NERO - A Post Maximum Supernova Radiation Transport Code

TL;DR

NERO is a new supernova radiation transport code capable of modeling the intermediate nebular phase with full NLTE treatment, filling a gap in existing tools for supernova spectral analysis between 50 and 500 days post-explosion.

Contribution

The paper introduces NERO, a novel NLTE radiation transport code for supernovae that covers intermediate epochs not addressed by previous models.

Findings

NERO accurately reproduces supernova spectra between 50 and 350 days.

Comparison shows NERO's reliability against established codes.

Application to SN 2005cf demonstrates spectral feature identification.

Abstract

The interpretation of supernova (SN) spectra is essential for deriving SN ejecta properties such as density and composition, which in turn can tell us about their progenitors and the explosion mechanism. A very large number of atomic processes are important for spectrum formation. Several tools for calculating SN spectra exist, but they mainly focus on the very early or late epochs. The intermediate phase, which requires a NLTE treatment of radiation transport has rarely been studied. In this paper we present a new SN radiation transport code, NERO, which can look at those epochs. All the atomic processes are treated in full NLTE, under a steady-state assumption. This is a valid approach between roughly 50 and 500 days after the explosion depending on SN type. This covers the post-maximum photospheric and the early and the intermediate nebular phase. As a test, we compare NERO to the radiation transport code of Jerkstrand et al. (2011) and to the nebular code of Mazzali et al. (2001). All three codes have been developed independently and a comparison provides a valuable opportunity to investigate their reliability. Currently, NERO is one-dimensional and can be used for predicting spectra of synthetic explosion models or for deriving SN properties by spectral modelling. To demonstrate this, we study the spectra of the 'normal' SN Ia 2005cf between 50 and 350 days after the explosion and identify most of the common SN Ia line features at post maximum epochs.