Contents

Chapter 1
INTRODUCTION

1.1  Overview

1.2  The OGIP Caldb at NASA/GSFC

1.2.1  Location

• Internet: legacy.gsfc.nasa.gov

1.2.2  Basic Structure

• data - containing the calibration dataset directory tree.
• software - containing the caltools software tasks, the callib subroutine library and a number of other software-related items.
• docs - containing related calibration documentation

1.2.3  Calibration Data File Classes

1.3  Conventions used within this Document

1.4  Acknowledgments

Chapter 2
ROSAT XRT CALIBRATION FILES

2.1  Summary of Available Files

2.2  BCF: Standard Energy Grid

2.2.1  xrt_v1.egrid

• The same standard energy grid is shared by many XRT & PSPC calibration files (see also Section 3.2.1)

2.3  BCF: Effective Areas

2.3.1  xrt_v#.eff_area

• the gas efficiency: pspc_v1.gas_eff
• the window transmission: pspcb_v1.wind_trans

• The XRT effective area is assumed to be independent of azimuthal angle.
• The dataset xrt_v1.eff_area was only used for a short period early in the mission, until it was superceded by xrt_v2.eff_area.
• The area_b_2.asc dataset from which this dataset is derived appears to be identical to that known as SASS_AREA_B_NEW2.FITS by the SASS processing software (and distributed on US (Rev0) GO tapes within the rp*****.oar file)

2.4  BCF: Vignetting Function

2.4.1  xrt_v2.vignet

• the gas efficiency: pspc_v1.gas_eff
• the window transmission: pspcb_v1.wind_trans
• the on-axis effective area (stroed within area_b_2.asc)

• The vignetting is assumed to be independent of azimuthal angle.
• The area_b_2.asc dataset from which this dataset is derived appears to be identical to that known as SASS_AREA_B_NEW2.FITS by the SASS processing software (and distributed on US (Rev0) GO tapes within the rp*****.oar file)

Chapter 3
ROSAT PSPC CALIBRATION FILES

3.1  Summary of Available Files

3.2  BCF: Standard Energy Grid

3.2.1  pspc_v1.egrid

• The same standard energy grid is shared by many XRT & PSPC calibration files (see also Section 2.2.1)

3.3  BCF: Detector Window Transmissions

3.3.1  pspc#_v1.wind_trans

• These datasets DO NOT include the effects of the window support ribs, but DO include the reduction in transmission due to the wire mesh.

3.4  BCF: Filter Transmissions

3.4.1  boron_v1.trans

3.5  BCF: Detector Efficiency

3.5.1  pspc_v1.gas_eff

3.6  BCF: ADC non-linearity correction

3.6.1  adc_bins.fits

• None

3.7  BCF: Al-K gain history files

3.7.1  alkhist_v1_#.fits

• 1995 Oct 17 (Ian M George, HEASARC)
  • It should be noted that there are a number of other corrections must be applied to correct for various other detector effects. See http://heasarc.gsfc.nasa.gov/docs/heasarc/caldb/docs/summary/cal_ros_95_010_summary.html for for further details.
  • The file alkhist_v1_b.fits is only valid for the PSPCB detector, which was used after the destruction of PSPCC on 1991 Jan 25 (Spacecraft clock time: 20606971.33 s). It should be noted that on 1991 Oct 11 (Spacecraft clock time: approx 42910000.0 s), the High Voltage of the detector was intentially lowered from 3060 to 3000 V which results in the gain (and hence peak channel of the Al measurements to decrease by approximately 30%).
  • The file alkhist_v1_c.fits is only valid for the PSPCC detector, which was used during the PV and All-Sky-Survey phases of the mission until its destruction on 1991 Jan 25 (Spacecraft clock time: 20606971.33 s)

3.8  BCF: Position-dependent terms for Spatial Gain Correction

3.8.1  gain_kor3_#.fits

• 1995 Oct 17 (Ian M George, HEASARC)
  • It should be noted that a further vector, which is a function of pulse height (only), is also required to correct the position of each event for these electronic effects. Furthermore, an additional correction due to the bulging of the detector window must be performed on the position of each event before totally linearized detector coordinates are obtained.

3.9  BCF: Energy-dependent terms for Spatial Gain Correction

3.9.1  gnampl_new.fits

• 1995 Oct 17 (Ian M George, HEASARC)
  • It should be noted that further vectors, which are a function of position (only), are also required to correct the position of each event for these electronic effects. Furthermore, an additional correction due to the bulging of the detector window must be performed on the position of each event before totally linearized detector coordinates are obtained. Finally it should be noted that PH_3 is NEITHER observed PHA channel NOR derived PI channel, but is instead a partially corrected pulse-height bin.

3.10  BCF: Energy-dependent terms for Window Correction

3.10.1  scal3.fits

• 1995 Oct 17 (Ian M George, HEASARC)
  • It should be noted that further vectors, which are functions of position (only), are also required to correct the position of each event for the window distortion. Furthermore, an additional correction due to electronic effects in the detector window must be performed on the position of each event (first) before totally linearized detector coordinates are obtained.

3.11  BCF: Position-dependent maps for Window Correction

3.11.1  tab#_093_#.fits

• 1995 Oct 17 (Ian M George, HEASARC)
  • It should be noted that a further vector, which is a function of energy (only), is also required to correct the position of each event for the window distortion. Furthermore, the correction due to electronic effects in the detector window must be performed on the position of each event (first) before totally linearized detector coordinates are obtained.

3.12  BCF: Maps of mean chan from Al-K calibration obs

3.12.1  al_#-#.fits

• None

3.13  CPF: Dectector Spectral Response

3.13.1  pspc#_v#.spec_resp

• the XRT effective area (including vignetting & obscurration)
• the PSPC gas efficiency
• the PSPC window transmission

• X is the PSPC detector (X= b or c) for which the gas efficiency & window transmission is included
• i is the version of the XRT effective area included (i = 1 or 2) - see Section 2.3.1.

• These datasets are NOT 'detector response matrices'
• These datasets DO NOT include the effects of the window support ribs, but DO include the reduction in transmission due to the wire mesh.

3.14  CPF: PSPC Detector Efficiency Maps

3.14.1  det_#_#_#.fits

Band Name       PI range        Energy
R1              8-19            0.11-0.284
R1L             11-19           0.11-0.284
R2              20-41           0.14-0.284
R3              42-51           0.20-0.83
R4              52-69           0.44-1.01
R5              70-90           0.56-1.21
R6              91-131          0.73-1.56
R7              132-201         1.05-2.04

• Jane Turner (ROSAT GOF) 1995 Nov 17
  • The maps for the two PSPCs are not the same. Besides detector-specific artifacts, there is a small shift in the position of the window support structures and the windows have slightly different thickness distributions. The main survey was done with the first PSPC ( ~ 180 days), and there were ~ 11 days of survey with the second PSPC to extend the sky coverage in exposure gaps of the main survey. Because of this, data exist to create maps for both detectors. However, the statistics of the second PSPC data are obviously significantly worse than those of the main survey, and are inadequate for determining the fine structure in the maps for bands R3 through R7. For these bands, templates were created by shifting the maps of the first PSPC to correctly align the shadows of the window support wires and ribs with the second PSPC. The shifted maps were then normalized to the maps of the second PSPC over overlapping 5'x5' regions to give the correct telescope vignetting and detector quantum efficiency. Unfortunately, the systematics of the detector artifacts in the R1 and R2 bands are sufficiently different between the two detectors to preclude using the same scheme for these bands. So, despite the worse statistics, the maps for the second PSPC for these bands were created using only the 11 days of survey data taken with this detector.
  • The pixel size of the maps is 14.947" x 14.947". The reason for this somewhat obscure pixel size is that the PSPC detector position digitization is 0.934208"and the detector coordinates were binned by 16 for the maps. Note that this is not an integral number of SASS event-position intervals (0.5"), or the same pixel size as the SASS event images (15"x15"). The maps were normalized to the on-axis value by fitting the radial distribution of the inner 18' radius region of the PSPC to the theoretical vignetting function (Molendi 1993). The average shadowing by the window support wires is therefore not included in the exposure correction; however, it is included in the window transmission for modelling purposes. The spatial structure of the shadowing caused by the window support wires and the window support ribs is included in the exposure correction produced by the maps.
  • The effects of electronic ghost images are very obvious in the regularly spaced bright spots and somewhat less-bright lines. The PSPC is an imaging proportional counter that makes use of induced charge on crossed cathode wires to obtain the position of accepted events. The two-dimensional position determination is done using the largest signals on the crossed cathodes, essentially interpolating the event position between the two nearest cathode wires in each direction. For very low pulse-height events, there is the possibility that only one cathode in one or both directions will have signals above the lower level discriminator of the analog electronics chain. In this case, the position determination degenerates to the center of the nearest cathode, yielding a line (if only one axis has a single nonzero cathode value) or a point (if both axes have only one nonzero cathode value each).
  • Also visible in the detector maps is a slight bending of the electronic ghost-image lines. This detector artifact is due to the position correction algorithm. The algorithm corrects the event position based on the assumption that the X-ray was absorbed in the counter gas near the window. The bulging of the window support structure by the pressure of the counter gas bends the electric field lines in the electron drift region of the PSPC. This causes a displacement of the event position, an effect which has been calibrated and is included in the SASS event position-correction procedure. Since the low pulse-height events which contribute to the electronic ghost images have detected positions shifted to the wire positions, this correction is not the appropriate one.
  • Electronic ghost images strongly affect only the R1 and R1L band maps, although the R2 band map also shows some irregularities. However, since the electronic ghost images are pulse height and not energy dependent, the R1 map created from the high-gain data is reasonably appropriate for correcting the R1L band data collected in the low-gain state (where no survey data exist to produce a flat field). This works because the R1L band at low gain includes the same pulse heights at its low end as the R1 band at high gain. The weighting by the source spectrum is of course slightly different, but this is a small effect in this energy range. The R1 maps should be used for R1 band analysis for data collected during high-gain operation. The R1 map should also be used for R1L band analysis for data collected during low-gain operation. We have created R1L maps for both detectors to be used in R1L band analysis ONLY for data collected during high-gain operation. (Note that the R1L band nomenclature refers to the 11-19 channel band, which must be used for observations taken at low gain. However, the R1L band can also be used for observations taken at high gain. This is even preferable if an image derived from high-gain data will be compared with an image derived from low-gain data. To make sense of all this, remember that the PI channels are adjusted to always correspond to the same energy, so the corresponding pulse height will change with gain.)
  • The maps are described in more detail in Snowden et al 1994 (ApJ 424, 728), Snowden et al. (1992, ApJ, 393 819) and Plucinsky et al. (1993, ApJ, 418, 519).

3.15  CPF: PSPC Particle Background Maps

3.15.1  detp_#_#_#.fits

detp_i_l_b.fits
detp_i_h_c.fits
detp_i_h_b.fits
detp_e_l.fits
detp_e_h.fits
detp_ap_l.fits
detp_ap_h.fits

• i denotes the internally produced component,
• e denotes an externally produced component, and
• ap denotes the component made up from low pulse-height events which follow a precursor event.

• Jane Turner (ROSAT GOF) 1995 Nov 17
  • The maps are described in more detail in Snowden et al 1994 (ApJ 424, 728), Snowden et al. (1992, ApJ, 393 819) and Plucinsky et al. (1993, ApJ, 418, 519).

3.16  CPF: PSPC Detector Redistribution Matrices

3.16.1  pspc#_gain#_256.rmf

• pspcb_gain1_256.rmf
  - valid for PSPCB data taken BEFORE 1991 Oct 14
• pspcb_gain2_256.rmf
  - valid for PSPCB data taken AFTER 1991 Oct 14
• pspcc_gain1_256.rmf
  - valid for ALL PSPCC data (detector destroyed on 1991 Jan 25)

• The accuracy of the PSPC Spatial/Temporal Gain Calibration used in the construction of this dataset is described in OGIP Calibration Memo http://heasarc.gsfc.nasa.gov/docs/heasarc/caldb/docs/summary/cal_ros_95_003_summary.html
• ARFs can be constructed using the FTOOLS task ftools/rosat/pcarf

3.16.2  pspc#_gain#_256.rsp

• pspcb_gain1_256.rsp
  - valid for PSPCB data taken BEFORE 1991 Oct 14
  (formerly known as pspcb_92mar11.rmf)
• pspcb_gain2_256.rsp
  - valid for PSPCB data taken AFTER 1991 Oct 14
  (formerly known as pspcb_93jan12.rmf)
• pspcc_gain1_256.rsp
  - valid for ALL PSPCC data (detector destroyed on 1991 Jan 25)
  (formerly known as pspcc_92mar11.rmf)

• These datasets are valid on-axis ONLY
• The accuracy of the PSPC Spatial/Temporal Gain Calibration used in the construction of this dataset is described in OGIP Calibration Memo http://heasarc.gsfc.nasa.gov/docs/heasarc/caldb/docs/summary/cal_ros_95_003_summary.html

3.16.3  pspc#_gain#_34.rmf

• pspcb_gain1_34.rmf
  - valid for PSPCB data taken BEFORE 1991 Oct 14
• pspcb_gain2_34.rmf
  - valid for PSPCB data taken AFTER 1991 Oct 14
• pspcc_gain1_34.rmf
  - valid for ALL PSPCC data (detector destroyed on 1991 Jan 25)

• These datasets use the 34 SASS channels (rather than the full 256 channels provided by the PSPCs).
• The accuracy of the PSPC Spatial/Temporal Gain Calibration used in the construction of this dataset is described in OGIP Calibration Memo http://heasarc.gsfc.nasa.gov/docs/heasarc/caldb/docs/summary/cal_ros_95_003_summary.html
• ARFs can be constructed using the FTOOLS task ftools/rosat/pcarf

3.16.4  pspc#_gain#_34.rsp

• pspcb_gain1_34.rsp
  - valid for PSPCB data taken BEFORE 1991 Oct 14
• pspcb_gain2_34.rsp
  - valid for PSPCB data taken AFTER 1991 Oct 14
• pspcc_gain1_34.rsp
  - valid for ALL PSPCC data (detector destroyed on 1991 Jan 25)

• These datasets are valid on-axis ONLY
• These datasets use the 34 SASS channels (rather than the full 256 channels provided by the PSPCs).
• The accuracy of the PSPC Spatial/Temporal Gain Calibration used in the construction of this dataset is described in OGIP Calibration Memo http://heasarc.gsfc.nasa.gov/docs/heasarc/caldb/docs/summary/cal_ros_95_003_summary.html

Chapter 4
ROSAT HRI CALIBRATION FILES

4.1  Summary of Available Files

4.2  CPF: HRI Detector Redistribution Matrices

4.2.1  hri_90dec01.rsp

• Photon Redistribution Matrix (dummy 1 chan version)
• Q.Efficiency of the HRI (version unknown)
• Transmission of the shields (version unknown)
• Effective Area of the optics (hri_90dec01.ear)

• Matrices have on-axis effective area of the XRT folded in, and thus are ONLY VALID ON AXIS.
• 1995 Feb 25: This file was renamed from hri_90dec01.rsp

4.3  CPF: HRI Detector Maps

4.3.1  be.fits

• Map is for the vignetted component of HRI data, and should be used to cast effective exposure.

4.3.2  de_corr.fits

• Map is for the unvignetted component of HRI data, and should be used to cast the particle background.
• The raw map was corrected for residual vignetted X-rays

Chapter 5
ROSAT MISCELLANEOUS CALIBRATION FILES

5.1  Summary of Available Files

USEFUL LINKS TO OTHER HTML PAGES

• The HEASARC Home Page
• The NASA/GSFC ROSAT GOF Home Page
• The OGIP Calibration Database Home Page