Sergio’s research

My main involvement is in the Swift mission where I led the calibrations of the X-Ray Telescope (XRT), which is the most strategic instrument onboard Swift, providing an accurate position (2-3 arcsec) for almost
every Gamma-Ray Burst (GRB) observed. Calibrating an instrument, by itself, is not a highly rewarding activity in terms of papers (just a few refereed papers and a number of SPIE contributions). However, calibrating the XRT gave me a deep insight in all the problems and technicalities of the instrument, putting me in the best position to exploit its science. More than 50 papers came from this research line and m
ore than 10 have me as a leading author. These include single burst papers but also statistical analysis of GRB properties and theoretical papers on the emission mechanisms. Among them, there are 7 papers on Nature and 1 paper on Science. One Nature paper has me as the leading author and deals with the first supernova (pinpointed by the GRB explosion) caugh
t in the act of exploding. The observation started less than an hour before the explosion and this is even earlier than the famous 1987A in the Large Magellanic Cloud. In parallel with the high-energy data on GRBs I am also involved in the optical/NIR follow-up of these high energetic transients. Here my contribution is mainly in the data interpretation and modeling. More than 150 papers came from these activities. Among these, there are 10 paper on Nature and 3 paper on Science both involving supernovae associated (or not) to GRBs.

Recently I became interested in tidal disruption events. First I pull it out of the bag a new model to
explain the peculiarities of GRB 101225A, in terms of a minor body falling onto a Galactic neutron star. The minor body gets tidally disrupted accounting for the peculiarities of the “GRB”. A few months later Swift discovered another jewel: Sw J1644+57, the reactivation of an AGN’s jet caused by the tidal disruption of a star. Recently we found a very peculiar AGN, showing two bright very similar flares, which we interpreted as the first recurrent TDE due to an orbiting star. The next passage is predicted to occur in 2019. Two Nature papers come out from these discoveries.

Before my involvement in GRB science, my main research activity was in the study of the accretion onto compact object, high-energy astrophysics and relativity in general. These studies concentrate on the different accretion regimes that can experiment a magnetic, fastly rotating neutron star when matter accretes onto its surface (ranging from accretion to ejection to the reactivation of a radio
pulsar). I wrote a review on these topics more than 10 years ago and it is still copiously cited. For this research I make extensive use of X-ray facilities (basically every X-ray satellite from ROSAT onwards) as well as optical/NIR (ESO and TNG) and radio observations (Arecibo and Parkes). I am author more than 90 refereed papers (one on Nature), including more than 30 having me as leading author.
Scientific curiosity took me to undertake the development of a detection algorithm based on the wavelet transform to detect point as well as extended sources in X-ray images. We systematically applied this algorithm to the entire dataset of ROSAT HRI data creating the Brera Multi-scale Wavelet catalog of HRI sources (BMW
-HRI)including more than 29,000 sources. We also analyzed all sources looking for pulsed signals. We found RX J0806.3+1527 consisting of two white dwarfs orbiting every 321 s.

The algorithm then tailored to Chandra ACIS-I data for which we build the BMW-Chandra catalog including more than 15,000 sources. I supervised and worked to the entire projects from data analysis to the creation of a public catalog and associated (retrievable) products as well as the exploitation of the scientific content of the catalog, often made in collaboration with other groups. More than 15 papers came out from these studies.

Finally, in close collaboration with the technological group at OAB, I am involved in the theoretical design of wide-field X-ray telescopes. Thanks to my expertise in the mirror design, fabrication and calibration, as well as science exploitation I am (and have been) involved at different levels in a (large) number of foreseen X-ray missions ranging from JET-X, Panoram-X, EXTRA, HEXIT, Simbol-X, Duet, ESTREMO, EDGE, XIAO, Xenia, WFXT, EXIST, NHXM, LOFT, Theseus. I led the Joint UV Survey Telescope (JUST) proposal in response to the ESA small mission call and I am PI of the Son of X-Shooter (SOXS) spectrograph at ESO/NTT.

December 2009

(slightly updated November 2015)