409 research outputs found
The superluminous supernova SN 2017egm in the nearby galaxy NGC 3191: a metal-rich environment can support a typical SLSN evolution
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 Z at the nucleus and ~1.3 Z for a star forming region at a
radial offset similar to SN 2017egm. Archival radio-to-UV photometry reveals a
star-formation rate ~15 M yr (with ~70% dust-obscured), which
can account for a Swift X-ray detection, and stellar mass ~
M. 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 ejecta mass 2-4 M, spin period 4-6 ms, magnetic field
(0.7-1.7)G, and kinetic energy 1-2 erg. These
parameters are consistent with the overall distributions for SLSNe, modeled by
Nicholl et al (2017), although the derived mass and spin are towards the low
end, possibly indicating 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 ~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 MJD
. 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.Comment: Accepted for publication in ApJ
Searching for Cooling Signatures in Strong Lensing Galaxy Clusters: Evidence Against Baryons Shaping the Matter Distribution in Cluster Cores
The process by which the mass density profile of certain galaxy clusters
becomes centrally concentrated enough to produce high strong lensing (SL)
cross-sections is not well understood. It has been suggested that the baryonic
condensation of the intra-cluster medium (ICM) due to cooling may drag dark
matter to the cores and thus steepen the profile. In this work, we search for
evidence of ongoing ICM cooling in the first large, well-defined sample of
strong lensing selected galaxy clusters in the range 0.1 < z < 0.6. Based on
known correlations between the ICM cooling rate and both optical emission line
luminosity and star formation, we measure, for a sample of 89 strong lensing
clusters, the fraction of clusters that have [OII]3727 emission in their
brightest cluster galaxy (BCG). We find that the fraction of line-emitting BCGs
is constant as a function of redshift for z > 0.2 and shows no statistically
significant deviation from the total cluster population. Specific star
formation rates, as traced by the strength of the 4000 angstrom break, D_4000,
are also consistent with the general cluster population. Finally, we use
optical imaging of the SL clusters to measure the angular separation, R_arc,
between the arc and the center of mass of each lensing cluster in our sample
and test for evidence of changing [OII] emission and D_4000 as a function of
R_arc, a proxy observable for SL cross-sections. D_4000 is constant with all
values of R_arc, and the [OII] emission fractions show no dependence on R_arc
for R_arc > 10" and only very marginal evidence of increased weak [OII]
emission for systems with R_arc < 10". These results argue against the ability
of baryonic cooling associated with cool core activity in the cores of galaxy
clusters to strongly modify the underlying dark matter potential, leading to an
increase in strong lensing cross-sections.Comment: 9 Pages, 5 Figures, 1 Tabl
An Extensive Study of the Offset and Host Light Distributions of Type I Superluminous Supernovae
We present an extensive ()
rest-frame ultraviolet (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 . Using precise astrometric matching with SN images, we determine the
distributions of physical and host-normalized offsets relative to the host
centers, as well as the fractional flux distribution relative to the underlying
UV light distribution. 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 times their host half-light radius. The
SLSNe normalized offsets are systematically larger than those of long gamma-ray
bursts (LGRBs), and even Type Ib/c and II SNe. Furthermore, we find that about
40\% of all SLSNe occur in the dimmest regions of their host galaxies
(fractional flux of 0), in stark contrast to LGRBs and Type Ib/c and 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 lights 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 km s.Comment: 31 pages, 14 figures, 5 tables. Submitted to ApJ. Comments welcome
The Intermediate Luminosity Optical Transient SN 2010da: The Progenitor, Eruption and Aftermath of a Peculiar Supergiant High-mass X-ray Binary
We present optical spectroscopy, ultraviolet to infrared imaging and X-ray
observations of the intermediate luminosity optical transient (ILOT) SN 2010da
in NGC 300 (d=1.86 Mpc) spanning from -6 to +6 years relative to the time of
outburst in 2010. Based on the light curve and multi-epoch SEDs of SN 2010da,
we conclude that the progenitor of SN 2010da is a ~10-12 Msol yellow supergiant
possibly transitioning into a blue loop phase. During outburst, SN 2010da had a
peak absolute magnitude of M<-10.4 mag, dimmer than other ILOTs and supernova
impostors. We detect multi-component hydrogen Balmer, Paschen, and Ca II
emission lines in our high-resolution spectra, which indicate a dusty and
complex circumstellar environment. Since the 2010 eruption, the star has
brightened by a factor of ~5 and remains highly variable in the optical.
Furthermore, we detect SN 2010da in archival Swift and Chandra observations as
an ultraluminous X-ray source (L~6x10^{39} erg/s). We additionally attribute He
II 4686 Angstrom and coronal Fe emission lines in addition to a steady X-ray
luminosity of ~10^{37} erg/s to the presence of a compact companion.Comment: published; updated citations and other minor edit
The Pre-Explosion Mass Distribution of Hydrogen-Poor Superluminous Supernova Progenitors and New Evidence for a Mass-Spin Correlation
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 modelled 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
M, with a sharp decline at lower masses, and is best fit by a broken
power law described by at
M and at 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 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.Comment: 18 pages, 11 figures, Submitted to Ap
Luminous Supernovae: Unveiling a Population Between Superluminous and Normal Core-collapse Supernovae
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 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 \textit{luminous
supernovae} (LSNe), SNe with peak magnitudes of to 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 sub-classify
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
over-abundant production of Ni or by weak magnetar engines, and may
serve as the missing link between the two populations.Comment: 39 pages, 16 figures, submitted to Ap
Nebular-phase spectra of superluminous supernovae: physical insights from observational and statistical properties
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 -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 7774 line and higher-ionisation
states of oxygen. The iron-dominated region around 5000 \AA\ is more similar to
broad-lined SNe Ic than to normal SNe Ic. Principal Component Analysis shows
that 5 `eigenspectra' capture 75% of the variance, while a clustering analysis
shows no clear evidence for multiple SLSN sub-classes. Line velocities are
5000--8000 km/s, and show stratification of the ejecta. O I 7774
likely arises in a dense inner region that also produces calcium emission,
while [O I] 6300 comes from further out until 300--400 days. The
luminosities of O I 7774 and Ca II suggest significant clumping, in
agreement with previous studies. Ratios of [Ca II]7300/[O
I]6300 favour progenitors with relatively massive helium cores, likely
M, though more modelling is required here. SLSNe with broad
light curves show the strongest [O I] 6300, suggesting larger ejecta
masses. We show how the inferred velocity, density and ionisation structure
point to a central power source.Comment: Accepted in ApJ, updated to match accepted versio
SN 2016iet: The Pulsational or Pair Instability Explosion of a Low Metallicity Massive CO Core Embedded in a Dense Hydrogen-Poor Circumstellar Medium
We present optical photometry and spectroscopy of SN 2016iet, an
unprecedented Type I supernova (SN) at with no obvious analog in the
existing literature. The peculiar light curve has two roughly equal brightness
peaks ( mag) separated by 100 days, and a subsequent slow decline
by 5 mag in 650 rest-frame days. The spectra are dominated by emission lines of
calcium and oxygen, with a width of only km s, superposed on a
strong blue continuum in the first year, and with a large ratio of at late times. There is no clear evidence
for hydrogen or helium associated with the SN at any phase. We model the light
curves with several potential energy sources: radioactive decay, central
engine, and circumstellar medium (CSM) interaction. Regardless of the model,
the inferred progenitor mass near the end of its life (i.e., CO core mass) is
M and up to M, placing the event in the
regime of pulsational pair instability supernovae (PPISNe) or pair instability
supernovae (PISNe). The models of CSM interaction provide the most consistent
explanation for the light curves and spectra, and require a CSM mass of
M ejected in the final decade before explosion. We further
find that SN 2016iet is located at an unusually large offset ( kpc) from
its low metallicity dwarf host galaxy ( Z, M), supporting the PPISN/PISN interpretation. In the final
spectrum, we detect narrow H emission at the SN location, likely due to
a dim underlying galaxy host or an H II region. Despite the overall consistency
of the SN and its unusual environment with PPISNe and PISNe, we find that the
inferred properties of SN\,2016iet challenge existing models of such events.Comment: 26 Pages, 17 Figures, Submitted to Ap
Can the UNAIDS modes of transmission model be improved? A comparison of the original and revised model projections using data from a setting in west Africa.
OBJECTIVE: The UNAIDS modes of transmission model (MoT) is a user-friendly model, developed to predict the distribution of new HIV infections among different subgroups. The model has been used in 29 countries to guide interventions. However, there is the risk that the simplifications inherent in the MoT produce misleading findings. Using input data from Nigeria, we compare projections from the MoT with those from a revised model that incorporates additional heterogeneity. METHODS: We revised the MoT to explicitly incorporate brothel and street-based sex-work, transactional sex, and HIV-discordant couples. Both models were parameterized using behavioural and epidemiological data from Cross River State, Nigeria. Model projections were compared, and the robustness of the revised model projections to different model assumptions, was investigated. RESULTS: The original MoT predicts 21% of new infections occur in most-at-risk-populations (MARPs), compared with 45% (40-75%, 95% Crl) once additional heterogeneity and updated parameterization is incorporated. Discordant couples, a subgroup previously not explicitly modelled, are predicted to contribute a third of new HIV infections. In addition, the new findings suggest that women engaging in transactional sex may be an important but previously less recognized risk group, with 16% of infections occurring in this subgroup. CONCLUSION: The MoT is an accessible model that can inform intervention priorities. However, the current model may be potentially misleading, with our comparisons in Nigeria suggesting that the model lacks resolution, making it challenging for the user to correctly interpret the nature of the epidemic. Our findings highlight the need for a formal review of the MoT
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