Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004apj...605..573h&link_type=abstract
The Astrophysical Journal, Volume 605, Issue 1, pp. 573-574.
Astronomy and Astrophysics
Astronomy
1
Errata, Addenda
Scientific paper
We report a subtle error in the normalization of the absolute flux published in our original article (hereafter HWK98), and some minor updates. The normalization problem is related to the post-processing. As a consequence, the reported line fluxes are too large at early times. Note that Figure 1 of P. Höflich (ApJ, 492, 228 [1998]) has been transferred from HWK98. Results of previous papers are not affected (E. Müller, P. Höflich, A. M. Khokhlov, & E. Müller, ApJ, 492, 228 [1998]; P. Höflich, A. M. Khokhlov, & E. Müller, ApJ, 492, 228 [1998]).
For calculating the γ-ray spectra, the γ-ray transport is solved via a Monte Carlo code that produces an output file containing the Eddington flux, the energy input by radioactive decay and escape probability, ζ, of γ-ray photons. In a postprocessing step, the spectrum is renormalized and convolved with the instrumental response function of the γ-ray telescope. A two-step procedure is used to obtain the emergent spectra to separate the CPU-intensive Monte Carlo transport calculation from the ``fast'' second step, allowing us to study the influence of the instrument on the observables (e.g., E. Müller, P. Höflich, A. M. Khokhlov, & E. Müller, ApJ, 492, 228 [1998]]). The normalization error could be traced back to the postprocessing code and, for HWK98, its use on a UNIX system rather than a Cray computer for which it had been developed and tested several years earlier. The problem was caused by the different representation of numbers in combination with type conversion on Cray supercomputers (Real*8 and Integer*8) and UNIX systems (Real*4 and Integer*4). As a result, the numbers for the escape probabilities were read incorrectly and set to unity. To correct this, all monochromatic and integrated fluxes must be multiplied by π×ζ and ζ, respectively. The ζ values can be found in Figure 11 of HWK98, and Figure 1 here.
In addition to these normalization corrections for HWK98, we report recent updates to physical data and improved implementations of physical processes. The largest changes, between line spectra produced by the old one-dimensional (E. Müller, P. Höflich, A. M. Khokhlov, & E. Müller, ApJ, 492, 228 [1998]; P. Höflich, A. M. Khokhlov, & E. Müller, ApJ, 492, 228 [1998]; HWK98) and the current three-dimensional version of our code (P. Höflich, ApJ, 492, 228 [1998]), arise from the use of updated line branching ratios (original ratios from E. Browne et al., in Table of Isotopes, ed. C. M. Lederer & V. S. Shirley [New York: Wiley; 1978], pp. 160ff); updated ratios from H. Jundo, Nuclear Data Sheets, 86, 315 [1999]). The branching ratios typically changed by roughly 5% from past values, with as high as a 13% change for the 56Ni line at 812 keV. The past version of this code was tailored toward the simulation of high photon energies (E>=mec2) in order to calculate γ-ray spectra at energies relevant for CGRO and INTEGRAL. Physical approximations that took advantage of this limit have now been replaced with more general expressions, and a few additional minor corrections have been made in the current version to calculate continuum fluxes at low energies. The changes in physical approximations and minor corrections affect the line profiles at only the few percent level (Fig. 2).
Finally, we want to summarize explicitly the effects of the reported changes on the quantitative conclusions in HWK98. In the original paper we studied spectral properties for various scenarios between day +9 and +231 after the explosion. We demonstrated that detailed line profiles are needed to distinguish different scenarios and models, and that the instrumental responses and properties must be taken into account when comparing models to observations. Absolute fluxes and equivalent widths1 of lines alone are not sufficient because the 56Ni production varies widely within each scenario (P. Höflich & A. M. Khokhlov, ApJ, 492, 228 [1998]).
Although these major conclusions of HWK98 remain unchanged because most sections discuss only the line profile shapes or line ratios, some of the quantitative estimates and the time evolution of the fluxes are modified by the time-dependent normalization corrections (Fig. 1). For all models, the fluxes before maximum light are significantly reduced, and the time of maximum flux in the 56Co lines are later by about 10-15 days. However, a 10%-20% reduction of the flux at minimum light in γ-rays hardly changes the supernovae detection rate. The biggest impact is on the conclusion based on early-time fluxes: for the normally bright helium detonation model HeD10, the fluxes are smaller by factors of 6, 1.13, and 1.004 at about day 11 (maximum in the 56Ni line at 0.81 MeV), day 60 (maximum in Co[0.84 MeV]), and day 231, respectively. It is still correct that the helium-triggered detonation models (HeDs) can be distinguished by the much stronger early-time 56Ni lines from all other scenarios, but with the CGRO the 56Ni lines will be detectable only up to a distance of 6 rather than 15 Mpc.
Apart from the normalization, the updates alter the fluxes and line ratios by a few percent. The biggest change is caused by the new branching ratios, which affect Ni more significantly than Co. In particular, we showed that the 56Ni(0.81 MeV)/ 56Co(0.84 MeV) is fairly model independent (within ~20%), and in principle can be used to determine the time of the thermonuclear explosion. As a result of the change of the relative line strengths, the estimated time of the explosion would shift by, e.g., ~1-2 days if measured at day 20.
We thank Peter Milne (P. Milne et al. 2004, in preparation) for pointing out the problem with the fluxes published in HWK98, for pointing us towards branching ratios, and help with updating the code.
Höflich Peter
Wheeler Justin C.
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