Exploring diffuse radio emission in galaxy clusters and groups with the uGMRT and the SKA

Diffuse radio emission has been detected in a considerable number of galaxy clusters and groups, revealing the presence of pervasive cosmic magnetic fields, and of relativistic particles in the large-scale structure (LSS) of the Universe. Since cluster radio emission is faint and steep spectrum, its observations are largely limited by the instrument sensitivity and frequency of observation, leading to a dearth of information, more so for lower-mass systems. The unprecedented sensitivity of recently commissioned low-frequency radio telescope arrays, aided by the development of advanced calibration and imaging techniques, have helped in achieving unparalleled image quality. At the same time, the development of sophisticated numerical simulations and the availability of supercomputing facilities have paved the way for high-resolution numerical modeling of radio emission, and the structure of the cosmic magnetic fields in LSS, leading to predictions matching the capabilities of observational facilities. In view of these rapidly-evolving scenerio in modeling and observations, in this review, we summarise the role of the new telescope arrays and the development of advanced imaging techniques and discuss the detections of various kinds of cluster radio sources. In particular, we discuss observations of the cosmic web in the form of supercluster filaments, studies of emission in poor clusters and groups of galaxies, and of ultra-steep spectrum sources. We also review the current theoretical understanding of various diffuse cluster radio sources and the associated magnetic field and polarization. As the statistics of detections improve along with our theoretical understanding, we update the source classification schemes based on their intrinsic properties. We conclude by summarising the role of the upgraded GMRT and our expectations from the upcoming Square Kilometre Array (SKA) observatories.Comment: 32 pages, 10 figures, accepted for publication in the Journal of Astrophysics and Astronomy (JoAA) (to appear in the special issue on "Indian participation in the SKA"

Stability of Non-asymptotically flat thin-shell wormholes in generalized dilaton-axion gravity

We construct a new type of thin-shell wormhole for non-asymptotically flat charged black holes in generalized dilaton-axion gravity inspired by low-energy string theory using cut-and-paste technique. We have shown that this thin shell wormhole is stable. The most striking feature of our model is that the total amount of exotic matter needed to support the wormhole can be reduced as desired with the suitable choice of the value of a parameter. Various other aspects of thin-shell wormhole are also analyzed.Comment: 15 pages and 11 figures. Minor revisions have been done. Accepted in Int.J.Theor.Phy

Two new eriophyoid mites (Acari: Eriophyoidea) from West Bengal, India

Sur, Surajit, Roy, Sourav, Chakrabarti, Samiran (2018): Two new eriophyoid mites (Acari: Eriophyoidea) from West Bengal, India. Zootaxa 4434 (1): 193-200, DOI: https://doi.org/10.11646/zootaxa.4434.1.1

New genera, a new species, and a key to the genera of Ashieldophyinae (Acari, Eriophyoidea) from India

Two new genera, Brevishieldophyes Chakrabarti & Pandit, gen. n. and Mesoshieldophyes Chakrabarti & Pandit, gen. n., and a new species Mesoshieldophyes varecae Chakrabarti & Pandit, sp. n. are described. These mites are leaf vagrants. The morphological characters of the afore-mentioned genera and those of Ashieldophyes Mohanasundaram are compared. A key for separating the genera within the subfamily Ashieldophyinae is provided. The diagnostic characters of the subfamily Ashieldophyinae are also revised

New genera, a new species, and a key to the genera of Ashieldophyinae (Acari, Eriophyoidea) from India

Two new genera, Brevishieldophyes Chakrabarti & Pandit, gen. n. and Mesoshieldophyes Chakrabarti & Pandit, gen. n., and a new species Mesoshieldophyes varecae Chakrabarti & Pandit, sp. n. are described. These mites are leaf vagrants. The morphological characters of the afore-mentioned genera and those of Ashieldophyes Mohanasundaram are compared. A key for separating the genera within the subfamily Ashieldophyinae is provided. The diagnostic characters of the subfamily Ashieldophyinae are also revised