The detection of ultra-relativistic electrons in low Earth orbit

Aims. To better understand the radiation environment in low Earth orbit (LEO), the analysis of in-situ observations of a variety of particles, at different atmospheric heights, and in a wide range of energies, is needed. Methods. We present an analysis of energetic particles, indirectly detected by the Large Yield RAdiometer (LYRA) instrument on board ESA's Project for On-board Autonomy 2 (PROBA2) satellite as background signal. Combining Energetic Particle Telescope (EPT) observations with LYRA data for an overlapping period of time, we identified these particles as electrons with an energy range of 2 to 8 MeV. Results. The observed events are strongly correlated to geo-magnetic activity and appear even during modest disturbances. They are also well confined geographically within the L=4-6 McIlwain zone, which makes it possible to identify their source. Conclusions. Although highly energetic particles are commonly perturbing data acquisition of space instruments, we show in this work that ultra-relativistic electrons with energies in the range of 2-8 MeV are detected only at high latitudes, while not present in the South Atlantic Anomaly region.Comment: Topical Issue: Flares, CMEs and SEPs and their space weather impacts; 20 pages; 7 figures; Presented during 13th European Space Weather Week, 201

Diffuse Light in the Virgo Cluster

We present deep optical imaging of the inner 1.5 x 1.5 degrees of the Virgo cluster to search for diffuse intracluster light (ICL). Our image reaches a 1 sigma depth of mu_v=28.5 mag/arcsec^2 -- 1.5 mag/arcsec^2 deeper than previous surveys -- and reveals an intricate web of diffuse intracluster light. We see several long (>100 kpc) tidal streamers, as well as a myriad of smaller-scale tidal tails and bridges between galaxies. The diffuse halo of M87 is traced out to nearly 200 kpc, appearing very irregular on these scales, while significant diffuse light is also detected around the M84/M86 pair. Several galaxies in the core are embedded in common envelopes, suggesting they are true physical subgroups. The complex substructure of Virgo's diffuse ICL reflects the hierarchical nature of cluster assembly, rather than being the product of smooth accretion around a central galaxy.Comment: 4 pages, 3 figures, accepted for publication in ApJ Letter

Eclipse observations of high-frequency oscillations in active region coronal loops

One of the mechanisms proposed for heating the corona above solar active regions is the damping of magnetohydrodynamic (MHD) waves. Continuing on previous work, we provide observational evidence for the existence of high-frequency MHD waves in coronal loops observed during the August 1999 total solar eclipse. A wavelet analysis is used to identify twenty 4x4 arcsec2 areas showing intensity oscillations. All detections lie in the frequency Hz (5-3 s), last for at least 3 periods at a confidence level of more than 99% and arise just outside known coronal loops. This leads us to suggest that they occur in low emission-measure or different temperature loops associated with the active region.Comment: 6 pages, 6 figure

Re-Arrest Among Juvenile Justice-Involved Youth: An Examination Of The Static And Dynamic Risk Factors

The purpose of this study is to investigate the static and dynamic risk factors for re-arrest among detained youth by examining gender, race/ethnicity, age, special education and mental health variables (i.e., anger/irritability, depression/anxiety, somatic complaints, suicide ideation, thought disturbances, and traumatic experiences). The demographic profiles of detained youth with one admit were also compared with those with multiple admits to the juvenile detention center. With regards to static risk factors, older, white, and special education were significantly at risk of re-arrest. Concerning dynamic risk factors, only anger/irritability predicted re-arrest. Practice implications are also discussed

Discovery of the benchmark metal poor T8 dwarf BD+01 2920B

We have searched the WISE first data release for widely separated (<10,000AU) late T dwarf companions to Hipparcos and Gliese stars. We have discovered a new binary system containing a K-band suppressed T8p dwarf WISEP J1423+0116 and the mildly metal poor ([Fe/H]=-0.38+-0.06) primary BD+01 2920 (Hip 70319), a G1 dwarf at a distance of 17.2pc. This new benchmark has Teff=680+-55K and a mass of 20-50 Mjup. Its spectral properties are well modelled except for known discrepancies in the Y and K bands. Based on the well determined metallicity of its companion, the properties of BD+01 2920B imply that the currently known T dwarfs are dominated by young low-mass objects. We also present an accurate proper motion for the T8.5 dwarf WISEP J075003.84+272544.8.Comment: MNRAS, accepted 2012 January 1