HEAO-1 Software: The Discovery Scalars of the A2 Detectors
Based on information from "HEAO-1 A-2 Experiment: The Configuration of
the Hard X-ray Detectors" F.E. Marshall 1983.
The discovery scalars are the eight rates (four from large field of
view data and four from small field of view data) accumulated in various
combinations of spatial and spectral windows.
The HEDs were a composite of two layers (M1 and M2) consisting of a
single row of anodes each. Alternate groups of anodes were under different
collimators. Anodes under the 3.0° x 3.0° collimators were
known as L1 (for layer one) and L2 (for layer two). Anodes under
the other collimator were called R1 and R2. The final layer of
anodes generated the veto signal V1. For HED-1 and HED-3, the
side cells were also included in the V1 signal. For HED-2 and
the MED which lacked the front veto layer, V1 consisted of the
bottom layer and V2 consisted of the two side rows.
The first four discovery
scalars were fixed and unchanging throughout the course of the mission
and were defined to be L1, R1, L2, and R2 in order. These discovery
scalars identified also the small and large FOV as follows:
HED-1 & HED-2
HED-3 & MED
Large FOV
R1 & R2
L1 & L2
Small FOV
L1 & L2
R1 & R2
For example the Large FOV for the HED-3 detector would correspond
to selecting discovery scalars 1 and 3. The small FOV would
correspond to 2 and 4.
Discovery scalars 5 and 7 are for the left; scalars 6 and 8 are for
the right. Table 1 below gives the approximate energy ranges for the
six windows for the HEDs (which were nominally identical) and the
MED.
Table 1: Spectral Windows for HEAO-1 A2 Discovery Scalars
Window
MED energy (keV)
HED energy (keV)
1A
1.5 - 6
2 - 6
1B
6 - 8
6 - 8
1C
8 - 10
8 - 32
1D
10 - 20
32 - 60
2A
2 - 3.9
9 - 32
2B
3.9 - 20
32 - 60
The definitions for discovery scalars 5-8 changed throughout the
course of the missions and were formed from combinations of six
pre-designed spectral windows: Layer 1 - 1A, 1B, 1C, and 1D; Layer 2
- 2A and 2B. Table 2 lists the different configurations of discovery
scalars 5 through 8 over the course of the mission.
