The Indian Pulsar Timing Array Data Release 2: III. Search for a Stochastic Gravitational Wave Background
Abstract
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, log10 ACURN = −13.71+1.06−3.28, with an unconstrained spectral index γCURN = 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 γ= 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 AGWB < 3.4×10−14, stable across solar elongation cuts of 10∘, 20∘, and 30∘. 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.
Related
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BibTeX
@misc{tahbildar2026indian,
title = {{The Indian Pulsar Timing Array Data Release 2: III. Search for a Stochastic Gravitational Wave Background}},
author = {Hemanga Tahbildar and Kunjal Vara and Mayuresh Surnis and Churchil Dwivedi and Bhal Chandra Joshi and Sharika Dhakappa and Aman Srivastava and Shantanu Desai and Abhimanyu Susobhanan and Adya Shukla and Himanshu Grover and P Arumugam and Manjari Bagchi and Neelam Dhanda Batra and Manoneeta Chakraborty and Shaswata Chowdhury and Debabrata Deb and A Gopakumar and Sushovan Mondal and Kuldeep Meena and K Nobleson and Avinash Kumar Paladi and Arul Pandian B and Kaustubh Rai and Prerna Rana and Shubhit Sardana and Vidit Singh and Jaikhomba Singha and Keitaro Takahashi and Pratik Tarafdar and Zenia Zuraiq},
howpublished = {HAL},
year = {2026},
month = sep,
eprint = {2608.02808},
archivePrefix = {arXiv},
url = {https://hal.science/hal-05737562v1},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - The Indian Pulsar Timing Array Data Release 2: III. Search for a Stochastic Gravitational Wave Background
AU - Hemanga Tahbildar
AU - Kunjal Vara
AU - Mayuresh Surnis
AU - Churchil Dwivedi
AU - Bhal Chandra Joshi
AU - Sharika Dhakappa
AU - Aman Srivastava
AU - Shantanu Desai
AU - Abhimanyu Susobhanan
AU - Adya Shukla
AU - Himanshu Grover
AU - P Arumugam
AU - Manjari Bagchi
AU - Neelam Dhanda Batra
AU - Manoneeta Chakraborty
AU - Shaswata Chowdhury
AU - Debabrata Deb
AU - A Gopakumar
AU - Sushovan Mondal
AU - Kuldeep Meena
AU - K Nobleson
AU - Avinash Kumar Paladi
AU - Arul Pandian B
AU - Kaustubh Rai
AU - Prerna Rana
AU - Shubhit Sardana
AU - Vidit Singh
AU - Jaikhomba Singha
AU - Keitaro Takahashi
AU - Pratik Tarafdar
AU - Zenia Zuraiq
PY - 2026
DA - 2026/09/04
PB - HAL
UR - https://hal.science/hal-05737562v1
AB - 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_CURN = −13.71^+1.06_−3.28, with an unconstrained spectral index γ_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 γ= 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_GWB < 3.4×10^−14, stable across solar elongation cuts of 10^∘, 20^∘, and 30^∘. 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.
ER -