Effects of model incompleteness on the drift-scan calibration of radio telescopes
Authors: Gehlot Bharat K , Jacobs Daniel C , Bowman Judd D , Mahesh Nivedita , Murray Steven G , Kolopanis Matthew , Beardsley Adam P , Abdurashidova Zara , Aguirre James E , Alexander Paul , Ali Zaki S , Balfour Yanga , Bernardi Gianni , Billings Tashalee S , Bradley Richard F , Bull Phil , Burba Jacob , Carey Steve , Carilli Chris L , Cheng Carina , DeBoer David R , Dexter Matt , de Lera Acedo Eloy , Dillon Joshua S , Ely John , Ewall-Wice Aaron , Fagnoni Nicolas , Fritz Randall , Furlanetto Steven R , Gale-Sides Kingsley , Glendenning Brian , Gorthi Deepthi , Greig Bradley , Grobbelaar Jasper , Halday Ziyaad , Hazelton Bryna J , Hewitt Jacqueline N , Hickish Jack , Julius Austin , Kern Nicholas S , Kerrigan Joshua , Kittiwisit Piyanat , Kohn Saul A , Lanman Adam , La Plante Paul , Lekalake Telalo , Lewis David , Liu Adrian , Ma Yin-Zhe , MacMahon David , Malan Lourence , Malgas Cresshim , Maree Matthys , Martinot Zachary E , Matsetela Eunice , Mesinger Andrei , Molewa Mathakane , Monsalve Raul A , Morales Miguel F , Mosiane Tshegofalang , Neben Abraham R , Nikolic Bojan , Parsons Aaron R , Pascua Robert , Patra Nipanjana , Pieterse Samantha , Pober Jonathan C , Razavi-Ghods Nima , Ringuette Jon , Robnett James , Rosie Kathryn , Santos Mario G , Sims Peter , Smith Craig , Syce Angelo , Tegmark Max , Thyagarajan Nithyanandan , Williams Peter K G , Zheng Haoxuan 
Published: July 2021

ABSTRACT
Precision calibration poses challenges to experiments probing the redshifted 21-cm signal of neutral hydrogen from the Cosmic Dawn and Epoch of Reionization (z ∼ 30–6). In both interferometric and global signal experiments, systematic calibration is the leading source of error. Though many aspects of calibration have been studied, the overlap between the two types of instruments has received less attention. We investigate the sky based calibration of total power measurements with a HERA dish and an EDGES-style antenna to understand the role of autocorrelations in the calibration of an interferometer and the role of sky in calibrating a total power instrument. Using simulations we study various scenarios such as time variable gain, incomplete sky calibration model, and primary beam model. We find that temporal gain drifts, sky model incompleteness, and beam inaccuracies cause biases in the receiver gain amplitude and the receiver temperature estimates. In some cases, these biases mix spectral structure between beam and sky resulting in spectrally variable gain errors. Applying the calibration method to the HERA and EDGES data, we find good agreement with calibration via the more standard methods. Although instrumental gains are consistent with beam and sky errors similar in scale to those simulated, the receiver temperatures show significant deviations from expected values. While we show that it is possible to partially mitigate biases due to model inaccuracies by incorporating a time-dependent gain model in calibration, the resulting errors on calibration products are larger and more correlated. Completely addressing these biases will require more accurate sky and primary beam models.