1 Introduction

ACIS Extract (AE) is a software package that provides innovative and automated solutions to the varied challenges found in the analysis of X-ray data taken by the ACIS instrument on NASA's Chandra observatory (Broos et al., 2012,2010). AE is written in the IDL language. What does AE do? Well, suppose you have Level 2 event data from one or multiple ACIS observations, and you have a catalog of proposed point sources. AE can perform virtually all the data processing and analysis tasks that lie between your Level 2 ACIS data and publishable L^ATEX tables of point-like and diffuse source properties and spectral models.

The Point Source Catalog
Source detection is not part of AE. However, source position estimates and source significance statistics produced by AE can be used to improve a proposed catalog of point sources.

The Extraction Regions
AE constructs two sets of regions for the point sources: The source extraction region are contours of the local PSF enclosing whatever PSF fraction is desired. Crowded fields are handled by shrinking the extractions regions so they do not overlap. The ``mask regions'', which completely cover the sources, are used to construct a background data set.

Extraction of Event Data and Backgrounds
Source and scaled local background spectra are extracted.

Calibration Products
ARFs and RMFs are constructed for each source. The ARFs are corrected to account for the light missed by the finite extraction regions.

Timing Analysis
Source variability is quantified. Three time series are produced for each source:

• A ``grouped light curve'', i.e. source flux measured in a set of independent, unequally sized time bins with constant significance.
• The median energy of events in each time bin.
• An ``adaptively smoothed light curve'', i.e. source flux measured in a set of overlapping, unequally sized time intervals with constant significance.

Photometry
Source photometry is performed over any desired set of energy bands.

Spectral Modeling
Source spectra are grouped and spectral models are fit with XSPEC.

Collation of Results
Source properties, statistics, photometry, and spectral models are collated into a large FITS file for analysis, generation of L^ATEX tables, etc.

Visual Review
Source extraction region files help the observer review the observation for spurious and missed sources. A variety of interactive plots are produced showing various source properties across the catalog.

Multiple Observations
The source catalog can be extracted from any number of observations (at different aim points or roll angles). AE combines the extraction data products prior to position estimation, photometry, timing analysis, and spectral modeling.

Diffuse Sources
If you can define extraction and background regions for diffuse sources, then AE can extract and analyze them in much the same way as is done for point sources.

The implementation strategy for AE is to use CIAO tools for specific computations whenever possible, and DS9 for display and editing of extraction regions. Section 5 of this manual describes the algorithms used to compute various data products, with an emphasis towards scientific concerns. Section 6 and section 7 describe how to install and use the AE software.

The authors happily acknowledge that AE is derived from the ideas, software, and testing efforts of David Alexander, George Chartas, Eric Feigelson, Nicolas Grosso, Scott Koch, Bertil Olsson, Yohko Tsuboi, and the authors of various CIAO threads and manuals. Support for this effort was provided by NASA contract NAS8-38252 to Gordon Garmire, the ACIS Principal Investigator

Please contact Patrick Broos if you have problems, questions, or suggestions for improving these tools. Please join the ACIS Extract email list to receive announcements of AE releases.

Note that several other tools for extracting Chandra data have been developed:

• XAssist
• yaxx
• psextract
• specextract
• the Level 3 pipeline at the CXC