arXiv subjects
Publications and source records attributed to P. A. Milne.
The late light curves of SN 1989B exhibited an emission excess relative to other type Ia supernovae. We investigate whether this emission excess suggests light echo emission from this supernova, or rather intense background galaxy contamination at the location of the supernova. We conclude that stellar emission can better explain the late spectra, and that the emission excess is likely due to background contamination.
Radioactive nuclei, especially those created in SN explosion, have long been suggested to be important contributors of galactic positrons. In this paper we describe the findings of three independent OSSE/SMM/TGRS studies of positron annihilation radiation, demonstrating that the three studies are largely in agreement as to the distribution of galactic annihilation radiation. We then assess the predicted yields and distributions of SN-synthesized radionuclei, determining that they are marginally compatible with the findings of the annihilation radiation studies.
The Advanced Compton Telescope (ACT) has been suggested to be the optimal next-generation instrument to study nuclear gamma-ray lines. In this work, we investigate the potential of three hypothetical designs of the ACT to perform SN science. We provide estimates of 1) the SN detection rate, 2) the SN Ia discrimination rate, and 3) which gamma-ray lines would be detected from specific supernova remnants. We find that the prompt emission from a SN Ia is such that it is unlikely that one would be within the range that an INTERMEDIATE ACT would be able to distinguish between explosion scenarios, although such an instrument would detect a handful of SNRs. We further find that the SUPERIOR ACT design would be a truly breakthrough instrument for SN science. By supplying these estimates, we intend to assist the gamma-ray astrophysics community in deciding the course of the next decade of gamma-ray SN science.
Positron annihilation radiation from the Galaxy has been observed by the OSSE, SMM and TGRS instruments. Improved spectral modeling of OSSE observations has allowed studies of the distribution of both positron annihilation radiation components, the narrow line emission at 511 keV and the positronium continuum emission. The results derived for each individual annihilation component are then compared with each other. These comparisons reveal approximate agreement between the distribution of these two emissions. In certain regions of the sky (notably in the vicinity of the previously reported positive latitude enhancement), the distribution of the emissions differ. We discuss these differences and the methods currently being employed to understand whether the differences are physical or a systematic error in the present analysis.
Gamma-ray line emission is a direct probe of the nucleosynthesis that occurs in Type Ia supernovae. In this work we describe the wealth of information obtainable from observations of this emission. Advanced Compton telescope designs are being studied by the Naval Research Laboratory, with the goal being the construction of a telescope which would be capable of detecting SNe Ia to distances in excess of 100 Mpc. We describe the instrument capabilities and the design issues that are being addressed. We assume a SN Ia rate and quantify the frequency at which an advanced Compton telescope could detect, discriminate between, and diagnose Type Ia supernovae. From these estimates, we argue that an advanced Compton telescope would be a powerful astrophysical tool.
The energy deposition into the ejecta of type Ia supernovae is dominated at late times by the slowing of positrons produced in the $β^{+}$ decays of $^{56}$Co. Fits of model-generated light curves to observations of type Ia supernovae suggest that a significant number of positrons escape the ejecta and annihilate as a delayed emission. In this work, the isotopic yields of the $β^{+}$ decay unstable nuclei, $^{56}$Co, $^{44}$Ti & $^{26}$Al are combined with the delayed annihilation fractions of each isotope for types Ia, Ib, II supernovae to generate an estimate of the positron production rate due to supernovae. It is shown that SN produced positrons can explain a sizeable fraction of the galactic positron annihilation radiation, as measured at 511 keV by the CGRO/OSSE, SMM and TGRS instruments.
By combining OSSE, SMM and TGRS observations of the galactic center region, Purcell et al. (1997) and Cheng et al. (1997) produced the first maps of galactic positron annihilation. That data-set has been augmented with additional data, both recent and archival, and re-analyzed to improve the spectral fitting. The improved spectral fitting has enabled the first maps of positronium continuum emission and the most extensive maps of 511 keV line emission. Bulge and disk combinations have been compared with the 511 keV line data, demonstrating that extended bulges are favored over a GC point source for every disk model tested. This result is independent of whether OSSE-only, OSSE/SMM, or OSSE/SMM/TGRS data-sets are used. The estimated bulge to disk ratio (and to a lesser extent the total flux) is shown to be dependent upon the assumption of bulge shape. A positive latitude enhancement is shown to have an effect upon the B/D ratio, but this effect is secondary to the choice of bulge shape.
A beam test of GLAST (Gamma-ray Large Area Space Telescope) components was performed at the Stanford Linear Accelerator Center in October, 1997. These beam test components were simple versions of the planned flight hardware. Results on the performance of the tracker, calorimeter, and anti-coincidence charged particle veto are presented.
We generate bolometric light curves for a variety of type Ia supernova models at late times, simulating gamma-ray and positron transport for various assumptions about the magnetic field and ionization of the ejecta. These calculated light curve shapes are compared with light curves of specific supernovae for which there have been adequate late observations. %The selection of models is generally not based upon the %ability to fit the late observations, but rather because the %model has been demonstrated by other authors to approximate the spectra %and early light curves of that specific SN. From these comparisons we draw two conclusions: whether a suggested model is an acceptable approximation of a particular event, and, given that it is, the magnetic field characteristics and degree of ionization that are most consistent with the observed light curve shape. For the ten SNe included in this study, five strongly suggest $^{56}$Co positron escape as would be permitted by a weak or radially-combed magnetic field. Of the remaining five SNe, none clearly show the upturned light curve expected for positron trapping in a strong, tangled magnetic field. Chandrasekhar mass models can explain normally, sub-, and super- luminous supernova light curves; sub-Chandrasekhar mass models have difficulties with sub- (and potentially normally) luminous SNe. An estimate of the galactic positron production rate from type Ia SNe is compared with gamma-ray observations of Galactic 511 keV annihilation radiation. Additionally, we emphasize the importance of correctly treating the positron transport for calculations of spectra, or any properties, of type Ia SNe at late epochs ($\geq$ 200 d).