The HEAO-1 A4
The FITS data products were created as part of an ADP (PI Duane Gruber) and delivered to the HEASARC which created the GIF plots for the A4 spectra. No other data are available from the HEASARC for the A4 experiment.
There are 10 maps of the sky available in the HEAO1 FTP area at the HEASARC archive. These maps are in FITS, using the primary header, and store counts (16 bit integers) in a ecliptic longitude and latitude projection. The maps covers the following energy ranges:
map 1: 13-25 KeV map 2: 25-40 KeV map 3: 40-80 KeV map 4: 80-180 KeVand there is one set for each of the Low energy detectors (d3 and d6). An additional file contains the detector life time, stored as well in the primary header with single precision. There is one lifetime map per detector.
In pointing mode the A4-LED instrument look axis was kept in a 1 deg dead band centered on the target position. In the "ping-pong" mode the look axis was regularly alternated with a secondary target a few degrees away, usually for background determination. The A4SPECTRA database accesses the spectra (and associated files) obtained from the A4-LED detectors in the ping-pong mode. There are 59 source spectra for d3 and 59 for the d6 detectors. These are all accompanied by a background spectra and the appropriate response matrix. A plot showing the LED-3 and LED-6 background subtracted spectra is also available in GIF format.
Note on the products
A few spectra give negative c/s after background subtraction, not consistent with one sigma error. The background spectrum obtained for the LED-3 detector for the position ra=300.0 and dec=39.7 deg (spectral file a4_d3_2000p397_a.bkg) shows strong evidence for a point source which most likely coincide with Cyg X-1. On the contrary the pointing spectrum (a4_d3_2000p397_a.pha) probably is consistent with a blank sky. The LED-3 and LED-6 source spectra for the position ra=268.5 and dec=-23.4 (spectral file a4_d3_1754m234_a.pha and a4_d6_1754m234_a.pha) correspond to a pointing of Jupiter, but the background spectra (a4_d3_1754m234_a.bkg, a4_d6_1754m234_a.bkg) is contaminated by a fairly strong source, GX 5-1.