Chandra X-Ray Observatory

CDA - ZTF Scroll

Data Analysis Links
CDA Status
  • The archive is fully functional.
Reprocessing Status
    Reprocessing IV has been completed in December 2014.
Current Software Releases
  • ASCDSVER: 10.12.4
  • CALDBVER: 4.11.1
What's New
  • Electrical Outage 11/05/21 - 11/06/21
    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
    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
    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
    The fifth major reprocessing of the archive (Repro V) has started! Details can be found here.
  • Past Notices
CDA-ZTF Scroll

There's a lot of data in the Chandra archive -- terabytes of it. The more actively it is used, the happier we are. We are also aware that we can better support usage of archival data by extending their discoverability through cross-domain/cross-mission search criteria that are not necessarily based on X-ray parameters and properties of the Chandra observations. The enrichment of Chandra archival data via external, multi-wavelength information regarding known astronomical sources located in their footprints, in order to enhance their information content, more succinctly called “the annotation of the Chandra Data Archive," is an exciting approach that would make Chandra data more easily discoverable. Two years ago we started a pilot project to develop and test tools and methods to enhance the archive using specific annotations based on optical synoptic observations that have disclosed an entirely new window on the dynamical Universe. Today, we present the results of that pilot project.

The "ZTF Scroll" (see link below) is our first version of the results. It is a web page grounded in a Python-based code that presents a list of Chandra archival observations with spatially coincident transient and variable events, as observed and classified by the Zwicky Transient Facility (ZTF) ALeRCE alert broker ( according to their lightcurve. The ‘discovery’ software (a code that collects ZTF events lying in the field of view of archival Chandra observations, a subset of properties for these observations and Chandra Source Catalog (CSC) sources in the vicinity of the ZTF alert coordinates, if any is found) runs on a daily basis, and the scroll highlights results from the most recent month of runs – though earlier files are always available (see below). The software underpinning the ZTF scroll can be easily deployed to run on data channeled through the same broker from a different mission (Vera Rubin Observatory, for example).

ZTF Scroll

Older ZTF FITS files

Scroll Columns

Following is an explication of the columns in the ZTF scroll:

CDA and CSC matches

Users may download FITS files (for CDA matches) from the links (rightmost column) in the linked ZTF Scroll page. If a user wishes to find an older file, they will be available via the "Older ZTF FITS files" link.

This page maintained by the Chandra Data Archive (

Last modified: 2023-02-06

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