Lucia Ballo

ESA XMM-Newton Postdoc

I graduated in Physics at the University of Milano with a work on
variability of blazars carried out at the Brera Observatory. After
obtaining a pre-doctoral grant at the Brera Observatory to work on
X-ray emission from AGNs, I moved to the International School for
Advanced Studies in Trieste, where I got my PhD in October 2006.

My research interest addresses different aspects of AGN activity:
from the variability of powerful blazars or the problem of dust
obscuration, to the accretion rate of local low luminous AGNs as
well as the relationship between the AGN activity and the host
galaxy evolution.

In particular, during my degree my work was focused on the emission
observed in the blazar 3C 279. Comparing Spectral Energy
Distributions obtained at all epochs with adequate multiwavelength
(simultaneous) coverage, we investigated the origin of the strong
and rapid variability observed in the emission of this blazar at
all frequencies.  After discussing the contribution of different
mechanisms to the high energy emission, we ascribed the observed
variability mainly to a change in the Lorenz factor of the matter
in the jet.

Then, I've worked on the relation between AGN and host galaxy,
investigating the sources responsible for the X-ray background. In
this field, I addressed two issues:
- the search of obscured AGNs in the population of Luminous
  Infrared Galaxies, which were proposed as candidates to host
  bright and heavily obscured sources, using their hard X-ray
  emission to search for the presence of powerful activity. Our SAX
  observations and archival XMM data clearly unveiled a strongly
  absorbed AGN of high intrinsic luminosity in the merging system
  Arp 299, suggesting the possibility that both galaxies host an
  AGN.
- in the bulk of my PhD project, a two-dimensional fit to galaxy
  profiles allowed us to derive optical magnitudes for bulge, disk
  and nucleus components for a sample of X-ray selected AGNs at
  intermediate redshift in the GOODS fields. Our finding suggest
  that in this sample, representative of the sources making up the
  X-ray background, we are observing a renewal of activity in
  previously formed objects.

Alongside of this work, I've studied the X-ray emission of one
source discovered in the ASCA Hard Serendipitous Survey for which
the hardness ratios suggested the presence of very high column
densities. Our XMM observations showed that its hard X-ray colors
are due to a strong line complex (with an extremely high equivalent
width) rather than to absorption effects; this complex is very
likely produced by a combination of relativistic and non
relativistic Iron lines.

Finally, my work at ESAC will mainly focus on studying high energy
spectral features of X-ray weak QSOs, i.e. AGNs with high
optical-UV luminosity showing an emission of low intensity in the
X-ray band.