We successfully carried out the first high-altitude balloon flight of a wide-field hard X-ray coded-aperture telescope ProtoEXIST1 , which was launched from the Columbia Scientific Balloon Facility at Ft. Sumner , New Mexico on October 9 , 2009 . ProtoEXIST1 is the first implementation of an advanced CdZnTe ( CZT ) imaging detector in our ongoing program to establish the technology required for next generation wide-field hard X-ray telescopes such as the High Energy Telescope ( HET ) in the Energetic X-ray Imaging Survey Telescope ( EXIST ) .
The CZT detector plane in ProtoEXIST1 consists of an 8 \times 8 array of closely tiled 2 cm \times 2 cm \times 0.5 cm thick pixellated CZT crystals , each with 8 \times 8 pixels , mounted on a set of readout electronics boards and covering a 256 cm { } ^ { 2 } active area with 2.5 mm pixels .
A tungsten mask , mounted at 90 cm above the detector provides shadowgrams of X-ray sources in the 30 – 600 keV band for imaging , allowing a fully coded field of view of 9 ^ { \circ } \times 9 ^ { \circ } ( and 19 ^ { \circ } \times 19 ^ { \circ } for 50 % coding fraction ) with an angular resolution of 20 ^ { \prime } .
In order to reduce the background radiation , the detector is surrounded by semi-graded ( Pb/Sn/Cu ) passive shields on the four sides all the way to the mask .
On the back side , a 26 cm \times 26 cm \times 2 cm CsI ( Na ) active shield provides signals to tag charged particle induced events as well as \gtrsim 100 keV background photons from below .
The flight duration was only about 7.5 hours due to strong winds ( 60 knots ) at float altitude ( 38–39 km ) .
Throughout the flight , the CZT detector performed excellently .
The telescope observed Cyg X-1 , a bright black hole binary system , for \sim 1 hour at the end of the flight .
Despite a few problems with the pointing and aspect systems that caused the telescope to track about 6.4 deg off the target , the analysis of the Cyg X-1 data revealed an X-ray source at 7.2 \sigma in the 30–100 keV energy band at the expected location from the optical images taken by the onboard daytime star camera .
The success of this first flight is very encouraging for the future development of the advanced CZT imaging detectors ( ProtoEXIST2 , with 0.6 mm pixels ) , which will take advantage of the modularization architecture employed in ProtoEXIST1 .