Update 29 June 2008
Greetings from SLAC. This week I am here at the LAT Instrument Science Operations Center with many others from the international LAT team, all working together around the clock to study the detailed engineering data and to prepare for science observations.
What has GLAST been doing lately?
Everything continues to go very well and the work is proceeding on schedule.
The LAT is an advanced particle detector with many adjustable parameters to tune, and for the past few days data have been taken with different values for many of those key parameters. In addition, special data-taking periods are being devoted to characterizing the fluxes of background particles hitting the instrument. The very detailed work is going smoothly. The additional diagnostic data taking is keeping the onboard temporary data storage (solid state recorder, or SSR) and data transmission paths well exercised. Over time, the data rate from the LAT will be reduced to the planned science operations level of about 1.2 megabits per second.
The GBM is continuing on-orbit calibrations and checkout as well. A few days ago, the GBM rehearsed the burst-alert message chain. (When an instrument on GLAST detects a gamma-ray burst, a special communications channel is immediately opened to the ground, and an alert is put onto the internet (here is what GLAST will report) so that other observatories can repoint to study the burst.)
The observatory is powered electrically by solar panels that also charge an onboard battery. The battery is important because during every 95-minute orbit GLAST spends some time in earth’s shadow (night time for GLAST). Engineers in the Mission Operations Center at Goddard made adjustments this week on the rate at which the powerful solar arrays are allowed to charge the battery, based on operating experience. These adjustments will help ensure a long life for the battery.
While work is proceeding to make sure the instruments are ready for science observations, we can’t help thinking about what we will soon be seeing for the first time in the months ahead! Here are some thoughts from LAT team member Isabelle Grenier, from the Service d’Astrophysique, CEA Saclay
Soon we will have a first look at the sky with the sharpest ‘gamma-ray glasses’ ever built! A sky that will at last appear as magnificent at the night sky we can admire with our naked eyes, filled with thousands of gamma-ray stars and barred by the bright shades of the Milky Way. But we will see a much more lively and tumultuous sky than the peaceful starry nights we are accustomed to. Intense flashes will last seconds to hours and many stars will blaze and fade away over days and months. A sky showing us how animated the Universe can be, how powerful too, with many objects capable of producing particles and light of incredible energy.
Looking back at the successes of the previous telescopes that had discovered a handful of gamma-ray sources in the seventies, tens of them in the eighties, two hundred in the nineties, the team is preparing to detect thousands of them with GLAST. The task is complex because they appear on top of the bright emission from the clumpy nebulae of the Milky Way. It is equivalent to seeing small sail boats lost among big waves during a tempest: a small error on predicting the surface of the rough sea and we miss the tiny sails. We unfortunately don’t know so well our own galaxy and it impacts our ability to detect point sources.
The team then needs to identify in other lights (radio to X rays) what black holes, neutron stars, supernova remnants, or binary stars are responsible for the gamma-ray sources. This is also a challenge because bright gamma-ray sources can be very faint in other lights and because the sky can be very crowded compared to the precision with which we can locate a source in the sky. It is often like looking for a needle in a haystack, even if the needle is as weird an object as a giant black hole! It took twenty years to identify the second brightest gamma-ray source, Geminga, with one of the nearest and faintest pulsars. Half of the currently known sources has remained unidentified for 17 years. We all hope that GLAST will solve those mysteries and replace them with many new surprises. For the moment, we look eagerly forward to the avalanche of new sources.
More details on instrument tuning and performance, checking the alignment of the LAT with the spacecraft, observatory maneuvers, and more reports from some of the international team members. Please check back every few days for updates.