Following the creation of the viceroyalty of Río de la Plata in 1776, the elites of Buenos Aires, Córdoba, and Montevideo turned time and again to the Spanish crown for intercession, mediation, and ...support to maintain their privileged position during the tumultuous years before the May Revolution of 1810. Their loyalty was in part a result of the social status, political opportunities, and economic benefits that produced their privileged style of life. But of greater importance were the various internal and external factors that threatened their privileges, including inter-group rivalries, the presence of subversive ideas linked to the French Revolution, growing numbers of black slaves who engaged in various forms of resistance, indigenous groups who blocked the exploitation of the viceroyalty’s resources, Portuguese interlopers, and British imperial ambitions that culminated with the invasions of the viceroyalty in 1806 and 1807. To retain their privileges and their tenuous hold over the region, the viceroyalty’s urban elites looked to Spain for help, ensuring their continuing loyalty to the Spanish crown in increasingly troubling times.
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.
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.
Some reports of supernova (SN) discoveries turn out not to be true core-collapse explosions. One such case was SN 2009ip, which was recognized to be the eruption of a luminous blue variable (LBV) ...star. This source had a massive (50-80 M), hot progenitor star identified in pre-explosion data; it had documented evidence of pre-outburst variability and it was subsequently discovered to have a second outburst in 2010. In 2012, the source entered its third known outburst. Initial spectra showed the same narrow-line profiles as before, suggesting another LBV-like eruption. We present new photometry and spectroscopy of SN 2009ip, indicating that the 2012 outburst transitioned into a genuine SN explosion. The most striking aspect of these data is that unlike any previous episodes, the spectrum developed Balmer lines with very broad P-Cygni profiles characteristic of normal Type II supernovae (SNe II), in addition to overlying narrow emission components. The emission lines exhibit unprecedented (for any known non-terminal LBV-like eruption) full width at half-maximum intensity values of ∼8000 km s−1, while the absorption components seen just before the main brightening had blue wings extending out to −13 000 km s−1. These velocities are typical of core-collapse SN explosions, but have never been associated with emission lines from a non-terminal LBV-like eruption. SN 2009ip is the first object to have both a known massive blue progenitor star and LBV-like eruptions with accompanying spectra observed a few years prior to becoming a SN. Immediately after the broad lines first appeared, the peak absolute magnitude of M
V
−14.5 was fainter than that of normal SNe II. However, after a brief period of fading, the source quickly brightened again to M
R
= −17.5 mag in ∼2 d, suggesting a causal link to the prior emergence of the broad-line spectrum. Once the bright phase began, the broad lines mostly disappeared, and the spectrum resembled the early optically thick phases of luminous SNe IIn. The source reached a peak brightness of −18 mag about 2 weeks later, after which broad emission lines again developed in the spectrum as the source faded. We conclude that the most recent 2012 outburst of SN 2009ip was the result of a true core-collapse SN IIn that occurred when the progenitor star was in an LBV-like outburst phase, and where the SN was initially faint and then rapidly brightened due to interaction with circumstellar material. The pulsational pair instability, LBV-like eruptions or other instabilities due to late nuclear burning phases in massive stars may have caused the multiple pre-SN eruptions.
At redshift z = 0.03, the recently discovered SN 2017egm is the nearest Type I superluminous supernova (SLSN) to date and first near the center of a massive spiral galaxy (NGC 3191). Using SDSS ...spectra of NGC 3191, we find a metallicity ∼2 at the nucleus and ∼1.3 for a star-forming region at a radial offset similar to SN 2017egm. Archival radio-to-UV photometry reveals a star formation rate of ∼15 yr−1 (with ∼70% dust obscured), which can account for a Swift X-ray detection and a stellar mass of . We model the early UV-optical light curves with a magnetar central-engine model, using the Bayesian light curve fitting tool MOSFiT. The fits indicate an ejecta mass of 2-4 , a spin period of 4-6 ms, a magnetic field of G, and a kinetic energy of erg. These parameters are consistent with the overall distributions for SLSNe, modeled by Nicholl et al., although the derived mass and spin are toward the low end, possibly indicating an enhanced loss of mass and angular momentum before explosion. This has two implications: (i) SLSNe can occur at solar metallicity, although with a low fraction of ∼10%, and (ii) metallicity has at most a modest effect on their properties. Both conclusions are in line with results for long gamma-ray bursts. Assuming a monotonic rise gives an explosion date of MJD 57889 1. However, a short-lived excess in the data relative to the best-fitting models may indicate an early-time "bump." If confirmed, SN 2017egm would be the first SLSN with a spectrum during the bump phase; this shows the same O ii lines seen at maximum light, which may be an important clue for explaining these bumps.
Abstract
Stripped-envelope core-collapse supernovae can be divided into two broad classes: the common Type Ib/c supernovae (SNe Ib/c), powered by the radioactive decay of
56
Ni, and the rare ...superluminous supernovae (SLSNe), most likely powered by the spin-down of a magnetar central engine. Up to now, the intermediate regime between these two populations has remained mostly unexplored. Here, we present a comprehensive study of 40
luminous supernovae
(LSNe), SNe with peak magnitudes of
M
r
= −19 to −20 mag, bound by SLSNe on the bright end and by SNe Ib/c on the dim end. Spectroscopically, LSNe appear to form a continuum between Type Ic SNe and SLSNe. Given their intermediate nature, we model the light curves of all LSNe using a combined magnetar plus radioactive decay model and find that they are indeed intermediate, not only in terms of their peak luminosity and spectra, but also in their rise times, power sources, and physical parameters. We subclassify LSNe into distinct groups that are either as fast evolving as SNe Ib/c or as slow evolving as SLSNe, and appear to be either radioactively or magnetar powered, respectively. Our findings indicate that LSNe are powered by either an overabundant production of
56
Ni or by weak magnetar engines, and may serve as the missing link between the two populations.
Abstract
We present optical photometry and spectroscopy of SN 2019stc (=ZTF19acbonaa), an unusual Type Ic supernova (SN Ic) at a redshift of
z
= 0.117. SN 2019stc exhibits a broad double-peaked light ...curve, with the first peak having an absolute magnitude of
M
r
= −20.0 mag, and the second peak, about 80 rest-frame days later,
M
r
= −19.2 mag. The total radiated energy is large,
E
rad
≈ 2.5 × 10
50
erg. Despite its large luminosity, approaching those of Type I superluminous supernovae (SLSNe), SN 2019stc exhibits a typical SN Ic spectrum, bridging the gap between SLSNe and SNe Ic. The spectra indicate the presence of Fe-peak elements, but modeling of the first light-curve peak with radioactive heating alone leads to an unusually high nickel mass fraction of
f
Ni
≈ 0.31 (
M
Ni
≈ 3.2
M
⊙
). Instead, if we model the first peak with a combined magnetar spin-down and radioactive heating model we find a better match with
M
ej
≈ 4
M
⊙
, a magnetar spin period of
P
spin
≈ 7.2 ms, and magnetic field of
B
≈ 10
14
G, and
f
Ni
≲ 0.2 (consistent with SNe Ic). The prominent second peak cannot be naturally accommodated with radioactive heating or magnetar spin-down, but instead can be explained as circumstellar interaction with ≈0.7
M
⊙
of hydrogen-free material located ≈400 au from the progenitor. Accounting for the ejecta mass, circumstellar shell mass, and remnant neutron star mass, we infer a CO core mass prior to explosion of ≈6.5
M
⊙
. The host galaxy has a metallicity of ≈0.26
Z
⊙
, low for SNe Ic but consistent with SLSNe. Overall, we find that SN 2019stc is a transition object between normal SNe Ic and SLSNe.
Abstract
We present an extensive Hubble Space Telescope rest-frame UV imaging study of the locations of Type I superluminous supernovae (SLSNe) within their host galaxies. The sample includes 65 ...SLSNe with detected host galaxies in the redshift range
z
≈ 0.05–2. Using precise astrometric matching with SN images, we determine the distributions of the physical and host-normalized offsets relative to the host centers, as well as the fractional flux distribution relative to the underlying UV light distributions. We find that the host-normalized offsets of SLSNe roughly track an exponential disk profile, but exhibit an overabundance of sources with large offsets of 1.5–4 times their hosts' half-light radii. The SLSNe normalized offsets are systematically larger than those of long gamma-ray bursts (LGRBs), and even Type Ib/c and Type II SNe. Furthermore, we find from a Monte Carlo procedure that about
37
−
8
+
6
%
of SLSNe occur in the dimmest regions of their host galaxies, with a median fractional flux value of 0.16, in stark contrast to LGRBs and Type Ib/c and Type II SNe. We do not detect any significant trends in the locations of SLSNe as a function of redshift, or as a function of explosion and magnetar engine parameters inferred from modeling of their optical light curves. The significant difference in SLSN locations compared to LGRBs (and normal core-collapse SNe) suggests that at least some of their progenitors follow a different evolutionary path. We speculate that SLSNe arise from massive runaway stars from disrupted binary systems, with velocities of ∼10
2
km s
−1
.
The zirconates Ln2Zr2O7 (Ln = lanthanoid) have been studied using a combination of Zr L-edge X-ray absorption near edge structure (XANES) and synchrotron X-ray and neutron powder diffraction methods. ...These studies demonstrate that as the size of the lanthanoid cation decreases, the local structure evolves smoothly from the ideal pyrochlore toward the defect fluorite rather than undergoing an abrupt transformation. The Zr L-edge spectrum is found to be extremely sensitive to changes in the local coordination environment and demonstrates an increase in local disorder across the pyrochlore oxides. The sensitivity of the XANES measurements enables us to identify the progressive nature of the transition that could not be detected using bulk diffraction techniques.
Gamma-ray bursts (GRBs) are divided into two populations
; long GRBs that derive from the core collapse of massive stars (for example, ref.
) and short GRBs that form in the merger of two compact ...objects
. Although it is common to divide the two populations at a gamma-ray duration of 2 s, classification based on duration does not always map to the progenitor. Notably, GRBs with short (≲2 s) spikes of prompt gamma-ray emission followed by prolonged, spectrally softer extended emission (EE-SGRBs) have been suggested to arise from compact object mergers
. Compact object mergers are of great astrophysical importance as the only confirmed site of rapid neutron capture (r-process) nucleosynthesis, observed in the form of so-called kilonovae
. Here we report the discovery of a possible kilonova associated with the nearby (350 Mpc), minute-duration GRB 211211A. The kilonova implies that the progenitor is a compact object merger, suggesting that GRBs with long, complex light curves can be spawned from merger events. The kilonova of GRB 211211A has a similar luminosity, duration and colour to that which accompanied the gravitational wave (GW)-detected binary neutron star (BNS) merger GW170817 (ref.
). Further searches for GW signals coincident with long GRBs are a promising route for future multi-messenger astronomy.
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