Low-frequency radio study of MACS clusters at 610 and 235 MHz using the GMRT

Studies have shown that mergers of massive galaxy clusters produce shocks and turbulence in the intra-cluster medium, the possible event that creates radio relics, as well as the radio halos. Here we present GMRT dual-band (235 and 610~MHz) radio observations of four such clusters from the MAssive Cluster Survey (MACS) catalogue. We report the discovery of a very faint, diffuse, elongated radio source with a projected size of about 0.5~Mpc in cluster MACSJ0152.5-2852. We also confirm the presence of a radio relic-like source (about 0.4~Mpc, previously reported at 325~MHz) in MACSJ0025.4-1222 cluster. Proposed relics in both these clusters are found apparently inside the virial radius instead of their usual peripheral location, while no radio halos are detected. These high-redshift clusters (z=0.584 and 0.413) are among the earliest merging systems detected with cluster radio emissions. In MACSJ1931-2635 cluster, we found a radio mini-halo and an interesting highly bent pair of radio jets. Further, we present here a maiden study of low frequency (GMRT 235&610~MHz) spectral and morphological signatures of a previously known radio cluster MACSJ0014.3-3022 (Abell~2744). This cluster hosts a relatively flat spectrum (α610235∼−1.15), giant (∼1.6~Mpc each) halo-relic structure and a close-by high-speed (1769±148359~km~s−1) merger-shock (M=2.02±0.170.41) originated from a possible second merger in the cluster

Effects of CME and CIR induced geomagnetic storms on low-latitude ionization over Indian longitudes in terms of neutral dynamics

This paper presents the response of the ionosphere during the intense geomagnetic storms of October 12-20, 2016 and May 26-31, 2017 which occurred during the declining phase of the solar cycle 24. Total Electron Content (TEC) from GPS measured at Indore, Calcutta and Siliguri having geomagnetic dips varying from 32.23{\deg}N, 32{\deg}N and 39.49{\deg}N respectively and at the International GNSS Service (IGS) stations at Lucknow (beyond anomaly crest), Hyderabad (between geomagnetic equator and northern crest of EIA) and Bangalore (near magnetic equator) in the Indian longitude zone have been used for the storms. Prominent peaks in diurnal maximum in excess of 20-45 TECU over the quiet time values were observed during the October 2016 storm at Lucknow, Indore, Hyderabad, Bangalore and 10-20 TECU for the May 2017 storm at Siliguri, Indore, Calcutta and Hyderabad. The GUVI images onboard TIMED spacecraft that measures the thermospheric O/N2 ratio, showed high values (O/N2 ratio of about 0.7) on October 16 when positive storm effects were observed compared to the other days during the storm period. The observed features have been explained in terms of the O/N2 ratio increase in the equatorial thermosphere, CIR-induced High Speed Solar Wind (HSSW) event for the October 2016 storm. The TEC enhancement has also been explained in terms of the Auroral Electrojet (AE), neutral wind values obtained from the Horizontal Wind Model (HWM14) and equatorial electrojet strength from magnetometer data for both October 2016 and May 2017 storms. These results are one of the first to be reported from the Indian longitude sector on influence of CME- and CIR-driven geomagnetic storms on TEC during the declining phase of solar cycle 24.Comment: 41 pages, 14 figures. Accepted for publication in Advances in Space Researc

Plans for building a prototype SKA regional centre in India

In order to deliver the full science potential of the Square Kilometer Array (SKA) telescope, several SKA Regional Centres (SRCs) will be required to be constructed in different SKA member countries around the world. These SRCs will provide high performance compute and storage for the generation of advanced science data products from the basic data streams generated by the SKA Science Data Handling and Processing system, critically necessary to the success of the key science projects to be carried out by the SKA user community. They will also provide support to astronomers to enable them to carry out analysis on very large SKA datasets. Construction of such large data centres is a technical challenge for all SKA member nations. In such a situation, each country plans to construct a smaller SRC over the next few years (2022 onwards), known as a proto-SRC. In India, we propose to construct a proto-SRC which will be used for the analysis of data from SKA pathfinders and precursors with strong Indian involvement such as uGMRT, Meerkat and MWA. We describe our thinking on some aspects of the the storage, compute and network of the proto-SRC and how it will be used for data analysis as well as for carrying out various simulations related to SKA key science projects led by Indian astronomers. We also present our thoughts on how the proto-SRC plans to evaluate emerging hardware and software technologies and to also begin software development in areas of relevance to SKA data processing and analysis such as algorithm implementation, pipeline development and data visualisation software.Comment: 7 pages, 2 figures, accepted for publication for the special issue on "Indian participation in the SKA" in the Journal of Astrophysics and Astronomy (JoAA

Comparative studies of Ionospheric models with GNSS and NavIC over the Indian Longitudinal sector during geomagnetic activities

This paper presents the storm time comparative analysis of the performances of latest versions of global ionospheric models: International Reference Ionosphere (IRI) 2016, NeQuick 2 (NeQ) and the IRI extended to Plasmasphere (IRI-P) 2017 with respect to Navigation with Indian Constellation (NavIC) and Global Navigation Satellite System (GNSS) derived ionospheric Total Electron Content (TEC). The analysis is carried out under varying geomagnetic storm conditions during September 2017-November 2018, falling in the declining phase of solar cycle 24. TEC data from Indore, located near the northern crest of the Equatorial Ionization Anomaly (EIA) along with data obtained from the International GNSS Service (IGS) stations at Lucknow, located beyond the anomaly crest; Hyderabad, located between anomaly crest and magnetic equator and Bangalore, located near the magnetic equator have been analysed. The models generally overestimated during the storm periods with the exception of IRI-P, which matched (with an offset of about 3-5 TECU) with the enhancement observed on September 7, 2017 (during the strong storm of September 2017), from stations around the anomaly crest. No significant match was observed by the other two models. This match of IRI-P is attributed to the plasmaspheric contribution as well as the capability of assimilating measured TEC values into this model. In the present study, to the best of our knowledge, first comparisons of the empirical model derived TEC with NavIC and GNSS measurements from an anomaly crest location, combined with the IGS observations from the magnetic equator to locations beyond the anomaly crest, are conducted during geomagnetically disturbed conditions. Since NavIC satellites are at higher altitudes(~ 36000 km), the inclusion of NavIC data to the existing model could give better ionospheric predictions over the Indian subcontinent.Comment: 42 pages, 13 figures. Accepted for publication in Advances in Space Researc

Performance of NavIC for studying the ionosphere at an EIA region in India

This paper emphasizes on NavIC's performance in ionospheric studies over the Indian subcontinent region. The study is performed using data of one year (2017-18) at IIT Indore, a location near the northern crest of Equatorial Ionization Anomaly (EIA). It has been observed that even without the individual error corrections, the results are within $\pm20\%$ of NavIC VTEC estimates observed over the 1\ensuremath{^{\circ}} x 1\ensuremath{^{\circ}} grid of IPP surrounding the GPS VTEC estimates for most of the time. Additionally, ionospheric response during two distinct geomagnetic storms (September 08 and 28, 2017) at the same location and other IGS stations covering the Indian subcontinent using both GPS and NavIC has also been presented. This analysis revealed similar variations in TEC during the geomagnetic storms of September 2017, indicating the suitability of NavIC to study space weather events along with the ionospheric studies over the Indian subcontinent.Comment: 38 Pages, 16 Figures, Accepted for publication in Advances in Space Researc

Bone metastasis in head and neck squamous cell carcinoma – 5-year experience of an Indian Cancer Institute

Introduction. Bone metastasis (BM), a common and awful complication of advanced malignancy, is comparatively infrequent in head and neck squamous cell carcinoma (HNSCC). Having a discouraging survival of around 6-months only, BM decreases the quality of life in such patients. We reported 13 cases of BM in HNSCC patients in respect to clinical patterns, treatment modalities and outcome. Material and methods. This is a retrospective study conducted in a tertiary cancer institute of India. Records of all HNSCC patients reviewed and patients having BM were identified. Results. Total 13 cases of BM were found over a 5-year period; 5 patients having synchronous BM and the rest had developed metastasis later. Monostotic and polyostotic diseases were found in 8 and 5 patients, respectively, bone exclusive disease was seen in 6 patients only. Overall median survival was 6.7 months. Conclusions. Palliation seems to be the only option once BM is diagnosed in HNSCC. All of our patients received local palliative radiation, and systemic chemotherapy to increase survival. As there is no standardized treatment for such occurrence, more case series and prospective studies are welcomed

Bone metastasis in head and neck squamous cell carcinoma – 5-year experience of an Indian Cancer Institute

Introduction. Bone metastasis (BM), a common and awful complication of advanced malignancy, is comparatively infrequent in head and neck squamous cell carcinoma (HNSCC). Having a discouraging survival of around 6-months only, BM decreases the quality of life in such patients. We reported 13 cases of BM in HNSCC patients in respect to clinical patterns, treatment modalities and outcome. Material and methods. This is a retrospective study conducted in a tertiary cancer institute of India. Records of all HNSCC patients reviewed and patients having BM were identified. Results. Total 13 cases of BM were found over a 5-year period; 5 patients having synchronous BM and the rest had developed metastasis later. Monostotic and polyostotic diseases were found in 8 and 5 patients, respectively, bone exclusive disease was seen in 6 patients only. Overall median survival was 6.7 months. Conclusions. Palliation seems to be the only option once BM is diagnosed in HNSCC. All of our patients received local palliative radiation, and systemic chemotherapy to increase survival. As there is no standardized treatment for such occurrence, more case series and prospective studies are welcomed

Diffuse radio emission in the galaxy cluster SPT-CL J2031-4037: a steep spectrum intermediate radio halo?

The advent of sensitive low frequency radio observations has revealed a number of diffuse radio objects with peculiar properties that are challenging our understanding about the physics of the intracluster medium. Here, we report the discovery of a steep spectrum radio halo surrounding the central Brightest Cluster Galaxy (BCG) in the galaxy cluster SPT-CL J2031-4037. This cluster is morphologically disturbed yet has a weak cool core, an example of cool core/non-cool core transition system, which harbours a radio halo of $\sim 0.7$ Mpc in size. The halo emission detected at 1.7 GHz is less extended compared to that in the 325 MHz observation, and the spectral index of the part of the halo visible at 325 MHz to 1.7 GHz frequencies was found to be $-1.35 \pm 0.07$. Also, $P_{1.4\ \mathrm{GHz}}$ was found to be $0.77 \times 10^{24}$ W Hz$^{-1}$ which falls in the region where radio mini-halos, halo upper limits and ultra-steep spectrum (USS) halos are found in the $P_{1.4\ \mathrm{GHz}} - L_\mathrm{X}$ plane. Additionally, simulations presented in the paper provide support to the scenario of the steep spectrum. The diffuse radio emission found in this cluster may be a steep spectrum "intermediate" or "hybrid" radio halo which is transitioning into a mini-halo.Comment: 6 pages, 3 figures; Accepted for publication in MNRAS Lette