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 (https://alerce.online/) 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:

• ZTF oid: ID for ZTF event
• Class Name: type of object (AGN, LPV, etc) according to ALeRCE alert broker Light-Curve classification
• Probability: probability that object belongs to the most likely class
• Obs. Date: observation date
• lastMJD - firstMJD: observation length in Modified Julian Date (MJD) days
• FPS link: link to Chandra Footprint Service page displaying the area of the sky of interest
• ObsIDs: matching Chandra ObsIDs
• Total CDA exposure: total Chandra exposure time (sum of exposure times for all overlapping ObsIDs)
• CSC Properties: if CSC coverage exists, links for CSC Quick Search within 1) 3 arcsec of position; 2) 20 arcsec of position (including master sources properties - if any CSC counterpart exists - and limiting sensitivity in the location of the ZTF object)
• CSC Name: master source name of the CSC counterpart, if existing
• FITS: link to download file for CDA matches

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.