3 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
Low-frequency radio observations of recurrent nova RS Ophiuchi with MeerKAT and LOFAR
We report low-frequency radio observations of the 2021 outburst of the
recurrent nova RS Ophiuchi. These observations include the lowest frequency
observations of this system to date. Detailed light curves are obtained by
MeerKAT at 0.82 and 1.28 GHz and LOFAR at 54 and 154 MHz. These low-frequency
detections allow us to put stringent constraints on the brightness temperature
that clearly favour a non-thermal emission mechanism. The radio emission is
interpreted and modelled as synchrotron emission from the shock interaction
between the nova ejecta and the circumbinary medium. The light curve shows a
plateauing behaviour after the first peak, which can be explained by either a
non-uniform density of the circumbinary medium or a second emission component.
Allowing for a second component in the light curve modelling captures the steep
decay at late times. Furthermore, extrapolating this model to 15 years after
the outburst shows that the radio emission might not fully disappear between
outbursts. Further modelling of the light curves indicates a red giant mass
loss rate of . The spectrum cannot
be modelled in detail at this stage, as there are likely at least four emission
components. Radio emission from stellar wind or synchrotron jets are ruled out
as the possible origin of the radio emission. Finally, we suggest a strategy
for future observations that would advance our understanding of the physical
properties of RS Oph.Comment: submitted to MNRA
Classical novae at radio wavelengths
We present radio observations (1-40 GHz) for 36 classical novae, representing data from over five decades compiled from the literature, telescope archives, and our own programs. Our targets display a striking diversity in their optical parameters (e.g., spanning optical fading timescales, t 2 = 1-263 days), and we find a similar diversity in the radio light curves. Using a brightness temperature analysis, we find that radio emission from novae is a mixture of thermal and synchrotron emission, with nonthermal emission observed at earlier times. We identify high brightness temperature emission (T B > 5 104 K) as an indication of synchrotron emission in at least nine (25%) of the novae. We find a class of synchrotron-dominated novae with mildly evolved companions, exemplified by V5589 Sgr and V392 Per, that appear to be a bridge between classical novae with dwarf companions and symbiotic binaries with giant companions. Four of the novae in our sample have two distinct radio maxima (the first dominated by synchrotron and the later by thermal emission), and in four cases the early synchrotron peak is temporally coincident with a dramatic dip in the optical light curve, hinting at a common site for particle acceleration and dust formation. We publish the light curves in a machine-readable table and encourage the use of these data by the broader community in multiwavelength studies and modeling efforts