RadioAstron mission overview

Transcription

1 RadioAstron mission overview Yuri Kovalev and Nikolai Kardashev Astro Space Center of Lebedev Physical Institute, Moscow 30 November 2015 MPIfR VLBI workshop, Bonn

2 Launch in 2011

3 RadioAstron: general information Space radio telescope: 10-m; launched in 2011 Frequency bands: 0.3, 1.6, 5, 22 (18-25) GHz Highest resolution (at 1.3 cm): ~7 μas. Orbit: gravitationally perturbed by Moon, perigee 10,000 km, apogee ~300,000 km, ~9 days period Five methods of orbit measurements including Doppler measurements, laser ranging, VLBI. Required accuracy of the orbit reconstruction: distance 500 m, velocity 2 cm/s. Expected lifetime: 5 years (general estimate). Currently extended until the end of Control stations: Ussurijsk, Bear Lakes. Tracking station: Pushchino, Russia; Green Bank, USA; South Africa expected. Bit rate: 128 Mbps coming from space. Two methods of time synchronization: on-board (open loop at 8 and 15 GHz) and ground (closed loop at 7, 8, and15 GHz) hydrogen maser. Software correlators: ASC, DiFX-Bonn, JIVE SFXC.

4 RadioAstron: polarization properties Bands: 92 cm, 18 cm, 1.3 cm allow for polarization experiments in the traditional style (dual circular polarization). 6 cm can observe only left circular polarization due to a failure, most probably in the LNA. Polarization experiments were successfully performed at 18 and 1.3 cm. Space radio telescope polarization performance is found as expected: leakage < 10% at 18 cm and 1.3 cm. No polarization imaging experiments at 92 cm requested by users so far. Pulsar polarization data at 92 cm confirm its specs as expected.

5 Tracking stations (15/8/7 GHz) Default mode: single way, closed loop possible Green Bank 140-ft Pushchino 22-meter

6 RadioAstron support by ground radio telescopes Ground VLBI: Kvazar: Sv, Bd, Zc (Russia); Kalyazin (Russia); Evpatoriya (Ukraine); Effelsberg (Germany); WSRT (The Netherlands); Torun (Poland); Medicina, Noto, Sardinia (Italy); Yebes, Robledo (Spain); Jodrell Bank 1 & 2 (UK); EVN; Usuda (Japan); Shanghai 25 & 65, Urumqi (China); VLA, GBT, Arecibo, VLBA (USA); HartRAO (ZA); KVN (S. Korea), LBA, Tidbinbila (Australia). Single-dish support: RATAN-600 (Russia); ATCA (Australia); WSRT (The Netherlands); Urumqi (China); Effelsberg (Germany); Oven Valley (USA); GBT (USA).

7 Sensitivity improvements from original reports estimates to work about properly the factor for > 4 of years 2 The active hydrogen maser was turned on and 1.3 cm 6 cm

8 Baseline projection: 50 Mλ SRT-Effelsberg

9 First RadioAstron images 6 cm: stokes I, 18 cm: polarization Kardashev et al. (2013) Lobanov et al. (2015)

10 ASC correlator statistics until October 2015

11 Bonn correlator statistics from G. Bruni

12 Typical orbit accuracy Required accuracy of the orbit reconstruction: distance 500 m, velocity 2 cm/s. Actual orbit accuracy was poorer with the original reconstruction algorithm. A more sophisticated approach was introduced which takes into account telemetry information on the actual gyros unloading, solar wind, etc. Well within the specs. Will require us to recorrelate some of the early experiments. See details in the poster by Voytsik.

13 RadioAstron mission science organization Started from the Early Science program being coordinated by the mission with an involvement of international partners. Objectives: achieve first scientific results in the completely unexplored territory and allow for most efficient planning of the key science program. The goals were successfully reached. Since July 2013 RadioAstron observes within the open sky policy: 100% of time is open, proposals are to be submitted once per year by the end of January, they are evaluated by the RadioAstron Program Evaluation Committee. Already three calls were made, AO3 started in July AO4 call will be announced in several weeks. Deadline: January 25, GRTs: partly available through special agreements, partly through separate open calls. EVN introduced OoS mode of observations which allows to plan RadioAstron-EVN experiments most efficiently. Science areas: active galactic nuclei (dominate), other galaxies, masers and mega-masers, pulsars, interstellar medium, micro-quasars. Gravitational experiment.

14 Notes on the current statis of RadioAstron RadioAstron is extended by Roscosmos until the end of Budgetary situation is uneasy which complicates contract payments for GBES but so far we manage to continue with an extra support from Roscosmos. Further extension of the mission is expected as long as t continues to provide useful science results. A degradation of the equipment onboard Spektr-R is being observed. So far it did not result in a significant limitations of the SRT characteristics. The science program is being observed as approved.

15 Thank you

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