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A2SPECBACK - HEAO 1 A2 Spectra Background



The A2 experiment was flown on the HEAO-1 satellite, between August, 1977 until January 1979.

The experiment consisted of six multi-layer multi-anode collimated gas proportional counters. These were two LEDs (Low Energy Detectors), a MED (Medium Energy Detector), and three HEDs (High Energy Detectors). The first 6-months of mission were dedicated to an all-sky scan after which a pointing phase started.

This database table accesses all the background files available at HEASARC obtained from the A2 MED (small and large field of view) and HEDs (1 and 3 small and large filed of view) detectors during the pointed phase.

Data Products

The MED and HEDs have two different field of views a small and a large, which sizes are from various combination of 3.0 X 1.5 degrees 3.0 x 3.0 degrees, 3.0 x 6.0 degrees (FWHM). The collimators were aligned so the 3.0 degree response was aligned with the spin axis.

Several background files were derived from the a2 pointing observations. Each entry in this database has associated one background file obtained with one of the detectors, MED or HD1 or HD3, either with the small or large field of view.

Most of these background files were derived when the A1 was the primary pointing experiment. The A2 instrument was mounted on the opposite side of the HEAO-1 satellite from most of the detectors in the A1 instrument. Thus when A1 performed a pointed observation, A2 made a pointed observation of the opposite direction in the sky. From the black sky A2 observations background spectral file were derived.


The parameter 'name' contains the value stored in the OBJECT keyword of the FITS file.

The Right Ascension of the pointing.

The Declination of the pointing.

The Galactic Longitude of the pointing.

The Galactic Latitude of the pointing.

The count rate from the spectrum obtained in the following energy range for the different detectors: MED between 2-10 keV and HED3 and HED1 between 8-15 keV. The count rate are not background subtracted.

The error for the count rate from the MED-S detector.

The exposure time of the observation, in seconds.

The date and time of the start of the observation, given as DD/MM/YY hh:mm:ss (string).

The date and time of the end of the observation, given as DD/MM/YY hh:mm:ss (string).

The start time of the observation.

The stop time of the observation.

The response matrix file name.

Name for the background spectral file. This product is in FITS format.

Contact Person

Questions regarding the A2SPECBACK database table can be addressed to the HEASARC User Hotline.
Page Author: Browse Software Development Team
Last Modified: Friday, 20-Mar-2015 16:48:22 EDT