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## “RadioAstron” Project. Calibration of the Space Radio Telescope in Flight at the Wavelengths of 6.2, 18 and 92 cm in 2015–2018

Transactions of IAA RAS, issue 54, 32–39 (2020)

Keywords: RadioAstron, space telescope, main antenna parameters, SRT calibration, VLBI, telemetry, data auto reduction

### Abstract

Goals and objectives. Using a new automated system, the results of processing the radiometric observations have been obtained relative to primary astronomical flux density calibrators (Cassiopea-A and Crab Nebula). The measurements had been done at the wavelengths of 6.2, 18 and 92 cm in the left and right circular polarizations with the space radio telescope (SRT) in calibration sets in 2015–2018. The goals are 1) to calibrate the SRT’s System Equivalent Flux Density (SEFD) and the internal calibration noise sources (Jy) as secondary calibrators for using them in calibrations of the ground-space interferometer “RadioAstron”; 2) to investigate their time stability. Methods. The automated system converts the initial binary telemetry data from the radiometric outputs of interferometric receivers into a calibrated result for the SRT noise and four noise sources in each polarization channel. The results are calibrated in units of spectral flux density (Jy) and antenna temperature (K) to the time of observation. They are weighted averaged in the time and compared between the results obtained relative to both primary calibrators and with the earlier SEFD measurements for the SRT in flight. Conclusions. 1. The SEFD and the internal calibration noise signal sources for the SRT were calibrated at the wavelengths of 6.2, 18 and 92 cm in left and right circular polarization relative to Cassiopea-A and Crab Nebula. They were independently used for further verification or calibration of the SRT in the operating modes for both a single telescope and for a space element of the ground-space VLBI in 2015–2018. 2. It is shown that the SEFD as measured in 2015–2018 and calibrated relative to Cassiopeia-A is close to the SEFD in the first years of SRT operation — within 11 % for 6.2 and 18 cm and within 17 % for 92 cm wavelengths. 3. The systematic differences between the calibrated values relative to Cassiopeia-A and to Crab Nebula were found at all wavelengths. Further analysis of the reasons for these differences is required. The “RadioAstron” project is led by the Astro Space Center of the Lebedev Physical Institute of the Russian Academy of Sciences and the Lavochkin Scientific and Production Association under a contract with the State Space Corporation ROSCOSMOS, in collaboration with partner organizations in Russia and other countries.

### Citation

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Yu. A. Kovalev, V. I. Vasil'kov, A. N. Ermakov, E. N. Vinyajkin, M. V. Popov, V. A. Soglasnov, M. G. Larionov, N. Ya. Nikolaev, E. N. Mironova, M. S. Burgin, Yu. Yu. Kovalev, P. A. Voitsik, M. M. Lisakov, A. M. Kutkin, A. V. Alakoz, N. N. Shakhvorostova, K. G. Belousov, A. V. Kovalenko. “RadioAstron” Project. Calibration of the Space Radio Telescope in Flight at the Wavelengths of 6.2, 18 and 92 cm in 2015–2018 // Transactions of IAA RAS. — 2020. — Issue 54. — P. 32–39. @article{kovalev2020, abstract = {Goals and objectives. Using a new automated system, the results of processing the radiometric observations have been obtained relative to primary astronomical flux density calibrators (Cassiopea-A and Crab Nebula). The measurements had been done at the wavelengths of 6.2, 18 and 92 cm in the left and right circular polarizations with the space radio telescope (SRT) in calibration sets in 2015–2018. The goals are 1) to calibrate the SRT’s System Equivalent Flux Density (SEFD) and the internal calibration noise sources (Jy) as secondary calibrators for using them in calibrations of the ground-space interferometer “RadioAstron”; 2) to investigate their time stability. Methods. The automated system converts the initial binary telemetry data from the radiometric outputs of interferometric receivers into a calibrated result for the SRT noise and four noise sources in each polarization channel. The results are calibrated in units of spectral flux density (Jy) and antenna temperature (K) to the time of observation. They are weighted averaged in the time and compared between the results obtained relative to both primary calibrators and with the earlier SEFD measurements for the SRT in flight. Conclusions. 1. The SEFD and the internal calibration noise signal sources for the SRT were calibrated at the wavelengths of 6.2, 18 and 92 cm in left and right circular polarization relative to Cassiopea-A and Crab Nebula. They were independently used for further verification or calibration of the SRT in the operating modes for both a single telescope and for a space element of the ground-space VLBI in 2015–2018. 2. It is shown that the SEFD as measured in 2015–2018 and calibrated relative to Cassiopeia-A is close to the SEFD in the first years of SRT operation — within 11 % for 6.2 and 18 cm and within 17 % for 92 cm wavelengths. 3. The systematic differences between the calibrated values relative to Cassiopeia-A and to Crab Nebula were found at all wavelengths. Further analysis of the reasons for these differences is required. The “RadioAstron” project is led by the Astro Space Center of the Lebedev Physical Institute of the Russian Academy of Sciences and the Lavochkin Scientific and Production Association under a contract with the State Space Corporation ROSCOSMOS, in collaboration with partner organizations in Russia and other countries.}, author = {Yu.~A. Kovalev and V.~I. Vasil'kov and A.~N. Ermakov and E.~N. Vinyajkin and M.~V. Popov and V.~A. Soglasnov and M.~G. Larionov and N.~Ya. Nikolaev and E.~N. Mironova and M.~S. Burgin and Yu.~Yu. Kovalev and P.~A. Voitsik and M.~M. Lisakov and A.~M. Kutkin and A.~V. Alakoz and N.~N. Shakhvorostova and K.~G. Belousov and A.~V. Kovalenko}, doi = {10.32876/ApplAstron.54.32-39}, issue = {54}, journal = {Transactions of IAA RAS}, keyword = {RadioAstron, space telescope, main antenna parameters, SRT calibration, VLBI, telemetry, data auto reduction}, pages = {32--39}, title = {“RadioAstron” Project. Calibration of the Space Radio Telescope in Flight at the Wavelengths of 6.2, 18 and 92 cm in 2015–2018}, url = {http://iaaras.ru/en/library/paper/2060/}, year = {2020} } TY - JOUR TI - “RadioAstron” Project. Calibration of the Space Radio Telescope in Flight at the Wavelengths of 6.2, 18 and 92 cm in 2015–2018 AU - Kovalev, Yu. A. AU - Vasil'kov, V. I. AU - Ermakov, A. N. AU - Vinyajkin, E. N. AU - Popov, M. V. AU - Soglasnov, V. A. AU - Larionov, M. G. AU - Nikolaev, N. Ya. AU - Mironova, E. N. AU - Burgin, M. S. AU - Kovalev, Yu. Yu. AU - Voitsik, P. A. AU - Lisakov, M. M. AU - Kutkin, A. M. AU - Alakoz, A. V. AU - Shakhvorostova, N. N. AU - Belousov, K. G. AU - Kovalenko, A. V. PY - 2020 T2 - Transactions of IAA RAS IS - 54 SP - 32 AB - Goals and objectives. Using a new automated system, the results of processing the radiometric observations have been obtained relative to primary astronomical flux density calibrators (Cassiopea-A and Crab Nebula). The measurements had been done at the wavelengths of 6.2, 18 and 92 cm in the left and right circular polarizations with the space radio telescope (SRT) in calibration sets in 2015–2018. The goals are 1) to calibrate the SRT’s System Equivalent Flux Density (SEFD) and the internal calibration noise sources (Jy) as secondary calibrators for using them in calibrations of the ground-space interferometer “RadioAstron”; 2) to investigate their time stability. Methods. The automated system converts the initial binary telemetry data from the radiometric outputs of interferometric receivers into a calibrated result for the SRT noise and four noise sources in each polarization channel. The results are calibrated in units of spectral flux density (Jy) and antenna temperature (K) to the time of observation. They are weighted averaged in the time and compared between the results obtained relative to both primary calibrators and with the earlier SEFD measurements for the SRT in flight. Conclusions. 1. The SEFD and the internal calibration noise signal sources for the SRT were calibrated at the wavelengths of 6.2, 18 and 92 cm in left and right circular polarization relative to Cassiopea-A and Crab Nebula. They were independently used for further verification or calibration of the SRT in the operating modes for both a single telescope and for a space element of the ground-space VLBI in 2015–2018. 2. It is shown that the SEFD as measured in 2015–2018 and calibrated relative to Cassiopeia-A is close to the SEFD in the first years of SRT operation — within 11 % for 6.2 and 18 cm and within 17 % for 92 cm wavelengths. 3. The systematic differences between the calibrated values relative to Cassiopeia-A and to Crab Nebula were found at all wavelengths. Further analysis of the reasons for these differences is required. The “RadioAstron” project is led by the Astro Space Center of the Lebedev Physical Institute of the Russian Academy of Sciences and the Lavochkin Scientific and Production Association under a contract with the State Space Corporation ROSCOSMOS, in collaboration with partner organizations in Russia and other countries. DO - 10.32876/ApplAstron.54.32-39 UR - http://iaaras.ru/en/library/paper/2060/ ER -