http://hdl.handle.net/2289/142 Sun, 19 Apr 2026 03:29:56 GMT 2026-04-19T03:29:56Z http://hdl.handle.net/2289/8706 Title: Revisiting wideband pulsar timing measurements Authors: Susobhanan, Abhimanyu; Paladi, Avinash Kumar; Desmecht, Réka; Amarnath; Bagchi, Manjari; Chakraborty, Manoneeta; Chowdhury, Shaswata; Das, Suruj Jyoti; Deb, Debabrata; Desai, Shantanu; Dwivedi, Churchil; Grover, Himanshu; Jose, Jibin; Joshi, Bhal Chandra; Kala, Shubham; Kareem, Fazal; Meena, Kuldeep; Mondal, Sushovan; Nobleson, K; Pandian, B Arul; Rai, Kaustubh; Shukla, Adya; Singh, Manpreet; Srivastava, Aman; Surnis, Mayuresh; Tahbildar, Hemanga; Takahashi, Keitaro; Tarafdar, Pratik; Vara, Kunjal; Vyasraj, Vaishnavi; Zuraiq, Zenia Abstract: In the wideband paradigm of pulsar timing, the time of arrival of a pulsar pulse is measured simultaneously with the corresponding dispersion measure from a frequency-resolved integrated pulse profile. We present a new method for performing wideband measurements that rigorously accounts for measurement noise. We demonstrate this method using observations of PSR J2124−3358 made as part of the Indian Pulsar Timing Array experiment using the upgraded Giant Metre-wave Radio Telescope, and show that our method produces more realistic measurement uncertainty estimates compared to the existing wideband measurement method. Description: Open Access. Also available at arXiv.org (one of the alternative locations) Mon, 09 Mar 2026 00:00:00 GMT http://hdl.handle.net/2289/8706 2026-03-09T00:00:00Z http://hdl.handle.net/2289/8704 Title: The indian pulsar timing array data release 2: II. Customised single-pulsar noise analysis and noise budget Authors: Nobleson, K; Dwivedi, Churchil; Desai, Shantanu; Joshi, Bhal Chandra; Grover, Himanshu; Deb, Debabrata; Vyasraj, Vaishnavi; Vara, Kunjal; Tahbildat, Hemanga; Susobhanah, Abhimanyu; Surnis, Mayuresh; Srivastava, Aman; Sardana, Shubhit; Takahashi, Keitaro; Amarnath; Arumugam, P; Bagchi, Manjari; Batra, Neelam Dhanda; Chakraborty, Manoneeta; Chowdhury, Shaswata; Jacob, Shebin Jose; Jose, Jibin; Kala, Shubham; Kato, Ryo; Krishnakumar, M A; Meena, Kuldeep; Paladi, Avinash Kumar; Pandian, Arul; Rai, Kaustubh; Rana, Prerna; Singh, Manpreet; Singha, Jaikhomba; Shukla, Adya; Tarafdar, Pratik; Thiagraj, Prabu; Zuraiq, Zenia Abstract: We present the results of customised single-pulsar noise analysis of 27 millisecond pulsars from the second data release of the Indian Pulsar Timing Array (InPTA-DR2). We model various stochastic noise sources present in the dataset using stationary Gaussian processes and estimate the noise budget of the InPTA-DR2 using Bayesian inference, involving model selection, Fourier harmonics selection, and parameter estimation for each pulsar. We check the efficacy of our noise characterisation by performing the Anderson-Darling test for Gaussianity on the noise-subtracted residuals. We find that all 11 pulsars with time baseline  ≲ 2.5 yr show Gaussian residuals and do not have evidence for any red noise process in the optimal model, except for PSR J1944 + 0907, which shows presence of DM noise. PSRs J0437 - 4715, J1909 - 3744 and J1939 + 2134 show preference for the most complicated noise model, having achromatic and chromatic red noise processes. Only 4 out of 15 pulsars with time baseline  ≳ 2.5 yr show significant non-Gaussianity in noise-subtracted residuals. We suspect that this may require more advanced methods to model noise processes properly. A comparative study of six pulsars with data removed near solar conjunctions showed deviations from the parameter estimates obtained with the original dataset, indicating potential bias in red noise processes due to unmodeled solar-wind effects. The results presented in this work remain broadly consistent with the InPTA-DR1 noise budget, with better constraints obtained on noise processes for several pulsars and support for achromatic red noise in PSR J1012 + 5307 due to the extended time baseline. Description: Restricted Access. An open-access version is available at arXiv.org (one of the alternative locations) Wed, 01 Jul 2026 00:00:00 GMT http://hdl.handle.net/2289/8704 2026-07-01T00:00:00Z http://hdl.handle.net/2289/8700 Title: Synchrotron Radiation from NGC 470 HLX1—a Hidden Hyperluminous Accreting Neutron Star? Authors: Ghosh, Tanuman; Sethi, Shiv; Dewangan, Gulab Chand; Bachetti, Matteo; Rana, Vikram; Misra, Ranjeev Abstract: The origin of the large-amplitude, quasi-periodic X-ray flux variations in several classes of the Galactic microquasar GRS 1915+105 remains unresolved. We address this issue through flux-resolved, broadband (0.8–20 keV) spectral modeling and simultaneous covariance spectral analysis during two κ and two ω class observations using AstroSat/SXT and LAXPC. The lightcurves show strong, quasi-periodic oscillations involving rapid transitions between bright bursts and deep dips on timescales of a few tens of seconds. Flux-resolved spectroscopy indicates that high-flux intervals in both classes are dominated by a hot, optically thick accretion disk with steep Comptonized emission, whereas low-flux intervals correspond to a cooler or partially recessed disk and a harder coronal continuum. These transitions involve a systematic 1–2 keV drop in disk temperature and a pronounced hardening of the Comptonized component, with flux reductions of up to a factor of five. Using covariance spectra across 0.015–5 Hz, we show that the rapid coherent variability arises almost entirely from the disk, which exhibits strong energy-dependent variations, while the Comptonized component contributes minimally. The combined results suggest that radiation-pressure-driven structural changes in the disk, with a slower coronal response, produce the observed oscillations, consistent with cyclic disk evacuation and refilling in the κ and ω classes. Description: Open Access Mon, 16 Mar 2026 00:00:00 GMT http://hdl.handle.net/2289/8700 2026-03-16T00:00:00Z http://hdl.handle.net/2289/8699 Title: Observing octupolar charge orders and their transition dynamics in Coulomb clusters Authors: Ayyadevara, Akhil; Prakash, Anand; Dutta, Shovan; Paramekanti, Arun; Rangwala, S A Abstract: Interacting many-particle systems can self-organize into a rich variety of crystalline structures. While symmetry provides a powerful framework for predicting whether transitions between crystal states are continuous or discontinuous, collective lattice dynamics offer complementary insights into the microscopic mechanisms that drive these transitions. Trapped laser-cooled ions present a pristine and highly controllable system for studying this interplay of symmetry and dynamics. Here, we use real-time fluorescence imaging while deforming the trap potential to observe a variety of structural transitions in three-dimensional (3D), unit-cell-like ion clusters. We identify a set of unexplored transitions signaled by parity-odd octupole order parameters and probe their distinct dynamical signatures. Our experiments reveal the softening of a collective Higgs-like mode, indicating spontaneous symmetry breaking, hysteresis resulting from a catastrophe where a metastable state vanishes abruptly, and stochastic switching between metastable states of distinct symmetries. We also uncover a remarkable coincidence of symmetry-breaking and discontinuous transitions, analogous to a thermodynamic triple point. Our results establish 3D trapped-ion clusters as a versatile platform for engineering complex potential energy landscapes, opening avenues for studying collective phenomena such as geometric frustration with multipolar orders and the stochastic kinetics of rare events in exotic mesoscopic settings. Description: Open Access. Also available at arXiv.org (one of the alternative locations) Wed, 18 Mar 2026 00:00:00 GMT http://hdl.handle.net/2289/8699 2026-03-18T00:00:00Z