| Authors : | S. Saha (1) , S.K. Gupta (2), B. Hariharan (2), Y. Hayashi (3), P. Jagadeesan (3), A. Jain (2), P. Jain (1), S. Kawakami (3), H. Kojima (4), P.K. Mohanty (2), P.K. Nayak (2), T. Nonaka (5), A. Oshima (4), M. Rameez (2), K. Ramesh (2), S. Shibata (4),F. Varsi (1), and M. Zuberi (2)
1. Indian Institute of Technology Kanpur, Kanpur 208016, India.
2. Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India
3. Graduate School of Science, Osaka City University, Osaka 558-8585, Japan
4. College of Engineering, Chubu University, Kasugai, Aichi 487-8501, Japan
5. Institute for Cosmic Ray Research, Tokyo University, Kashiwa, Chiba 277-8582, Japan |
| Abstract : | Interferometers (synthesis arrays) and phased arrays (aperture arrays) are presently the major topics of active research and exploration in the development of modern radio telescopes. While interferometery improves angular resolution of the telescope, phased array beamforming enhances the signal-to-noise ratio (SNR) at the detection level. Therefore, these two principles are complementary to each other, hence can be deployed in a hierarchical array configuration to augment the sensitivity of radio (signal) detection. However, in comparison to the sources in radio astronomy, in cosmic ray radio detection, the source(s) of radio impulse(s) is extended, relativistically moving and generally resides in the radiative near-field region (Fresnel region) of the detection site. So, the point source and plane wave approximations do not hold anymore. Consequently, signal strength drops off rapidly away from the core. Therefore, a faint CR induced signal differs substantially from a faint astronomical signal, hence detection of the former is more challenging and yet to be achieved. So, available highly sensitive radio telescopes or interferometers such as LOFAR, LOFAR Super Station, MWA, SKA etc. are not suitable stand-alone instruments for detection of CR induced radio signals at the desired sensitivity, in a typical non-radio-quiet environment. Hence, most of these instruments serve primarily for radio astronomical purposes and cosmic ray detection as secondary objective, only at a higher detection threshold. A hierarchical phased array system, with “Radio Interferometric Technique” analysis-framework has promising potential to bring down the the lower detection threshold to few tens of PeV, of course, with the unprecedented core resolution of existing GRAPES-3 scintillator detector array. Technologically, such a demonstration could potentially be first of its own kind. |
