The Padova-Trento Virgo group: Data Analysis in Virgo

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2 Data Analysis in Virgo


The Padova-Trento group is also deeply involved in the activities performed by the Burst Data Analysis group, a joint LIGO-Virgo working group in charge of pursuing searches for gravitational wave transients from any detectable source. In particular, Padova-Trento, LIGO UFL and GEO AEI groups developed the data analysis pipeline coherent-WaveBurst (cWB), which is considered the reference method for the most general searches of gravitational wave transients. This pipeline identifies coherent responses of the detectors of the network, consistent with generic properties of gravitational waves with duration in the range 1ms to tens of seconds and incoming from any sky direction. Padova-Trento is also a reference group for the analysis of all-sky searches for generic transients and is supporting LIGO-Virgo users of the pipeline.

The cWB pipeline is a major discovery tool for the LIGO-Virgo collaborations, and is the most effective available method to detect transient signals, whose emission process either is unknown or is still lacking a comprehensive model, such as in the case of Supernovae and Neutron Stars emissions. The same cWB analysis covers simultaneously also well-known sources classes, as e.g. coalescences of Black Holes binaries. In these cases, it usually approaches the Signal-to-Noise Ratio achievable by optimal methods based on matched filtering to the signal template, and therefore provides a validation of the results achieved in the wider context of generic-transient observations. Moreover, the computational efficiency of cWB allows a real time analysis, within a few minutes latency, which is suitable for triggering electromagnetic follow-up observations to quest for the counterpart of the gravitational wave source.

Further developments of the analysis methods are ongoing, in particular to improve performances concerning the non-parametric reconstruction of the gravitational wave waveform, the rapid classification of transients and the estimated error regions for the source location in the sky. These are fundamental assets for surveys of the transient sky and for multi-messenger observations of a wide class of astrophysical processes, where the complementary information carried by gravitational waves, photons and neutrinos can boost our horizons. In addition, Padova-Trento is extending the pipeline’s features to pursue specific astrophysical investigations, as e.g. constraining the equation of state of Neutron Stars from the comparison of observable and predicted emissions during the merger and post-merger phases of a binary coalescence, searching for mergers of intermediate mass Black Holes and searching for compact binary coalescences with high residual eccentricity.

Map of the sensitivity of the Gravitational Wave network of detectors, consisting in Advanced Virgo (V in the figure) and the two Advanced LIGO detectors (H and L in the figure). Dimensions of detectors have been exaggerated for clarity. The sensitivity {is averaged over gravitational wave polarizations and} is shown by the color scale at each geographic coordinate, where the unitary value corresponds to the maximum sensitivity of one detector. The LIGO-Virgo network gives a satisfactory coverage for most of the directions. In general, at least three detectors are required to spot the location of the gravitational wave source within tens of square degrees.

Example of gravitational wave transient as seen by the cWB analysis of the Padova-Trento group: this event is consistent with what is expected by the coalescence of a binary system as that of two black-holes or a black-hole and a neutron star. This event was not a real signal but a simulated one, which was blind injected into the data stream: this is done to train and test the search procedures so to be confident they can really detect incoming signals.
For more detals in this specific example see: Big Dog

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