Grupo de Astrofísica de Rayos X

Instituto Argentino de Radioastronomía (IAR-CONICET-CICPBA-UNLP)


X-ray binaries

high-mass and low-mass X-ray binaries; catalogs; accretion/ejection; variability; spectral-timing; quasi-periodic oscillations; highly-absorbed systems; microquasars

Supernova remnants

thermal emission; chemical abundances; shocks; particle-acceleration; synchrotron emission; radio continuum and gamma-ray emission.

Binary Evolution

formation and evolution of high-mass X-ray binaries; connection to sgHMXBs and SFXTs; neutron-star kicks; binary compact-objects progenitors; gravitational wave coalesces.



Simultaneous NICER and NuSTAR observations of the Ultraluminous source NGC 4190 ULX-1

Combi, Jorge A.; Fogantini, Federico A.; Saavedra, Enzo A.; Romero, Gustavo E.; Abaroa, Leandro a.; García, Federico; Luque Escamilla, Pedro L.; Martí, Josep; Cruz-Sanchez, Nelson (A&A, accepted for publication, March 2024)

We investigated NGC 4190 ULX-1, an ultraluminous X-ray source, using XMM-Newton, NICER, and NuSTAR. Through temporal and spectral analyses, we identified no pulsations. The ULX spectrum, resembling typical ULX emission, suggests a super-Eddington black hole, possibly obscured by a dense wind, with emission mechanisms explained by geometric beaming and Comptonization.

NuSTAR and XMM-Newton observations of the binary 4FGL J1405.1-6119. A Gamma-ray emitting microquasar?

Saavedra, Enzo A. ; Fogantini, Federico A. ; Escobar, Gastón J. ; Romero, Gustavo E. ; Combi, Jorge A.; Marcel, Estefania (A&A 680, A88, December 2023)

We studied the binary 4FGL J1405.1-6119, a high-mass gamma-ray emitter, with NuSTAR and XMM-Newton. We use a parabolic and slightly relativistic lepto-hadronic jet scenario to explain the spectral energy distribution, suggesting that 4FGL J1405.1-6119 could be a supercritical microquasar similar to SS433.

Relativistic X-ray reflection and photoionized absorption in the neutron star low-mass X-ray binary GX 13+1

Saavedra, Enzo A.; García, Federico; Fogantini, Federico A.; Méndez, Mariano ; Combi, Jorge A.; Luque-Escamilla, Pedro L. ; Martí, Josep (MNRAS 522, 3367, July 2023)

We studied the neutron-star binary GX 13+1 with NuSTAR, finding its transition from normal to flaring states. Spectral analysis revealed evidence of relativistic reflection, constraining inner disc radius and magnetic field strength. A hot wind with photo-ionised absorption of Fe and Ni was detected. The study suggests high electron densities in the accretion disk, challenging previous models and impacting our understanding of GX 13+1's physical conditions.

A NuSTAR view of SS433. Precessional evolution of the jet-disk system

Fogantini, Federico A.; García, Federico; Combi, Jorge A.; Chaty, Sylvain; Martí, Josep; Luque Escamilla, Pedro L. (A&A 669, A149, January 2023)

We studied the famous microquasar SS433 using 10 NuSTAR observations that span almost 2 precessional cycles of the system. Using a combination of a thermal leptonic jet and relativistic reflection from an accretion disk, we found that the precessional motion of the system successfully explains the modulation seen in several spectral parameters.

We introduce a dynamic Comptonization model, explaining low-frequency quasi-periodic oscillations in black hole LMXBs. Modeling the accretion disc as a multi-temperature blackbody, we compare it with a spherical blackbody model. Applying our model to BH LMXBs (e.g., MAXI J1438-630, GRS 1915 + 105) shows better fits and compatibility, affirming its ability to reproduce QPO characteristics.

The model is openly available on GitHub.

The evolving properties of the corona of GRS 1915+105: a spectral-timing perspective through variable-Comptonization modelling

García, Federico; Karpouzas, Konstantinos; Méndez, Mariano, Zhang, Liang; Zhang, Yuexin; Belloni, Tomaso; Altamirano, Diego (MNRAS 513, 4196, July 2022)

We explore the role of inverse Compton processes in shaping X-ray spectra in black hole low-mass X-ray binaries, focusing on GRS 1915+105. Our spectral-timing Comptonization model, applied to 398 observations, reveals consistent trends in corona properties over 15 years. Connecting with 15 GHz radio monitoring, we propose disc-corona interactions influencing the radio jet launch.