CDA - Data Products
The Archive
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- The archive is fully functional.
-
Reprocessing IV has been completed in December 2014.
- ASCDSVER: 10.13
- CALDBVER: 4.11.6
- Electrical Outage 11/05/21 - 11/06/21
2021-11-05
There will be a planned electrical outage Friday, November 5 2021, 5:30PM - Saturday, November 6 2021, 6:00PM EDT. During this time period ChaSeR and other archive interfaces will be unavailable. - Electrical Outage on 07/28/21
2021-07-26
There will be a planned electrical outage Wednesday, July 28 2021, 8:00PM - 10:00PM EDT. During this time period ChaSeR and other archive interfaces will be unavailable. - Downtime on 6/12/21
2021-06-10
Due to electrical work, the public interfaces of the Chandra Data Archive will not be available on Saturday 6/12 from 4 AM to 9 PM. - Repro V Begins
2020-10-26
The fifth major reprocessing of the archive (Repro V) has started! Details can be found here. - Past Notices
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.
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
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.
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 |