Abstract
In May 2010, an intermediate luminosity optical transient was discovered in the nearby galaxy NGC 300 by a South African amateur astronomer. In the decade since its discovery, multi-wavelength observations of the misnamed “SN 2010da” have continually reshaped our understanding of this high mass X-ray binary system. In this review, we present an overview of the multi-wavelength observations and attempt to understand the 2010 transient event, and later, the reclassification of this system as NGC 300 ULX-1: a red supergiant + neutron star ultraluminous X-ray source.
Highlights
In May 2010, an intermediate luminosity optical transient was discovered in the nearby galaxy NGC 300 by a South African amateur astronomer
Follow-up spectroscopy confirmed that the transient event was not a genuine SN, and instead resembled a luminous blue variable (LBV)-like outburst from a dust-enshrouded, massive star [4,5]
SN 2010da joined the heterogeneous group of objects known as “supernova impostors," which are frequently interpreted as massive stars experiencing non-terminal eruptions or outbursts [5,6]
Summary
On May 25 2010, the amateur astronomer L.A.G. Monard of Pretoria, South Africa, reported the discovery of an optical transient in the nearby spiral galaxy NGC 300, shown in Figure 1 [1]. The blue continuum emission of SN 2010da shortly after the outburst was dominated by strong Hα emission, with a full width at half maximum (FWHM) of ∼1000 km s−1 and no evidence of a P Cygni profile, along with other narrow Balmer lines and a possible detection of weak He II λ4686 [5] These results stood in contrast to those obtained with near-simultaneous GMOS on Gemini-South by Chornock and Berger [4], which observed an Hα FWHM of ∼660 km s−1 and higher-order Balmer lines with clear P-Cygni profiles. It was proposed that the SN 2010da progenitor was enshrouded by a thick cocoon of dust (AV > 12 mag), most of which was destroyed in the subsequent outburst This hypothesis accommodated the optical upper limits, Berger and Chornock [19] noted that the 24 μm flux limit was still roughly “an order of magnitude lower than expected based on the SED of AG Car”
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