CTC Seminar for 2023-04-05

Series: CTC Seminar
Date: Wednesday 05-Apr-2023
Time: 11:30-12:30 pm
Location: PSC 1136
Speaker: Vanessa López-Barquero and Greg Marcel (University of Cambridge)
Title: "Chaos, Magnetic Fields, and the Cosmic Ray Anisotropy" and "A unified accretion ejection paradigm for X-ray binaries : the JED-SAD paradigm"

"Chaos, Magnetic Fields, and the Cosmic Ray Anisotropy"

Over the past decades, various experiments, such as IceCube and HAWC, have observed cosmic-ray anisotropy at different angular scales in a wide energy range. However, no comprehensive or satisfactory explanation has been put forth to date. One of the difficulties is that these particles interact with magnetic fields; therefore, their directional information is distorted as they travel. In addition, as cosmic rays (CRs) propagate in the Galaxy, they can be affected by magnetic structures that temporarily trap them and cause their trajectories to display chaotic behavior, therefore modifying the simple diffusion scenario.

Here, we examine the effects of chaos and trapping on the TeV CR anisotropy. Concretely, we apply this method to study the behavior of CRs in the heliosphere since its effects can be remarkably significant for this anisotropy. Specifically, how the distinct heliospheric structures can affect chaos levels. We model the heliosphere as a coherent magnetic structure given by a static magnetic bottle and the presence of temporal magnetic perturbations. This configuration is used to describe the draping of the local interstellar magnetic field lines around the heliosphere and the effects of magnetic field reversals induced by the solar cycles.

In this work, we explore the possibility that particle trajectories may develop chaotic behavior while traversing and being temporarily trapped in this heliospheric-inspired toy model and the potential consequences that it can have on the cosmic ray arrival distribution. It was found that the level of chaos in a trajectory is linked to the time the particles remain trapped in the system. This relation is described by a power law that could prove inherently characteristic of the system. Also, the arrival distribution maps show areas where the different chaotic behaviors are present, which can constitute a source of time-variability in the CR maps and can prove critical in understanding the anisotropy on Earth.


"A unified accretion ejection paradigm for X-ray binaries : the JED-SAD paradigm"

The hysteresis behavior of X-ray binaries during their outbursts remains a mystery. In this work, we developed a paradigm where the disk material accretes in two possible, mutually exclusive, ways (Ferreira et al. 2006). In the usual alpha-disk mode (SAD, Shakura & Sunayev 73), the dominant local torque is due to a radial transport of the disk angular momentum. In the jet-emitting disk mode (JED), magnetically-driven jets carry away mass, energy, and all the angular momentum vertically. Within this framework, the transition from one mode to another is related to the magnetic field distribution, an unknown.

We have shown that typical hard states of X-ray binaries can be reproduced up to unprecedented X-ray luminosities in this paradigm (Marcel+18a). In addition, we used a simple physical model to estimate the radio fluxes (at 8.6-9 GHz) radiated by the jets for any given set of parameter. Strikingly, both spectral features fit extremely well. We have shown that the X-ray spectral behavior of the X-ray binary GX 339-4 can be covered, both in X-ray and radio (Marcel+18b, A&A 617, A46). We then extended this work to 3 more outbursts from GX 339-4 Marcel et al., 2019, A&A 626, A115). This is, to our knowledge, the first time that accretion-ejection cycles are being reproduced, using both accretion (X-rays) and ejection (radio) constraints.

We have since improved the fitting procedure with direct spectral fits on XMM-Newton+NuSTAR data from the AGN HE 1143-1810 (Ursini et al,. 2020, A&A 634, A92), XRT+NICER+NuSTAR+BAT data from the X-ray binary MAXI J1820+070 (Marino et al. 2021, A&A 656, A63), and RXTE data from the X-ray binary GX 339-4 (Barnier et al. 2022, A&A 657, A11). Moreover, we have addressed the production of low frequency quasi-periodic oscillations during the outbursts (Marcel et al. 2020, A&A 640, A18), as well as the radiative efficiency of the accretion flow and the associated radio--X-ray correlation (Marcel et al. 2022, A&A 659, A194). The timing properties have also since been addressed (Malzac et al., to be submitted, Marcel et al, in prep.).

I will introduce the model and present some of its associated results.

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