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LMCHRIXRAY: Help

LMCHRIXRAY - ROSAT HRI Catalog of LMC X-Ray Sources (Sasaki et al.)


Overview

All 543 pointed observations of the ROSAT High Resolution Imager (HRI) with exposure times higher than 50 seconds, and performed between 1990 and 1998 in a field of 10 by 10 degrees covering the Large Magellanic Cloud were analyzed, and a source catalogue was produced that contains 397 X-ray sources whose properties have been measured with the HRI. The list was cross-correlated with the ROSAT Position Sensitive Proportional Counter (PSPC) LMC source catalogue of Haberl and Pietsch (1999, A&AS, 139, 277; the HEASARC database LMCROSXRAY) in order to obtain the (PSPC) hardness ratios for the X-ray sources detected by both instruments. 138 HRI sources are contained in the PSPC Catalogue, while 259 sources are new detections. The spatial resolution of the HRI being better than that of the PSPC, source positions could be determined with errors smaller than 15 arcsec which are dominated by systematic errors. After cross-correlating the source catalogue with the SIMBAD database and the Tycho Catalogue, 94 HRI sources were identified with known objects based on their positional coincidences and X-ray properties. Whenever more accurate coordinates were given in catalogues or the literature, the X-ray coordinates were corrected and the systematic error of the X-ray position was reduced. For other sources observed simultaneously with an identified source, the positional coordinates were also improved. In total, the X-ray positions of 254 sources were newly determined. The sources identified in this study include 39 foreground stars, 24 supernova remnants (SNR), 5 supersoft sources, 9 X-ray binaries, and 9 active galactic nuclei (AGN) well-known from the literature. Another 8 sources were identified with known candidates for these source classes. An additional 21 HRI sources were suggested by the authors as candidates for SNR, X-ray binaries in the LMC, or background AGN, because of their spatial extents, hardness ratios, X-ray to optical flux ratios, or flux variability.

Catalog Bibcode

2000A&AS..143..391S

References

'ROSAT HRI catalogue of X-ray sources in the LMC region', Sasaki M., Haberl F., Pietsch W. 2000, A&AS, 143, 391 (SIMBAD/NED Bibcode = 2000A&AS..143..391S ).

Provenance

This database was created at the HEASARC in June 2000 based on the ADC/CDS Catalog J/A+AS/143/391, and is derived from Table 4 of the reference.

Parameters

Name
The source identification recommended by the CDS Dictionary of Nomenclature of Celestial Objects, where the HEASARC has prefixed the running number given in the original computer-readable table with the acronym 'SHP2000'.

RA
The right ascension of the X-ray source in the specified equinox. In the original table the RA was given in equinox 2000 and with a precision of 0.1 seconds of time.

Dec
The declination of the X-ray source in the specified equinox. In the original table this was given in equinox 2000 and with a precision of 1 arcsecond.

LII
The galactic longitude.

BII
The galactic latitude.

Shp2000
The catalog source number.

Error_Radius
The spatial resolution of the HRI being better than that of the PSPC, source positions could be determined with errors smaller than 15 arcsec, which are dominated by a systematic positional uncertainty of 7 arcsec. After cross-correlating the source catalogue with the SIMBAD database and the Tycho Catalogue, 94 HRI sources were identified with known objects based on their positional coincidences and X-ray properties. Whenever more accurate coordinates were given in catalogues or the literature, the X-ray coordinates were corrected and the systematic error of the X-ray position was reduced. For other sources observed simultaneously with an identified source, the positional coordinates were also improved. In total, the X-ray positions of 254 out of 397 sources were newly determined.

In cases where positional correction was possible, the remaining error consists of the error in the optical position and the statistical error of the identified X-ray source. For sources whose positions were not corrected, the systematic error was set to 7 arcsec. The positional error was finally computed as the composite of the statistical (90% confidence) error in the X-ray position and the systematic error. After the source detection procedure the mean positional error was 8.3 arcsec. The coordinate correction reduced the mean positional error of all the sources to 6.4 arcsec (for the position-corrected sources the mean positional error is 5.1 arcsec).

Detect_Likelihood
The likelihood of existence for the source determined by the maximum likelihood technique. Sources were accepted if their likelihood of existence was larger than 10.0 and the telescope off-axis angle was less than 15 arcmin.

Count_Rate
The net HRI count rate, in counts per second. The count rate from the observation in which the positional error of the source (as determined by the maximum likelihood technique) was the smallest, is quoted here. Therefore, this count rate is representative of one single observation of the source.

For extended sources like SNRs with ringlike structures, the net count rates were determined interactively by integrating the counts within a circle around the source. For the background the counts were averaged in a ring around the source that was distant enough so as not to be influenced by the source emission. In some cases of extended SNRS, the quoted count rate may correspond to a knot within the source and not the whole source.

Count_Rate_Error
The error in the HRI count rate, in counts per second.

Source_Extent
The X-ray source extent, in arcsec, determined by the maximum likelihood technique fitting the source intensity distribution with a Gaussian profile. The count rates resulting from this calculation are correct only for sources with small extents and brightness profiles peaking in the center. For extended sources like SNRs with ringlike structures, the net count rates were determined interactively by integrating the counts within a circle around the source. For the background the counts were averaged in a ring around the source that was distant enough so as not to be influenced by the source emission.

Source_Extent_Error
The error in the X-ray source extent, in arcsec.

Extent_Likelihood
The likelihood for the extent determined by the maximum likelihood technique.

Pspc_Upper_Limit
A flag which, if set to '<', indicates that that there is no PSPC detection of the HRI X-ray source and that the quoted PSPC count rate is a 2-sigma upper limit derived from the PSPC pointing with the the higest exposure time.

Pspc_Count_Rate
The PSPC count rate, in counts per second (or the 2-sigma upper limit from the maximum likelihood algorithm, if pspc_upper_limit = '<'). The count rate from the observation in which the positional error of the source (as determined by the maximum likelihood technique) was the smallest, is quoted here. Therefore, this count rate is representative of one single PSPC observation of the source. PSPC count rates are taken from the LMC PSPC Catalog of Haberl and Pietsch (1999, A&AS, 139, 277: the HEASARC LMCROSXRAY database) if available. If the source was too too close to the rim or the window support structure of the PSPC detector, no PSPC count rate value is given here. Nor was it possible to determine PSPC count rates or upper limits for sources located in regions with diffuse X-ray emission.

Hp99
The PSPC source number from the LMC X-ray source catalogue of Haberl and Pietsch (1999, A&AS, 139, 277; the HEASARC database LMCROSXRAY).

Hardness_Ratio_1
The hardness ratio HR1 of the associated PSPC source, defined as HR1 = (H-S)/(H+S), where S and H are the count rates in the 0.1-0.4 keV and 0.5-2.0 keV bands, respectively. This is not calculated in cases where not all of the required count rates are available.

Hardness_Ratio_1_Error
The error in the PSPC hardness ratio HR1 (hardness_ratio_1).

No_HR1_Uncertainty
This flag is set to 'N' when no uncertainty in the PSPC hardness ratio HR1 value is given.

Hardness_Ratio_2
The hardness ratio HR2 of the associated PSPC source, defined as HR2 = (H2-H1)/(H1+H2), where H1 and H2 are the count rates in the 0.5-0.9 keV and 0.9-2.0 keV bands, respectively. This is not calculated in cases where not all of the required count rates are available.

Hardness_Ratio_2_Error
The error in the PSPC hardness ratio HR2 (hardness_ratio_2).

No_HR2_Uncertainty
This flag is set to 'N' when no uncertainty in the PSPC hardness ratio HR2 value is given.

Remarks
Remarks on the source classification and relevant references ('fg' means foreground, notice). Candidates from the literature are marked with a '?' after the source class, while new classifications are put between angle brackets '< >'. The reference codes are as follows:

  [C97]    1997AJ....113.1815C Chu Y.-H.
  [CKS97]  1997PASP..109..554C Chu Y.-H., Kennicutt R.C., Snowden S.L., et al.
  [CCH84]  1984ApJ...286..196C Cowley A.P., Crampton D., Hutchings J.B., et al.
  [CSM97]  1997PASP..109...21C Cowley A.P., Schmidtke P.C., McGrath T.K., et al.
  [CGC97]  1997AJ....114.2353C Crampton D., Gussie G., Cowley A.P.,
                               and Schmidtke P.C.
  [DPH96]  ................... Dennerl K., Haberl F., Pietsch W.
           1996, in: Zimmermann et al. (eds.) Proceedings of "Rontgenstrahlung
           from the Universe'', Sept. 25-29 1995, MPE report 263, 131
  [GGO93]  1993A&AS...99..591G Gochermann J., Grothues H.-G.,
                               Oestreicher M.O., et al.
  [GOG97]  1997A&AS..121..247G Grothues H.-G., Ostreicher M.O.,
                               Gochermann J., et al.
  [HDP95a] 1995A&A...302L...1H Haberl F., Dennerl K., Pietsch W.
  [HDP95b] 1995A&A...303L..49H Haberl F., Pietsch W., Dennerl K.
  [HDP97]  1997A&A...318..490H Haberl F., Dennerl K., Pietsch W.
  [HP99a]  1999A&A...344..521H Haberl F., Pietsch W.
  [HP99b]  1999A&AS..139..277H Haberl F., Pietsch W.
  [M94b]   1994A&AS..103..235M Morgan D.H.
  [OG99]   1999A&A...344L..13O Orio M., Greiner J.
  [SCF94]  1994PASP..106..843S Schmidtke P.C., Cowley A.P.,Frattare L.M., et al.
  [SCC99]  1999AJ....117..927S Schmidtke P.C., Cowley A.P., Crane J.D., et al.
  [WHHW91] 1991ApJ...374..475W Wang Q., Hamilton T., Helfand D.J., Wu X.
  

Contact Person

Questions regarding the LMCHRIXRAY database table can be addressed to the HEASARC User Hotline.
If you have any problems, please consult the help page or mail ledas-help@star.le.ac.uk
 
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