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Accepted manuscript

A measurement of Galactic synchrotron emission using MWA drift scan observations

Published online by Cambridge University Press:  10 July 2025

Suman Chatterjee
Affiliation:
Department of Physics and Astronomy, University of the Western Cape, 7535 Bellville, Cape Town, South Africa
Shouvik Sarkar
Affiliation:
Centre for Strings, Gravitation and Cosmology, Department of Physics, Indian Institute of Technology Madras, Chennai 600036, India
Samir Choudhuri*
Affiliation:
Centre for Strings, Gravitation and Cosmology, Department of Physics, Indian Institute of Technology Madras, Chennai 600036, India
Khandakar Md Asif Elahi
Affiliation:
Centre for Strings, Gravitation and Cosmology, Department of Physics, Indian Institute of Technology Madras, Chennai 600036, India Department of Physics, Indian Institute of Technology Kharagpur, Kharagpur - 721 302, India.
Somnath Bharadwaj
Affiliation:
Department of Physics, Indian Institute of Technology Kharagpur, Kharagpur - 721 302, India.
Shiv Sethi
Affiliation:
Raman Research Institute, C. V. Raman Avenue, Sadashivanagar, Bengaluru 560080, India.
Akash Kumar Patwa
Affiliation:
Raman Research Institute, C. V. Raman Avenue, Sadashivanagar, Bengaluru 560080, India.
*
Author for correspondence: Samir Choudhuri, Email: samir@iitm.ac.in.
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Abstract

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Studying the diffuse Galactic synchrotron emission (hereafter, DGSE) at arc-minute angular scale is important to remove the foregrounds for the cosmological 21-cm observations. Statistical measurements of the large-scale DGSE can also be used to constrain the magnetic field and the cosmic ray electron density of our Galaxy’s interstellar medium (ISM). Here, we have used the Murchison Widefield Array (MWA) drift scan observations at 154.2 MHz to measure the angular power spectrum (C) of the DGSE of a region of the sky from right ascension (RA) 349° to 70.3° at the fixed declination –26.7°. In this RA range, we have chosen 24 pointing centers (PCs), for which we have removed all the bright point sources above ∼ 430 mJy (3σ), and applied the Tapered Gridded Estimator (TGE) on residual data to estimate the C. We use the angular multipole range 65 ≤ ℓ ≤ 650 to fit the data with a model, , where we interpret the model as the combination of a power law (∝ –β) nature of the DGSE and a constant part due to the Poisson fluctuations of the residual point sources. We are able to fit the model for six PCs centered at α = 352.5°, 353°, 357°, 4.5°, 4° and 1°. We run the Markov Chain Monte Carlo (MCMC) ensemble sampler to get the best-fit values of the parameters A, β and C for these PCs. We see that the values of A vary in the range 155 to 400 mK2, whereas the β varies in the range 0.9 to 1.7. We find that the value of β is consistent at 2 – σ level with the earlier measurement of the DGSE at similar frequency and angular scales.

Information

Type
Research Article
Creative Commons
Creative Common License - CCCreative Common License - BY
This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution and reproduction, provided the original article is properly cited.
Copyright
© The Author(s), 2025. Published by Cambridge University Press on behalf of Astronomical Society of Australia