ROSAT Status Report #58:
May 10, 1993
AO4 targets:
Following the resolution of target conflicts at the International Users Committee meeting in Germany, a list of targets accepted for the AO4 period is now available on anonymous ftp on the new legacy account. Users should ftp to heasarc.gsfc.nasa.gov and the target list can be found under rosat/timelines/ao4.targets and also rosat/nra_info/ao4.targets.
The document in ~ 200 kbytes in size, or ~400 blocks. The column headings are (left to right)
PI country prop# target# target name alternative name requested exp (ksec) intrument config (102=PSPC, 012=HRI) time critical flag Y/N offset pointing? Y/N (for timing studies targets can be offset to 40') RA (J2000) DEC (J2000) target priority (1,2,3)
Note that priority 3 targets may not be scheduled for the requested exposure time, and are not guaranteed to be scheduled at all.
The schedule for the first half of AO-4 is expected to be defined in the next 2 weeks.
Highlights from the UK ROSAT VAXNOTES conference
Handling PSPC PI data
The rebinning of PSPC PI spectra is recommended to avoid poor spectral fits due to uncertainty in the width of the individual PI channels. Many rebinning schemes are possible, but the one used in the standard analysis (SASS) may become widely used. Steve Snowden has also suggested a rebinning into 7 standard bands (R1 - R7). Both of these schemes are described below. They are based on a constant oversampling of the resolution function width as a function of energy.
The SASS rebinning scheme is tabulated below. Unfortunately, it includes pha channel 7 in its lowest output bin. This channel can be incompletely filled, and should never be used. I suggest that implementations of the SASS rebinning scheme include pha channels 8, 9 & 10 in the lowest bin. This bin can simply be ignored when analysing data taken after the PSPC gain change (14 Oct 1991), the lowest useable pha channel being 11 in the case.
first channel used is #7
OVERSAMPLING FACTOR 2.450000
34
chan energy in chan width nr. of compressed
the centre 256 channels
[keV] [keV]
1 8.0000006E-02 2.0000001E-02 2 [7-8]
2 0.1000000 2.0000001E-02 2 [9-10]
3 0.1250000 3.0000001E-02 3 [11-13]
4 0.1550000 3.0000001E-02 3 [14-16]
5 0.1850000 3.0000001E-02 3 [17-19]
6 0.2200000 4.0000003E-02 4 [20-23]
7 0.2600000 4.0000003E-02 4 [24-27]
8 0.3000000 4.0000003E-02 4 [28-31]
9 0.3450000 5.0000001E-02 5 [32-36]
10 0.3950000 5.0000001E-02 5 [37-41]
11 0.4450000 5.0000001E-02 5 [42-46]
12 0.4950000 5.0000001E-02 5 [47-51]
13 0.5500000 6.0000002E-02 6 [52-57]
14 0.6100000 6.0000002E-02 6 [58-63]
15 0.6700000 6.0000002E-02 6 [64-69]
16 0.7350000 7.0000000E-02 7 [70-76]
17 0.8050001 7.0000000E-02 7 [77-83]
18 0.8750001 7.0000000E-02 7 [84-90]
19 0.9500000 8.0000006E-02 8 [91-98]
20 1.030000 8.0000006E-02 8 [99-106]
21 1.110000 8.0000006E-02 8 [107-114]
22 1.190000 8.0000006E-02 8 [115-122]
23 1.275000 9.0000004E-02 9 [123-130]
24 1.365000 9.0000004E-02 9 [131-139]
25 1.455000 9.0000004E-02 9 [140-148]
26 1.550000 0.1000000 10 [149-158]
27 1.650000 0.1000000 10 [159-168]
28 1.750000 0.1000000 10 [169-178]
29 1.855000 0.1100000 11 [179-189]
30 1.965000 0.1100000 11 [190-200]
31 2.075000 0.1100000 11 [201-211]
32 2.185000 0.1100000 11 [212-222]
33 2.300000 0.1200000 12 [223-234]
34 2.420000 0.1200000 12 [235-246]
The 7 standard bands (R1-R7) suggested by Steve Snowden ("Analysis Procedures for ROSAT XRT/PSPC Observations of Extended Objects and the Diffuse Background", Snowden etal 1993 APJ Submitted) can be defined for XSPEC .PHA files with the following CHANPHA command
CHANPHA> group 8 19 12 20 41 22 42 51 10 52 69 18 70 90 21 91 131 41 132 201 70
As can be seen, this rebinning scheme is includes pha channels 8-10. For observations made after the gain change the R1L bin is defined:
CHANPHA> group 11 19 9 20 41 22 42 51 10 52 69 18 70 90 21 91 131 41 132 201 70
PSPC Gas Flow Policy
Gas consumption up to now has been a uniform 0.442 bar/day, and the current predicted date for the total depletion of the last gas tank at this rate of use is late November 1993.
Assuming continued nominal operation, the gas flow rate to the PSPC will be reduced to half its current value at the start of AO-4 (mid June 1993). This will extend the useful life of the PSPC by some 4-5 months. The extra PSPC life will be spent on observations proposed for in AO-5, ie after the 6 months of HRI operation in the first half of 1994. Because of the likely effect of the differential gas diffusion through the PSPC window on the calibration of the detector, extra calibration observations will be scheduled early in AO-4.
This plan to extend the life of the PSPC depends upon the stability of the detector. As you will know, the occurrence of an increasingly bright hot spot required a reduction in the PSPC HT setting on Oct 14 1991. More recently, on March 24 1993, a bright source appeared to cause breakdown (corona) in the detector. If this happens again, the HT will have to be reduced further, and the gas flow rate may have to be increased. Because of the threat posed by such breakdown, HT and gas flow changes will occur without notice. Should the gas flow rate be have to be increased, the PSPC gas would not then last to the end of the first half of AO-4.
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