The SWIFT BAT Software Guide Version 6.3 30 ... - HEASARC - Nasa

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6.2. CURRENT ISSUES 57 TIME EXPOSURE s s 1 145293915.000000 360.000000000000 2 145294995.000000 244.000000000000 This file has two exposures separated by about 700 seconds. It is possible to use batbinevt to combine these entries into a single DPH, like this, csh> batbinevt file.dph summed.dph DPH 0 uniform INFILE chatter=5 clobber=YES csh> ftlist summed.dph T columns=TIME,TIME_STOP,EXPOSURE TIME TIME_STOP EXPOSURE s s s 1 125293915.000000 125295239.000000 604.000000000000 The “0 uniform” portion of the command line causes batbinevt to sum all input DPHs into a single output DPH. The new file, summed.dph, has the correct start and stop time, and the exposure is correct as well. A check of the good time interval (GTI) extension shows that it is also correct. Everything looks fine. However, this file cannot be re-input to batbinevt, because batbinevt makes a fundamental assumption that DPHs are always contiguous in time. csh> batbinevt summed.dph summed.dpi DPI 0 u 14-194.9 chatter=5 clobber=YES csh> ftlist summed.dpi K | grep EXPOSURE EXPOSURE= 1324. / [s] Accumulated on-time The exposure has now increased incorrectly to 1324 from 604 seconds. The work-around procedure is to not sum the input DPHs into a single output DPH. Instead, use the INFILE time binning option to merge but not sum the inputs. The result will be a single file with multiple DPHs which can be operated on normally. csh> batbinevt file.dph merged.dph DPH 0 INFILE INFILE chatter=5 clobber=YES While this example is rather meaningless for a single input file, it will permit multiple input files to be merged. The merged file can be input to batbinevt if desired. 6.2.4 batcelldetect: newly detected sources may be deleted Task: batcelldetect Version: 1.50 - 1.55 What builds: HEASoft 6.2 and earlier Problem: Newly detected sources may mysteriously disappear Status: Closed (HEASoft 6.3) Updated: 24 Apr 2007 NOTE: This bug was fixed in HEASoft 6.3 (task version 1.56 and greater). A bug in the CFITSIO library may cause newly detected sources to “disappear” from the output catalog. The problem occurs with the operation of the “keepbadsources” parameter, which
58 CHAPTER 6. BAT ANALYSIS ISSUES was added in version 1.50, and was meant to remove from the output catalog sources with bad DETECT STATUS values. However, new sources were also removed by the CFITSIO library routine when they shouldn’t have been. The workaround is to set “keepbadsources=YES” and filter the output catalog manually based on DETECT STATUS. 6.2.5 batcelldetect: the correct point spread function is gaussian Task: batcelldetect Version: 1.11-1.59 What builds: HEASoft 6.2 and earlier Problem: Default point spread function of PYRAMID is incorrect Status: Closed Updated: 17 Jul 2007 NOTE: This problem was fixed in HEASoft 6.3 (task version 1.60 and greater). Fluxes derived from batcelldetect are based on a fit of a point spread function (PSF) to the sky image intensities. In particular, the reported flux is the intensity at the center of the PSF. As one might expect, the flux depends on fitting the correct PSF model to the data. Based on a number of incorrect assumptions, the BAT team reported that the PSF was a truncated pyramidal frustum. However, this is incorrect. In fact, the PSF is very nearly a gaussian function (with full-width half-maximum of 22 arcmin). This PSF can be selected by using the psfshape=GAUSSIAN option to batcelldetect (the default is psfshape=PYRAMID). Using the incorrect frustum function will result in fluxes that are too high by 4.0% compared to the true flux. The signal to noise ratios are high by about 3.5%. For the most part, this effect is only significant for the brightest sources, where the statistical errors are smaller than 4%. Note that this problem applies only to fluxes from batcelldetect. It doesn’t affect mask-weighted light curves and spectra made from batbinevt. 6.2.6 Analysis: Passive materials distort the off-axis counts/rates Task: All flux extraction (batfftimage/batmaskwtevt/batmaskwtimg/batbinevt) Version: All versions What builds: All builds Problem: Passive materials introduce errors in mask-weighted counts/rates Status: Corrective Procedure (HEASoft 6.0.3) Updated: 15 Oct 2005 The BAT image system works by forming shadow patterns cast by the mask onto the detector array. The mask is made from lead tiles. However, the mask support structure also contains significant absorbing materials. The edge of the support structure is a particular problem because (a) extra absorbing materials (e.g. epoxy) were applied, and (b) this material rises up above the plane of the mask. The net result is that for sensitive imaging and spectroscopy of off-axis sources, the full mask aperture cannot be used. The BAT team has provided a new set of aperture files in CALDB, tied to the HEASoft 6.0.3 release. These apertures have been reduced in size to appropriately block out the shadows of most of the absorbing material. However, this does reduce solid angle sky coverage by 5-10%. The aperture files are now divided into two classes:
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The SWIFT BAT Software Guide Versio
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ii CONTENTS 4.4 How Sky Fluxes are
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iv CONTENTS 6 BAT Analysis Issues 5
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vi CONTENTS D.1.6 SEE ALSO . . . .
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viii CONTENTS D.10.2 USAGE . . . .
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x CONTENTS D.18.5 EXAMPLES . . . .
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xii CONTENTS
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2 CHAPTER 1. INTRODUCTION • Appen
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