OSSERVATORIO ASTRONOMICO DI PALERMO GIUSEPPE S. VAIANA

Welcome to the PWDetect Home Page

New: PWDetect version 1.3 is available!

PWDetect is the wavelet-based source detection code for Chandra X-ray data developed at the Osservatorio Astronomico di Palermo (OAPA). It performs a multiscale analysis of the data, allowing detection of both pointlike and moderately extended sources in the entire field of view. Various Chandra detectors are supported: HRC-I, ACIS-I, and individual ACIS chips (from both ACIS-I and ACIS-S); analysis of HRC-S images is not supported.

PWDetect V.1.0 (executable only) is available for various platforms: Linux statically linked under Red-Hat 6.2 should run on any Red-Hat 6.x/7.x like system, SunOS linked under solaris V5.7, OSF1/True-64 statically linked under True-64 V4.0F. You will also need its parameter file (pwdetect.par), and please do not forget to read the instructions for use.

PWDetect needs as input a valid Chandra FITS event file, and its associate FITS exposure map (mandatory), binned to 2 arcsec pixels. The exposure map is strictly needed since it contains important information used throughout the analysis. It should be computed using the CIAO task mkexpmap.

The input event list is not read using the DataModel interface, and therefore filtering "on the fly" is not possible. Any time or energy filtering must be applied before calling PWDetect (and coherently to both event file and exposure map). We however discourage the use of spatial filters (sub-images), that may cause PWDetect to misidentify the image border and produce a large number of spurious detections.

PWDetect uses the parameter file pwdetect.par to read/save its parameters. This file must reside in the current directory, and its name must not be changed. Command-line parameters will not work, but if you don't like interactive parameters setting you may use the `pset' command, as with any other parameter file.

Beside input/output file names, PWDetect requires two most important input parameters to be set, namely the detection threshold and the maximum scale to be used in the analysis. The number of expected spurious detections depends sensitively on the choice of these parameters, and on the image integrated background. Plots describing this dependence are available for both HRC-I and ACIS-I.

PWDetect generates the following products:

• a list of detected sources (root_src, root_src.fits), in both ASCII and FITS format, including various computed source properties (position, counts, count rate, size, exposure time, background value, etc.).
• an ASCII list describing at which individual scales was a source detected (root_signif), and to which significance level.
• a DS9-style region file (root_overlay.ds9), for ready visualization of detected sources using the DS9 display. Also, an overlay file (bounds.ds9) is created to show the region being analyzed by PWDetect.
• a short log file.
• two FITS background maps: a zero-order map (bkgroot0.fits), and a second map (bkgroot.fits) with bright sources removed.

There is a limit of 3 million photons maximum that can be handled by the standard PWDetect. Should you need to analyze a larger dataset, please ask us.

We ask people using Pwdetect to send to F. Damiani the reference of the article based on its use and to aknowledge its use (apart from citation to Damiani et al. 1997, ApJ, 483, 350; and Damiani et al. 1997, ApJ, 483, 370) with a statement like the following:

"Pwdetect has been developed by scientists at Osservatorio Astronomico di Palermo G. S. Vaiana thanks to italian CNAA and MURST (COFIN) grants.

Should you have problems or questions, you may contact Francesco Damiani, main author of the PWDetect code. Please note, however, that we are currently able to give only limited support.