Allen Telescope Array, Arcminute Microkelvin Imager Large Array, and MeerKAT observations of an unprecedented flare from the X-ray Binary GRS 1915+105

ATel #16188; Joe Bright (Oxford, Breakthrough Listen), Sara Motta (INAF), Wael Farah (SETI Institute), Ian Heywood (Oxford, Breakthrough Listen), Alexander Pollak (SETI Institute), Andrew Siemion, David DeBoer (Berkeley, Breakthrough Listen), James Miller-Jones (Curtin), Patrick Woudt (UCT), Rob Fender, Lauren Rhodes (Oxford), David A. Green, Paul F. Scott (Cambridge)
on 14 Aug 2023; 12:48 UT
Credential Certification: Joe Bright (joe.bright@physics.ox.ac.uk)

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Upon receiving notification of bright radio flaring from the microquasar GRS 1915+105 as observed by the RATAN-600 radio telescope (ATel #16168) we initiated observations with the Allen Telescope Array (ATA), Arcminute Microkelvin Imager Large Array (AMI-LA), and MeerKAT radio telescopes.

The field of GRS 1915+105 was observed by the ATA between UTC 11:16:23 and UTC 11:46:23.9 at 3 GHz and 8 GHz on 04/08/2023. 3C48 was used to calibrate the absolute flux density scale and bandpass response of the ATA and J1922+1530 was observed for 10 minutes both before and after the scan on GRS 1915+105 to calibrate the time dependent complex gains. Data reduction and calibration were performed in CASA using standard techniques. The flux density at 8 GHz was 2.7 +/- 0.3 Jy assuming a conservative 10% error on the absolute flux density scale. High percentages of flagging prevented us from imaging the 3 GHz data.

The field of GRS 1915+105 was observed by the AMI-LA between UTC 20:30:51.8 and UTC 00:28:28.4 on 03/08/2023 at 15.5 GHz. 3C286 was used to calibration the absolute flux density scale and bandpass response of the AMI-LA and J1922+1530 was used to calibrate the time dependent complex gains and was observed for 100 seconds for every 600 seconds on source. Data calibration is performed using a custom pipeline, reduce_dc, and imaging was performed in CASA. We measure a flux density of 1.7 +/- 0.2 Jy assuming a conservative 10% error on the flux density scale. We note that only two AMI-LA antennas participated in this observation.

We observed the field of GRS 1915+105 with the MeerKAT radio telescope as part of the ThunderKAT LSP between UTC 17:08:30 and UTC 17:23:17 on 06/08/2023 at 1.28 GHz. J1939-6342 was used to calibrate the absolute flux scale and bandpass response of MeerKAT and J2011-0644 was used to calibrate the time dependent complex gains and was observed for 2 minutes before and after 15 minutes on source. Calibration and imaging was performed with the oxkat (https://github.com/IanHeywood/oxkat) pipeline. We measure a flux density of 6.1 +/- 0.3 Jy assuming a 5% error on the flux density scale.

Our AMI-LA follow-up observations indicate that this exceptionally bright flare from GRS 1915+105 has now faded significantly, to a level of around 300 mJy at 15.5 GHz.

Further monitoring of GRS 1915+105 is ongoing. We thank the staff at the Hat Creek Radio Observatory for maintaining and operating the ATA. The Allen Telescope Array (ATA) refurbishment program and its ongoing operations receive substantial support from Franklin Antonio. Additional contributions from Frank Levinson, Jill Tarter, Jack Welch, the Breakthrough Listen Initiative and other private donors have been instrumental in the renewal of the ATA. Breakthrough Listen is managed by the Breakthrough Initiatives, sponsored by the Breakthrough Prize Foundation. The Paul G. Allen Family Foundation provided major support for the design and construction of the ATA, alongside contributions from Nathan Myhrvold, Xilinx Corporation, Sun Microsystems, and other private donors. The ATA has also been supported by contributions from the US Naval Observatory and the US National Science Foundation. We thank the staff at the Mullard Radio Astronomy Observatory for scheduling and operating the AMI-LA. The MeerKAT telescope is operated by the South African Radio Astronomy Observatory, which is a facility of the National Research Foundation, an agency of the Department of Science and Innovation.

ThunderKAT will run for 5 years and targets X-ray binaries, Cataclysmic Variables, Supernovae and Gamma-Ray Bursts. As part of this programme, we perform weekly monitoring observations of all bright, active, southern hemisphere X-ray binaries in the radio band. For further information on this programme please contact Rob Fender and/or Patrick Woudt.

oxkat