CAPTURE: a continuum imaging pipeline for the uGMRT
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CAPTURE: a continuum imaging pipeline for the uGMRT Ruta Kale1
· C. H. Ishwara-Chandra1
Received: 9 April 2020 / Accepted: 28 September 2020 / © Springer Nature B.V. 2020
Abstract We present the first fully automated pipeline for making images from the interferometric data obtained from the upgraded Giant Metrewave Radio Telescope (uGMRT) called CAsa Pipeline-cum-Toolkit for Upgraded Giant Metrewave Radio Telescope data REduction - CAPTURE. It is a python program that uses tasks from the NRAO Common Astronomy Software Applications (CASA) to perform the steps of flagging of bad data, calibration, imaging and self-calibration. The salient features of the pipeline are: i) a fully automatic mode to go from the raw data to a self-calibrated continuum image, ii) specialized flagging strategies for short and long baselines that ensure minimal loss of extended structure, iii) flagging of persistent narrow band radio frequency interference (RFI), iv) flexibility for the user to configure the pipeline for step-by-step analysis or special cases and v) analysis of data from the legacy GMRT. CAPTURE is available publicly on github (https://github.com/ruta-k/ uGMRT-pipeline, release v1.0.0). The primary beam correction for the uGMRT images produced with CAPTURE is made separately available at https://github.com/ ruta-k/uGMRTprimarybeam. We show examples of using CAPTURE on uGMRT and legacy GMRT data. In principle, CAPTURE can be tailored for use with other radio interferometric data. Keywords Radio interferometer · Data analysis pipeline · Radio continuum · GMRT
1 Introduction Radio interferometric data require post-processing that involves calibration and inverse Fourier transform to obtain an image of the sky. The Giant Metrewave Radio Telescope (GMRT), located near Pune, India, is a radio interferometer that consists Ruta Kale
[email protected] 1
National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, S. P. Pune University Campus, Ganeshkhind, Pune, 411007, India
Experimental Astronomy
of 30 antennas of 45 m diameter each, with the longest baseline ∼ 25 km, that recently underwent an upgrade of the receivers. Before the upgrade it operated in 5 frequency bands in the range of 120 - 1450 MHz with instantaneous bandwidths of 33.3 MHz. The upgrade included broadbanding of receivers and backend which now allows recording data with instantaneous bandwidths of up to 400 MHz [3]. We will refer to the older GMRT with narrow band receivers as the “legacy GMRT” and the one after the upgrade as the upgraded GMRT (uGMRT). The uGMRT is currently operational in four frequency bands, namely, 120 - 250 MHz (band-2), 250 - 500 MHz (band-3), 550 - 850 MHz (band-4) and 1000 - 1460 MHz (band-5). The standard data analysis software for the legacy GMRT was the NRAO Astronomical Image Processing System (AIPS1 ). An AIPS based continuum imaging pipeline, Source Peeling and Atmospheric Modelling (SPAM) [4] has been available mainly for the lower frequency bands (< GHz) of the GMRT [5]. Analysis of the uGMRT wide
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