My research interests are in the areas of experimental space physics and high energy astrophysics. Specific topics in space physics include solar flares and solar cosmic rays; plasma phenomena in the interplanetary medium and the Earth’s magnetosphere such as collisionless shock waves, particle acceleration, magnetic reconnection, and wave-particle interactions; and lunar, planetary, and cometary studies. In high energy astrophysics I have concentrated on high resolution gamma-ray and hard X-ray spectroscopy and imaging of line and continuum emissions from the Sun, cosmic sources, and the Earth. These emissions provide detailed information on processes such as the interaction of accelerated particles with matter, radioactive decay of newly formed isotopes in supernovae, positron annihilation near black holes, cyclotron emission in the strong magnetic fields of neutron stars, etc. My approach is to develop innovative instruments and fly them on spacecraft, rockets, and balloons.
The Sun is the most powerful particle accelerator in the solar system, accelerating ions up to tens of GeV and electrons to hundreds of MeV. Solar flares are the most powerful explosions in the solar system, releasing up to 1032 - 1033 ergs in 102 - 103 s. The accelerated 10 -100 keV electrons (and possibly >~1 MeV ions) appear to contain a significant fraction, perhaps the bulk, of this energy, indicating that the particle acceleration and energy release processes are intimately linked. How the Sun releases this energy, presumably stored in the magnetic fields of the corona, and how it rapidly accelerates electrons and ions with such high efficiency, and to such high energies, is presently unknown. The hard X-ray/gamma-ray continuum and gamma-ray lines are the most direct signatures of energetic electrons and ions at the Sun, respectively. My group developed the High Energy Solar Spectroscopic Imager (HESSI) space mission (launch 2001), to provide high spatial (~2 arcsec) and spectral resolution (~ keV) of solar flare hard X-rays/gamma-rays, including the first hard X-ray imaging spectroscopy, the first high-resolution spectroscopy of solar gamma-ray lines, the first imaging above 100 keV, and the first imaging of solar gamma-ray lines.
We also have programs of high resolution gamma-ray and hard X-ray spectroscopy of cosmic and terrestrial sources. We have developed the most powerful High-REsolution Gamma-ray Spectrometer for astrophysics in the world (HIREGS), consisting of an actively shielded array of large, liquid-nitrogen cooled, segmented germanium detectors. In 1995 and 1998 HIREGS was flown on Long Duration Balloon Flights (LDBF) from Antarctica to study the Galactic Center, flaring black hole candidates, and several neutron star sources. The pulse-shape-discrimination electronics we developed for the SPectrometer Instrument (SPI) is the only US hardware on the International Gamma Ray Astrophysics Laboratory (INTEGRAL) mission, to be launched by the European Space Agency in 2002. We are presently developing germanium detectors with 3D spatial resolution for the next generation of astrophysical gamma-ray spectroscopy space missions. In 2000 an Antarctic LDBF with a small germanium spectrometer provided a survey of terrestrial MeV X-ray bursts, a phenomena we discovered in a 1996 balloon flight.
The interaction of the Earth’s magnetosphere with the solar wind leads to magnetic storms, aurorae, and the creation of the radiation belts. This interaction involves fundamental plasma processes, such as magnetic reconnection , particle acceleration, and the formation of collisionless shock waves, that are not well understood. Our space plasma group fabricated experiments for in situ measurements of plasma and fields on at least eight presently operating spacecraft located in the Earth’s magnetosphere and upstream, to study these processes. The measurements upstream also provide information on the origin and dynamics of the solar wind. We are developing new experiments for the STEREO mission (launch 2005) which involves two spacecraft in heliocentric orbit to study coronal mass ejections (CMEs), where a large part of the Sun’s corona is thrown into the interplanetary space.
We have instruments on the Mars Global Surveyor and Lunar Prospector spacecraft which are mapping the surface magnetic fields of Mars and the Moon by means of electron reflection magnetometry, i.e. the detection of electrons reflected back from a region of enhanced magnetic field strength. Although neither of these bodies have global magnetic fields now, the crust of both bodies is magnetized, indicating the presence of strong fields in the past. Correlations of the distribution of the near-surface magnetic fields with surface geological features can then give detailed information on the origin and history of Mars and lunar magnetism.
For more information about my research programs see “Research” on the Space Sciences Laboratory Website: http://ssl.berkeley.edu/
R. P. Lin and the HESSI Team, “The High Energy Solar Spectroscopic Imager (HESSI) small explorer mission for the next (2000) solar maximum,” SPIE Conf. on Missions to the Sun II 3442, 2 (1998).
J. E. Foat, R. P. Lin, D. M. Smith, F. Fenrich, R. Millan, I. Roth, K. R. Lorentzen, M. P. McCarthy, G. K. Parks, J. P. Treihou, “First detection of a terrestrial MeV X-ray burst,” Geophys. Res. Lett. 25, 4109 (1998).
R. P. Lin, D. L. Mitchell, D. W. Curtis, K. A. Anderson, C. W. Carlson, J. McFadden, M. H. Acuña, L. L. Hood and A. Binder, “Lunar surface magnetic fields and their interaction with the solar wind: Results from lunar prospector,” Science 281, 1480 (1998).
R. P. Lin, “Particle acceleration in solar flares and coronal mass ejections,” IAU Symposium, 195, 15 (2000).
D. E. Larson, R. P. Lin, and J. Steinberg, “Extremely cold electrons within the January 1997 magnetic cloud,” Geophys. Res. Lett. 27, 157 (2000).