Homepage of Laurens Keek

Senior Scientist at cosine Measurement Systems in Warmond, The Netherlands. I perform data analysis as part of the development of Silicon Pore Optics for ESA's next-generation X-ray observatory Athena.

• Official publication of the largest catalog of X-ray burst observations: the Multi-Instrument Burst Archive (MINBAR). One of my contributions was a prototype for the web interface.
• My first paper on the development of Silicon Pore Optics for the Athena mission has been published in the proceedings of the SPIE.
• First science paper with X-ray observations taken with NICER on the International Space Station! We observed how the surroundings of a neutron star light up as they are irradiated by X-rays from a thermonuclear explosion on the star. Our exciting results are featured on AAS Nova.
• If you have an hour, watch my JINA-CEE online seminar, where I discuss our recent work on the long helium burst from IGR J17062-6143.
• New studies on the impact of a day-long X-ray burst on the surroundings of the accreting pulsar IGR J17062-6143. Published as a paper and a letter in the Astrophysical Journal. Also covered on Phys.org and AstroNews.
• Last November I visited the new Space Institute of McGill University in Montreal, Canada, where I presented the Joint Astrophysics Colloquium and a lecture at the Public Astro Night. I was interviewed by Sebastien Guillot for the AstroMcGill Podcast: Listen and learn more about X-ray bursts!
• New press releases by SRON (Dutch) and GaTech (English) for our discovery of the speed record set by thermonuclear X-ray bursts on neutron stars (see also Volkskrant, Phys.org).
• We presented a study in Physical Review Letters on the measurement of a key reaction for X-ray bursts. The measurement was performed by colleagues at the NSCL with the GRETINA experiment.
• We recently published a letter in Nature on a new strong neutrino cooling mechanism in neutron stars and its impact on superbursts and X-ray transients (see also MSU Today, Ars Technica, Scientific Computing, Astronomy Magazine).

Research Interests

I study Type I X-ray bursts from accreting neutron stars. When a neutron star accretes matter from a binary companion, a layer of hydrogen and/or helium piles up on its surface. Due to the high gravity at the neutron star surface, this layer is highly compressed. When the layer is just a few meters thick, the temperature and density at the bottom are already high enough for thermonuclear fusion to start. This fusion "burns" hydrogen into helium and helium into carbon. Under certain conditions, this burning can proceed in an unstable manner, causing all the fuel to burn within one second. During such a flash the temperature is high enough for a series of proton captures, that turn carbon into much heavier isotopes, with mass numbers up to 100. These flashes are observed as X-ray bursts. Since the 1970's several thousands bursts have been observed from approximately 90 sources in our Galaxy. Many of the observed features cannot be explained well with our current models. For example, the observed conditions for which the burning is stable or unstable do not match the theory. An exciting new discovery in recent years are rare long bursts, that last from half an hour up to an entire day. This is much longer than the 10 to 100 seconds a normal burst is observable. The longest and most energetic catagory are referred to as "superbursts". They are thought to be caused by the unstable burning of a carbon-rich layer.

I work on both observations and models of Type I X-ray bursts. On the observational side, we collaborate with groups around the world to create large catalogs of thousands of observed bursts. This will give us a better understanding of the different types of burning behavior neutron stars exhibit in a wide range of conditions. This helps us to improve our models. We develop computer codes that model the evolution of the neutron star envelope in time. An important part of these codes are the reaction networks that model the nuclear burning reactions. We use the best available reaction rates, through our collaborations within JINA-CEE, the Joint Institute of Nuclear Astrophysics.

Contact

Email: laurens@xrb.space