SAXHELLAS - BeppoSAX High-Energy Large Area Survey (HELLAS) X-Ray Source Catalog

Overview

The BeppoSAX High Energy Large Area Survey (HELLAS) has surveyed about 85 deg² of sky in the 4.5 - 10 keV band down to a flux of 4 - 5 x 10^-14 erg/cm²/s using 142 high Galactic latitude (|b| > 20^o) observations made by the BeppoSAX Medium Energy Concentrator Spectrometer (MECS). The source surface density of 16.9 +/- 6.4 deg² at the survey limit corresponds to a resolved fraction of the 5 - 10 keV X-ray background (XRB) of the order of 20-30 per cent.

Hardness ratio analysis indicates that the spectra of a substantial fraction of the HELLAS sources (at least one-third) are harder than a alpha_E = 0.6 power law. This hardness may be caused by large absorbing columns. The hardness ratio analysis also indicates that many HELLAS sources may have a spectrum more complex than a single absorbed power law. A soft component, superimposed on a strongly cut-off power law, is likely to be present in several sources.

There is no overlap among the 142 fields used and, wherever possible, multiple observations of the same field have been merged in one single pointing to increase the sensitivity. Fields were selected among public data (such as that of March 1999) and the authors' proprietary data. Fields centered on bright extended sources and bright Galactic sources were excluded from the survey, as were fields close to the Large Magellanic Cloud (LMC), Small Magellanic Cloud (SMC) and M 33. Most of the fields have exposures between 30 and 100 ks, and 20 fields have an exposure higher than 80 ks (see Fig. 1 of reference paper). Sources were detected in images accumulated between 4.5 and 10 keV. Source count rates in four bands (1.3 - 10 keV, total or T; 1.3 - 2.5 keV, low band or L; 2.5 - 4.5 keV, middle band or M; 4.5 - 10 keV, high band or H) were extracted and corrected for the energy-dependent vignetting and for the MECS PSF. The count rates were converted to fluxes using a conversion factor of 7.8 x 10^-11 erg cm^-2 s^-1 (5 - 10 keV flux) per one '3 ECS count' (4.5 - 10 keV) appropriate for a power-law spectrum with alpha_E = 0:6. The factor is not strongly sensitive to the spectral shape, owing to the narrow band: thus, for alpha_E = 0.4 and 0.8 it is 8.1 and 7.6 x 10^-11 erg cm^-2 s^-1, respectively. A conversion factor of 9:9 x 10^-11 erg cm^-2 s^-1 per one '3 MECS count' has been used for sources under the 550 micron (um) beryllium strongback supporting the MECS window to account for the reduced detector sensitivity.

Catalog Bibcode

2001MNRAS.327..771F

References

The BeppoSAX High Energy Large Area Survey (HELLAS).
II. Number counts and X-ray spectral properties.
    Fiore F., Giommi P., Vignali C., Comastri A., Matt G., Perola G.C.,
    La Franca F., Molendi S., Tamburelli F., Antonelli L.A.
   <Mon. Not. R. Astron. Soc. 327, 771 (2001)>
   =2001MNRAS.327..771F

Provenance

This table was created by the HEASARC in July 2014 based on CDS Catalog J/MNRAS/327/771 file table2.dat.

Parameters

Name
The BeppoSAX HELLAS source designation as recommended by the CDS Dictionary of Nomenclature of Celestial Objects, using the 'HELLAS' prefix (for High Energy Large Area Survey) and the source identification number, replacing the underscore ('_') character in some of the source numbers with a period ('.').

RA
The Right Ascension of the X-ray source in the selected equinox. This was given in J2000.0 sexagesimal coordinates to a precision of 0.1 seconds of time in the original table. The location of an X-ray source by the BeppoSAX MECS is affected by statistical and systematical uncertainties, as discussed in some detail in the Appendix of the reference paper. Source positions in this table were corrected for the systematic effects discussed there by performing a simple foresight correction with respect to the known positions of the target and of any other known bright source in each field.

Dec
The Declination of the X-ray source in the selected equinox. This was given in J2000.0 sexagesimal coordinates to a precision of 1 arcsecond in the original table. The location of an X-ray source by the BeppoSAX MECS is affected by statistical and systematical uncertainties, as discussed in some detail in the Appendix of the reference paper. Source positions in this table were corrected for the systematic effects discussed there by performing a simple foresight correction with respect to the known positions of the target and of any other known bright source in each field.

LII
The Galactic Longitude of the X-ray source.

BII
The Galactic Latitude of the X-ray source

Off_Axis
The off-axis angle of the X-ray source from the field center, in arcminutes.

Flux
The flux of the X-ray source in the 5-10 keV band, in erg cm^-2 s^-1.

SNR
The signal-to-noise ratio of the X-ray detection in the 5-10 keV band.

Softness_Ratio
The softness ratio of the X-ray source, SR = (S-H)/(S+H), where S is the count rate in the 1.3 - 4.5 keV band (and hence S is the sum of the count rates in the 1.3 - 2.5 keV band -L- and in the 2.5 - 4.5 keV band - M) and H is the count rate in the 4.5 - 10 keV band.

Softness_Ratio_Error
The rms uncertainty in the softness ratio of the X-ray source, SR.

Softness_Ratio_Flag
This flag parameter is set to 'b' to indicate that the X-ray source is partly obscured by the Medium Energy Concentrator Spectrometer (MECS) beryllium strongback Softness ratios have not been calculated for such sources because their observed hardness may be systematically higher than is realistic.

Hardness_Ratio_1
The hardness ratio of the X-ray source, HR₁ = (M-L)/(M+L), where L is the count rate in the 1.3 - 2.5 keV band and M is the count rate in the 2.5 - 4.5 keV band.

Hardness_Ratio_1_Error
The rms uncertainty in the hardness ratio of the X-ray source, HR₁.

Hardness_Ratio_1_Flag
This flag parameter is set to 'b' to indicate that the X-ray source is partly obscured by the Medium Energy Concentrator Spectrometer (MECS) beryllium strongback, or to 'c' if the signal-to-noise ratio of the source is < 3.8. Hardness ratios have not been calculated for flagged sources because their observed hardness may be systematically higher than is realistic ('b' values) or statistically insignificant ('c' values).

Hardness_Ratio_2
The hardness ratio of the X-ray source, HR₂ = (H-M)/(H+M), where M is the the count rate in the 2.5 - 4.5 keV band and H is the count rate in the 4.5 - 10 keV band.

Hardness_Ratio_2_Error
The rms uncertainty in the hardness ratio of the X-ray source, HR₂.

Hardness_Ratio_2_Flag
This flag parameter is set to 'b' to indicate that the X-ray source is partly obscured by the Medium Energy Concentrator Spectrometer (MECS) beryllium strongback, or to 'c' if the signal-to-noise ratio of the source is < 3.8. Hardness ratios have not been calculated for flagged sources because their observed hardness may be systematically higher than is realistic ('b' values) or statistically insignificant ('c' values).

HELLAS_ID
The unique HELLAS source identification number.

Contact Person

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

Page Author: Browse Software Development Team
Last Modified: Monday, 14-Jul-2014 15:18:35 EDT