arXiv subjects

Manjari Bagchi

Publications and source records attributed to Manjari Bagchi.

At least 19 recordsLinked to original sources

arXiv2026

On coordinate frames relevant for pulsar physics

Pulsars can be either isolated or binary (or even in triple) systems. Observational features of pulsars are used to probe various aspects of fundamental physics, including emission mechanism, gravitational physics, etc. Theoretical models of various phenomena need different coordinate frames. Often different physical processes affect each other and we need to use multiple coordinate frames and relations between those. This short review presents an extensive set of coordinate frames and relations between those.

astro-ph.HE↗

arXiv2026

Profile Reconstruction from Temporally Stable Emission Components for Timing PSR J1713+0747

The assumption of long-term pulse-profile stability underpins high-precision pulsar timing and forms the basis of pulsar timing array experiments. However, several millisecond pulsars exhibit temporal profile variability that can introduce systematic biases in pulse time of arrival measurements and compromise timing precision. We present a profile-domain analysis of PSR J1713+0747 at low radio frequencies, in the 300-500 MHz band, using upgraded GMRT observations for the Indian Pulsar Timing Array experiment. We model frequency-resolved pulse profiles using a Bayesian Gaussian decomposition framework in which individual Gaussian components are associated with persistent emission regions through informative phase priors that permit modest temporal variations. By tracking the evolution of the decomposed components across observing epochs and frequency sub-bands, we identify central Gaussian components that remain precisely localized despite changes in the integrated pulse morphology. We then reconstruct pulse profiles with realistic noise using these central components and perform timing analysis. Our approach provides a physically motivated framework for mitigating pulse-profile variability and offers a generic methodology for recovering robust timing information from pulsars exhibiting profile evolution.

astro-ph.HE↗

arXiv2026

The Indian Pulsar Timing Array Data Release 2: III. Search for a Stochastic Gravitational Wave Background

We present the first independent search for an isotropic stochastic gravitational wave background in the second data release of the Indian Pulsar Timing Array, comprising of 27 millisecond pulsars monitored simultaneously in two frequency bands with the upgraded Giant Metrewave Radio Telescope over a maximum 7.2 year baseline. Building on a comprehensive single pulsar noise analysis, we search for a common uncorrelated red noise process within a Bayesian inference framework and with the noise-marginalized optimal statistics, and we test the robustness of the result through per-pulsar dropout analyses and solar-wind exclusion cuts. Leaving the spectral index free, we recover a broad amplitude posterior, $\log_{10} A_{\rm CURN} = -13.71^{+1.06}_{-3.28}$, with an unconstrained spectral index $\gamma_{\rm CURN} = 2.98^{+3.62}_{-2.70}$ and a Savage-Dickey Bayes factor of $2.5$ for a common red process over the no signal model. The optimal-statistic signal to noise ratios for the monopole, dipole, and Hellings-Downs correlations are all consistent with zero. Fixing the spectral index to $\gamma = 13/3$, the value predicted by an idealized toy model in which the background is sourced by a population of supermassive black hole binaries in circular orbits evolving purely under leading-order gravitational radiation reaction, we place a $95\%$ upper limit on the common-process amplitude of $A_{\rm GWB} < 3.4\times10^{-14}$, stable across solar elongation cuts of $10^\circ$, $20^\circ$, and $30^\circ$. This limit lies approximately an order of magnitude above the amplitudes reported by other, longer-running pulsar timing array experiments. We also demonstrate through simulated datasets with the addition of simple chromatic and achromatic noise components that it will take at least a 10 year baseline to start recovering the common red noise signal.

astro-ph.HE↗

arXiv2026

Probing Neutron Star Interiors and the Properties of Cold Ultra-dense Matter with the SKAO

Matter inside neutron stars is compressed to densities several times greater than nuclear saturation density, while maintaining low temperatures and large asymmetries between neutrons and protons. Neutron stars, therefore, provide a unique laboratory for testing physics in environments that cannot be recreated on Earth. To uncover the highly uncertain nature of cold, ultra-dense matter, discovering and monitoring pulsars is essential, and SKAO will play a crucial role in this endeavour. In this chapter, we will present the current state-of-the-art in dense matter physics and dense matter superfluidity, and discuss recent advances in measuring global neutron star properties (masses, moments of inertia, and maximum rotation frequencies) as well as non-global observables (pulsar glitches and free precession). We will specifically highlight how radio observations of isolated neutron stars and those in binaries -- such as those performed with SKAO in the near future -- inform our understanding of ultra-dense physics and address in detail how SKAO's telescopes unprecedented sensitivity, large-scale survey and sub-arraying capabilities will enable novel dense matter constraints. We will also address the potential impact of dark matter and modified gravity models on these constraints and emphasise the role of synergies between SKAO and other facilities, specifically X-ray telescopes and next-generation gravitational wave observatories.

astro-ph.HE↗

arXiv2025

The Indian Pulsar Timing Array Data Release 2: II. Customised Single-Pulsar Noise Analysis and Noise Budget

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 $\lesssim2.5\,\text{yr}$ 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 $\gtrsim2.5\,\text{yr}$ 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.

astro-ph.HE↗

arXiv2025

Pulsars in Globular Clusters With the SKAO

Because of their extreme stellar densities, globular clusters are highly efficient factories of X-ray binaries and radio pulsars: per unit of stellar mass, they contain about 1000 times more of these exotic objects. Thus far, 345 radio pulsars have been found in globular clusters. These can be used as precision probes of the structure, gas content, magnetic field, and dynamic history of their host clusters; some of them are also highly interesting in their own right because they probe exotic stellar evolution scenarios as well as the physics of dense matter, accretion, and gravity; one of them (PSR~J0514$-$4002E) might even be the first pulsar - black hole system known. Deep searches with SKA-MID and SKA-LOW will only require one to a few tied-array beams, and can be done during early commissioning of the telescope, before an all-sky pulsar survey using hundreds to thousands of tied-array beams is feasible. Even a conservative approach predicts new discoveries only with the core of SKA-MID AA*, and the full AA* and eventually AA4 is expected to increase the number of discoveries even more, leading to more than doubling the current known population. This offers a great opportunity for early SKAO pulsar science, even before all the collecting area is in place. On the other hand, a more optimistic prediction calls for a 4-5 times growth of the population, leading to a total of about 1700 pulsars to be detectable with SKA-MID AA4 configuration in all Galactic GCs visible by SKA telescopes. Thus, a dedicated search for pulsars in globular clusters will fully exploit the best possible natural laboratories to study many branches of physics and astrophysics, including properties of dense matter, stellar evolution, and the dynamical history of the Galactic globular cluster systems.

astro-ph.HE↗

arXiv2025

Probing neutron star interiors and the properties of cold ultra-dense matter with the SKAO

Matter inside neutron stars is compressed to densities several times greater than nuclear saturation density, while maintaining low temperatures and large asymmetries between neutrons and protons. Neutron stars, therefore, provide a unique laboratory for testing physics in environments that cannot be recreated on Earth. To uncover the highly uncertain nature of cold, ultra-dense matter, discovering and monitoring pulsars is essential, and the SKA will play a crucial role in this endeavour. In this paper, we will present the current state-of-the-art in dense matter physics and dense matter superfluidity, and discuss recent advances in measuring global neutron star properties (masses, moments of inertia, and maximum rotation frequencies) as well as non-global observables (pulsar glitches and free precession). We will specifically highlight how radio observations of isolated neutron stars and those in binaries -- such as those performed with the SKA in the near future -- inform our understanding of ultra-dense physics and address in detail how SKAO's telescopes unprecedented sensitivity, large-scale survey and sub-arraying capabilities will enable novel dense matter constraints. We will also address the potential impact of dark matter and modified gravity models on these constraints and emphasise the role of synergies between the SKA and other facilities, specifically X-ray telescopes and next-generation gravitational wave observatories.

astro-ph.HE↗

arXiv2025

Revisiting wideband pulsar timing measurements

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.

astro-ph.IM↗

arXiv2025

Effects of Coronal Mass Ejection on PSR J1022+1001 and Possible Mode Change of PSR J2145-0750 in the InPTA DR2

The Indian Pulsar Timing Array (InPTA) has recently published its second data release (DR2), comprising the timing analysis of seven years of data on 27 millisecond pulsars (MSPs), observed simultaneously in the 300-500 MHz (band 3) and 1260-1460 MHz (band 5), using the upgraded Giant Metrewave Radio Telescope (uGMRT). The low-frequency data, particularly in band 3, is highly sensitive to propagation effects such as dispersion measure (DM) fluctuations, which can be imprints of some astrophysical phenomena (scientific outliers). Here, we analyze the two outliers of possible astrophysical origin coming from the band 3 DM time series of two pulsars: PSR J1022+1001, with an ecliptic latitude of -0.06 degree, and PSR J2145-0750, one of the brightest MSPs, with multi-component profile morphology. Our study reveals compelling evidence for a coronal mass ejection (CME) event traced in the data of PSR J1022+1001, and reports evidence for a potential mode-changing event in PSR J2145-0750. By contrasting these two cases, we show that DM fluctuations due to CME interacions and intrinsic mode-changing events produce distinct observational signatures, enabling a physically informed classification of scientific outliers in PTA datasets. Extending the analyses presented here to the full sample of InPTA-DR2 pulsars is expected to reveal additional CME events, and possible mode-changing events. Such detections will not only improve our understanding of solar and pulsar magnetospheric plasma interactions but will also enable more accurate modelling of DM variations, leading to improved pulsar timing solutions, which are crucial for high-precision Pulsar Timing Array (PTA) science.

astro-ph.HE↗

arXiv2025

The Indian Pulsar Timing Array Data Release 2: I. Dataset and Timing Analysis

The Indian Pulsar Timing Array (InPTA) employs unique features of the upgraded Giant Metrewave Radio Telescope (uGMRT) to monitor dozens of the International Pulsar Timing Array (IPTA) millisecond pulsars (MSPs), simultaneously in the 300-500 MHz and the 1260-1460 MHz bands. This dual-band approach ensures that any frequency-dependent delays are accurately characterized, significantly improving the timing precision for pulsar observations, which is crucial for pulsar timing arrays. We present details of InPTA's second data release that involves 7 yrs of data on 27 IPTA MSPs. This includes sub-banded Times of Arrival (ToAs), Dispersion Measures (DM), and initial timing ephemerides for our MSPs. A part of this dataset, originally released in InPTA's first data release, is being incorporated into IPTA's third data release which is expected to detect and characterize nanohertz gravitational waves in the coming years. The entire dataset is reprocessed in this second data release providing some of the highest precision DM estimates so far and interesting solar wind related DM variations in some pulsars. This is likely to characterize the noise introduced by the dynamic inter-stellar ionised medium much better than the previous release thereby increasing sensitivity to any future gravitational wave search.

astro-ph.IM↗

arXiv2025

On the effect of the light bending phenomenon for a pulsar in a binary with a Kerr black hole

We study the effect of light-bending on the signal of a pulsar in binaries with rotating black hole companions, focusing on stellar mass black holes. We show that the impacts of various parameters on the bending delays visually match with those observed for a non-rotating black holes, because the magnitude of the spin as well as the orientation of the spin axis of the black hole introduce changes in the nanosecond order and other parameters do so in the microsecond order. Consequently, the distortion of the beam and the resulting changes in the pulse shape are minimally influenced by spin-related parameters of the black hole. We also investigate the impact of various parameters on the difference of the delays with and without the spin of the black hole and notice nanosecond scale discontinuities at orbital phases where the path of the light ray changes its direction with respect to the direction of the spin of the black hole. Moreover, as in the Schwarzschild case, the bending delays become irregular (on the microsecond scale) near the superior conjunction. We also explore the effect of bending on the pulse profiles and bending delays if the companion of the pulsar is a rotating super-massive black hole. We find significant enhancement and change in the shape of the profiles at and near the superior conjunction in comparison to stellar mass black holes. Moreover, bending delays are about three orders of magnitude higher than those in case of the stellar mass black holes.

gr-qc↗

arXiv2025

Astrophysics with Compact Objects: An Indian Perspective, Present Status and Future Vision

Astrophysical compact objects, viz., white dwarfs, neutron stars, and black holes, are the remnants of stellar deaths at the end of their life cycles. They are ideal testbeds for various fundamental physical processes under extreme conditions that are unique in nature. Observational radio astronomy with uGMRT and OORT facilities has led to several important breakthroughs in studies of different kinds of pulsars and their emission mechanisms. On the other hand, accretion processes around compact objects are at the core of Indian astronomy research. In this context, AstroSat mission revolutionized spectro-temporal observations and measurements of accretion phenomena, quasi-periodic oscillations, and jet behaviour in binary systems hosting compact objects. Moreover, recently launched XPoSat mission is set to provide an impetus to these high-energy phenomena around compact objects by enabling us to conduct polarization measurements in the X-ray band. Further, during the past decade, numerous gravitational wave signals have been observed from coalescing black holes and neutron stars in binary systems. Recent simultaneous observation of the GW170817 event in both gravitational waves and electromagnetic channels has ushered in the era of multi-messenger astronomy. In the future, synergistic efforts among several world-class observational facilities, e.g., LIGO-India, SKA, TMT, etc., within the Indian astrophysics community will provide a significant boost to achieve several key science goals that have been delineated here. In general, this article plans to highlight scientific projects being pursued across Indian institutions in this field, the scientific challenges that this community would be focusing on, and the opportunities in the coming decade. Finally, we have also mentioned the required resources, both in the form of infrastructural and human resources.

astro-ph.HE↗

arXiv2025

Quasi-normal f-modes of anisotropic quark stars in full general relativity

We investigate f-mode oscillations of anisotropic quark stars within the framework of full general relativity. We consider two different equations of state (EOSs), one is the MIT bag model EOS and the other is EOS-A. Our study examines the impact of the pressure anisotropy on the equilibrium structure, as well as on the frequencies and damping times of f-mode oscillations. Our results confirm that the f-mode frequency scales linearly with the square root of the average density, with anisotropy influencing both the slope and intercept of this relation. The dependence of the f-mode frequency on total mass reveals distinct trends based on the relative dominance of tangential and radial pressure. When the tangential pressure exceeds the radial pressure, the frequency increases with mass, exhibiting rapid growth for massive quark stars. When the radial pressure dominates, the frequency increases with mass; however, in cases where the radial pressure is significantly greater than the tangential pressure, the frequency decreases as mass increases. For low-mass quark stars, stronger tangential pressure leads to an increase in frequency, while beyond a threshold mass, a further increase in tangential pressure results in a decrease in frequency. For the chosen range of anisotropic strengths, the frequency varies between 1.3 kHz and 2.3 kHz for the MIT bag EOS and between 1.8 kHz and 3.4 kHz for EOS-A. We find that the normalized damping time follows a linear trend with compactness. For a fixed stellar mass, an increase in tangential pressure relative to radial pressure reduces the damping time, whereas a decrease in tangential pressure significantly increases it. The damping time ranges from 83 ms to 900 ms for the MIT bag EOS and from 60 ms to 761 ms for EOS-A. We present semi-empirical expressions for both the frequency and damping time as functions of mass, radius, and anisotropic strength.

gr-qc↗

arXiv2025

Discovery and Timing of 49 Pulsars from the Arecibo 327-MHz Drift Survey

We present 18 pulsar discoveries from the AO327 pulsar survey, along with their timing solutions and those for an additional 31 AO327-discovered pulsars. Timing solutions were constructed using observations from a follow-up timing campaign taken between the periods of 2013 -- 2019 using the Arecibo Observatory's 327-MHz receiver. Aside from PSR J0916+0658, an isolated pulsar that shows evidence for partial recycling, the remaining discoveries are non-recycled pulsars. We present a brief census of emission features for all pulsars with the following standouts. PSR~J1942+0142 is found to exhibit the very rare phenomenon of subpulse bi-drifting and PSR~J0225+1727 has an interpulse. We also report distance estimates using the NE2001, YMW16, and NE2025 Galactic electron density models, and identify at least 10 sources where either one or more models underestimate the maximum Galactic line of sight dispersion measure. We compare our discoveries with those of the GBNCC survey, finding that off the Galactic plane, the majority of failures arise from YMW16, while in the Galactic plane, NE2025 shows a marginal degradation of performance relative to NE2001.

astro-ph.HE↗

arXiv2024

Exploring the Impact of Extra Dimensions on Neutron Star Structure and Equation of State

In this work, we explore the impact of higher dimensional spacetime on the stellar structure and thermodynamic properties of neutron stars. Utilizing the density-dependent relativistic hadron field theory, we introduce modifications to incorporate the influence of higher dimensionality, a novel approach not explored in existing literature to our best knowledge. Our methodology involves solving the essential stellar structure equations in D-dimensional spacetime ($D \geq 4$), starting with the modification of the Einstein-Hilbert action, derivation of the Einstein field equation in D dimensions, and application of the resulting exterior Schwarzschild spacetime metric for D-dimension. Our findings reveal that with incremental dimensions, the central density $ρ_{c} G_D$ and central pressure $p_c G_D$ gradually increase, leading to progressively stiffer neutron matter. Incremental dimensionality also results in a gradual increase in the maximum mass attained, limited to our study between $D=4$ and $D=6$, as no maximum mass value is obtained for $D>6$. We consistently observe the criteria $dM/dρ_c>0$ fulfilled up to the maximum mass point, supported by stability analysis against infinitesimal radial pulsations. The validity of our solution is confirmed through causality conditions, ensuring that the matter sound speed remains within the speed of light for all cases. Additionally, our examination indicates that the total mass-to-radius ratio for all discussed D-dimensional cases comfortably resides within the modified Buchdahl limit, which exhibits the physical validity of achieved results.

gr-qc↗

arXiv2023

Low-frequency pulse-jitter measurement with the uGMRT I : PSR J0437$-$4715

High-precision pulsar timing observations are limited in their accuracy by the jitter noise that appears in the arrival time of pulses. Therefore, it is important to systematically characterise the amplitude of the jitter noise and its variation with frequency. In this paper, we provide jitter measurements from low-frequency wideband observations of PSR J0437$-$4715 using data obtained as part of the Indian Pulsar Timing Array experiment. We were able to detect jitter in both the 300 - 500 MHz and 1260 - 1460 MHz observations of the upgraded Giant Metrewave Radio Telescope (uGMRT). The former is the first jitter measurement for this pulsar below 700 MHz, and the latter is in good agreement with results from previous studies. In addition, at 300 - 500 MHz, we investigated the frequency dependence of the jitter by calculating the jitter for each sub-banded arrival time of pulses. We found that the jitter amplitude increases with frequency. This trend is opposite as compared to previous studies, indicating that there is a turnover at intermediate frequencies. It will be possible to investigate this in more detail with uGMRT observations at 550 - 750 MHz and future high sensitive wideband observations from next generation telescopes, such as the Square Kilometre Array. We also explored the effect of jitter on the high precision dispersion measure (DM) measurements derived from short duration observations. We find that even though the DM precision will be better at lower frequencies due to the smaller amplitude of jitter noise, it will limit the DM precision for high signal-to-noise observations, which are of short durations. This limitation can be overcome by integrating for a long enough duration optimised for a given pulsar.

astro-ph.HE↗

arXiv2023

Multi-band Extension of the Wideband Timing Technique

The wideband timing technique enables the high-precision simultaneous estimation of pulsar Times of Arrival (ToAs) and Dispersion Measures (DMs) while effectively modeling frequency-dependent profile evolution. We present two novel independent methods that extend the standard wideband technique to handle simultaneous multi-band pulsar data incorporating profile evolution over a larger frequency span to estimate DMs and ToAs with enhanced precision. We implement the wideband likelihood using the libstempo python interface to perform wideband timing in the tempo2 framework. We present the application of these techniques to the dataset of fourteen millisecond pulsars observed simultaneously in Band 3 (300 - 500 MHz) and Band 5 (1260 - 1460 MHz) of the upgraded Giant Metrewave Radio Telescope (uGMRT) with a large band gap of 760 MHz as a part of the Indian Pulsar Timing Array (InPTA) campaign. We achieve increased ToA and DM precision and sub-microsecond root mean square post-fit timing residuals by combining simultaneous multi-band pulsar observations done in non-contiguous bands for the first time using our novel techniques.

astro-ph.IM↗

arXiv2023

Discovery and Timing of Millisecond Pulsars with the Arecibo 327 MHz Drift-Scan Survey

We present the discovery and timing solutions of four millisecond pulsars (MSPs) discovered in the Arecibo 327 MHz Drift-Scan Pulsar Survey. Three of these pulsars are in binary systems, consisting of a redback (PSR J2055+1545), a black widow (PSR J1630+3550), and a neutron star-white dwarf binary (PSR J2116+1345). The fourth MSP, PSR J2212+2450, is isolated. We present the multiyear timing solutions as well as polarization properties across a range of radio frequencies for each pulsar. We perform a multiwavelength search for emission from these systems and find an optical counterpart for PSR J2055+1545 in Gaia DR3, as well as a gamma-ray counterpart for PSR J2116+1345 with the Fermi-LAT telescope. Despite the close colocation of PSR J2055+1545 with a Fermi source, we are unable to detect gamma-ray pulsations, likely due to the large orbital variability of the system. This work presents the first two binaries found by this survey with orbital periods shorter than a day; we expect to find more in the 40% of the survey data that have yet to be searched.

astro-ph.HE↗