792 research outputs found
Interaction Between The Broad-lined Type Ic Supernova 2012ap and Carriers of Diffuse Interstellar Bands
The diffuse interstellar bands (DIBs) are absorption features observed in
optical and near-infrared spectra that are thought to be associated with
carbon-rich polyatomic molecules in interstellar gas. However, because the
central wavelengths of these bands do not correspond with electronic
transitions of any known atomic or molecular species, their nature has remained
uncertain since their discovery almost a century ago. Here we report on
unusually strong DIBs in optical spectra of the broad-lined Type Ic supernova
SN 2012ap that exhibit changes in equivalent width over short (~30 days)
timescales. The 4428 and 6283 Angstrom DIB features get weaker with time,
whereas the 5780 Angstrom feature shows a marginal increase. These nonuniform
changes suggest that the supernova is interacting with a nearby source of the
DIBs and that the DIB carriers possess high ionization potentials, such as
small cations or charged fullerenes. We conclude that moderate-resolution
spectra of supernovae with DIB absorptions obtained within weeks of outburst
could reveal unique information about the mass-loss environment of their
progenitor systems and provide new constraints on the properties of DIB
carriers.Comment: 6 pages, 3 figures, accepted for publication in ApJ
Zooming In on the Progenitors of Superluminous Supernovae With the HST
We present Hubble Space Telescope (HST) rest-frame ultraviolet imaging of the
host galaxies of 16 hydrogen-poor superluminous supernovae (SLSNe), including
11 events from the Pan-STARRS Medium Deep Survey. Taking advantage of the
superb angular resolution of HST, we characterize the galaxies' morphological
properties, sizes and star formation rate (SFR) densities. We determine the
supernova (SN) locations within the host galaxies through precise astrometric
matching, and measure physical and host-normalized offsets, as well as the SN
positions within the cumulative distribution of UV light pixel brightness. We
find that the host galaxies of H-poor SLSNe are irregular, compact dwarf
galaxies, with a median half-light radius of just 0.9 kpc. The UV-derived SFR
densities are high ( ~ 0.1 M_sun/yr/kpc^2), suggesting that SLSNe
form in overdense environments. Their locations trace the UV light of their
host galaxies, with a distribution intermediate between that of long-duration
gamma-ray bursts (LGRBs) (which are strongly clustered on the brightest regions
of their hosts) and a uniform distribution (characteristic of normal
core-collapse SNe), though cannot be statistically distinguished from either
with the current sample size. Taken together, this strengthens the picture that
SLSN progenitors require different conditions than those of ordinary
core-collapse SNe to form, and that they explode in broadly similar galaxies as
do LGRBs. If the tendency for SLSNe to be less clustered on the brightest
regions than are LGRBs is confirmed by a larger sample, this would indicate a
different, potentially lower-mass progenitor for SLSNe than LRGBs.Comment: ApJ in press; matches published version. Minor changes following
referee's comments; conclusions unchange
Hydrogen-Poor Superluminous Supernovae and Long-Duration Gamma-Ray Bursts Have Similar Host Galaxies
We present optical spectroscopy and optical/near-IR photometry of 31 host
galaxies of hydrogen-poor superluminous supernovae (SLSNe), including 15 events
from the Pan-STARRS1 Medium Deep Survey. Our sample spans the redshift range
0.1 < z < 1.6 and is the first comprehensive host galaxy study of this specific
subclass of cosmic explosions. Combining the multi-band photometry and
emission-line measurements, we determine the luminosities, stellar masses, star
formation rates and metallicities. We find that as a whole, the hosts of SLSNe
are a low-luminosity ( ~ -17.3 mag), low stellar mass ( ~ 2 x 10^8
M_sun) population, with a high median specific star formation rate ( ~ 2
Gyr^-1). The median metallicity of our spectroscopic sample is low, 12 +
log(O/H}) ~ 8.35 ~ 0.45 Z_sun, although at least one host galaxy has solar
metallicity. The host galaxies of H-poor SLSNe are statistically distinct from
the hosts of GOODS core-collapse SNe (which cover a similar redshift range),
but resemble the host galaxies of long-duration gamma-ray bursts (LGRBs) in
terms of stellar mass, SFR, sSFR and metallicity. This result indicates that
the environmental causes leading to massive stars forming either SLSNe or LGRBs
are similar, and in particular that SLSNe are more effectively formed in low
metallicity environments. We speculate that the key ingredient is large core
angular momentum, leading to a rapidly-spinning magnetar in SLSNe and an
accreting black hole in LGRBs.Comment: ApJ in press; updated to match accepted version. Some additional data
added, discussion of selection effects expanded; conclusions unchanged. 22
pages in emulateapj forma
Ultra-Luminous Supernovae as a New Probe of the Interstellar Medium in Distant Galaxies
We present the Pan-STARRS1 discovery and light curves, and follow-up MMT and
Gemini spectroscopy of an ultra-luminous supernova (ULSN; dubbed PS1-11bam) at
a redshift of z=1.566 with a peak brightness of M_UV=-22.3 mag. PS1-11bam is
one of the highest redshift spectroscopically-confirmed SNe known to date. The
spectrum is characterized by broad absorption features typical of previous
ULSNe (e.g., CII, SiIII), and by strong and narrow MgII and FeII absorption
lines from the interstellar medium (ISM) of the host galaxy, confirmed by an
[OII]3727 emission line at the same redshift. The equivalent widths of the
FeII2600 and MgII2803 lines are in the top quartile of the quasar intervening
absorption system distribution, but are weaker than those of gamma-ray burst
intrinsic absorbers (i.e., GRB host galaxies). We also detect the host galaxy
in pre-explosion Pan-STARRS1 data and find that its UV spectral energy
distribution is best fit with a young stellar population age of tau~15-45 Myr
and a stellar mass of M \sim (1.1-2.6)x10^9 M_sun (for Z=0.05-1 Z_sun). The
star formation rate inferred from the UV continuum and [OII]3727 emission line
is ~10 M_sun/yr, higher than in any previous ULSN host. PS1-11bam provides the
first direct demonstration that ULSNe can serve as probes of the interstellar
medium in distant galaxies. At the present, the depth and red sensitivity of
PS1 are uniquely suited to finding such events at cosmologically interesting
redshifts (z~1-2); the future combination of LSST and 30-m class telescopes
promises to extend this technique to z~4.Comment: Submitted to ApJL; 9 pages; 4 figures; 1 tabl
PS1-10afx at z=1.388: Pan-STARRS1 Discovery of a New Type of Superluminous Supernova
We present the Pan-STARRS1 discovery of PS1-10afx, a unique
hydrogen-deficient superluminous supernova (SLSN) at z=1.388. The light curve
peaked at z_P1=21.7 mag, making PS1-10afx comparable to the most luminous known
SNe, with M_u = -22.3 mag. Our extensive optical and NIR observations indicate
that the bolometric light curve of PS1-10afx rose on the unusually fast
timescale of ~12 d to the extraordinary peak luminosity of 4.1e44 erg/s (M_bol
= -22.8 mag) and subsequently faded rapidly. Equally important, the SED is
unusually red for a SLSN, with a color temperature of 6800 K near maximum
light, in contrast to previous H-poor SLSNe, which are bright in the UV. The
spectra more closely resemble those of a normal SN Ic than any known SLSN, with
a photospheric velocity of 11,000 km/s and evidence for line blanketing in the
rest-frame UV. Despite the fast rise, these parameters imply a very large
emitting radius (>5e15 cm). We demonstrate that no existing theoretical model
can satisfactorily explain this combination of properties: (i) a nickel-powered
light curve cannot match the combination of high peak luminosity with the fast
timescale; (ii) models powered by the spindown energy of a rapidly-rotating
magnetar predict significantly hotter and faster ejecta; and (iii) models
invoking shock breakout through a dense circumstellar medium cannot explain the
observed spectra or color evolution. The host galaxy is well detected in
pre-explosion imaging with a luminosity near L*, a star formation rate of 15
M_sun/yr, and is fairly massive (2e10 M_sun), with a stellar population age of
1e8 yr, also in contrast to the dwarf hosts of known H-poor SLSNe. PS1-10afx is
distinct from known examples of SLSNe in its spectra, colors, light-curve
shape, and host galaxy properties, suggesting that it resulted from a different
channel than other hydrogen-poor SLSNe.Comment: 17 pages, 12 figures, accepted to ApJ, minor revisions, including
expanded discussion of lensing hypothesi
Cosmological Constraints from Measurements of Type Ia Supernovae discovered during the first 1.5 years of the Pan-STARRS1 Survey
We present griz light curves of 146 spectroscopically confirmed Type Ia
Supernovae () discovered during the first 1.5 years of the
Pan-STARRS1 Medium Deep Survey. The Pan-STARRS1 natural photometric system is
determined by a combination of on-site measurements of the instrument response
function and observations of spectrophotometric standard stars. We find that
the systematic uncertainties in the photometric system are currently 1.2\%
without accounting for the uncertainty in the HST Calspec definition of the AB
system. A Hubble diagram is constructed with a subset of 113 out of 146 SNe Ia
that pass our light curve quality cuts. The cosmological fit to 310 SNe Ia (113
PS1 SNe Ia + 222 light curves from 197 low-z SNe Ia), using only SNe and
assuming a constant dark energy equation of state and flatness, yields
.
When combined with BAO+CMB(Planck)+, the analysis yields and including all
identified systematics (see also Scolnic et al. 2014). The value of is
inconsistent with the cosmological constant value of at the 2.3
level. Tension endures after removing either the BAO or the constraint,
though it is strongest when including the constraint. If we include WMAP9
CMB constraints instead of those from Planck, we find
, which diminishes the discord to . We
cannot conclude whether the tension with flat CDM is a feature of dark
energy, new physics, or a combination of chance and systematic errors. The full
Pan-STARRS1 supernova sample with 3 times as many SNe should provide
more conclusive results.Comment: 38 pages, 16 figures, 14 tables, ApJ in pres
Systematic Uncertainties Associated with the Cosmological Analysis of the First Pan-STARRS1 Type Ia Supernova Sample
We probe the systematic uncertainties from 113 Type Ia supernovae (SNIa) in
the Pan-STARRS1 (PS1) sample along with 197 SN Ia from a combination of
low-redshift surveys. The companion paper by Rest et al. (2013) describes the
photometric measurements and cosmological inferences from the PS1 sample. The
largest systematic uncertainty stems from the photometric calibration of the
PS1 and low-z samples. We increase the sample of observed Calspec standards
from 7 to 10 used to define the PS1 calibration system. The PS1 and SDSS-II
calibration systems are compared and discrepancies up to ~0.02 mag are
recovered. We find uncertainties in the proper way to treat intrinsic colors
and reddening produce differences in the recovered value of w up to 3%. We
estimate masses of host galaxies of PS1 supernovae and detect an insignificant
difference in distance residuals of the full sample of 0.037\pm0.031 mag for
host galaxies with high and low masses. Assuming flatness in our analysis of
only SNe measurements, we find . With additional constraints from BAO,
CMB(Planck) and H0 measurements, we find and
(statistical and systematic errors added in
quadrature). Significance of the inconsistency with depends on whether
we use Planck or WMAP measurements of the CMB:
.Comment: 24 pages, 20 figures. Accepted by Ap
Telomeric expression sites are highly conserved in trypanosoma brucei
Subtelomeric regions are often under-represented in genome sequences of eukaryotes. One of the best known examples of the use of telomere proximity for adaptive purposes are the bloodstream expression sites (BESs) of the African trypanosome Trypanosoma brucei. To enhance our understanding of BES structure and function in host adaptation and immune evasion, the BES repertoire from the Lister 427 strain of T. brucei were independently tagged and sequenced. BESs are polymorphic in size and structure but reveal a surprisingly conserved architecture in the context of extensive recombination. Very small BESs do exist and many functioning BESs do not contain the full complement of expression site associated genes (ESAGs). The consequences of duplicated or missing ESAGs, including ESAG9, a newly named ESAG12, and additional variant surface glycoprotein genes (VSGs) were evaluated by functional assays after BESs were tagged with a drug-resistance gene. Phylogenetic analysis of constituent ESAG families suggests that BESs are sequence mosaics and that extensive recombination has shaped the evolution of the BES repertoire. This work opens important perspectives in understanding the molecular mechanisms of antigenic variation, a widely used strategy for immune evasion in pathogens, and telomere biology
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