A. Pastorello, M. Fraser
Besides supernovae, few astrophysical processes can release close to 10^51 erg of energy. A growing number of stellar outbursts are now recognised to have energy releases matching those of faint supernovae. These transients can be triggered by a variety of mechanisms, and their discrimination is sometimes a tricky issue.
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We propose that the energetic major outburst of the supernova (SN) impostor SN 2009ip in September 2012 (outburst 2012b) was a mergerburst event, where two massive stars merged. The previous outbursts of 2009 and 2011 might have occurred near periastron passages of the binary system prior to the merger, in a similar manner to the luminosity peaks in the nineteenth century Great Eruption of the massive binary system Eta Carinae. The major 2012b outburst and the 2012a pre-outburst, resemble the light curve of the mergerburst event V838 Mon. A merger of an evolved star with a mass of M1~60-100Mo …
We present new, late-time Hubble Space Telescope and Spitzer Space Telescope observations of the archetypal supernova (SN) impostor SN 1997bs. We show that SN 1997bs remains much fainter than its progenitor, posing a challenge for the canonical picture of late-time obscuration by dust forming in a shell ejected during the transient. The possibility that the star survived cloaked behind a dusty, steady wind is also disfavored. The simplest explanation is that SN 1997bs was a subluminous Type IIn SN, although it is currently impossible to rule out the possibility that the star survived either be…
We report the results of the photometric and spectroscopic monitoring campaign of the transient SN 2007sv. The observables are similar to those of type IIn supernovae, a well-known class of objects whose ejecta interact with pre-existing circum-stellar material. The spectra show a blue continuum at early phases and prominent Balmer lines in emission, however, the absolute magnitude at the discovery of SN 2007sv (M_R = - 14.25 +/- 0.38) indicate it to be most likely a supernova impostor. This classification is also supported by the lack of evidence in the spectra of very high velocity material …
This paper presents one of the first environmental analyses of the locations of the class of `interacting transients', namely type IIn supernovae and supernova Impostors. We discuss the association of these transients with star formation, host galaxy type, metallicity, and the locations of each event within the respective host. Given the frequent assumption of very high mass progenitors for these explosions from various studies, most notably a direct progenitor detection, it is interesting to note the weak association of these subtypes with star formation as traced by Hα emission, particularly…
We report the results of our follow-up campaign of the supernova impostor PSN J09132750+7627410, based on optical data covering $\sim250\,\rm{d}$. From the beginning, the transient shows prominent narrow Balmer lines with P-Cygni profiles, with a blue-shifted absorption component becoming more prominent with time. Along the $\sim3\,\rm{months}$ of the spectroscopic monitoring, broad components are never detected in the hydrogen lines, suggesting that these features are produced in slowly expanding material. The transient reaches an absolute magnitude $M_r=-13.60\pm0.19\,\rm{mag}$ at maximum, a…
We report photometric and spectroscopic observations of the optical transient LSQ13zm. Historical data reveal the presence of an eruptive episode (that we label as `2013a') followed by a much brighter outburst (`2013b') three weeks later, that we argue to be the genuine supernova explosion. This sequence of events closely resemble those observed for SN2010mc and (in 2012) SN2009ip. The absolute magnitude reached by LSQ13zm during 2013a ($M_R=-14.87\pm0.25\,\rm{mag}$) is comparable with those of supernova impostors, while that of the 2013b event ($M_R=-18.46\pm0.21\,\rm{mag}$) is consistent wit…
Observational surveys are now able to detect an increasing number of transients, such as core-collapse supernovae (SN) and powerful non-terminal outbursts (SN impostors). Dedicated spectroscopic facilities can follow up these events shortly after detection. Here we investigate the properties of these explosions at early times. We use the radiative transfer code CMFGEN to build an extensive library of spectra simulating the interaction of supernovae and their progenitor's winds/circumstellar medium (CSM). We consider a range of progenitor mass-loss rates (Mdot = 5e-4 to 1e-2 Msun/yr), abundance…
SN 1954J in NGC 2403 and SN 1961V in NGC 1058 were two luminous transients whose definitive classification as either non-terminal eruptions or supernovae remains elusive. A critical question is whether a surviving star can be significantly obscured by dust formed from material ejected during the transient. We use three lines of argument to show that the candidate surviving stars are not significantly optically extincted ($τ\lesssim 1$) by dust formed in the transients. First, we use SED fits to new HST optical and near-IR photometry. Second, neither source is becoming brighter as required by a…
We present optical photometry and spectroscopy of the optical transient SN 2011A. Our data spans 140 days after discovery including $BVRIu'g'r'i'z'$ photometry and 11 epochs of optical spectroscopy. Originally classified as a type IIn supernova (SN IIn) due to the presence of narrow H$α$ emission, this object shows exceptional characteristics. Firstly, the light curve shows a double plateau; a property only observed before in the impostor SN 1997bs. Secondly, SN 2011A has a very low luminosity ($M_{V}=-15.72$), placing it between normal luminous SNe IIn and SN impostors. Thirdly, SN 2011A show…
Using hydrodynamical numerical simulations we show that high-velocity ejecta with 10,000 km/s in the outbursts of the supernova impostor SN 2009ip and similar luminous blue variable (LBV) stars can be explained by the interaction of fast jets, having velocity of 2000-3000 km/s, with a circumbinary shell (extended envelope). The density profile in the shell is very steep such that the shock wave, that is excited by the jets' interaction with the shell, accelerates to high velocities as it propagates outward. The amount of very fast ejecta is small, but sufficient to account for some absorption …
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 J…
Some transients, although classified as novae based on their maximum and early decline optical spectra, cast doubts on their true nature and whether nova impostors might exist. We monitored a candidate nova which displayed a distinctly unusual light curve at maximum and early decline through optical spectroscopy (3000-10000 Å, 500<R<100000) complemented with Swift UV and AAVSO optical photometry. We use the spectral line series to characterize the ejecta dynamics, structure, and mass. We found that the ejecta are in free ballistic expansion and structured as typical of classical novae. However…
The missing historical record of the Cassiopeia A (Cas A) supernova (SN) event implies a large extinction to the SN, possibly greater than the interstellar extinction to the current SN remnant. Here we investigate the possibility that the guest star that appeared near Cas A in 1592--1593 in Korean history books could have been an `impostor' of the Cas A SN, i.e., a luminous transient that appeared to be a SN but did not destroy the progenitor star, with strong mass loss to have provided extra circumstellar extinction. We first review the Korean records and show that a spatial coincidence betwe…
More luminous than classical novae, but less luminous than Supernovae, lies the exotic stellar eruptions known as Intermediate luminosity optical transients (ILOTs). They are divided into a number of sub-groups depending on the erupting progenitor and the properties of the eruption. A large part of the ILOTs is positioned on the slanted Optical Transient Stripe (OTS) in the Energy-Time Diagram (ETD) that shows their total energy vs. duration of their eruption. We describe the different kinds of ILOTs that populate the OTS and other parts of the ETD. The high energy part of the OTS hosts the su…
Reports of the death of the precursor of Supernova (SN) 1961V in NGC 1058 are exaggerated. Consideration of the best astrometric data shows that the star, known as "Object 7," lies at the greatest proximity to SN 1961V and is the likely survivor of the "SN impostor" super-outburst. SN 1961V does not coincide with a neighboring radio source and is therefore not a radio SN. Additionally, the current properties of Object 7, based on data obtained with the Hubble Space Telescope, are consistent with it being a quiescent Luminous Blue Variable (LBV). Furthermore, post-explosion non-detections by th…
SN 1961V, one of Zwicky's defining Type V supernovae (SN), was a peculiar transient in NGC 1058 that has variously been categorized as either a true core collapse SN leaving a black hole (BH) or neutron star (NS) remnant, or an eruption of a luminous blue variable (LBV) star. The former case is suggested by its association with a decaying non-thermal radio source, while the latter is suggested by its peculiar transient light curve and its low initial expansion velocities. The crucial difference is that the star survives a transient eruption but not an SN. All stars identified as possible survi…
(ABRIDGED) The canonical picture of a supernova impostor is a -11 < M_V < -14 optical transient from a massive (M > 40Msun) star during which the star ejects a dense shell of material. Dust formed in the ejecta then obscures the star. In this picture, the geometric expansion of the shell leads to clear predictions for the evolution of the optical depths and hence the evolution of the optical through mid-IR emissions. Here we review the theory of this standard model and then examine the impostors SN1954J, SN1997bs, SN1999bw, SN2000ch, SN2001ac, SN2002bu, SN2002kg and SN2003gm, as well as the po…
Spectroscopy of AT 2016blu's recurring supernova impostor outbursts
本研究分析AT 2016blu十年光谱，发现其由LBV主星的偏心双星近星点触发约113天准周期爆发，谱线特征与相位无关，揭示伴星与主星风相互作用，验证第21次爆发预测，为LBV爆发机制提供新线索。
We present new light curves and spectra for a number of extragalactic optical transients or "SN impostors" related to giant eruptions of LBVs, and we provide a comparative discussion of LBV-like giant eruptions known to date. New data include photometry and spectroscopy of SNe1999bw, 2000ch, 2001ac, 2002bu, 2006bv, and 2010dn. SN2010dn resembles SN2008S and NGC 300-OT, whereas SN2002bu shows spectral evolution from a normal LBV at early times to a twin of these cooler transients at late times. SN2008S, NGC300-OT, and SN2010dn appear to be special cases of a broader eruptive phenomenon where th…
In the last 20 years, modern wide-field surveys discovered a new class of peculiar transients, which lie in the luminosity gap between standard supernovae and classical novae. These transients are often called 'intermediate luminosity optical transients' or 'gap transients'. They are usually distinguished in subgroups based on their phenomenology, such as supernova impostors, intermediate luminosity red transients, and luminous red novae. In this review, we present a brief overview of their observational features and possible physical scenarios to date, in the attempt to understand their natur…
Recurring outbursts of the supernova impostor AT 2016blu in NGC 4559
本文首次对超新星冒名者AT 2016blu进行光度分析，发现其以约113天周期反复爆发，并提出该现象源于含LBV的偏心双星系统近星点相互作用，且可能预示未来灾难性爆发。
We report the results of a 3 year-long dedicated monitoring campaign of a restless Luminous Blue Variable (LBV) in NGC 7259. The object, named SN 2009ip, was observed photometrically and spectroscopically in the optical and near-infrared domains. We monitored a number of erupting episodes in the past few years, and increased the density of our observations during eruptive episodes. In this paper we present the full historical data set from 2009-2012 with multi-wavelength dense coverage of the two high luminosity events between August - September 2012. We construct bolometric light curves and m…
We present very early UV to optical photometric and spectroscopic observations of the peculiar Type IIn supernova (SN) 2011ht in UGC 5460. The UV observations of the rise to peak are only the second ever recorded for a Type IIn SN and are by far the most complete. The SN, first classified as a SN impostor, slowly rose to a peak of M_V \sim -17 in \sim55 days. In contrast to the \sim2 magnitude increase in the v-band light curve from the first observation until peak, the UV flux increased by >7 magnitudes. The optical spectra are dominated by strong, Balmer emission with narrow peaks (FWHM\sim6…
SN2011ht has been described both as a true supernova and as an impostor. In this paper, we conclude that it does not match some basic expectations for a core-collapse event. We discuss SN2011ht's spectral evolution from a hot dense wind to a cool dense wind, followed by the post-plateau appearance of a faster low density wind during a rapid decline in luminosity. We identify a slow dense wind expanding at only 500--600 km/s, present throughout the eruption. A faster wind speed V ~ 900 km/s may be identified with a second phase of the outburst. There is no direct or significant evidence for any…
A core-collapse supernova occurs when exothermic fusion ceases in the core of a massive star, typically due to exhaustion of nuclear fuel. Theory predicts that fusion could be interrupted earlier, by merging of the star with a compact binary companion. We report a luminous radio transient, VT J121001+495647, found in the Very Large Array Sky Survey. The radio emission is consistent with supernova ejecta colliding with a dense shell of material, potentially ejected by binary interaction in the centuries prior to explosion. We associate the supernova with an archival X-ray transient, which impli…
A systematic search for rapid transients in the Subaru HSC-SSP transient survey
本文基于Subaru HSC-SSP巡天的3381个超新星候选体，开发机器学习分类器筛选出14个中高红移快速暂现源，并估计了其与Ibn型超新星候选体的事件率及物理特征。
Giant eruptions or supernova-impostor events are far more mysterious than true supernovae. An extreme example can release as much radiative energy as a SN, ejecting several M_sun of material. These events involve continuous radiation-driven outflows rather than blast waves. They constitute one of the main unsolved problems in stellar astrophysics, but have received surprisingly little theoretical effort. Here I note some aspects that are not yet familiar to most astronomers.
We present the public release of the Complete History of Interaction-Powered Supernovae (CHIPS) code, suited to model a variety of transients that arise from interaction with a dense circumstellar medium (CSM). Contrary to existing modellings which mostly attach the CSM by hand, CHIPS self-consistently simulates both the creation of the CSM from mass eruption of massive stars prior to core-collapse, and the subsequent supernova light curve. We demonstrate the performance of CHIPS by presenting examples of the density profiles of the CSM and the light curves. We show that the gross light curve …
We give an overview of recent efforts to model Type Ia supernovae and related astrophysical transients resulting from thermonuclear explosions in white dwarfs. In particular we point out the challenges resulting from the multi-physics multi-scale nature of the problem and discuss possible numerical approaches to meet them in hydrodynamical explosion simulations and radiative transfer modeling. We give examples of how these methods are applied to several explosion scenarios that have been proposed to explain distinct subsets or, in some cases, the majority of the observed events. In case we com…
We investigate the expected rates and bolometric light-curve properties of stripped-envelope electron-capture supernovae (ECSNe) using stellar models from the Binary Population and Spectral Synthesis (BPASS) code. We find that 0.8 per cent (Z = 0.020) and 1.2 per cent (Z = 0.004) of core-collapse supernovae are stripped-envelope ECSNe. Their typical ejecta masses are estimated to be about 0.3 Msun (Z = 0.020) and 0.6 Msun (Z = 0.004). Assuming ECSN explosion properties from numerical explosion simulations, an explosion energy of 1.5e50 erg and a 56Ni mass of 2.5e-3 Msun, we find that stripped-…
We present an online application, the SuperNova Interactive Fitter (SNIF), which can be used to interactively fit one-zone, analytical models to optical transient light curves powered by (1) the radioactive decay of 56Ni, (2) the spin-down of newly born magnetars, or (3) the interaction between supernova ejecta and pre-existing circumstellar material. This application utilizes the Open Astronomy Catalogs API to connect the user to thousands of publicly available transient light curves from the literature.
The Landscape of Thermal Transients from Supernova Interacting with a Circumstellar Medium
本文通过解析标度关系和辐射流体力学模拟，系统分类了超新星抛射物与球对称星周介质壳层相互作用产生的热瞬变光变曲线形态，并验证其对多种观测瞬变现象的解释力。
We show that for supergiants, net angular momentum is not a necessary condition for forming accretion discs during core-collapse. Even absent net rotation, convective motions in the outer parts of supergiants generate mean horizontal flows at a given radius with velocities of order 1 km/s; the direction of the mean flow will vary as a function of height through the convection zone. We confirm these analytic estimates using Cartesian Boussinesq convection simulations. These mean horizontal flows lead to a random angular momentum in supergiant convection zones that exceeds that of the last stabl…
The absence of Type IIP core-collapse supernovae arising from progenitors above 17 solar masses suggests the existence of another evolutionary path by which massive stars end their lives. The direct collapse of a stellar core to a black hole without the production of a bright, explosive transient is expected to produce a long-lived, dim, red transient known as a failed supernova. Despite the detection of a number of candidates for disappearing massive stars in recent years, conclusive observational evidence for failed supernovae remains elusive. A custom-built pipeline designed for the detecti…
Type Ic supernovae represent the explosions of the most stripped massive stars, but their progenitors and explosion mechanisms remain unclear. Larger samples of observed supernovae can help characterize the population of these transients. We present an analysis of 44 spectroscopically normal Type Ic supernovae, with focus on the light curves. The photometric data were obtained over 7 years with the Palomar Transient Factory (PTF) and its continuation, the intermediate Palomar Transient Factory (iPTF). This is the first homogeneous and large sample of SNe Ic from an untargeted survey, and we ai…
The majority of thermonuclear explosions in the Universe seem to proceed in a rather standardised way, as explosions of carbon-oxygen (CO) white dwarfs in binary systems, leading to 'normal' Type Ia supernovae (SNe Ia). However, over the years a number of objects have been found which deviate from normal SNe Ia in their observational properties, and which require different and not seldom more extreme progenitor systems. While the 'traditional' classes of peculiar SNe Ia - luminous '91T-like' and faint '91bg-like' objects - have been known since the early 1990s, other classes of even more unusu…
We use non-local thermal equilibrium radiative transport modeling to examine observational signatures of sub-Chandrasekhar mass double detonation explosions in the nebular phase. Results range from spectra that look like typical and subluminous Type Ia supernovae (SNe) for higher mass progenitors to spectra that look like Ca-rich transients for lower mass progenitors. This ignition mechanism produces an inherent relationship between emission features and the progenitor mass as the ratio of the nebular [Ca II]/[Fe III] emission lines increases with decreasing white dwarf mass. Examining the [Ca…
Long-rising Type II Supernovae in the Zwicky Transient Facility Census of the Local Universe
本研究基于ZTF CLU实验识别13颗长上升期II型超新星，给出光变与光谱特征，并首次测得体积率为总核心坍缩超新星率的1.4%。
We present the compilation of the first 221 supernovae classified during the Asiago Classification Program (ACP). The details of transients classification and the preliminarily reduced spectra, in fits format, are immediately posted on the Padova-Asiago SN group web site. The achieved performances for the first 2 years of the ACP are analysed, showing that half of all our classifications were made within 5 days from transient detection. The distribution of the supernova types of this sample resembles the distribution of the general list of all the supernovae listed in the Asiago SN catalog (AS…
The recent discovery of the unprecedentedly superluminous transient ASASSN-15lh (or SN 2015L) with its UV-bright secondary peak challenges all the power-input models that have been proposed for superluminous supernovae. Here we examine some of the few viable interpretations of ASASSN-15lh in the context of a stellar explosion, involving combinations of one or more power inputs. We model the lightcurve of ASASSN-15lh with a hybrid model that includes contributions from magnetar spin-down energy and hydrogen-poor circumstellar interaction. We also investigate models of pure circumstellar interac…
We present multi-wavelength observations of two gap transients followed by the Carnegie Supernova Project-II and supplemented with data obtained by a number of different programs. Here in the first of two papers, we focus on the intermediate luminosity red transient (ILRT) designated SNhunt120, while in a companion paper we examine the luminous red novae AT 2014ej. Our data set for SNhunt120 consists of an early optical discovery, estimated to be within 3 days after outburst, the subsequent optical and near-infrared broadband followup extending over a $\sim$2 month period, two visual- and two …
Some supernovae such as pair-instability supernovae are predicted to have the duration of more than a year in the observer frame. To constrain the rates of supernovae lasting for more than a year, we conducted a long-term deep transient survey using Hyper Suprime-Cam (HSC) on the 8.2m Subaru telescope. HSC is a wide-field (a 1.75 deg2 field-of-view) camera and it can efficiently conduct transient surveys. We observed the same 1.75 deg2 field repeatedly using the g, r, i, and z band filters with the typical depth of 26 mag for 4 seasons (from late 2016 to early 2020). Using these data, we searc…
This work examines the relationships between the properties (flux ratios, full width at half-maximum velocities) of the [O I] $λλ$6300, 6364, [Ca II] $λλ$7291, 7323, and the Ca II near-infrared triplet, emission lines of a large sample of core-collapse supernovae (SNe) and Ca-rich transients (509 spectra of 86 transients, of which 10 transients are Ca-rich events). Line-flux ratios as a function of time were investigated with differences identified between the transient classes, in particular the Type II SNe were found to have distinct line-flux ratios compared to stripped-envelope (SE) SNe. N…
Blue supergiants as a progenitor of intermediate-luminosity red transients
本研究探究蓝超巨星的其他爆发情景，通过模拟不同参数下的爆发光变曲线，发现其爆发可产生两类超新星，解释了相关观测与预期占比的差异，拓展了对蓝超巨星爆发多样性的认知。
We analyze a sample of 45 Type II supernovae from the Zwicky Transient Facility (ZTF) public survey using a grid of hydrodynamical models in order to assess whether theoretically-driven forecasts can intelligently guide follow up observations supporting all-sky survey alert streams. We estimate several progenitor properties and explosion physics parameters including zero-age-main-sequence (ZAMS) mass, mass-loss rate, kinetic energy, 56Ni mass synthesized, host extinction, and the time of explosion. Using complete light curves we obtain confident characterizations for 34 events in our sample, w…
Monte Carlo Radiation Transport for Astrophysical Transients Powered by Circumstellar Interaction
本文提出开源蒙特卡罗辐射输运程序 SuperLite，用于模拟星周相互作用驱动的瞬变现象光谱，并通过与 SuperNu、CMFGEN 对比及标准测试验证其能准确再现 Ia、IIP、IIn 型超新星光谱。
Semi-analytical Light Curve Model for Transients Preceding Binary Mergers. I: Supernova Precursor Emission from Compact Object Companions
构建双星系统半解析光变曲线模型，应用于超新星前身，能推断质量转移历史、约束前身双星系统，其模型及参数推断框架封装在脚本中，可用于现有及未来发现的超新星前身。
We present medium-resolution spectroscopy and multicolor photometry for the optical transient PSN J09093496+3307204 (SN 2015bh) in the galaxy NGC 2770, which has transferred into the supernova phase. The observations were carried out between February 2015 to May 2016. Both at the phase of the SN impostor (2015a) and at the supernova phase (2015b), besides Balmer emissions, the strong Fe II emissions are seen in the spectrum; so, these spectra resemble those of Williams Fe II type classical novae. The star is located near the edge of a dark nebula and notably absorbed (Av = 1.14 +/-0.15 mag). T…
Type Ibn Supernovae (SNe Ibn) show signatures of strong interaction between the SN ejecta and hydrogen-poor circumstellar matter (CSM). Deriving the ejecta and CSM properties of SNe Ibn provides a great opportunity to study the final evolution of massive stars. In the present work, we present a light curve (LC) model for the ejecta-CSM interaction, taking into account the processes in which the high-energy photons originally created at the forward and reverse shocks are converted to the observed emission in the optical. The model is applied to a sample of SNe Ibn and `SN Ibn' rapidly evolving …
ULTIMATE-Subaru (Ultra-wide Laser Tomographic Imager and MOS with AO for Transcendent Exploration on Subaru) and WFIRST (Wide Field Infra-Red Survey Telescope) are the next generation near-infrared instruments that have a large field-of-view. They allow us to conduct deep and wide transient surveys in near-infrared. Such a near-infrared transient survey enables us to find very distant supernovae that are redshifted to the near-infrared wavelengths. We have performed the mock transient surveys with ULTIMATE-Subaru and WFIRST to investigate their ability to discover Population III pair-instabili…
Pulsational pair-instability supernovae in gravitational-wave and electromagnetic transients
本文利用binary_c群体合成模拟双黑洞并合，研究脉动对不稳定性超新星对黑洞质量分布的影响，发现35 M⊙峰难以由PPISNe解释，除非将CO核心质量范围下移约15 M⊙，但这与恒星模型和超亮超新星观测存在张力。
There are currently many large-field surveys operational and planned including the powerful Vera C. Rubin Observatory Legacy Survey of Space and Time. These surveys will increase the number and diversity of transients dramatically. However, for some transients, like supernovae (SNe), we can gain more understanding by directed observations (e.g. shock breakout, $γ$-ray detections) than by simply increasing the sample size. For example, the initial emission from these transients can be a powerful probe of these explosions. Upcoming ground-based detectors are not ideally suited to observe the ini…
We provide additional observational evidence that some Type Ia supernovae (SNe Ia) show signatures of circumstellar interaction (CSI) with hydrogen-rich material. Early phase optical and near-infrared (NIR) light curves and spectroscopy of SN 2008J obtained by the Carnegie Supernova Project are studied and compared to those of SNe 2002ic and 2005gj. Our NIR spectrum is the first obtained for a 2002ic-like object extending up to 2.2 $μ$m. A published high-resolution spectrum is used to provide insight on the circumstellar material (CSM). SN 2008J is found to be affected by $A_V\sim$ 1.9 mag of …
Superluminous supernovae radiate up to 100 times more energy than normal supernovae. The origin of this energy and the nature of their stellar progenitors are poorly understood. We identify neutral iron lines in the spectrum of one such transient, SN 2006gy, and show that they require a large mass of iron (>~0.3 Msun) expanding at 1500 km/s. We demonstrate that a model of a standard Type Ia supernova hitting a shell of circumstellar material produces a light curve and late-time iron-dominated spectrum that match SN 2006gy. In such a scenario, common envelope evolution of the progenitor system …
This paper discusses a model where a violent periastron collision of stars in an eccentric binary system induces an eruption or explosion seen as a brief transient source, attributed to LBVs, SN impostors, or other transients. The key ingredient is that an evolved primary increases its photospheric radius on relatively short timescales, to a point where the radius is comparable to or larger than the periastron separation in an eccentric binary. In such a configuration, a violent and sudden collision would ensue, possibly leading to substantial mass ejection instead of a binary merger. Repeated…
We identify a "supernova rate problem": the measured cosmic core-collapse supernova rate is a factor of ~ 2 smaller (with significance ~ 2 sigma) than that predicted from the measured cosmic massive-star formation rate. The comparison is critical for topics from galaxy evolution and enrichment to the abundance of neutron stars and black holes. We systematically explore possible resolutions. The accuracy and precision of the star formation rate data and conversion to the supernova rate are well supported, and proposed changes would have far-reaching consequences. The dominant effect is likely t…
We report our observations of HSC16aayt (SN 2016jiu), which was discovered by the Subaru/Hyper Suprime-Cam (HSC) transient survey conducted as part of Subaru Strategic Program (SSP). It shows very slow photometric evolution and its rise time is more than 100 days. The optical magnitude change in 400 days remains within 0.6 mag. Spectra of HSC16aayt show a strong narrow emission line and we classify it as a Type IIn supernova. The redshift of HSC16aayt is 0.6814 +/- 0.0002 from the spectra. Its host galaxy center is at 5 kpc from the supernova location and HSC16aayt might be another example of …
Recent searches by unbiased, wide-field surveys have uncovered a group of extremely luminous optical transients. The initial discoveries of SN 2005ap by the Texas Supernova Search and SCP-06F6 in a deep Hubble pencil beam survey were followed by the Palomar Transient Factory confirmation of host redshifts for other similar transients. The transients share the common properties of high optical luminosities (peak magnitudes ~ -21 to -23), blue colors, and a lack of H or He spectral features. The physical mechanism that produces the luminosity is uncertain, with suggestions ranging from jet-drive…
We examine rare evolutionary routes of binary systems where the initially more massive primary star of ~5.5-8.5Mo, forms a white dwarf (WD), while the secondary star of 4Mo < M_2,0 < M_1,0 accretes mass from the evolved primary and later terminates as a core collapse supernova (CCSN). In such a WD-NS reverse evolution a neutron star (NS) or a potential NS-progenitor massive core is formed after the WD. These SN explosions are likely to be preceded by strong interaction of the WD with the giant secondary's core, leading to an Intermediate-Luminosity Optical Transient (ILOT; Red Transient; Red N…
We present the first results of the High cadence Transient Survey (HiTS), a survey whose objective is to detect and follow up optical transients with characteristic timescales from hours to days, especially the earliest hours of supernova (SN) explosions. HiTS uses the Dark Energy Camera (DECam) and a custom made pipeline for image subtraction, candidate filtering and candidate visualization, which runs in real-time to be able to react rapidly to the new transients. We discuss the survey design, the technical challenges associated with the real-time analysis of these large volumes of data and …
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