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The X-ray Spectral-Timing Revolution
The X-ray Spectral-Timing Revolution - Scientific Report
Phil Uttley, Ed Cackett, Chris Done, Andy Fabian and Barbara De Marco
Description and Aims
X-ray spectral-timing is a new approach to combining spectral and variability information from X-ray observations of accreting black holes and neutron stars in order to reveal the structure and behaviour of matter in their innermost regions, which are impossible to image with any current or foreseen technology. Key science questions are: how can we use X-ray reverberation mapping to image the innermost regions and search for General Relativistic effects? What is the best way to model spectral-timing behaviour of quasi-periodic oscillations? How can we understand the variability associated with the accretion flow as well as jets/outflows? In order to start to answer these questions the primary aim of the workshop was to address the outstanding practical and theoretical issues in modelling spectral-timing data and set up a common framework for modelling and fitting the data, so that the techniques and models become accessible to a wider community and are not limited to specialists with their own bespoke code, as is the current situation.
In this sense, our workshop was a starting point in getting solutions to some key problems in understanding accreting compact objects using spectral-timing data. As noted in our proposal, we think our workshop will have been a success if it stimulates:
The workshop itself was very stimulating and we had an
enormous amount of positive feedback from participants. Besides a lot of valuable science discussion,
the most important outcome was setting up a collaboration to develop the next
generation spectral-timing software 'Stingray' (https://github.com/StingraySoftware/stingray/),
following the approach of the Astropy project (http://www.astropy.org/),
which the final software will become part of.
Crucially, this software project is being led by the younger scientists
who attended the workshop, notably Daniela Huppenkothen,
Matteo Bachetti and Abigail Stevens. Other workshop attendees are contributing on
a case-by-case basis. There is also work
underway to integrate this new software with existing spectral-fitting packages
XSPEC (developer and attendee Keith Arnaud) and Sherpa (key developer attendee Aneta Siemiginowska). These projects are currently ongoing and may
benefit from an even more focussed smaller workshop next year. Overall we feel that this outcome satisfies
very strongly our original goals, but it is important to keep up the momentum of
this development process over the next couple of years.
One aim we have not yet implemented was the production of
a white paper or similar in order to make recommendations to the community as
to the best approaches for spectral-timing modelling approaches. Partly this was down to lack of time on the
part of the organisers after the workshop, but also because it needs to
incorporate some of the early lessons learned via the software development
which is currently in its early stages.
For this reason we do wish to move forward with producing a formal
document such as a white paper but this will happen later than anticipated.
We spent most of the week in 3-4 smaller more focussed discussion groups combined with summary sessions with the whole workshop at the end of each day and for most of the last day. We only had a limited number of morning plenary talks for the first few days. We had uniformly positive feedback on this approach - the smaller groups were much more effective for communication and for everyone to participate, and we would recommend this approach for future workshops.
We also found that the whole organisation of the workshop by the Lorentz Center staff themselves was fantastic and also uniformly positive - we had no negative feedback from the participants.