Detect

The detect package contains several tasks which may be run seperately or all together (sequentially) by a script, LDETECT. Each task has an on-line HELP file, and a longer discussion is given in the on-line file EXPLAIN_DETECT. The current version of DETECT is based on the Einstein and ROSAT/HRI level 1 processing algorithms. It is a "sliding-box" routine which uses a detect cell and derives the background from a frame around the cell.

A clone of the "map detect" used in SASS processing is now available in xproto: "imdetect". In this case, the background is taken to be a constant rather than being measured in a frame around the detect cell (the so called 'ldetect', or 'local detect'). The other difference is that imdetect works on image files as well as qpoe files. NB: there was a bug in PROS 2.5 which caused imdetect to crash when using an image file. This bug was corrected in the patch PROS 2.5.1 (1998Apr01). See the help file for more details.

There are 5 basic tasks in the current DETECT package:

CELLMAP -- prepares x-ray qp file for DETECT. The qp file is blocked into an image of resolution d/3 (where d = the chosen size of the detect cell). Any other desired x-ray filters (e.g. PHA or PI) are also applied.

SNRMAP -- computes the signal-to-noise ratio (snr) map for the image prepared by CELLMAP.

LPEAKS -- scans the snr map line by line for local peaks above a user-defined threshold.

BKDEN -- computes the mean background density in counts/sq. arcmin. in a user-defined region of the image prepared by CELLMAP. Image pixels with values which deviate from the mean by more than a user-defined threshold are rejected.

BEPOS -- determines the maximum liklihood position for each peak identified by LPEAKS, using the original qp file. Signal-to-noise ratios in detect cells centered on the final positions are computed and positions with snr's greater than a second user- defined threshold are identified as sources.

In addition, the following auxiliary tasks are provided:

LDETECT -- runs the above 5 tasks in sequence, for a single detect cell size and threshold.

DETMKREG -- makes a region file from Detect output positions (_ruf.tab, _pos.tab, _unq.tab, _mch.tab). The file(s), when overlayed onto SAOIMAGE are a visual tool indicating where source detection in the image was determined.

LBMAP -- generates background and background variance maps at the same resolution as in CELLMAP. These maps are for illustrative purposes only and are not used in other DETECT tasks. The equations used to build the background map use the same algorithms as implemented in BEPOS.

LMATCHSRC -- consolidates detections from one or more runs of ldetect on the same qpoe file into unique sources in a field. The distance between input detections are computed and those falling within a match tolerance are determined to be the same source.

In the examples below we give a minimal run to show the basic operation. Other parameters may be used by experimentation or by reading the help files.

EXAMPLE 1 - running LDETECT - ROSAT HRI

In this case we specified only the cellsize, leaving the default thresholds and default circle for the background measurement.

  xp> ldetect

qpoe file : xdata$rh110267.qp
Output table root: rh110267
ROSAT HRI Cellsize in arcsecs - 6|9|12|24|36|48: 24

... Running Cellmap ...

xdata$rh110267.qp[bl=16] -> rh110267.imh
add rh110267.imh,cellsize = 24
rh110267.imh updated
xdata$rh110267.qp

... Running Snrmap ...

Convolving 3x3 cells

Convolving 5x5 cells

Calculating Snrmap with equation:

snrmap=(1.7777*cell3-frame)/((1.7777**2*cell3+oframe)**0.5)

Writing Snrmap Image:
rh110267_snr.imh

... Running Lpeaks ...

src#  logx    logy     physx     physy    cellx/y     snr
---------------------------------------------------------

   1  149.00  177.00   2384.00   2832.00   24   24     5.954
   2  146.00  276.00   2336.00   4416.00   24   24    30.197

Writing to Output file:  rh110267_ruf.tab

... Running Bkden ...

Bkden region is circle 256.00 256.00 7.50'


Bkden = 12.8558464 counts/arcmin**2

... Running Bepos ...

*** PI bands must be Respecified with input QPOE ***


Input Qpoe: xdata$rh110267.qp
bkden = 12.8558464 (cts/sq arc-min), 0.0008928 (cts/sq pixel)

2 Rough Position(s) Input

 src#      ra            dec       physx    physy  cellcnts framecnts snr
---------------------------------------------------------------------------
   1    22:08:38.4    45:31:24.2   2380.1   2829.1      95      67     5.3
   2    22:08:41.4    45:44:33.4   2323.5   4407.7    1506     394    31.8

Writing 2 Sources to Output file:  rh110267_pos.tab

EXAMPLE 2 - running the 5 components separately - ROSAT PSPC

de> cellmap

Input xray Qpoe: xdata$rp110590.qp
Output xray image : rp110590_cmp
ROSAT PSPC Cellsize in arcsecs - 30 [h/b]| 45 [s]| 60 [s/h/b]| 120 [s/h/b]: 30
Energy Band (soft|hard|broad) (broad): hard

xdata$rp110590.qp[bl=20,pi=52:201][128:639,128:639] -> rp110590_cmp.imh
add rp110590_cmp.imh,cellsize = 30
rp110590_cmp.imh updated
xdata$rp110590.qp[pi=52:201]

de> snrmap
Input xray image : rp110590_cmp
Output snrmap image [root_snr.imh]: rp110590

Convolving 3x3 cells

Convolving 5x5 cells

Calculating Snrmap with equation:

snrmap=(1.7777*cell3-frame)/((1.7777**2*cell3+oframe)**0.5)

de> lpeaks
Input Snrmap Image: rp110590_snr
Output Rough Positions Table: rp110590

src#  logx    logy     physx     physy    cellx/y     snr
---------------------------------------------------------

   1  224.00  263.00   7020.00   7800.00   30   30     4.372
   2  220.00  340.00   6940.00   9340.00   30   30    12.945

Writing to Output file:  rp110590_ruf.tab

xp> bkden
Input Image: rp110590_cmp
Region Descriptor (default): BOX(226,115,344.00,94.00)
	[This box was determined by examining the cellmap and finding
	a source free region.]
Bkden region is BOX(226,115,344.00,94.00)

Bkden = 0.6401532 counts/arcmin**2

xp> bepos.snr_thresh=3.5
xp> bepos

*** PI bands must be Respecified with input QPOE ***

Input qpoe file: xdata$rp110590.qp[pi=(41:240)]
Field background density in cts/arcmin**2 (0.82384938001633):
Input rough pos table: rp110590_ruf.tab
Output bepos table file: rp110590

Input Qpoe: xdata$rp110590.qp[pi=52:201]
bkden = 0.6401532 (cts/sq arc-min), 0.0000445 (cts/sq pixel)


2 Rough Position(s) Input

 src#      ra            dec       physx    physy  cellcnts framecnts snr
---------------------------------------------------------------------------
   1    22:08:37.8    45:31:46.7   7008.0   7794.9      41      19     4.3
   2    22:08:41.6    45:44:45.4   6929.6   9352.5    1607    1865    11.9

Writing 2 Sources to Output file:  rp110590_pos.tab

EXAMPLE using LMATCHSRC -

Two table files are output. The first (_unq.tab) is a unique list of all input detections where each has a unique row reference; the second file (_mch.tab) is the output of the match. This file is a match reference list with one row for each source. Match columns refer to the detections listed in the _unq.tab file.

Match sources from 4 runs of ldetect at different detect cell sizes.

  de> lmatchsrc 

Reference Qpoe file name: xdata$rh110267.qp
List of detect tables to match [_pos.tab]: rh12_pos,rh24_pos,rh36_pos,rh48_pos
Root name for Match Source table: rharlac

... Merging the list of input tables

... Sorting the list in y,x order

... Matching the detections into Sources

      Avg ra       Avg dec   Avg x     Avg y     Best x    Best y   Src ref
                             (physical pixels)   (physical pixels)  (row #)
-----------------------------------------------------------------------------
  1 22:08:38.4   45:31:24.3  2380.332  2829.285  2380.510  2829.540  3 2 1
  2 22:09:01.3   45:37:14.3  1902.477  3531.475  1902.477  3531.475  4
  3 22:08:41.4   45:44:33.4  2323.537  4407.728  2323.539  4407.733  6 8 7 5 9

Writing to Match Results table:  rharlac_mch.tab
Writing to Match Reference table: rharlac_unq.tab