We report the time variability of the late-time radio emission in a Type-I superluminous supernova (SLSN), PTF10hgi, at z = 0.0987. The Karl G. Jansky Very Large Array 3 GHz observations at 8.6 and 10 years after the explosion both detected radio emission with a ~40% decrease in flux density in the second epoch. This is the first report of a significant variability of the late-time radio light curve in a SLSN. Through combination with previous measurements in two other epochs, we constrained both the rise and decay phases of the radio light curve over three years, peaking at approximately 8-9 years after the explosion with a peak luminosity of L(3GHz) = 2 x 10^21 W/Hz. Possible scenarios for the origin of the variability are an active galactic nucleus (AGN) in the host galaxy, an afterglow caused by the interaction between an off-axis jet and circumstellar medium, and a wind nebula powered by a newly-born magnetar. Comparisons with models show that the radio light curve can be reproduced by both the afterglow model and magnetar wind nebula model. Considering the flat radio spectrum at 1-15 GHz and an upper limit at 0.6 GHz obtained in previous studies, plausible scenarios are a low-luminosity flat-spectrum AGN or a magnetar wind nebula with a shallow injection spectral index.
Recently, researches performed by two groups have revealed that the magnetar spin-down energy injection model with full energy trapping can explain the early-time light curves of SN 2010gx, SN 2013dg, LSQ12dlf, SSS120810 and CSS121015, but fails to fit the late-time light curves of these Superluminous Supernovae (SLSNe). These results imply that the original magnetar-powered model is challenged in explaining these SLSNe. Our paper aims to simultaneously explain both the early- and late-time data/upper limits by considering the leakage of hard emissions. We incorporate quantitatively the leakag…
The light curve diversity of hydrogen-poor superluminous supernovae (SLSNe) has kept open the possibility that multiple power sources account for the population. Specifically, pair-instability explosions (PISNe), which produce large masses of $^{56}$Ni, have been argued as the origin of some slowly-evolving SLSNe. Here we present detailed observations of SN 2016inl (=PS16fgt), a slowly-evolving SLSN at $z=0.3057$, whose unusually red spectrum matches PS1-14bj, a SLSN with an exceptionally long rise time consistent with a PISN. Ground-based and Hubble Space Telescope data, spanning about 800 re…
We present the results of 3 GHz radio continuum observations of 23 superluminous supernovae (SLSNe) and their host galaxies by using the Karl G. Jansky Very Large Array conducted 5-21 years after the explosions. The sample consists of 15 Type I and 8 Type II SLSNe at z < 0.3, providing one of the largest sample of SLSNe with late-time radio data. We detected radio emission from one SLSN (PTF10hgi) and 5 hosts with a significance of >5$σ$. No time variability is found in late-time radio light curves of the radio-detected sources in a timescale of years except for PTF10hgi, whose variability is …
Optical imaging polarimetry was conducted on the hydrogen poor superluminous supernova 2020znr during 3 phases after maximum light (approximately +34 days, +288 days and +289 days). After instrumental and interstellar polarization correction, all measurements are consistent with null-polarization detection. Modelling the light curve with a magnetar spin-down model shows that SN 2020znr has similar magnetar and ejecta parameters to other SLSNe. A comparison of the best-fit values discussed in the literature on SN 2017egm and SN 2015bn, two hydrogen poor SLSNe showing an increase of polarization…
We present results of a search for late-time radio emission and Fast Radio Bursts (FRBs) from a sample of type-I superluminous supernovae (SLSNe-I). We used the Karl G. Jansky Very Large Array to observe ten SLSN-I more than 5 years old at a frequency of 3 GHz. We searched fast-sampled visibilities for FRBs and used the same data to perform a deep imaging search for late-time radio emission expected in models of magnetar-powered supernovae. No FRBs were found. One SLSN-I, PTF10hgi, is detected in deep imaging, corresponding to a luminosity of $1.2\times10^{28}$ erg s$^{-1}$. This luminosity, c…
Observations of Gaia16apd revealed extremely luminous ultraviolet emission among superluminous supernovae (SLSNe). Using radiation hydrodynamics simulations we perform a comparison of UV light curves, color temperatures and photospheric velocities between the most popular SLSN models: pair-instability supernova, magnetar and interaction with circumstellar medium. We find that the interaction model is the most promising to explain the extreme UV luminosity of Gaia16apd. The differences in late-time UV emission and in color evolution found between the models can be used to link an observed SLSN …
We investigate the light-curve properties of a sample of 26 spectroscopically confirmed hydrogen-poor superluminous supernovae (SLSNe-I) in the Palomar Transient Factory (PTF) survey. These events are brighter than SNe Ib/c and SNe Ic-BL, on average, by about 4 and 2~mag, respectively. The peak absolute magnitudes of SLSNe-I in rest-frame $g$ band span $-22\lesssim M_g \lesssim-20$~mag, and these peaks are not powered by radioactive $^{56}$Ni, unless strong asymmetries are at play. The rise timescales are longer for SLSNe than for normal SNe Ib/c, by roughly 10 days, for events with similar de…
We present photometry and spectroscopy of PS1-14bj, a hydrogen-poor superluminous supernova (SLSN) at redshift $z=0.5215$ discovered in the last months of the Pan-STARRS1 Medium Deep Survey. PS1-14bj stands out by its extremely slow evolution, with an observed rise of $\gtrsim 125$ rest-frame days, and exponential decline out to $\sim 250$ days past peak at a measured rate of $0.01~{\rm mag~day}^{-1}$, consistent with fully-trapped $^{56}$Co decay. This is the longest rise time measured in a SLSN to date, and the first SLSN to show a rise time consistent with pair-instability supernova (PISN) …
Almost all superluminous supernovae (SLSNe) whose peak magnitudes are $\lesssim -21$ mag can be explained by the $^{56}$Ni-powered model, magnetar-powered (highly magnetized pulsar) model or ejecta-circumstellar medium (CSM) interaction model. Recently, iPTF13ehe challenges these energy-source models, because the spectral analysis shows that $\sim 2.5M_\odot$ of $^{56}$Ni have been synthesized but are inadequate to power the peak bolometric emission of iPTF13ehe, while the rebrightening of the late-time light-curve (LC) and the H$α$ emission lines indicate that the ejecta-CSM interaction must …
iPTF13ehe is a hydrogen-poor superluminous supernova (SLSN) at z=0.3434, with a slow-evolving light curve and spectral features similar to SN2007bi. It rises within (83-148)days (rest-frame) to reach a peak bolometric luminosity of 1.3x$10^{44}$erg/s, then decays very slowly at 0.015mag. per day. The measured ejecta velocity is 13000km/s. The inferred explosion characteristics, such as the ejecta mass (67-220$M_\odot$), the total radiative and kinetic energy ($10^{51}$ & 2x$10^{53}$erg respectively), is typical of a slow-evolving H-poor SLSN event. However, the late-time spectrum taken at +251…
Superluminous supernovae (SLSNe) are a rare class of stellar explosions with luminosities ~10-100 times greater than ordinary core-collapse supernovae. One popular model to explain the enhanced optical output of hydrogen-poor (Type I) SLSNe invokes energy injection from a rapidly spinning magnetar. A prediction in this case is that high-energy gamma rays, generated in the wind nebula of the magnetar, could escape through the expanding supernova ejecta at late times (months or more after optical peak). This paper presents a search for gamma-ray emission in the broad energy band from 100 MeV to …
We present the largest and deepest late-time radio and millimeter survey to date of superluminous supernovae (SLSNe) and long duration gamma-ray bursts (LGRBs) to search for associated non-thermal synchrotron emission. Using the Karl G. Jansky Very Large Array (VLA) and the Atacama Large Millimeter/submillimeter Array (ALMA), we observed 43 sources at 6 and 100 GHz on a timescale of $\sim 1 - 19$ yr post-explosion. We do not detect radio/mm emission from any of the sources, with the exception of a 6 GHz detection of PTF10hgi (Eftekhari et al. 2019), as well as the detection of 6 GHz emission n…
We present observations of two new hydrogen-poor superluminous supernovae (SLSN-I), iPTF15esb and iPTF16bad, showing late-time H-alpha emission with line luminosities of (1-3)e+41 erg/s and velocity widths of (4000-6000) km/s. Including the previously published iPTF13ehe, this makes up a total of three such events to date. iPTF13ehe is one of the most luminous and the slowest evolving SLSNe-I, whereas the other two are less luminous and fast decliners. We interpret this as a result of the ejecta running into a neutral H-shell located at a radius of ~ 1.0e+16cm. This implies that violent mass l…
We study the spectroscopic evolution of superluminous supernovae (SLSNe) later than 100 days after maximum light. We present new data for Gaia16apd and SN2017egm, and analyse these with a larger sample comprising 41 spectra of 12 events. The spectra become nebular within 2-4 $e$-folding times after light curve peak, with the rate of spectroscopic evolution correlated to the light curve timescale. Emission lines are identified with well-known transitions of oxygen, calcium, magnesium, sodium and iron. SLSNe are differentiated from other Type Ic SNe by a prominent O I $λ$7774 line and higher-ion…
We present the light curves of the hydrogen-poor superluminous supernovae (SLSNe-I) PTF12dam and iPTF13dcc, discovered by the (intermediate) Palomar Transient Factory. Both show excess emission at early times and a slowly declining light curve at late times. The early bump in PTF12dam is very similar in duration (~10 days) and brightness relative to the main peak (2-3 mag fainter) compared to those observed in other SLSNe-I. In contrast, the long-duration (>30 days) early excess emission in iPTF13dcc, whose brightness competes with that of the main peak, appears to be of a different nature. We…
Newly-born, rapidly-spinning magnetars have been invoked as the power sources of super-luminous transients, including the class of "fast-luminous optical transients" (FBOTs). The extensive multi-wavelength analysis of AT2018cow, the first FBOT discovered in real time, is consistent with the magnetar scenario and offers an unprecedented opportunity to comprehend the nature of these sources and assess their broader implications. Using AT2018cow as a prototype, we investigate high-energy neutrino and cosmic ray production from FBOTs and the more general class of superluminous supernovae (SLSNe). …
Lightcurve Features of Magnetar-Powered Superluminous Supernovae with Gravitational-Wave Emission and High-Energy Leakage
Peking University（北京大学）；Kavli Institute for Astronomy and Astrophysics, Peking University（北京大学科维理天文与天体物理研究所）；Central China Normal University（华中师范大学）；Institute of Astrophysics, Central China Normal University（华中师范大学天体物理研究所）；Education Research and Application Center, National Astronomical Data Center（国家天文台教育研究与应用中心）
(Abridged). The optical light curve of some SNe may be powered by the outward diffusion of the energy deposited by the explosion shock in optically thick circumstellar matter (CSM). Recently, it was shown that the radiation-mediated and -dominated shock in an optically thick wind must transform into a collisionless shock and can produce hard X-rays. The X-rays are expected to peak at late times, relative to maximum visible light. Here we report on a search, using Swift and Chandra, for X-ray emission from 28 SNe that belong to classes whose progenitors are suspected to be embedded in dense CSM…
SN 2006gy was the most luminous SN ever observed at the time of its discovery and the first of the newly defined class of superluminous supernovae (SLSNe). The extraordinary energetics of SN 2006gy and all SLSNe (>10^51 erg) require either atypically large explosion energies (e.g., pair-instability explosion) or the efficient conversion of kinetic into radiative energy (e.g., shock interaction). The mass-loss characteristics can therefore offer important clues regarding the progenitor system. For the case of SN 2006gy, both a scattered and thermal light echo from circumstellar material (CSM) h…
A Quark-Nova (QN, the sudden transition from a neutron star into a quark star) which occurs in the second common envelope (CE) phase of a massive binary (Ouyed et al., 2015a&b), gives excellent fits to super-luminous, hydrogen-poor, Supernovae (SLSNe) with double-peaked light curves including DES13S2cmm, SN 2006oz and LSQ14bdq (http://www.quarknova.ca/LCGallery.html). In our model, the H envelope of the less massive companion is ejected during the first CE phase while the QN occurs deep inside the second, He-rich, CE phase after the CE has expanded in size to a radius of a few tens to a few th…
We describe the late spectral variability and flux evolution of TDF Sw J1644+57, a Tidal Disruption Flare which left the typical potential trend proportional to $t^{-5/3}$ in 2012, maintaining a quiescent flux until nowadays. Sixteen X-ray observations of ESA satellite \emph{XMM-Newton} have been used in this study, including the one performed on 17$^{\rm th}$July, 2013. A search for optical emission in BOOTES/CASANDRA database has been performed too. Late X-ray fluxes show that the source flux decline does not follow the expected TDF trend at the time of the last \emph{XMM-Newton} observation…
SN 2015bn is a nearby hydrogen-poor superluminous supernova (SLSN-I) that has been intensively observed in X-rays with the goal to detect the spin-down powered emission from a magnetar engine. The early-time UV/optical/infrared (UVOIR) data fit well to the magnetar model, but require leakage of energy at late times of $\lesssim 10^{43}$ erg s$^{-1}$, which is expected to be partially emitted in X-rays. Deep X-ray limits until $\sim$300 days after explosion revealed no X-ray emission. Here, we present the latest deep 0.3--10 keV X-ray limit at 805 days obtained with \textit{XMM-Newton}. We find…
An unusual Eddington-limited thermonuclear X-ray burst was detected from the accreting neutron star in 2S 0918-549 with the Rossi X-ray Timing Explorer. The burst commenced with a brief (40 ms) precursor and maintained near-Eddington fluxes during the initial 77 s. These characteristics are indicative of a nova-like expulsion of a shell from the neutron star surface. Starting 122 s into the burst, the burst shows strong (87 +/- 1% peak-to-peak amplitude) achromatic fluctuations for 60 s. We speculate that the fluctuations are due to Thompson scattering by fully-ionized inhomogeneities in a res…
In this paper we propose and examine a physical mechanism which can lead to the generation of noise in the mass accretion rate of low mass X-ray binaries on time-scales comparable to the orbital period of the system. We consider modulations of mass captured by the compact object from the companion star's stellar wind in binaries with late type giants, systems which usually have long orbital periods. We show that a hydrodynamical interaction of the wind matter within a binary system even without eccentricity results in variability of the mass accretion rate with characteristic time-scales close…
SN 2008es is one of the rare cases of a Type II superluminous supernova (SLSN) showing no relatively narrow features in its early-time spectra, and therefore its powering mechanism is under debate between circumstellar interaction (CSI) and magnetar spin-down. Late-time data are required for better constraints. We present optical and near-infrared (NIR) photometry obtained from Gemini, Keck, and Palomar Observatories from 192 to 554 days after explosion. Only broad H$α$ emission is detected in a Gemini spectrum at 288 days. The line profile exhibits red-wing attenuation relative to the early-t…
Recent work has revealed that the light curves of hydrogen-poor (Type I) superluminous supernovae (SLSNe), thought to be powered by magnetar central engines, do not always follow the smooth decline predicted by a simple magnetar spin-down model. Here we present the first systematic study of the prevalence and properties of "bumps" in the post-peak light curves of 34 SLSNe. We find that the majority (44-76%) of events cannot be explained by a smooth magnetar model alone. We do not find any difference in supernova properties between events with and without bumps. By fitting a simple Gaussian mod…
SN 2018bsz: significant dust formation in a nearby superluminous supernova
National Central University（中央大学）；Stockholm University（斯德哥尔摩大学）；Max-Planck-Institut für Extraterrestrische Physik（马克斯·普朗克地外物理学研究所）；University College Dublin（都柏林大学学院）；University College London（伦敦大学学院）；Cardiff University（卡迪夫大学）；Northwestern University（西北大学）；Queen’s University Belfast（贝尔法斯特女王大学）；European Southern Observatory（欧洲南方天文台）
Deriving physical parameters from gamma-ray burst afterglow observations remains a challenge, even now, 20 years after the discovery of afterglows. The main reason for the lack of progress is that the peak of the synchrotron emission is in the sub-mm range, thus requiring radio observations in conjunction with X-ray/optical/near-infrared data in order to measure the corresponding spectral slopes and consequently remove the ambiguity wrt. slow vs. fast cooling and the ordering of the characteristic frequencies. We observed GRB 151027B, the 1000th Swift-detected GRB, with GROND in the optical-NI…
In the last 10 years multi-wavelength fast variability studies of low mass X-ray binaries have shown a dramatic development. A key discovery was the detection of O-IR sub-second fluctuations in two black-hole transients, lagging the X-rays by $\approx$0.1 s. This demonstrated how the fluctuations observed in the inflow could be transferred to the jet, allowing therefore also to study in a completely new way the physical processes which take place at the base of the jet. In this paper we review the latest developments of the study of jets with this new approach, focusing on the results obtained…
Even thought a large amount of long gamma ray bursts (LGRBs) present quiescent periods, their origin remains unclear. In this talk, it is shown how different angular momentum distributions, as a function of the stellar radius), can lead to neutrino luminosity variability and the possibility of quiescent epochs in LGRBs.
CSS J102913+404220 is a peculiar narrow line Seyfert 1 galaxy with an energetic nuclear optical outburst. We present a detailed analysis of its multi-wavelength photometric and spectroscopic observations covering a period of decade since outburst. We detect mid-infrared (MIR) flares delayed by about two months relative to the optical outburst, with an extremely high peak luminosity of log(L_4.6um)>44 erg/s. The MIR peak luminosity is at least an order of magnitude higher than any known supernovae explosions, suggesting the optical outburst might be due to a stellar tidal disruption event (TDE)…
