Deep uGMRT observations for enhanced calibration of 21cm arrays – I. First image and source catalogue

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dc.contributor.authorBull, Philip
dc.contributor.authorElahi, Khandakar Md Asif
dc.contributor.authorChoudhuri, Samir
dc.date.accessioned2026-01-20T09:51:51Z
dc.date.available2026-01-20T09:51:51Z
dc.date.issued2025
dc.description.abstractRadio-interferometric arrays require very precise calibration to detect the Epoch of Reionization 21-cm signal. A remarkably complete and accurate sky model is therefore needed in the patches of the sky used to perform the calibration. Instruments such as Hydrogen Epoch of Reionization Array (HERA), which use a redundant calibration strategy, also require a reference sky model to fix degenerate gain solutions. We have carried out a deep (20h) observation using the upgraded Giant Metrewave Radio Telescope (GMRT) to make a high-fidelity sky model of one of the HERA calibration fields GLEAM 02H (J0200–3053). Here, we present the results from a 16.7, MHz bandwidth data centred at 147.4, MHz. Using multiple GMRT pointings, we have made a 6.9° x 6.9° mosaic, which yields a median rms of 3.9+3.7-1.4 mJybeam−1 that reduces to ~ 2mJy beam−1 at source-free regions. In the overlapping patch, this rms is deeper than the GaLactic and Extragalactic All-sky MWA Survey (GLEAM) catalogue, which is used for HERA calibration. We produce a catalogue of 640 sources (26 percent extended) in the flux range 0.01 - 19.08Jy. The catalogue has a sub-arcsec positional accuracy, and the estimated fluxes are consistent with existing catalogues. The differential source counts are found to be deeper than GLEAM and consistent with LOw Frequency ARray Two Meter Sky Survey. Preliminary simulations of the sky models from GLEAM and our catalogue show ~ 10 - 25 per cent difference in the visibility amplitude, with relatively small phase difference (≈ 2°). Future work is planned for larger survey areas and wider bandwidth to reduce the rms and measure the in-band source spectral indices, which are expected to enhance the fidelity of the HERA calibration model.
dc.identifier.citationElahi, K.M.A., Choudhuri, S., Roy, N., Rashid, M., Bull, P. and Lal, D.V., 2025. Deep uGMRT observations for enhanced calibration of 21 cm arrays–I. First image and source catalogue. Monthly Notices of the Royal Astronomical Society, 544(1), pp.321-342.
dc.identifier.urihttps://doi.org/10.1093/mnras/staf1764
dc.identifier.urihttps://hdl.handle.net/10566/21765
dc.language.isoen
dc.publisherOxford University Press
dc.subjectdark ages
dc.subjectreionization
dc.subjectfirst stars
dc.subjectinstrumentation: interferometers
dc.subjectmethods: data analysis
dc.titleDeep uGMRT observations for enhanced calibration of 21cm arrays – I. First image and source catalogue
dc.typeArticle

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