HEAO (E0): HEAO A-1 X-ray Source Catalog; 1984 (19950113)
FILE: heao.e0 (842 sources)
CONTENTS: HEAO A-1 X-ray Source Catalog; Wood et al. 1984
DATASET: This file comes in HyperSky dataset E-9, version 19950113. Availability on HyperSky CD-ROM: Vol. 2 (1995)
DESCRIPTION: This datafile contains 842 X-ray sources detected with the NRL Large Area Sky Survey Experiment on the HEAO 1 (High Energy Astronomical Obsrvatory) satellite. The primary objective of the Naval Research Laboratory (NRL) Large Area Sky Survey Experiment (LASS) flown aboard the HEAO 1 satellite was to conduct an all-sky survey for the brightest X-ray sources in the energy range 0.25 to 25 keV. The instrumentation consisted of an array of large proportional counter modules with collimators of varying fields of view, and with sufficient sensitivity to detect sources as faint as 0.25 micro-Jy (250 mJy) at 5 keV, assuming a Crab-like spectrum (1.1 micro-Jy at 5 keV = 1 UFU for a Crab-like spectrum).
Full sky coverage was achieved within 6 months by continuously scanning great circles perpendicular to the Earth-Sun line. The catalog is considered 90 percent complete at the 250 mJy level. The intensity given for each source is a mean value over the observing interval rather than an extreme value.
The HyperSky file is based on the version of the catalog available through the U.S. National Space Sciences Data Center (NSSDC) as Astronomical Data Center (ADC) catalog #7080.
DATA: The HyperSky datafile contains the following data from the catalog:
POSITION: Right Ascension and Declination are based on the catalog 1950 positions, precessed to equinox 2000. Catalog positions were provided to an accuracy of 1 second in Right Ascension and 1" in declination.
MAG: No magnitudes or equivalents were provided in the catalog. A set of artificial magnitudes is provided, however, in the HyperSky catalog strictly to allow use of HyperSky's limiting-magnitude controls. In this way, users can display only those sources above a desired threshold. The artificial magnitude system is based on the relation (from Pogson) used to define visual magnitudes:
m1 - m2 = 2.5 * log10 (S1/S2)
where { m1, m2 } are magnitudes, and { S1, S2 } are source strengths. For the HyperSky catalog, the brightest source (S1 = 37.2 flux) is arbitrarily assigned the magnitude m1 = 1.0. Given this, any other source S2 can have its relative magnitude, m2, derived using the relation:
m2 = m1 + 2.5 * log10 (S1 / S2);
Or in this case:
m2 = 1.0 + 2.5 * log10 (37.2 / S2);
In this system, the faintest catalog source (.0007 flux) has a magnitude of 12.8. The following table summarizes the relation between magnitude and source strength for catalog extremes and intermediate magnitudes:
Magnitude Source Strength (flux units)
----------|-----------------------------------------
1.0 37.2 (brightest source; Sco X-1)
3.4 4.2
4.0 2.3
5.1 0.88
6.0 0.37
7.0 0.15
8.0 0.057
9.0 0.023
10.0 0.0091
11.0 0.0038
12.0 0.0015
12.8 0.0007 (faintest source)
With the above table, you can set HyperSky's limiting magnitude (for emission sources) to mask out catalog sources below a desired strength. Except for this use, the derived source magnitudes have NO significance. It should be emphasized again that the magnitudes are NOT provided in the original catalog; only the source strengths are fundamental catalog values.
IDENTIFICATION: The 1H catalog designation is composed of the prefix "1H", followed by the right ascension in hours and minutes and the declination in degrees and tenths of a degree (equinox B1950.0)
COMMENTS: The comment lines following the identification contain the following information, where available, for each X-ray source:
* A line starting with "flux=", giving the X-ray intensity, in counts/cm**2/s (s is solid angle) for 0.5-25 keV.
* A line starting with "err=", giving a HyperSKy-derived linear position error. The HyperSky value is calculated as the square root of the catalog solid angle (in square degrees) enclosed by the position error box. The size of the glyph representing the source in the HyperSky field is scaled to approximately match the HyperSky derived linear error value.
* Up to 7 Lines starting with "x-ray id:", giving alternate designations of the source in other X-ray catalogs. Catalog cross-identifications were selected according to certain criteria. For X-ray catalogs (4U, 2A, 1M, etc.), where error boxes of up to several degrees are sometimes reported, the cross reference is given whenever the other error box intersects the HEAO-1 error box. Identifiers are also given in certain cases where boxes do not strictly intersect but are sufficiently close to suggest a possible relationship. The criterion used is that the separation between box centers must be less than the sum of the two largest dimensions. The designation "XRS" is from Amnuel, Guseinov and Rakhamimov (1979), which summarizes much of the older X-ray literature.
* Up to 7 Lines starting with "other:", giving alternate non-X-ray cross identifications. Whenever an identification has been firmly established, for example, by a precise position from a modulation collimator or from the Einstein Observatory, it is always shown, but so are many additional tentative identifications. Some of these have been suggested by earlier work, and the remainder have been found by searching non-X-ray catalogs listed by the reference authors (see below).
REFERENCE
Wood, K.S., Meekins, J.F., Yentis, D.J., Smathers, H.W., McNutt, D.P.,
Bleach, R.D., Byram, E.T., Chubb, T.A., Friedman, H., and Meidav, M.
1984, "The HEAO A-1 X-ray Source Catalog", Astrophys. J. Suppl. 56,
507-649.