Conveners
Day 4 / Session 2: Poster B
- There are no conveners in this block
Day 4 / Session 2: Talk
- Amir Caspi (Southwest Research Institute)
What powers the hard, non-thermal X-rays from the coronae of accreting black holes—against the strong inverse Compton cooling losses due to the scattering by soft accretion disk photons—is an unsolved mystery in astrophysics. We perform 2D particle-in cell simulations of reconnection in magnetically dominated (σ>>1) electron-positron and electron-ion plasmas subject to strong Compton cooling....
The standard Big Bang Nucleosythesis (BBN) model predicted the abundances of light elements that led to one of the main observational supports of the Big Bang theory. However, current observational data no longer confirm the standard BBN (SBBN) confidently. Measurements of Li abundances in metal-poor stars clearly contradict the SBBN value by more than a factor of 3-4 [1,2]. In addition, a...
Sun shows short and long term periodicity in various kinds of solar phenomena. 11 year cycle is very common in many solar activity parameters, 22 year cycle in magnetic polarity reversal and also slowly varying component of solar radio emission shows periodicity of 27 days. Studies of periodicities in these parameters provide information about physical state of the sun i.e. it quit or in...
Recent multi-wavelength observations (e.g., by EOVSA, RHESSI, and STIX) show that nonthermal emissions could fill up a significant portion of the solar flare reconnection region. The electrons responsible for these emissions contain a substantial fraction of the released magnetic energy and often develop power-law energy tails. In this study, we model the large-scale electron acceleration by...
The study of stellar flares has been greatly advanced by MAXI (Monitor of All-sky X-ray Image), which started its operation in 2009. MAXI observes a large area of the sky once per 92-minute orbital cycle and makes it possible to search for stellar flares effectively. All these flares are found to be at the upper ends for stellar flares with the total energy of $10^{34-39}$ erg (e.g, Tsuboi et...
The observed soft X-ray flux during solar flares is produced by electron bremsstrahlung, when accelerated electrons that move from magnetic loop top to the footpoints slow down by dense layers of the sun. In order to explain the observed soft X-ray flux during solar flares, if electron acceleration happens at loop top, nearly 100% electrons need to be accelerated. No acceleration mechanism is...
We present diagnostic tools for particle energy and pitch angle distributions at acceleration in 3D Harris-type reconnecting current sheets with a single or multiple X-nullpoints taking into account the ambient plasma feedback to the presence of accelerated particles. We explore accel- eration of particles during their passage through 3D reconnecting current sheets occurring in the...
Relativistic jets from Active Galactic Nuclei (AGN) are likely magnetically-dominated, i.e. the magnetic energy per particle exceeds the rest mass. Since there is a huge separation of scales between the transverse size of the jet and the Larmor radius of the particles that emit the observed radiation, the dissipation of the magnetic energy is mediated by a turbulent cascade.The advent of...
Solar flares result from impulsive energy release due to magnetic reconnection in the solar atmosphere. Observational evidence suggests that the flaring plasma consists of a thermal distribution of particles heated to higher temperatures during the process and a non-thermal distribution of particles. As this hot plasma emits copiously in the X-ray wavelengths, X-ray spectral measurements...
Solar flare plasma temperatures are fundamental to our understanding of flare dynamics and energy transport. GOES-XRS broadband flux ratios are often used to estimate flare temperature. Though an approximation, a single temperature isothermal plasma is still a reasonable approximation for many applications. We compare the flare temperatures (single or two temperatures) derived using spectra...
Lower Hybrid Oscillation (LHO) is a coupled oscillation between ions and electrons under cyclotron motion by coulomb force. The condition for LHO is the presence of a local electric field in a weakly magnetised plasma. A theoretical study shows that, in a collision less magnetised gravitational plasma, this condition is satisfied where the Lower Hybrid (LH) coupling is made possible by an...
Charged particles energized by coronal flares or travelling shocks at young active stars may significantly impact the habitability of exoplanets. We used test-particle simulations to investigate the diffusive transport of ∼GeV protons throughout turbulent active astrospheres, from stellar corona to planet atmosphere. The 3D turbulent and magnetised stellar wind of a TRAPPIST-1-like system has...
In the past decade, the capability to focus hard X-rays from the Sun has become a reality. Though no solar-dedicated space observatory yet exists, glimpses of the Sun at hard and soft X-ray energies from the FOXSI sounding rocket and the NuSTAR spacecraft have opened windows to show us what can be explored. Most notably, these missions have investigated solar flares down to far smaller scales...
