# Discovery of a rapid, luminous nova in NGC 300 by the KMTNet Supernova Program

## TL;DR

This paper reports the discovery and analysis of a fast, luminous nova in galaxy NGC 300 using the high-cadence KMTNet supernova survey, providing detailed light-curve measurements and progenitor constraints.

## Contribution

It introduces KSP as a novel high-cadence survey capable of detecting rapid transients and presents the first detailed characterization of a luminous, fast-evolving nova in NGC 300.

## Key findings

- Discovered a nova with a decay time of ~1.7 days.
- Measured a peak absolute magnitude between -9.25 and -9.65.
- Identified a short pre-maximum halt in the light curve.

## Abstract

We present the discovery of a rapidly evolving transient by the Korean Microlensing Telescope Network Supernova Program (KSP). KSP is a novel high-cadence supernova survey that offers deep ($\sim21.5$ mag in $BVI$ bands) nearly continuous wide-field monitoring for the discovery of early and/or fast optical transients. KSP-OT-201509a, reported here, was discovered on 2015 September 27 during the KSP commissioning run in the direction of the nearby galaxy NGC~300, and stayed above detection limit for $\sim$ 22 days. We use our $BVI$ light-curves to constrain the ascent rate, $-3.7(7)$ mag day$^{-1}$ in $V$, decay time scale, $t^{V}_{2}=1.7(6)$ days, and peak absolute magnitude, $-9.65\leq M_{V}\leq -9.25$ mag. We also find evidence for a short-lived pre-maximum halt in all bands. The peak luminosity and lightcurve evolution make KSP-OT-201509a consistent with a bright, rapidly decaying nova outburst. We discuss constraints on the nature of the progenitor and its environment using archival HST/ACS images and conclude with a broad discussion on the nature of the system.