Indian Institute of Astrophysics
http://prints.iiap.res.in:80
The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.2018-10-11T00:01:30ZLeptonic and hadronic modeling of Fermi-LAT hard spectrum quasars and predictions for high-energy polarization
http://hdl.handle.net/2248/7354
Title: Leptonic and hadronic modeling of Fermi-LAT hard spectrum quasars and predictions for high-energy polarization
Authors: Paliya, Vaidehi S; Zhang, H; Bottcher, M; Ajello, M; Domínguez, A; Joshi, M; Hartmann, D; Stalin, C. S
Abstract: We present the results of a study of the time-averaged spectral energy distributions (SEDs) of eight flat spectrum radio quasars (FSRQs) present in the second catalog of high energy sources detected beyond 50 GeV by the Fermi Large Area Telescope (2FHL). Both leptonic and hadronic scenarios are adopted to explain the multiwavelength SEDs and we find them to be marginally consistent with the 2FHL spectra above 50 GeV. We derive the expected degree of X-ray and γ-ray polarizations both for the average and elevated activity states and note that (i) a hadronic radiative model consistently predicts a higher degree of high energy polarization compared to leptonic ones and (ii) the X-ray polarization degree is higher than the γ-ray polarization in the leptonic scenario, but similar to the γ-ray polarization if the observed radiation is powered by hadronic processes. From the leptonic modeling, the location of the γ-ray emitting region is found to be at the outer edge of the broad line region (BLR) and is consistent with the γγ opacity estimates for the γ-ray absorption by the BLR. We conclude that a majority of the FSRQs could be detected by the upcoming Cherenkov Telescope Array, though future high energy polarimeters will be able to detect them only during elevated activity states, which could provide supportive evidence for the hadronic origin of the X-ray and γ-ray emission.
Description: Restricted Access2018-08-10T00:00:00ZHelioseismic inversion to infer the depth profile of solar meridional flow using spherical born kernels
http://hdl.handle.net/2248/7353
Title: Helioseismic inversion to infer the depth profile of solar meridional flow using spherical born kernels
Authors: Mandal, K; Hanasoge, S. M; Rajaguru, S. P; Antia, H. M
Abstract: Accurate inferences of solar meridional flow are crucial for understanding solar dynamo processes. Wave travel times, as measured on the surface, will change if the waves encounter perturbations, e.g., in the sound speed or flows, as they propagate through the solar interior. Using functions called sensitivity kernels, we can image the underlying anomalies that cause measured shifts in travel times. The inference of large-scale structures, e.g., meridional circulation, requires computing sensitivity kernels in spherical geometry. Mandal et al. have computed such spherical kernels in the limit of the first-Born approximation. In this work, we perform an inversion for meridional circulation using travel-time measurements obtained from 6 years of Solar Dynamics Observatory/Helioseismic and Magnetic Imager data and those sensitivity kernels. We enforce mass conservation by inverting for a stream function. The number of free parameters is reduced by projecting the solution onto cubic B-splines in radius and derivatives of the Legendre-polynomial basis in latitude, thereby improving the condition number of the inverse problem. We validate our approach for synthetic observations before performing the actual inversion. The inversion suggests a single-cell profile with a return flow occurring at depths below 0.78 R ⊙.
Description: Restricted Access2018-08-10T00:00:00ZThe inner coronagraph on board ADITYA-L1 and automatic detection of CMEs
http://hdl.handle.net/2248/7352
Title: The inner coronagraph on board ADITYA-L1 and automatic detection of CMEs
Authors: Banerjee, D; Ritesh Patel; Pant, V; ADITYA Team
Abstract: Visible Emission Line Coronagraph (VELC) on board ADITYA-L1 is an internally occulted coronagraph with mirror as its primary objective element. It has a field of view (FOV) starting from 1.05 R⊙ – 3 R⊙. It will observe the corona in continuum centered at 5000 Å and will perform spectroscopic observations of inner corona in two visible (5303 Å and 7892 Å) and one infrared (10747 Å) wavelengths. VELC will be capable of observing the corona with high spatial and temporal resolutions. We present an overview of the inner coronagraph (VELC) design and introduce the concept of an on-board automated coronal mass ejections (CMEs) detection logic proposed for this payload
Description: Restricted Access2018-08-01T00:00:00ZMinkowski tensors in three dimensions: probing the anisotropy generated by redshift space distortion
http://hdl.handle.net/2248/7351
Title: Minkowski tensors in three dimensions: probing the anisotropy generated by redshift space distortion
Authors: Appleby, S; Pravabati, C; Park, C; Yogendran, K. P; Joby, P. K
Abstract: We apply the Minkowski tensor statistics to three-dimensional Gaussian random fields. Minkowski tensors contain information regarding the orientation and shape of excursion sets that is not present in the scalar Minkowski functionals. They can be used to quantify globally preferred directions and also provide information on the mean shape of the subsets of a field. This makes them ideal statistics to measure the anisotropic signal generated by redshift space distortion in the low-redshift matter density field. We review the definition of the Minkowski tensor statistics in three dimensions, focusing on two coordinate invariant quantities, ${W}_{1}^{0,2}$ and ${W}_{2}^{0,2}$. We calculate the ensemble average of these 3 × 3 matrices for an isotropic Gaussian random field, finding that they are proportional to products of the identity matrix and a corresponding scalar Minkowski functional. We show how to numerically reconstruct ${W}_{1}^{0,2}$ and ${W}_{2}^{0,2}$ from discretely sampled fields and apply our algorithm to isotropic Gaussian fields generated from a linear ΛCDM matter power spectrum. We then introduce anisotropy by applying a linear redshift space distortion operator to the matter density field and find that both ${W}_{1}^{0,2}$ and ${W}_{2}^{0,2}$ exhibit a distinct signal characterized by inequality between their diagonal components. We discuss the physical origin of this signal and how it can be used to constrain the redshift space distortion parameter Upsilon ≡ f/b.
Description: Restricted Access2018-08-20T00:00:00Z