Accretion, Pulsar timing and ULX.

Much of my research involves the study of accreting X sources, typically neutron stars or black holes. Although I also study these objects from a spectroscopic and/or aperiodic timing point of view, I am often involved in work that needs pulsar timing, because of my experience in this type of analysis and the software I have written and run (see below). I am recognized as one of the key names in the study of Ultraluminous X-ray sources (ULX; as evidenced by the many invited talks to speak on the subject). In particular, I contributed to the first XMM+NuSTAR campaign of ULX observations, publishing the first solid evidence of a spectral break above 10 keV, and in 2014 I discovered the first ultraluminous pulsar in M82 X-2, and still coordinate its follow-up (and recently, measured its orbital decay). I have several collaborations in place for these studies in Italy and many other countries, notably the USA, France, UK, Spain and the Netherlands (see network plot at the end of this section). Recently, I coordinated the HEX-P ULX working group, that made a feasibility study for ULX science with the NASA Probe mission concept HEX-P.

Spectral timing (/polarimetry).

Together with Daniela Huppenkothen and others, I have written and continuously maintain one of the leading spectral timing analysis software for high-energy data, Stingray. This analysis is a link between traditional spectral and temporal analysis, and is considered one of the keys to unhinging many of the uncertainties about accretion on compact objects. We coordinate the work and gather input from many contributors at all career levels, from young Google Summer of Code students to experienced researchers and developers. With Daniela Huppenkothen, I recently wrote a reviewon this topic, as a chapter in the book on temporal analysis (eds. T. Belloni, D. Bhattacharya) of the Handbook of X-ray and Gamma-ray Astrophysics, edited by Cosimo Bambi. I was the national PI of thePRIN TEC INAF 2019-Spectempolar, and with expert spectral timing assignee Guglielmo Mastroserio we optimized Stingray for use with future and present ultra-high throughput instruments such aseXTP and NICER, and added polarimetric information from instruments such as the gas pixel detectors of IXPE and eXTP. With Eleonora Veronica Lai, we are further optimizing the code for use in parallel architecture, as part of Spoke 3 of the PNRR-fundingNational Centre for HPC, Big Data and Quantum Computingproject.

Development and calibration of observational instruments.

I am on the Science Team and/or calibration/operational teams of several ongoing space missions (IXPE, NuSTAR) and the Sardinia Radio Telescope. One of my most important jobs in this regard was the coordination of the time calibration of the NuSTAR satellite, which began immediately after launch in 2012 and was completed during my visit as aFulbright Scholar at Caltech in 2019. Our work has improved by two orders of magnitude the accuracy in correcting the arrival times of photons to the satellite, making NuSTAR suitable, for example, for studying millisecond pulsars. This work, which even in its early stages helped the discovery of pulsars in M82 X-2, earned me aNASA Medal for Exceptional Scientific Achievement in 2016. For NuSTAR, I contributed to the last two Senior Reviews, both of which were favorably evaluated by NASA with mission continuation. For the IXPE mission, I wrote much of the automatic reduction pipeline of ground test data. I am part of the IACHEC (International astronomical consortium for high-energy calibration) consortium as a timing representative for the NuSTAR mission, and I coordinate the work of comparing the timing performance of all space missions using observations of Crab and other pulsars, as a member of the Timing WG. For the Sardinia Radio Telescope I am on the operations team and manage and develop the single dish imaging code used to teach these techniques in the Radio Astronomy Laboratory course and for quicklook data during observations. Over the years I have collaborated on the work of the science WGs of many mission proposals, and am particularly co-I of proposals for new missions, the latest of which is HEX-P.

Statistics, new algorithms, citizen science.

I pursue various innovative algorithm development projects, either to overcome systematic instrumental effects or barriers due to prohibitive computational costs, or in an attempt to overcome inherent limitations in the accuracy of traditional data analysis methods. Some examples: new analysis algorithms and machine learning and simulation based inference for modeling dead time and correlation between different components of variability (with Daniela Huppenkothen); the development of 3D computer games for pulsar search with citizen science(I am scientific PI of the CICLOPSproject with the company Infora, see figure); the adaptation of statistics traditionally used in high-energy astrophysics to classify pulsar candidates (theZn2or the H-test) to data at all wavelengths


(source: NASA ADS, UT 2023-12-17):

  • 163 articles in international refereed journals, 12 as first author
  • 17115 citations from 12469 refereed articles
  • 969 refereed citations of my first-name papers from 785 articles
  • H-index: 45