36th Annual Report (2023-24)

26 Schaffner-Bielich [JCAP 12, 008 (2023)]. It was shown how nuclear parameters can be constrained from next-generation detectors using gravitational waves from glitch- powered f-mode oscillations in Neutron Stars by B K. Pradhan, D. Pathak and D. Chatterjee [Astrophys. J. 956, 38 (2023)]. An additional tidal contribution comes from the higher-order tidal terms and can impact the GW waveform. The following works have been done in this direction by B. K. Pradhan, A. Vijaykumar, and D. Chatterjee [Phys. Rev. D 107, 023010 (2023)], who investigated the impact of URs and the tidal corrections on the NS properties inferred from GW170817 as well as from future binary events. B K. Pradhan, T. Ghosh, D. Pathak and D. Chatterjee [Astrophys. J. 966, 79 (2023)] investigated the effect of the dynamical tidal correction on the inferred nuclear physics from a binary system Distinguishing Strange Stars (SSs) using Gravitational Waves: NSs and SSs follow a different relation between f - mo d e f r e q u e n c y a n d t i d a l deformability (f-Love relation). B.K. Pradhan, S. Shirke, and D. Chatterjee [arXiv:2311.15745 (2023)] outlined the methodology and showed that the next- generation GW detectors will be able to gather “substantial evidence” for or against the existence of strange stars in a single GW170817-like event, demonstrating the potential of GW to settle the long-standing fundamental physics problem of the true ground state ofmatter. Constraining Neutron Star Physics: Unstable rotational r-modes can also be sources of continuous GW from isolated pulsars. The frequency of the emitted GW depends on the compactness of the star but it is universal i.e. independent of neutron star EOS. The Universal relation updated in Ghosh et al. [ApJ 944, 53 (2023)] determines the search parameters from known pulsars to be implemented in the O4 run. From a ¬ ¬ ContinuousWaves future detection, measurement of frequency and spin down can give independent measurements of Compactness and moment of inertia which was shown to be useful in constraining the dense matter EOS inside a neutron star. [MNRAS 525, 448 (2023)] Improving the spin-down limits for the continuous gravitational waves: Recently, Abbott et al. ApJ 935, 1 (2022) gave spin-down limits for a set of 237 pulsars out of which only 144 were corrected for dynamical effects in spin frequency derivative, that too using an inexact traditional approach. D. Pathak and D. Chatterjee [A&A 679, A17 (2023)] improved the values of the spin-down limit of the continuous gravitational wave strain (assuming pulsars as triaxial rotators) for the set of pulsars given in Abbott et al. (2022) by using ‘GalDynPsr’, a python-based public package used to calculatemore realistic values of intrinsic spin frequency derivatives, on which the spin-down limit depends. It was found that for 2 pulsars (PSRs J2222-0137 and J1400- 1431) percentage increase in spin- down limit values was greater than 100% and for 3 pulsars (PSRs J2322- 2650, J1709+2313, and J2010-1323), the percentage increase in spin-down limit values was between 20% and 100%. Gopalkrishna Prabhu and Shasvath J. Kapadia, in collaboration with Aditya Sharma and R. Prasad at ICTS-TIFR constrained the abundance of spinning, deformed, isolated compact objects (such as highly elliptical neutron stars) in our Milky Way Galaxy, from the non-detection of continuous gravitational waves. They are working on constraining other interesting physics from these non-detections. [arXiv:2403.00502 (2024)]. LIGO control system: Shivaraj Kandhasamy, along with other IUCAA members, set up a LIGO-like but ¬ ¬ ¬ Instrumentation smaller-scale Control and Data System (CDS) using hardware and software used in LIGO. It was also interfaced with a small rigid Michelson interferometer. The Michelson interferometer was locked using the built CDS (see figure), and the interferometer output was calibrated to physical units. This was a significant milestone in understanding and using the LIGO CDS, one of the critical subsystems in LIGO. The experience gained from such a system will be helpful for LIGO-India operations. ¬ S e i sm i c i s o l a t o r a n d s e n s o r development: Suresh Doravari has developed a novel single-stage seismic isolator based on a well known mechanical linkage known as “Roberts Linkage”. The seismic isolator (presently under fabrication) acts as a low pass filter with a tunable corner frequency of about 0.1 Hz in all the six degrees of freedom of motion. A multiple-input-multiple-output (MIMO) feedback control system utilising