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Abstract We present a systematic search for radio counterparts of novae using the Australian Square Kilometer Array Pathfinder (ASKAP). Our search used the Rapid ASKAP Continuum Survey, which covered the entire sky south of declination $$+41^{\circ}$$ ( $$\sim$$ $34000$ square degrees) at a central frequency of 887.5 MHz, the Variables and Slow Transients Pilot Survey, which covered $$\sim$$ $5000$ square degrees per epoch (887.5 MHz), and other ASKAP pilot surveys, which covered $$\sim$$ 200–2000 square degrees with 2–12 h integration times. We crossmatched radio sources found in these surveys over a two–year period, from 2019 April to 2021 August, with 440 previously identified optical novae, and found radio counterparts for four novae: V5668 Sgr, V1369 Cen, YZ Ret, and RR Tel. Follow-up observations with the Australian Telescope Compact Array confirm the ejecta thinning across all observed bands with spectral analysis indicative of synchrotron emission in V1369 Cen and YZ Ret. Our light-curve fit with the Hubble Flow model yields a value of $$1.65\pm 0.17 \times 10^{-4} \rm \:M_\odot$$ for the mass ejected in V1369 Cen. We also derive a peak surface brightness temperature of $$250\pm80$$ K for YZ Ret. Using Hubble Flow model simulated radio lightcurves for novae, we demonstrate that with a 5 $$\sigma$$ sensitivity limit of 1.5 mJy in 15-min survey observations, we can detect radio emission up to a distance of 4 kpc if ejecta mass is in the range $$10^{-3}\rm \:M_\odot$$ , and upto 1 kpc if ejecta mass is in the range $$10^{-5}$$ – $$10^{-3}\rm \:M_\odot$$ . Our study highlights ASKAP’s ability to contribute to future radio observations for novae within a distance of 1 kpc hosted on white dwarfs with masses $0.4$ – $$1.25\:\rm M_\odot$$ , and within a distance of 4 kpc hosted on white dwarfs with masses $0.4$ – $$1.0\:\rm M_\odot$$ .
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Gravitational collapse of white dwarfs to neutron stars: From initial conditions to explosions with neutrino-radiation hydrodynamics simulations
Abstract Using general relativistic neutrino-radiation hydrodynamics simulations with the multi-group M1 scheme in one dimension, we investigate the collapse of massive, fully convective, and non-rotating white dwarfs (WDs), which are formed by accretion-induced collapse or merger-induced collapse, and the subsequent explosion. We produce initial WDs in hydrostatic equilibrium, which have super-Chandrasekhar mass and are about to collapse. The WDs have masses of $$1.6\, M_{\odot }$$ with different initial central densities specifically at $$1.0\times 10^{10}$$, $$4.0\times 10^{9}$$, $$2.0\times 10^{9}$$, and $$1.0\times 10^{9}\:\mbox{g}\:\mbox{cm}^{-3}$$. First, we examine the stability of initial WD in case weak interactions are turned off. Secondly, we calculate the collapse of WDs with weak interactions. We employ hydrodynamics simulations with Newtonian gravity in the first and second steps. Thirdly, we calculate the formation of neutron stars and accompanying explosions with general relativistic simulations. As a result, WDs with the highest density of $$10^{10}\:\mbox{g}\:\mbox{cm}^{-3}$$ collapse not by weak interactions but by the photodissociation of the iron, and three WDs with low central densities collapse by the electron capture as expected at the second step and succeed in the explosion with a small explosion energy of $$\sim\! 10^{48}\:$$erg at the third step. By changing the surrounding environment of WDs, we find that there is a minimum value of ejecta masses, which is $$\sim\! 10^{-5}\, M_{\odot }$$. With the most elaborate simulations of this kind so far, this value is one to two orders of magnitude smaller than previously reported values and is compatible with the estimated ejecta mass from FRB 121102.
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- PAR ID:
- 10562050
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Publications of the Astronomical Society of Japan
- Volume:
- 77
- Issue:
- 1
- ISSN:
- 0004-6264
- Format(s):
- Medium: X Size: p. 127-138
- Size(s):
- p. 127-138
- Sponsoring Org:
- National Science Foundation
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