Chandra X-Ray Observatory
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CDA - Data Products

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  • Reprocessing has been completed for
    • Phase I: 2005-11-13 to 2011-12-31
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A Guide to Chandra Archive Data Products

Pipelines
Subsystems
Road map


Data Products

The CXC Automated Processing system is capable of generating several hundred different data products derived from Chandra telemetry. This page provides a guide to these data products. To make it easier to follow, we will first define some terms and provide a context.

FITS

Almost all data products (notable exceptions are telemetry files) are formatted as FITS files. Each FITS file may contain one or more HDUs, but the first non-empty HDU is, by definition, the principal HDU. The properties of the principal HDU are taken to be the properties of the entire data product.

Note that file names are built up of the following components: instrument, 'f', a number that represents time or ObsId, version number, optional component, file identifier, and .fits.

The identity of a product can usually be determined on the basis of the instrument and the file identifier, if necessary in combination with the optional component.

CONTENT

Each product contains a FITS keyword CONTENT in the header of its principal HDU that uniquely identifies the type of product.

Processing Level

Beyond the telemetry data (TLM), we distinguish five processing levels in automated processing: L0, L0.5, L1, L1.5, L2.

Processing Pipelines

Products are created by one of 28 processing pipelines. Not all pipelines are used to process the data for any particular observation; the exact choice depends on the characteristics of the observation.

Chandra Automated Processing Pipelines
Pipeline Code Processing Level Pipeline
TP L0 Telemetry processing
EPHIN0 L0 EPHIN extractor
ENG0 L0 Engineering extractor
SIM0 L0 SIM extractor (technically, SIM-A and SIM-B)
ACIS0 L0 ACIS extractor
HRC0 L0 HRC extractor
ACAI L0 ACA-I extractor (the "regular" aspect pipeline)
ACAC L0 ACA-C extractor (for the calibration telemetry)
EPHEM0 L0 Ephemeris (predictive)
ASP0.5 L0.5 Aspect
OBIDET L0.5 Observation Interval Determination
SIM0.5 L0.5 SIM
ACIS0.5 L0.5 ACIS
HRC0.5 L0.5 HRC
ACIS1 L1 ACIS
HRC1 L1 HRC
ASP1 L1 Aspect
EPHIN1 L1 EPHIN
TEL1 L1 TEL
EPHEM1 L1 Ephemeris (definitive)
TG1.5 L1.5 TGrating
TGCC1.5 (TG1.5) L1.5 TG ACIS CC
ACISCC2 (ACIS2) L2 ACIS CC
ACISTE2 (ACIS2) L2 ACIS TE
HRC2 L2 HRC
TGCC2 (TG2) L2 TG ACIS CC
TGTE2 (TG2) L2 TG ACIS TE
TGHRC2 (TG2) L2 TG HRC

Proprietary Data

The information in most data products is public, but in the case of a proprietary Guest Observer observation, certain products will be available only to the GO (and authorized individuals in CXC) for the duration of the proprietary period (nominally one year). The potentially proprietary products are marked with a P.

Subsystems

Data products are grouped by the spacecraft subsystem in which the data originated. These subsystems, or instruments, arelisted in the following table

Chandra Subsystems
Subsystem Description
acis AXAF CCD Imaging Spectrometer subsystem
hrc High Resolution Camera subsystem
ephin Electron-Proton-Helium INstrument subsystem
pcad Pointing Control and Attitude Determination subsystem
tel Telescope subsystem
sim Science Instrument Module subsystem
obc On-Board Computer software subsystem
ccdm Communications Command and Data Management subsystem
cpe CPE hardware and software subsystem
eps Electrical Power Subystem
thm Thermal control subsystem
sms Structure subsystem
prop Propulsion and pyro subsystems
misc Other AXAF signals
orbit Orbit ephemeris
solar Solar ephemeris
lunar Lunar ephemeris
angles Viewing angles
clock Clock measurements
axaf Certain mission-level items

Engineering Data

The data products may be roughly divided into science-related and engineering. There are engineering data products for all spacecraft subsystems and the products come in two versions: TU and Cal. Measurements such as temparatures and voltages are sent down in telemetry units (TU), but the more useful version is after conversion (calibration) to engineering units.

Product Categories

In a functional sense, from the point of view of the user, the products are divided into three categories: primary, secondary, and supporting products. An approximate characterization is that an archival researcher would typically just want the primary products, while a serious GO would need the secondary products as well, in order to do a more sophisticated analysis and, possibly, limited reprocessing and fine-tuning. The supporting products contain everything else. The standard data distribution to GOs consists of primary and secondary products. Standard public data distribution packages consist of primary products, secondary products, or both. Supporting products may be obtained on an individual basis.

Data Delivery Mechanisms

Eventually, data selected for retrieval may be delivered through one of the following mechanisms or media:

  • Download immediately through the webbrowser
  • Stage in anonymous ftp area for later retrieval
  • CD-ROM (allow 4 weeks for delivery)

Data Products Road Map

The cells in this table link to lists of individual products.

Note that file names are built up of the following components: instrument, 'f', a number that represents time or ObsId, version number, optional component, file identifier, and .fits.

The identity of a product can usually be determined on the basis of the instrument and the file identifier, if necessary in combination with the optional component.

Categories of Products
Primary products List A
Secondary products List B
Science-related products
(includes Primary and Secondary Products)
List C
Engineering products List D
Telemetry products List E
Mission products (including OBIDET products) List F

This page maintained by the Chandra Data Archive (arcops@head.cfa.harvard.edu).

Last modified: 2010-12-22

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