Article

First terrestrial soft X-ray auroral observation by the Chandra X-ray Observatory

Department of Physics and Technology, University of Bergen, Bergen N-5007, Norway
Journal of Atmospheric and Solar-Terrestrial Physics (Impact Factor: 1.75). 01/2007; DOI: 10.1016/j.jastp.2006.07.011
Source: arXiv

ABSTRACT Northern auroral regions of Earth were imaged with energetic photons in the 0.1–10 keV range using the High-Resolution Camera (HRC-I) aboard the Chandra X-ray Observatory at 10 epochs (each duration) between mid-December 2003 and mid-April 2004. These observations aimed at searching for Earth's soft () X-ray aurora in a comparative study with Jupiter's X-ray aurora, where a pulsating X-ray “hot-spot” has been previously observed by Chandra. The first Chandra soft X-ray observations of Earth's aurora show that it is highly variable (intense arcs, multiple arcs, diffuse patches, at times absent). In at least one of the observations an isolated blob of emission is observed near the expected cusp location. A fortuitous overflight of DMSP satellite F13 provided SSJ/4 energetic particle measurements above a bright arc seen by Chandra on 24 January 2004, 20:01–20:22 UT. A model of the emissions expected strongly suggests that the observed soft X-ray signal is bremsstrahlung and characteristic K-shell line emissions of nitrogen and oxygen in the atmosphere produced by electrons.

Full-text

Available from: George Randall Gladstone, Apr 28, 2015
0 Followers
 · 
112 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: We found 217 X-ray brightening events in Earth's magnetosphere. These events occur in the high-energy band (0.5-4 Å) of the Geostationary Operational Environmental Satellite (GOES) X-ray light curves, although GOES X-ray light curves are frequently used as indices of solar flare magnitudes. We found that (1) brightening events are absent in the low-energy band (1-8 Å), unlike those associated with solar flares; and (2) the peak fluxes, durations, and onset times of these events depend on the magnetic local time (MLT). The events were detected in 2006, 2010, and 2011 at around 19-10 MLT, that is, from night to morning. They typically lasted for 2-3 hr. Their peak fluxes are less than 3 × 10–8 W m–2 in the 0.5-4 Å band and are maximized around 0-5 MLT. From these MLT dependencies, we constructed an MLT time profile of X-ray brightening events. Because 0.5-4 and 1-8 Å fluxes were observed and had the same order of magnitude when GOES 14 passed through Earth's shadow, we expected that X-ray brightening events in the 1-8 Å band are obscured by high-background X-ray fluxes coming from the Sun. We also found coincidence between X-ray brightening events and aurora substorms. In the majority of our events, the minimum geomagnetic field values (AL index) are below –400 nT. From these results and consideration of the GOES satellite orbit, we expect that these X-ray brightening events occur in the magnetosphere. We cannot, however, clarify the radiative process of the observed X-ray brightening events.
    The Astrophysical Journal 09/2013; 775(2):121. DOI:10.1088/0004-637X/775/2/121 · 6.28 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: While X-ray astronomy began in 1962 and has made fast progress since then in expanding our knowledge about where in the Universe X-rays are generated by which processes, it took one generation before the importance of a fundamentally different process was recognized. This happened in our immediate neighborhood, when in 1996 comets were discovered as a new class of X-ray sources, directing our attention to charge exchange reactions. Charge exchange is fundamentally different from other processes which lead to the generation of X-rays, because the X-rays are not produced by hot electrons, but by ions picking up electrons from cold gas. Thus it opens up a new window, making it possible to detect cool gas in X-rays (like in comets), while all the other processes require extremely high temperatures or otherwise extreme conditions. After having been overlooked for a long time, the astrophysical importance of charge exchange for the generation of X-rays is now receiving increased general attention. In our solar system, charge exchange induced X-rays have now been established to originate in comets, in all the planets from Venus to Jupiter, and even in the heliosphere itself. In addition to that, evidence for this X-ray emission mechanism has been found at various locations across the Universe. Here we summarize the current knowledge about solar system X-rays resulting from charge exchange processes.
    Astronomische Nachrichten 04/2012; 333(4):324-. DOI:10.1002/asna.201211663 · 1.12 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Within 40 years of the detection of the first extrasolar X-ray source in 1962,NASA's Chandra X-ray Observatory has achieved an increase in sensitivity of 10 orders of magnitude, comparable to the gain in going from naked-eye observations to the most powerful optical telescopes over the past 400 years. Chandra is unique in its capabilities for producing sub-arcsecond X-ray images with 100-200 eV energy resolution for energies in the range 0.08<E<10 keV, locating X-ray sources to high precision, detecting extremely faint sources, and obtaining high resolution spectra of selected cosmic phenomena. The extended Chandra mission provides a long observing baseline with stable and well-calibrated instruments, enabling temporal studies over time-scales from milliseconds to years. In this report we present a selection of highlights that illustrate how observations using Chandra, sometimes alone, but often in conjunction with other telescopes, have deepened, and in some instances revolutionized, our understanding of topics as diverse as protoplanetary nebulae; massive stars; supernova explosions; pulsar wind nebulae; the superfluid interior of neutron stars; accretion flows around black holes; the growth of supermassive black holes and their role in the regulation of star formation and growth of galaxies; impacts of collisions, mergers, and feedback on growth and evolution of groups and clusters of galaxies; and properties of dark matter and dark energy.
    Reports on Progress in Physics 05/2014; 77(6). DOI:10.1088/0034-4885/77/6/066902 · 15.63 Impact Factor