Possible evidence for the 478 keV emission line from ⁷Be decay during the outburst phases of V1369 Cen

¹ INAF, Osservatorio Astronomico di Capodimonte, salita Moiariello 16, I-80131, Naples, Italy
² DARK, Niels Bohr Institute, University of Copenhagen, Jagtvej 155A, 2200 Copenhagen, Denmark
³ Julius-Maximilians-Universität Würzburg, Fakultät für Physik und Astronomie, Institut für Theoretische Physik und Astrophysik, Lehrstuhl für Astronomie, Emil-Fischer-Str. 31, D-97074 Würzburg, Germany
⁴ Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, CNRS, CNES, Université Toulouse III Paul Sabatier, 9 avenue Colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
⁵ INAF, Osservatorio Astronomico di Trieste, Via G.B.Tiepolo 11, Trieste, I-34143, Italy
⁶ Institute of Fundamental Physics of the Universe, IFPU, Via Beirut, 2, Trieste, I-34151, Italy
⁷ LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS, 92190 Meudon, France
⁸ Astrophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA

^⋆ Corresponding author: luca.izzo@inaf.it

Received: 29 November 2024
Accepted: 28 April 2025

Abstract

After decades of uncertainty about the origin of lithium, recent evidence suggests Galactic novae as its main astrophysical source. In this work, we present possible evidence for the first detection of the ⁷Be line at 478 keV, observed with the INTEGRAL satellite. The emission temporally and spatially coincides with the outburst of the bright nova V1369 Cen, where line significance ranges from 2.5σ to ∼1.9σ, depending on the detection methodology used. A bootstrap analysis, assuming a fixed full width half maximum of 8 keV, provides a flux of (4.9±2.0)×10⁻⁴ ph/cm²/s centred at 479.0 ± 2.5 keV, with a 2.5σ significant excess. This flux implies a total ⁷Be mass of M_⁷Be = (1.2^+2.0_−0.6) × 10⁻⁸ M_⊙ at the distance determined using several indicators, including the Gaia satellite. For a nova ejected mass estimated via radio observations, this result implies a ⁷Be=Li yield corresponding to A(Li) = 7.1^+0.7_−0.3. This value is comparable to those measured in a dozen novae through optical observations. Crucially, we confirm optically derived ⁷Li yields and demonstrate the groundbreaking potential of using gamma-ray data to measure Li abundances.