VOEvent Sky Event Reporting Metadata Authors: Rob Seaman, National Optical Astronomy Observatory, USA Roy Williams, California Institute of Technology, USA Alasdair Allan, University of Exeter, UK Scott Barthelmy, NASA Goddard Spaceflight Center, USA Joshua Bloom, University of California, Berkeley, USA Frederic Hessman, University of Gottingen, Germany Szabolcs Marka, Columbia University, USA Arnold Rots, Harvard-Smithsonian Center for Astrophysics, USA Chris Stoughton, Fermi National Accelerator Laboratory, USA Tom Vestrand, Los Alamos National Laboratory, USA Robert White, LANL, USA Przemyslaw Wozniak, LANL, USA

IVOA Interoperability Meeting, Kyoto (May 2005) 1 What is this VOEvent thing anyway? VOEvent defines the content and meaning of a standard information packet for representing, transmitting, publishing and archiving the discovery of a transient celestial event, with the common implication that timely follow-up is being requested.

IVOA Interoperability Meeting, Kyoto (May 2005) 2 Why would you want to do that? Providers of the event stream including the SWIFT and synoptic surveys coming online now and planned for the future. There are robotic telescope networks that will respond in seconds to these discovery events, giving a comprehensive, panchromatic view. Until now, events have been distributed in various formats and protocols, so that aggregation and federation have been difficult. The objective of the VOEvent working group is to build an open standard for exchanging messages about these immediate astronomical events, including publication, archiving, query, subscription, and aggregation.

IVOA Interoperability Meeting, Kyoto (May 2005) 3 What VOEvent is not… A way to produce a phase zero description of an telescope and instrument package. A way to build an document to request an observation from a robotic telescope. For these cases you should use Remote Telescope Markup Language (RTML), see

IVOA Interoperability Meeting, Kyoto (May 2005) 4 So what have we been doing? A preliminary VOEvent standard has been agreed in rough form during the workshop at Cal Tech in April. Buy-in for the new standard from many places, including: GCN, LSST, Pan-STARRS, Palomar- Quest, LIGO, eSTAR, RAPTOR/TALON, PAIRITEL, ATEL, and the Hands-On Universe (HOU) projects. We shalt not reinvent the wheel, but only market it…

IVOA Interoperability Meeting, Kyoto (May 2005) 5 Simplicity vs. rich semantic content Perhaps the major debate at the Caltech workshop was the balance between simplicity and the richness of the semantic content. If we make things too complex, even if ratified the standard will not be adopted by the people who matter, the event publishers. If we make things too light weight, even if adopted by the event publishers, it will not be used by consumers.

IVOA Interoperability Meeting, Kyoto (May 2005) 6 Who, What, Where, When & How A VOEvent document is divided in distinct sections detailing the Who, What, WhereWhen and How of an event. In addition there are also sections which deal with Hypothesis, the initial scientific assessment of the event… …plus Citations, which provide references to other documents, and Description which contains human readable content.

IVOA Interoperability Meeting, Kyoto (May 2005) 7 Adoption and integration… Adopted the IVOA Space-Time Coordinate (STC) schema to represent. Integrated with Remote Telescope Markup Language (RTML) so that VOEvent can both include instrument descriptions, and form the basis of an RTML document which can be used to drive robotic telescopes. Make heavy use of references…

IVOA Interoperability Meeting, Kyoto (May 2005) 8 Citations and identifiers An VOEvent message includes a global identifier so they can be cited in future messages, Message typing, such as discovery, follow-up, retraction and supersede to provide a coherent picture of distributed knowledge about a discovery. ivo://raptor.lanl/ This is animproved observation of the earlier event.

IVOA Interoperability Meeting, Kyoto (May 2005) 9 Modular syntax We have built VOEvent in a modular manner… It can be parsed easily without special tools, although special tools will allow you to get more semantic content from the message. It should have easy to extend, however when dealing with messages intended for real time operations it is crucial to avoid complications and bloat.

IVOA Interoperability Meeting, Kyoto (May 2005) 10 UCDs and rich content A VOEvent message will try and provide rich semantic content through the use of the IVOA UCD standard to both express content in a provider neutral manner… …and allow the messages to be automatically parsed by software. Hope to push this forward by extending UCDs to allow us to describe the scientific nature of the event, or how it is changing with time.

IVOA Interoperability Meeting, Kyoto (May 2005) 11 A simple example This VOEvent packet is an imaginary report from the Raptor project at Los Alamos, that a magnitude 13 star was seen at RA = , Dec = , with an error radius of 0.1 degrees. It is reported as "fast orphan optical transient", so we infer that the same source was not seen in that position before.

IVOA Interoperability Meeting, Kyoto (May 2005) 12 A simple example <VOEvent id="ivo://raptor.lanl/ /sn2005k" role="actual" version="0.90" xmlns:stc=" xmlns:crd=" xmlns:xi=" xmlns:xsi=" xsi:schemaLocation=" stc-v1.22.xsd"> ivo://raptor.lanl/ T14:34: T23:59: Fast Orphan Optical Transient

IVOA Interoperability Meeting, Kyoto (May 2005) 13 A “typical” example Will be longer than the one shown. For instance it may contain citations to other documents, ivo://raptor.lanl/23569 This is an observation of the earlier event but with improved square-galaxy discrimination. This is the light curve associated with the observation. … or more semantic content describing the event.

IVOA Interoperability Meeting, Kyoto (May 2005) 14 A redirection example The capability to distribute a very lightweight alert consisting of a pointer to a stored event packet. The ID is set to that of the original packet, allowing an intervening client such as an aggregator to persist the message in a backend database.

IVOA Interoperability Meeting, Kyoto (May 2005) 15 Implementation Rick Hessman is hosting the collaborative schema development at, Two reference implementations. One in Perl by the eSTAR project, and the other in C++ by the RAPTOR project. Software development hosted by Sourceforge at,

IVOA Interoperability Meeting, Kyoto (May 2005) 16 Why are we telling you guys? We want your (fresh) brains, err, input… There is a VOEvent session in Conference Room K on Thursday morning. You are invited to attend and contribute, promise I won’t shout at you too much. Err, probably…

IVOA Interoperability Meeting, Kyoto (May 2005) 17 In conclusion… There is an emerging standard, and this is the point where you can make a real difference and influence its evolution. An draft release of version 0.9 of the standards document can be found at, Comments welcome…

IVOA Interoperability Meeting, Kyoto (May 2005) 18 The HTN Workshop July Aims Interoperability between robotic telescope networks Interoperability with the Virtual Observatory (VO) for event notification Establishment of an e-market for the exchange of telescope time See htn-workshop2005.ex.ac.ukhtn-workshop2005.ex.ac.uk Science Goal Monitor