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ASCASIS - ASCA SIS Source Catalog



This preliminary ASCA SIS Source Catalog contains a list of point sources detected by the Solid-state Imaging Spectrometers (SIS) on-board the ASCA Observatory. This catalog was generated by searching for point-like sources in all data available from the HEASARC's ASCA public archive (ASCAPUBLIC) as of 24 Oct 1996; and is populated by both target and serendipitous sources in the SIS field-of-view.

For each catalogued source various information is available, which includes the celestial coordinates of the source, the count rate, the significance of detection, and the hardness ratio, total aperture counts, exposure time, and start time of the observation. In addition, a set of three GIF "thumbnail" images is available in the broad (0.5 - 12 keV), soft (2 < keV), and hard (> 2 keV) spectral bands centered on the apparent detection. These images are convenient for accessing the quality of the source detection.

The current catalog is preliminary, the goal of the catalog authors being to make the SIS source list available as quickly as possible. To accomplish this, they took an incremental approach and placed their "work in progress" on-line, warts and all. They urge caution in using and citing these preliminary results, as they point out that the information is not, as yet, 100% reliable.

Catalog Bibcode



A full description of the ASCA archive and how to use it can be found at or at

The current best reference for this catalog is: Gotthelf, E.V. and White, N.E. 1997, in "X-Ray Imaging and Spectroscopy of Cosmic Hot Plasmas", p. 31.


This catalog was generated in January 1997 by Drs. Eric Gotthelf and Nicholas White and resulted from their search for point-like sources in all of the then-available SIS data files in the HEASARC's Public ASCA Data Archive as of 24 Oct 1996. The catalog is populated with both targeted and serendipitous sources that were present in the SIS field-of-view.

Data Products

Entries in the ASCASIS table have associated with them the standard ASCA public data products for the observation in which the source was detected (see, as well as three GIF files containing the soft-band, hard-band, and broad-band images of the source that were specially constructed for this catalog.


A unique identifier for each ASCA observation set.

The source designation within this catalog. The name is derived from the AXS prefix (for ASCA SIS X-ray source) and the apparent J2000 R.A. and Declination.

The apparent Right Ascension of the source in the selected equinox.

The apparent Declination of the source in the selected equinox.

The galactic longitude of the source.

The galactic latitude of the source.

The apparent Right Ascension of the source in the B1950 equinox and in decimal degrees.

The apparent Declination of the source in the B1950 equinox and in decimal degrees.

The estimated total broad-band (0.5 to 12 keV) count rate at the telescope, in counts/second.

The error in the estimated total broad-band (0.5 to 12 keV) count rate at the telescope, in counts/second. (not currently populated).

The estimated significance of this source detection. Because of the complex ASCA mirror response function this number should be considered with caution.

The estimated hardness ratio defined as the difference over the sum of the hard (2 - 12 keV) and soft (0.5 - 2 keV) band count rates at the source position (= [S-H] / [S+H]).

The estimated error on the hardness ratio (not currently populated).

The accumulated total counts within in a 6 arcmin aperture centered on the source.

The total "good" exposure time in seconds.

The start time of the observation.

The root filename for accessing the GIF image.

Contact Person

If you have questions regarding the ASCA SIS catalog, please contact Eric Gotthelf <> or Nick White <> for science issues. If you have questions or problems related to the HEASARC database implementation, please contact the HEASARC Help Desk.
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Last Modified: Wednesday, 09-Feb-2022 19:48:50 EST