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ATNF ATUC MEMORANDUM

To: ATUC
From: Lister Staveley-Smith, BДrbel Koribalski
Date: 25 November, 2005
Subject: Recent Astrophysics Highlights



Recent Astrophysics Highlights


1. THE GALACTIC SUPERSHELL GSH 242-03+37
A new survey of the Milky Way with the Parkes telescope has produced its
first major discovery, a massive shell of expanding gas powered by an
energy equivalent to 30 supernova explosions. The Galactic All-Sky Survey
(GASS) commenced its two-year program of observations at the Parkes
telescope earlier this year and, almost immediately, an energetic
Galactic supershell (GSH 242-03+37) was found by McClure-Griffiths and
collaborators. The radius of the shell is 560 parsecs, or 1800 light
years. It is believed that fragmentation of such shells may explain the
significant population of compact neutral hydrogen clouds recently
discovered by the Greenbank telescope. The results are due to be
published in the Astrophysical Journal (McClure-Griffiths, Ford, Pisano,
Gibson, Staveley-Smith., Dedes & Kalberla 2005, astro-ph/0510304).
[pic]



Figure 1: HI image of the Galactic supershell GSH 242-03+37 at a
velocity of 42 km/s. The supershell is one of the largest in the
Galaxy, with a diameter of over 1 kpc. New HI data from the
Galactic All-Sky Survey (GASS) reveal that the supershell is
broken at both the top and bottom. Large billowy filaments extend
from the shell in the disk for more than 1.5 kpc into the lower
Galactic halo (McClure-Griffiths et al. 2005 ).


2. PULSAR PROPER MOTION
A new study of pulsar polarization properties with the Parkes telescope
has led Johnston et al. to the important discovery that the rotation axis
of pulsars is consistently aligned with the direction of their motion.
This provides confirmation of the so-called "rocket effect", where an
offset magnetic dipole causes the stars to accelerate along their
rotation axis. The results are due to be published in the Monthly Notices
of the Royal Astronomical Society (Johnston, Hobbs, Vigeland, Weisberg,
Kramer & Lyne 2005, astro-ph/0510260).

[pic]
Figure 2: Example of a pulsar whose velocity axis and rotation
axis are aligned. The bottom panel shows the pulsar profile in
total intensity (black), linear polarization (red) and circular
polarization (green). The dashed line marks the location of the
rotation axis. The top panel shows the position angle of the
linear polarization (black dots). The angle of the velocity vector
on the sky is shown by the light blue line. At the location of the
rotation axis, the position angle of the velocity vector and the
linear polarization are the same, showing the angles are aligned
(Johnston et al., astro-ph/0510260).



3. ALFA RELATIVISTIC BINARY
A young, highly relativistic binary pulsar (J1906+0746) has been found in
the ALFA pulsar survey. The expected gravitational wave coalescence time
is only 300 Myr and the rate of orbital periastron advance is 8 deg/yr.
Geodetic precession may already have been seen. This may be a younger
version of the double pulsar system but intensive searches for radio
pulses from the companion have been unsuccessful so far. Parkes
observations were used to provide "pre-discovery" data and timing and
polarimetry observations. The paper has been submitted to the
Astrophysical Journal (Lorimer, Stairs, Freire, Cordes et al. 2005).
[pic]

Figure 3: Phase-time diagram of the binary pulsar J1906+0746 as
observed with Parkes at 1374 MHz in August 1998. While radio
interference prevented a detection at the time, the pulsar was
quite visible with the hindsight of the Arecibo detection made in
September 2004 (Lorimer et al. 2005, submitted).



4. GIANT DOUBLE RADIO SOURCES
Using the Sydney University Molonglo Sky Survey (SUMSS) Saripalli et al.
(2005) compiled a complete sample of double radio sources with projected
linear sizes larger than 0.7 Mpc (assuming Ho = 71 km/s/Mpc),
significantly enhancing the database of known giant radio sources. Using
ATCA high-resolution imaging as well as low-resolution optical spectra
from the 2.3m ANU telescope, they determine an abundance of (215 Mpc)-3
at the sensitivity of the survey. The results are published in the
Astronomical Journal (Saripalli, Hunstead, Subrahmanyan, & Boyce 2005, AJ
130, 896).


[pic]


Figure 4: Examples of re-starting giant radio galaxies (Saripalli
et al. 2005). SGRS J0143-5431 (left) lies at a redshift of
z=0.1791 and has a size of 1 Mpc, while SGRS J1336-8019 (right)
lies at z = 0.2478 and has a size of 2.5 Mpc. The figures consist
of SUMSS 843 MHz images (color) and ATCA 1.4 GHz images
(contours). The central core and two inner 'lobes' are the
signatures of re-starting radio galaxies.







5. PRECESSING JETS
Subrahmanyan et al. (astro-ph/0509275) have imaged, using the Compact
Array, the SUMSS giant radio source SGRS J0515-8100. The radio lobes
of this galaxy are very wide and are hypothesised to have been created
as the result of a highly variable and intermittent jet whose axis
direction also varied significantly. As the host galaxy also shows
evidence for an ongoing galaxy-galaxy interaction, it is possible that
this interaction is also sufficient to perturb the inner accretion
disk that produces and sustains AGN jets. If this applied to other
radio galaxies with similar morphology, it may be unnecessary to
invoke the coalescence of black holes, and that the corresponding
event rates predicted for gravity wave detection experiments may be
overestimated. The results are due to be published in the
Astrophysical Journal (Subrahmanyan, Hunstead, Cox & McIntyre 2005).
















6. ASTROMETRY IN THE SOUTHERN SKY
Very Large Baseline Interferometry (VLBI) 8.4 GHz observations of a total
of 111 radio sources in the southern hemisphere (Ojha et al. 2005) reveal
their structure at milli-arcsecond resolution. Only the most compact of
these sources are useful for astrometry. The imaging results represent
the most extensive VLBI survey of southern hemisphere International
Celestial Reference Frame (ICRF) sources to date. The results are
published in the Astronomical Journal (Ojha, Fey, Charlot, Jauncey,
Johnston, Reynolds, Tzioumis et al. 2005, AJ 130, 2529).

[pic]

Figure 6: Radio sources at 8.4 GHz with structures ranging from
very compact (index 1, top left) to extended (index 4, bottom
right). Sources with index 3,4 should be avoided in astrometric
and geodetic VLBI experiments (Ojha et al. 2005).


7. 12CO (1-0) MOLECULAR RIDGE IN THE LMC
The molecular ridge near 30 Doradus, which is the most prominent feature
in the Large Magellanic Cloud (LMC), has now been mapped with the Mopra
22-m telescope in the 12CO(1-0) line at 115.271 GHz. The map consists of
about 120 fields, each of which was observed for two hours. The extent of
the molecular ridge southwards from 30 Dor allows us to trace the effects
of the radiation field on the molecular gas. A first analysis of the
H2/CO conversion factor (X-factor) by Ott et al. revealed a gradient from
2.5 XGalactic near 30Dor to Galactic values at the very tip of the ridge.
The results are currently being prepared for publication (Ott, Wong,
Muller, Hughes, Pineda, et al. ).










Figure 7: 12CO(1-0) Mopra map of the molecular ridge south of 30
Doradus in the Large Magellanic Cloud (by Ott, Wong, Muller,
Hughes, Pineda et al.)




Awards
An international team of scientists, including the ATNF's Dr David
Jauncey, has won a prestigious international award for their involvement
in the Japanese VSOP/Halca orbiting radio telescope. The International
Academy of Astronautics (IAA) presented its Laurels for Team Achievement
award to the team of 15 scientists and engineers from five countries at
the 56th International Astronautics Congress in Fukuoka, Japan, on
October 16. The IAA created the Laurels for Team Achievement award in
2001 to recognise extraordinary performance and achievement by a team of
scientists, engineers and managers in the field of astronautics. The
previous winners of this award are the Russian Mir Space Station Team
(2001), the US Space Shuttle Team (2002), the Solar and Heliospheric
Observatory (SOHO) Team (2003), and the Hubble Space Telescope Team
(2004).The International Academy of Astronautics was founded in 1960 in
Stockholm, Sweden, by Theodore Von Karman, a pioneer of space
exploration. Its objective is to foster the development of astronautics
for peaceful purposes and to recognise individuals who have distinguished
themselves in a related branch of science or technology.

An article by Rosslyn Beeby appeared on p.3 of the Canberra Times on
October 14.
See: http://www.csiro.au/index.asp?type=mediaRelease&id=192award.

[pic]

Figure 6: Artist impression of the Japanese VSOP/Halca radio
telescope VSOP orbiting the Earth. Insert (bottom right): picture
of Dave Jauncey (CSIRO, ATNF).