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Some of the things I work on,  include....

 

 

Eddington Accretion onto compact objects:

 

My URF is particularly focused in Eddington Accretion onto compac objects. Right now I am studying  the evidence (and their implication) for very high accretion rates on to Black Holes and Neutron Star systems. The result that started to motivate my recent studies was published in The Astrophysical Journal Letters, and has the title  The Faint "Heartbeats" of IGR J17091-3624: An Exceptional Black Hole Candidate (click HERE to get a free copy of the article -- See also the NASA press release "NASA's RXTE Detects 'Heartbeat' of Smallest Black Hole Candidate").

 

The upper and lower panels of each frame show a light curve of the black hole candidates IGR J17091–3624 and GRS 1915+105, respectively. Count rates are given in 1 s bins, per PCU (RXTE), 2-60 keV and background subtracted. Greek letters on the side indicate the variability class (a type of classification of these light curves -- see "A model-independent analysis of the variability of GRS 1915+105", by Belloni et al 2000, for  details on the different type of classes). For more information about this figure, see the paper).

This first result lead to other discoveries and works on both IGR J17091-3624, and GRS 1915+105. For example, we reported the "Discovery of High-frequency Quasi-periodic Oscillations in the Black Hole Candidate IGR J17091-3624", which then lead to 2 other papers on GRS1915+105: "High-frequency quasi-periodic oscillations from GRS 1915+105" and "Discovery of a 34 Hz quasi-periodic oscillation in the X-ray emission of GRS 1915+105" (follow the arXiv e-print link for open access versions of these papers). Figures of these high-frequency quasi-periodic oscillations are shown below:

Upper panel : Averaged power spectra of all observa-
tions of IGR J17091–3624  (for a total of 74 ksec of data). Lower panel : Average power spectra of a single observation (ObsID: 80701-01-28-01) of GRS 1915+105. Both plots show the typical   variability class power spectra, with a strong broad bump at low frequencies. Insets show a zoom to the 65 − 67 Hz QPO. For more information on this figure, see paper.

Left panel: Average power spectrum of all observations after MJD 55841 (for a total of 48 ksec). The 66 ± 0.5 Hz QPO is 9 sigma significant, while the 164 ± 10 Hz is 4.5 sigma. Lower inset shows the rms amplitude vs. energy for the 66 Hz QPO. Right panel: Average power spectrum of all observations performed before MJD 55830, when the average intensity of IGR J17091–324 was higher than 46 mCrab (corresponding to 100 cts s−1 PCU−1; we used a total of 235 ksec). Note the difference the y axis scales. The broad (Q=1) QPO at 70 ± 6 is 4.5 significant. In both panels we used data in the 2-25 keV range. Insets on the top: light curves marking with grey area the data used to produce each power spectrum. For more information on this figure, see paper.

If you are interested in this subject, please also check the ISSI team:

 

The extreme physics of Eddington and

super Eddington accretion onto Black Holes

 

http://www.issibern.ch/teams/eddingtonaccretion/

 

 

 

And .....  soon to be be expanded, sorry didn't have time yet :-(

 

  • Thermonuclear burning on the neutron star surface (including marginally stable burning, type I X-ray bursts, etc)
     

  • Accreting millisecond X-ray pulsars
     

  • Quasi-periodic oscillations in the X-ray light curves of Neutron Star and Black-Hole X-ray binaries...
     

  • Multi-wavelength observations of accreting objects
     

  • Timing techniques

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