160 research outputs found
Evolution of the Radio Remnant of Supernova 1987A: Morphological Changes from Day 7000
We present radio imaging observations of supernova remnant 1987A at 9 GHz,
taken with the Australia Telescope Compact Array over 21 years from 1992 to
2013. By employing a Fourier modeling technique to fit the visibility data, we
show that the remnant structure has evolved significantly since day 7000
(mid-2006): the emission latitude has gradually decreased, such that the
overall geometry has become more similar to a ring structure. Around the same
time, we find a decreasing trend in the east-west asymmetry of the surface
emissivity. These results could reflect the increasing interaction of the
forward shock with material around the circumstellar ring, and the relative
weakening of the interaction with the lower-density material at higher
latitudes. The morphological evolution caused an apparent break in the remnant
expansion measured with a torus model, from a velocity of 4600+150-200 km/s
between day 4000 and 7000 to 2400+100-200 km/s after day 7000. However, we
emphasize that there is no conclusive evidence for a physical slowing of the
shock at any given latitude in the expanding remnant, and that a change of
radio morphology alone appears to dominate the evolution. This is supported by
our ring-only fits which show a constant expansion of 3890+/-50 km/s without
deceleration between days 4000 and 9000. We suggest that once the emission
latitude no longer decreases, the expansion velocity obtained from the torus
model should return to the same value as that measured with the ring model.Comment: 11 pages, 5 figures, accepted for publication in ApJ, Figure 1 has
been scaled dow
Active Galaxies and Candidate Remnants in the Core of the Shapley Concentration
We present preliminary results of a multifrequency and multiresolution study carried out with the Australia Telescope Compact Array for nine of the ten extended radio galaxies located in the merging cluster complexes A3558 and A3528, at the centre of the Shapley Concentration. We found that 5 out of the 9 extended radio galaxies are active radio galaxies, i.e. they have a clear active radio nucleus coincident with the central region of the associated optical galaxy, radio jets and extended lobes; the remaining four lack an obvious radio nucleus, have a very diffuse and amorphous morphology and exhibit peculiar spectral properties. We call these radio sources as remnants and propose that they are (a) either radio galaxies where the nuclear activity has ceased; or (b) regions where pre-existing electrons have been reaccelerated as consequence of shocks due to cluster mergers
High-resolution radio observations of SNR 1987A at high frequencies
We present new imaging observations of the remnant of Supernova (SN) 1987A at
44 GHz, performed in 2011 with the Australia Telescope Compact Array (ATCA).
The 0\farcs35\times0\farcs23 resolution of the diffraction-limited image is
the highest achieved to date in high-dynamic range. We also present a new ATCA
image at 18 GHz derived from 2011 observations, which is super-resolved to
0\farcs25. The flux density is 402 mJy at 44 GHz and 816 mJy at 18
GHz. At both frequencies, the remnant exhibits a ring-like emission with two
prominent lobes, and an east-west brightness asymmetry that peaks on the
eastern lobe. A central feature of fainter emission appears at 44 GHz. A
comparison with previous ATCA observations at 18 and 36 GHz highlights higher
expansion velocities of the remnant eastern side. The 18-44 GHz spectral index
is (). The spectral index map
suggests slightly steeper values at the brightest sites on the eastern lobe,
whereas flatter values are associated with the inner regions. The remnant
morphology at 44 GHz generally matches the structure seen with contemporaneous
X-ray and H observations. Unlike the H emission, both the radio
and X-ray emission peaks on the eastern lobe. The regions of flatter spectral
index align and partially overlap with the optically-visible ejecta. Simple
free-free absorption models suggest that emission from a pulsar wind nebula or
a compact source inside the remnant may now be detectable at high frequencies,
or at low frequencies if there are holes in the ionised component of the
ejecta.Comment: References updated. High resolution version may be found at
http://ict.icrar.org/store/staff/gio/Papers/Zanardo_2013.pd
STEM education from the perspective of The University of Sydney STEM Teacher Enrichment Academy
While STEM education is attracting much attention and is strongly advocated for, delivering on the promise of STEM education is still being researched (Rosicka, 2016; Margot & Kettler, 2019). The quest is on for understanding the essentials of STEM education and how to prepare teachers to capture the essence of STEM education in their professional practice. Drawing on ongoing research, the STEM Teacher Enrichment Academy, established within The University of Sydney in 2014, has developed in-service programs for teachers of both primary and secondary schools. The Academy is driven by the belief that STEM education is not a âfadâ and has the potential to transform pedagogy, thus motivating and enthusing students to participate more fully in the STEM disciplines, continue into senior secondary STEM subjects and beyond, ultimately addressing a shortage in STEM-related careers. With an expanding alumnus, currently at 800 teachers from 139 high schools and 370 teachers from 90 primary schools, the Academy has gathered scholarly evidence for the effectiveness and impact of its programs (Anderson, 2019; Anderson, Wilson, Tully, & Way, 2019).
This presentation will share the design and structure of the Academyâs evidence-based programs as well as research on its efficacy.
REFERENCES
Margot, K. C. & Kettler, T. (2019). Teachersâ perception of STEM integration and education: a systematic literature review. International Journal of STEM Education, 6(2). https://doi.org/10.1186/s40594-018-0151-2
Anderson, J. (2019). Supporting STEM curriculum implementation with professional learning: The University of Sydney STEM Teacher Enrichment Academy. Journal of Physics: Conference Series. 1340 012001
Anderson, J., Wilson, K., Tully, D., & Way, J. (2019). âCan we build the wind powered car again?â Studentsâ and teachersâ responses to a new integrated STEM curriculum. Journal of Research in STEM Education, 5(1), 20â39.
Rosicka, C. (2016). Translating STEM education research into practice. Camberwell, Vic.: Australian Council for Educational Research
HD 93129A at different radio scales
Recent observations toward the O2 If* star HD 93129A have revealed important non-thermal radio emission, and that it has an early O companion 140 AU away if at 2.5 kpc (FGS-HST data). These facts strongly support the possibility of a massive stars wind-collision region as the acceleration site of the synchrotron-emitting relativistic electrons. We have carried out LBA VLBI observations at 2.37 GHz to resolve the non-thermal source, and search for a bow-shock shape, typical of a wind-collision region. Preliminary results are presented here.Fil: Benaglia, Paula. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico la Plata. Instituto Argentino de Radioastronomia (i); ArgentinaFil: Dougherty, S. M.. National Research Council of Canada, Herzberg Institute for Astrophysics, Dominion Radio Astrophysical Observatory; CanadĂĄFil: Phillips, C.. Australia Telescope National Facility, CSIRO; AustraliaFil: Koribalski, B.. Australia Telescope National Facility, CSIRO; AustraliaFil: Tzioumis, T.. Australia Telescope National Facility, CSIRO; Australi
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