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ABSTRACT Classical novae in the Milky Way have now been well-established as high-energy GeV $$\gamma$$-ray sources. In novae with main-sequence companions, this emission is believed to result from shocks internal to the nova ejecta, as a later fast wind collides with an earlier slow outflow. To test this model and constrain the $$\gamma$$-ray production mechanism, we present a systematic study of a sample of recent Galactic novae, comparing their $$\gamma$$-ray properties ($$\gamma$$-ray luminosity and duration) with their outflow velocities, peak V-band magnitudes, and the decline times of their optical light curves ($$t_2$$). We uniformly estimate distances in a luminosity-independent manner, using spectroscopic reddening estimates combined with three-dimensional Galactic dust maps. Across our sample, $$\gamma$$-ray luminosities ($>$100 MeV) vary by three orders of magnitude, spanning $$10^{34}{{-}}10^{37}$$ erg s$$^{-1}$$. Novae with larger velocity of the fast outflow (or larger differential between the fast and slow outflow) have larger $$\gamma$$-ray luminosities, but are detectable for a shorter duration. The optical and $$\gamma$$-ray fluxes are correlated, consistent with substantial thermal emission in the optical from shock-heated gas. Across six novae with $$\gamma$$-ray and infrared light curves, evidence for dust formation appears soon after the end of the detected $$\gamma$$-ray emission. Dusty and non-dusty novae appear to have similar $$\gamma$$-ray luminosities, though novae that have more material processed by the shocks may be more likely to form dust. We find that the properties of the $$\gamma$$-ray emission in novae depend heavily on the ejecta properties, and are consistent with expectations for internal shocks.
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Revisiting the classics: on the statistics of dust formation in novae
ABSTRACT While nova eruptions produce some of the most common and dramatic dust formation episodes among astrophysical transients, the demographics of dust-forming novae remain poorly understood. Here, we present a statistical study of dust formation in 40 novae with high-quality optical/IR light curves, quantitatively distinguishing dust-forming from non-dust-forming novae while exploring the properties of the dust events. We find that 50–70 per cent of novae produce dust, significantly higher than previous estimates. Dust-forming novae can be separated from those that do not show dust formation by using the largest redward ($V-K$) colour change from peak visible brightness; ($V-J$) or ($V-H$) offer useful but less sensitive constraints. This makes optical+IR photometry a powerful tool to quantify dust formation in novae. We find that novae detected in GeV $$\gamma$$-rays by Fermi-LAT appear to form dust more often than novae not detected by Fermi, implying a possible connection between $$\gamma$$-ray-producing shocks and dust production. We also find that novae that evolve very quickly ($$t_2 < 10$$ d) are much less likely to form dust, in agreement with previous findings. We confirm a correlation between $$t_2$$ and the time of the onset of dust formation (which occurs $$\sim$$1 week–3 months after maximum light), but conclude that it is primarily an observational artefact driven by dust formation determining when a nova drops 2 mag below peak. The significant fraction of novae that form dust make them ideal laboratories in our Galactic backyard to tackle the puzzle of dust formation around explosive transients.
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- PAR ID:
- 10618589
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 541
- Issue:
- 2
- ISSN:
- 0035-8711
- Page Range / eLocation ID:
- 980 to 1001
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1093/mnras/staf1001
