IPC rates for internal pulsars may be high because of a contribution from surrounding diffuse emission. For example, the HRI data for the Vela pulsar and for PSR 1509-58, show bright diffuse emission within 1 minute of the point-like sources, so the IPC rates for these objects include some diffuse emission.
For weak remnants, uncertainties listed for IPC rates are due to counting statistics and background subtraction. For the small, bright remnants, systematic uncertainties in scattering and vignetting corrections dominate. Rates for remnants made from merges of several fields were calculated by determining the total number of counts above background in the merged image and then using a bright spot to normalize to the IPC rate measured in one field. Here the largest uncertainties are in the determin- ation of the background and in the counting rate of the area used for normalization.
The conversion of counting rate to energy flux depends on the spectrum. Tables to aid in doing this are in the Einstein Observatory Revised User's Manual (Harris, 1984) which can be obtained by request.
HRI rates given in table 2 have been corrected for vignetting, scattering in the telescope, and deadtime. Uncertainties are both statistical and systematic. Counting statistics are the dominant uncertainty for weaker sources and short observations. Possible errors in scattering correction and HRI sensitivity are dominant for the bright sources. The scattering correction is uncertain because it depends on the sometimes unknown energy spectrum. The efficiency of the HRI is uncertain because it decreased during the observatory lifetime, dropping 20% in 28 months. HRI rates have been corrected to January 1979, the first use of HRI #3, the detector used for all SNR observations, and the closest time to the preflight calibration.
HRI coverage of the larger remnants was usually not complete (eg. Cyg Loop, IC 443). In seven cases, with coverage from 35% to 90%, we have calculated an HRI rate for the entire SNR by using the observed IPC data and assuming the ratio of HRI to IPC rates was the same for the observed and the unobserved parts of the remnant. Such rates are footnoted in table 2.
The collimation was 45 minutes FWHM. Rates from remnants with diameters < 4 minutes, if centered in the field of view, needed no correction for transmission through the collimator. Rates for small remnants, off center, were corrected using the ground-measured collimator transmission. Remnants with sizes between 4 minutes and 60 minutes, were assumed to appear as uniform rings (SNR 1006) or disks (IC 443) of emission and correction factors were calculated.
The largest remnants, Vela XYZ and the Cygnus Loop, were observed using a raster of pointings with regular spacing of 60 minutes and 30 minutes respectively between field centers. Thus the Cygnus Loop was observed in entirety with efficiency (calculated by adding the collimator-transmission efficiency of overlapping observations) varying between 1.5 and 2.0, and an MPC rate for the entire remnant could be calculated. Similarly, the efficiency of the Vela SNR observations varied between 0 and 1.0. Regions with 0 efficiency were small and most of the SNR was observed with efficiency ~ 0.5 (50%).
A possible source of error in MPC rates could be caused by counts from sources at the edge of the MPC field of view but just outside the smaller field of view of the imaging detector. In this way, a bright source might produce a moderate rate in the MPC and give no other clue to its existence. Positions of the bright bulge sources and remnants in the galactic plane are known and the rates in table 2 are free of the effects of these. No MPC rate is given for Kes 69 because of nearby G21.5-0.9. Similarly, the rate for G327.1-1.1 is contaminated by 2S 1553-542 and other weak nearby sources. There are also transient sources, always a possibility, and an unusually high MPC rate should not be accepted without reservation.
Aside from the obvious interest in objects which might be neutron stars formed in the SN explosion, this table is a useful supplement to other catalogs which sometimes do not search "messy" fields for weak sources. IPC and HRI rates quoted are total counting rates in the detector. All energy channels of the IPC are included and corrections have been made for mirror-scattering and dead time. Identifications are given when known and in these cases the coordinates listed are those of the optical or radio counterpart. If the source is not identified, the coordinates are those derived from IPC or HRI data.
Sources are listed as being outside the boundary of the SNR(O), inside the boundary, (I), or at the approximate center of the SNR (C).