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Gamma-Ray Light Curves and Spectra of Classical Novae

Leung, Shing-Chi and Siegert, Thomas (2021) Gamma-Ray Light Curves and Spectra of Classical Novae. . (Unpublished)

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The nucleosynthesis in classical novae, in particular that of radioactive isotopes, is directly measurable by its γ-ray signature. Despite decades of observations, MeV γ-rays from novae have never been detected -- neither individually at the time of the explosion, nor as a result of radioactive decay, nor the diffuse Galactic emission from the nova population. Thanks to recent developments in modeling of instrumental background for MeV telescopes such as INTEGRAL/SPI and Fermi/GBM, the prospects to finally detect these elusive transients are greatly enhanced. This demands for updated and refined models of γ-ray spectra and light curves of classical novae. In this work, we develop numerical models of nova explosions using sub- and near-Chandrasekhar CO white dwarfs as the progenitor. We study the parameter dependence of the explosions, their thermodynamics and energetics, as well as their chemical abundance patterns. We use a Monte-Carlo radiative transfer code to compute γ-ray light curves and spectra, with a focus on the early time evolution. We compare our results to previous studies and find that the expected 511-keV-line flash at the time of the explosion is heavily suppressed, showing a maximum flux of only 10⁻⁹ ph cm⁻² s⁻¹ and thus making it at least one million times fainter than estimated before. This finding would render it impossible for current MeV instruments to detect novae within the first day after the outburst. Nevertheless, our time-resolved spectra can be used for retrospective analyses of archival data, thereby improving the sensitivity of the instruments.

Item Type:Report or Paper (Discussion Paper)
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URLURL TypeDescription Paper
Leung, Shing-Chi0000-0002-4972-3803
Siegert, Thomas0000-0002-0552-3535
Additional Information:© 2021 The Authors. S.C.L. acknowledges support by NASA grants HST-AR-15021.001-A and 80NSSC18K1017. Thomas Siegert is supported by the German Research Foundation (DFG-Forschungsstipendium SI 2502/3-1) and acknowledges support by the Bundesministerium für Wirtschaft und Energie via the Deutsches Zentrum für Luft- und Raumfahrt (DLR) under contract number 50 OX 2201. Data Availability: The data underlying this article will be shared on reasonable request to the corresponding author. This project is done with the use of software MESA (Paxton et al. 2011, 2013, 2015, 2018, 2019) version 8118 and Python libraries: Matplotlib (Hunter 2007), Pandas (pandas development team 2020), Numpy (Harris et al. 2020).
Funding AgencyGrant Number
NASA Hubble FellowshipHST-AR-15021.001-A
Deutsche Forschungsgemeinschaft (DFG)SI 2502/3-1
Bundesministerium für Wirtschaft und Energie (BMWK)UNSPECIFIED
Deutsches Zentrum für Luft- und Raumfahrt (DLR)50 OX 2201
Subject Keywords:transients: novae - gamma-rays: stars - nuclear reactions, nucleosynthesis, abundances - radiative transfer
Record Number:CaltechAUTHORS:20220411-225137953
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:114219
Deposited By: George Porter
Deposited On:12 Apr 2022 19:14
Last Modified:12 Apr 2022 19:14

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