AR-2019-2020

(see Fig. 12), especially when the intensity of the source is weak, and it dramatically improves the stability of deconvolution. Effect of induced seismicity on advanced gravitational wave interferome- ters Advanced LIGO and the next generation of ground-based detectors aim to capture a large number of binary coalescences through improving sensitivity and duty cycle. Earthquakes have always been a limiting factor at lower frequencies, where neither the pendulum suspension nor the active controls provide sufficient isolation to the test mass mirrors. Several control strategies have been proposed to reduce the impact of teleseismic events by switching to a robust configuration with less aggressive feedback. The continental United States has witnessed a huge increase in the number of induced earthquake events primarily associated with hydraulic fracking-related waste water re- injection. Effects from these differ from teleseismic earthquakes primarily because of their depth which is in turn linked to their triggering mechanism. N. Mukund, B. O’Reilly, S. Somala and Sanjit Mitra discuss the impact caused by these low magnitude regional earthquakes and explore ways to minimize the impact of induced seismicity on the detector. Hierarchical search for detecting gravitational waves from compact coa- lescing binaries (CBC). Standard searches are currently restricted to the parameter space which assumes aligned spins. A larger parameter space allowing precession will entail far more number of templates escalating the computational cost. Optimising the consequential increase in false alarms poses a serious computational challenge. Bhushan Gadre, Sanjit Mitra and Sanjeev Dhurandhar propose here a hierarchical strategy to search for CBCs for a network of detectors. The methodology is essentially as follows: In the first step, a search with a coarse bank at low sampling rate is performed with a relatively low threshold and then the candidate triggers are followed up with a fine search with the requisite threshold. This method of search is more efficient. They demonstrate the computational advantage of about 20 over the usual search in real data. This saving in the computational cost will allow them to free up computational resources and time. Optimal chi-square vetos for sine-Gaussian glitches The traditional chi-square veto has been applied to the gravitational wave data with fair amount of success. However, this test is ad hoc and is not guaranteed to be optimal. In this work, R. Dhurkunde, P. Joshi, Sanjeev Dhurandhar and Sukanta Bose construct an optimal chi-square test for glitches in the data, which can be modelled as sine-Gaussians, because such glitches are ubiquitous in the data. The method for constructing any chi-square has been fully discussed in our previous work on unified chi-squares ( Sanjeev Dhurandhar , et al., 2017). The parameter space of sine-Gaussians is adequately sampled and a vector space spanned by these sampled glitches is obtained. However, this space is very large from the computational point of view. By applying singular value decomposition techniques, it is possible to whittle down this space to a much lower dimensional subspace which best approximates the glitches. This procedure eventually leads to the required optimal chi-square for sine-Gaussian glitches. Improving the anisotropic stochastic background search with a natural set of basis functions The anisotropic stochastic background is estimated using the radiometric search, in which one cross- correlates the time series data from two detectors in short data segments, and then takes the noise weighted sum to arrive at a statistic. However, this statistic results in point spread function, which maps a point source to a diffused image. Therefore, the image obtained of any source is dirty