2,436 research outputs found
SN 2007bg: The Complex Circumstellar Environment Around One of the Most Radio-Luminous Broad-Lined Type Ic Supernovae
In this paper we present the results of the radio light curve and X-ray
observations of broad-lined Type Ic SN 2007bg. The light curve shows three
distinct phases of spectral and temporal evolution, implying that the SNe shock
likely encountered at least 3 different circumstellar medium regimes. We
interpret this as the progenitor of SN 2007bg having at least two distinct
mass-loss episodes (i.e., phases 1 and 3) during its final stages of evolution,
yielding a highly-stratified circumstellar medium. Modelling the phase 1 light
curve as a freely-expanding, synchrotron-emitting shell, self-absorbed by its
own radiating electrons, requires a progenitor mass-loss rate of
\dot{M}~1.9x10^{-6}(v_{w}/1000 km s^{-1}) Solar masses per year for the last
t~20(v_{w}/1000 km s^{-1}) yr before explosion, and a total energy of the radio
emitting ejecta of E\sim1x10^{48} erg after 10 days from explosion. This places
SN 2007bg among the most energetic Type Ib/c events. We interpret the second
phase as a sparser "gap" region between the two winds stages. Phase 3 shows a
second absorption turn-on before rising to a peak luminosity 2.6 times higher
than in phase 1. Assuming this luminosity jump is due to a circumstellar medium
density enhancement from a faster previous mass-loss episode, we estimate that
the phase 3 mass-loss rate could be as high as \dot{M}<~4.3x10^{-4}(v_{w}/1000
km s^{-1}) Solar masses per year. The phase 3 wind would have transitioned
directly into the phase 1 wind for a wind speed difference of ~2. In summary,
the radio light curve provides robust evidence for dramatic global changes in
at least some Ic-BL progenitors just prior (~10-1000 yr) to explosion. The
observed luminosity of this SN is the highest observed for a
non-gamma-ray-burst broad-lined Type Ic SN, reaching L_{8.46 GHz}~1x10^{29} erg
Hz^{-1} s^{-1}, ~567 days after explosion.Comment: 11 pages, 5 figures, accepted for publication in MNRA
The balanced scorecard : structure and use in Canadian companies
This thesis develops a balanced scorecard model based on the attributes of Kaplan and Norton’s Balanced Scorecard (1992, 1996, 2001). The model is then operationalized using a survey that is administered to CMAs (Certified Management Accountants) employed by for profit, Canadian companies with greater than 51 employees. One hundred and forty nine usable responses were received. The thesis attempts to answer two research questions: (1) What attributes of a Kaplan & Norton (hereafter K&N) Balanced Scorecard (BSC) are present in the performance measurement systems of Canadian organizations? and (2) What are the differences between organizations with different levels of K&N Balanced Scorecard adoption? Of the 149 responses, 110 (73.8%) organizations were classified as BSC firms (Levels 1 to 4) and 39 (26.2%) were classified as non-BSC firms. The 110 BSC firms were further classified as follows: 15 (13.6%) as Level 1 BSC firms, 14 (12.7%) as Level 2A BSC firms, 20 (18.2%) as Level 2B BSC firms, 25 (22.7%) as Level 3 BSC firms and 36 (32.7%) as Level 4 BSC firms. Thus, based on our conceptual model, we can say that 32.7% of the BSC firms (24.2% of the total respondents) had a fully developed K&N BSC. The study found several differences between Level 4 and Level 1 BSC organizations. For example, respondents in 83% of the Level 4 organizations, versus in 67% of the Level 1 organizations, indicated that their organizations reviewed their performance measures when their strategy changed. This study adds to academic research by conceptualizing Kaplan and Norton’s (1996, 2001) Balanced Scorecard and comparing this to the performance measurement systems of Canadian companies. Although there are numerous academic studies on the balanced scorecard (e.g., Chan & Ho 2000; Hoque & James 2000; Lipe & Salterio 2000, 2002; Malina & Selto 2001; Ittner & Larcker 2003; Speckbacher et al. 2003; Stemsrudhagen 2004), only the Speckbacker et al. 2003 study has developed a conceptual model of Kaplan and Norton’s (1992, 1996, 2001) Balanced Scorecard and used it to examine the extent of its adoption. Our study mirrors theirs, with two notable exceptions: we have a different and noteworthy conceptualization of Kaplan and Norton’s Balanced Scorecard and we apply this to a Canadian setting
The host of GRB/XRF 030528 - an actively star forming galaxy at z=0.782
An important parameter for the distinction of X-ray flashes, X-ray rich
bursts and Gamma-ray bursts in the rest frame is the distance to the explosion
site. Here we report on the spectroscopic redshift determination of the host
galaxy of XRF/GRB 030528 using the ESO VLT FORS2 instrument. From the strong
oxygen and hydrogen emission lines the redshift was measured to be
z=0.782+-0.001. Obtaining the line luminosities and ratios we find that the
host is consistent with being an actively star forming galaxy with sub-solar
metallicity. With a stellar mass of ~10E10 Msun the host is placed among the
most massive GRB host galaxies at a similar redshift. Estimating the redshifted
properties of the prompt emission, we find that XRF/GRB 030528 would be
classified as an X-ray rich bursts in the rest frame rather than an X-ray flash
in the typically used observer frame.Comment: 6 pages, 2 figures, accepted for publication in A&
Dust in the wind: the role of recent mass loss in long gamma-ray bursts
We study the late-time (t>0.5 days) X-ray afterglows of nearby (z<0.5) long
Gamma-Ray Bursts (GRB) with Swift and identify a population of explosions with
slowly decaying, super-soft (photon index Gamma_x>3) X-ray emission that is
inconsistent with forward shock synchrotron radiation associated with the
afterglow. These explosions also show larger-than-average intrinsic absorption
(NH_x,i >6d21 cm-2) and prompt gamma-ray emission with extremely long duration
(T_90>1000 s). Chance association of these three rare properties (i.e. large
NH_x,i, super-soft Gamma_x and extreme duration) in the same class of
explosions is statistically unlikely. We associate these properties with the
turbulent mass-loss history of the progenitor star that enriched and shaped the
circum-burst medium. We identify a natural connection between NH_x,i Gamma_x
and T_90 in these sources by suggesting that the late-time super-soft X-rays
originate from radiation reprocessed by material lost to the environment by the
stellar progenitor before exploding, (either in the form of a dust echo or as
reprocessed radiation from a long-lived GRB remnant), and that the interaction
of the explosion's shock/jet with the complex medium is the source of the
extremely long prompt emission. However, current observations do not allow us
to exclude the possibility that super-soft X-ray emitters originate from
peculiar stellar progenitors with large radii that only form in very dusty
environments.Comment: 6 pages, Submitted to Ap
An Atlas of Spectrophotometric Landolt Standard Stars
We present CCD observations of 102 Landolt standard stars obtained with the
R-C spectrograph on the CTIO 1.5 m telescope. Using stellar atmosphere models
we have extended the flux points to our six spectrophotometric secondary
standards, in both the blue and the red, allowing us to produce flux-calibrated
spectra that span a wavelength range from 3050 \AA to 1.1 \micron. Mean
differences between UBVRI spectrophotometry computed using Bessell's standard
passbands and Landolt's published photometry is found to be 1% or less.
Observers in both hemispheres will find these spectra useful for
flux-calibrating spectra and through the use of accurately constructed
instrumental passbands be able to compute accurate corrections to bring
instrumental magnitudes to any desired standard photometric system
(S-corrections). In addition, by combining empirical and modeled spectra of the
Sun, Sirius and Vega, we calculate and compare synthetic photometry to observed
photometry taken from the literature for these three stars.Comment: Added referee's comments, minor corrections, replaced Table 1
Ultracold molecules: vehicles to scalable quantum information processing
We describe a novel scheme to implement scalable quantum information
processing using Li-Cs molecular state to entangle Li and Cs
ultracold atoms held in independent optical lattices. The Li atoms will
act as quantum bits to store information, and Cs atoms will serve as
messenger bits that aid in quantum gate operations and mediate entanglement
between distant qubit atoms. Each atomic species is held in a separate optical
lattice and the atoms can be overlapped by translating the lattices with
respect to each other. When the messenger and qubit atoms are overlapped,
targeted single spin operations and entangling operations can be performed by
coupling the atomic states to a molecular state with radio-frequency pulses. By
controlling the frequency and duration of the radio-frequency pulses,
entanglement can either be created or swapped between a qubit messenger pair.
We estimate operation fidelities for entangling two distant qubits and discuss
scalability of this scheme and constraints on the optical lattice lasers
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