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A2LED - HEAO 1 A-2 LED Catalog

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Overview

The HEAO 1 A-2 LED Catalog of High-Energy X-ray Sources is the result of a study of the diffuse X-ray sky over the bands of X-ray energies 0.18-0.44 keV and 0.44-2.8 keV from August 1977 until January 1979 using data obtained with the A-2 Low Energy Detector on the HEAO 1 satellite. 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. The detectors surveyed over 95 percent of the sky in the spectral bands listed above to typical limiting sensitivities of 1x10**-11 and 3x10**-11 respectively. Using a significance criterion of 6 sigma for existence, 114 sources are cataloged. The catalog contains a list of all counterpart identifications and a cross-reference to all HEAO 1 A-2 LED team publications on the catalog sources complete through the end of 1981.

The identified sources fall into several categories, primarily dependent on observing energy interval. In the 1 KeV band the sources include: 20 galactic stellar sources, 19 extragalactic sources, 13 SNR's, 11 galactic bulge sources, 2 globular cluster sources, and 2 previously reported sources without optical counterparts. In the .25 KeV band the sources include: 24 galactic stellar objects, 12 extragalactic sources, 5 SNR's, 1 bulge source, and 1 globular cluster source.


Catalog Bibcode

1983ApJS...51....1N

References

The instrumentation, observations, and analysis techniques used to produce the A-2 catalog are described in detail in "The HEAO A-2 Soft X-ray Catalog", J.J. Nugent et al., Ap.J.Suppl., 51:1-28, 1983 January.

Description

One of the primary goals of the HEAO 1 mission was to survey the diffuse low X-ray energy sky (0.18 < E < 2.8 keV) with the LED instrument (A-2). Over 16 months were spent carrying out this survey. This catalog gives the positions of the centers and four corners of both the best fit and Overlap error boxes. In addition, intensities and errors of both energy bands above are cataloged. Count rates are given as the intensities in counts/sec in the two energy bands (0.18-0.44 KeV) and (0.44-2.8 KeV).

Parameters

Name
The name of the X-ray source. The names begin with the letter `H`, followed by the RA and Dec of the center of the Overlap Error Box (OEB).

RA
The right ascension of the celestial position which is the center of the Overlap Error Box (OEB), in the selected equinox. This was given in B1950.0 decimal degrees to a precision of 0.01 degrees in the published form of this catalog.

Dec
The declination of the celestial position which is the center of the Overlap Error Box (OEB), in the selected equinox. This was given in B1950.0 decimal degrees to a precision of 0.01 degrees in the published form of this catalog.

LII
The galactic longitude corresponding to the position of the center of the OEB.

BII
The galactic latitude corresponding to the position of the center of the OEB.

RA1
The right ascension (B1950.0), in degrees, of the first corner of the Overlap Error Box (OEB) for the source. This was given to a precision of 0.01 degrees in the published form of this catalog.

Dec1
The declination (B1950.0), in degrees, of the first corner of the Overlap Error Box (OEB) for the source. This was given to a precision of 0.01 degrees in the published form of this catalog.

RA2
The right ascension (B1950.0), in degrees, of the second corner of the Overlap Error Box for the source. This was given to a precision of 0.01 degrees in the published form of this catalog.

Dec2
The declination (B1950.0), in degrees, of the second corner of the Overlap Error Box for the source. This was given to a precision of 0.01 degrees in the published form of this catalog.

RA3
The right ascension (B1950.0), in degrees, of the third corner of the Overlap Error Box for the source. This was given to a precision of 0.01 degrees in the published form of this catalog.

Dec3
The declination (B1950.0), in degrees, of the third corner of the Overlap Error Box for the source. This was given to a precision of 0.01 degrees in the published form of this catalog.

RA4
The right ascension (B1950.0), in degrees, of the fourth corner of the Overlap Error Box for the source. This was given to a precision of 0.01 degrees in the published form of this catalog.

Dec4
The declination (B1950.0), in degrees, of the fourth corner of the Overlap Error Box for the source. This was given to a precision of 0.01 degrees in the published form of this catalog.

Boxarea_Oeb
The area of the Overlap Error Box in units of deg**2.

Best_Fit_RA
The right ascension, in degrees B1950.0, of the celestial position which is the center of the Best Fit Error Box (BEB). This was given to a precision of 0.01 degrees in the published form of this catalog. This box is omitted if the data are inconsistent with a constant source.

Best_Fit_Dec
The declination, in degrees B1950.0, of the celestial position which is the center of the Best Fit Error Box (BEB). This was given to a precision of 0.01 degrees in the published form of this catalog. This box is omitted if the data are inconsistent with a constant source.

Best_Fit_LII
The galactic longitude corresponding to the given position for the center of the BEB.

Best_Fit_BII
The galactic latitude corresponding to the given position for the center of the BEB.

Corner1_RA_Beb
The right ascension (B1950.0), in degrees, of the celestial position which is the upper left corner of the Best Fit Error Box. This was given to a precision of 0.01 degrees in the published form of this catalog.

Corner1_Dec_Beb
The declination (B1950.0), in degrees, of the celestial position which is the upper left corner of the Best Fit Error Box. This was given to a precision of 0.01 degrees in the published form of this catalog.

Corner2_RA_Beb
The right ascension (B1950.0), in degrees, of the celestial position which is the upper right corner of the Best Fit Error Box. This was given to a precision of 0.01 degrees in the published form of this catalog.

Corner2_Dec_Beb
The declination (B1950.0), in degrees, of the celestial position which is the upper right corner of the Best Fit Error Box. This was given to a precision of 0.01 degrees in the published form of this catalog.

Corner3_RA_Beb
The right ascension (B1950.0), in degrees, of the celestial position which is the lower left corner of the Best Fit Error Box. This was given to a precision of 0.01 degrees in the published form of this catalog.

Corner3_Dec_Beb
The declination (B1950.0), in degrees, of the celestial position which is the lower left corner of the Best Fit Error Box. This was given to a precision of 0.01 degrees in the published form of this catalog.

Corner4_RA_Beb
The right ascension (B1950.0), in degrees, of the celestial position which is the lower right corner of the Best Fit Error Box. This was given to a precision of 0.01 degrees in the published form of this catalog.

Corner4_Dec_Beb
The declination (B1950.0), in degrees, of the celestial position which is the lower right corner of the Best Fit Error Box. This was given to a precision of 0.01 degrees in the published form of this catalog.

Boxarea_Beb
The area of the best fit error box, in units of deg**2. This box is omitted if the data are inconsistent with a constant source.

Count_Rate
The measured intensity, in units of counts/sec, with its 1 sigma uncertainty of the source in the so-called 1 keV (0.44-2.8 keV) band. The intensity is derived from the data in a uniform way, without regard to any source identication. To the extent that the A2 LED source locations differ from the true source locations, the quoted intensities are underestimates of the true source intensities. The parameter tfval is a transmission factor based on the offset between the A2 LED source position given here and the previously determined position, if known. (The value of tfval is set to 1.00 if the source was not previously known). Under the assumption that all the flux detected by the A2 LED is coming from the known source, the true source intensity is the product of the transmission factor and the quoted intensity.

Count_Rate_Error
The source intensity error in the 1 keV band, in ct/s.

Int_250ev
The measured intensity, in units of counts/sec, with its 1 sigma uncertainty of the source in the so-called 1/4 keV (0.18-0.44 keV) band. The intensity is derived from the data in a uniform way, without regard to any source identication. To the extent that the A2 LED source locations differ from the true source locations, the quoted intensities are underestimates of the true source intensities. The parameter tfval is a transmission factor based on the offset between the A2 LED source position given here and the previously determined position, if known. (The value of tfval is set to 1.00 if the source was not previously known). Under the assumption that all the flux detected by the A2 LED is coming from the known source, the true source intensity is the product of the transmission factor and the quoted intensity.

Int_250ev_Error
The source intensity error in the 1/4 keV band, in ct/s.

Tfval
A transmission factor based on the offset between the source position given here and the previously determined position, if known. (The value of tfval is set to 1.00 if the source was not previously known). Under the assumption that all the flux detected by the A2 LED is coming from the known source, the true source intensity is the product of the transmission factor and the quoted intensity.

Othername
Alternate name of source, if present. Aliases are given if the source has a positive identification or has been previously discovered in other X-ray surveys.

Othername2
Alternate name of source, if present. Aliases are given if the source has a positive identification or has been previously discovered in other X-ray surveys.

Othername3
Alternate name of source, if present. Aliases are given if the source has a positive identification or has been previously discovered in other X-ray surveys.

Comments
Comments include possible identifications, anomalies in the analysis of the LED data, and mention of unusual source characteristics. UV contamination refers to probable contamination of the 1/4 keV band by ultraviolet readiation from the object. The comment "confused" denotes a case that required a second source within 3 degrees of the best-fit position of the catalogued source to adequately account for the data. "New MED source" denotes a previously unknown source that was detected by other HEAO A-2 detectors sensitive to photons with energies >= 2 keV. If further discussion of the LED data analysis for a catalogued source appears in the literature, a reference number (or numbers) is given. The actual reference to which the number refers can be found in Table 2 of the published catalog.


Contact Person

Questions regarding the A2LED database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 9-Nov-2004