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CHANDRAPUB: Help

CHANDRAPUB - Chandra Public Observations


Overview

This database table contains all of the archived observations made by the Chandra X-Ray Observatory (CXO, formerly known as the Advanced X-ray Astrophysics Facility or AXAF) that are available to the public.

The HEASARC constructs 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. Data products stored at the CXC can be accessed through the Browse Web interface using this database table.

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 http://asc.harvard.edu/ 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:

http://cxc.harvard.edu/               for general Chandra information
http://cxc.harvard.edu/cda/           for the Chandra Data Archive
http://cxc.harvard.edu/cal/           for calibration information
http://cxc.harvard.edu/caldb/         for the calibration database
http://cxc.harvard.edu/ciao/          for data analysis
http://cxc.harvard.edu/ciao/download/ for analysis software
http://cxc.harvard.edu/ciao/threads/  for analysis threads
http://cda.harvard.edu/chaser/        for WebChaSeR

References

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

Provenance

The HEASARC constructs this database table on a twice-weekly basis based on information obtained from the Chandra Data Archive at the CXC web site. This version of the CHANDRAPUB database table has fewer entries than the original version because a number of observations which were either canceled or discarded have been removed.

Data Products

Links to the CXC data archive are accessible through the Browse Web interface for table entries where the status is 'archived'. The current links allow the user to select Chandra data products in one of two ways:

(i) select a set of files, either all (but Level 0), and/or Intermediate Level 1/1.5, and/or Level 2 processed data products, and then create a TAR file at the CXC for immediate or later download. This is done via a cgi-bin query of the Chandra Data Archive (CDA) Provisional Data Retrieval Interface at the CXC. The various links for a given observation will all point to the same page, but different subsets of the full archival data for the observation will be presented there for selection. The TAR file is created at the CXC, and separate TAR files must be created for each observation. Using this method, there is no way to combine data retrieval from multiple observations (although this capability is available via a direct WebChaSer query at http://cda.harvard.edu/chaser/), or to combine the retrieval of Chandra data with data from other missions.

(ii) select the data products that are available in the Chandra Data Archive (CDA) anonymous FTP area. These product categories are more detailed than for option (i) and 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.


Parameters

ObsID
A unique Chandra Observation Identifier.

Name
The name of the target of the observation.

RA
The Right Ascension of the target in the selected equinox.

Dec
The Declination of the target in the selected equinox.

LII
The Galactic Longitude of the target.

BII
The Galactic Latitude of the target.

Time
The start time of the observation (UTC).

Detector
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.

Grating
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).

Exposure
The requested or actual exposure time, in kiloseconds.

Type
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 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.

PI
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 http://cxc.harvard.edu/target_lists/ be consulted for the full PI name for all accepted proposals.

Cycle
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.

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

Public_Date
The public release date for this dataset.

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

Data_Mode
The operational 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.

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

Class
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 CHANDRAPUB database table can be addressed to the HEASARC User Hotline.
If you have any problems, please consult the help page or mail ledas-help@star.le.ac.uk
 
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