Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userOptical Observations and Modeling of the Superluminous Supernova 2018lfe
118
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present optical imaging and spectroscopy of SN,2018lfe, which we classify as a Type I superluminous supernova (SLSN-I) at a redshift of $z = 0.3501$ with a peak absolute magnitude of $M_rapprox -22.1$ mag, one of the brightest SLSNe discovered. SN,2018lfe was identified for follow-up using our FLEET machine learning pipeline. Both the light curve and the spectra of SN,2018lfe are consistent with the broad population of SLSNe. We fit the light curve with a magnetar central engine model and find an ejecta mass of $M_{rm ej}approx 3.8$ M$_odot$, a magnetar spin period of $Papprox 2.9$ ms and a magnetic field strength of $B_{perp}approx 2.8times 10^{14}$ G. The magnetic field strength is near the top of the distribution for SLSNe, while the spin period and ejecta mass are near the median values of the distribution for SLSNe. From late-time imaging and spectroscopy we find that the host galaxy of SN,2018lfe has an absolute magnitude of $M_rapprox -17.85$, ($L_B approx 0.029$ $L^*$), and an inferred metallicity of $Zapprox 0.3$ Z$_odot$, and star formation rate of $approx 0.8$ M$_odot$ yr$^{-1}$.
rate research
Read More
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 interaction with a massive hydrogen-deficient shell and discuss the lack of interaction features in the observed spectra. We find that, as a supernova ASASSN-15lh can be best modeled by the energetic core-collapse of a ~40 Msun star interacting with a hydrogen-poor shell of ~20 Msun. The circumstellar shell and progenitor mass are consistent with a rapidly rotating pulsational pair-instability supernova progenitor as required for strong interaction following the final supernova explosion. Additional energy injection by a magnetar with initial period of 1-2 ms and magnetic field of 0.1-1 x 10^14 G may supply the excess luminosity required to overcome the deficit in single-component models, but this requires more fine-tuning and extreme parameters for the magnetar, as well as the assumption of efficient conversion of magnetar energy into radiation. We thus favor a single-input model where the reverse shock formed in a strong SN ejecta-CSM interaction following a very powerful core-collapse SN explosion can supply the luminosity needed to reproduce the late-time UV-bright plateau.
The non-detection of companion stars in Type Ia supernova (SN) progenitor systems lends support to the notion of double-degenerate (DD) systems and explosions triggered by the merging of two white dwarfs. This very asymmetric process should lead to a conspicuous polarimetric signature. By contrast, observations consistently find very low continuum polarization as the signatures from the explosion process largely dominate over the pre-explosion configuration within several days. Critical information about the interaction of the ejecta with a companion and any circumstellar matter is encoded in the early polarization spectra. In this study, we obtain spectropolarimetry of SN,2018gv with the ESO Very Large Telescope at $-$13.6 days relative to the $B-$band maximum light, or $sim$5 days after the estimated explosion --- the earliest spectropolarimetric observations to date of any Type Ia SN. These early observations still show a low continuum polarization ($lesssim$0.2%) and moderate line polarization (0.30$pm$0.04% for the prominent ion{Si}{2} $lambda$6355 feature and 0.85$pm$0.04% for the high-velocity Ca component). The high degree of spherical symmetry implied by the low line and continuum polarization at this early epoch is consistent with explosion models of delayed detonations and is inconsistent with the merger-induced explosion scenario. The dense UV and optical photometry and optical spectroscopy within the first $sim$100 days after the maximum light indicate that SN,2018gv is a normal Type Ia SN with similar spectrophotometric behavior to SN,2011fe.
The discovery of a population of superluminous supernovae (SLSNe), with peak luminosities a factor of ~100 brighter than normal SNe (typically SLSNe have M_V <-21), has shown an unexpected diversity in core-collapse supernova properties. Numerous models have been postulated for the nature of these events, including a strong interaction of the shockwave with a dense circumstellar environment, a re-energizing of the outflow via a central engine, or an origin in the catastrophic destruction of the star following a loss of pressure due to pair production in an extremely massive stellar core (so-called pair instability supernovae). Here we consider constraints that can be placed on the explosion mechanism of Hydrogen-poor SLSNe (SLSNe-I) via X-ray observations, with XMM-Newton, Chandra and Swift, and show that at least one SLSNe-I is likely the brightest X-ray supernovae ever observed, with L_X ~ 10^45 ergs/s, ~150 days after its initial discovery. This is a luminosity 3 orders of magnitude higher than seen in other X-ray supernovae powered via circumstellar interactions. Such high X-ray luminosities are sufficient to ionize the ejecta and markedly reduce the optical depth, making it possible to see deep into the ejecta and any source of emission that resides there. Alternatively, an engine could have powered a moderately relativistic jet external to the ejecta, similar to those seen in gamma-ray bursts. If the detection of X-rays does require an engine it implies that these SNe do create compact objects, and that the stars are not completely destroyed in a pair instability event. Future observations will determine which, if any, of these mechanisms are at play in superluminous supernovae.
We present a simple and well defined prescription to compare absorption lines in supernova (SN) spectra with lists of transitions drawn from the National Institute of Standards and Technology (NIST) database. The method is designed to be applicable to simple spectra where the photosphere can be mostly described by absorptions from single transitions with a single photospheric velocity. These conditions are plausible for SN spectra obtained shortly after explosion. Here we show that the method also works well for spectra of hydrogen-poor (Type I) superluminous supernovae (SLSNe-I) around peak. Analysis of high signal to noise spectra leads to clear identification of numerous spectroscopic features arising from ions of carbon and oxygen, that account for the majority of absorption features detected in the optical range, suggesting the outer envelope of SLSN-I progenitors is dominated by these elements. We find that the prominent absorption features seen in the blue are dominated by numerous lines of OII, as previously suggested, and that the apparent absorption feature widths are dominated by line density and not by doppler broadening. In fact, we find that while the expansion velocities of SLSNe-I around peak are similar to those of normal SNe, the apparent velocity distribution (manifest as the width of single transition features) is much lower (~1500 km/s) indicating emission from a very narrow photosphere in velocity space that is nevertheless expanding rapidly. We inspect the controversial case of ASASSN-15lh, and find that the early spectrum of this object is not consistent with those of SLSNe-I. We also show that SLSNe that initially lack hydrogen features but develop these at late phases, such as iPTF15esb and iPTF16bad, also differ in their early spectra from standard SLSNe-I.
We present nebular-phase imaging and spectroscopy for the hydrogen-poor superluminous supernova SN 2015bn, at redshift z=0.1136, spanning +250-400 d after maximum light. The light curve exhibits a steepening in the decline rate from 1.4 mag/(100 d) to 1.7 mag/(100 d), suggestive of a significant decrease in the opacity. This change is accompanied by a transition from a blue continuum superposed with photospheric absorption lines to a nebular spectrum dominated by emission lines of oxygen, calcium and magnesium. There are no obvious signatures of circumstellar interaction or large nickel mass. We show that the spectrum at +400 d is virtually identical to a number of energetic Type Ic supernovae such as SN 1997dq, SN 2012au, and SN 1998bw, indicating similar core conditions and strengthening the link between `hypernovae/long gamma-ray bursts and superluminous supernovae. A single explosion mechanism may unify these events that span absolute magnitudes of -22 < M_B < -17. Both the light curve and spectrum of SN 2015bn are consistent with an engine-driven explosion ejecting 7-30 M$_odot$ of oxygen-dominated ejecta (for reasonable choices in temperature and opacity). A strong and relatively narrow O II $lambda$7774 line, seen in a number of these energetic events but not in normal supernovae, may point to an inner shell that is the signature of a central engine.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
