% were spatially coincident with cataloged optical galaxies. This led to 4 × 10−4 transients per square degree above a flux threshold of 3 × 10^(−12) erg cm^−2 s^−1 (0.2–2 keV) which might be confused with LIGO/Virgo counterparts. This represents the first extragalactic measurement of the soft X-ray transient rate within the Advanced LIGO/Virgo horizon. Our search revealed six objects that were spatially coincident with previously cataloged galaxies, lacked evidence for optical active galactic nuclei, displayed high luminosities ~10^(43) erg s^−1, and varied in flux by more than a factor of 10 when compared with the ROSAT All-Sky Survey. At least four of these displayed properties consistent with previously observed tidal disruption events