Superluminous supernovae: an explosive decade Nicholl, Matt
Astronomy & geophysics : the journal of the Royal Astronomical Society,
10/2021, Letnik:
62, Številka:
5
Journal Article
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Abstract
Ten years on from the discovery of mysterious events 100 times brighter than conventional stellar explosions, Matt Nicholl charts our understanding of superluminous supernovae
We explore and demonstrate the capabilities of the upcoming Large Synoptic Survey Telescope (LSST) to study Type I superluminous supernovae (SLSNe). We fit the light curves of 58 known SLSNe at z ...0.1-1.6, using a magnetar spin-down model. We use the posterior distributions of the magnetar and ejecta parameters to generate synthetic SLSN light curves, and we inject those into the LSST Operations Simulator to generate ugrizy light curves. We define metrics to quantify the detectability and utility of the light curve. We combine the metric efficiencies with the SLSN volumetric rate to estimate the discovery rate of LSST and find that 104 SLSNe per year with >10 data points will be discovered in the Wide-Fast-Deep (WFD) survey at z 3.0, while only 15 SLSNe per year will be discovered in each Deep Drilling Field at z 4.0. To evaluate the information content in the LSST data, we refit representative output light curves. We find that we can recover physical parameters to within 30% of their true values from 18% of WFD light curves. Light curves with measurements of both the rise and decline in gri-bands, and those with at least 50 observations in all bands combined, are most information rich. WFD survey strategies, which increase cadence in these bands and minimize seasonal gaps, will maximize the number of scientifically useful SLSNe. Finally, although the Deep Drilling Fields will provide more densely sampled light curves, we expect only 50 SLSNe with recoverable parameters in each field in the decade-long survey.
ABSTRACT
We present a rapid analytic framework for predicting kilonova light curves following neutron star (NS) mergers, where the main input parameters are binary-based properties measurable by ...gravitational wave detectors (chirp mass and mass ratio, orbital inclination) and properties dependent on the nuclear equation of state (tidal deformability, maximum NS mass). This enables synthesis of a kilonova sample for any NS source population, or determination of the observing depth needed to detect a live kilonova given gravitational wave source parameters in low latency. We validate this code, implemented in the public mosfit package, by fitting it to GW170817. A Bayes factor analysis overwhelmingly (B > 1010) favours the inclusion of an additional luminosity source in addition to lanthanide-poor dynamical ejecta during the first day. This is well fit by a shock-heated cocoon model, though differences in the ejecta structure, opacity or nuclear heating rate cannot be ruled out as alternatives. The emission thereafter is dominated by a lanthanide-rich viscous wind. We find the mass ratio of the binary is q = 0.92 ± 0.07 (90 per cent credible interval). We place tight constraints on the maximum stable NS mass, MTOV $=2.17^{+0.08}_{-0.11}$ M⊙. For a uniform prior in tidal deformability, the radius of a 1.4-M⊙ NS is R1.4 ∼ 10.7 km. Re-weighting with a prior based on equations of state that support our credible range in MTOV, we derive a final measurement R1.4 $=11.06^{+1.01}_{-0.98}$ km. Applying our code to the second gravitationally detected NS merger, GW190425, we estimate that an associated kilonova would have been fainter (by ∼0.7 mag at 1 d post-merger) and declined faster than GW170817, underlining the importance of tuning follow-up strategies individually for each GW-detected NS merger.
We study the spectroscopic evolution of superluminous supernovae (SLSNe) later than 100 days after maximum light. We present new data for Gaia16apd and SN 2017egm and analyze 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 SNe Ic by a prominent O i λ7774 line and higher ionization states of oxygen. The iron-dominated region around 5000 is more similar to broad-lined SNe Ic than to normal SNe Ic. Principal component analysis shows that five "eigenspectra" capture 70% of the variance, while a clustering analysis shows no clear evidence for multiple SLSN subclasses. Line velocities are 5000-8000 km s−1 and show stratification of the ejecta. O i λ7774 likely arises in a dense inner region that also produces calcium emission, while O i λ6300 comes from farther out until 300-400 days. The luminosities of O i λ7774 and Ca ii suggest significant clumping, in agreement with previous studies. Ratios of Ca ii λ7300/O i λ6300 favor progenitors with relatively massive helium cores, likely 6 , though more modeling is required here. SLSNe with broad light curves show the strongest O i λ6300, suggesting larger ejecta masses. We show how the inferred velocity, density, and ionization structure point to a central power source.
The energy liberated by fallback accretion has been suggested as a possible engine to power hydrogen-poor superluminous supernovae (SLSNe). We systematically investigate this model using the Bayesian ...light curve (LC) fitting code MOSFiT (Modular Open Source Fitter for Transients), fitting the LCs of 37 hydrogen-poor SLSNe assuming a fallback accretion central engine. We find that this model can yield good fits to their LCs, with a fit quality that rivals the popular magnetar engine models. Examining our derived parameters for the fallback model, we estimate the total energy requirements from the accretion disk to be 0.002-0.7 c2. If we adopt a typical conversion efficiency ∼10−3, the required mass to accrete is thus 2-700 . Many SLSNe, therefore, require an unrealistic accretion mass, and so only a fraction of these events could be powered by fallback accretion unless the true efficiency is much greater than our fiducial value. The SLSNe that require the smallest amounts of fallback mass are still fallback accretion-powered supernova candidates, but they are difficult to distinguish solely by their LC properties.
Despite indications that superluminous supernovae (SLSNe) originate from massive progenitors, the lack of a uniformly analyzed statistical sample has so far prevented a detailed view of the ...progenitor mass distribution. Here we present and analyze the pre-explosion mass distribution of hydrogen-poor SLSN progenitors as determined from uniformly modeled light curves of 62 events. We construct the distribution by summing the ejecta mass posteriors of each event, using magnetar light-curve models presented in our previous works (and using a nominal neutron star remnant mass). The resulting distribution spans 3.6-40 M , with a sharp decline at lower masses, and is best fit by a broken power law described by at 3.6-8.6 M and at 8.6-40 M . We find that observational selection effects cannot account for the shape of the distribution. Relative to Type Ib/c SNe, the SLSN mass distribution extends to much larger masses and has a different power-law shape, likely indicating that the formation of a magnetar allows more massive stars to explode as some of the rotational energy accelerates the ejecta. Comparing the SLSN distribution with predictions from single and binary star evolution models, we find that binary models for a metallicity of Z 1/3 Z are best able to reproduce its broad shape, in agreement with the preference of SLSNe for low metallicity environments. Finally, we uncover a correlation between the pre-explosion mass and the magnetar initial spin period, where SLSNe with low masses have slower spins, a trend broadly consistent with the effects of angular momentum transport evident in models of rapidly rotating carbon-oxygen stars.
MOSFiT: Modular Open Source Fitter for Transients Guillochon, James; Nicholl, Matt; Villar, V. Ashley ...
The Astrophysical journal. Supplement series,
05/2018, Letnik:
236, Številka:
1
Journal Article
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Much of the progress made in time-domain astronomy is accomplished by relating observational multiwavelength time-series data to models derived from our understanding of physical laws. This goal is ...typically accomplished by dividing the task in two: collecting data (observing), and constructing models to represent that data (theorizing). Owing to the natural tendency for specialization, a disconnect can develop between the best available theories and the best available data, potentially delaying advances in our understanding new classes of transients. We introduce MOSFiT: the Modular Open Source Fitter for Transients, a Python-based package that downloads transient data sets from open online catalogs (e.g., the Open Supernova Catalog), generates Monte Carlo ensembles of semi-analytical light-curve fits to those data sets and their associated Bayesian parameter posteriors, and optionally delivers the fitting results back to those same catalogs to make them available to the rest of the community. MOSFiT is designed to help bridge the gap between observations and theory in time-domain astronomy; in addition to making the application of existing models and creation of new models as simple as possible, MOSFiT yields statistically robust predictions for transient characteristics, with a standard output format that includes all the setup information necessary to reproduce a given result. As large-scale surveys such as that conducted with the Large Synoptic Survey Telescope (LSST), discover entirely new classes of transients, tools such as MOSFiT will be critical for enabling rapid comparison of models against data in statistically consistent, reproducible, and scientifically beneficial ways.
Abstract
Tidal disruption events (TDEs), in which a star is destroyed by the gravitational field of a supermassive black hole (SMBH), are being observed at a high rate owing to the advanced state of ...survey science. One of the properties of TDEs that is measured with increasing statistical reliability is the TDE luminosity function,
d
N
̇
TDE
/
dL
, which is the TDE rate per luminosity (i.e., how many TDEs are within a given luminosity range). Here we show that if the luminous emission from a TDE is directly coupled to the rate of return of tidally destroyed debris to the SMBH, then the TDE luminosity function is in good agreement with observations and scales as ∝
L
−2.5
for high luminosities, provided that the SMBH mass function
dN
•
/
dM
•
—the number of SMBHs (
N
•
) per SMBH mass (
M
•
)—is approximately flat in the mass range over which we observe TDEs. We also show that there is a cutoff in the luminosity function at low luminosities that is a result of direct captures, and this cutoff has been tentatively observed. If
dN
•
/
dM
•
is flat, which is in agreement with some observational campaigns, these results suggest that the fallback rate feeds the accretion rate in TDEs. Contrarily, if
dN
•
/
d
log
M
•
is flat, which has been found theoretically and is suggested by other observational investigations, then the emission from TDEs is likely powered by another mechanism. Future observations and more TDE statistics, provided by the Rubin Observatory/LSST, will provide additional evidence as to the reality of this tension.
We perform one-dimensional radiation-hydrodynamic simulations of energetic supernova (SN) ejecta colliding with a massive circumstellar medium (CSM) aimed at explaining SN 2016aps, likely the ...brightest SN observed to date. SN 2016aps was a superluminous Type IIn SN, which released as much as erg of thermal radiation. Our results suggest that the multiband light curve of SN 2016aps is well explained by the collision of a SN ejecta with the explosion energy of 1052 erg and a wind-like CSM with the outer radius of 1016 cm, that is, a hypernova explosion embedded in a massive CSM. This finding indicates that very massive stars with initial masses larger than , which supposedly produce highly energetic SNe, occasionally eject their hydrogen-rich envelopes shortly before the core collapse. We suggest that the pulsational pair-instability SNe may provide a natural explanation for the massive CSM and the energetic explosion. We also provide the relations among the peak luminosity, the radiated energy and the rise time for interacting SNe with the kinetic energy of 1052 erg, which can be used for interpreting SN 2016aps-like objects in future surveys.
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