Gamma ray constraints on the Galactic supernova rate

We perform Monte Carlo simulations of the expected gamma ray signatures of Galactic supernovae of all types to estimate the significance of the lack of a gamma ray signal due to supernovae occurring during the last millenium. Using recent estimates of the nuclear yields, we determine mean Galactic supernova rates consistent with the historic supernova record and the gamma ray limits. Another objective of these calculations of Galactic supernova histories is their application to surveys of diffuse Galactic gamma ray line emission

Three Dimensional Simulation of Gamma Ray Emission from Asymmetric Supernovae and Hypernovae

Hard X- and $\gamma$-ray spectra and light curves resulting from radioactive decays are computed for aspherical (jet-like) and energetic supernova models (representing a prototypical hypernova SN 1998bw), using a 3D energy- and time-dependent Monte Carlo scheme. The emission is characterized by (1) early emergence of high energy emission, (2) large line-to-continuum ratio, and (3) large cut-off energy by photoelectric absorptions in hard X-ray energies. These three properties are not sensitively dependent on the observer's direction. On the other hand, fluxes and line profiles depend sensitively on the observer's direction, showing larger luminosity and larger degree of blueshift for an observer closer to the polar ($z$) direction. Strategies to derive the degree of asphericity and the observer's direction from (future) observations are suggested on the basis of these features, and an estimate on detectability of the high energy emission by the {\it INTEGRAL} and future observatories is presented. Also presented is examination on applicability of a gray effective $\gamma$-ray opacity for computing the energy deposition rate in the aspherical SN ejecta. The 3D detailed computations show that the effective $\gamma$-ray opacity $\kappa_{\gamma} \sim 0.025 - 0.027$ cm$^{2}$ g$^{-1}$ reproduces the detailed energy-dependent transport for both spherical and aspherical (jet-like) geometry.Comment: 24 pages, 13 figures. Figure 7 added in the accepted version. ApJ, 644 (01 June 2006 issue), in press. Resolution of figures lower than the published versio

Gamma ray constraints on the galactic supernova rate

Monte Carlo simulations of the expected gamma-ray signatures of galactic supernovae of all types are performed in order to estimate the significance of the lack of a gamma-ray signal due to supernovae occurring during the last millenium. Using recent estimates of nuclear yields, we determine galactic supernova rates consistent with the historic supernova record and the gamma-ray limits. Another objective of these calculations of galactic supernova histories is their application to surveys of diffuse galactic gamma-ray line emission

Late Light Curves of Normal Type Ia Supernovae

We present late-epoch optical photometry (BVRI) of seven normal/super-luminous Type Ia supernovae: SN 2000E, SN 2000ce, SN 2000cx, SN 2001C, SN 2001V, SN 2001bg, SN 2001dp. The photometry of these objects was obtained using a template subtraction method to eliminate galaxy light contamination during aperture photometry. We show the optical light curves of these supernovae out to epochs of up to ~640 days after the explosion of the supernova. We show a linear decline in these data during the epoch of 200-500 days after explosion with the decline rate in the B,V,& R bands equal to about 1.4 mag/100 days, but the decline rate of the I-band is much shallower at 0.94 mag/100 days.Comment: 33 pages, 11 figures, Accepted for publication in The Astronomical Journa

Operation and performance of the OSSE instrument

The Oriented Scintillation Spectrometer Experiment (OSSE) on the Arthur Holly Compton Gamma Ray Observatory is described. An overview of the operation and control of the instrument is given, together with a discussion of typical observing strategies used with OSSE and basic data types produced by the instrument. Some performance measures for the instrument are presented that were obtained from pre-launch and in-flight data. These include observing statistics, continuum and line sensitivity, and detector effective area and gain stability

Are Ti44-Producing Supernovae Exceptional?

According to standard models supernovae produce radioactive $^{44}$Ti, which should be visible in gamma-rays following decay to $^{44}$Ca for a few centuries. $^{44}Ti production is believed to be the source of cosmic$^{44}$Ca, whose abundance is well established. Yet, gamma-ray telescopes have not seen the expected young remnants of core collapse events. The$^{44}$Ti mean life of$\tau \simeq$89 y and the Galactic supernova rate of$\simeq$3/100 y imply$\simeq$several detectable$^{44}Ti gamma-ray sources, but only one is clearly seen, the 340-year-old Cas A SNR. Furthermore, supernovae which produce much $^{44}Ti are expected to occur primarily in the inner part of the Galaxy, where young massive stars are most abundant. Because the Galaxy is transparent to gamma-rays, this should be the dominant location of expected gamma-ray sources. Yet the Cas A SNR as the only one source is located far from the inner Galaxy (at longitude 112 degree). We evaluate the surprising absence of detectable supernovae from the past three centuries. We discuss whether our understanding of SN explosions, their$^{44}Ti yields, their spatial distributions, and statistical arguments can be stretched so that this apparent disagreement may be accommodated within reasonable expectations, or if we have to revise some or all of the above aspects to bring expectations in agreement with the observations. We conclude that either core collapse supernovae have been improbably rare in the Galaxy during the past few centuries, or $^{44}Ti-producing supernovae are atypical supernovae. We also present a new argument based on$^{44}$Ca/$^{40}$Ca ratios in mainstream SiC stardust grains that may cast doubt on massive-He-cap Type I supernovae as the source of most galactic$^{44}$Ca.Comment: 23 pages, 14 figures, accepted for publication in Astronomy and Astrophysics 2006. Correcting the SN type of Tycho in Table B.1. and add its associated reference

Exploring the Trade-offs of Aggregated versus Disaggregated Architectures for Environmental Monitoring in Low-Earth Orbit

Traditionally, government space agencies have developed aggregated systems that co-host multiple capabilities on shared spacecraft buses. However, in response to cost growth and schedule delays on past programs, leaders in the government space community have expressed an interest in disaggregation, or distributing their capabilities across multiple spacecraft. Since their aggregated National Polar-orbiting Operational Satellite System (NPOESS) program was cancelled in 2010, both the National Oceanic and Atmospheric Administration (NOAA) and the Department of Defense (DoD) have investigated opportunities to reduce program costs through disaggregation. This paper expands their initial investigation and explores the cost impacts of aggregation and disaggregation across a large trade space of candidate architectures for environmental monitoring in low-Earth orbit. We find that on average, aggregated architectures are less costly than fully disaggregated ones but also find opportunities for cost savings by developing semi-aggregated systems, or systems with one or two satellites per orbital plane. Finally, we investigate several trades that are currently under consideration by NOAA and the DoD and make recommendations for future environmental monitoring systems in low-Earth orbit.Massachusetts Institute of Technology (Sandia Corporation Excellence in Engineering Graduate Fellowship)Skolkovo Institute of Science and Technolog

Positron Escape from Type Ia Supernovae

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).Comment: 82 pages including 25 figure

Late Light Curves of Normally-Luminous Type Ia Supernovae

The use of Type Ia supernovae as cosmological tools has reinforced the need to better understand these objects and their light curves. The light curves of Type Ia supernovae are powered by the nuclear decay of $^{56}Ni \to ^{56}Co \to ^{56}Fe$. The late time light curves can provide insight into the behavior of the decay products and their effect of the shape of the curves. We present the optical light curves of six "normal" Type Ia supernovae, obtained at late times with template image subtraction, and the fits of these light curves to supernova energy deposition models.Comment: Proceedings of Astronomy with Radioactivities V Conferenc