Welcome to the Chandra Data Archive
===================================

This directory provides direct, deterministic access to all public
observations in the anonymous ftp version of the CDA, based on the
Observation Identifier (ObsId).

There are ten directories, 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. 

In other words, the data products for ObsId 1040 would be found at:
  ftp://cdaftp.cfa.harvard.edu/pub/byobsid/0/1040/

Each ObsId directory contains 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.