...
Donggeun Tak - Thermal and non-thermal emission study in GRB160709A
Toggle Cloak Cloak GRB160709A is one of the small sample of short Gamma-ray Bursts detected by both the Gamma-ray Burst Monitor and the Large Area Telescope on-board the Fermi Gamma-ray Space Telescope. We performed a detailed spectral analysis of the Fermi gamma-ray data for this GRB. The spectrum is best described by a combination of thermal and non-thermal spectral components. In time-resolved analysis, a combination of thermal and non-thermal spectral components is observed. A thermal component with a temperature of about 340 keV is dominant in several time-intervals. Two non-thermal components are required. One being a time-varying power-law with exponential cutoff component and the other a hard power-law component with photon index constant in time. This analysis suggests that the emission process producing the hard power law component is independent to other emission processes happening during the prompt phase.
AbstractDivya Palaniswamy - Fast Radio Bursts
Toggle Cloak Cloak AbstractFRBs are a short duration (~ ms), bright (~ Jy), highly dispersed, and probably polarized radio pulses. Twenty-six FRBs have been reported thus far. The physical interpretation for FRBs remains unclear but is thought to involve highly compact objects hosted in galaxies at cosmological distances. The progenitor source of FRBs has not been identified and is a highly debated topic. Except for one, none of other FRBs have been detected to repeat. There are more progenitor’s models than the FRB themselves! I will briefly talking about the current state of the art in FRB world and my work at UNLV.
Tang Qingwen
- Orel Gueta
- Tejaswita Sharma
- Israel Martinez
...
Suttiwat Madlee - Earth’s gamma-ray emission in geographical coordinates with Fermi-LAT data
Toggle Cloak Cloak AbstractThe Earth’s gamma ray emission is produced from the interactions between cosmic rays (CRs), high-energy particles in space, and the Earth’s upper atmosphere. These gamma rays are measured by the Large Area telescope (LAT), the instrument onboard the Fermi Gamma-ray Space Telescope (Fermi) which was launched in 2008 to orbit the Earth at the altitude of ~540 km. Here we present preliminary results of the Earth’s gamma-ray intensity, which for the first time has been analyzed in geographical coordinates, using the latest version of LAT data. This study will provide better understanding of the geomagnetic field, the Earth’s upper atmosphere, and CRs.
Carlo van Rensburg - Spatially-Dependent Modelling of Pulsar Wind Nebula G0.9+0.1
Toggle Cloak Cloak We present results from a leptonic emission code that models the spectral energy density of a pulsar wind nebula by solving a Fokker-Planck-type transport equation and calculating inverse Compton and synchrotron emissivities. We have created this time-dependent, multi-zone model to investigate changes in the particle spectrum as they traverse the pulsar wind nebula, by considering a time and spatially-dependent magnetic field, spatially-dependent bulk particle speed implying convection and adiabatic losses, diffusion, as well as radiative losses. Our code predicts the radiation spectrum at different positions in the nebula, yielding the surface brightness versus radius and the nebular size as function of energy. We compare our new model against more basic models using the observed spectrum of pulsar wind nebula G0.9+0.1, incorporating data from H.E.S.S. as well as radio and X-ray experiments. We show that simultaneously fitting the spectral energy density and the energy-dependent source size leads to more stringent constraints on several model parameters.
Abstract- Tyler Williamson
- Laila Vleeschower
- Sheridan Lloyd
...
Janeth Valverde - B2 1215+30 Long Term Gamma-ray Study with Fermi-LAT & VERITAS
Toggle Cloak Cloak AbstractWe characterize the blazar B2 1215+30 (z=0.131) in the high (HE) and very high (VHE) gamma- ray energy domains. Blazars are a type of active galactic nucleus, very powerful systems with a super massive black hole at their center that outshines the rest of the galaxy, and whose relativistic jets point approximately in the direction of the Earth. These extreme objects are prolific gamma-ray emitters and all their subclasses are particularly variable at all wavelengths. The study of blazar variability at different wavelengths is crucial to test models attempting to identify the nature of the jet particles and the scale of the gamma-rays emission zones. For B2 1215+30, the largest HE flares detected by Fermi-LAT occurred in Oct. 2008 and Feb. 2014, this last one having its brightest counterpart at VHE detected by VERITAS.
We will report on our progress on the temporal and spectral analysis of the BL Lac blazar B2 1215+30, with all the Fermi-LAT and VERITAS available data, from year 2008 to 2016. The detailed Fermi-LAT light curve we have obtained will allow us to run variability tests, which in turn might provide us with some clues about the physical processes underneath.
Marcin Marculewicz - Weak emission-line quasars (WLQ)
Toggle Cloak Cloak Abstract Weak emission-line quasars (WLQ) are objects with enormous weak emission-lines (e.g. EW (Ly a) ≤ 10Å ; Diamond-Stanic et al. 2009). The properties of WLQs are different from those of BL Lac objects but consistent with normal AGNs (Plotkin et al. 2010). There are several explanations of weakness ofemission- lines. The first possibility is existence of a cold accretion disk (Laor & Davis 2011) or a radiatively inefficient accretion flow (Yuan & Narayan 2004). The next explanation is a presence of shielding gas, which could be a part of a slim disk. This part prevents ionizing photons from reaching the broad emission-line region(BELR). The following description provides Shemmer et al. (2010) who propose the BELR is built anemic. Hryniewicz et al. (2009) proposed the next explanation that perhaps in all weak emission line quasars the activity has just started. Any explanation of WLQ phenomena is still not given.
Fabio Carfado
- Monica Breed
- Hannes Thiersen
- Isabella Mereu
...