Radio light curves and imaging of the helium nova V445 Puppis reveal seven years of synchrotron emission
ABSTRACT V445 Puppis is the only helium nova observed to date; its eruption in late 2000 showed high velocities up to 8500 km s−1, and a remarkable bipolar morphology cinched by an equatorial dust disc. Here we present multifrequency radio observations of V445 Pup obtained with the Very Large Array (VLA) spanning 1.5–43.3 GHz, and between 2001 January and 2008 March (days ∼89–2700 after eruption). The radio light curve is dominated by synchrotron emission over these 7 yr, and shows four distinct radio flares. Resolved radio images obtained in the VLA’s A configuration show that the synchrotron emission hugs the equatorial disc, and comparisons to near-IR images of the nova clearly demonstrate that it is the densest ejecta – not the fastest ejecta – that are the sites of the synchrotron emission in V445 Pup. The data are consistent with a model where the synchrotron emission is produced by a wind from the white dwarf impacting the dense equatorial disc, resulting in shocks and particle acceleration. The individual synchrotron flares may be associated with density enhancements in the equatorial disc and/or velocity variations in the wind from the white dwarf. This overall scenario is similar to a common picture of shock production in hydrogen-rich classical novae, more »
Authors:
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Award ID(s):
Publication Date:
NSF-PAR ID:
10225221
Journal Name:
Monthly Notices of the Royal Astronomical Society
Volume:
501
Issue:
1
Page Range or eLocation-ID:
1394 to 1412
ISSN:
0035-8711
3. ABSTRACT V3890 Sgr is a recurrent nova that has been seen in outburst three times so far, with the most recent eruption occurring on 2019 August 27 ut. This latest outburst was followed in detail by the Neil Gehrels Swift Observatory, from less than a day after the eruption until the nova entered the Sun observing constraint, with a small number of additional observations after the constraint ended. The X-ray light curve shows initial hard shock emission, followed by an early start of the supersoft source phase around day 8.5, with the soft emission ceasing by day 26. Together with the peak blackbody temperature of the supersoft spectrum being ∼100 eV, these timings suggest the white dwarf mass to be high, $\sim 1.3\, {\rm M_{\odot }}$. The UV photometric light curve decays monotonically, with the decay rate changing a number of times, approximately simultaneously with variations in the X-ray emission. The UV grism spectra show both line and continuum emission, with emission lines of N, C, Mg, and O being notable. These UV spectra are best dereddened using a Small Magellanic Cloud extinction law. Optical spectra from SMARTS show evidence of interaction between the nova ejecta and wind from the donormore »