169 research outputs found
Type IIn supernovae at z ~ 2 from archival data
Supernovae have been confirmed to redshift z ~ 1.7 for type Ia (thermonuclear
detonation of a white dwarf) and to z ~ 0.7 for type II (collapse of the core
of the star). The subclass type IIn supernovae are luminous core-collapse
explosions of massive stars and, unlike other types, are very bright in the
ultraviolet, which should enable them to be found optically at redshifts z ~ 2
and higher. In addition, the interaction of the ejecta with circumstellar
material creates strong, long-lived emission lines that allow spectroscopic
confirmation of many events of this type at z ~ 2 for 3 - 5 years after
explosion. Here we report three spectroscopically confirmed type IIn
supernovae, at redshifts z = 0.808, 2.013 and 2.357, detected in archival data
using a method designed to exploit these properties at z ~ 2. Type IIn
supernovae directly probe the formation of massive stars at high redshift. The
number found to date is consistent with the expectations of a locally measured
stellar initial mass function, but not with an evolving initial mass function
proposed to explain independent observations at low and high redshift.Comment: 8 pages, 2 figures, includes supplementary informatio
Multi-epoch high-spectral-resolution observations of neutral sodium in 14 Type Ia supernovae
One of the main questions concerning Type Ia supernovae is the nature of the binary companion of the exploding white dwarf. A major discriminant between different suggested models is the presence and physical properties of circumstellar material at the time of explosion. If present, this material will be ionized by the ultraviolet radiation of the explosion and later recombine. This ionization-recombination should manifest itself as time-variable absorption features that can be detected via multi-epoch high-spectral-resolution observations. Previous studies have shown that the strongest effect is seen in the neutral sodium D lines. We report on observations of neutral sodium absorption features observed in multi-epoch high-resolution spectra of 14 Type Ia supernova events. This is the first multi-epoch high-resolution study to include multiple SNe. No variability in line strength that can be associated with circumstellar material is detected in the events presented in this paper. If we include previously published events, we find that ~18 per cent of the events in the extended sample exhibit time-variable sodium features associated with circumstellar material. We explore the implication of this study on our understanding of the progenitor systems of Type Ia supernovae via the current Type Ia supernova multi-epoch high-spectral-resolution sample
Characteristics of transposable element exonization within human and mouse
Insertion of transposed elements within mammalian genes is thought to be an
important contributor to mammalian evolution and speciation. Insertion of
transposed elements into introns can lead to their activation as alternatively
spliced cassette exons, an event called exonization. Elucidation of the
evolutionary constraints that have shaped fixation of transposed elements
within human and mouse protein coding genes and subsequent exonization is
important for understanding of how the exonization process has affected
transcriptome and proteome complexities. Here we show that exonization of
transposed elements is biased towards the beginning of the coding sequence in
both human and mouse genes. Analysis of single nucleotide polymorphisms (SNPs)
revealed that exonization of transposed elements can be population-specific,
implying that exonizations may enhance divergence and lead to speciation. SNP
density analysis revealed differences between Alu and other transposed
elements. Finally, we identified cases of primate-specific Alu elements that
depend on RNA editing for their exonization. These results shed light on TE
fixation and the exonization process within human and mouse genes.Comment: 11 pages, 4 figure
Type II Supernovae as Probes of Cosmology
- Constraining the cosmological parameters and understanding Dark Energy have
tremendous implications for the nature of the Universe and its physical laws.
- The pervasive limit of systematic uncertainties reached by cosmography
based on Cepheids and Type Ia supernovae (SNe Ia) warrants a search for
complementary approaches.
- Type II SNe have been shown to offer such a path. Their distances can be
well constrained by luminosity-based or geometric methods. Competing,
complementary, and concerted efforts are underway, to explore and exploit those
objects that are extremely well matched to next generation facilities.
Spectroscopic follow-up will be enabled by space- based and 20-40 meter class
telescopes.
- Some systematic uncertainties of Type II SNe, such as reddening by dust and
metallicity effects, are bound to be different from those of SNe Ia. Their
stellar progenitors are known, promising better leverage on cosmic evolution.
In addition, their rate - which closely tracks the ongoing star formation rate
- is expected to rise significantly with look- back time, ensuring an adequate
supply of distant examples.
- These data will competitively constrain the dark energy equation of state,
allow the determination of the Hubble constant to 5%, and promote our
understanding of the processes involved in the last dramatic phases of massive
stellar evolution.Comment: Science white paper, submitted to the Decadal committee Astro201
PTF10iya: A short-lived, luminous flare from the nuclear region of a star-forming galaxy
We present the discovery and characterisation of PTF10iya, a short-lived (dt
~ 10 d, with an optical decay rate of ~ 0.3 mag per d), luminous (M_g ~ -21
mag) transient source found by the Palomar Transient Factory. The
ultraviolet/optical spectral energy distribution is reasonably well fit by a
blackbody with T ~ 1-2 x 10^4 K and peak bolometric luminosity L_BB ~ 1-5 x
10^44 erg per s (depending on the details of the extinction correction). A
comparable amount of energy is radiated in the X-ray band that appears to
result from a distinct physical process. The location of PTF10iya is consistent
with the nucleus of a star-forming galaxy (z = 0.22405 +/- 0.00006) to within
350 mas (99.7 per cent confidence radius), or a projected distance of less than
1.2 kpc. At first glance, these properties appear reminiscent of the
characteristic "big blue bump" seen in the near-ultraviolet spectra of many
active galactic nuclei (AGNs). However, emission-line diagnostics of the host
galaxy, along with a historical light curve extending back to 2007, show no
evidence for AGN-like activity. We therefore consider whether the tidal
disruption of a star by an otherwise quiescent supermassive black hole may
account for our observations. Though with limited temporal information,
PTF10iya appears broadly consistent with the predictions for the early
"super-Eddington" phase of a solar-type star disrupted by a ~ 10^7 M_sun black
hole. Regardless of the precise physical origin of the accreting material, the
large luminosity and short duration suggest that otherwise quiescent galaxies
can transition extremely rapidly to radiate near the Eddington limit; many such
outbursts may have been missed by previous surveys lacking sufficient cadence.Comment: 18 pages, 8 figures; revised following referee's comment
GRIPS - Gamma-Ray Imaging, Polarimetry and Spectroscopy
We propose to perform a continuously scanning all-sky survey from 200 keV to
80 MeV achieving a sensitivity which is better by a factor of 40 or more
compared to the previous missions in this energy range. The Gamma-Ray Imaging,
Polarimetry and Spectroscopy (GRIPS) mission addresses fundamental questions in
ESA's Cosmic Vision plan. Among the major themes of the strategic plan, GRIPS
has its focus on the evolving, violent Universe, exploring a unique energy
window. We propose to investigate -ray bursts and blazars, the
mechanisms behind supernova explosions, nucleosynthesis and spallation, the
enigmatic origin of positrons in our Galaxy, and the nature of radiation
processes and particle acceleration in extreme cosmic sources including pulsars
and magnetars. The natural energy scale for these non-thermal processes is of
the order of MeV. Although they can be partially and indirectly studied using
other methods, only the proposed GRIPS measurements will provide direct access
to their primary photons. GRIPS will be a driver for the study of transient
sources in the era of neutrino and gravitational wave observatories such as
IceCUBE and LISA, establishing a new type of diagnostics in relativistic and
nuclear astrophysics. This will support extrapolations to investigate star
formation, galaxy evolution, and black hole formation at high redshifts.Comment: to appear in Exp. Astron., special vol. on M3-Call of ESA's Cosmic
Vision 2010; 25 p., 25 figs; see also www.grips-mission.e
Offspring of Mothers Fed a High Fat Diet Display Hepatic Cell Cycle Inhibition and Associated Changes in Gene Expression and DNA Methylation
The association between an adverse early life environment and increased susceptibility to later-life metabolic disorders such as obesity, type 2 diabetes and cardiovascular disease is described by the developmental origins of health and disease hypothesis. Employing a rat model of maternal high fat (MHF) nutrition, we recently reported that offspring born to MHF mothers are small at birth and develop a postnatal phenotype that closely resembles that of the human metabolic syndrome. Livers of offspring born to MHF mothers also display a fatty phenotype reflecting hepatic steatosis and characteristics of non-alcoholic fatty liver disease. In the present study we hypothesised that a MHF diet leads to altered regulation of liver development in offspring; a derangement that may be detectable during early postnatal life. Livers were collected at postnatal days 2 (P2) and 27 (P27) from male offspring of control and MHF mothers (n = 8 per group). Cell cycle dynamics, measured by flow cytometry, revealed significant G0/G1 arrest in the livers of P2 offspring born to MHF mothers, associated with an increased expression of the hepatic cell cycle inhibitor Cdkn1a. In P2 livers, Cdkn1a was hypomethylated at specific CpG dinucleotides and first exon in offspring of MHF mothers and was shown to correlate with a demonstrable increase in mRNA expression levels. These modifications at P2 preceded observable reductions in liver weight and liver∶brain weight ratio at P27, but there were no persistent changes in cell cycle dynamics or DNA methylation in MHF offspring at this time. Since Cdkn1a up-regulation has been associated with hepatocyte growth in pathologic states, our data may be suggestive of early hepatic dysfunction in neonates born to high fat fed mothers. It is likely that these offspring are predisposed to long-term hepatic dysfunction
Alu Exonization Events Reveal Features Required for Precise Recognition of Exons by the Splicing Machinery
Despite decades of research, the question of how the mRNA splicing machinery precisely identifies short exonic islands within the vast intronic oceans remains to a large extent obscure. In this study, we analyzed Alu exonization events, aiming to understand the requirements for correct selection of exons. Comparison of exonizing Alus to their non-exonizing counterparts is informative because Alus in these two groups have retained high sequence similarity but are perceived differently by the splicing machinery. We identified and characterized numerous features used by the splicing machinery to discriminate between Alu exons and their non-exonizing counterparts. Of these, the most novel is secondary structure: Alu exons in general and their 5′ splice sites (5′ss) in particular are characterized by decreased stability of local secondary structures with respect to their non-exonizing counterparts. We detected numerous further differences between Alu exons and their non-exonizing counterparts, among others in terms of exon–intron architecture and strength of splicing signals, enhancers, and silencers. Support vector machine analysis revealed that these features allow a high level of discrimination (AUC = 0.91) between exonizing and non-exonizing Alus. Moreover, the computationally derived probabilities of exonization significantly correlated with the biological inclusion level of the Alu exons, and the model could also be extended to general datasets of constitutive and alternative exons. This indicates that the features detected and explored in this study provide the basis not only for precise exon selection but also for the fine-tuned regulation thereof, manifested in cases of alternative splicing
SN 2020udy: a SN Iax with strict limits on interaction consistent with a helium-star companion
Early observations of transient explosions can provide vital clues to their
progenitor origins. In this paper we present the nearby Type Iax (02cx-like)
supernova (SN), SN 2020udy that was discovered within hours (7 hr) of
estimated first light. An extensive dataset of ultra-violet, optical, and
near-infrared observations was obtained, covering out to 150 d after
explosion. SN 2020udy peaked at -17.860.43 mag in the r band and evolved
similarly to other 'luminous' SNe Iax, such as SNe 2005hk and 2012Z. Its
well-sampled early light curve allows strict limits on companion interaction to
be placed. Main-sequence companion stars with masses of 2 and 6 M are
ruled out at all viewing angles, while a helium-star companion is allowed from
a narrow range of angles (140-180 away from the companion). The spectra
and light curves of SN2020udy are in good agreement with those of the 'N5def'
deflagration model of a near Chandrasekhar-mass carbon-oxygen white dwarf.
However, as has been seen in previous studies of similar luminosity events, SN
2020udy evolves slower than the model. Broad-band linear polarisation
measurements taken at and after peak are consistent with no polarisation, in
agreement with the predictions of the companion-star configuration from the
early light curve measurements. The host galaxy environment is low metallicity
and is consistent with a young stellar population. Overall, we find the most
plausible explosion scenario to be the incomplete disruption of a CO white
dwarf near the Chandrasekhar-mass limit, with a helium-star companion.Comment: 18 pages, 14 figures, submitted to MNRA
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