Image credit: NASA/JPL-Caltech

Ultra-luminous X-ray Pulsars

6 - 8 June 2018
European Space Astronomy Centre (ESAC)
Villafranca del Castillo
Madrid, Spain


Scientific Background

Ultra-luminous X-ray sources (ULXs) are accreting compact objects in nearby galaxies, which emit X-rays in excess of their spherical Eddington limit. Due their brightness, most of them are believed to be black holes. However, recently a new class of ULXs was discovered, through the detection of coherent pulsations:

Ultra-luminous X-ray pulsars (ULPs)

The presence of pulsations unambiguously identifies the compact objects as neutron stars, which are typically less massive than black holes.  In ULPs the neutron star accretes matter from a companion star at inferred rates much higher than previously expected.

Currently three of these systems are known: M82 X-2, NGC 5907 ULX, and NGC 7793 P13 (with NGC 300 ULX-1 a likely fourth). Their existence challenges our understanding of accretion physics and stellar evolution. Today, no widely accepted theory has emerged to explain all their observational properties. Furthermore, a clear path forward to obtain a full sample of the ULP population is missing.

In order to further our understanding of ULPs, we will have a workshop at ESAC from June 6 to June 8, 2018.

At this workshop, we will bring together experts in observations, accretion models, and stellar evolution for an exchange of knowledge, ideas, and expertise. The goal of the workshop is to collect the observational evidence, make progress on our theoretical understanding, and identify open questions and projects to work on for the coming years in order to obtain a better understanding of the physics and evolution of ULPs.

To this end, the format of the workshop will consist of a mix between review talks by international experts, talks and posters by all participants, and ample time for discussion and project work.

We will in particular discuss observational opportunities with current (e.g. XMM-Newton, Chandra, NuSTAR and the Neil Gehrels Swift Observatory) and upcoming (e.g. XARM and Athena) X-ray telescopes and multi-wavelength follow up.

For questions please contact Felix Fuerst ( or any of the SOC members.


Scientific Goals

  • What are the observational facts we have about ULPs? What are similarities, what are differences between the known sources?
  • How do they compare to standard ULXs? Are their other properties besides pulsations to identifiy neutron star accretors?
  • How do they compare to transient X-ray binaries in our galaxy and the SMC/LMC, which can reach Eddington luminosities? What can we learn from those sources?
  • How can we explain the apperant super-Eddington luminosity? What can we infer about the properties of the neutron star?
  • Where do the super-orbital periods come from? How do they influence the pulse and orbital period?
  • What evolutionary tracks are available to form ULPs? What kind of environment is needed?
  • Is it more or less likely to form neutron star ULXs instead of black hole ULXs? What does the ratio of accretors imply about stellar and galaxy evolution?
  • What can we learn from other exotic neutron stars, like magnetars, and what does the ULPs phase imply about neutron star-neutron star mergers and kilo-novae?


Registration and abstract submission

The registration and abstract submission page can be found here.

The number of participants is strictly limited to 50 people, and registration will happen on a first-come, first-serve basis, with an additional waiting list. There is no conference fee.

The deadline for registration and abstract submission is March 31st. Registration has now closed.

Laptops will be provided for talks, with Powerpoint, Adobe Acrobat, and Keynote available. Poster size is A0.

Invited speakers

Review talks

Tim Roberts Durham, UK
Juri Poutanen Turku, Finland
Jean-Pierre Lasota Paris, France
Selma de Mink Amsterdam, the Netherlands


Invited speakers

Matteo Bachetti INAF/OA Cagliari
Fabio Pintore IASF Milano
Christian Motch Observatoire Astronomique de Strasbourg
Marianne Heida Caltech
Alexander Mushtukov University of Amsterdam
Kyle Parfrey Lawrence Berkeley National Laboratory
Tassos Fragos Observatoire Astronomique de l'Univerite de Geneve
Thomas Tauris Argelander Institut fur Astronomie, Universitat Bonn
Nanda Rea Institute of Space Sciences (IEEC-CSIC)
Ken Ohsuga University of Tsukuba


Scientific Organising Committee

Fiona Harrison (chair) Caltech, USA
Matteo Bachetti INAF/OA Cagliari, Italy
Felix Fuerst ESA/ESAC, Spain
Marianne Heida Caltech, USA
Gian Luca Israel INAF/OA Roma, Italy
Andrew King Leicester, UK
Michela Mapelli University of Innsbruck, Austria and INAF/OA Padova, Italy
Ken Ohsuga University of Tsukuba, Japan
Philipp Podsiadlowski Oxford, UK
Sergey Tsygankov Turku, Finland
Dominic Walton Cambridge, UK
Natalie Webb IRAP, France


Local Organising Committee

Peter Kretschmar
Ana Willis
Celia Sanchez Fernandez
Felix Fuerst
Michael Parker