Journal articles: 'GMRT Observations'

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Lal, Dharam Vir, and A. Pramesh Rao. "3C 129: The GMRT observations." Astronomy & Astrophysics 420, no. 2 (2004): 491–99. http://dx.doi.org/10.1051/0004-6361:20035777.

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Rao, A. Pramesh. "GMRT — Current Status." Symposium - International Astronomical Union 199 (2002): 439–46. http://dx.doi.org/10.1017/s0074180900169542.

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The Giant Metrewave Radio Telescope (GMRT) is a major new facility available for observations at metre wavelengths. This paper describes the the GMRT with emphasis on the features that are of relevance to a potential user. The current state of the GMRT is also described.

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Ishwara-Chandra, C. H., and A. Pramesh Rao. "GMRT Observations of Microquasar V4641 Sgr." Chinese Journal of Astronomy and Astrophysics 5, S1 (2005): 269–72. http://dx.doi.org/10.1088/1009-9271/5/s1/269.

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Omar, A., J. N. Chengalur, and D. A. Roshi. "Multifrequency GMRT observations of HII regions." Symposium - International Astronomical Union 199 (2002): 313–14. http://dx.doi.org/10.1017/s0074180900169207.

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The electron temperatures of the compact cores of the galactic HII regions S206 and S209 have been determined by radio continuum observations near 235, 327 and 610 MHz using the Giant Meterwave Radio Telescope (GMRT). The resolution of our maps are 11″ and 6″ at 327 and 610 MHz respectively. These are the highest resolution low frequency maps of these HII regions.

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Chengalur, J. N. "HI with the GMRT." Symposium - International Astronomical Union 199 (2002): 96–101. http://dx.doi.org/10.1017/s0074180900168615.

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The Giant Metrewave Radio Telescope (GMRT) has recently come into operation. This paper reports on observations of the HI line made using the GMRT during its commissioning phase. These include observations of the nearby Low Surface brightness galaxy Cepheus 1, as well as of a number of low and medium redshift damped Ly-α systems. The derived spin temperatures for these systems is typically higher than that characteristic of the gas in the disk of the Galaxy. Higher spin temperatures were known to be characteristic of high redshift damped Ly-α absorbers, and had been earlier attributed to evolutionary effects. Our observations suggest that high spin temperatures are not a consequence of evolutionary effects since the look back time to these low z absorbers is modest. We also report on the short time scale (days) variability of the absorption profile of the z = 0.3127 system in front of B1127-145. This is the second damped Ly-α system to show such variation (the other being the z = 0.524 absorber in front of AO 0235+164).

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Seth, A. C. "Supernova Remnant G11.2—0.3 and the ISM." Symposium - International Astronomical Union 199 (2002): 311–12. http://dx.doi.org/10.1017/s0074180900169190.

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We present 610 and 235 MHz GMRT observations of the supernova remnant (SNR) G11.2—0.3 which shows a very large roation measure gradient (ΔRM∼1600 rad m−2) across it. The GMRT observations are the first high-resolution observations of this object at low frequencies. There are differences between the structure observed at 610 and at 235 MHz only some of which can be explained by free-free absorption.

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A. Irwin, Judith, and D. J. Saikia. "GMRT Observations of M 82 and NGC 3079." Symposium - International Astronomical Union 199 (2002): 241–42. http://dx.doi.org/10.1017/s0074180900169013.

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Murgia, M., D. Eckert, F. Govoni, et al. "GMRT observations of the Ophiuchus galaxy cluster." Astronomy and Astrophysics 514 (May 2010): A76. http://dx.doi.org/10.1051/0004-6361/201014126.

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Ishwara-Chandra, C. H., and D. J. Saikia. "Giant Radio Sources: Evolution and GMRT Observations." Symposium - International Astronomical Union 199 (2002): 199–202. http://dx.doi.org/10.1017/s0074180900168871.

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We study the evolution of giant radio sources and show that they are less luminous than the smaller-sized sources, and are roughly consistent with the evolutionary scenarios where the smaller-sized sources evolve to giants undergoing radiative and expansion losses. Inverse-Compton radiation losses due to the microwave background radiation dominates over the synchrotron losses for giant sources, while for the smaller sources, the latter dominates. We show that giant radio galaxies and quasars are consistent with the unified scheme, and their large sizes are not due to stronger cores. We also present preliminary GMRT images of three giant sources.

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Roy, Subhashis, and A. Pramesh Rao. "GMRT Observations of the Galactic Centre region." Symposium - International Astronomical Union 199 (2002): 274–75. http://dx.doi.org/10.1017/s0074180900169104.

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We have started a project to study the Galactic Centre region using the GMRT in all it's frequency bands. For the first time, Galactic Centre have been imaged with high resolution at 610 MHz. Also, at 325 MHz, we have observed a few of the suspected supernovae remnants (SNRs) close to the Galactic Centre. Here we present some of the preliminary results of our 610 and 325 MHz observations.

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Pick, Monique. "Solar Radio Astronomy at Low Frequencies." Symposium - International Astronomical Union 199 (2002): 415–25. http://dx.doi.org/10.1017/s0074180900169499.

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This review is concerned to study of sun at frequencies lower than 1.4 GHz. Emphasis is made on results which illustrate the topics in which GMRT could play a major role. Coordinated studies including spectral and imaging radio observations are important for research in solar physics. Joint observations between the Giant Meter Radio Telescope (GMRT) with radio instruments located in the same longitude range are encouraged. This review inludes three distinct topics: Electron beams and radio observations- Radio signatures of Coronal Mass Ejections- Radio signatures of coronal and interplanetary shocks.

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Narang, Mayank. "The nature of the radio source detected towards the exoplanet system 1RXS1609.1−210524." Monthly Notices of the Royal Astronomical Society 515, no. 2 (2022): 2015–19. http://dx.doi.org/10.1093/mnras/stac1902.

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ABSTRACT Several studies have been carried out to detect radio emissions from known exoplanets. Some of these studies have resulted in tentative detections of radio sources near the position of known exoplanets. One such planet/brown dwarf around which a radio source was detected is 1RXS1609.1−210524 (hereafter 1RX) b. A radio source near 1RX was detected with the TIFR GMRT Sky Survey (TGSS) at 150 MHz and the NRAO VLA Sky Survey (NVSS) at 1.4 GHz. However, since these surveys’ spatial resolution was low, it was not possible to ascertain whether the radio emission originated from the system or a background source. This work presents results from the 1RX field’s targeted observations at 150, 325, and 610 MHz with Giant Meterwave Radio Telescope (GMRT). These observations have a higher angular resolution as compared to TGSS and NVSS. I detected the radio source near the position of 1RX at all frequencies with GMRT. I further used the Very Large Array Sky Survey (VLASS) data at 3 GHz to determine the flux density and position at high frequency. With the targeted GMRT observations and observations from VLASS, I show that the radio emission does not originate from the 1RX b but is from a background source about ∼13 arcsec away from the host star. Further, no radio emission was detected from the position of 1RX.

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Gupta, Y., P. Gothoskar, B. C. Joshi, et al. "Pulsar Research with the GMRT: A Status Report." International Astronomical Union Colloquium 177 (2000): 277–78. http://dx.doi.org/10.1017/s0252921100059716.

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AbstractThe Giant Metrewave Radio Telescope (GMRT) coming up near Pune, India will be one of the important instruments for pulsar research work at metre wavelengths. Here we describe the capabilities of the GMRT for pulsar work and give the current status of the telescope in this context. Results from recent test observations are also summarised.

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Ray, Alak, Naveen Yadav, Sayan Chakraborti, Alicia Soderberg, and Poonam Chandra. "Radio studies of relativistic SN 2009bb." Proceedings of the International Astronomical Union 9, S296 (2013): 395–96. http://dx.doi.org/10.1017/s174392131300999x.

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AbstractA local sub-population of type Ib/c supernovae (stripped envelope SNe) with mildly relativistic outflows have been detected as sub-energetic Gamma Ray Bursts (GRBs) or X-ray Flashes (XRFs) and as radio afterglows without detected GRB counterpart. SN 2009bb belongs to the last class of objects. The long term radio observations with (J)VLA and GMRT of this SN map the dynamics of the relativistic ejecta characteristic of Central Engines associated with GRBs. We present here GMRT observations of this SN from October 2009 onwards.

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Lal, Dharam V. "Upgraded GMRT Observations of the Coma Cluster of Galaxies: The Observations." Astrophysical Journal Supplement Series 250, no. 1 (2020): 22. http://dx.doi.org/10.3847/1538-4365/abacd2.

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Zic, Andrew, Christene Lynch, Tara Murphy, David L. Kaplan, and Poonam Chandra. "Low-frequency GMRT observations of ultra-cool dwarfs." Monthly Notices of the Royal Astronomical Society 483, no. 1 (2018): 614–23. http://dx.doi.org/10.1093/mnras/sty3163.

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Roy, Subhashis, and Sabyasachi Pal. "Observations and discoveries of supernova remnants with GMRT." Proceedings of the International Astronomical Union 9, S296 (2013): 197–201. http://dx.doi.org/10.1017/s1743921313009460.

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AbstractWe have measured HI absorption distance to the youngest Galactic supernova remnant G1.9+0.3. Absorption by known anomalous velocity features near the Galactic centre (GC) puts a lower limit on its distance from Sun as 10 kpc, 2 kpc further away from the GC. We have found a small diameter (1.6′) shell like structure G354.4+0.0, that shows polarised emission in the NVSS. Based on its morphology, angular size, HI distance and its spectrum between 1.4 GHz and 330 MHz, it is perhaps the second youngest SNR in the Galaxy that is expanding in a dense environment of an HII region surrounding it. Our pilot observation of the inner Galactic 4th quadrant within 337° < l < 354° with a fixed Galactic latitude of 0.37° has confirmed G345.1−0.2 as an SNR.

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Kale, Ruta. "Low frequency observations of radio relics and halos." Proceedings of the International Astronomical Union 14, S342 (2018): 37–43. http://dx.doi.org/10.1017/s1743921318003861.

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AbstractDiffuse radio emission from galaxy clusters in the form of radio halos and relics are tracers of the shocks and turbulence in the intra-cluster medium. The imprints of the physical processes that govern their origin and evolution can be found in their radio morphologies and spectra. The role of mildly relativistic population of electrons may be crucial for the acceleration mechanisms to work efficiently. Low frequency observations with telescopes that allow imaging of extended sources over a broad range of low frequencies (<2 GHz) offer the best tools to study these sources. I will review the Giant Metrewave Radio Telescope (GMRT) observations in the past few years that have led to: i) statistical studies of large samples of galaxy clusters, ii) opening of the discovery space in low mass clusters and iii) tracing the spectra of seed relativistic electrons using the Upgraded GMRT.

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Marthi, V. R., D. Simard, R. A. Main, et al. "Scintillation of PSR B1508+55 – the view from a 10 000-km baseline." Monthly Notices of the Royal Astronomical Society 506, no. 4 (2021): 5160–69. http://dx.doi.org/10.1093/mnras/stab1970.

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ABSTRACT We report on the simultaneous Giant Metrewave Radio Telescope (GMRT) and Algonquin Radio Observatory (ARO) observations at 550–750 MHz of the scintillation of PSR B1508+55, resulting in an ∼10 000-km baseline. This regime of measurement lies between the shorter few 100- to 1000-km baselines of earlier multistation observations and the much longer earth–space baselines. We measure a scintillation cross-correlation coefficient of 0.22, offset from zero time lag due to a ∼45-s traversal time of the scintillation pattern. The scintillation time of 135 s is 3× longer, ruling out isotropic as well as strictly one-dimensional scattering. Hence, the low cross-correlation coefficient is indicative of highly anisotropic but two-dimensional scattering. The common scintillation detected on the baseline is confined to low delays of ≲1μs, suggesting that this correlation may not be associated with the parabolic scintillation arc detected at the GMRT. Detection of pulsed echoes and their direct imaging with the Low-Frequency Array (LOFAR) by a different group enable them to measure a distance of 125 pc to the screen causing these echoes. These previous measurements, alongside our observations, lead us to propose that there are at least two scattering screens: the closer 125-pc screen causing the scintillation arc detected at GMRT, and a screen further beyond causing the scintillation detected on the GMRT-ARO baseline. We advance the hypothesis that the 125-pc screen partially resolves the speckle images on the screen beyond leading to loss of coherence in the scintillation dynamic spectrum to explain the low cross-correlation coefficient.

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Mandal, S., H. T. Intema, T. W. Shimwell, et al. "Ultra-steep spectrum emission in the merging galaxy cluster Abell 1914." Astronomy & Astrophysics 622 (February 2019): A22. http://dx.doi.org/10.1051/0004-6361/201833992.

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A number of radio observations have revealed the presence of large synchrotron-emitting sources associated with the intra-cluster medium. There is strong observational evidence that the emitting particles have been (re-)accelerated by shocks and turbulence generated during merger events. The particles that are accelerated are thought to have higher initial energies than those in the thermal pool but the origin of such mildly relativistic particles remains uncertain and needs to be further investigated. The galaxy cluster Abell 1914 is a massive galaxy cluster in which X-ray observations show clear evidence of merging activity. We carried out radio observations of this cluster with the LOw Frequency ARay (LOFAR) at 150 MHz and the Giant Metrewave Radio Telescope (GMRT) at 610 MHz. We also analysed Very Large Array (VLA) 1.4 GHz data, archival GMRT 325 MHz data, CFHT weak lensing data and Chandra observations. Our analysis shows that the ultra-steep spectrum source (4C38.39; α ≲ −2), previously thought to be part of a radio halo, is a distinct source with properties that are consistent with revived fossil plasma sources. Finally, we detect some diffuse emission to the west of the source 4C38.39 that could belong to a radio halo.

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Basu, Aritra, Dipanjan Mitra, Yogesh Wadadekar, and C. H. Ishwara-Chandra. "GMRT 333-MHz observations of six nearby normal galaxies." Monthly Notices of the Royal Astronomical Society 419, no. 2 (2011): 1136–52. http://dx.doi.org/10.1111/j.1365-2966.2011.19764.x.

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Castelletti, G., B. C. Joshi, M. P. Surnis, L. Supán, and G. Dubner. "GMRT Observations of SNR G15.4+0.1/HESS J1818–154." Proceedings of the International Astronomical Union 9, S296 (2013): 366–67. http://dx.doi.org/10.1017/s174392131300985x.

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AbstractWe report here on the first dedicated simultaneous imaging and pulsar observations towards the supernova remnant (SNR) G15.4+0.1, the possible counterpart of the very high energy (VHE) source HESS J1818–154. The observations were carried out using the Giant Metrewave Radio Telescope (GMRT) at 610 and 1400 MHz. Preliminary analysis of data suggests absence of pulsations towards the centroid of HESS J1818–154, with upper limits of 0.6 and 0.3 mJy at 610 and 1400 MHz, respectively. Analysis of data with a larger beam is in progress, which may confirm the presence of a putative pulsar and its wind nebula if it is offset from the centroid of HESS J1818–154.

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Saha, Lab, та Pijushpani Bhattacharjee. "TeV γ-ray source MGRO J2019+37 : PWN or SNR?" Proceedings of the International Astronomical Union 9, S296 (2013): 300–304. http://dx.doi.org/10.1017/s1743921313009629.

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AbstractMilagro has recently reported an extended TeV γ-ray source MGRO J2019+37 in the Cygnus region. It is the second brightest TeV source after Crab nebula in their source catalogue. No confirmed counterparts of this source are known although possible associations with several known sources have been suggested. We study leptonic as well as hadronic models of TeV emission within the context of Pulsar Wind Nebulae (PWN) and Supernova Remnant (SNR) type sources, using constraints from multi-wavelength data from observations made on sources around MGRO J2019+37. These include radio upper limit given by GMRT, GeV observations by Fermi-LAT, EGRET and AGILE and very high energy data taken from Milagro. We find that, within the PWN scenario, while both leptonic as well as hadronic models can explain the TeV flux from this source, the GMRT upper limit imposes a stringent upper limit on the size of the emission region in the case of leptonic model. In the SNR scenario, on the other hand, a purely leptonic origin of TeV flux is inconsistent with the GMRT upper limit. At the same time, a dominantly hadronic origin of the TeV flux is consistent with all observations, and the required hadronic energy budget is comparable to that of typical supernovae explosions.

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Gupta, Y., P. Gothoskar, and N. D. Ramesh Bhat. "First Results from Simultaneous Dual Frequency Observations of Pulsars." Symposium - International Astronomical Union 199 (2002): 369–72. http://dx.doi.org/10.1017/s0074180900169347.

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One of the unique capabilities of the GMRT is the facility for simultaneous multi-frequency observations of pulsars. We have initiated such observations with the aims of (i) studying frequency dependence of pulsar emission, (ii) accurate estimates of pulsar dispersion measure and its variations and (iii) multi-frequency interstellar scintillation studies. Here we present some results from the ongoing dual frequency observations of pulsars.

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Green, D. A., and N. Madhusudhan. "Search for radio emission from the exoplanets Qatar-1b and WASP-80b near 150 MHz using the giant metrewave radio telescope." Monthly Notices of the Royal Astronomical Society 500, no. 1 (2020): 211–14. http://dx.doi.org/10.1093/mnras/staa3208.

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ABSTRACT We present radio observations made towards the exoplanets Qatar-1b and WASP-80b near 150 MHz with the Giant Meterwave Radio Telescope (GMRT). These targets are relatively nearby irradiated giant exoplanets, a hot Jupiter and a hot Saturn, with sizes comparable to Jupiter but different masses and lower densities. Both the targets are expected to host extended H/He envelopes like Jupiter, with comparable or larger magnetic moments. No radio emission was detected from these exoplanets, with 3σ limits of 5.9 and 5.2 mJy for Qatar-1b and WASP-80b, respectively, from these targeted observations. These are considerably deeper limits than those available for exoplanets from wide-field surveys at similar frequencies. We also present archival Very Large Array (VLA) observations of a previously reported radio source close to 61 Vir (which has three exoplanets). The VLA observations resolve the source, which we identify as an extragalactic radio source, i.e. a chance association with 61 Vir. Additionally, we cross-match a recent exoplanet catalogue with the TIFR GMRT Sky Survey ADR1 radio catalogue, but do not find any convincing associations.

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Roy, Subhashis, and Souvik Manna. "Low-radio frequency observations of seven nearby galaxies with GMRT." Monthly Notices of the Royal Astronomical Society 507, no. 4 (2021): 4734–51. http://dx.doi.org/10.1093/mnras/stab2441.

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ABSTRACT We have observed seven nearby large-angular-sized galaxies at 0.33 GHz using Giant Metrewave Radio Telescope with an angular resolution of ∼10 arcsec and sub-mJy sensitivity. Using archival higher frequency data at 1.4 or ∼6 GHz, we have then determined their spatially resolved non-thermal spectrum. As a general trend, we find that the spectral indices are comparatively flat at the galaxy centres and gradually steepen with increasing galactocentric distances. Using archival far-infrared (FIR) MIPS 70-${\mu }\mathrm{m}$ data, we estimate the exponent of radio–FIR correlation. One of the galaxies (NGC 4826) was found to have an exponent of the correlation of ∼1.4. Average exponent from 0.33-GHz data for the rest of the galaxies was 0.63 ± 0.06 and is significantly flatter than the exponent 0.78 ± 0.04 obtained using 1.4-GHz data. This indicates cosmic-ray electron (CRe) propagation to have reduced the correlation between FIR and 0.33-GHz radio. Assuming a model of simple isotropic diffusion of CRe, we find that the scenario can explain the frequency-dependent CRe propagation length-scales for only two galaxies. Invoking streaming instability could, however, explain the results for the majority of the remaining ones.

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Mohan, Nithin, Suresh Raju Chellappan Pillai, Govind Swarup, and Divya Oberoi. "Polarization and brightness temperature observations of Venus with the GMRT." Monthly Notices of the Royal Astronomical Society 487, no. 4 (2019): 4819–26. http://dx.doi.org/10.1093/mnras/stz1556.

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Ishwara-Chandra, C. H., A. Pramesh Rao, Mamta Pandey, R. K. Manchanda, and Philippe Durouchoux. "Low Frequency Radio Observations of GRS 1915+105 with GMRT." Chinese Journal of Astronomy and Astrophysics 5, S1 (2005): 87–92. http://dx.doi.org/10.1088/1009-9271/5/s1/87.

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Bhatnagar, Sanjay. "Confirmation of three candidate Galactic supernova remnants from GMRT observations." Monthly Notices of the Royal Astronomical Society 317, no. 2 (2000): 453–59. http://dx.doi.org/10.1046/j.1365-8711.2000.03610.x.

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Kundu, M. R., S. M. White, V. I. Garaimov, P. Subramanian, S. Ananthakrishnan, and P. Janardhan. "The Morphology of Decimetric Emission from Solar Flares: GMRT Observations." Solar Physics 236, no. 2 (2006): 369–87. http://dx.doi.org/10.1007/s11207-006-0059-8.

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Tasse, C., H. J. A. Röttgering, P. N. Best, A. S. Cohen, M. Pierre, and R. Wilman. "GMRT observations of the XMM large scale structure survey field." Astronomy & Astrophysics 471, no. 3 (2007): 1105–16. http://dx.doi.org/10.1051/0004-6361:20066986.

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Smolčić, Vernesa, Huib Intema, Bruno Šlaus, et al. "The XXL Survey." Astronomy & Astrophysics 620 (November 20, 2018): A14. http://dx.doi.org/10.1051/0004-6361/201732336.

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We present the 25 square-degree GMRT-XXL-N 610 MHz radio continuum survey, conducted at 50 cm wavelength with the Giant Metrewave Radio Telescope (GMRT) towards the XXL Northern field (XXL-N). We combined previously published observations of the XMM-Large Scale Structure (XMM-LSS) field, located in the central part of XXL-N, with newly conducted observations towards the remaining XXL-N area, and imaged the combined data-set using the Source Peeling and Atmospheric Modeling (SPAM) pipeline. The final mosaic encompasses a total area of 30.4 square degrees, with rms <150 μJy beam−1 over 60% of the area. The rms achieved in the inner 9.6 square degree area, enclosing the XMM-LSS field, is about 200 μJy beam−1, while that over the outer 12.66 square degree area (which excludes the noisy edges) is about 45 μJy beam−1. The resolution of the final mosaic is 6.5 arcsec. We present a catalogue of 5434 sources detected at ≥7 ×rms. We verify, and correct the reliability of, the catalog in terms of astrometry, flux, and false detection rate. Making use of the (to date) deepest radio continuum survey over a relatively large (2 square degree) field, complete at the flux levels probed by the GMRT-XXL-N survey, we also assess the survey’s incompleteness as a function of flux density. The radio continuum sensitivity reached over a large field with a wealth of multi-wavelength data available makes the GMRT-XXL-N 610 MHz survey an important asset for studying the physical properties, environments and cosmic evolution of radio sources, in particular radio-selected active galactic nuclei (AGN).

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George, Lijo T., Ruta Kale, and Yogesh Wadadekar. "Imaging results from the legacy Giant Metrewave Radio Telescope Galaxy Cluster Key Project." Monthly Notices of the Royal Astronomical Society 507, no. 3 (2021): 4487–506. http://dx.doi.org/10.1093/mnras/stab2309.

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ABSTRACT We have used archival Giant Metrewave Radio Telescope (GMRT) data to image and study 39 galaxy clusters. These observations were made as part of the GMRT Key Project on galaxy clusters between 2001 and 2004. The observations presented in this sample include 14 observations at 610 MHz, 29 at 325 MHz, and three at 244 MHz covering a redshift range of 0.02–0.62. Multifrequency observations were made for eight clusters. We analysed the clusters using the spam processing software and detected the presence of radio halo emission for the first time in the clusters RXC J0510−0801 and RXC J2211.7−0349. We also confirmed the presence of extended emission in 11 clusters which were known from the literature. In clusters where haloes were not detected, upper limits were placed using our own semi-automated program. We plot our detections and non-detections on the empirical LX−P1.4 and M500−P1.4 relation in radio halo clusters and discuss the results. The best fits follow a power law of the form $L_{500} \propto P_{1.4}^{1.82}$ and $M_{500} \propto P_{1.4}^{3.001}$ which is in accordance with the best estimates in the literature.

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Bharadwaj, S., B. B. Nath, and S. K. Sethi. "Probing Large Scale Structures in HI with GMRT." Symposium - International Astronomical Union 199 (2002): 108–9. http://dx.doi.org/10.1017/s0074180900168640.

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The redshifted 1420 MHz emission from the HI in unresolved Lyman-α clouds (DLA) at high z will appear as a background radiation in low frequency radio observations. We calculate the brightness temperature and the angular two-point correlation function of the fluctuations of this radiation. This can be an important probe of the large-scale structure at high z.

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Narang, Mayank, Manoj P. та C. H. Ishwara Chandra. "GMRT Observations of the Exoplanetary Systems τ Boötis and 55 Cancri". Research Notes of the AAS 5, № 7 (2021): 158. http://dx.doi.org/10.3847/2515-5172/ac0fe0.

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Pandey, M., R. K. Manchanda, A. P. Rao, P. Durouchoux, and Ishwara-Chandra. "GMRT observations of the field of INTEGRAL X-ray sources - I." Astronomy & Astrophysics 446, no. 2 (2006): 471–83. http://dx.doi.org/10.1051/0004-6361:20042317.

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Masqué, Josep M., Solai Jeyakumar, Miguel A. Trinidad, Tatiana Rodríguez-Esnard, and C. H. Ishwara-Chandra. "GMRT observations of the protostellar jet associated with IRAS 16547-4247." Monthly Notices of the Royal Astronomical Society 483, no. 1 (2018): 1184–91. http://dx.doi.org/10.1093/mnras/sty3179.

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Pandey, M., A. P. Rao, R. Manchanda, P. Durouchoux, and C. H. Ishwara-Chandra. "GMRT observations of the field of INTEGRAL X-ray sources. II." Astronomy & Astrophysics 453, no. 1 (2006): 83–89. http://dx.doi.org/10.1051/0004-6361:20054267.

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Roy, Subhashis, and A. Pramesh Rao. "GMRT observations of four suspected supernova remnants near the Galactic Centre." Monthly Notices of the Royal Astronomical Society 329, no. 4 (2002): 775–86. http://dx.doi.org/10.1046/j.1365-8711.2002.05007.x.

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Begum, Ayesha, Jayaram N. Chengalur, I. D. Karachentsev, M. E. Sharina, and S. S. Kaisin. "FIGGS: Faint Irregular Galaxies GMRT Survey – overview, observations and first results." Monthly Notices of the Royal Astronomical Society 386, no. 3 (2008): 1667–82. http://dx.doi.org/10.1111/j.1365-2966.2008.13150.x.

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Kantharia, N. G., and D. Anish Roshi. "Preliminary Results of Galactic Radio Recombination Line Observations using the GMRT." Symposium - International Astronomical Union 199 (2002): 343–44. http://dx.doi.org/10.1017/s007418090016927x.

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A pilot project to observe recombination lines of hydrogen and carbon from Galactic HII regions near 20cm (n = 168) and 49cm (n = 220) using the 30-station correlator at the Giant Metre-wave Radio Telescope was undertaken. The preliminary results from observations of the HII regions W3 and S106 are presented here.

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Roy, Subhashis, and A. Pramesh Rao. "Observations of the Galactic Centre at 610 MHz with the GMRT." Astronomische Nachrichten 324, S1 (2003): 391–95. http://dx.doi.org/10.1002/asna.200385113.

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Swarup, G., and T. L. Venkatasubramani. "RFI Survey for the Giant Metrewave Radio Telescope in India." International Astronomical Union Colloquium 112 (1991): 190–93. http://dx.doi.org/10.1017/s0252921100003985.

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ABSTRACTA Giant Meterwave Radio Telescope (GMRT) is being set up at Khodad about 80 km north of Pune in India for operation in the frequency range of about 30 to 1500 MHz. It is to be completed by 1992 and is being designed to investigate many outstanding problems in the fields of galactic and extragalactic astronomy. We present here measurements of man-made radio frequency interference (RFI) conducted at the GMRT site in 1985 and 1988. It is seen that highly sensitive radio astronomy observations can still be made at selected bands in the above frequency range because of the relatively low level of RFI in India. However, this advantage may not remain for more than a decade or two.

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Quiroga-Nuñez, L. H., H. T. Intema, J. R. Callingham, et al. "Differences in radio emission from similar M dwarfs in the binary system Ross 867-8." Astronomy & Astrophysics 633 (January 2020): A130. http://dx.doi.org/10.1051/0004-6361/201936491.

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Serendipitously, we rediscovered radio emission from the binary system Ross 867 (M4.5V) and Ross 868 (M3.5V) while inspecting archival Giant Metrewave Radio Telescope (GMRT) observations. The binary system consists of two M-dwarf stars that share common characteristics such as spectral type, astrometric parameters, age, and emission at infrared, optical, and X-ray frequencies. The GMRT data at 610 MHz taken on July 2011 shows that the radio emission from Ross 867 is polarized and highly variable on hour timescales with a peak flux of 10.4 ± 0.7 mJy beam−1. Additionally, after reviewing archival data from several observatories (VLA, GMRT, JVLA, and LOFAR), we confirm that although the two stars are likely coeval, only Ross 867 was detected, while Ross 868 remains undetected at radio wavelengths. As the stars have a large orbital separation, this binary stellar system provides a coeval laboratory to examine and constrain the stellar properties linked to radio activity in M dwarfs. We speculate that the observed difference in radio activity between the dwarfs could be due to vastly different magnetic field topologies or that Ross 867 has an intrinsically different dynamo.

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Castelletti, G., G. Dubner, K. Golap, and W. M. Goss. "A Spectral Analysis of the Central Component of CTB 80." Symposium - International Astronomical Union 218 (2004): 211–12. http://dx.doi.org/10.1017/s0074180900180994.

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Based on observations of the extended supernova remnant CTB 80 carried out with the Giant Metrewave Radio Telescope (GMRT, India) at 240 and 618 MHz we have analyzed the spectral behavior of the ∼ 10′ nebula formed near the pulsar PSR B1951+32, finding signatures of the interaction of the pulsar with the surrounding plasma.

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Nandi, S., M. Das, and K. S. Dwarakanath. "Tracing the evolution of ultraluminous infrared galaxies into radio galaxies with low frequency radio observations." Monthly Notices of the Royal Astronomical Society 503, no. 4 (2021): 5746–62. http://dx.doi.org/10.1093/mnras/stab275.

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ABSTRACT We present radio observations of ultraluminous infrared galaxies (ULIRGs) using the Giant Metrewave Radio Telescope (GMRT) and combine them with archival multifrequency observations to understand whether ULIRGs are the progenitors of the powerful radio loud galaxies in the local Universe. ULIRGs are characterized by large infrared luminosities (LIR &gt; 1012 L⊙), large dust masses (∼108 M⊙), and vigorous star formation (star formation rates ∼10–100 M⊙ yr−1). Studies show that they represent the end stages of mergers of gas-rich spiral galaxies. Their luminosity can be due to both starburst activity and active galactic nuclei (AGNs). We study a sample of 13 ULIRGs that have optically identified AGN characteristics with 1.28 GHz GMRT observations. Our aim is to resolve any core-jet structures or nuclear extensions and hence examine whether the ULIRGs are evolving into radio loud ellipticals. Our deep, low frequency observations show marginal extension for only one source. However, the integrated radio spectra of 9 ULIRGs show characteristics that are similar to that of GPS/CSS/CSO/young radio sources. The estimated spectral ages are 0.4–20 Myr and indicate that they are young radio sources and possible progenitors of radio galaxies. Hence, we conclude that although most ULIRGs do not show kpc scale extended radio emission associated with nuclear activity, their radio spectral energy distributions do show signatures of young radio galaxies.

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Mohan, R., K. S. Dwarakanath, G. Srinivasan, and J. N. Chengalur. "HI 21cm-line Observations with the GMRT Towards Interstellar Clouds Previously Seen in Optical Absorption." Symposium - International Astronomical Union 199 (2002): 341–42. http://dx.doi.org/10.1017/s0074180900169268.

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We have made HI 21cm-line absorption measurements using the GMRT towards 15 directions in the Galaxy which are known to have high random velocity clouds as seen in the optical absorption lines of CaII and NaI. For the first time, in 6 out of these 15 directions we detect HI absorption features corresponding to the high random velocity optical absorption lines. The mean optical depth of these detections is ∼ 0.08.

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Srivastava, Shweta, and Ashok K. Singal. "GMRT observations of IC 711 – the longest head-tail radio galaxy known." Monthly Notices of the Royal Astronomical Society 493, no. 3 (2020): 3811–24. http://dx.doi.org/10.1093/mnras/staa520.

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ABSTRACT We present low frequency, GMRT observations at 240, 610, and 1300 MHz of IC 711, a narrow angle tail (NAT) radio galaxy. The total angular extent of the radio emission, ∼22 arcmin, corresponds to a projected linear size of ∼900 kpc, making it the longest among the known head-tail radio galaxies. The objectives of the GMRT observations were to investigate the radio morphology, especially of the long tail structure, at low frequencies. The radio structure, especially initial ∼10 arcmin of tail being a long straight feature, does not seem to be consistent with a simple circular motion around the cluster centre, as previously suggested in the literature. Two sharp bends after the straight section of the tail cast doubt on the prevailing idea in the literature that the long narrow tails represent trails left behind by the fast moving parent optical galaxy with respect to the cluster medium, as the optical galaxy could not have undergone such sharp bends in its path, under any conceivable gravitational influence of some individual galaxy or of the overall cluster gravitational potential. In fact, the tail does not seem to have been influenced by the gravitational field of any of the cluster-member galaxies. The radio spectrum of the head, coinciding with the optical galaxy, is flat ($\alpha \stackrel{\lt }{_{\sim }}0.4$ for S∝ ν−α), but steadily steepens along the radio tail, with the end part of the tail showing the steepest spectrum ($\alpha \, {\sim}$ 4–5) ever seen in any diffuse radio emission region.

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Supan, L., G. Castelletti, B. C. Joshi, M. P. Surnis, and D. Supanitsky. "A complete radio study of SNR G15.4+0.1 from new GMRT observations." Astronomy & Astrophysics 576 (April 2015): A81. http://dx.doi.org/10.1051/0004-6361/201425284.

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Knowles, Kenda, Andrew J. Baker, J. Richard Bond, et al. "GMRT 610 MHz observations of galaxy clusters in the ACT equatorial sample." Monthly Notices of the Royal Astronomical Society 486, no. 1 (2019): 1332–49. http://dx.doi.org/10.1093/mnras/stz823.

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Abstract We present Giant Metrewave Radio Telescope (GMRT) 610 MHz observations of 14 Atacama Cosmology Telescope (ACT) clusters, including new data for nine. The sample includes 73 per cent of ACT equatorial clusters with M500 &gt; 5 × 1014 M⊙. We detect diffuse emission in three of these (27$^{+20}_{-14}$ per cent): we detect a radio minihalo in ACT-CL J0022.2–0036 at z = 0.8, making it the highest redshift minihalo known; we detect potential radio relic emission in ACT-CL J0014.9–0057 (z = 0.533); and we confirm the presence of a radio halo in low-mass cluster ACT-CL J0256.5+0006, with flux density S610 = 6.3 ± 0.4 mJy. We also detect residual diffuse emission in ACT-CL J0045.9–0152 (z = 0.545), which we cannot conclusively classify. For systems lacking diffuse radio emission, we determine radio halo upper limits in two ways and find via survival analysis that these limits do not significantly affect radio power scaling relations. Several clusters with no diffuse emission detection are known or suspected mergers, based on archival X-ray and/or optical measures; given the limited sensitivity of our observations, deeper observations of these disturbed systems are required in order to rule out the presence of diffuse emission consistent with known scaling relations. In parallel with our diffuse emission results, we present catalogues of individual radio sources, including a few interesting extended sources. Our study represents the first step towards probing the occurrence of diffuse emission in high-redshift (z ≳ 0.5) clusters, and serves as a pilot for statistical studies of larger cluster samples with the new radio telescopes available in the pre-SKA era.

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Journal articles on the topic 'GMRT Observations'

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