SN 2017eaw, the tenth supernova observed in NGC 6946, was a normal Type II-P supernova with an estimated 11 - 13 Msun supergiant progenitor. Here we present nebular phase spectra of SN 2017eaw at +545 and +900 days post-max, extending approximately 50 - 400 days past the epochs of previously published spectra. While the +545 day spectra is similar to spectra taken between days +400 and +493, the +900 day spectrum shows dramatic changes both in spectral features and emission line profiles. The Halpha emission is flat-topped and box-like with sharp blue and red profile velocities of ~ -8000 and +7500 km/s. These late-time spectral changes indicate strong circumstellar interaction with a mass-loss shell, expelled ~ 1700 years before explosion. SN 2017eaw's +900 day spectrum is similar to those seen for SN 2004et and SN 2013ej observed 2 - 3 years after explosion. We discuss the importance of late-time monitoring of bright SNe II-P and the nature of pre-supernova mass-loss events for SN II-P evolution.
We present late-time Hubble and Spitzer Space Telescope imaging of SN 2008S and NGC 300 2008OT-1, the prototypes of a common class of stellar transients whose true nature is debated. Both objects are still fading and are now >15 times fainter than the progenitors in the mid-IR and are undetected in the optical and near-IR. Data from the Large Binocular Telescope and Magellan show that neither source has been variable in the optical since fading in 2010. We present models of surviving sources obscured by dusty shells or winds and find that extreme dust models are needed for surviving stars to b…
We present optical observations of supernova SN 2014C, which underwent an unprecedented slow metamorphosis from H-poor type Ib to H-rich type IIn over the course of one year. The observed spectroscopic evolution is consistent with the supernova having exploded in a cavity before encountering a massive shell of the progenitor star's stripped hydrogen envelope. Possible origins for the circumstellar shell include a brief Wolf-Rayet fast wind phase that overtook a slower red supergiant wind, eruptive ejection, or confinement of circumstellar material by external influences of neighboring stars. A…
We present panchromatic observations and modeling of calcium-strong supernovae (SNe) 2021gno in the star-forming host galaxy NGC 4165 (D = 30.5 Mpc) and 2021inl in the outskirts of elliptical galaxy NGC 4923 (D = 80 Mpc), both monitored through the Young Supernova Experiment (YSE) transient survey. The multi-color light curves of both SNe show two peaks, the former peak being derived from shock cooling emission (SCE) and/or shock interaction with circumstellar material (CSM). The primary peak in SN 2021gno is coincident with luminous, rapidly decaying X-ray emission ($L_x = 5 \times 10^{41}$ e…
We report on sensitive 1.4-GHz VLBI radio observations of the unusually luminous supernova remnant SNR 4449-1 in the galaxy NGC 4449, which gave us the first well-resolved image of this object. The remnant's radio morphology consists of two approximately parallel bright ridges, suggesting similarities to the barrel shape seen for many older Galactic supernova remnants or possibly to SN 1987A. The angular extent of the remnant is 65 x 40 mas, corresponding to (3.7 x 2.3) x 10^{18} (D/3.8 Mpc) cm. We also present a new, high signal-to-noise optical spectrum. By comparing the remnant's linear siz…
No Evidence for Nearby Circumstellar Material in the Type Ia Supernova 2025rbs
University of California, Davis（加州大学戴维斯分校）；University of California, San Diego（加州大学圣地亚哥分校）；Rutgers, The State University of New Jersey（新泽西州立罗格斯大学）；Gemini Observatory/NSF’s NOIRLab（双子座天文台/美国国家光学红外天文实验室）；Steward Observatory, University of Arizona（亚利桑那大学斯图尔德天文台）；NASA Exoplanet Science Institute / Caltech-IPAC（NASA系外行星科学研究所/加州理工学院IPAC）；NSF’s NOIRLab（美国国家光学红外天文实验室）
Supernova (SN) 2021ocs was discovered in the galaxy NGC 7828 ($z = 0.01911$) within the interacting system Arp 144, and subsequently classified as a normal type-Ic SN around peak brightness. VLT/FORS2 observations in the nebular phase at 148 d reveal that the spectrum is dominated by oxygen and magnesium emission lines of different transitions and ionization states: O I, [O I], [O II], [O III], Mg I, and Mg II. Such a spectrum has no counterpart in the literature, though it bears a few features similar to those of some interacting type Ibn and Icn SNe. Additionally, SN 2021ocs showed a blue co…
The relatively nearby spiral galaxy NGC~6946 is one of the most actively star forming galaxies in the local Universe. Ten supernovae (SNe) have been observed since 1917, and hence NGC6946 surely contains a large number of supernova remnants (SNRs). Here we report a new optical search for these SNRs using narrow-band images obtained with the WIYN telescope. We identify 147 emission nebulae as likely SNRs, based on elevated [SII]:Halpha ratios compared to HII regions. We have obtained spectra of 102 of these nebulae with Gemini North-GMOS; of these, 89 have [SII]:Halpha ratios greater than 0.4, …
This paper presents late-time near-infrared and {\it Spitzer} mid-infrared photometric and spectroscopic observations of warm dust in the Type IIn SN 2005ip in NGC 2906. The spectra show evidence for two dust components with different temperatures. Spanning the peak of the thermal emission, these observations provide strong constraints on the dust mass, temperature, and luminosity, which serve as critical diagnostics for disentangling the origin and heating mechanism of each component. The results suggest the warmer dust has a mass of $\sim 5 \times 10^{-4}~$\msolar, originates from newly form…
The optical and ultra-violet broadband photometric and spectroscopic observations of the Type II supernova (SN) 2016gfy are presented. The $V$-band light curve (LC) shows a distinct plateau phase with a slope, $s_2$ $\sim$ 0.12 mag / 100 d and a duration of 90 $\pm$ 5 d. Detailed analysis of SN 2016gfy provided a mean $\rm^{56}Ni$ mass of 0.033 $\pm$ 0.003 $\rm M_{\odot}$, a progenitor radius of $\sim$ 350-700 $\rm R_{\odot}$, a progenitor mass of $\sim$ 12-15 $\rm M_{\odot}$ and an explosion energy of 0.9-1.4$\rm \times 10^{51}\ erg\ s^{-1}$. The P-Cygni profile of H$\rm α$ in the early phase…
The Eye of Sauron in SN 2025ngs: a Short-plateau Cousin of SN 1998S with Evidence for a Ring-like Circumstellar Medium
Steward Observatory, University of Arizona（亚利桑那大学斯图尔德天文台）；Department of Physics and Astronomy, University of California, Davis（加州大学戴维斯分校物理与天文学系）；Gemini Observatory（Gemini 天文台）；School of Physical and Chemical Sciences – Te Kura Matū, University of Canterbury（坎特伯雷大学物理与化学科学学院）；Center for Astrophysics | Harvard & Smithsonian（哈佛史密松天体物理中心）
SN 2025ngs 是一个介于强相互作用超新星（IIn型）和IIP型之间的短平台超新星，其光谱特征显示与SN 1998S相似，但峰值亮度较低，且有环状周围介质的证据。
We present pre-explosion photometry of the likely progenitor star of the Type II supernova (SN II) 2017eaw in NGC 6946. We use a Hubble Space Telescope (HST) image of SN 2017eaw to perform relative astrometry with HST and Spitzer Space Telescope (Spitzer) imaging, finding a single point source consistent with its position. We detect the progenitor star in $>$40 epochs of HST and Spitzer imaging covering 12.9 years to 43 days before discovery. While the progenitor luminosity was roughly constant for most of this period, there was a $\sim$20% increase in its $4.5~μ$m luminosity over the final 3 …
We presented a detailed analysis of progenitor properties of type IIP supernova 2017eaw in NGC 6946, based on the pre-explosion images and early-time observations obtained immediately after the explosion. An unusually red star, with M$_{F814W}$ = $-$6.9 mag and m$_{F606W}$$-$ m$_{F814W}=$2.9$\pm$0.2 mag, can be identified at the SN position in the pre-discovery Hubble Space Telescope(HST) images taken in 2016. The observed spectral energy distribution of this star, covering the wavelength of 0.6-2.0$\ \mathrm{μm}$, matches that of an M4-type red supergiant (RSG) with a temperature of about 355…
JWST Nebular Spectroscopy of SN 2023qov: Circumstellar Dust Emission in a Normal Type Ia Supernova
Purdue University（普渡大学）；Rutgers, the State University of New Jersey（新泽西州立罗格斯大学）；Space Telescope Science Institute（太空望远镜科学研究所）；Northwestern University（西北大学）；University of Pittsburgh（匹兹堡大学）；Stockholm University（斯德哥尔摩大学）；European Southern Observatory（欧洲南方天文台）
Supernova remnants (SNRs) represent a powerful laboratory to study the Cosmic-Ray acceleration processes at the shocks, and their relation to the properties of the circumstellar medium. With the aim of studying the high-frequency radio emission and investigating the energy distribution of accelerated electrons and the magnetic field conditions, we performed single-dish observations of the large and complex Cygnus Loop SNR from 7.0 to 24.8 GHz with the Medicina and the Sardinia Radio Telescope, focusing on the northern filament (NGC 6992) and the southern shell. Both regions show a spectrum wel…
