Ph.D. in Astronomy, 1995, UNLP, Argentina, "High-energy components in the regions of Upper-Sco and Ara"
Current position: Researcher (CONICET)
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Contact: jcombi@fcaglp.unlp.edu.ar
Since 1992 I have been working on topics related to the high-energy astrophysics and radio astronomy. These subjects include:
- Unidentified gamma-ray sources. One of the most exciting mysteries of astronomy involves the large number of unidentified gamma-ray (EGRET) sources whose nature is unknown. Search for radio counterparts of these detections can give us additional information about the structure of the ISM in the line of sight to these sources. By eliminating the background diffuse radiation originated by the galactic disk from the radio images, with filtering techniques, we have unveiled possible radio counterparts of several gamma-ray objects and gathered information on the high-energy radiation mechanisms.
- Multifrequency investigations of new Supernova Remnants (SNRs), discovered from 408 MHz, 1.4 GHz and 2.4 GHz surveys. Several candidates for SNRs have been detected in the southern sky at these frequencies after removing the diffuse background radiation permeating the Galaxy. We have used these data to examine spectral index characteristics over faint and extended regions of SNRs.
- Studies on the origin of galactic and extragalactic cosmic rays (CR). The origin of the highest energy cosmic rays detected in the neighborhood of Earth is still an unsettled issue. In the last years our work have been directed to the use of multifrequency observations in order to estimate the arrival energy of protons accelerated by strong shock fronts in the outer parts of radio galaxies and in the terminal shock of galactic superwinds generated in starburst galaxies. In a series of papers on possible source candidates, different energy losses have been discussed for the rays as well as the associated changes in the arrival spectra.
- Radio and optical microvariability of Active Galactic Nuclei (AGNs). Intraday variability of AGNs like quasars and BL Lac objects was discovered 10 years ago during extensive monitoring campaigns of large samples of northern objects. The origin of these variations is still unknown. Shocks propagating down the parsec-scale jet of the objects have been suggested as a possible cause, but the most extreme cases of variability impose severe constraints on the shock thickness and required Doppler factors. Extrinsic models invoke refractive interstellar scintillation and gravitational microlensing. Since 1990s we have made numerous observations of rapid variability in southern AGNs, detecting many outstanding outbursts (including the first observation of extreme intraday events with brightness temperatures above 1021 K).
- The radio environment of accreting sources. The sources in this category are neutron stars or black holes -the results of a supernova explosion- which orbit a normal star. These sources are powered by the energy released when matter is transferred from the normal star to the compact star. I am interested in the study of the surrounding of LMXRBs and HMXRBs. These investigations can be made searching for the presence of SNRs, cavities, shocks, or large-scale jets using radio continuum and HI observations.