Transient processing and analysis using $\texttt{AMPEL}$: Alert
  Management, Photometry and Evaluation of Lightcurves
  Both multi-messenger astronomy and new high-throughput wide-field surveys
require flexible tools for the selection and analysis of astrophysical
transients. We here introduce the Alert Management, Photometry and Evaluation
of Lightcurves (AMPEL) system, an analysis framework designed for
high-throughput surveys and suited for streamed data. AMPEL combines the
functionality of an alert broker with a generic framework capable of hosting
user-contributed code, that encourages provenance and keeps track of the
varying information states that a transient displays. The latter concept
includes information gathered over time and data policies such as access or
calibration levels.
  We describe a novel ongoing real-time multi-messenger analysis using AMPEL to
combine IceCube neutrino data with the alert streams of the Zwicky Transient
Facility (ZTF). We also reprocess the first four months of ZTF public alerts,
and compare the yields of more than 200 different transient selection functions
to quantify efficiencies for selecting Type Ia supernovae that were reported to
the Transient Name Server (TNS). We highlight three channels suitable for (1)
the collection of a complete sample of extragalactic transients, (2) immediate
follow-up of nearby transients and (3) follow-up campaigns targeting young,
extragalactic transients. We confirm ZTF completeness in that all TNS
supernovae positioned on active CCD regions were detected.
  AMPEL can assist in filtering transients in real time, running alert reaction
simulations, the reprocessing of full datasets as well as in the final
scientific analysis of transient data. This text introduces how users can
design their own channels for inclusion in the AMPEL live instance that parses
the ZTF stream and the real-time submission of high quality extragalactic
supernova candidates to the TNS.
