arXiv subjects

Peter Hoeflich

Publications and source records attributed to Peter Hoeflich.

At least 55 records · Page 3Linked to original sources

arXiv2018

Thermonuclear Supernovae: Prospecting in the Age of Time-Domain and Multi-Wavelength Astronomy

We show how new and upcoming advances in the age of time-domain and multi-wavelength astronomy will open up a new venue to probe the diversity of SN~Ia. We discuss this in the context of the ELT (ESO), as well as space based instrument such as James Webb Space Telescope (JWST). As examples we demonstrate how the power of very early observations, within hours to days after the explosion, and very late-time observations, such as light curves and mid-infrared spectra beyond 3 years, can be used to probe the link to progenitors and explosion scenarios. We identify the electron-capture cross sections of Cr, Mn, and Ni/Co as one of the limiting factors we will face in the future.

astro-ph.HE↗

arXiv2018

Red vs Blue: Early observations of thermonuclear supernovae reveal two distinct populations?

We examine the early phase intrinsic $(B-V)_{0}$ color evolution of a dozen Type~Ia supernovae discovered within three days of the inferred time of first light ($t_{first}$) and have $(B-V)_0$ color information beginning within 5 days of $t_{first}$. The sample indicates there are two distinct early populations. The first is a population exhibiting blue colors that slowlybevolve, and the second population exhibits red colors and evolves more rapidly. We find that the early-blue events are all 1991T/1999aa-like with more luminous slower declining light curves than those exhibiting early-red colors. Placing the first sample on the Branch diagram (i.e., ratio of \ion{Si}{2} $λλ$5972, 6355 pseudo-Equivalent widths) indicates all blue objects are of the Branch Shallow Silicon (SS) spectral type, while all early-red events except for the 2000cx-like SN~2012fr are of the Branch Core-Normal (CN) or CooL (CL) type. A number of potential processes contributing to the early emission are explored, and we find that, in general, the viewing-angle dependance inherent in the companion collision model is inconsistent with all SS objects with early-time observations being blue and exhibiting an excess. We caution that great care must be taken when interpreting early-phase light curves as there may be a variety of physical processes that are possibly at play and significant theoretical work remains to be done.

astro-ph.HE↗

arXiv2018

Magneto-Hydrodynamical Effects on Nuclear Deflagration Fronts in Type Ia Supernovae

This article presents the study of the effects of magnetic fields on non-distributed nuclear burning fronts as a possible solution to a fundamental problem for the thermonuclear explosion of a Chandrasekhar mass ($M_{Ch}$) white dwarf (WD), the currently favored scenario for the majority of Type Ia SNe (SNe~Ia). All existing 3D hydrodynamical simulations predict strong global mixing of the burning products due to Rayleigh-Taylor (RT) instabilities, which is in contradiction with observations. As a first step and to study the flame physics we present a set of computational magneto-hydrodynamic (MHD) models in rectangular flux tubes, resembling a small inner region of a WD. We consider initial magnetic fields up to $10^{12}\,\,\mathrm{G}$ of various orientations. We find an increasing suppression of RT instabilities starting at about $10^9\,\,\mathrm{G}$. The front speed tends to decrease with increasing magnitude up to about $10^{11}\,\,\mathrm{G}$. For even higher fields new small scale finger-like structures develop, which increase the burning speed by a factor of 3 to 4 above the field-free RT-dominated regime. We suggest that the new instability may provide sufficiently accelerated energy production during the distributed burning regime to go over the Chapman-Jougey limit and trigger a detonation. Finally we discuss the possible origins of high magnetic fields during the final stage of the progenitor evolution or the explosion.

astro-ph.SR↗

arXiv2016

ASASSN-15lh: A Superluminous Ultraviolet Rebrightening Observed by Swift and Hubble

We present and discuss ultraviolet and optical photometry from the Ultraviolet/Optical Telescope and X-ray limits from the X-Ray Telescope on Swift and imaging polarimetry and ultraviolet/optical spectroscopy with the Hubble Space Telescope of ASASSN-15lh. It has been classified as a hydrogen-poor superluminous supernova (SLSN I) more luminous than any other supernova observed. ASASSN-15lh is not detected in the X-rays in individual or coadded observations. From the polarimetry we determine that the explosion was only mildly asymmetric. We find the flux of ASASSN-15lh to increase strongly into the ultraviolet, with a ultraviolet luminosity a hundred times greater than the hydrogen-rich, ultraviolet-bright SLSN II SN 2008es. We find objects as bright as ASASSN-15lh are easily detectable beyond redshifts of ~4 with the single-visit depths planned for the Large Synoptic Survey Telescope. Deep near-infrared surveys could detect such objects past a redshift of ~20 enabling a probe of the earliest star formation. A late rebrightening -- most prominent at shorter wavelengths -- is seen about two months after the peak brightness, which is itself as bright as a superluminous supernova. The ultraviolet spectra during the rebrightening are dominated by the continuum without the broad absorption or emission lines seen in SLSNe or tidal disruption events and the early optical spectra of ASASSN-15lh. Our spectra show no strong hydrogen emission, showing only LyA absorption near the redshift previously found by optical absorption lines of the presumed host. The properties of ASASSN-15lh are extreme when compared to either SLSNe or tidal disruption events.

astro-ph.HE↗

arXiv2015

Type Ia Supernovae and their Environment: Theory and Applications to SN 2014J

We present theoretical semi-analytic models for the interaction of stellar winds with the interstellar medium (ISM) or prior mass loss implemented in our code SPICE (Supernovae Progenitor Interaction Calculator for parameterized Environments, available on request), assuming spherical symmetry and power-law ambient density profiles and using the Pi-theorem. This allows us to test a wide variety of configurations, their functional dependencies, and to find classes of solutions for given observations. Here, we study Type Ia (SN~Ia) surroundings of single and double degenerate systems, and their observational signatures. Winds may originate from the progenitor prior to the white dwarf (WD) stage, the WD, a donor star, or an accretion disk (AD). For M_Ch explosions,the AD wind dominates and produces a low-density void several light years across surrounded by a dense shell. The bubble explains the lack of observed interaction in late time SN light curves for, at least, several years. The shell produces narrow ISM lines Doppler shifted by 10-100 km/s, and equivalent widths of approximately 100 mA and 1 mA in case of ambient environments with constant density and produced by prior mass loss, respectively. For SN 2014J, both mergers and M_Ch mass explosions have been suggested based on radio and narrow lines. As a consistent and most likely solution, we find an AD wind running into an environment produced by the RG wind of the progenitor during the pre-WD stage, and a short delay, 0.013 to 1.4 Myr, between the WD formation and the explosion. Our framework may be applied more generally to stellar winds and star-formation feedback in large scale galactic evolution simulations.

astro-ph.SR↗

arXiv2015

The 2D Distribution of Iron Rich Ejecta in the Remnant of SN 1885 in M31

We present Hubble Space Telescope (HST) ultraviolet Fe I and Fe II images of the remnant of Supernova 1885 (S And) which is observed in absorption against the bulge of the Andromeda galaxy, M31. We compare these Fe I and Fe II absorption line images to previous HST absorption images of S And, of which the highest quality and theoretically cleanest is Ca II H & K. Because the remnant is still in free expansion, these images provide a 2D look at the distribution of iron synthesized in this probable Type Ia explosion, thus providing insights and constraints for theoretical SN Ia models. The Fe I images show extended absorption offset to the east from the remnant's center as defined by Ca II images and is likely an ionization effect due to self-shielding. More significant is the remnant's apparent Fe II distribution which consists of four streams or plumes of Fe-rich material seen in absorption that extend from remnant center out to about 10,000 km/s. This is in contrast to the remnant's Ca II absorption, which is concentrated in a clumpy, roughly spherical shell at 1000 to 5000 km/s but which extends out to 12,500 km/s. The observed distributions of Ca and Fe rich ejecta in the SN 1885 remnant are consistent with delayed detonation white dwarf models. The largely spherical symmetry of the Ca-rich layer argues against a highly anisotropic explosion as might result from a violent merger of two white dwarfs.

astro-ph.HE↗

arXiv2014

Late-time near-infrared observations of SN 2005df

We present late-time ($200-400$ days) near-infrared spectral evolution for the Type Ia supernova SN 2005df. The spectra show numerous strong emission features of [CoII], [CoIII], and [FeII] throughout the $0.8-1.8$μm region. As the spectrum ages, the cobalt features fade as would be expected from the decay of $^{56}$Co to $^{56}$Fe. We show that the strong and isolated [FeII] emission line at $1.644$μm provides a unique tool to analyze near-infrared spectra of Type Ia supernovae. Normalization of spectra to this line allows separation of features produced by stable versus unstable isotopes of iron group elements. We develop a new method of determining the initial central density, $ρ_c$, and the magnetic field, $B$, of the white dwarf using the width of the $1.644$μm line. The line width is sensitive because of electron capture in the early stages of burning, which increases as a function of density. The sensitivity of the line width to $B$ increase with time and the effects of the magnetic field shift towards later times with decreasing $ρ_c$. The initial central density for SN 2005df is measured as $ρ_c=0.9(\pm0.2)$ (in $10^9$g/cm$^3$), which corresponds to a white dwarf close to the Chandrasekhar mass ($\rm M_{Ch}$) with $\rm M_{WD}=1.313(\pm0.034)$M$_{\odot}$ and systematic error less than $0.04$M$_{\odot}$. Within $\rm M_{Ch}$ explosions, however, the central density found for SN 2005df is very low for a H-accretor, possibly suggesting a helium star companion or a tidally-disrupted white dwarf companion. As an alternative, we suggest mixing of the central region. We find some support for high initial magnetic fields of strength $10^6$G for SN 2005df, however, $0$G cannot be ruled out because of noise in the spectra combined with low $ρ_c$.

astro-ph.SR↗

arXiv2011

Two exercises about neutrino departure times at CERN

Two simple exercises are solved, which educators can use to awake interest of their students in subtleties of the CERN Neutrino beam to Grand Sasso (CNGS) experiment. The first one is about the statistical error of the average departure time of neutrinos from CERN. The second one about a hypothetical bias in the departure times.

physics.pop-ph↗

arXiv2009

Dust and the type II-plateau supernova 2004et

We present mid-infrared (MIR) observations of the Type II-plateau supernova (SN) 2004et, obtained with the {\it Spitzer Space Telescope} between days 64 and 1406 past explosion. Late-time optical spectra are also presented. For the period 300-795 days past explosion, we argue that the spectral energy distribution of SN 2004et comprises (a) a hot component due to emission from optically thick gas, as well as free-bound radiation, (b) a warm component due to newly formed, radioactively heated dust in the ejecta, and (c) a cold component due to an IR echo from the interstellar-medium dust of the host galaxy, NGC 6946. There may also have been a small contribution to the IR SED due to free-free emission from ionised gas in the ejecta. We reveal the first-ever spectroscopic evidence for silicate dust formed in the ejecta of a supernova. This is supported by our detection of a large, but progressively declining, mass of SiO. However, we conclude that the mass of directly detected ejecta dust grew to no more than a few times 10^(-4)Msun. We also provide evidence that the ejecta dust formed in comoving clumps of fixed size. We argue that, after about two years past explosion, the appearance of wide, box-shaped optical line profiles was due to the impact of the ejecta on the progenitor circumstellar medium and that the subsequent formation of a cool, dense shell was responsible for a later rise in the MIR flux. This study demonstrates the rich, multi-faceted ways in which a typical core-collapse supernova and its progenitor can produce and/or interact with dust grains. The work presented here adds to the growing number of studies which do not support the contention that SNe are responsible for the large mass of observed dust in high-redshift galaxies.

astro-ph.SR↗

arXiv2007

Signatures of Delayed Detonation, Asymmetry, and Electron Capture in the Mid-Infrared Spectra of Supernovae 2003hv and 2005df

We present the first mid-infrared (5.2-15.2 micron) spectra of Type Ia supernovae (SNe 2003hv and 2005df). The detection of Ni emission in SN 2005df 135 days after the explosion provides direct observational evidence of high-density nuclear burning forming a significant amount of stable Ni in a Type Ia supernova. The observed emission line profiles in the SN 2005df spectrum indicate a chemically stratified ejecta structure. The SN 2005df Ar lines also exhibit a two-pronged emission profile implying that the Ar emission deviates significantly from spherical symmetry. The spectrum of SN 2003hv also shows signs of asymmetry, exhibiting blueshifted [Co III] which matches the blueshift of [Fe II] lines in nearly coeval NIR spectra. Finally, local thermodynamic equilibrium abundance estimates for the yield of radioactive 56Ni give ~0.5 Msun, for SN 2003hv, but only ~0.13-0.22 Msun for the apparently subluminous SN 2005df, supporting the notion that the luminosity of SNe Ia is primarily a function of the radioactive 56Ni yield. The chemically stratified ejecta structure observed in SN 2005df matches the predictions of delayed-detonation (DD) models, but is entirely incompatible with current three-dimensional deflagration models. Furthermore the degree that this layering persists to the innermost regions of the supernova is difficult to explain even in a DD scenario, where the innermost ejecta are still the product of deflagration burning. Thus, while these results are roughly consistent with a delayed detonation, it is clear that a key piece of physics is still missing from our understanding of the earliest phases of SN Ia explosions.

astro-ph↗

arXiv2005

Pre-Maximum Spectropolarimetry of the Type Ia SN 2004dt

We report observations of SN 2004dt obtained with the Very Large Telescope of the European Southern Observatory on August 13.30, 2004 when the supernova was more than a week before optical maximum. SN 2004dt showed strong lines of \ion{O}{1}, \ion{Mg}{2}, \ion{Si}{2}, and \ion{Ca}{2} with typical velocities of absorption minimum around 17,000 \kms. The line profiles show material moving at velocities as high as 25,000 \kms in these lines. The observations also reveal absorption lines from \ion{S}{2} and \ion{Si}{3} with a velocity of only 11,000 \kms. The highest velocity in the \ion{S}{2} features can be traced no higher than 15,000 \kms, much lower than those of O, Mg, Si, and Ca. SN 2004dt has a polarization spectrum unlike any previously observed. The variation of the polarization across some \ion{Si}{2} lines approaches 2%, making SN 2004dt the most highly polarized SN Ia ever observed. In contrast, the strong line of O I at 777.4 nm shows little or no polarization signature. The degree of polarization points to a richly-structured partially burned silicon layer with substantial departure from spherical symmetry. A geometry that would account for the observations is one in which the distribution of oxygen is essentially spherically symmetric, but with bubbles of intermediate-mass elements with significant opacity within the oxygen substrate.

astro-ph↗

arXiv2005

SN 2005cg: Explosion Physics and Circumstellar Interaction of a Normal Type Ia Supernova in a Low-Luminosity Host

We present the spectral evolution, light curve, and corresponding interpretation for the "normal-bright" Type Ia Supernova 2005cg discovered by ROTSE-IIIc. The host is a low-luminosity (M_r = -16.75), blue galaxy with strong indications of active star formation and an environment similar to that expected for SNe Ia at high redshifts. Early-time (t ~ -10 days) optical spectra obtained with the HET reveal an asymmetric, triangular-shaped Si II absorption feature at about 6100 Åwith a sharp transition to the continuum at a blue shift of about 24,000 km s^-1. By 4 days before maximum, the Si II absorption feature becomes symmetric with smoothly curved sides. Similar Si II profile evolution has previously been observed in other supernovae, and is predicted by some explosion models, but its significance has not been fully recognized. Although the spectra predicted by pure deflagration and delayed detonation models are similar near maximum light, they predict qualitatively different chemical abundances in the outer layers and thus give qualitatively different spectra at the earliest phases. The Si line observed in SN 2005cg at early times requires the presence of burning products at high velocities and the triangular shape is likely to be formed in an extended region of slowly declining Si abundance that characterizes delayed detonation models. The spectra show a high-velocity Ca II IR feature that coincides in velocity space with the Si II cutoff. This supports the interpretation that the Ca II is formed when the outer layers of the SN ejecta sweep up about 5 x 10^-3 M_sun of material within the progenitor system. (Abridged)

astro-ph↗

arXiv2005

On the Sensitivity of Deflagrations in Chandrasekhar Mass White Dwarf to Initial Conditions

We analyze the sensitivity of the flame propagation in a Chandrasekhar mass white dwarf to initial conditions during the subsonic burning phase, using 2D simulations of the full WD. Results are presented for a wide variety of initial flame distributions including central and off-center single point and multi-point, simultaneous and non-simultaneous, ignitions. We also examine the effects of convective velocity field which should exist at the core before the thermo-nuclear runaway. Our main conclusion suggests that the amounts of burning products and their distributions through the deflagration phase are extremely sensitive to initial conditions, much more sensitive than presented in previous studies. In particular, we find that more complex configurations such as even slight off-center ignitions, non-simultaneous multi-point ignitions and velocity fields tend to favor solutions in which individual plumes rise faster than the bulk of a typical Rayleigh-Taylor driven, unstable burning front. The difference to previous calculations for an octant of a WD may be understood as a consequence of the suppression of l=1,2 modes. Our results are consistent with full star calculations by the Chicago group. Moreover, the total amount of nuclear burning during the phase of subsonic burning depends sensitively on the initial conditions and may cause the WD to pulsate or to become unbound. We discuss the implications of the results on current models for Type Ia SNe, limitations imposed by the 2-D nature of our study, and suggest directions for further study.

astro-ph↗

arXiv2005

Early-time Spitzer observations of the type II-Plateau supernova, 2004dj

We present mid-infrared observations with the Spitzer Space Telescope of the nearby type II-P supernova, SN 2004dj, at epochs of 89 to 129 days. We have obtained the first mid-IR spectra of any supernova apart from SN 1987A. A prominent [NiII] 6.64 micron line is observed, from which we deduce that the mass of stable nickel must be at least 2.2e10(-4) Msun. We also observe the red wing of the CO-fundamental band. We relate our findings to possible progenitors and favour an evolved star, most likely a red supergiant, with a probable initial mass between ~10 and 15 Msun.

astro-ph↗

arXiv2004

Signature of Electron Capture in Iron-Rich Ejecta of SN 2003du

Late-time near-infrared and optical spectra are presented for the normal-bright SN2003du. At about 300 days after the explosion, the emission profiles of well isolated [FeII] lines (in particular that of the strong 1.644mu feature) trace out the global kinematic distribution of radioactive material in the expanding. In SN2003du, the 1.644 mu [FeII] line shows a flat-topped, profile, indicative of a thick but hollow-centered expanding shell, rather than a strongly-peaked profile that would be expected from a ``center-filled'' distribution.Based on detailed models for exploding Chandrasekhar mass white dwarfs, we show that the feature is consistent with spherical explosion models.Our model predicts central region of non-radioactive electron-capture elements up to 2500--3000km/s as a consequence of burning under high density, and an extended region of 56Ni up to 9,000--10,000km/s. Furthermore our analysis indicates that the 1.644mu [FeII] profile is not consistent with strong mixing between the regions of electron- capture isotopes and the 56Ni layers as is predicted by detailed 3D models for nuclear deflagration fronts. We discuss the possibility that the flat-topped profile could be produced as a result of an infrared catastrophe and conclude that such an explanation is unlikely. We put our results in context to other SNeIa and briefly discuss the implications of our result for the use of SNe Ia as cosmological standard candles.

astro-ph↗

arXiv2003

On The Hydrogen Emission From The Type Ia Supernova 2002ic

The discovery of SN 2002ic and subsequent spectroscopic studies have led to the surprising finding that SN 2002ic is a Type Ia supernova with strong ejecta-circumstellar interaction. Here we show that nearly 1 year after the explosion the supernova has become fainter overall, but the H$α$ emission has brightened and broadened dramatically compared to earlier observations. We have obtained spectropolarimetry data which show that the hydrogen-rich matter is highly aspherically distributed. These observations suggest that the supernova exploded inside a dense, clumpy, disk-like circumstellar environment.

astro-ph↗

arXiv2003

Expected Changes of Supernovae with Redshift due to Evolution of their Progenitors

We have analyzed the influence of the stellar populations, from which SN progenitors come from, on the observational outcome, including the metal free Pop. III. We use our models to study the evolution of the progenitor, the subsequent explosion and the light curves. For Type Ia, the variation of the main sequence mass of the progenitor of the exploding WD, produces an offset in the maximum-decline relation of 0.2 mag. This effect is critical for the use of high redshift Type Ia SNe as cosmological standard candles. In contrast, the metallicity does not change the above relation (at maximum, Delta M_V < 0.06 mag). For Type II, we find a dependence of the light curve properties with both, main sequence mass and metallicity of the progenitor, and we identify a rather homogeneous subclass, {\it Extreme} II-P, that may be used as a quasi-standard candle. Note that, although not as good as Type Ia for distance determinations, Type II are expected to occur since the first stars were formed.

astro-ph↗

arXiv2003

Spectropolarimetry of SN 2001el in NGC 1448: Asphericity of a Normal Type Ia Supernova

High-quality spectropolarimetry (range 417-860 nm; spectral resolution 1.27 nm and 0.265 nm/pixel) of the SN Ia 2001el were obtained with the ESO Very Large Telescope Melipal (+ FORS1) at 5 epochs. The spectra a week before maximum and around maximum indicate photospheric expansion velocities of about 10,000 km s$^{-1}$. Prior to optical maximum, the linear polarization of the continuum was $\approx 0.2 - 0.3 %$ with a constant position angle, showing that SN 2001el has a well-defined axis of symmetry. The polarization was nearly undetectable a week after optical maximum. The spectra are similar to those of the normally-bright SN 1994D with the exception of a strong double-troughed absorption feature seen around 800 nm (FWHM about 22 nm). This feature could be an important clue to the binary nature of SN Ia, perhaps associated with an accretion disk, or to the nature of the thermonuclear burning. If modeled in terms of an oblate spheroid, the continuum polarization implies a minor to major axis ratio of around 0.9 if seen equator-on; this level of asymmetry would produce an absolute luminosity dispersion of about 0.1 mag when viewed at different viewing angles. If typical for SNe Ia, this would create an RMS scatter of several hundredths of a magnitude around the mean brightness-decline relation.

astro-ph↗