Main results of the experimental and theoretical research completed in 2010
Search and localization of water rich areas near the lunar poles based on measurements of Lunar Exploration Neutron Detector (LEND), a Russian instrument aboard NASA’s Lunar Reconnaissance Orbiter
LEND lunar neutron telescope’s investigation and data processing in 2010 allowed to locate a number of areas, tens of kilometers in size, with rich hydrogen
abundances corresponding to water content of 0.5-4%. It was found that these areas do not correspond to permanently shadowed regions on the lunar poles,
despite the expectations. This discovery imposes a number of questions on the nature of moon’s water, its source and mechanisms of water transport and
accumulation. It will have big impact on the exploration of the moon.
|Image: Epithermal neutrons emission map above the
south pole of the Moon from the LEND instrument. Blue color corresponds to lower neutron emissions and thus higher hydrogen content.
Yellow and red areas show, correspondingly, higher neutron flux and thus lower hydrogen content in the lunar regolith. Moon’s topography is shown based on
LOLA laser altimeter data, white contour shows a permanently shadowed region and a white rhomb indicates LCROSS spacecraft impact location.
These results were obtained by a team of Space Research Institute scientists, I. G. Mitrofanov, A. B. Sanin, A. B. Varenikov, A. A. Vostrukhin, D. V. Golovin, A. S. Kozyrev, M. L. Litvak, A. V. Malakhov, M. I. Mokrousov, I. Nuzhdin, V. I. Tretyakov, also in collaboration with MSU Sternberg Astronomical Institute, Joint Institute for Nuclear Research in Dubna, NASA’s Goddard Space Flight Center, Arizona and Maryland Universities. This result is published in Science, vol. 339, p. 483 in 2010.
Observation and theoretical model of the Earthward electric field in the magnetotail
Quasi-stationary electric field in the outer magnetosphere of Earth drives the global plasma convection but is too small to be detected directly. Multi spacecraft Cluster project observations helped to reveal a new earthward electric field in the thin current sheet of the Earth magnetotail. We consider the statistics of 59 thin current sheet crossings observed by CLUSTER spacecraft. It is shown that the sum of electron diamagnetic and curvature drifts can explain less than a half of the value of electron bulk velocity. The remaining part of electron velocity is thus related to the Ex õ Bz cross field drift.
The measurements of the typically negative shift of the central part of proton velocity distribution also confirm the existence of
positive Ex field. Thus experimentfl estimate of Ex is 0.1-0.2 mV/m. Finally we suggest the mechanism of Ex formation in the thin
current sheet based on a difference between motion of non-adiabatic ions and magnetized electrons in weakly 2D geometry.
This field plays an essential role in the redistribution of intensities of cross-tail proton and electron currents, resulting in observed unexpected domination of electron currents.
Zelenyi, L. M., A. V. Artemyev, and A. A. Petrukovich, Earthward electric field in the magnetotail: Cluster observations and theoretical estimates, Geophys. Res. Lett., 37, L06105, doi:10.1029/2009GL042099, 2010.
Ultra deep survey of the sky in hard X-rays, performed by INTEGRAL observatory
INTEGRAL observatory has completed the first and the most sensitive survey of the sky in hard X-ray energy band. New method of analysis of data obtained by IBIS telescope of INTEGRAL observatory was developed in IKI. This method allowed us for the first time to overcome limitations, caused by severe systematic uncertainties and allowed us to dramatically improve sensitivity of the survey. Now we are able to reach almost the theoretical limit of the sensitivity, which is set only by photon counting statistics. This survey provides us a very powerful tool to study the formation and history of evolution of compact objects in our Galaxy. Success of INTEGRAL observatory in discovering a new X-ray sources in our Galaxy can be compared only with success of first dedicated X-ray observatory UHURU, launched almost 40 years ago. According to the published catalog of detected sources INTEGRAL has detected 521 objects, among which 262 are located in our Galaxy or in nearby galaxies (like Large and Small Magellanic Clouds), 219 – active galactic nuclei in more distant galaxies, 40 sources are still not identified.
Map of the Galactic Bulge region, obtained by INTEGRAL observatory over seven years of observations. Artefacts, clearly visible on previous map of this region, are removed with the help of newly developed method of data analysis. The map has extremely high dynamic range - the faintest sources on this map (the flux about 0.26 mCrab) are 3000 times fainter than the brighest source.
Authors: R.Krivonos, M.Revnivtsev, S. Grebenev, S. Tsygankov, S. Sazonov, A. Vikhlinin, M. Pavlinsky, E. Churazov, R. Sunyaev.
- R.Krivonos, et al. "INTEGRAL/IBIS 7-year All-Sky Hard X-ray Survey. I. Image reconstruction", Astronomy and Astrophysics, v. 519, p. A107, 2010.
- R.Krivonos, et al. "INTEGRAL/IBIS 7-year All-Sky Hard X-ray Survey. II. Catalog of Sources", Astronomy and Astrophysics, v. 523, p. A61, 2010.
Progenitors of type Ia supernovae in early type galaxies
Type Ia Supernovae are used as standard candles to determine the cosmological distance scale. As such, they played a major role in establishing that the expansion of
the Universe accelerated with time, the fact that directly pointed at the existence of the dark energy. However, the nature of their progenitors is still unknown. Although
there is a wide agreement that SNeIa are associated with the thermonuclear disruption of a CO white dwarf, details are still being debated. The nuclear runaway that leads to
the explosion could start in a white dwarf gradually accumulating matter from a companion star until it reaches the Chandrasekhar limit, or could be triggered by the
merger of two white dwarfs in a compact binary system. The X-ray signatures of these two possible paths are very different. Whereas no strong electromagnetic
emission is expected in the merger scenario until shortly before the supernova, the white dwarf accreting material from the normal star becomes a source of copious Xrays
for about 10^7 years before the explosion. This offers a means of determining which path dominates. We showed that the observed X-ray flux from six nearby
elliptical galaxies and galaxy bulges is a factor of ~30–50 less than predicted in the accretion scenario. We conclude that no more than about five per cent of type Ia
supernovae in early-type galaxies can be produced by white dwarfs accreting from a companion star in a binary systems and detonating at the Chandrasekhar limit.
A multi-wavelength image of Andromeda galaxy composed of X-ray data from NASA's
Chandra X-ray Observatory (gold), optical data from the Digitized Sky Survey (light blue)
and near-infrared data from the Spitzer Space Telescope (red). The inset box shows Chandra
X-ray image only. Bright compact sources seen on the Chandra image are accreting neutron
stars and stellar mass black holes located in Andromeda galaxy. They are surrounded by
extended emission that is the sum of emission from hot ionized interstellar medium and
combined emission from a large number of faint compact sources. Their total luminosity is by
a factor of ~30-50 smaller than should have been expected if all type Ia supernovae were
associated with white dwarfs accreting from a donor star in a binary system and detonating at
the Chandrasekhar limit. (Image credit – Chandra CXC)