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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Content• The Pierre Auger Observatory

• Particle detectors at home

• The VATLY Radio telescope

• Radio astronomy

• Teaching and training

• Conclusion

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THE PIERRE AUGEROBSERVATORY

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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 DETECTORSAT 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.

Cable hole

#4 #3

#6 #5

162

120

80

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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.

Each spectrum has been reduced into peaks associated with different clouds of atomic hydrogen.

Galactic longitude

Dop

pler

vel

ocit

y w

rt S

un

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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.

Unambiguous

Ambiguous

Spitzer

Peak positions Map of power density

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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).

LEARMONTH

HA NOI

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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.

A3

A2

A1G

G’

B

HST

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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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No velocity gradient

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

Pot. 1

Pot. 2

Evidence for velocity gradient at 4.5 s.d.

arcsec

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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 ANDTRAINING

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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

promotion of training and research in modern astrophysics.

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Diep 2003

Nhung2003

Huyen 2005

K.Phuong 2006

V.Phuong 2006

The 2007

Lion 2009

Huong 2008

Hoai 2009

Dung 2011

Hiep 2010

Phuong 2013

Undergraduate dissertationsStudy of the effect of

atmospheric pressure on the cosmic muon rate in Ha Noi

Study of the effect of temperature on the cosmic

muon rate in Ha Noi

Measurement of the muon life time

A simple model of the longitudinal development of

electromagnetic showers

The black hole in the centre of the Milky Way

Optical properties of a Cherenkov counter

Galaxy collisions as possible sources of ultra high energy

cosmic rays

Extensive air showers and LPM effect

X ray binaries and three body capture

Global warming and cosmic rays

Gravitational lensing and Einstein rings

Construction, operation and exploitation of a

scintillator hodoscope

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Duong 2003

Nhung 2006

Dong 2006

Diep 2006

Thao 2007

The2010

T. Anh2010

Hoai2012

Hiep2012

Measurement of the east-west asymmetry of the cosmic

muon flux in Ha Noi

Performance study of water Cherenkov counters

The Cherenkov counters of the VATLY laboratory

Detection and study of ultra-high energy cosmic rays

An original approach to the simulation of the

development of extensive air showers up to extreme high

energies

The detection of extensive air showers in Ha Noi

Radio detection of the Sun

Diffusive shock acceleration in SNR shocks

Observation of the 21cm sky using the VATLY

radio telescope

Master theses

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Nhung 2009

Dong2010

Diep2010

PhD Theses (+Tuan Anh and Hoai in the mill)

Measurement of the angular distribution of the cosmic muon flux in Ha Noi

Contribution to the study of extensive air showers using the surface detector of the Pierre Auger Observatory

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

Contribution to the identification of the nature of ultra high energy cosmic rays at the Pierre Auger Observatory

The VATLY Cherenkov detector and its response to electrons and muons

Thao2013

Thieu 2006

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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!