We have all suffered through the limitations of viewing the stars from beneath the blanket of our thick atmosphere, especially thickened by summer humidity here in Kansas.
While ground based optical observations suffer from dust and small atmospheric fluctuations, some wavelengths are just not possible to view due to absorption by water vapor and other gases. Space based telescopes, orbiting above the limitations of the atmosphere, have literally opened our eyes to higher resolution and extended our viewing to higher and lower wavelengths.
With its successful launch on June 11, 2008, GLAST, the Gamma-Ray Large Area Space Telescope, became our latest eye in the sky. It extends our frequency range into the highest energy yet, from 10 keV to 300 GeV.
Beyond the deep UV frequency range, we give up describing the color of the light by its wavelength and switch to the energy of each photon. The Chandra X-Ray Space Telescope, launched in 1999, through its four different detectors, is sensitive from 0.09 keV to 10 keV. This is compared to the 0.1 to 0.2 keV range of x-rays used in medical applications.
Typically the higher the photon energy, the more energetic the process created the radiation. X-rays generally are created by electrons in highly ionized plasmas interacting with stellar or galactic magnetic fields.
The Gamma Ray part of the spectrum begins at about 100 keV. One source of Gamma Rays is the annihilation of matter and antimatter. When an electron and positron annihilate, they produce a Gamma Ray of about 500 keV or 0.5 MeV. Measuring the spectrum of the Gamma Rays is an important first step in determining the possible radiating source.
The most energetic objects ever observed in the universe so far are Gamma Ray Bursters (GRB). They were first observed by the Vela satellite system, originally launched to detect terrestrial clandestine nuclear explosions. Imagine the surprise of the military observers when they started picking up Gamma-Ray bursts having the signature slightly different from that from a nuclear blast. It was only by triangulation with multiple satellites that their extra terrestrial origin was confirmed.
GLAST is currently going through the normal bring up phase of a new satellite. According to Instrument Science Operations Center manager Rob Cameron from SLAC, “Powering up the LAT has been even smoother than we had hoped. Everything has worked well—in fact, it’s going great. We’re already receiving high-quality data that we can use to get the instrument ready for the best science return.”
After first light, expected in October, GLAST is expected to detect about 200 GRBs per year and resolve how the spectra changes in the seconds immediately after the onset of the burst. It will transmit near real time information so that coordinated, multi wavelength measurements can be taken during the few seconds of these fast, transient events.
With the Spitzer Space Telescope extending to the low end of the spectrum in the far infrared, to the GLAST extending up o the far Gama-Ray end, we will shortly be able to create composite, multi-wavelength images of the sky spanning over 11 orders of magnitude in photon energy.
Above is an example of a multiwavelength image of M101, from infra red to X-Ray, from http://chandra.harvard.edu/photo/2009/m101/more.html#scale
For more information, check out the home page on earth for GLAST.
Published in Aug 2008 Cosmic Messenger
