The Atmospheric Infrared Sounder (AIRS) is a hyperspectral IR spectrometer orbiting on the EOS/Aqua spacecraft since May 2002. In late October 2002, AIRS detected lower tropospheric sulfur dioxide ...and ash emitted by an eruption of Mt. Etna (Italy), in plumes which could be tracked over 1000 km from the volcano into north Africa. We report retrievals of SO2 and ash column amounts and ash particle size in the Etna plumes. AIRS total SO2 compares favorably with contemporaneous ground‐based correlation spectrometry (COSPEC) measurements. Retrieval of ash cloud parameters in the eruption plumes permits quantitative studies of distal ash fallout. The Etna data demonstrate the potential of AIRS to improve measurements of volcanic SO2 and ash loading in the troposphere, and to refine our understanding of volcanic cloud composition, structure and evolution.
Radio pulsar PSR J1028-5819 was recently discovered in a high-frequency search (at 3.1 GHz) in the error circle of the Energetic Gamma-Ray Experiment Telescope (EGRET) source 3EG J1027-5817. The ...spin-down power of this young pulsar is great enough to make it very likely the counterpart for the EGRET source. We report here the discovery of g-ray pulsations from PSR J1028-5819 in early observations by the Large Area Telescope (LAT) on the Fermi Gamma-Ray Space Telescope. The g-ray light curve shows two sharp peaks having phase separation of 0.460 ± 0.004, trailing the very narrow radio pulse by 0.200 ± 0.003 in phase, very similar to that of other known g-ray pulsars. The measured g-ray flux gives an efficiency for the pulsar of ~10-20% (for outer magnetosphere beam models). No evidence of a surrounding pulsar wind nebula is seen in the current Fermi data but limits on associated emission are weak because the source lies in a crowded region with high background emission. However, the improved angular resolution afforded by the LAT enables the disentanglement of the previous COS-B and EGRET source detections into at least two distinct sources, one of which is now identified as PSR J1028-5819.
The Large Area Telescope (LAT) on--board the Fermi Gamma ray Space Telescope began its on--orbit operations on June 23, 2008. Calibrations, defined in a generic sense, correspond to synchronization ...of trigger signals, optimization of delays for latching data, determination of detector thresholds, gains and responses, evaluation of the perimeter of the South Atlantic Anomaly (SAA), measurements of live time, of absolute time, and internal and spacecraft boresight alignments. Here we describe on orbit calibration results obtained using known astrophysical sources, galactic cosmic rays, and charge injection into the front-end electronics of each detector. Instrument response functions will be described in a separate publication. This paper demonstrates the stability of calibrations and describes minor changes observed since launch. These results have been used to calibrate the LAT datasets to be publicly released in August 2009.
PDF
