VLITE/VLA Detection of Nova V3890 Sgr Reveals Sub-GHz Turnover

ATel #13185; E. Polisensky (NRL), J. D. Linford (NRAO), S. Giacintucci (NRL), T. Clarke (NRL), N. Kassim (NRL), K. V. Sokolovsky (MSU), A. J. van der Horst (GWU), M. Rupen (NRC-HIA), L. Chomiuk (MSU), J. L. Sokoloski (Columbia), K. Mukai (UMBC/NASA GSFC), A. Mioduszewski (NRAO), E. Aydi (MSU), P. Barrett (GWU), A. Babul (Columbia) and A. Kawash (MSU)
on 11 Oct 2019; 21:24 UT
Credential Certification: Emil Polisensky (Emil.Polisensky@nrl.navy.mil)

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We report a detection of the known recurrent nova V3890 Sgr (e.g., ATel #13047, ATel #13050)
with the Karl G. Janksy Very Large Array (VLA) and the VLA Low-band Ionosphere and Transient
Experiment (VLITE), a commensal system capable of continuously accessing the new 236-492 MHz
low band system deployed on the VLA. Previous radio detections of V3890 Sgr were reported with
MeerKAT at 1.28 GHz (ATel #13089) and GMRT at 1.4 GHz (ATel #13092). The first joint detection
with both VLA and VLITE occurred on 2019 September 22. The center frequency for the VLITE
observation was 340 MHz with a bandwidth of 34 MHz. The VLA observed the nova at both L-band
(1-2 GHz) and C-band (4-8 GHz). Our bandwidth at L-band is 1 GHz and our bandwidth at C-band is
4 GHz. We split each VLA band into 2 side-bands for better spectral coverage. The total time on
source for the VLA observations was about 8 minutes in each band, leading to about 16 minutes
on-source for VLITE.

The VLA observations were calibrated using the VLA CASA pipeline. The VLITE observations were
calibrated with the NRL VLITE pipeline. Both the VLITE and VLA calibrations used the Perley &
Butler 2017 flux density scale.

The resulting flux densities were as follows:
0.340 GHz: 15 ± 5 mJy
1.260 GHz: 39 ± 1 mJy
1.780 GHz: 34 ± 1 mJy
5.000 GHz: 27 ± 1 mJy
7.000 GHz: 23 ± 1 mJy

The spectrum from 0.34 to 8 GHz is broadly consistent with self-absorbed synchrotron emission
with a 1.26-7.0 GHz spectral index of -0.3, turning over to a 0.34-1.26 GHz spectral index of +0.7.
The radio synchrotron emission is likely associated with a shock. This same shock is likely
responsible for creating the population of accelerated particles needed to generate the gamma-ray
photons (ATel #13114). As the nova evolves and the shock front emerges from the surrounding
medium, we expect the radio spectrum to evolve as well.

We will continue to monitor this source at radio wavelengths. We encourage additional
monitoring at all possible wavelengths.

VLA Low-band Ionosphere and Transient Experiment