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AMI-LA, e-MERLIN and MeerKAT radio detections of RS Oph in outburst

ATel #14849; David Williams (JBCA/Manchester), Tim O'Brien (JBCA/Manchester), Patrick Woudt (UCT), Miriam Nyamai (UCT), Dave Green (MRAO, Cambridge), David Titterington (MRAO, Cambridge), Rob Fender (Oxford), Greg Sivakoff (U. Alberta)
on 11 Aug 2021; 19:59 UT
Credential Certification: Tim O'Brien (tim.obrien@manchester.ac.uk)

Subjects: Radio, Nova

Referred to by ATel #: 14855, 14857, 14858, 14860, 14882, 14885, 14886, 14894, 14895

Following multi-wavelength reports of a new outburst of the recurrent nova RS Ophiuchi, http://ooruri.kusastro.kyoto-u.ac.jp/mailarchive/vsnet-alert/26131 (see also ATel #14834, #14838, #14840, #14844, #14845, #14846, #14848), we requested observations in the radio band with the Arcminute Microkelvin Imager Large Array (AMI-LA; Zwart et al. 2008; Hickish et al. 2018) at 15.5 GHz, e-MERLIN at 5 GHz and MeerKAT at 1.28 GHz. AMI-LA observations were requested as part of a long term transients monitoring programme (PI: Fender). They started on 2021-08-09.77 and 2021-08-10.77 and each epoch lasted for 4 hours. We used a custom pipeline, REDUCE_DC (Perrott et al. 2015) to calibrate the data, using 3C286 as the flux calibrator and J1804+0101 as the phase calibrator. Due to a reduced number of antennas in the array, we conservatively use flux uncertainties of 10%. In our preliminary analysis, we detect RS Oph at a flux density of 0.80+/-0.08 mJy on 2021-08-09.77 and 1.50+/-0.15 mJy on 2021-08-10.77. The image noise levels were 0.15mJy/beam on 2021-08-09.8 and 0.2mJy/beam on 2021-08-10.8, respectively. The e-MERLIN observations were obtained via a director's discretionary time request. They started on 2021-08-10.60 and lasted 12 hours, including all calibrators. In this observation, 3C286 was used as a flux calibrator, OQ208 was used as a band pass calibrator and J1745-0753 was used as a phase calibrator. The data were calibrated using the e-MERLIN CASA Pipeline (Moldon et al. 2018). In our preliminary analysis, we detect RS Oph at a flux density of 0.38 +/- 0.06 mJy with an image noise of 40 uJy/beam. The MeerKAT data were obtained as part of a director's discretionary time request and started on 2021-08-10.95, for an 0.5 hour observation. The initial SARAO SDP quick-look image detects RS Oph at a flux density of 0.29 +/- 0.03 mJy, with an image noise of 12 uJy/beam. The previous earliest detection of radio emission from RS Oph in outburst was 4.4 days after the peak of the visual light curve (Eyres et al. 2009). All of the detections presented here were obtained ~2 days after the start of the outburst and are the earliest radio detections of this source in outburst. We plan to continue monitoring this source to follow the radio evolution with AMI, and have requested further e-MERLIN and MeerKAT observations. We would like to thank the MRAO, JBO and SARAO staff for carrying out these observations. AMI-LA is supported by the Universities of Cambridge and Oxford. e-MERLIN is a National Facility operated on behalf of the Science & Technology Facilities Council by the University of Manchester at Jodrell Bank Observatory. The MeerKAT telescope is operated by SARAO, which is a facility of the National Research Foundation, an agency of the Department of Science and Innovation.