Welcome to the Chandra Data Archive =================================== This is the root directory of the anonymous ftp version of the CDA. It contains all primary and secondary products of all public Chandra observations and is being kept up-to-date in real time. That means that observations that are released to the public are available from this ftp archive almost immediately and that old data versions are replaced by new, reprocessed ones as soon as they are released. At this level there are four main directories: science Contains all public GO, GTO, TOO, and DDT observations cal Contains all (celestial) calibration observations er Contains all engineering (non-celestial) observations byobsid Provides direct access to data products by ObsId The er directory has one subdirectory for each calendar year. science and cal directories --------------------------- The science and cal directories each have one subdirectory per AO cycle ("ao"), where ao00 is the on-orbit checkout period. Each AO directory contains up to nine subdirectories ("cat"), one for each of the observation categories: 0 Non-celestial (Engineering) Observation 1 Solar System 2 Normal Stars and WD 3 WD Binaries and CV 4 BH and NS Binaries 5 SN, SNR, and Isolated NS 6 Normal Galaxies 7 Active Galaxies and Quasars 8 Clusters of Galaxies 9 Extragalactic Diffuse Emission and Surveys and Galactic Diffuse Emission and Surveys These categories are assigned by the proposer. WebChaSeR (see below) allows searches on category. Each Cat directory contains one subdirectory per observation, named after the observation ID (ObsId). The ObsId directories contain the V&V report, an observation index file (oif.fits), a primary directory, and a secondary directory. The primary directory holds the primary data products for the ObsId: All Level-2 products: event file, FITS and JPG images, source list, spectra, summary products, as applicable Aspect solution Field-of-view file Bad pixel file Livetime file Orbit ephemeris file The secondary directory holds the secondary data products for the ObsId: Level-1 event file Mask file GTI file Mission timeline file Alignment offsets file Aspect offsets file Exposure statistics file Bias files Parameter block file All data products are gzipped. As an example, the full URL for the L2 event file of ObsId 1040 is: ftp://cdaftp.cfa.harvard.edu/pub/science/ao02/cat5/1040/primary/acisf01040N001_evt2.fits.gz byobsid directory ----------------- The "byobsid" directory allows users to access the data products for any particular ObsId directly, by passing the "science", "cal", "ao", and "cat" directory tree. There are ten subdirectories, 0 through 9, that correspond to the last digit of the ObsId; each of these directories contains a separate subdirectory for each ObsId that has the directory's name as its last digit. And each ObsId directory has the same content as above. In other words, the primary products for ObsId 1040 would be found at: ftp://cdaftp.cfa.harvard.edu/pub/byobsid/0/1040/primary/ Contact ------- Questions? Contact us at: arcops@head.cfa.harvard.edu See also our main website http://cxc.harvard.edu/cda which contains more information on the various data products and points to more powerful Search & Retrieval tools, such as WebChaSeR. Note that in order to retrieve data products from this ftp archive one needs to know the ObsId, AO, and Science Category one is interested in, whereas WebChaSeR provides search capabilities that allow users to find ObsIds of interest, as well as downloads of additional products. Mirror sites ------------ Institutions that are interested in providing a mirror site of this anonymous ftp archive are encouraged to contact us at arcops@head.cfa.harvard.edu Details on Science Categories ----------------------------- More details on the categories (as provided by Chandra Director's Office) 1 Solar System Asteroid Comet Planet 2 Normal Stars and WD A,F,G,K Stars Globular Cluster M,L,T Stars O,B,WR Stars OB Association Open Cluster Planetary Nebula T Association RS CVn Star WD Stars 3 WD Binaries and CV Cataclysmic Variables Intermediate Polar(DQ Her) Nova Polar(AM Her) 4 BH and NS Binaries Black Hole Binary HMXB LMXB X-Ray Transient 5 SN, SNR, and Isolated NS Dark Cloud Gamma Ray Bursts ISM Neutron Star/Pulsar Supernova SNR (Supernova Remnant) 6 Normal Galaxies Dwarf Elliptical High-Redshift Galaxy Irregular Spiral 7 Active Galaxies and Quasars BL Lac Gravitational Lens Interacting Galaxy Liner QSO Quasar Radio Galaxy Seyfert Starburst Ultraluminous IR Galaxy 8 Clusters of Galaxies Group High-Redshift Cluster Poor Cluster Rich Cluster(Low-Redshift) 9 Extragalactic Diffuse Emission and Surveys and Galactic Diffuse Emission and Surveys Extragalactic Survey Galactic Survey Unidentified Objects