IX/24 The Einstein Observatory HRI Source List (Giacconi+, 1979)
The Einstein Observatory HRI Source List Giacconi et al. <The Einstein Observatory (HEAO-2) (1979)>
ADC_Keywords: X-ray sources ; Surveys ; Observatory log Mission_Name: Einstein Description: The Einstein Observatory is the second of NASA's three High Energy Astrophysical Observatories, HEAO-2, renamed Einstein after launch, and was the first fully imaging X-ray telescope put into space. It observed in the energy range 0.2-20keV. It was launched on 12 November 1978, and remained in operation until April 1981. The High Resolution Imager (HRI) is one fo the four instruments aboard the Einstein Observatory, operating in the 0.2-3.0keV energy range, with a spatial resolution of a few arcseconds, and a field of view of 25arcmin. Field and source parameters observed with this instrument are given here. The HRI Instruments: The High Resolution Imager (HRI) has been described by Henry et al (Proc. SPIE, 106, 196, 1977) and by Giacconi, et al (1979ApJ...230..540G). The following summary is meant only as a convenient reference for features of the HRI with which users should be familiar. The Instrument: --------------- The performance characteristics of the telescope-HRI combination included: spatial resolution (FWHM): 3 arcsec at the telescope focus field of view: 24 arcmin on a side temporal resolution: 7.8125 microsec background in orbit: 0.46 cts/sec/arcmin**2 (away from the South Atlantic Anomaly) quantum efficiency: ∼10% at 1 keV maximum event rate: 100 counts/sec. (telemetry limited) dead time correction: median of 1.02 for mission energy range: 0.15-3.0 keV (HRI-2) 0.15-3.5 keV (HRI-3) The mirror effective area decreased as a function of off-axis angle to 0.9 at 15 arcminutes. This "vignetting" must be taken into account when calculating count rates. The quantum efficiency of the microchannel plates varied by ±5% across the field of view of the HRI, which must also be allowed for in determining source strengths. The two-dimensional HRI used a pair of cascaded microchannel plates (MCPs) as an X-ray image converter and photoelectron multiplier, and a crossed-wire grid as a two-dimensional position-sensitive charge detector. Position determination was accomplished by electronic interpolation between the coarse grid wires. The detector provided the arrival time and position of each X-ray event which occurred within the field of view. The MCP photocathode surface was shielded from ultraviolet light and ions by a thin, metallized self-supporting plastic filter. This UV/ion shield was the only component to differ among the three HRIs on-board the Einstein Observatory. HRI-2 showed a splotchy artifact early in the mission; from December 15, 1978, therefore, HRI-3 was used instead. An Objective Grating Spectrometer (OGS) could be used in conjunction with the HRI. 53 sequences were observed with this configuration. These sequences have not been included in the current HRI source list. Point Response Function: ------------------------ An analytical approximation to the Point Response Function (PRF) for the HRI at 1.5 keV has been given by J.P. Henry: PSF(r) = 0.02885 x [ exp (-r/1.96") + 0.01 exp (-r/12.94") ] /arcsec**2 This was derived from long exposures of point sources on axis, and appears to be a reasonably accurate description within 5 arcminutes of the field center for sources such as Cyg X-2 and 3C273 (i.e., for sources with non-pathological spectra). The formula is also a good fit to the 1.5 keV ground calibration data. It is valid for r < 1'. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file. hrifield.dat 232 870 Field Parameters for the HRI Source List hrisrc.dat 69 600 Source Parameters for the HRI Source List obsnames.dat 61 435 Einstein Observers
See Also: http://heasarc.gsfc.nasa.gov/docs/einstein/heao2.html : the Einstein Observatory Home Page IX/22 : The CfA Einstein observatory extended deep X-ray survey IX/23 : Einstein Observatory Source Catalog IX/25 : Einstein Observatory Imaging Proportional Counter (IPC) Parameters IX/26 : Einstein Observatory, Revision 1B. Processings IX/27 : Einstein Observatory Catalog (OCAT or Yellow Book) Byte-by-byte Description of file: hrifield.dat
Bytes Format Units Label Explanations
2- 3 I2 h RAh Right Ascension (B1950) (hour) 5- 6 I2 min RAm Right Ascension (B1950) (min) 8- 9 I2 s RAs Right Ascension (B1950) (sec) 11 A1 --- DE- Declination sign (B1950) 12- 13 I2 deg DEd Declination (B1950) (deg) 15- 16 I2 arcmin DEm Declination (B1950) (arcmin) 18- 19 I2 arcsec DEs Declination (B1950) (arcsec) 21- 25 I5 --- Seqno Sequence number of observation (G1) 27- 32 F6.2 deg GLON Galactic longitude of field center (1) 34- 39 F6.2 deg GLAT Galactic latitude of field center (1) 41- 47 E7.2 cm-2 nH Column density (2) 49- 56 F8.5 rad rollAng Angle which measures the roll of spacecraft (3) 58- 66 F9.2 s ExpTime Effective exposure time (4) 68- 74 F7.2 pix Ypos Average y offset in pixels (5) 76- 82 F7.2 pix Zpos Average z offset in pixels (5) 84- 91 F8.5 rad Rot Average rotation offset (5) 93- 97 A5 --- Instr Focal plane detector (6) 99-101 I3 --- Obs Observer number (7) 103-105 I3 d Strt.D Date (Day) the observation started (8) 107-110 I4 yr Strt.Y Date (Year) the observation started (8) 112-114 I3 d Stop.D Date (Day) the observation ended (8) 116-119 I4 yr Stop.Y Date (Year) the observation ended (8) 121-128 F8.2 s Strt.s Start time of observation (8) 130-137 F8.2 s Stop.s End time of observation (8) 139-148 E10.5 d JD-2442500 Offseted Julian date of observation (9) 150-154 I5 ph/pix datamax Maximum number of detected photons/pixel (10) 156-158 A3 --- FlgFld Field Flag (11) 160-171 A12 --- FITSname FITS file name (12) 173-232 A60 --- ObsTitle The title of the observation
Note (1): The pointing position approximates the center of the field of view for the observation. Note (2): The 'nH' column gives the column density of neutral hydrogen in atoms/cm2 integrated along the line of sight through our galaxy in the direction of the target of the observation. Specified in exponential notation, the NH values are obtained from sky surveys of neutral hydrogen using 21cm radio observations. For declinations north of -40 °, they are from the Bell Lab survey (Stark, Heiles, Bally, and Linke, see Cat. VIII/28). For declinations south of -40 °, the column densities are from Heiles and Cleary (1979AuJPA..47....1H) and Cleary, Heiles, and Haslam (1979A&AS...36...95C), see Cat. VIII/8. Note (3): The roll angle is the angle, in radians, which measures the roll of the spacecraft about the axis pointing towards the field center. It provides the angular orientation of the focal plane detectors with respect to the celestial coordinate grid. A positive value of the roll angle indicates a clockwise rotation of the (detector's projected) field when viewing the celestial sphere. Note (4): The 'livetime', in seconds, is a measure of the effective exposure time for the field center. It is the total number of seconds during which the detectors were able to gather data. It excludes intervals lost because of Earth occultation, because of passage through the South Atlantic Anomaly, or because of unacceptable aspect solution. The livetime has been corrected for detector dead time, a fractional correction for the time during which the detector is unable to record events because it is "processing" a prior event. Note (5): These columns give the average offset (in pixels, for y and z coordinates) and the average rotation angle offset (in radians) of the aspect solution for the observation. The average offset is the average, over the exposure, of the offset between the initial pointing direction and all subsequent data. For the coordinates, it is given in pixels, each pixel being 0.5"/pixel. For the rotation angle, it is given in radians. Note (6): The Instr column lists which instrument was in the focal plane at the time of the observation. The instrument will either be the HRI-2 or HRI-3. The HRI-2 instrument was used only before 12/15/78. See "The HRI Instruments" section above for more details. Note (7): The observer column gives a code which identifies the observer of the observation. The following are defined: 0=CFA 1=CAL 2=MIT 3=GSFC 4+=Guest The list of the observer names is in the file "obsnames.dat" (identical to the similar file in Cat. IX/27). Note (8): These columns give the start and stop time, day, and year of the observation. The start and stop days are given as integers between 1 and 365. The start and stop times are given in seconds from 00:00UT. Note (9): This column gives the number of days from noon on March 28, 1975 (2442500 JD). Note (10): The datamax column is the maximum number of detected photons per pixel found in the FITS file created for the cdrom version of this database. Since the files were created at zoom 4, this is the number of photons in a 2" pixel, not in a 0.5" instrument pixel. Note (11): The field flag is given in this column. The format will be one or more strings, usually of 1 character, which indicate where to find ancillary information. The following flags are defined: N - The automated source detection analysis was not run for this field. W - The detection threshold was set to too low a value (typically by 1 to 2 counts) for this field. As this results in the detection of spurious sources, appearance of this flag almost always implies that some HRI Rev 1 detections in this field have been deleted from the HRI Source List. X - There is at least one extended source in the field. Y - This HRI field contains a bright source (count rate typically > 1 ct/sec), giving rise to detection of spurious sources in the wings of the bright source. These sources do not appear in the HRI Source List. Z - There are regions of source confusion (many real point sources so close together that they could not be resolved by the source detection algorithm used in the Rev 1 processing) in this field; the nucleus of M31 is an example of such a field. Q - A splotch due to artifacts in HRI-2 (used only from launch until mid-December 1978) is visible in the image. These flags are stacked, so to search for a source which is extended, the 'X' may be preceded/followed by other flag characters. Note (12): The filename column gives the FITS file name, used to reference the observation when accessing the Einstein cdroms distributed throughout the astronomical community (see http://nssdc.gsfc.nasa.gov/cd-rom/set_bd/sssmcp.html)
Byte-by-byte Description of file: hrisrc.dat
Bytes Format Units Label Explanations
2- 3 I2 h RAh Right Ascension (B1950) (
hour) 5- 6 I2 min RAm Right Ascension (B1950) ( min) 8- 9 I2 s RAs Right Ascension (B1950) ( sec) 11 A1 --- DE- Declination sign ( B1950) 12- 13 I2 deg DEd Declination (B1950) ( deg) 15- 16 I2 arcmin DEm Declination (B1950) ( arcmin) 18- 19 I2 arcsec DEs Declination (B1950) ( arcsec) 21- 25 I5 --- Seqno Sequence number for the observation (G1) 27- 28 I2 --- FOSno Field Ordered Source Number (1) 30- 36 E7.2 rad errPos Positional uncertainty (90% confidence) (2) 38- 46 E9.4 ct/s cCRate Corrected Count rate of source (3) 48- 56 E9.4 ct/s e_cCRate Corrected Count rate error (3) 58- 66 F9.3 --- SNR Signal to noise ratio (4) 68- 69 A2 --- srcflag Source flags (5)
Note (1): The source number may differ from that of the original "standard" processing because some previously detected sources were not included in this list while other, doubtless real sources, were not found by the automated system. Sources will not be present in this source list for any of the following reasons: 1) Source was not detected in the 12"x12" detect cell. All sources found only in 24"x24" and larger detect cells were rejected. In theory, this could result in the rejection of some real sources at large off-axis angles or of non-zero extent. In practice, most detections in the larger cells were rediscoveries of 12"x12" sources. 2) Source detected in the wings of another strong source. Because the assumption of a constant background over the field is grossly in error when a strong source is present, spurious detections in such cases were common. Detections in 111 HRI fields were excluded for this reason. 3) Source is at threshold. The detection thresholds for sources were designed to give information on any possible source in the field. Thus the threshold was set to give an average of 1 false source per field. For the present data base, we are instead concerned to list only sources whose existence is established at a high confidence level. This is achieved by raising slightly the threshold below which no source detection will be accepted (by 1 to 2 counts for typical exposures). 4) Field dominated by a strong, extended source. Small irregularities in surface brightness led to the detection of many separate "sources" which are clearly part of the one large source. Note (2): The positional error listed gives the positional uncertainty (in radians) for the 90% confidence level. This includes a statistical contribution added in quadrature to a systematic term. Note (3): The corrected count rate and error are given in these two columns. The count rate for each source (cCRate) is obtained by summing all counts within a circle of radius 18" centered on the final source position, and then applying the appropriate correction factors for exposure time, vignetting, deadtime, mirror scattering, and quantum efficiency. The error (e_cCRate) was estimated as follows: As a preliminary and conservative (i.e., high) estimate for the uncertainty in this rate, we have used sqrt(BCTS) Error = ----------- x Count Rate BCTS where BCTS is the sum of all counts inside the Detection box of side = 12". Note (4): The 'SNR' column gives the signal-to-noise ratio, the count rate divided by the error. This is a conservative estimate since for small number of counts the Poisson errors are significantly asymmetric. Note (5): The 'srcflag' column lists the source flag. The source will be marked with a source flag if one of the following conditions exists: C - The source lies in a confused region; its position and count rate may be seriously in error. X - This source shows obvious extent. U - The count rate for this source has been underestimated, either because it is extended, confused, or at the edge of the field of view. These flags are stacked, so to search for a source which is extended, the 'X' may be preceded/followed by other flag characters.
Byte-by-byte Description of file: obsnames.dat
Bytes Format Units Label Explanations
1- 3 I3 --- Obs The observer's identifying number 5- 60 A56 --- ObsName The observer's name and institution
Global Notes: Note (G1): The Seqno lists the sequence number, a unique numeric identifier for each observation. The sequence number was allocated sequentially at the time of proposal submission, and is an internal index used to key on all references to an observation.
History: Prepared from the tables available at the "ADS Catalogue Service" (CfA, Harvard-Smithsonian Center for Astrophysics, Cambrigde MA) Acknowledgements: References: Henry et al. 1977, Proc. SPIE, 106, 196.
(End) Francois Ochsenbein [CDS] 23-Apr-1999
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