GLAST Update 6 July
Early operations continue to go remarkably smoothly and according to plan. The GBM spent the week doing on-orbit calibrations and setting up the automatic onboard system that maintains the calibration. The LAT team was very busy tuning up the instrument and doing detailed data checks. Data taking and processing are becoming routine.
“When do we see pictures?”
Soon! The first-light images will be released in just a few weeks, when NASA also plans to rename the observatory. Arrangements are being made now for this event, which we expect will be at the end of July or in early August. I’ll post the date when we have it.
In the meantime, the LAT has now posted single event displays, which show the detector information in graphical form. These are really beautiful!! It takes some time to learn how to read these pictures. First, as referenced in previous posts, please see a brief description of the LAT and how it works. Particles traverse the LAT many thousands of times every second, and the information reported by the sensors about that particle’s interaction in the LAT is called an event. Notice that the charged particles in the events linked above are detected with very high efficiency in every layer. Now, realize that the tracking detector has about 880,000 individual sensing strips and yet they are not registering anything where charged particles are not passing through them. Like the dog that didn’t bark in the famous Sherlock Holmes story, this is profoundly important: the noise is remarkably low, while the detection efficiency is very high.
[These events help illustrate how the experiment works, but not all events look like these relatively simple, low-energy gamma-ray event candidates. Very high-energy gamma-ray events are more complicated, because there is more energy available to make more particles. An even more impressive display occurs when a cosmic-ray proton smashes into the spacecraft or the massive LAT calorimeter: hundreds of particles spew up through the instrument, and the event looks like a trainwreck. The instrument and analysis software are carefully designed to handle all these types of events.]
Remember, the LAT takes “pictures” one particle of light (photon) at a time, and since we measure the incoming direction on the sky (as well as the energy and other information) for each, those photons can be added together over time to form an image of any part (or all) of the sky. You’ll start seeing these in just a few more weeks.
Report from Japan
The event pictures linked above are just one representation of the beautiful performance of the instruments. The LAT tracking detector was designed and built by a collaboration of scientists, engineers, and technicians from institutions in the United States, Italy, and Japan. The charged particle sensors in the tracker were all built in Japan, and they are truly remarkable. About 70 square meters of these precision sensors (called Silicon Strip Detectors, or SSDs) are onboard the LAT! Without them, GLAST would simply be impossible.
Here is a note from someone who was deeply involved in the design and production of the SSDs. Prof Takashi Ohsugi, from Hiroshima University, is one of the key GLAST collaborators in Japan. He and many others there are also looking forward to doing science with GLAST.
A major Japanese newspaper and some web news sites in Japan covered the GLAST launch. It was a very exciting day for us! We are preparing an article for the monthly report of Astronomical society of Japan (The Astronomical Herald). A special seminar is planned in Hiroshima University to make a more detailed briefing of the GLAST project and science for students and university staff.
To connect the breakthrough observations expected from GLAST with what is known about the universe in other wavelengths, coordinated “multi-wavelength” observations wordwide are important. In Japan, the staff of the KANATA telescope (1.5m optical, near-infrared telescope) will start a photo-polarimetric monitoring of some bright blazars for GLAST.
More details about the calibrations, observations, and getting ready for the first year of science operations. Please check back for updates. Thanks, also, for your comments!