EWOCS ongoing project: A New pulsator found!

The analysis of light curves and the power spectral densities of the brightest sources (> 100 detected photons)  led to the discovery of a new pulsator close to the cluster core. The pulsator shows a period of about 3.1 hours and possible dips/eclipses in the light curve. Besides, its X-ray spectrum is very hard, which may indicate that it is more absorbed than the other X-ray sources of the cluster.


The nature of the new pulsator is still not clear. The closest HST source, separated by 0.46 arcsec from the X-ray source, is too faint for the pulsator being a High Mass X-ray Binary. Besides, as estimated by P. Esposito, the object is associated with Westerlund 1 with a 99% confidence. This would rule out the possibility of a background object, such as a Cataclismic Variable. The remaining option is a Low Mass X-ray Binary. The team led by M. Mapelli (specifically, G. Iorio and S. Rastello) are running specific simulations of population synthesis to estimate the chances of such an object to form in a few Myrs in a cluster as massive and dense as Westerlund 1.


If confirmed, this will be the second compact object discovered in the cluster, after the bright pulsar CXOU J164710.2-455216. This finding motivates the search for other compact objects in the clusters, which, according to the study published by Portogies Zwart and collaborators in 2004, meets the requirements for the environment where intermediate massive black holes can for by runaway collisions.


Rayleigh periodogram and folded light curve of the new pulsators


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