EXOSAT/High ivo://nasa.heasarc/exohgls NASA/GSFC HEASARC Giommi et al. 2026-10-09 NASA/GSFC HEASARC help desk heasarc-vo at athena.gsfc.nasa.gov Survey Source A survey of serendipitous source performed in the very soft X-ray band (0.05-2.0 keV) using the EXOSAT imaging telescopes is presented. The survey covers 783 square degrees of high galactic latitude sky and includes 210 serendipitous sources which define a complete (flux-limited) sample. An extensive program of optical and radio observatories together with cross-correlations with catalogs of known objects lead to the identification of 200 of the 210 detected sources. The 10 remaining objects have been preliminarily classified on the basis of their X-ray to optical flux ratios, thus making the sample essentially fully identified. Twenty-three additional serendipitous sources which did not satisfy the requirements for inclusion in the complete sample were also identified during the optical observations program. The complete sample has been used to study the logN-logS relation and the average spectral slope of AGN. It is found that the logN-logS slope is consistent with that of the Einstein Extended Medium Sensitivity Survey (EMSS) and with the "Euclidean" value of 1.5. The normalization of the logN-logS is a strong function of the assumed spectral slope of AGN. Consistency with the results of the EMSS implies that the average (energy) slope of extragalactic sources in the soft X-ray band is very steep (alpha ~ 1.5). An analysis of the association between AGN detection and Galactic NH also shows that alpha is steep and inconsistent with the canonical value of 0.7. The survey was particularly successful in detecting nearby Galactic soft X-ray emitters and includes a significantly higher percentage of stars than the Einstein EMSS, five White Dwarfs, and three previously unknown AM Her type systems. The sample of sources in this catalog has been selected from the CMA database, which it has been generated using a standard processing on the LE data. The source detection algorithm used a sliding cell method. The size of the search cell is such as to maximize the sensitivity across the field of view. For more information about the LE processing see the documentation in the CMA database. This is a service provided by NASA HEASARC . 1991ApJ...378...77G https://heasarc.gsfc.nasa.gov/W3Browse/all/exohgls.html Catalog Research served-by HEASARC TAP https://heasarc.gsfc.nasa.gov/xamin/vo/cone?showoffsets&table=exohgls& GET text/xml 180 99999 true 98.4415730319784 -75.6293093053991 0.0166666666666667 https://heasarc.gsfc.nasa.gov/xamin/vo/tap https://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/getvotable.pl?name=exohgls GET text/xml https://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/w3query.pl?tablehead=name=heasarc_exohgls&Action=More+Options&Action=Parameter+Search&ConeAdd=1 EXOSAT 0.0166666666666667 X-ray public exohgls EXOSAT/CMA High Galactic Latitude Survey name Target Designation meta.id;meta.main char nullable count_rate Count Rate (counts/sec) for Source ct/s phot.count;em.X-ray float nullable count_rate_error Error in Count Rate ct/s stat.error;phot.count;em.X-ray float nullable ra Right Ascension degree pos.eq.ra;meta.main double nullable dec Declination degree pos.eq.dec;meta.main double nullable class Browse Object Classification src.class short nullable "__x_ra_dec" System unit vector column double nullable "__y_ra_dec" System unit vector column double nullable "__z_ra_dec" System unit vector column double nullable "__row" System index column char nullable ub_color U-B Color phot.color;em.opt.U;em.opt.B float nullable expected_variance_ta1 Expected Variance in TA1 float nullable al_count_rate Al-Par Count Rate ct/s float nullable res_of_lc Bin Width in Rate Buffer (sec) s float nullable id_number Source Order Number short nullable me_3_to_6_count_rate_err ME Count Rate Error in 3-6 keV Band ct/s float nullable file_bglcurve File with Background Light Curve char nullable point_source_flag Point Source Flag short nullable lii Galactic Longitude degree pos.galactic.lon double nullable file_lcurve File with Light Curve char nullable last_update Date of Last Record Update mjd time.creation double nullable ipc_count_rate IPC Count Rate ct/s float nullable quality_check Visual Quality of Detection short nullable lightcurve_prefix Rates Buffer Identifier (First Letter) char nullable expected_variance_ta2 Expected Variance in TA2 float nullable ipc_count_rate_error IPC Count Rate Error ct/s float nullable y_pixels Centroid Y (pixel*10) short nullable rosat_id ROSAT Identifier (spare) short nullable me_1_to_3_count_rate_err ME Count Rate Error in 1-3 keV Band ct/s float nullable vmag Visual Magnitude phot.mag;em.opt.V float nullable redshift Redshift or HD Number of Counterpart src.redshift float nullable iras_flux_4 100-micron IRAS Flux Jy float nullable old_nh_21cm NH (10^19 cm^-2) in the Galaxy 10^19_cm^-2 short nullable x_pixels Centroid X (pixel*10) short nullable filter Filterwheel Position short nullable radio_5ghz_flux Radio Flux (mJy) at 5 GHz mJy float nullable proposal_type Proposal Type (HLX, etc.) char nullable radio_flag Flag for Radio Emission short nullable nh_21cm 21-cm NH Through the Galaxy cm^-2 float nullable qflag_me ME Quality Flag short nullable error_radius Error Radius (arcsec) arcsec stat.error;pos short nullable sequence_number Sequence Number meta.id;obs short nullable offset_detection_angle Distance from xpix=15, ypix=15 arcmin float nullable me_count_rate ME Count Rate ct/s float nullable bo_count_rate Boron Count Rate ct/s float nullable bv_color B-V Color phot.color;em.opt.B;em.opt.V float nullable pi_code Principal Investigator Code short nullable deadtime_correction Detector Deadtime Correction Factor float nullable background_per_sqpix Background Level (counts/sq.pixel) ct/square_pixel float nullable me_1_to_3_count_rate ME Count Rate in 1-3 keV Band ct/s float nullable instrument Experiment Code char nullable diamond_filter OBC Configuration short nullable me_3_to_6_count_rate ME Count Rate in 3-6 keV Band ct/s float nullable old_deadtime Dead Time Correction s short nullable iras_flux_1 12-micron IRAS Flux Jy float nullable me_count_rate_error ME Count Rate Error ct/s float nullable "time" Start Time of Observation mjd time.start;obs double nullable iras_flux_2 25-micron IRAS Flux Jy float nullable iras_flux_3 60-micron IRAS Flux Jy float nullable bii Galactic Latitude degree pos.galactic.lat double nullable bo_count_rate_error Boron Count Rate Error ct/s float nullable exposure_time Exposure Time (seconds) s int nullable observed_variance_ta2 Observed Variance in TA2 float nullable al_count_rate_error Al-Par Count Rate Error ct/s float nullable alt_name Alternate Target Designation meta.id char nullable tape_no Archive Tape Number Where Files Are Stored short nullable serendipity_flag Flag for Serendipitous Sources short nullable detection_significance Probability That Source Is Fluctuation of Background float nullable qflag_le Quality Flag: 0(unusable)->5(best) short nullable observed_variance_ta1 Observed Variance in TA1 float nullable processed_date Date of Buffer Creation mjd time.processing double nullable file_image Compressed Image Name char nullable