Research on X-ray bursts

Matter accreting to a weakly-magnetized NS can cause thermonuclear explosion on the NS surface. These X-ray bursts have been discovered already more than 40 years ago, but still there are many mysteries. One of the goals of our research is to develop tools to understand the X-ray bursts properties in order to determine NS masses and radii, which would seriously constrain the equation of state of cold dense matter. In collaboration with the group from Univ. of Tubingen (Germany) we are developing NS atmosphere models. For the first time, we have used the exact Compton scattering kernel to construct the most accurate atmosphere models for hot NSs (Suleimanov et al. 2012). We have proposed a novel “cooling tail” method to determine NS parameters. We have also discovered that the cooling tail properties strongly depend on the accretion rate and showed that only the low-accretion-rate, hard-state X-ray bursts can potentially be used for NS parameter determination (Kajava et al. 2014; Poutanen et al. 2014). Using the cooling tail method, we find that the NS radius in a couple of known X-ray bursters is above 12.5 km (Suleimanov et al. 2011b; Poutanen et al. 2014), which supports stiff equation of state and is consistent with the existence of 2 solar mass pulsars.

Our current projects include development of the atmosphere model for rapidly rotating NSs and determination of the NS masses and radii for a set of bursters using the hard-state, low-accretion-rate bursts.



Figure 1: Mass-radius constraints from the hard-state bursts of 4U 1608–52 (Poutanen et al. 2014).

Selected publications:

Working groups

X-ray binaries

Description of the group activity.
Group meetings take place on Wednesdays (first and third of each month), 15.00 in the coffee room.

Stellar explosions

Description of the group activity.
Group meetings take place on Mondays, 15.00 in the coffee room.

AGNs and Very High Energy Astrophysics

Description of the group activity.
Group meetings take place on Wednesday (second and fourth of each month), 15.00 in the coffee room.