arXiv subjects

Immanuel Maurer

Publications and source records attributed to Immanuel Maurer.

4 recordsLinked to original sources

arXiv2010

Abundance stratification in Type Ia supernovae - III. The normal SN 2003du

The element abundance distributions in the ejecta of Type Ia supernova (SN) is studied by modelling a time series of optical spectra of SN 2003du until ~1 year after the explosion. Since SN 2003du is a very normal Type Ia SN both photometrically and spectroscopically, the abundance distribution derived for it can be considered as representative of normal Type Ia SNe. We find that the innermost layers are dominated by stable Fe-group elements, with a total mass of ~ 0.2 Msun, which are synthesized through electron capture. Above the core of stable elements there are thick 56Ni-rich layers. The total mass of 56Ni is 0.65 Msun. The Si- and S-rich layers are located above the 56Ni-rich layers. The dominant element in the outermost layers (M_r > 1.1 Msun, v > 13000 km/s) is O, with a small amount of Si. Little unburned C remains, with an upper limit of 0.016 Msun. The element distributions in the ejecta are moderately mixed, but not fully mixed as seen in three-dimensional deflagration models.

astro-ph.SR↗

arXiv2010

Oxygen Recombination in the nebular phase of supernovae 1998bw and 2002ap

Late-time spectra of stripped-envelope CC-SNe are dominated by strong [O {\sc i}] $λλ$6300,6363 emission, caused by thermal electron excitation of forbidden [O {\sc i}] transitions. The permitted O {\sc i} 7774 Å line is also often observed. This line cannot result from thermal electron excitation of the oxygen ground state. In this work tests are performed to verify whether the line can be powered by oxygen recombination alone, using the examples of two of the best studied type Ic SNe, 1998bw and 2002ap. Temperature-dependent effective recombination coefficients for neutral oxygen are calculated using available atomic data. Missing atomic data are computed in a temperature range typical for SN nebulae. Core ejecta models for SNe 1998bw and 2002ap are obtained from modelling their nebular emission spectra so that oxygen recombination line formation is computed consistently with oxygen forbidden line emission. While SN 2002ap can be explained well by a one dimensional shell model, this seems not to be possible for SN 1998bw, for which a two dimensional model is found. At very late epochs the formation of the O {\sc i} 7774 Å line can be explained by recombination radiation for both SNe, but at earlier epochs strong absorption is present which may determine the strength of this line even at $\sim$ 200 days.

astro-ph.HE↗

arXiv2007

Ignition latitude and the shape of Type I X-ray bursts

The shape of the lightcurve during the rising phase of Type I X-ray bursts is determined by many factors including the ignition latitude, the accretion rate, and the rotation rate of the star. We develop a phenomenological model of the burst rise process and show that simple measures of the burst morphology can be robust diagnostics of ignition latitude and burning regime. We apply our results to the large sample of bursts from the Low Mass X-ray Binary 4U 1636-536, and find evidence for off-equatorial ignition for many of the bursts. We argue that such behaviour may be associated with the transition from hydrogen to helium ignition at accretion rates a few percent of Eddington. We show that this model can also explain variations in the detectability of burst oscillations, and discuss the implications for other burst sources.

astro-ph↗

arXiv2007

Accretion rate and the occurrence of multi-peaked X-ray bursts

Most Type I X-ray bursts from accreting neutron stars have a lightcurve with a single peak, but there is a rare population of faint bursts that are double or even triple peaked. Suggested mechanisms include polar ignition with equatorial stalling, or multi-step energy release; the latter being caused by hydrodynamic instabilities or waiting points in the nuclear reaction sequence. We present an analysis of the accretion rate dependence of the multi-peak bursts, and discuss the consequences for the various models. The observations pose particular challenges for the polar ignition mechanism given current models of ignition latitude dependence.

astro-ph↗