Observations of the Optical Transient in NGC 300 with AKARI/IRC: Possibilities of Asymmetric Dust Formation

Abstract

We present the results of near-infrared (NIR) multi-epoch observations of the optical transient in the nearby galaxy NGC300 (NGC300-OT) at 398 and 582 days after the discovery with the Infrared Camera (IRC) onboard AKARI. NIR spectra (2--5 um) of NGC300-OT were obtained for the first time. They show no prominent emission nor absorption features, but are dominated by continuum thermal emission from the dust around NGC300-OT. NIR images were taken in the 2.4, 3.2, and 4.1 um bands. The spectral energy distributions (SED) of NGC300-OT indicate the dust temperature of 810 (+-14) K at 398 days and 670 (+-12) K at 582 days. We attribute the observed NIR emission to the thermal emission from dust grains formed in the ejecta of NGC300-OT. The multi-epoch observations enable us to estimate the dust optical depth as larger than about 12 at 398 days and larger than about 6 at 582 days at 2.4 um, by assuming an isothermal dust cloud. The observed NIR emission must be optically thick, unless the amount of dust grains increases with time. Little extinction at visible wavelengths reported in earlier observations suggests that the dust cloud around NGC300-OT should be distributed inhomogeneously so as to not screen the radiation from the ejecta gas and the central star. The present results suggest the dust grains are not formed in spherically symmetric geometry, but rather in a torus, a bipolar outflow, or clumpy cloudlets.

arXiv comment4 pages, 2 figures, 2 tables; compiled with emulateapj; accepted in ApJ

References in corpus (15)

• The Infrared Camera (IRC) for AKARI - Design and Imaging Performance
• The Evolution of Dust in the Early Universe with Applications to the Galaxy SDSS J1148+5251
• Dust Formation In Early Galaxies
• A New Class of Luminous Transients and A First Census of Their Massive Stellar Progenitors
• SN 1997bs in M66: Another Extragalactic Eta Carinae Analog?
• The 2008 Luminous Optical Transient in the Nearby Galaxy NGC 300
• An Intermediate Luminosity Transient in NGC300: The Eruption of a Dust-Enshrouded Massive Star
• Massive stars exploding in a He-rich circumstellar medium III. SN 2006jc: IR echoes from new and old dust in the progenitor CSM
• Near-infrared and Mid-infrared Spectroscopy with the Infrared Camera (IRC) for AKARI
• EC-SNe from super-AGB progenitors: theoretical models vs. observations
• A Spitzer/IRS Spectrum of the 2008 Luminous Transient in NGC 300: Connection to Proto-Planetary Nebulae
• The NGC 300 Transient: An Alternative Method For Measuring Progenitor Masses
• Properties of newly formed dust by SN2006jc based on near-to-mid infrared observation with AKARI
• Census of Self-Obscured Massive Stars in Nearby Galaxies with Spitzer: Implications for Understanding the Progenitors of SN 2008S-Like Transients
• VLT Spectropolarimetry of the optical transient in NGC300. Evidence for asymmetry in the circumstellar dust

Cited by in corpus (12)

• Unmasking the Supernova Impostors
• Almost Gone: SN~2008S and NGC~300 2008OT-1 are Fainter than their Progenitors
• Dusty Explosions from Dusty Progenitors: The Physics of SN2008S and the 2008 NGC300-OT
• The Photometric and Spectral Evolution of the 2008 Luminous Optical Transient in NGC 300
• Dust to Dust: 3 years in the Evolution of the Unusual SN 2008S
• The Carnegie Supernova Project II. Observations of the intermediate luminosity red transient SNhunt120
• Gap Transients Interacting with Circumstellar Medium
• The Blue Supergiant Progenitor of the Supernova Imposter AT~2019krl
• The Carnegie Supernova Project II. Observations of SN 2014ab possibly revealing a 2010jl-like SN IIn with pre-existing dust
• A study in scarlet -- I. Photometric properties of a sample of Intermediate Luminosity Red Transients
• The SN 2008S Progenitor Star: Gone or Again Self-Obscured?
• The fate of the progenitors of luminous red novae: Infrared detection of LRNe years after the outburst