分类： 天文学 >> 天文学 提交时间： 2023-02-19
Danielle Dickinson
Nathan Smith
Jennifer E. Andrews
Peter Milne
Charles D. Kilpatrick
Dan Milisavljevic
摘要： We present a series of ground-based photometry and spectroscopy of the superluminous Type IIn supernova (SN) ASASSN-15ua, which shows evidence for strong interaction with pre-existing dense circumstellar material (CSM). Our observations constrain the speed, mass-loss rate, and extent of the progenitor wind shortly before explosion. A narrow P Cygni absorption component reveals a progenitor wind speed of $\sim$100 km s$^{-1}$. As observed in previous SNe IIn, the intermediate-width H$\alpha$ emission became progressively more asymmetric and blueshifted, suggesting either an asymmetric CSM, an asymmetric explosion, or increasing selective extinction from dust within the post-shock shell or SN ejecta. Based on the CSM radius and speed, we find that the progenitor suffered extreme eruptive mass loss on the order of 0.1-1 M$_\odot$ yr$^{-1}$ during the $\sim$12 years immediately preceding its death, imparting $\sim$ 8 $\times$ 10$^{47}$ erg of kinetic energy to the CSM. Integrating its light curve over the first 200 days after discovery, we find that ASASSN-15ua radiated at least 3.1$\times$10$^{50}$ erg in visual light alone, giving a lower limit to the total radiated energy that may have approached 10$^{51}$ erg. ASASSN-15ua exhibits many similarities to two well-studied superluminous SNe IIn: SN 2006tf and SN 2010jl. Based on a detailed comparison of these three, we find that ASASSN-15ua falls in between these two events in a wide variety of observed properties and derived physical parameters, illustrating a continuum of behavior across superluminous SNe IIn.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Mojgan Aghakhanloo
Nathan Smith
Peter Milne
Jennifer E. Andrews
Alexei V. Filippenko
Jacob E. Jencson
David J. Sand
Schuyler D. Van Dyk
Samuel Wyatt
WeiKang Zheng
摘要： We present the first analysis of photometric observations of the supernova (SN) impostor AT 2016blu located in the galaxy NGC 4559. This transient source was discovered by the Lick Observatory Supernova Search in January 2012 and has continued its eruptive variability since then. Photometry of AT 2016blu reveals at least 19 outbursts in 2012-2022. AT 2016blu's outbursts show irregular variability with multiple closely spaced peaks of varying brightness. While the individual outbursts have irregular light curves, concentrations of these peaks seem to repeat with a period of roughly 110-115 d. Based on this period, the next outburst of AT 2016blu should occur around February 2023. AT 2016blu shares some similarities with SN 2000ch in NGC 3432, where it has been proposed that brightening episodes are caused by violent encounters at periastron in a binary system containing a luminous blue variable (LBV). We propose that AT 2016blu outbursts are also driven by binary interactions that intensify around times of periastron in an eccentric system. The intrinsic variability of the LBV-like primary star may cause different intensity and duration of binary interaction at each periastron passage. The binary interaction of AT 2016blu also resembles the periastron encounters of $\eta$ Carinae leading up to its Great Eruption and the erratic pre-SN eruptions of SN 2009ip. This similarity suggests that AT 2016blu might also be headed for a catastrophe, making it a target of great interest.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Mojgan Aghakhanloo
Nathan Smith
Peter Milne
Jennifer E. Andrews
Alexei V. Filippenko
Jacob E. Jencson
David J. Sand
Schuyler D. Van Dyk
Samuel Wyatt
WeiKang Zheng
摘要： We analyse photometric observations of the supernova (SN) impostor SN 2000ch in NGC 3432 covering the time since its discovery. This source was previously observed to have four outbursts in 2000-2010. Observations now reveal at least three additional outbursts in 2004-2007, and sixteen outbursts in 2010-2022. Outburst light curves are irregular and multipeaked, exhibiting a wide variety of peak magnitude, duration, and shape. The outbursts after 2008 repeat with a period of 200.7$\pm{2}$ d, while the outburst in 2000 seems to match with a shorter period. The next outburst should occur around January/February 2023. We propose that these periodic eruptions arise from violent interaction around times of periastron in an eccentric binary system, similar to the periastron encounters of $\eta$ Carinae leading up to its Great Eruption, and resembling the erratic pre-SN eruptions of SN 2009ip. We attribute the irregularity of the eruptions to the interplay between the orbit and the variability of the luminous blue variable (LBV) primary star, wherein each successive periastron pass may have a different intensity or duration due to the changing radius and mass-loss rate of the LBV-like primary. Such outbursts may occasionally be weak or undetectable if the LBV is relatively quiescent at periastron, but can be much more extreme when the LBV is active. The observed change in orbital period may be a consequence of mass lost in outbursts. Given the similarity to the progenitor of SN 2009ip, SN 2000ch deserves continued attention in the event it is headed for a stellar merger or a SN-like explosion.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Wen-fai Fong
Anya E. Nugent
Yuxin Dong
Edo Berger
Kerry Paterson
Ryan Chornock
Andrew Levan
Peter Blanchard
Kate D. Alexander
Jennifer Andrews
Bethany E. Cobb
Antonino Cucchiara
Derek Fox
Chris L. Fryer
Alexa C. Gordon
Charles D. Kilpatrick
Ragnhild Lunnan
Raffaella Margutti
Adam Miller
Peter Milne
摘要： We present a comprehensive optical and near-infrared census of the fields of 90 short gamma-ray bursts (GRBs) discovered in 2005-2021, constituting all short GRBs for which host galaxy associations are feasible ($\approx$ 60% of the total Swift short GRB population). We contribute 245 new multi-band imaging observations across 49 distinct GRBs and 25 spectra of their host galaxies. Supplemented by literature and archival survey data, the catalog contains 335 photometric and 40 spectroscopic data sets. The photometric catalog reaches $3\sigma$ depths of $\gtrsim 24-27$ mag and $\gtrsim 23-26$ mag for the optical and near-infrared bands, respectively. We identify host galaxies for 84 bursts, in which the most robust associations make up 54% (49/90) of events, while only a small fraction, 6.7%, have inconclusive host associations. Based on new spectroscopy, we determine 17 host spectroscopic redshifts with a range of $z\approx 0.15-1.6$ and find that $\approx$ 25-44% of Swift short GRBs originate from $z>1$. We also present the galactocentric offset catalog for 83 short GRBs. Taking into account the large range of individual measurement uncertainties, we find a median of projected offset of $\approx 7.9$ kpc, for which the bursts with the most robust associations have a smaller median of $\approx 4.9$ kpc. Our catalog captures more high-redshift and low-luminosity hosts, and more highly-offset bursts than previously found, thereby diversifying the population of known short GRB hosts and properties. In terms of locations and host luminosities, the populations of short GRBs with and without detectable extended emission are statistically indistinguishable. This suggests that they arise from the same progenitors, or from multiple progenitors which form and evolve in similar environments. All of the data products are available on the BRIGHT website.
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