Wednesday Colloquium


"Modeling the X-ray Emissions from Accreting Black Holes"

Javier Garcia (CalTech, Pasadena)

In the region close to compact object such as black holes or neutron stars, the extreme conditions created by the strong gravitational field produces copious amounts of energetic radiation (ultra-violet, X-rays, and Gamma-rays). The interaction of this radiation with the surrounding material results in observables that carry important physical information. X-ray spectral and timing techniques provide direct access to the accretion physics on these systems, such as the black hole spin, the location of the inner-edge of the accretion disk, its ionization stage and composition, among others. In this talk, I will discuss the current state of modern relativistic reflection models computed specifically for modeling the X-ray spectrum from supermassive black holes in AGN and black hole binary systems. I will show examples of the implementation of our new models to observational data from several X-ray observatories (e.g., RXTE, Swift, XMM-Newton, Suzaku, and NuSTAR), and discuss current outstanding issues, such as the large iron abundances frequently required to fit the reflection spectra, controversies on the disk truncation, the origin of the soft excess in AGN, and the effects of high density in the observed spectra.


"Net-baryon fluctuations in Magnetized QCD matter"

Marcio Ferreira (University of Coimbra)

The kurtosis and skewness of net baryon-number fluctuations are studied for the magnetized phase diagram of three-flavor quark matter within the Polyakov extended Nambu–Jona-Lasinio model. The effect of magnetic catalysis and inverse magnetic catalysis is considered using two distinct scalar interactions. Special attention is given to the fluctuations dependence near the critical end points (CEPs). Regions with large fluctuations but no CEP in non-magnetized matter develop a CEP under the action of a strong magnetic field.


"Interstellar nanoparticles and millimeter measurement of high redshifts"

Alain Omont (IAP, Paris)

1. Interstellar carbon nanoparticles. Carbonaceous nanoparticles are one of the main reservoirs of interstellar carbon together with dust grains and gaseous C+, C and CO. I shall briefly review their different known and possible forms and the likelihood that they could bring a solution to various problems of the interstellar medium, especially the nature of the carriers of the diffuse interstellar bands (DIBs). I shall consider in turn polycyclic aromatic hydrocarbons (PAHs), fullerenes, carbon chains, nanodiamonds and nanotubes. In particular, I shall briefly present our recent work about the interest of polyacene PAHs (linear chains of N fused hexagons) as possible DIB carriers. 2. Measurement of high redshifts of submillimeter galaxies from CO lines. Redshift determination is the main difficulty for exploiting the few 105 high-redshift submillimeter galaxies (SMGs) discovered, e.g., by the Herschel Space Observatory, at z~2-4. CO line blind search is the most efficient way for such redshift determination. The broad band (twice that of ALMA) of the new receptor system of the IRAM NOEMA interferometer is very efficient for that, as we have just proved in a pilot project. It is now extended in a NOEMA large program for determining 120 redshifts of strongly lensed or hyper-luminous (LFIR > 1013 Lsun) Herschel SMGs, which should bring new light on these exceptional objects.


"The repercussions of pulsar glitches"

Cristobal Manuel Espinoza Romo (Pontificia Universidad Católica de Chile)

Glitches are discrete positive steps in spin frequency that occasionally interrupt the smooth rotation of pulsars. Our current understanding points to an internal origin, in which a neutron superfluid component that rotates at a higher rate than the rest of the star sometimes shares its angular momentum, thereby causing the observed glitches. Observations show a broad range of glitch sizes, covering more than 7 decades, and exhibiting a clear bimodal distribution. The largest events distribute narrowly in size, show different occurrence rates to the small glitches and more regular times between glitches. Furthermore, large glitches are followed by significant negative changes in spin-down rate. Enhanced spin-down rate regimes, known as glitch recoveries, are seen to last for months and slowly evolve towards pre-glitch values over years, or even decades. We have characterised the long-term (>20 yr) evolution of a number of pulsars with three or more large glitches and found that all of them evolve with particularly low frequency second derivatives. I will show that such findings suggest that large glitches and their transient recoveries are perturbations that alter the rotational behaviour of pulsars over long periods of time. Moreover, their cumulative effect can be substantial and should be considered when assessing the spin evolution of the young population and their ages.