34 research outputs found
Synchrotron emission from double-peaked radio light curves of the symbiotic recurrent nova V3890 Sagitarii
We present radio observations of the symbiotic recurrent nova V3890 Sagitarii
following the 2019 August eruption obtained with the MeerKAT radio telescope at
1.28 GHz and Karl G. Janksy Very Large Array (VLA) at 1.26 to 5 GHz. The radio
light curves span from day 1 to 540 days after eruption and are dominated by
synchrotron emission produced by the expanding nova ejecta interacting with the
dense wind from an evolved companion in the binary system. The radio emission
is detected early on (day 6) and increases rapidly to a peak on day 15. The
radio luminosity increases due to a decrease in the opacity of the
circumstellar material in front of the shocked material and fades as the
density of the surrounding medium decreases and the velocity of the shock
decelerates. Modelling the light curve provides an estimated mass-loss rate of
from the red giant star and ejecta mass in the range of from the surface of the white dwarf.
V3890 Sgr likely hosts a massive white dwarf similar to other symbiotic
recurrent novae, thus considered a candidate for supernovae type Ia (SNe Ia)
progenitor. However, its radio flux densities compared to upper limits for SNe
Ia have ruled it out as a progenitor for SN 2011fe
Shocks and dust formation in nova V809 Cep
The discovery that many classical novae produce detectable GeV -ray
emission has raised the question of the role of shocks in nova eruptions. Here
we use radio observations of nova V809 Cep (Nova Cep 2013) with the Jansky Very
Large Array to show that it produced non-thermal emission indicative of
particle acceleration in strong shocks for more than a month starting about six
weeks into the eruption, quasi-simultaneous with the production of dust.
Broadly speaking, the radio emission at late times -- more than a six months or
so into the eruption -- is consistent with thermal emission from of freely expanding, ~K ejecta. At 4.6 and 7.4 GHz, however, the
radio light-curves display an initial early-time peak 76 days after the
discovery of the eruption in the optical (). The brightness temperature at
4.6 GHz on day 76 was greater than , an order of magnitude above what
is expected for thermal emission. We argue that the brightness temperature is
the result of synchrotron emission due to internal shocks within the ejecta.
The evolution of the radio spectrum was consistent with synchrotron emission
that peaked at high frequencies before low frequencies, suggesting that the
synchrotron from the shock was initially subject to free-free absorption by
optically thick ionized material in front of the shock. Dust formation began
around day 37, and we suggest that internal shocks in the ejecta were
established prior to dust formation and caused the nucleation of dust
A Detailed Observational Analysis of V1324 Sco, the Most Gamma-Ray Luminous Classical Nova to Date
It has recently been discovered that some, if not all, classical novae emit
GeV gamma rays during outburst, but the mechanisms involved in the production
of the gamma rays are still not well understood. We present here a
comprehensive multi-wavelength dataset---from radio to X-rays---for the most
gamma-ray luminous classical nova to-date, V1324 Sco. Using this dataset, we
show that V1324 Sco is a canonical dusty Fe-II type nova, with a maximum ejecta
velocity of 2600 km s and an ejecta mass of few
M. There is also evidence for complex shock interactions, including a
double-peaked radio light curve which shows high brightness temperatures at
early times. To explore why V1324~Sco was so gamma-ray luminous, we present a
model of the nova ejecta featuring strong internal shocks, and find that higher
gamma-ray luminosities result from higher ejecta velocities and/or mass-loss
rates. Comparison of V1324~Sco with other gamma-ray detected novae does not
show clear signatures of either, and we conclude that a larger sample of
similarly well-observed novae is needed to understand the origin and variation
of gamma rays in novae.Comment: 26 pages, 13 figure