Division X/Commission 40:
Radio Astronomy
Report to the IAU General
Assembly
Sydney,
2003
PRESIDENT: Lucia Padrielli
VICE PRESIDENT: Luis Rodriguez
BOARD: Leonardo Bronfman, Francoise Combes, Peter
Dewdney, Philip John Diamond, Anne Green,
Masato Ishiguro, Leonid Litvinenko, Juan-Maria Marcaide, W Miller
Goss, Jim M Moran, Ren-Dong Nan, George Nicolson, A Pramesh Rao, Richard
Schilizzi, Jean L Turner
1.
Introduction
Radio Astronomy has seen important advances in the last three
years. New instruments and new sophisticated technologies allowed extremely
deep radio observations, which have brought to the definition of new radio
source populations. Studies of regions very close to the central engine of the
powerful radio sources have been possible with the higher angular resolutions
reached by space and millimeter VLBI.
The development of radio spectroscopy has opened new ways to the
physical and chemical investigation of the galactic molecular cloud regions and
of the chemical evolution of extragalactic systems. The extension toward higher
frequencies has represented a powerful tool
for the studies of star-forming galaxies and molecular clouds. The study of non thermal processes in galaxy clusters
has largely progressed opening new lines of investigation. The comparison with
observations in other frequency domains has allowed a more comprehensive
insight of the physical phenomena in radio sources.
This report does not claim to be complete, but gives a sample
of instrumental developments and
scientific achievements.
2. New
Developments at Telescope Facilities
2.1. Centimeter-Wavelength Facilities
Arecibo Observatory, NAIC
The Arecibo 305-m radio telescope is available for astronomical
observations at wavelengths between 6 m and 3 cm (frequencies of 47 MHz - 10
GHz) and in the declination range of -1 to +38 degrees. The 327- and 610-MHz
receivers are currently undergoing upgrading to improve performance.
Preliminary observations with the X-Band receiver (8-10 GHz) have been obtained
and this new system is expected to have a sensitivity in the range of 2 to 4.5
K/Jy.
A 6.0 - 8.0 GHz receiver is planned for 2003. At present, Arecibo
commits up to 4% of its observing time to VLBI. Work on the primary reflector
adjustment is in progress with significant improvements in performance already
achieved. (http://www.naic.edu)
Australia Telescope National Facility
(ATNF)
The six-element Compact Array in Narrabri (ATCA) is being upgraded
to cover the bands 16-25, 30-50 and 80-115 GHz. First light on two antennas
with the new 3 mm receivers was obtained in late 2000. At present, 3 of the 6
antennas of ATCA have 3 mm receivers.
A four-channel atmospheric monitoring system will provide phase
correction. Future upgrades may include monitoring receivers at 180-220 GHz and
a 10 Gbit/s correlator. (http://www.atnf.csiro.au)
Effesberg Radiotelescope - Max Planck Institute for Radio Astronomy (MPIfR)
The MPIfR is heavily involved in a number of large international
radio astronomy projects. Numerous instruments have been built by MPIfR for use
on other telescopes. New 5 and 11 cm receivers as well as 7 beam Ka and L band
arrays are being build for the Effelsberg 100-m telescope.
(http://www.mpifr-bonn.mpg.de)
Giant Metrewave Radio Telescope (GMRT)
The GMRT is located near Pune, India, and is operated by the
National Centre for Radio Astrophysics (NCRA-TIFR). It consists of 30 fully
steerable parabolic dishes, each 45 m in diameter. The GMRT telescope is
already operating at 5 frequencies, 150, 233, 327, 610, and 1420 MHz. A 50 MHz
system is being developed.
A 30-antenna FX-based 256-channel correlator with a bandwidth of
16 MHz is operational. Special purpose back ends for the GMRT include a
coherent de-disperser and search engine for pulsars.
(http://www.gmrt.ncra.tifr.res.in)
Green Bank Telescope (GBT)
Outfitting and commissioning of the GBT started in fall of 2000. A
first call for early science proposals has been made. At present, available
observing modes include spectral line, continuum, pulsar, and VLBI/VLBA.
Receivers include (in GHz): 0.290-0.920, 1.15-1.73, 1.73-2.60, 3.95-5.85,
8.0-10.1, 12.0-15.4 and 18.0-26.5. The higher frequencies will become available
progressively. (http://www.gb.nrao.edu/GBT/GBT.html)
Institute of Radio Astronomy, Ukraine
The giant decameter wavelength radio telescope UTR-2 (150,000 m2)
and the URAN VLBI system have been upgraded. The RT-70 telescope in Evpatoria,
Crimea, is in operation from 0.3 to 4.8 GHz. (http://www.ira.kharkov.ua)
Instituto Argentino de Radioastronomia
(IAR)
IAR operates two 30 meter radio telescopes. One is mainly dedicated to line observations
(HI, OH, various recombination lines in the 1420 - 1720 MHz band). The second one is mainly
dedicated to continuum polarimetry studies. The polarimetric receiver for the
continuum and CH line near 3.3 GHz is now operational.
(http://www.iar.unlp.edu.ar)
Istituto di Radioastronomia, Italy (IRA)
The Institute operates two stations, respectively in Medicina (Bologna) and Noto (Siracusa), with a total of 3 radio
telescopes: The "Northern Cross"
(600 m x 600 m) mainly for pulsar observations and 2 single-dish
antennas (32 m) designed mainly for VLBI observations. In the last three years
the Noto antenna was implemented with a system of active optics, allowing the
on-line correction of gravitational
deformations. The parabola can now observe at 40 GHz with an efficiency of 40%. The Institute is building
a 64 meter parabola, Sardinia Radio Telescope (SRT), in San Basilio (Sardinia).
(http://www.ira.cnr.it/)
Jodrell Bank Observatory (JBO)
The University of Manchester, through JBO, runs the UK National
Facility for radio astronomy. It consists of MERLIN, a sensitive six-element
interferometer network (seven when the Lovell Telescope is included) with
baselines between 11 and 217 km that routinely produces radio images with an
angular resolution matching that of the Hubble Space Telescope. MERLIN will be
upgraded to e-MERLIN. E-MERLIN will
have much wider bandwidth than MERLIN and a 30-fold increase in sensitivity for
continuum observations. It is expected
to be completed by 2007. The National Facility is also a regular participant in
European and global VLBI observations. An upgrade of the Lovell Telescope's surface
is now complete and will permit operation at up to 10 GHz. This upgrade
includes a new reflecting surface, pointing control system and refurbishment of
the track and foundations. (http://www.jb.man.ac.uk)
Mauritius Radio Telescope (MRT)
The MRT is a joint collaboration between the University of
Mauritius, the Raman Research Institute, and the Indian Institute of
Astrophysics. The MRT is located on Mauritius at a latitude of -20° and
operates at 151 MHz. It consists of a fixed east-west arm 2 km long, made of
1,024 helical antennas arranged in groups of 32. A north arm is made of 16
trolleys (each carrying four helical elements), movable over an 880 m railway
track. The effective angular resolution of the telescope is 4' x 4.6' when data
is gathered at 64 different positions of the north-south elements. The MRT has
completed data collection for a radio survey of the southern sky at 151 MHz
with a sensitivity comparable to that of the 6C survey.
(http://icarus.uom.ac.mu/mrt2.html)
Miyun Station Radio Telescope (MSRT)
The MSRT is operated by the Beijing Astronomical Observatory. A
survey of the sky north of +30° declination has been completed at 232 MHz,
which comprises 33,348 radio sources and images of 152 fields. A phased-array
mode has been developed for the MSRT. The observatory has received funding to
construct a new 50-m diameter telescope which will be used for single-dish
studies and VLBI observations.
(http://www.bao.ac.cn/bao/station/my/MSRT-e.html)
RATAN-600 radio telescope (Special Astrophysical
Observatory RAS)
It continued to operate for some large programs: the CMB
anisotropy investigation, with new sensitive 30-GHz 8-beam radiometer (MARS),
Sun, micro quasars, and AGN multi-frequency monitoring. Also the 21-cm line
Galactic plane survey is continuing (see www.sao.ru).
The sensitive radiometer continuum complex includes receivers at
610, 960, 2300, 3900, 7700, 11200 and 21700 MHz. But the 610-960 MHz band is not useful for
astrophysical observations because of the TV and mobile telephone interference.
A very large radio astronomical data base (CATS) is updated
continuously and includes near 400 different catalogues in radio continuum
bands. Probably CATS includes all catalogues or tables with more than 1000
sources. The CATS procedure for plotting
'on-line' radio spectra have been developed for some multi-frequency
catalogues of bright sources (WMAP, PKSCAT).
(http://cats.sao.ru)
Very Large Array (VLA)
In cooperation with UNAM (Mexico) and MPIfR (Germany), the
installation of 7 mm (40-50 GHz) receivers on all 28 VLA antennas is
practically completed. This band is particularly useful for imaging thermal
continuum and SiO sources. Using holographic maps, the figure of all the
antenna surfaces has been adjusted for better efficiency.
A real-time link to the Pie Town VLBA antenna has been
established, providing a factor of ~3 increase in the VLA angular resolution
for northern sources (105 km baseline). The 22 GHz receivers are being upgraded
to systems with three times better performance (50K) and they have been
installed in 21 antennas. The plan is to have all VLA antennas equipped with
new K-band receivers in mid-2003.
The proposal to transform the VLA into the EVLA (Expanded VLA) has
been approved by the NSF. This phase of the VLA expansion will accomplish a
major instrumentation upgrade for the VLA receiving system, including: (1)
installation of InP HFET amplifiers to cover all frequencies from 1.2 to 50
GHz, (2) installation of a fiber optic IF transmission system with a bandwidth of
at least 4 GHz, and (3) installation of a correlator with capability for both
broadband continuum observations (4-8 GHz per polarization) and the very high
frequency resolution needed for spectroscopy of thermal lines. This phase will
increase the sensitivity of the array by a factor of ten or more and will be
completed by the year 2010.
A second phase of the VLA expansion plan would connect the imaging
scale of the VLA with that of the VLBA. This requires the addition of
approximately eight new antennas within 300 km of the VLA. Each of these
antennas would be connected by optical fibers to the VLA correlator, forming a
real-time array of 37 antennas.
(http://www.nrao.edu/doc/vla/html/VLAhome.shtml)
Westerbork Synthesis Radio Telescope
(WSRT)
The new multifrequency front end receiver systems provide eight
observational windows between 250 MHz and 8.7 GHz. The DZB correlator system is
now operative, together with a 160 MHz dual-polarization IF system. In
tied-array mode the telescope is equivalent to a 95 m single dish, which
supports VLBI operations and pulsar observations using a state-of-the-art
pulsar processor. A major research effort is underway to investigate and
implement RFI suppression and cancellation instrumentation at WSRT. This
technology will be critical for the next-generation telescopes.
(http://www.nfra.nl)
2.2 Millimeter and Submillimeter Wavelength Facilities
Berkeley Illinois Maryland Association
(BIMA)
The BIMA Millimeter Array is a 10 antenna (6.1 meters in diameter)
aperture synthesis telescope, which operates at wavelengths of 3 mm and 1 mm,
at the Hat Creek Radio Observatory. The installation of high sensitivity
optical guidescopes on the elements of the BIMA array have facilitated a very
precise comparison of optical and radio pointing characteristics.
(http://bima.astro.umd.edu)
Caltech Submillimeter Observatory (CSO)
CSO consists of a
10.4-meter diameter Leighton radio dish situated in a compact dome near the
summit of Mauna Kea, Hawaii. In 2002, a background limited camera at 0.35 and
0.45 millimeters wavelength (SHARC II) was commissioned. The detector is a 12 x
32 bolometer array. The sensitivity is 4 times greater than that of SHARC I.
The heterodyne receivers
on the telescope were used to make the first detection of triply deuterated
ammonia (ND3) in the interstellar medium. No other molecules containing three
deuterium atoms have ever been detected in the ISM.
(http://www.submm.caltech.edu/cso/)
Delingha Millimeter Telescope
It is operated by Purple Mountain Observatory, Chinese Academy of
Sciences as an open facility of mm-wave radio astronomy. It is located at 97E
and 37N with an altitude of 3200m. The
random-enclosed telescope of 45-foot aperture is equipped with a low-noise
superconductor-Insulator-Superconductor (SIS) receiver at 85-115 GHz. The
backend consists of three AOS spectrometers. The telescope has been used in the
studies of Galactic interstellar molecular clouds, star forming regions,
masers, HII regions, lower- and high mass protostars, late-type stars, SNRs,
and Galactic structures.
The telescope is open to the outside researchers through routinely
accepted proposals and is operated every year from September to next June.
(http://www.pmodlh.ac.cn)
Institut de Radioastronomie Millimetrique
(IRAM)
IRAM - Interferometer
A substantial overhaul of all six elements of the Plateau deBure
interferometer was completed in September 2002. In spite of the difficulties
imposed by access to the site by helicopter and ground transportation, the
interferometer is expected to support observations in three configurations in
the winter 2002-2003. An important recent result was the imaging of Vega and
its dusty debris envelop at 3 and 1.3 millimeters wavelength. The envelope
showed two dust concentration which may have been created by the dynamical
influence of an unseen planet in a highly eccentric orbit that traps dust in
principal mean motion resonances.
Substantial progress has been made in the correction of images for
the effects of atmospheric phase fluctuations by the use of measurements at 13
millimeters of the atmospheric water vapor content. (http://www.iram.fr/IRAMFR/)
IRAM - 30m Telescope
Major instruments at the 30-m telescope include: (1) a set of four
dual polarization receivers at 3, 2 1.3 and 1.1 mm wavelength; (2) a 9 pixel
heterodyne receiver array operating at 0.9 mm wavelength (HERA); and a 117
pixel bolometer array at 1.2 mm wavelength (MAMBO-2). In addition a powerful
spectrometer was commissioned (VESPA), which can support HERA with 2000 channels
per pixel or the eight standard heterodyne receivers with 3000 channels per
receiver. Remote observing can be carried out from Madrid, Bonn, Granada,
Grenoble and Paris. (http://www.iram.fr/IRAMES)
James Clerk Maxwell Telescope (JCMT)
SCUBA continues to be the most used instrument on the 15-m
telescope. Several new instruments have been funded. These include: (1) ACSIS,
a large spectrometer designed to handle heterodyne arrays; (2) HARP-B, a 16
element heterodyne array operating in the 0.85 mm band, undergoing test during
the summer of 2002; (3) SCUBA-2, a 0.45/0.85 millimeter wavelength, wide field
imager using state-of-the-art technology and multiplexed readouts; (4) THUMPER,
a 7 element 0.2 millimeter wavelength array, to be commissioned in early 2003;
and (5) ROVER, a new heterodyne polarimeter.
(http://www.jach.hawaii.edu/JACpublic/JCMT)
Nobeyama Millimeter Array
The Millimeter Array now consists of 6 transportable 10-m
antennas, which are equipped with cryogenically cooled SIS receivers at 3, 2 and
1.4 millimeter wavelengths. The array can be used with the 45-m telescope as a seventh element to
produce a 21 baseline array at all wavelengths (RAINBOW). A new FX correlator
is capable of extremely high resolution of 31 kHz resolution over a 32 MHz band.
(http://spaceboy.nasda.go.jp)
Owens Valley Radio Observatory Millimeter
Array (OVRO)
The OVRO millimeter wavelength interferometer consists of six 10.4
meter telescopes with 35 micron surface accuracy. The Array is located on the
floor of Owen valley at an elevation of 1200 m, and operates at 3 and 1.4 mm
wavelength. Work has begun to combine the Array with the BIMA array at a higher
site in the White Mountains to form a new array, CARMA, which will have 15
elements. The wavelength coverage will be extended to 0.87 mm. Operation is
expected to begin in 2005. (http://www.ovro.caltech.edu/)
Submillimeter Array (SMA)
SMA is nearing completion on Mauna Kea and has begun limited
scientific observations. Five of the projected 8 telescopes are in operation at
1.4 and 0.85 mm wavelength. Images of CO emission in Mars, M51, as well as many
late type stars and regions of star formation in the Galaxy have been made. The
flux density of SgrA* has also been monitored at 1.4 mm. In addition,
preliminary observations with three elements at 0.44 millimeters have been
made. Remote operation of the array can
be carried out from Hilo, Cambridge and Taipei.
Completion of the array is expected in 2003.
(http://sma-www.harvard.edu)
2.3 Very Long Baseline Interferometry
The VLBI European Network (EVN) has concentrated on increasing
the reliability of its operations while at the same time increasing the
sensitivity of the observations carried out. A data rate of 512 Mbps is now a
routine mode of operation, although limited by tape supply. The Shanghai
telescope is now fully operational within the EVN; Urumqi in northwest China is
approaching this status. Phase referencing observations are routine, following improvement of the correlator
model and the station positions. A pipeline for calibrated data for both
continuum and spectral line from the EVN has been put into operation at the
Joint Institute for VLBI in Europe (JIVE). The capabilities of the EVN Mk4 data
processor at JIVE have been steadily improved for both continuum and spectral
line observations.
Over-sampling is operational; pulsar gating and speed-up
correlation have been tested successfully but are not yet operational. A
project has begun to increase the current output data rate from 1.5 Mbyte/sec
to 160 Mbyte/sec for wide-field imaging, recirculation for high spectral line
resolution, and pulsar work.
The VLBA 3-mm observing band has reached its initial goal, with
receivers having been installed at eight of the ten stations. A holography system has been developed with
a goal of improving aperture efficiency of the VLBA antennas to 30% at 3
mm. Since the necessary surface upgrade
will require refiguring of the subreflectors, a precision mechanical
measurement system also has been procured.
The first VLBI observations have been carried out on baselines to the
Green Bank Telescope and Arecibo Observatory.
Finally, a data-calibration pipeline has been developed and is being
used for all continuum data between 1.4 and 15 GHz; extension to higher
frequencies and spectral-line observations is well under way.
The end of the era of tape recorders for VLBI recording and data
transport appears to be in sight. Developments in PC hard-disk technology
(capacity and cost) have made this medium competitive with tape and potentially
much easier to use. The MIT Haystack Observatory with financial support from
NASA, NRAO, the EVN and other sources has developed the Mk5 system based on
disks, and has deployed a prototype version. Both the NRAO and EVN have
initiated programs to develop the necessary interfaces between the Mark 5
disc-based recording system (or alternatives) and the VLBA and EVN telescopes
and correlators. Fibre-linked networks
for VLBI are in use in Japan, replacing both tape and PC hard-disk, and
providing real-time VLBI for the first time. The first experimental
fibre-linked systems are under development in Europe and the US and can be
expected to assume greater importance in the coming few years. An international e-VLBI Working Group has
been established.
The HALCA satellite continued to produce high resolution images of
AGN, masers and pulsars for individual observers, as well as to carry out a
continuum survey. In 2002 the continuum
survey was given the highest priority, with observations continuing at a rate of about 10
observations per month. Studies have continued on the second-generation VLBI telescope in orbit, VSOP-2. The
RadioAstron project is now the highest priority space astronomy project in
Russia with an expected launch date of 2006. It will observe at wavelengths of
92, 18, 6 and 1.35 cm.
The southern hemisphere VLBI network, and the Coordinated
Millimeter VLBI Array continued to operate during the period.
(http://www.evlbi.org,
http://www.aoc.nrao.edu/vlba/html,
http://www.vsop.isas.ac.jp)
3.
Telescopes Under Construction and Under Development
Atacama Large Millimeter Array (ALMA)
ALMA is a joint project of the U.S. National Science Foundation
and the European Southern Observatory. Funding for the construction of the
observatory was approved in July 2002 by both partners and a formal agreement
will be signed in Chile in October 2002. When operational, hopefully in 2011,
ALMA will consist of 64 12-meter antennas, capable of astronomical observations
in all atmospheric windows from 30 - 900 GHz.
The array will be located in the Chajnantor region of the Andes in
Northern Chile, 60 km east of the village of San Pedro de Atacama. Over the
last two years enormous effort has been expended in the design and development
phase. With the recent approval of funding the project is now moving towards
the construction phase (http://www.eso.org/projects/alma).
Large Millimeter Telescope (LMT)
The Large Millimeter Telescope Project is the joint effort of the
University of Massachusetts and the
Instituto Nacional de Astrofísica, Optica, y Electronica (INAOE) in Mexico. The
LMT is a 50m diameter millimeter-wave telescope designed for principal
operation at wavelengths between 1mm
and 4mm. The telescope is being built atop Sierra Negra, a volcanic peak in the state of Puebla,
Mexico. Site construction and
fabrication of most of the major antenna parts is underway, with telescope
construction expected to be complete in
2004 (http://www.lmtgtm.org/)
The Low Frequency Array (LOFAR)
LOFAR is a low frequency radio telescope, being developed by a
consortium of three institutes. ASTRON in Dwingeloo (The Netherlands), MIT¹s
Haystack Observatory (USA) and the US Naval Research Laboratory (Washington
DC). The telescope will be a multi-element interferometer that consists of
about 100 phased array stations. The operating frequency will run from 10-240
MHz, allowing to probe beyond the Epoch
of Reionization to the era before galaxies formed . A key feature of the
telescope will be the ability to perform simultaneous full sensitivity
multi-beam observations (max. 8 beams). The total collecting area will exceed a
square kilometer at the lowest frequencies. Locations for the array under
consideration are: the North-East of the Netherlands, South-West USA (Texas-New
Mexico) and Western Australia. A final site will be selected early in 2003.
First observations are scheduled for 2006-2007. (http://www.lofar.org)
Square Kilometer Array (SKA)
Astronomers from around the world are planning the next generation
of radio telescope, the Square Kilometer Array (SKA). The SKA will be a massive
undertaking, costing about 1 billion of US dollars. Several viable concepts for the design of the telescope exist and
are being aggressively pursued by engineering and research teams around the
world. The International SKA Steering Committee (ISSC) expects to select the
concept(s) which will deliver the best science in 2006. At the same time, the
ISSC also expects to select a site,
which will most probably lie in a radio-quiet region of the globe. The SKA will
address an enormous range of science, for example it will study faint
radiogalaxy populations, and HI across the Universe. It will enable the first
true window to be opened on the transient sky. (http://www.skatelescope.org).
4.
Scientific Highlights 2000-2002
4.1 Our galaxy
Stellar radio emission
A recent review on radio emission from non degenerate stars has
been made by Guededel (2002). The brown dwarf LP944-20 was found to be a radio
emitter (Berger et al. 2001), although other brown dwarfs surveyed have not
been detected. The microquasar LS 5039 was proposed to be associated with an
unidentified source in the Energetic Gamma Ray Experiment Telescope (EGRET) on
board the COMPTON-Gamma Ray Observatory satellite, suggesting that microquasars
may be associated with these enigmatic sources (Paredes et al. 2000).
Circularly polarized radio emission was detected from the radio-jet X-ray
binary SS 433 (Fender et al. 2000). Proper motions have been detected along the
axis of several thermal jets (Rodriguez et al. 2000; 2001).
The radio emission from several of the massive stars forming the
Arches cluster near the galactic center was detected (Lang, Goss, &
Rodriguez 2001). The first direct measurement of the speed of energy flow
within an astrophysical jet was observed in Scorpius X-1 (Fomalont, Geldzahler,
& Bradshaw 2001).
Pulsar
Many exciting results have been achieved in pulsar research during the years 2000-2002. The Parkes Multibeam Survey was completed, resulting in a real boom of
pulsar counting: 650 new pulsars,
nearly doubling the sample (Morris et
al 2002; Manchester et al 2001).
Besides the quantitative aspects, the new sample contains a significant number objects intrinsically
rare, but very interesting for their
applications: new relativistic binary
systems (Lyne et al 2000; Kaspi et al 2000), young energetic pulsars, potential counterparts of the
Galactic EGRET sources (D'Amico et al
2001a), a radio pulsar in a binary system with
a very massive companion (Stairs et al 2001).
A new sensitive search of the Galactic Globular Cluster
systems carried out at Parkes has
produced 12 new millisecond pulsars in
6 globular clusters which where not previously
known to host radio pulsars. Among them there is a very intriguing
system, the eclipsing binary
pulsar PSR J1740-5340 in NGC6397
(D'Amico et al 2001b) with a bright
stellar companion (Ferero et al, 2001) which shows evidence of tidal distortions, an effect which was not observed
so far in binary pulsars. Another
outstanding result was the discovery of
millisecond pulsars in the core of NGC 6752
showing a large acceleration toward the cluster center, indicative of the presence of a high density of unseen
dark remnants in the cluster core,
probably black holes.
Precise timing
observations of a substantial sample of millisecond pulsars discovered in the globular cluster 47 Tucanae (Freire et
al 2001) has resulted in the first detection of ionized gas in a globular cluster.
Radio Supernovae
Bright and relatively nearby radio supernovae can be imaged and
resolved with cm-VLBI. Expansion rates and decelerations have been measured in a number of them: SN1993J
(Marcaide et al. 1997; Bartel et al.
2000), SN1979C (Marcaide et al. 2002), and SN1986J (Perez-Torres et al. 2002). Also a limit has been placed on the
deceleration of young supernova remnant 43.31+592 in M82 (McDonald et al.
2001). The Australia Telescope Compact Array has monitored the expansion of SN1987A (Gaensler et al. 1997; Manchester
2002). SN1993J in M81 is the best studied case: its shell structure is very
symmetric and expands self-similarly as a first approximation. SN2001gd,
spectrally very similar to SN1993J but
3 times further away, is also being studied with VLBI.
Molecular Clouds and Star forming regions
The first evidence for a massive protostar with an accretion disk
was provided by Shepherd et al. (2001).A detailed study to disentangle the
contributions of circumstellar envelope and disk in young stellar objects was completed
by Looney et al. (2000). Millimeter observations of star forming regions with
arrays have been very successful in detecting dense cores that probably are the
site of future star formation (Phillips et al., 2001).
A major observational effort now under way is the search for
high-mass protostars, and several candidates have been proposed (e. g. Furuya
et al. 2002; Zhang et al. 2002). A complete search for dense cores in Taurus
has been accomplished (Onishi et al. 2002). A new complete CO survey of the
Milky Way is finished (Dame et al., 2001).
The first results of the Submillimeter Wave Astronomy Satellite
were presented in volume 539 of the ApJ
Letters. The simplest sugar,
glycolaldehyde (CH2OHCHO),was detected in Sagittarius B2(N) (Hollis et al., 2000).
4.2 Extragalactic sources
Line emission and Absorption
In the last 3 years, several advances may be noted: the detection
of CO line emission well outside the optical disk of galaxies, and in tidal
dwarfs (Braine et al 2001), or the detection of CO in low surface brightness
galaxies, after long and negative searches (Matthews & Gao 2001). The first
results of a large survey of the CO line with the BIMA interferometer are
appearing, revealing the radial distribution, and the relation to bars, spirals,
etc.. Unexpected disk structures in the distribution of CO gas have been detected in a number of elliptical
galaxies (BIMA-SONG, 45 galaxies Regan
et al. 2002). After several attempts to detect molecular gas in cooling flow
galaxies at the center of galaxy clusters, CO line was detected in a few
cooling flow galaxies (Edge 2001), revealing an order of magnitude of the
molecular mass. A survey of atomic CI in galaxies is compared to CO emission
and their relative properties as coolants estimated (Gerin & Philips
2000). The first detection of molecular
gas in the shells of CenA has been reported, challenging the formation
mechanism of shells (Charmandaris et al. 2000). This detection may explain the
previous detection of HI in shells, and support the phase wrapping mechanism.
Active Galaxies and Quasars
Intraday variability in compact extragalactic radio sources has
been shown conclusively to be caused by interstellar scintillation, rather than
intrinsic variations within the quasar itself.
Simultaneous observations of J1819+3845 with the VLA and Westerbork have
shown that the variability seen at the two telescopes is offset in time by
minutes, implying that the different parts of the Earth successively move
through the same scintillation pattern.
This indicates that the compact radio source sizes in scintillators are
just a few microarcseconds, smaller than can be imaged by any telescope
(Dennett-Thorpe and de Bruyn, 2001).
Interstellar scintillation is also supported by the recent finding with
the VLA that weaker radio sources scintillate more strongly, presumably because
they are smaller in angular extent (Lovell et al. 2002).
Dan Harris and collaborators (2002) report the discovery of X-ray
emission aligned with the northern radio jet of the low power radio galaxy 3C
129, imaged by the VLA. Based on
comparisons with other X-ray detections in low power radio galaxies, the
favored explanation for the observed X-rays is synchrotron emission.
Marscher et al. (2002), using monthly imaging with the VLBA
combined with RXTE monitoring, find that the X-ray emission from 3C120 dims
every 10 months or so, followed a month later by a new radio component emerging
from the nucleus. This is probably due to parts of the inner accretion disk
breaking off and plunging into the black hole, fueling the emission of a new
blob in the radio jet. This phenomena
is also seen in microquasars within our own Galaxy, and indicates that the same
phenomenon is occurring over a range of about 109 in black hole
masses.
Galaxy Clusters, Interactions
In the past 3 years significant advances have been made on the
study of non-thermal processes in galaxy clusters. The properties of cluster
radio galaxies have been investigated to understand how they are affected by
the dynamic gaseous environment, in particular when the clusters are in the
process of merging (see Feretti & Venturi 2002 for a review). It was
confirmed that the environment does not increase the probability for elliptical
galaxies to develop a radio source. On the contrary, the cluster environment
could play an important role in the production of starburst emission.
Perhaps the most intriguing cluster sources are the diffuse
large-scale radio halos and relics (e.g. Coma C). These radio sources establish
the presence of relativistic particles and magnetic fields in the Intra Cluster
Medium. A wealth of radio and X-ray
data have allowed to sharpen our view of the processes involved (see review by
Giovannini & Feretti 2002). New
halos and relics (also in distant clusters) were found from radio surveys (NVSS and WENSS) allowing statistical
studies. Individual objects have been studied in detail, models have been
developed.
The clusters hosting radio halos are massive rich clusters with
high temperature and high X-ray luminosity. The diffuse sources appear to be
linked directly to the cluster merger activity and to the accompanying
turbulence and shock reacceleration of the radio emitting particles.
The cluster large scale magnetic fields have been investigated from studies of the Rotation
Measure of radio sources in or behind clusters. These studies have revealed that magnetic fields of strength of
the order of microGauss, and coherence length of the order of kpc, are
widespread in all clusters, even those not hosting radio halos or relics (see
Carilli & Taylor 2002 for a review).
The magnetic field intensities obtained by different approaches
(Rotation Measure, equipartition, Inverse Compton) are presently discrepant and
they still need to be reconciled.
4.3 Cosmology
Extragalactic Surveys
The Northern all-sky surveys carried out in the last '90s (NVSS,
FIRST, WENSS) are completed and fully released. They provide a unique view of
the radio sky at mJy flux levels.
The Sydney University Molonglo Sky Survey (SUMSS) is still ongoing and at present is 53% complete: an area of 3700 sq. degr. of the
sky south of declination -30° has been imaged at 843 MHz, down to and an rms
noise level of about 1 mJy/beam. In the mean time rapid progress has been made
in exploring the radio sky at lower
flux levels. At sub-mJy levels several surveys are available on scales of a few sq. degrees: f.i. the Phoenix
survey (ATCA), the Bootes field (WSRT), the ELAIS North (VLA) and the ELAIS
South (ATCA). The largest one is the ATESP 1.4 GHz survey carried out with the
ATCA, which covers an area of 26 sq. degr. with an rms noise level of about 80
microJy.
At micro-Jy levels, larger
and deeper surveys are in progress. After the HDF North (Richards et al 2000),
the HDF South has been covered at several frequencies with the ATCA (ongoing
analysis). Other larger fields are the VLA-VIRMOS field (17 microJy rms noise
over 1 sq. degr.) and the extension of the Phoenix survey which collects now
about 2000 sources with fluxes down to 60 microJy (both studies are close to
publication). Deeper VLA surveys (down to rms noise levels of the order of 1
microJy are being produced.
High-z Radio Galaxies
Submillimeter observations of deep fields has recently revealed the that the 850
microns background is essentially due to distant ultraluminous infrared
galaxies. The spatial positions of these objects are obtained by
radio-continuum surveys, since faint radio sources trace remote starbursts; the
redshift of these high-z sources have been estimated by a radio-photometric
redshift (ratio between centimetric and submillimetric flux), and are between 1
and 3 (Barger et al 2000). CO and dust emission were detected in new high
redshifts radio galaxies and quasars (Papadopoulos et al 2000, Carilli et al
2002). A radio-polarimetric survey of high-z radio galaxies suggests that the
fraction of powerful radio galaxies with extreme Faraday rotation increases
with redshift, as would be expected if their environment was denser at earlier
epochs (Pentericci et al 2000).
Gravitational Lenses
The
Cosmic Lens All-Sky Survey (CLASS) and
JVAS (Jodrell Bank-VLA) surveys are the
largest and most successful searches for arcsecond-scale radio-loud
gravitational lens systems. Among several thousand sources examined, 19 confirmed and 3 candidate
systems, currently under analysis, have
been so far discovered. The time delay measurements between variations of two different components leads to the calculation of the Hubble expansion constant. A
preliminary result from a lens system
studied at Jodrell gives a value for Ho ~ 65 km/s/Mpc. In addition it
is possible to model the mass distribution of the intervening
galaxies, and to estimate their masses.
See www.jb.man.ac.uk/research/gravlens for references.
A similar survey is being carried out in the southern hemisphere
with the VLA and ACTA telescopes. So far 4 confirmed and 3 candidate systems
have been discovered.
Cosmic Microwave Background
The CBI (Cosmic Background Imager) results released this year were
the first to clearly show the damping tail of the anisotropy power
spectrum. The CBI also saw evidence of
excess power on fine ~ 200-3500) angular scales beyond that expected from
primary density fluctuations. The most likely explanation for it is the
Sunyaev-Zel'dovich effect (SZE) from
distant clusters. John Carlstrom, on behalf of the DASI (Degree Angular Scale
Interferometer) team, announced the discovery of polarization in the Cosmic
Microwave Background. The observed polarization, produced by electron
scattering at recombination, confirms current models based on the angular power
spectrum.
The MAP (Microwave Anisotropy Probe) satellite has been orbiting
for a year now, and has completed the first-pass all sky maps at 22, 30, 40,
60, and 90 GHz. Maps and analysis are expected to be released in January, 2003.
The TopHat telescope, which rides on the top of a balloon, had a
successful flight in the South Pole last January, observing structure on scales
of 0.33-48 degrees in five bands between 150 and 650 GHz.
ACBAR (Arcminute Cosmology Bolometer Array Receiver has obtained a
lot of fine ~60-2700 scale CMB data this year.
5. Radio
Frequency Protection
One poorly known but very important task of radio astronomy is the
protection of the radio
astronomical frequencies. It is becoming increasingly difficult to protect
radio astronomy observatories from interference as the use of the electromagnetic
spectrum increases for both terrestrial and space-borne communications.
In the last three years,
international committees (IUCAF, CRAF, CORF, etc.) have devoted a large effort in
studying and coordinating the
requirements of radio astronomers and to make these requirements known
to the national and international bodies responsible for frequency allocations.
Meanwhile, other groups have studied technological solutions for
interference mitigation: interference rejection schemes, novel types of
modulation manifesting inherently low out-of-band emissions, state-of-the-art
RF filter technology and how it may be advanced, antenna null steering,
interference recognition, and data editing.
Acknowledgments : This report was compiled by Lucia
Padrielli from information supplied by Francoise Combes, Nichi D'Amico, Philip
J. Diamond, Luigina Feretti, Juan-Maria Marcaide, Jim M. Moran, Isabella
Prandoni, Luis Rodriguez, Richard
Schilizzi, Jean L. Turner
Lucia Padrielli
President of the Division
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