A2POINT - HEAO 1 A2 Pointing

Overview

The HEAO 1 A-2 Pointing Catalog of High-Energy X-ray Sources is the result of a study of selected targets using the three detectors of the A-2 Experiment. The detectors consisted of the HED (high energy detector) in the range 3-6 KeV, the MED (medium energy detector) in the range 1.5-15 KeV, and the LED (low energy detector) in the range 0.15-3 KeV. The HEAO A-2 Experiment was primarily designed for studying the diffuse X-ray background; however, it was also capable of studying point sources to good sensitivity. Thus, after several months of continuous scanning to survey 95% of the diffuse X-ray sky, the A-2 detectors began individual pointings at selected targets. The point maneuvers began on day 319, 15 November 1977 and ended on day 739, 9 January 1979.

References

"HEAO-1 and the A2 Experiment", by J. Allen, K. Jahoda, and L. Whitlock, Legacy, #5, November 1994.

The instrument is described in "The Cosmic X-Ray Experiment Aboard HEAO-1", R. Rothschild et al. 1979, Space Sci. Instr, 4, 269, and in "New Hard X-ray Sources Observed with HEAO A-2", F.E. Marshall et al. 1979, Ap.J. Suppl., 40, 657.

Description

The A-2 experiment consisted of six mechanically collimated, gas-filled, multilayer, multiwire proportional counters.

This catalog gives the start and stop times of each pointing and the position in the sky at which the A2 instrument was viewing. Target names correspond to those found in other catalogs in the position in the sky of the A2 instrument FOV.

The HEAO-A1 and HEAO-A2 instruments pointed in opposite directions on the sky: 6 of the 7 modules of the A1 instrument pointed in the direction of the spacecraft -Y ('MY') axis whereas the 6 A2 detectors pointed at or near (6 degrees awat from) the +Y ('PY') spacecraft direction. Thus, when the HEAO A-1 was observing a cosmic X-ray source, the HEAO A-2 instrument was observing a diametrically opposite patch of the sky: in this case, the resulting A-2 target name has been set to A1POINT and the instrument value to 'MY'.

The catalog consists of 479 targets: 342 PY targets, 134 MY targets, and 3 "??" targets (meaning the detector pointing and an identification were not known).

Parameters

BII
The Galactic latitude corresponding to the given right ascension in decimal degrees.

Dec
The Declination corresponding to the pointing direction of the A2 instrument.

Duration
The duration, in seconds, of the pointing.

End_Time
The end day and time of the point maneuver. Points begin on day 319 (1977-11-15) and end on day 739 (1979-01-09).

Instrument
This field contains either "MY" (for minus Y), "PY" (for positive Y), or "??" (for unknown). See the Overview above for more details on the meaning of this parameter.

LII
The Galactic longitude corresponding to the given right ascension in decimal degrees.

Name
This is the designation of the source as identified by cross-correlation with other X-ray source catalogs. The name "A1 Point" indicates that A1 was viewing a target and A2 was pointing 180 degrees away, possibly at blank sky. To avoid confusing the A2 RA and Dec with the A1 target name, the names were changed.

Pp
This field indicates whether the instrument was slowly precessing back and forth while the target was in the FOV.

RA
The Right Ascension corresponding to the pointing direction of the A2 instrument.

Time
The start day and time of the point maneuver. Points begin on day 319 (1977-11-15) and end on day 739 (1979-01-09).

Contact Person

Questions regarding the A2POINT database table can be addressed to the HEASARC Help Desk.

Page Author: Browse Software Development Team
Last Modified: Monday, 16-Sep-2024 17:23:54 EDT