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Research at VATLY
P.N. Diep
for P.T. Anh, P. Darriulat, P.N. Dong, D.T. Hoai, P.T. Nhung,
N.T. Phuong and N.T. Thao
(Institute for Nuclear Science and Technolgy, Hanoi, Vietnam)
Quy Nhon, August, 2013
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The Pierre Auger Observatory
Particle detectors at home
The VATLY Radio telescope
Radio astronomy
Teaching and training
Conclusion
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THE PIERRE AUGER
OBSERVATORY
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VATLY and PAO
Vietnam Auger Training LaboratorY was created twelve years
ago (with material and instruments given to us as gifts from CERN
research teams of all over the world) in association with the Pierre Auger
Observatory (PAO).
The PAO covers 50×60 km2 in Argentina and studies the ultra
high energy cosmic rays (UHECRs, 1018 to 20 eV). UHECRs are
extragalactic; their sources and nature are unknown. The PAO includes
1700 Cherenkov ground detectors, 1.5 km apart from each other, and 24
UV telescopes measuring the shower fluorescence in the atmosphere.
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The PAO has obtained evidence for the GZK cut-off (photoproduction
on the CMB) and for a positive but weak correlation with nearby
galaxies (Centaurus A).
Mass composition: at higher energies, “all sky” move from protons to Fe,
but insufficient statistics for Cen A and AGN’s to be confirmed.
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VATLY contributions include:
A study of low amplitude signals and the detection of decay electrons
from stopping muons; A measurement of shower divergences;
Contributions to the identification of the primaries (protons or iron) from
the muon density on ground; Identification of primaries from Cen A;
Response of the PAO PMTs as a function of photon impact (in Hanoi).
Detailed studies of long term stability and ageing of the PAO detectors;
Shower development studies.
The next generation of cosmic ray observatories will take at least one
decade to mature. In the past two to three years, the interest of the team
has been progressively shifting away from cosmic ray studies to radio
astronomy where the time scale and size of the research projects are
better adapted to a small, young and isolated group such as ours.
Without the Pierre Auger Collaboration, we would not have been able to
take off and come of age: our gratitude for their constant and friendly
support is immense.
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In our conversion from cosmic ray physics to astrophysics
and radio astronomy, we enjoy moral and material
support from astrophysicists, in particular in France and
at IAU, whom we express here our deepest gratitude.
The choice of radio astronomy as a particular branch of
astrophysics was dictated by a combination of physics
motivations (its presence at the forefront of most current
explorations on the frontier of modern astrophysics) as
well as by arguments of convenience (influence and
encouragements of Pr NQ Rieu, presence in Viet Nam of
Drs DV Trung and PB Ngoc, near impossibility to make
observations in the visible under the foggy tropical sky).
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PARTICLE DETECTORS
AT HOME
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Early studies explored some features
of the cosmic ray flux in Hanoi
where the rigidity cut-off reaches its
world maximum of 17 GV. In
particular, we measured the muon
flux, its zenith angle dependence and
the east-west asymmetry.
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We assembled a replica of a PAO ground detector on the roof of the
laboratory and added three smaller counters allowing for an
unbiased shower trigger. It is used for training and for making
detailed studies of its response.
#4
#3
80
120
162
#6
#5
Cable hole
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THE VATLY
RADIO TELESCOPE
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Three years ago, we acquired a 2.6 m diameter radio telescope tuned
on (and around) the 21 cm hydrogen line. It has been used to map HI
in the disk of the Milky Way and is currently taking data on the Sun
at its maximum of activity.
Accurate frequency spectra are collected every 8 seconds
displaying very clearly the 21 cm line.
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Velocity Doppler spectra have been collected along the disk of
the Milky Way over three quarters of the galactic longitude.
They show evidence for differential rotation.
Doppler velocity wrt Sun
Each spectrum has been reduced into peaks associated with
different clouds of atomic hydrogen.
Galactic longitude
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A map of atomic hydrogen in the Milky Way disk has been
constructed and compared with the known
arm and bar structure.
Peak positions
Map of power density
Spitzer
Ambiguous
Unambiguous
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The Sun, which is this year at its maximum of activity, has been
tracked for several months. A joint analysis of the collected data
with similar data taken by the Learmonth Solar Observatory in
Australia has shown the presence of flares and has given evidence
for mHz oscillations at the percent level (published in Solar
Physics); additional observations are necessary to understand their
origin (see P.T. Nhung’s presentation at the Conference).
Hanoi
Learmonth
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The peculiar position of Ha Noi on the geomagnetic equator, which is
causing the high rigidity cut-off for cosmic ray detection, is also causing
an exceptionally high scintillation index (meaning strong
inhomogeneities in the ionosphere) which might be a source of
multipathing (interferences between different photon paths).
HA NOI
LEARMONTH
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RADIO
ASTRONOMY
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In the context of two PhD theses made under joint supervision
with astrophysicists abroad (where the students spend 4 months a
year during three years), we collaborate with French institutes on
the study of data collected on large installations, in particular the
Plateau de Bure radio interferometer (PdBI).
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Under supervision of Dr Frederic Boone (IRAP, Toulouse) Tuan
Anh studies the host galaxy of a gravitationally lensed high
redshift quasar (z~2.8, look back 11.3 Gyr), RXJ0911. Detection
of the CO(7-6) line measures its gas content and the continuum
below its dust content, providing useful information on the star
formation rate in such early galaxies.
HST
G’
A3
A2
G
B
A1
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Lensing is complicated by the fact that the extended source
overlaps the lens caustic. We studied this peculiar situation in
detail (published in Research in Astronomy and Astrophysics)
~3”
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The results show that the source has a radius of 850±120 pc on the line
(~7 s.d.) and 260±130 pc (only 2 s.d.) in the continuum.
They also provide evidence for ellipticity and for a significant velocity
gradient (molecular outflow and/or rotation)
(Preliminary results published in Astronomy and Astrophysics Letters)
Ellipticity: 3.3 s.d.
away from circular
Evidence for velocity gradient
at 4.5 s.d.
Pot. 2
No velocity
gradient
Pot. 1
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arcsec
Under supervision of Dr Thibaut Le Bertre (LERMA, Paris) Hoai studies
an Asymptotic Giant Branch star in its thermal pulsing phase, RS Cnc,
using high resolution PdBI data on the CO(1-0) and CO(2-1) lines and
VLA data on HI. The star features a bipolar molecular outflow with a
wind velocity of ~8 km/s, superimposed on a lower velocity wind (~2
km/s). Detailed studies of the velocity spectra allow for constructing a
model of the star atmosphere accounting for many, but not all, of the
observed features.
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1.4 mas
1.4 mas
20 km/s
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TEACHING AND
TRAINING
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From the beginning we have given high priority to the promotion
of astrophysics in Vietnam, from where it is essentially absent,
by giving university lectures at the Hanoi University of Sciences
(Intron to astrophysics and cosmology); lectures at Summer
Schools in Hanoi (Intron to cosmology, IAU), in Da Nang (Black
holes, recent advances, VSOP/CNRS), in Saigon and Quy Nhon
(Intron to cosmic rays, IAU); Public lectures in Hanoi (Ha Noi à
l’écoute du cosmos) and in Saigon (Astrophysics and Vietnam).
We now contribute lab work (SRT, particle detectors, radiowaves)
to the University of Science and Technology of Hanoi master
Space & Applications (Alain Maestrini, Yannick Giraud-Heraud
et al).
In May this year, we invited to Ha Noi F. Combes, T. Le Bertre
and F. Boone to give lectures on topics related to the PhD
research work of Tuan Anh and Hoai.
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We do our utmost to establish close contacts with astronomers and
astrophysicists in the region and abroad.
In particular with the two astrophysicists doing active research in
Vietnam (Pr Dinh Van Trung in Ha Noi and Pr Phan Bao Ngoc in
Saigon) and with Pr Nguyen Quynh Lan who is heading the Department
of Astronomy at the Ha Noi University of Education.
Several VATLY members have attended Summer schools on astrophysics
in Ha Noi, Saigon, Grenoble and Granada (Tuan Anh and Hoai, IRAM),
in Castelgandolfo (Hiep, Pontifical Academy), in Li Jiang (Tuan Anh,
IAU) and/or astrophysics/cosmology conferences in the region (the
whole team in Vinh, Nhung and Diep in Quy Nhon, Thao in Malaysia,
Hiep and Nhung in Philippines, Tuan Anh in Thailand, Nhung and Diep
in China).
We joined SEAAN, the South East Asia Astronomy Network and
SEAYAC, the South East Asian Young Astronomers Collaboration and
have strongly contributed to the creation of a Vietnam Astrophysics
Group collecting the few of us who, in Vietnam, are acting for the
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promotion of training and research in modern astrophysics.
Undergraduate dissertations
Diep
2003
Study of the effect of
atmospheric pressure on the
cosmic muon rate in Ha Noi
Nhung
2003
Study of the effect of
temperature on the cosmic
muon rate in Ha Noi
Huyen
2005
Measurement of the muon
life time
V.Phuong
2006
A simple model of the
longitudinal development of
electromagnetic showers
K.Phuong The black hole in the centre of
2006
the Milky Way
The
2007
Optical properties of a
Cherenkov counter
Huong Galaxy collisions as possible
2008 sources of ultra high energy
cosmic rays
Lion Extensive air showers and LPM
2009
effect
Hoai X ray binaries and three body
2009
capture
Hiep
2010
Global warming and cosmic
rays
Dung
2011
Gravitational lensing and
Einstein rings
Phuong
2013
Construction, operation
and exploitation of a
scintillator hodoscope
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Master theses
Duong Measurement of the east-west
asymmetry of the cosmic
2003
muon flux in Ha Noi
Nhung
2006
Dong
2006
Diep
2006
Hoai
2012
Thao
2007
The detection of extensive
air showers in Ha Noi
Performance study of water
Cherenkov counters
The Cherenkov counters of
the VATLY laboratory
Detection and study of ultrahigh energy cosmic rays
An original approach to the
simulation of the development
of extensive air showers up to
extreme high energies
T. Anh
2010 Radio detection of the Sun
The Diffusive shock acceleration
2010
in SNR shocks
Hiep
2012
Observation of the 21cm
sky using the VATLY
radio telescope
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PhD Theses
(+Tuan Anh and Hoai in the mill)
Thieu
2006
Measurement of the angular distribution of the cosmic muon
flux in Ha Noi
Nhung
2009
Contribution to the study of extensive air showers using the
surface detector of the Pierre Auger Observatory
Dong
2010
Contribution to the study of the response to Cherenkov photons
of a large diameter photomultiplier tube and of its use at the
Pierre Auger Observatory
Diep
2010
Contribution to the identification of the nature of ultra high
energy cosmic rays at the Pierre Auger Observatory
Thao
2013
The VATLY Cherenkov detector and its response to electrons
and muons
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CONCLUSION
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Particle physics and astrophysics are not significantly
supported in Vietnam and only a very few individuals do
research in these fields, in the wake of contacts they had
with research teams abroad, where they studied for their
PhD. Experimental physics is still too often belittled with
respect to theoretical physics. Progress implies making the
science top deciders aware of the importance of
encouraging and supporting teams as much as individuals,
of making room for fundamental research at the frontier of
knowledge, of spelling out a clear scientific research
policy for the country. There is still a long way to go but
we hope for the future creation of a research institute that
would favor the progress and development of such
research.
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In order to survive, not to mention to progress, we need to
work in close collaboration with foreign colleagues.
I take this opportunity to express our deepest gratitude for
the help and support that they give us.
We receive invaluable support from the World Laboratory
in the form of fellowships.
In Vietnam, we enjoy financial support from the Institute
for Nuclear Science and Technology, which hosts us, and
from the National Foundation for Science and Technology
Development (NAFOSTED).
We are also grateful to IN2P3/CNRS, the French Embassy,
Rencontres du Vietnam and Odon Vallet fellowships for
occasional support.
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THANK YOU FOR YOUR ATTENTION!
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