arXiv subjects

O. Yaron

Publications and source records attributed to O. Yaron.

49 records · Page 3Linked to original sources

arXiv2014

A Wolf-Rayet-like progenitor of supernova SN 2013cu from spectral observations of a wind

The explosive fate of massive stripped Wolf-Rayet (W-R) stars is a key open question in stellar physics. An appealing option is that hydrogen-deficient W-R stars are the progenitors of some H-poor supernova (SN) explosions of Types IIb, Ib, and Ic. A blue object, having luminosity and colors consistent with those of some W-R stars, has been recently identified at the location of a SN~Ib in pre-explosion images but has not yet been conclusively determined to have been the progenitor. Similar previous works have so far only resulted in nondetections. Comparison of early photometric observations of Type Ic supernovae with theoretical models suggests that the progenitor stars had radii <10^12 cm, as expected for some W-R stars. However, the hallmark signature of W-R stars, their emission-line spectra, cannot be probed by such studies. Here, we report the detection of strong emission lines in an early-time spectrum of SN 2013cu (iPTF13ast; Type IIb) obtained ~15.5 hr after explosion ("flash spectroscopy"). We identify W-R-like wind signatures suggesting a progenitor of the WN(h) subclass. The extent of this dense wind may indicate increased mass loss from the progenitor shortly prior to its explosion, consistent with recent theoretical predictions.

astro-ph.HE↗

arXiv2014

Interaction-powered supernovae: Rise-time vs. peak-luminosity correlation and the shock-breakout velocity

Interaction of supernova (SN) ejecta with the optically thick circumstellar medium (CSM) of a progenitor star can result in a bright, long-lived shock breakout event. Candidates for such SNe include Type IIn and superluminous SNe. If some of these SNe are powered by interaction, then there should be a relation between their peak luminosity, bolometric light-curve rise time, and shock-breakout velocity. Given that the shock velocity during shock breakout is not measured, we expect a correlation, with a significant spread, between the rise time and the peak luminosity of these SNe. Here, we present a sample of 15 SNe IIn for which we have good constraints on their rise time and peak luminosity from observations obtained using the Palomar Transient Factory. We report on a possible correlation between the R-band rise time and peak luminosity of these SNe, with a false-alarm probability of 3%. Assuming that these SNe are powered by interaction, combining these observables and theory allows us to deduce lower limits on the shock-breakout velocity. The lower limits on the shock velocity we find are consistent with what is expected for SNe (i.e., ~10^4 km/s). This supports the suggestion that the early-time light curves of SNe IIn are caused by shock breakout in a dense CSM. We note that such a correlation can arise from other physical mechanisms. Performing such a test on other classes of SNe (e.g., superluminous SNe) can be used to rule out the interaction model for a class of events.

astro-ph.HE↗

arXiv2014

Precursors prior to Type IIn supernova explosions are common: precursor rates, properties, and correlations

There is a growing number of supernovae (SNe), mainly of Type IIn, which present an outburst prior to their presumably final explosion. These precursors may affect the SN display, and are likely related to some poorly charted phenomena in the final stages of stellar evolution. Here we present a sample of 16 SNe IIn for which we have Palomar Transient Factory (PTF) observations obtained prior to the SN explosion. By coadding these images taken prior to the explosion in time bins, we search for precursor events. We find five Type IIn SNe that likely have at least one possible precursor event, three of which are reported here for the first time. For each SN we calculate the control time. Based on this analysis we find that precursor events among SNe IIn are common: at the one-sided 99% confidence level, more than 50% of SNe IIn have at least one pre-explosion outburst that is brighter than absolute magnitude -14, taking place up to 1/3 yr prior to the SN explosion. The average rate of such precursor events during the year prior to the SN explosion is likely larger than one per year, and fainter precursors are possibly even more common. We also find possible correlations between the integrated luminosity of the precursor, and the SN total radiated energy, peak luminosity, and rise time. These correlations are expected if the precursors are mass-ejection events, and the early-time light curve of these SNe is powered by interaction of the SN shock and ejecta with optically thick circumstellar material.

astro-ph.HE↗

arXiv2013

PESSTO monitoring of SN 2012hn: further heterogeneity among faint type I supernovae

We present optical and infrared monitoring data of SN 2012hn collected by the Public ESO Spectroscopic Survey for Transient Objects (PESSTO). We show that SN 2012hn has a faint peak magnitude (MR ~ -15.7) and shows no hydrogen and no clear evidence for helium in its spectral evolution. Instead, we detect prominent Ca II lines at all epochs, which relates this transient to previously described 'Ca-rich' or 'gap' transients. However, the photospheric spectra (from -3 to +32 d with respect to peak) of SN 2012hn show a series of absorption lines which are unique, and a red continuum that is likely intrinsic rather than due to extinction. Lines of Ti II and Cr II are visible. This may be a temperature effect, which could also explain the red photospheric colour. A nebular spectrum at +150d shows prominent CaII, OI, CI and possibly MgI lines which appear similar in strength to those displayed by core-collapse SNe. To add to the puzzle, SN 2012hn is located at a projected distance of 6 kpc from an E/S0 host and is not close to any obvious starforming region. Overall SN 2012hn resembles a group of faint H-poor SNe that have been discovered recently and for which a convincing and consistent physical explanation is still missing. They all appear to explode preferentially in remote locations offset from a massive host galaxy with deep limits on any dwarf host galaxies, favouring old progenitor systems. SN 2012hn adds heterogeneity to this sample of objects. We discuss potential explosion channels including He-shell detonations and double detonations of white dwarfs as well as peculiar core-collapse SNe.

astro-ph.SR↗

arXiv2013

SN 2012ca: a stripped envelope core-collapse SN interacting with dense circumstellar medium

We report optical and near-infrared observations of SN 2012ca with the Public ESO Spectroscopy Survey of Transient Objects (PESSTO), spread over one year since discovery. The supernova (SN) bears many similarities to SN 1997cy and to other events classified as Type IIn but which have been suggested to have a thermonuclear origin with narrow hydrogen lines produced when the ejecta impact a hydrogen-rich circumstellar medium (CSM). Our analysis, especially in the nebular phase, reveals the presence of oxygen, magnesium and carbon features. This suggests a core collapse explanation for SN2012ca, in contrast to the thermonuclear interpretation proposed for some members of this group. We suggest that the data can be explained with a hydrogen and helium deficient SN ejecta (Type I) interacting with a hydrogen-rich CSM, but that the explosion was more likely a Type Ic core-collapse explosion than a Type Ia thermonuclear one. This suggests two channels (both thermonuclear and stripped envelope core-collapse) may be responsible for these SN 1997cy-like events.

astro-ph.SR↗

arXiv2013

An outburst from a massive star 40 days before a supernova explosion

Various lines of evidence suggest that very massive stars experience extreme mass-loss episodes shortly before they explode as a supernova. Interestingly, several models predict such pre-explosion outbursts. Establishing a causal connection between these mass-loss episodes and the final supernova explosion will provide a novel way to study pre-supernova massive-star evolution. Here we report on observations of a remarkable mass-loss event detected 40 days prior to the explosion of the Type IIn supernova SN 2010mc (PTF 10tel). Our photometric and spectroscopic data suggest that this event is a result of an energetic outburst, radiating at least 6x10^47 erg of energy, and releasing about 0.01 Solar mass at typical velocities of 2000 km/s. We show that the temporal proximity of the mass-loss outburst and the supernova explosion implies a causal connection between them. Moreover, we find that the outburst luminosity and velocity are consistent with the predictions of the wave-driven pulsation model and disfavor alternative suggestions.

astro-ph.HE↗

arXiv2013

Supernova 2012ec: Identification of the progenitor and early monitoring with PESSTO

We present the identification of the progenitor of the Type IIP SN 2012ec in archival pre-explosion HST WFPC2 and ACS/WFC F814W images. The properties of the progenitor are further constrained by non-detections in pre-explosion WFPC2 F450W and F606W images. We report a series of early photometric and spectroscopic observations of SN 2012ec. The r'-band light curve shows a plateau with M(r')=-17.0. The early spectrum is similar to the Type IIP SN 1999em, with the expansion velocity measured at Halpha absorption minimum of -11,700 km/s (at 1 day post-discovery). The photometric and spectroscopic evolution of SN 2012ec shows it to be a Type IIP SN, discovered only a few days post-explosion (<6d). We derive a luminosity for the progenitor, in comparison with MARCS model SEDs, of log L/Lsun = 5.15+/-0.19, from which we infer an initial mass range of 14-22Msun. This is the first SN with an identified progenitor to be followed by the Public ESO Spectroscopic Survey of Transient Objects (PESSTO).

astro-ph.SR↗

arXiv2012

The UV/optical spectra of the Type Ia supernova SN 2010jn: a bright supernova with outer layers rich in iron-group elements

Radiative transfer studies of Type Ia supernovae (SNe Ia) hold the promise of constraining both the time-dependent density profile of the SN ejecta and its stratification by element abundance which, in turn, may discriminate between different explosion mechanisms and progenitor classes. Here we present a detailed analysis of Hubble Space Telescope ultraviolet (UV) and ground-based optical spectra and light curves of the SN Ia SN 2010jn (PTF10ygu). SN 2010jn was discovered by the Palomar Transient Factory (PTF) 15 days before maximum light, allowing us to secure a time-series of four UV spectra at epochs from -11 to +5 days relative to B-band maximum. The photospheric UV spectra are excellent diagnostics of the iron-group abundances in the outer layers of the ejecta, particularly those at very early times. Using the method of 'Abundance Tomography' we have derived iron-group abundances in SN 2010jn with a precision better than in any previously studied SN Ia. Optimum fits to the data can be obtained if burned material is present even at high velocities, including significant mass fractions of iron-group elements. This is consistent with the slow decline rate (or high 'stretch') of the light curve of SN 2010jn, and consistent with the results of delayed-detonation models. Early-phase UV spectra and detailed time-dependent series of further SNe Ia offer a promising probe of the nature of the SN Ia mechanism.

astro-ph.SR↗

arXiv2012

Hubble Space Telescope studies of low-redshift Type Ia supernovae: Evolution with redshift and ultraviolet spectral trends

We present an analysis of the maximum light, near ultraviolet (NUV; 2900-5500 A) spectra of 32 low redshift (0.001<z<0.08) Type Ia supernovae (SNe Ia), obtained with the Hubble Space Telescope (HST). We combine this spectroscopic sample with high-quality gri light curves obtained with robotic telescopes to measure photometric parameters, such as stretch, optical colour, and brightness. By comparing our data to a comparable sample of SNe Ia at intermediate-z (0.4<z<0.9), we detect modest spectral evolution (3-sigma), in the sense that our mean low-z NUV spectrum has a depressed flux compared to its intermediate-z counterpart. We also see a strongly increased dispersion about the mean with decreasing wavelength, confirming the results of earlier surveys. These trends are consistent with changes in metallicity as predicted by contemporary SN Ia spectral models. We also examine the properties of various NUV spectral diagnostics in the individual spectra. We find a general correlation between stretch and the velocity (or position) of many NUV spectral features. In particular, we observe that higher stretch SNe have larger Ca II H&K velocities, that also correlate with host galaxy stellar mass. This latter trend is probably driven by the well-established correlation between stretch and stellar mass. We find no trends between UV spectral features and optical colour. Mean spectra constructed according to whether the SN has a positive or negative Hubble residual show very little difference at NUV wavelengths, indicating that the NUV evolution and variation we identify do not directly correlate with Hubble residuals. Our work confirms and strengthens earlier conclusions regarding the complex behaviour of SNe Ia in the NUV spectral region, but suggests the correlations we find are more useful in constraining progenitor models than improving the use of SNe Ia as cosmological probes.

astro-ph.CO↗

arXiv2012

The Palomar Transient Factory photometric catalog 1.0

We construct a photometrically calibrated catalog of non-variable sources from the Palomar Transient Factory (PTF) observations. The first version of this catalog presented here, the PTF photometric catalog 1.0, contains calibrated R_PTF-filter magnitudes for about 21 million sources brighter than magnitude 19, over an area of about 11233 deg^2. The magnitudes are provided in the PTF photometric system, and the color of a source is required in order to convert these magnitudes into other magnitude systems. We estimate that the magnitudes in this catalog have typical accuracy of about 0.02 mag with respect to magnitudes from the Sloan Digital Sky Survey. The median repeatability of our catalog's magnitudes for stars between 15 and 16 mag, is about 0.01 mag, and it is better than 0.03 mag for 95% of the sources in this magnitude range. The main goal of this catalog is to provide reference magnitudes for photometric calibration of visible light observations. Subsequent versions of this catalog, which will be published incrementally online, will be extended to a larger sky area and will also include g_PTF-filter magnitudes, as well as variability and proper motion information.

astro-ph.IM↗

arXiv2012

X-ray emission from supernovae in dense circumstellar matter environments: A search for collisionless shocks

(Abridged). The optical light curve of some SNe may be powered by the outward diffusion of the energy deposited by the explosion shock in optically thick circumstellar matter (CSM). Recently, it was shown that the radiation-mediated and -dominated shock in an optically thick wind must transform into a collisionless shock and can produce hard X-rays. The X-rays are expected to peak at late times, relative to maximum visible light. Here we report on a search, using Swift and Chandra, for X-ray emission from 28 SNe that belong to classes whose progenitors are suspected to be embedded in dense CSM (IIn/Ibn/SLSN-I). Two SNe in our sample have X-ray properties that are roughly consistent with the expectation for X-rays from a collisionless shock in optically thick CSM. Therefore, we suggest that their optical light curves are powered by shock breakout in CSM. We show that two other events were too X-ray bright during the SN maximum optical light to be explained by the shock breakout model. We conclude that the light curves of some, but not all, type-IIn/Ibn SNe are powered by shock breakout in CSM. For the rest of the SNe in our sample, including all the SLSN-I events, our X-ray limits are not deep enough and were typically obtained at too early times to conclude about their nature. We argue that the optical light curves of SNe, for which the X-ray emission peaks at late times, are likely powered by the diffusion of shock energy from a dense CSM. We comment about the possibility to detect some of these events in radio.

astro-ph.HE↗

arXiv2006

A Thousand and One Nova Outbursts

Multicycle nova evolution models have been calculated over the past twenty years, the number being limited by numerical constraints. Here we present a long-term evolution code that enables a continuous calculation through an unlimited number of nova cycles for an unlimited evolution time, even up to (or exceeding) a Hubble time. Starting with two sets of the three independent nova parameters -- the white dwarf mass, the temperature of its isothermal core, and the rate of mass transfer on to it -- we have followed the evolution of two models, with initial masses of 1 and 0.65 solar masses, accretion rates (constant throughout each calculation) of 1e-11 and 1e-9 solar-masses/yr, and relatively high initial temperatures (as they are likely to be at the onset of the outburst phase), through over 1000 and over 3000 cycles, respectively. The results show that although on the short-term consecutive outbursts are almost identical, on the long-term scale the characteristics change. This is mainly due to the changing core temperature, which decreases very similarly to that of a cooling white dwarf for a time, but at a slower rate thereafter. As the white dwarf's mass continually decreases, since both models lose more mass than they accrete, the central pressure decreases accordingly. The outbursts on the massive white dwarf change gradually from fast to moderately fast, and the other characteristics (velocity, abundance ratios, isotopic ratios) change, too. Very slowly, a steady state is reached, where all characteristics, both in quiescence and in outburst, remain almost constant. For the less massive white dwarf accreting at a high rate, outbursts are similar throughout the evolution.

astro-ph↗

arXiv2005

An Extended Grid of Nova Models: II. The Parameter Space of Nova Outbursts

This paper is a sequel to an earlier paper devoted to multiple, multicycle nova evolution models (Prialnik & Kovetz 1995, first paper of the series), which showed that the different characteristics of nova outbursts can be reproduced by varying the values of three basic and independent parameters: the white dwarf mass-M_{WD}, the temperature of its isothermal core-T_{WD} and the mass transfer rate-Mdot. Apart from being the largest computational classical novae parameter-space survey, we show here that the parameter space is constrained by several analytical considerations and find its limiting surfaces. Consequently, we extend the grid of multicycle nova evolution models presented in Paper I almost to its limits, adding multicycle nova outburst calculations for a considerable number of new parameter combinations. In particular, the extended parameter pace that produces nova eruptions includes low mass transfer rates down to 5e-13 Msun/yr, and more models for low T_{WD}. Resulting characteristics of these runs are added to the former parameter combination results, to provide a full grid spanning the entire parameter space for Carbon-Oxygen white dwarfs. The full grid covers the entire range of observed nova characteristics, even those of peculiar objects, which have not been numerically reproduced until now. Most remarkably, runs for very low Mdot lead to very high values for some characteristics, such as outburst amplitude A>~20, high super-Eddington luminosities at maximum, heavy element abundance of the ejecta Z_{ej}~0.63 and high ejected masses m_{ej}~7e-4 Msun.

astro-ph↗