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CHANMASTER - Chandra Observations



This database table contains all of the observations made by the Chandra X-Ray Observatory (CXO, formerly known as the Advanced X-ray Astrophysics Facility or AXAF) as part of the Performance Verification and Calibration (PVC) phase and also contains all of the subsequent Cycles' Guaranteed Time Observers (GTO) and General Observer (GO) targets, and any Director's Discretionary Time (DDT) targets that have been observed. It also includes scheduled and as-yet-not-scheduled targets.

The HEASARC updates this database table on a twice-weekly basis by querying the database table at the Chandra X-Ray Center (CXC) website, as discussed in the Provenance section. For observations whose status is 'archived', data products can be retrieved from the HEASARC's mirror of the CXC's Chandra Data Archive (CDA). The CXC should be acknowledged as the source of Chandra data.

The PVC phase was during the first few months of the CXO mission; some of the calibration observations that are for monitoring purposes will be performed in later mission cycles. All calibration data (entries with Type = CAL in this database) are placed immediately into the CXO public data archive at the Chandra X-Ray Observatory Center (CXC); please see the Web page at for more information on the CXC data archive). GTO observations during Cycle 1 or any subsequent Cycle will probably occupy 100% of months 3-4, 30% of months 5-22, and 15% of the available time for the remainder of the mission. Guaranteed Time Observers will have the same proprietary data rights as General Observers (i.e., their data will be placed in the public CXC archive 12 months after they have received the data in usable form).

For detailed information on the Chandra Observatory and datasets see:               for general Chandra information           for the Chandra Data Archive           for calibration information         for the calibration database          for data analysis for analysis software  for analysis threads        for WebChaSeR


The CHANMASTER database table was last updated on 19 May 2024.


Chandra data are provided to the HEASARC by the CXC as a mirror of the primary Chandra archive. The CXC should be acknowledged as the source of Chandra data.


The Chandra X-Ray Center (CXC) website at is the source of the information in this table and the associated data products.


The HEASARC updates this database table on a twice-weekly basis based on information obtained from the Chandra Data Archive at the CXC website.

Data Products

All Chandra data products can be retrieved directly from the CXC using their interface at

Links to the HEASARC's mirror of the Chandra Data Archive (CDA) are also accessible through the Browse Web interface for table entries where the status is 'archived'. These links allow the user to select the Chandra data products that are available in the CDA. These product categories include the observation summary file, the V&V Report, images and source lists (both FITS and JPEG), events lists, orbital ephemeris abd aspect solution files, gain plots, spectra, bad pixel lists, and miscellaneous files. Using this method, the TAR file is created on the fly, and data from multiple observations can be retrieved together. The CXC should be acknowledged as the source of all Chandra data.


A unique Chandra Observation Identifier.

The current status of the observation and its associated dataset: this is set to 'archived' if the dataset is available to the public in the CXC archive. The more-or-less self-explanatory values for the status are 'unobserved', 'scheduled', 'partially observed', 'observed', 'discarded', and 'archived'. Observations with 'discarded' status are ones for which the Chandra Project considered that there were no useful data. They were scheduled, provided telemetry, but did not yield any science data. These 'discarded' observations have been removed from the HEASARC's implementation of this database table as of April, 2016.

The name of the target of the observation.

The Right Ascension of the target in the selected equinox.

The Declination of the target in the selected equinox.

The Galactic Longitude of the target.

The Galactic Latitude of the target.

The start time of the observation (UTC).

The detector requested for the exposure. There are 2 focal-plane scientific instruments, the AXAF CCD Imaging Spectrometer (ACIS) and the High Resolution Camera (HRC). The ACIS has 2 arrays of CCDs: the ACIS imaging array (ACIS-I) is optimized for imaging wide fields, while the ACIS spectroscopic array (ACIS-S) is optimized for grating spectroscopy and for imaging smaller fields. The HRC consists of 2 microchannel plate array which are used as the primary detection devices: the HRC-I is optimized for direct imaging, while the HRC-S is optimized for imaging the dispersed flux from the Low Energy Transmission Grating (LETG). Thus, there are 4 possible detectors: ACIS-I, ACIS-S, HRC-I, and HRC-S.

The grating setting requested/used for the exposure. There are two objective transmission gratings: the High Energy Transmission Grating (HETG) and the Low Energy Transmission Grating (LETG). The ACIS-S detector is normally used to read out the HETG spectra, while the HRC-S detector is normally used to read out the LETG spectra. Thus, there are 3 possible grating selections: LETG, HETG, and NONE (i.e., no grating requested).

The actual exposure time, in seconds, if the observation has been made. If the observation has not been made yet, this is the approved exposure time, in seconds. This parameter was given with a precision of 0.01 kiloseconds in the original data file.

The type of observation. There are five general types of target: those accepted in a General Observer (GO) proposal (type = 'GO'), those accepted in a Guaranteed Time Observing (GTO) proposal (type ='GTO'), those used for a Calibration observation (type = 'CAL'), those observed as Chandra Cool Targets (type = 'CCT'), those accepted as Targets of Opportunity (type = 'TOO'), and those observed as Director's Discretionary Time (type = 'DDT'). Please note that some DDT targets may have been designated as TOO targets.

Chandra Cool Targets (CCTs) are intended to produce scientifically useful data while the observatory is cooling. The observatory is pointed at these CCTs during cooling instead of an empty sky. The mission planning team started observing CCTs during spacecraft cooling in December 2018. CCT data does not have associated proprietary time.

The last name of the assigned Principal Investigator (PI) for the observation. Notice that this is not always an unambiguous identifier, since there are a number of last names (e.g., Drake and White) which are shared by more than one astronomer. If in doubt, it is recommended that the target lists at be consulted for the full PI name for all accepted proposals.

The cycle number in which the proposal to observe the particular target was submitted. Note that any observations which the CXC have not assigned proposal numbers have been defaulted to a value of 0 for this parameter in this HEASARC database.

The proposal number to which the target corresponds as assigned by the CXC.

The public release date for this dataset.

The sequence number to which the observation corresponds (assigned by the CXC).

The operational (SI) mode of the detector. For ACIS it is of the form Ty_xxxxx or CC_xxxxx, where y is an uppercase letter and x is a hexadecimal digit; Ty indicates timed exposure, CC continuous clocking. For HRC it will be DEFAULT for most observations. More information on the ACIS SI modes is available at CXC website:

The subject category of the observation, as assigned by the CXC.

The Browse Object Classification, as derived from the Category parameter provided by the CXC. Note: This is done through a rather crude mapping. Some of the assigned classes will be incorrect. E.g., observations assigned to the isolated neutron stars and supernovae category will be mapped to the supernova remnant Browse object class, since all three are grouped in one Chandra category.

Contact Person

Questions regarding the CHANMASTER database table can be addressed to the HEASARC Help Desk.
Page Author: Browse Software Development Team
Last Modified: Monday, 13-Mar-2023 21:42:02 EDT