arXiv subjects

Adya Shukla

Publications and source records attributed to Adya Shukla.

6 recordsLinked to original sources

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↗

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

On Constraining the Proposed Hierarchical Triple Scenario for an Eccentric Milli-Second Pulsar Binary PSR J1618-3921

A very recent and meticulous timing effort suggests that an eccentric millisecond pulsar (eMSP) binary, namely PSR J1618-3921, is likely to be a part of a hierarchical triple (HT) system with a $0.6M_{\odot}$ companion in a $\sim 300$yr orbit. We investigate observational implications of the proposed HT scenario for PSR J1618-3921 and our ability to constrain the scenario. We model the MSP-Helium White Dwarf binary to be a part of bound point-mass HT, while incorporating the effects due to the quadrupolar interactions between the inner and outer binaries, along with dominant order general relativistic contributions to the periastron precession of the inner binary. If the proposed HT system is indeed undergoing Kozai oscillations at the present epoch, the orbital eccentricity ($e$) would be expected to decrease, while the rate of periastron advance ($\dot{\omega}$) would correspondingly increase, for plausible ranges of the HT parameters. Furthermore, the fractional variations in $e$ are anticipated to be at the level of a few parts in $10^{5}$-a magnitude that is substantially larger than the current measurement precision of $e$. We find that, for this eccentric MSP binary, the HT configurations that minimize the temporal evolution of orbital eccentricity and argument of periastron are mutually incompatible. This indicates that the continued high-precision timing of PSR J1618-3921-when analyzed within the framework introduced here-should place stringent limits on the presence and properties of a potential third body in the system.

astro-ph.GA↗

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↗