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HRIIMAGE: Help

HRIIMAGE - Einstein HRI Images


Overview

The HRIIMAGE database contains information from the High Resolution Imager aboard HEAO 2, the Einstein Observatory. Einstein incorporated a high-resolution X-ray telescope and a focal plane assembly capable of positioning at its focus one of four instruments: a high-resolution imaging detector (HRI), a broader-field imaging proportional counter (HRI), a solid state spectrometer (SSS), and a Bragg crystal spectrometer (FPCS). Einstein (HEAO 2) was launched on November 13, 1978, and operated successfully until April 1981.

References

The High Resolution Imager has been described by Henry et al. (Proc SPIE, 106, 196,1977).

Description

The HRI used a pair of cascaded microchannel plates as an X-ray image converter and photoelectron multiplier, and a crossed-wire grid as a two-dimensional position-sensitive charge detector. The detector provided an arrival time and position for each X-ray event occurring within the 24 arcmin FOV and within the energy range 0.15-3.5 keV. The spatial resolution of the HRI was 3 arcsec at the telescope focus and the temporal resolution was 7.8125 microsec. The nominal sensitivity of the HRI was 10 Uhuru counts per second, but this value depends on the assumed value of the low-energy cutoff parameter Ea. An Objective Grating Spectrometer (OGS) could be used in conjunction with the HRI. 53 sequences with this configuration are included in the 870 HRI image files of this database.

Data Products

This database contains the 870 High Resolution Imager FITS file images produced by the Harvard CfA. The images are within a 24 arcmin FOV of the target center and contain x-ray photons in the range 0.15-3.5 keV.

Parameters

Avg_Rotation_Offset
FITS keyword: AVG_ROT

Average rotational offsets (in radians) from nominal pointing direction.

BII
FITS keyword: GALB

Galactic Latitude of field center of the FITS image file.

Bscale
FITS keyword: BSCALE

Array elements are converted to integers, scaled to +/- 32767. This is done by finding the maximum and minimum (datamax and datamin) and using the equation:

                      BSCALE=(datamax-datamin)/(2*32767).
  

Dec
FITS keyword: CRVAL2

The DEC reference point value of the FITS image file. The declination (1950.0) in decimal degrees of the center of the image.

Delta_Dec
FITS keyword: CDELT2

The DEC increment along axis of the FITS image file.

Delta_RA
FITS keyword: CDELT1

The RA increment along axis of the FITS image file.

End_Time
FITS keyword: DATE_STP

Observation stop time.

File_Creation_Date
FITS keyword: DATE

FITS image file creation date.

File_GIF
File name of the GIF file created from the FITS image file. The file names follow the format `*HhhmmDdd.gif`. The `*` is a letter such as A, B, C, etc., to distinguish the files when the rest of the file name is not unique. The letters 'hhmm' denote the RA hour and minute. The `D` is either `N` or `S` for North or South, and `dd` is the declination in degrees.

File_Image
File name of the FITS image file in the database system. The files have been compressed with a routine called ZOO, so to separate the files from UNZOO'ed ones, the file has been renamed to the format `HhhmmDdd*.zoo`. The letters `hhmm` denote the RA hour and minute. The `D` is either `N` or `S` for North or South, and `dd` is the declination in degrees. The `*` is a letter such as A, B, C, etc., to distinguish the files when the rest of the file name is not unique. This occurs when more than one pointing was made at a given position.

File_Unzoo_Image
File name of the decompressed (UNZOO'ed) FITS image file placed in the current directory. These file names are of the form `HhhmmDdd.xi*`. The letters `hhmm` denote the RA hour and minute. The `D` is either `N` or `S` for North or South and `dd` is the Declination in degrees. The trailing `XI*` signifies `X-ray Intensity` and the final letters such as A, B, C, etc. distinguish XI files when the rest of the file name is not unique. This occurs when more than one pointing was made at a given position.

Focal_Plane_Detector
FITS keyword: INSTRUME

Focal plane detector, usually `HRI` in this catalog.

H_Column_Density
FITS keyword: NH

Column density of neutral hydrogen in atoms/cm**2 integrated along the line of sight through our galaxy in the direction of the target.

LII
FITS keyword: GALL

Galactic Longitude of field center of the FITS image file.

Minimum_Intensity
FITS keyword: DATAMIN

True minimum intensity within the FITS image file.

Net_Time
FITS keyword: NET_TIME

A measure of the effective exposure time for the field center. NET_TIME is the total number of seconds during which the detectors were able to gather data, corrected for Earth occultation, SAA, bad aspect solution and detector dead time.

Object
FITS keyword: OBJECT

Object sequence number in the Einstein source catalog.

Observer
FITS keyword: OBSERVER

Party responsible for collecting this particular observation, where 0 = CFA, 1 = CAL, 2 = MIT, 3 = GSFC.

Peak_Intensity
FITS keyword: DATAMAX

True peak intensity within the FITS image file.

RA
FITS keyword: CRVAL1

The RA reference point value of the FITS image file. The right ascension (1950.0) in decimal degrees of the center of the image.

Roll_Angle
FITS keyword: ROLL_ANG

The angle in degrees which measures the roll of the spacecraft about an axis pointing toward the field center. A positive value indicates a clockwise rotation of the detector's FOV.

Rotation_Dec
FITS keyword: CROTA2

DEC rotation.

Rotation_RA
FITS keyword: CROTA1

RA rotation.

Time
FITS keyword: DATE_OBS

Observation start time.

Title
FITS keyword: TITLE

Information on the nature of the target. Entries include catalog names (e.g., 4U0248-85) and observer's notes.

True_Pixel_Offset
FITS keyword: BZERO

`BZERO` is the offset to the true pixel values.

BZERO=(datamax-datamin)/2

The true pixel value is found using the scaled value TAPE in the following equations:

                      TAPE = (TRUE - BZERO)/BSCALE
                      TRUE = (TAPE*BSCALE) + BZERO
  

X_Pixel
FITS keyword: CRPIX1

Pixel coordinates of `RA` in image center of the FITS image file. The RA reference pixel location.

Y_Offset_Avg
FITS keyword: AVGOFFY

Average translation offsets (in 8 arcsec pixels) from nominal pointing direction on y axis.

Y_Pixel
FITS keyword: CRPIX2

Pixel coordinates of `DEC` in image center of the FITS image file. The declination reference pixel location.

Z_Offset_Avg
FITS keyword: AVGOFFZ

Average translation offsets (in 8 arcsec pixels) from nominal pointing direction on z axis.


Contact Person

Questions regarding the HRIIMAGE 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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