# "An Automated System for the Reduction and Analysis of X-ray Data From Galaxies"

# AISR Project NAG5-11193

## PI: Andrew Ptak (JHU)

## 1. Overview

XAssist ([http://www.xassist.org](http://xassist.pha.jhu.edu/)) is a
project funded from 1999-2002 by the AISR program to automate the
analysis of X-ray astrophysics data, with emphasis on galaxy data. The
project grew out of the Ph.D. thesis of the PI in which *ASCA* data
analysis was scripted using IDL. One of the project goals was the
development of code that was freely distributable, and accordingly
Python was chosen as the primary programming language, although much of
the analysis done by FTOOLS programs called from XAssist (with CIAO and
XMM-SAS being used for tasks specific to *Chandra* and *XMM-Newton*,
respectively). The code was used with a collaborator (E. Colbert) to
process all available *ROSAT* HRI data (\~ 2000 data sets) in search of
very bright extranuclear point sources in galaxies which resulted in a
press release and two recent paper (Colbert & Ptak 2002; Ptak & Colbert
2004). Currently, XAssist is analyzing *Chandra* and *XMM-Newton* data
as it becomes public (in both cases most often limited to fields that
contain an RC3 galaxy) and the pipeline products, as well as the code
for XAssist, are available at the XAssist web site. We have also
received several requests to processes specific samples of *Chandra* and
*XMM-Newton* data (in both cases AGN/QSO samples).

## 2. XAssist Functionality

XAssist currently works well for *Chandra* ACIS data, *XMM-Newton* CCD
data, and *ROSAT* HRI data. Ithas following capabilities:

1.  Downloading data

2.  Reprocessing the "raw" data (CIAO for *Chandra*, XMM-SAS for
    *XMM-Newton* and FTOOLS for *ROSAT* and *ASCA*)

3.  Detecting sources

4.  Filtering times of high background (i.e., due to flares)

5.  Fitting the image of each detected source with an elliptical
    Gaussian model to assess source significance and extent

6.  Computing the mean background level for each detector (or CCD in the
    case of Chandra)

7.  Extracting individual images, spectra and light curves for each
    source

8.  Fitting the spectra of bright sources (with \> 100 photons) with a
    power-law model

9.  Assessing source variability by comparing the source light curve to
    the background light curve with the K-S test.

10. Searching for counterparts in several databases, most notably the
    USNO-B star and 2MASS near-infrared source catalogs.

The download capability is not currently part of the main XAssist
application since, initially, direct access to the data (i.e., via FTP)
was not possible. However, scripts have been written for this purpose
and will be incorporated into future versions. The steps listed above
represent the bulk of the originally proposed effort, although, *ASCA*
and *ROSAT* PSPC support have been problematic due to their large point
spread functions.

## 3. Pipelines

Since the main strength of XAssist is its ability to process large
amounts of X-ray data, we are running XAssist on public *Chandra* and
*XMM-Newton* data sets. Previously all *ROSAT* HRI observations
correlating with the RC3 galaxy catalog were processed and the results
of that pipeline are still available on the XAssist web site. Similarly,
the *Chandra* and *XMM-Newton* pipelines are mainly observations that
include nearby galaxies (i.e., including serendipitous observations),
however there are also data sets that have been requested by external
users. Most notably, we have received requests for processing *Chandra*
observations of QSOs and *XMM-Newton* observations of nearby AGN. The PI
is also collaborating on a project to analyze *Chandra* observations
overlapping the Sloan Digital Sky Survey. Currently,
[www.xassist.org](http://www.xassist.org/) receives \~ 3000 hits per
month, dominated by page requests for the pipeline data. Here we
filtered out requests from obvious web crawlers although of course some
fraction may still be due to web crawlers (as evidenced by random page
requests).

## 4. Deficiencies and Future Work

The main deficiency of the project is the lack of adoption by individual
users, although we are aware of some usage of the project (e.g., we
receive bug reports and/or help requests on occasion). Increased
exposure of the project this is the main motivation of making pipeline
data publicly available. We also promote XAssist whenever possible:
there have been several presentations at astronomy (AAS and AAS-HEAD)
and scientific computing meetings (ADASS 2002 and SciPy 2002). However,
since both XAssist and underlying X-ray software need to be installed,
there is a non-negligible start up cost in using the software. We intend
to improve the documentation and user interface for XAssist to help with
this. Additionally there is the well-known "not-invented-here" bias in
the astronomical community. Again the pipeline output addresses both of
these issues by demonstrating the capabilities of XAssist, and we are
also moving toward improved capabilities for external users to request
processing of a given field. We have also been discussing the
integration of XAssist with Hera at NASA/GSFC. We will be experimenting
with other functionality that will allow XAssist to be used as a Virtual
Observatory "engine" for on-the-fly processing of X-ray data, such as
producing an X-ray web service.

The performance of XAssist with *ASCA* and *ROSAT* PSPC data needs
improvement. This is due largely to the PSF of these telescopes which
complicates both source detection and characterization. However, *ASCA*
support will benefit from the PI's involvement with *Astro-E2* data
since the two missions are similar, and advancements along these lines
will likely also benefit PSPC usage.

## 5. Presentations and Papers

Presentations describing XAssist:

1.  Ptak, A. & Griffiths, R. 2001, American Astronomical Society, 198th
    AAS Meeting, #03.11; BAAS, Vol. 33, p.1174

2.  Ptak, A. 2002, American Astronomical Society, 199th AAS Meeting,
    #145.08; BAAS, Vol. 33, p.1525

3.  Ptak, A., 2002, Space Telescope Institute Engineering Colloquium

4.  Ptak, A. & Griffiths, R. 2003, Astronomical Data Analysis Software
    and Systems XII ASP Conference Series, Vol. 295, H. E. Payne, R. I.
    Jedrzejewski, and R. N. Hook, eds., p.465

Papers citing use of XAssist:

1.  Ptak et al., "XMM-Newton Observation of NGC 3998**",** 2004, ApJ,
    606, 173

2.  Ptak, A. & Colbert E., "HRI ULX Statistics", 2004, ApJ, 606, 291

3.  Colbert, E. et al. "X-Ray Point Sources in Galaxies", 2004, ApJ,
    606, 231

4.  Dovciak, M., Karas, V., & Yaqoob, T. "X-Ray Spectra in Strong
    Gravity Regime", 2004, ApJS, 153, 205

5.  Ptak, A. et al. "Chandra Survey of the Nearest ULIRGs", 2003, ApJ,
    592, 782

6.  Turnshek, D. et al. "Chandra ACIS-S Observations of Three Quasars",
    2003, ApJ, 590, 730

7.  Moffat, A., et al. "NGC 3603 from X-Rays to Radio", 2002, ApJ, 573,
    191

8.  Colbert, E. & Ptak, A. "ROSAT HRI IXO Catalog", 2002, ApJS, 143, 25