Science Threads
Introduction
Beginners should start here. The Introductory threads provide an overview of the main components (GUI applications, parameter files) and concepts (the Data Model, filtering) in the CIAO data analysis software.
Getting Started:
General:
- Making Images & Filtering Data with the Data Model
- Using ASCII Files in CIAO
- Using CIAO Region Files
- Using Parameter Files
- Using SAOImage ds9
- The ds9 Users Manual has more threads on using ds9.
Data Preparation
When Chandra data goes through Standard Data Processing (SDP), the most recently available calibration is applied to it. Since this calibration is continuously being improved, one should check whether there are newer files available. Similarly, some science decisions are made during SDP; every user has the option to reprocess the data with different parameters.
Analysis Guides:
ACIS:
- Check the ACIS Data Caveats
- Why topic: -110 C Observations
- Why topic: Continuous Clocking Mode Data
-
The chandra_repro script may be used to easily reprocess Chandra datasets.
To reprocess your data step-by-step, follow the Reprocessing Data to Create a New Level=2 Event File thread.
- Customizing an ACIS Bad Pixel File
- Removing ACIS Background Flares
-
Analysing the ACIS Background with the "Blank-Sky" Files
![[Updated]](../imgs/updated.gif)
(7 Sep 2012)
- Remove the ACIS Readout Streak
-
Removing Warm ACIS Data
![[New]](../imgs/new.gif)
(2 Aug 2012)
HRC:
- Check the HRC Data Caveats
- New Observation-Specific HRC Bad Pixel File
-
The chandra_repro script may be used to easily reprocess Chandra datasets.
To reprocess your data step-by-step, follow the Reprocessing Data to Create a New Level=2 Event File thread.
- Computing Average HRC Dead Time Corrections
- The HRC-I Background Event Files
- The HRC-I Background Spectra Files
Imaging
The Imaging threads cover a wide range of topics that include source detection, creating exposure maps and normalized images, and calculating image statistics. How to create color images for publication is addressed, as well as merging data from multiple observations.
Analysis Guides:
General:
-
Analysing the ACIS Background with the "Blank-Sky" Files
(7 Sep 2012)
- The HRC-I Background Event Files
- The HRC-I Background Spectra Files
- Match the Binning of an Image
- An Estimated Background Image
- True Color Images
- True Color Images in ds9
-
An Image of Diffuse Emission
(24 Jul 2012)
- Using Data Cubes
-
Using Contrib Color Look-Up Tables
(10 Oct 2012)
-
Analysing the ACIS Background with the "Blank-Sky" Files
Reprojecting Data:
Coordinates, Astrometry, & Spatial Filtering:
Exposure Maps:
-
Using merge_obs to combine observations and create exposure-corrected images
(15 Oct 2012)
- Calculating Spectral Weights for mkinstmap
-
Single Chip ACIS Exposure Map and Exposure-corrected Image
(15 Oct 2012)
-
Multiple Chip ACIS Exposure Map and Exposure-corrected Image
(15 Oct 2012)
-
HRC-I Exposure Map and Exposure-corrected Image
(15 Oct 2012)
-
HRC-S Exposure Map and Exposure-Corrected Image
(15 Oct 2012)
- Match the Binning of an Image
-
Using merge_obs to combine observations and create exposure-corrected images
Modeling & Fitting Imaging Data with Sherpa
(from the Sherpa analysis threads):
Imaging Spectroscopy
After extracting source and background PI or PHA spectra from an imaging observation, the appropriate response files (ARF, RMF) are created so that the data may be modeled and fit. In the case of multiple or extended sources, a weighted ARF and RMF are built for the spectral analysis.
Extracting ACIS Spectra & Creating Response Files:
-
Extract Spectrum and Response Files for a Pointlike Source
(30 May 2012)
-
Extract Spectrum and Response Files
for an Extended Source
(16 Feb 2012)
-
Extract Spectrum and Response Files
for a Field of Sources
(05 Mar 2012)
-
Coadding Spectra and Responses
(16 Feb 2012)
- A Note on Responses for XSpec Users
-
Extract Spectrum and Response Files for a Pointlike Source
Special Science Cases:
Modeling & Fitting Spectral Data with Sherpa
(from the Sherpa analysis threads):- Introduction to Fitting PHA Spectra
- Changing the grouping scheme of a data set within Sherpa
- Introduction to Fitting ASCII Data with Errors: Single-Component Source Models
- Simultaneously Fitting Two Data Sets
- Simulating 1-D Data: the Sherpa FAKE_PHA Command
- Simulating Chandra ACIS-S Spectra with Sherpa
- Fitting PHA Data with Multi-Component Source Models
- Independent Background Responses
- Using A Pileup Model
Grating Spectroscopy
If new calibration has been applied to the event file, the grating spectrum should be re-extracted as well. It is then possible to build grating response files (gARF, gRMF) in order to model and fit the data.
- Chandra Grating Analysis Page
- WebGUIDE: Interactive GUIDE for ATOMDB
- Chandra Grating Data Archive and Catalog (TGCat): a browsable interface to analysis-quality spectral products.
-
The chandra_repro script may be
used to easily reprocess Chandra datasets.
Problems with the Zero Order:
Combining Spectra & Preparation for Fitting:
Modeling & Fitting Grating Data with Sherpa
(from the Sherpa analysis threads):
Timing Analysis
In order to perform absolute timing analysis on a dataset, a barycenter correction must first be applied to the data. One may then create lightcurves and phase-binned spectra to look for variability in the source. These threads also provide information on working with data taken in the ACIS continuous clocking (CC) mode.
General:
- Why topic: Continuous Clocking Mode
- Apply Barycenter Correction
-
Phase-binning a Spectrum
(24 Apr 2012)
Analyzing Lightcurves:
- Why topic: Timing Analysis with Lightcurves
- Basic Lightcurves
- Removing ACIS Background Flares
- Filtering Lightcurves
- Search for Variability in a Source
- See the S-lang/ISIS Timing Analysis Routines (SITAR) package which provides a set of functions and subroutines for timing analysis within ISIS.
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