| Description: ! The Soviet orbital observatory GRANAT was launched in December 1989 and was operational till November 1998. One of the main instruments of the observatory was the French-Soviet hard X-ray coded mask telescope SIGMA (Paul et al.1 1991, Adv.Space Res., 11, 279). It was the first space telescope that used coded aperture technique for reconstruction of sky images in hard X-rays (35-1300 keV). The angular resolution of the telescope was approximately 12' and the accuracy of a source localization is approximately 2-3'.p SIGMA discovered numerious interesting hard X-ray sources including GRS 1758-258, which is located only 40' from bright soft X-ray source GX 5-1. It detected hard X-ray flux from X-ray burster A1742-294, which is very near to bright black hole binary 1E1740.7-2942. SIGMA set an upper limit on the hard X-ray flux of from the central supermassive black hole in our Galaxy.p During the period 1990-1998 SIGMA observed more that one quarter of the sky with sensitivity better than 100 mCrab. The Galactic Center region had the deepest exposure ( approximately 9 million sec), with the sensitivity to a source discovery (S/N ~ 5) or approximately 10 mCrab.p A list of all detected sources with references to publications on them is presented in the paper of Revnivtsev et al. 2004, Astr. Lett. v.6. In these survey images (40-100 keV) all performed observations are averaged together. Transient sources that were discovered by SIGMA may not visible in the averaged image. p This survey has some features that users should keep in mind. The SIGMA telescope is a complicated instrument and is strongly dominated by the accuracy of the background subtraction. The presence of a very bright source in the field of view of the telescope sometimes can not be fully accounted for and as a result of it some 'ghost' sources can appear. Such features can be seen in the regions near very bright sources like Crab Nebula, Cyg X-1, Nova Per 1992, Nova Mus 1991, Nova Oph 1993, and in the Galactic Center region. In addition to its nominal field of view (~17x17 deg) located around the optical axis of the telescope, SIGMA had another window of relatively high transparency of its shield, approximately 20-30° apart from the optical axis. Becuase of this a very bright sources like Cyg X-1 can cause non zero illumination of the SIGMA detector if they are located approximately 20-30° from the optical axis. The ring-like features caused by this effect, can be seen around Cyg X-1, and Nova Per 1992. p The count rate of detected sources (or upper limits) can be roughly translated into mCrab using the fact that that Crab nebula gives the count rate approximately 2.8esup-3/sup cnts/s in the units, provided in 'flux' maps ]] |
| Completely compliant |
| Service URL |
| Input Parameter | Required | Present |
|---|---|---|
| Regular parameters: | ||
| POS | MUST | Yes |
| SIZE | MUST | Yes |
| INTERSECT | MAY | No |
| NAXIS | MAY | Yes |
| CFRAME | MAY | Yes |
| EQUINOX | MAY | Yes |
| CRPIX | MAY | No |
| CRVAL | MAY | No |
| CDELT | MAY | No |
| ROTANG | MAY | No |
| PROJ | MAY | Yes |
| FORMAT | MUST | Yes |
| Service specific parameters | ||
| INTERPOLATION | MAY | Yes |
| big | MAY | Yes |
| small | MAY | Yes |
| Field UCD | Required | Present | Required datatype |
Actual datatype |
|---|---|---|---|---|
| Regular fields: | ||||
| VOX:Image_Title | MUST | Yes | char | char |
| INST_ID | SHOULD | No | char | |
| VOX:Image_MJDateObs | SHOULD | No | double | |
| POS_EQ_RA_MAIN | MUST | Yes | double | double |
| POS_EQ_DEC_MAIN | MUST | Yes | double | double |
| VOX:Image_Naxes | MUST | Yes | int | int |
| VOX:Image_Naxis | MUST | Yes | int | int |
| VOX:Image_Scale | MUST | Yes | double | double |
| VOX:Image_Format | MUST | Yes | char | char |
| VOX:STC_CoordRefFrame | SHOULD | No | char | |
| VOX:STC_CoordEquinox | MAY | No | double | |
| VOX:WCS_CoordProjection | SHOULD | No | char | |
| VOX:WCS_CoordRefPixel | SHOULD | No | double | |
| VOX:WCS_CoordRefValue | SHOULD | No | double | |
| VOX:WCS_CDMatrix | SHOULD | No | double | |
| VOX:BandPass_ID | SHOULD | No | char | |
| VOX:BandPass_Unit | SHOULD | No | char | |
| VOX:BandPass_RefValue | SHOULD | No | double | |
| VOX:BandPass_HiLimit | SHOULD | No | double | |
| VOX:BandPass_LoLimit | SHOULD | No | double | |
| VOX:Image_PixFlags | SHOULD | Yes | char | char |
| VOX:Image_AccessReference | MUST | Yes | char | char |
| Service specific fields: | ||||
| VOX:LogicalName | MAY | YES | char | |