18 research outputs found
Type IA supernovae from very long delayed explosion of core - WD merger
We study the spinning down time scale of rapidly rotating white dwarfs (WDs)
in the frame of the core-degenerate (CD) scenario for type Ia supernovae (SNe
Ia). In the CD scenario the Chandrasekhar or super-Chandrasekhar mass WD is
formed at the termination of the common envelope phase or during the planetary
nebula phase, from a merger of a WD companion with the hot core of a massive
asymptotic giant branch star. In the CD scenario the rapidly rotating WD is
formed shortly after the stellar formation episode, and the delay from stellar
formation to explosion is basically determined by the spin-down time of the
rapidly rotating merger remnant. We find that gravitational radiation is
inefficient in spinning down WDs, while the magneto-dipole radiation torque can
lead to delay times that are required to explain SNe Ia.Comment: MNRAS, in pres
Extensive Nuclear Reprogramming Underlies Lineage Conversion into Functional Trophoblast Stem-like Cells
SummaryInduced pluripotent stem cells (iPSCs) undergo extensive nuclear reprogramming and are generally indistinguishable from embryonic stem cells (ESCs) in their functional capacity and transcriptome and DNA methylation profiles. However, direct conversion of cells from one lineage to another often yields incompletely reprogrammed, functionally compromised cells, raising the question of whether pluripotency is required to achieve a high degree of nuclear reprogramming. Here, we show that transient expression of Gata3, Eomes, and Tfap2c in mouse fibroblasts induces stable, transgene-independent trophoblast stem-like cells (iTSCs). iTSCs possess transcriptional profiles highly similar to blastocyst-derived TSCs, with comparable methylation and H3K27ac patterns and genome-wide H2A.X deposition. iTSCs generate trophoectodermal lineages upon differentiation, form hemorrhagic lesions, and contribute to developing placentas in chimera assays, indicating a high degree of nuclear reprogramming, with no evidence of passage through a transient pluripotent state. Together, these data demonstrate that extensive nuclear reprogramming can be achieved independently of pluripotency
Explaining the type Ia supernova PTF 11kx with a violent-prompt merger scenario
We argue that the multiple shells of circumstellar material (CSM) and the
supernovae (SN) ejecta interaction with the CSM starting 59 days after the
explosion of the Type Ia SN (SN Ia) PTF 11kx, are best described by a violent
prompt merger. In this prompt merger scenario the common envelope (CE) phase is
terminated by a merger of a WD companion with the hot core of a massive
asymptotic giant (AGB) star. In most cases the WD is disrupted and accreted
onto the more massive core. However, in the rare cases where the merger takes
place when the WD is denser than the core, the core will be disrupted and
accreted onto the cooler WD. In such cases the explosion might occur with no
appreciable delay, i.e., months to years after the termination of the CE phase.
This, we propose, might be the evolutionary route that could lead to the
explosion of PTF 11kx. This scenario can account for the very massive CSM
within ~1000 AU of the exploding PTF 11kx star, for the presence of hydrogen,
and for the presence of shells in the CSM.Comment: MNRAS, in pres
The detection rate of early UV emission from supernovae: A dedicated GALEX/PTF survey and calibrated theoretical estimates
The radius and surface composition of an exploding massive star,as well as
the explosion energy per unit mass, can be measured using early UV observations
of core collapse supernovae (SNe). We present the first results from a
simultaneous GALEX/PTF search for early UV emission from SNe. Six Type II SNe
and one Type II superluminous SN (SLSN-II) are clearly detected in the GALEX
NUV data. We compare our detection rate with theoretical estimates based on
early, shock-cooling UV light curves calculated from models that fit existing
Swift and GALEX observations well, combined with volumetric SN rates. We find
that our observations are in good agreement with calculated rates assuming that
red supergiants (RSGs) explode with fiducial radii of 500 solar, explosion
energies of 10^51 erg, and ejecta masses of 10 solar masses. Exploding blue
supergiants and Wolf-Rayet stars are poorly constrained. We describe how such
observations can be used to derive the progenitor radius, surface composition
and explosion energy per unit mass of such SN events, and we demonstrate why UV
observations are critical for such measurements. We use the fiducial RSG
parameters to estimate the detection rate of SNe during the shock-cooling phase
(<1d after explosion) for several ground-based surveys (PTF, ZTF, and LSST). We
show that the proposed wide-field UV explorer ULTRASAT mission, is expected to
find >100 SNe per year (~0.5 SN per deg^2), independent of host galaxy
extinction, down to an NUV detection limit of 21.5 mag AB. Our pilot GALEX/PTF
project thus convincingly demonstrates that a dedicated, systematic SN survey
at the NUV band is a compelling method to study how massive stars end their
life.Comment: See additional information including animations on
http://www.weizmann.ac.il/astrophysics/ultrasa
Supernova PTF 12glz: A Possible Shock Breakout Driven through an Aspherical Wind
We present visible-light and ultraviolet (UV) observations of the supernova PTF 12glz. The SN was discovered and monitored in the near-UV and R bands as part of a joint GALEX and Palomar Transient Factory campaign. It is among the most energetic SNe IIn observed to date (≈10^(51) erg). If the radiated energy mainly came from the thermalization of the shock kinetic energy, we show that PTF 12glz was surrounded by ~1 M⊙ of circumstellar material (CSM) prior to its explosive death. PTF 12glz shows a puzzling peculiarity: at early times, while the freely expanding ejecta are presumably masked by the optically thick CSM, the radius of the blackbody that best fits the observations grows at ≈7000 km s^(−1). Such a velocity is characteristic of fast moving ejecta rather than optically thick CSM. This phase of radial expansion takes place before any spectroscopic signature of expanding ejecta appears in the spectrum and while both the spectroscopic data and the bolometric luminosity seem to indicate that the CSM is optically thick. We propose a geometrical solution to this puzzle, involving an aspherical structure of the CSM around PTF 12glz. By modeling radiative diffusion through a slab of CSM, we show that an aspherical geometry of the CSM can result in a growing effective radius. This simple model also allows us to recover the decreasing blackbody temperature of PTF 12glz. SLAB-Diffusion, the code we wrote to model the radiative diffusion of photons through a slab of CSM and evaluate the observed radius and temperature, is made available online