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Recent Results from GMRT

Nearby Galaxies   
  • Eridanus Group of Galaxies : A collage of GMRT HI image of the Eridanus group of galaxies, is a prominent structure in the southern sky, at a distance of 23 Mpc. Its oveall extent is ~ 20 Mpc. HI emission from more than 60 galaxies of this group was imaged and these data have revealed a trend for HI deficiency among galaxies located in regions of higher galaxy concentration. (Omar & Dwarakanath, JA&A, 26, 71, 2005).
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  • A Dwarf Galaxy with a Giant HI Disk : The image shows the GMRT map of the integrated HI, overlayed on the optical B-band image of the nearby dwarf irregular galaxy NGC 3741 (MB ~ -13.1). The HI disk is found to extend to a record 8.3 times the Holmberg radius and the rotation curve could be measured out to 38 optical scale lengths (and found to remain flat)! (Begum, Chengalur & Karachentsev 2005 A&A, 433, L1)
 n3741.jpg
  • NGC 4438 : DSS optical band photograph of NGC4438 is shown in false colour, superimposed on it is the GMRT neutral atomic hydrogen emission line contours (in yellow). As seen in the image, the disk of the NGC4438 has been disturbed by the northern interacting companion NGC4435, while this 150 million solar mass elongated hydrogen cloud is seen shifted to the north-west. The most plausible explanation of the hydrogen gas seen on the west along with other known components of the ISM is, ram pressure stripping by the dense hot gaseous medium of the Virgo cluster as NGC4438 travels towards south-east with nearly 1000km/s speed.( Hota, A.; Saikia, D. J.; Irwin, J. A. 2006 ( in preparation)).
 hota1.jpg
  • A Metal Poor Galaxy SBS 1129+576 : Integrated HI emission map of metal-poor galaxy SBS 1129+576 using GMRT data. The galaxy is seen to be interacting with its companion SBS 1129+577. A bridge between the two and tidal arms can be noted. This interaction seems to have triggered the starburst in SBS 1129+576. (Ekta, Jayaram N. Chengalur and S. Pustilnik, 2006).
 ekta.jpg
  • A Peculiar Galaxy NGC 3079 : Superposition of the GMRT images of the peculiar galaxy NGC 3079 which has the rare property of a spiral ejecting radio synchrotron jets (like radio galaxies), as seen from the grey-scale image at 1.3 GHz. The contours showing 615 MHz emission have revealed radio "lobes" or "halo" extending upto ~10 kpc to either side of the disk of this edge-on spiral. Note the giant "loop" of synchrotron emission, with a diameter of ~5 kpc, at the northeastern edge of the radio halo. (Irwin & Saikia, MNRAS, 346, 977, 2003).
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   Interacting galaxies   
  •   NGC 452 - Mrk 1  : Figure shows the GMRT image of HI distribution associated with a pair of interacting galaxies, consisting of the spiral NGC 451 and the active galaxy Mrk 1. Both galaxies belong to a poor group of galaxies at z=0.017. The detection of patchy HI structure of Mrk 1 is evidence for a tidal interaction with NGC 451, which may have triggered the nuclear activity in Mrk 1 (Omar, A., et al., A&A, 394, 405, 2002).
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  •  Holmberg 124 Group of Galaxies : The contours of 330 MHz emission clearly show the faint "bridge" of synchrotron emission running along a chain of galaxies belonging to the group Holmberg 124. Also seen in this GMRT map is the extra-planar radio emisssion in the dominant (edge-on) spiral galaxy NGC 2820. The "bridge" has a very steep radio spectrum (a ~ -1.8) and is probably a result of an ongoing tidal interaction between the galaxies. (Kantharia et al., AA, 435, 483, 2005).
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  Transient Sources   
  •  Gaint Flare from magnetar SGR 1806-20 : Radio 'light curves' of the fading radio counterpart of the giant flare from the magnetar SGR 1806-20. Monitoring at the lowest two frequencies (0.24 and 0.61 GHz) was done with the GMRT. Analysis of the radio spectrum has yielded the first direct estimate of the distance to this magnetar (about 8 kpc). The rapidly decaying radio emission can be interpreted to  arise from the debris ejected during the explosion (Cameron et al., Nature  , 1112, 2005).
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  •  Supernova SN 1993J : GMRT and VLA measurements are combined to define the radio spectrum of the supernova SN 1993J on the day 3200 after its explosion on 1993 March 28 in the nearby galaxy M81. The precise knowledge of the age, when combined with the clearly detected spectral break has enabled a direct estimate of magnetic field in this object. This estimate is independent of the usual assumption about how the magnetic energy compares with the energy in relativistic particles. (Chandra, Ray & Bhatnagar, ApJL, 604, L97, 2004 & BASI, 32, 223)
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  •  Gamma Ray Brust GRB030329 : Radio light curve of the afterg low of the Gamma Ray Burst GRB030329 observed using the GMRT. Data at 1280 MHz a re shown in red and those at 610 MHz in blue. The solid lines show the predictio ns of a refreshed jet model of emission from the afterglow. The jet expands rel ativistically in the beginning and becomes sub-relativistic around 60 days after the burst. These GMRT data represent the longest ever radio follow-up of any G RB afterglow, and also the lowest frequency detections ever made.(L. Resmi and D. Bhattacharya )
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  •  Nova GK Persei : GMRT image of the faint 0.6 GHz radio emission associated with the nova GK Persei, overlayed on the grey-scale image of optical line emission (H-a+N[II]). Comparison with the archival data shows that since the initial explosion in 1901 the nebula is expanding at a speed of ~1500 kms–1. Also, its radio emission shows a secular decrease of 2.1% at 1.4 GHz, but at 0.3 GHz it has actually brightened up. This behaviour is similar to that shown by the young supernova remnant Cas A. (Anupama & Kantharia, AA, 435, 167, 2005).
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Galactic center 
    The figure shows the 620 MHz GMRT map of the source Sgr A located at the centre of our Galaxy. This is the first detection of the central compact source Sgr A* below 1 GHz. This source is believed to harbour a 2.6 X 10^6 M_o black hole. Its radio spectrumis extended below 1.4 GHz, using GMRT observations at 1.1, 0.6 and 0.3 GHz. The spectral continuity from higher frequencies suggests that Sgr A* is located in the foreground of the HII region complex Sgr A-West. (Roy, S. & Rao, A.P., MNRAS, 349, L25, 2004).
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Intergalactic Medium 
  •  Widespread acetaldehyde near the Galactic Center :  Contours show the widespread 1065 MHz line emission from acetaldehyde (CH3CHO) moleculer gas associated with the thermal radio continuum (greyscale) from the giant molecular cloud complex Sgr B2 which is located near the centre of our Galaxy. This spatial correlation revealed by GMRT observations suggests that the CH3CHO line is probably mased. The enhanced widespread abundance of CH3CHO is unlike most other molecules and is a puzzling result. This is probably related to the presence of numerous shocks in Sgr B2 complex, releasing the molecules by disrupting the mantle of the dust grains. (Chengalur & Kanekar, A&A, 403, L43, 2003). .
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Active Galaxies 
  • J1432+158 : The Most Distant Giant Quasar : The faint radio connection between the central core and the western lobe, seen in this GMRT map at 333 MHz, overlayed on the optical image, confirmed that this triple radio source, J1432+158 is the most distant member (z = 1.005) of the class 'Giant Radio Quasars' that measure at least a mega-parsec in overall size. (Singal, Konar & Saikia, MN, 347, L79, 2004).
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  •  X-shaped Radio Galaxy B1059+169 (Abell 1145) :  Well resolved GMRT images of the X-shaped radio galaxy B1059+169 (Abell 1145) at 607 MHz and 237 MHz. Detailed comparison of these images has led to the unexpected result that the (supposedly old) faded radio `wings' have flatter radio spectra at these low frequencies, compared to the two main lobes. (Lal & Rao, in preperation 2006)
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  •  Head-Tail Radio Galaxy 3C 129 : This 240 MHz GMRT image shows the large head-tail radio galaxy 3C 129 and its companion 3C 129.1 belonging to the X-ray cluster 4U 0446+44 at z = 0.021. By combining this map with the 610 MHz GMRT map and other published maps at higher frequencies, detailed spectral index gradient across the radio trail was mapped, leading to an age estimate of 2 X 10^8 yr. The measured relatively flat radio spectrum of the feature marked as "crosspiece" disfavours the idea that it is a "fossil" radio source. (Lal & Rao, A&A, 420, 491, 2004)
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Pulsars 
  • Discovery of the Binary Millisecond Pulsar J0514-4002A : The panel shows the binary millisecond pulsar PSR J0514-4002A, which is the first known pulsar in the globular cluster NGC 1851. The optical image of the globular clusture NGC 1851 is shown in the top panel. This is also the first pulsar discovered using the Giant Metrewave Radio Telescope. The pulsar has a rotational period of 4.99 ms, an orbital period of 18.8 days, and the most eccentric pulsar orbit yet measured (e=0.89). The companion has a minimum mass of 0.9 Msolar, and its nature is currently unclear. After accreting matter from a low-mass companion star that spun it up to a (few) millisecond spin period, the pulsar eventually exchanged the low-mass star for its more massive present companion. This is exactly the same process that could form a system containing a millisecond pulsar and a black hole; the discovery of NGC 1851A demonstrates that such systems might exist in the universe, provided that stellar mass black holes exist in globular clusters.(Freire P.,Gupta Y., Ransom S., Ishwara-Chandra C.,2004,APJ,606,L53)
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  •  Discovery of New Pulsar J1833-1024 : This panel shows the recent GMRT discovery of a new pulsar J1833-1024 in the supernova remnant G21.5-0.9, whose image taken with the Chandra X-ray telescope is shown in the top panel. This 61.96 millisec period pulsar with a characteristic age of ~ 4900 yrs is thought to be located very close to the centre of this supernova remnant, and found to have the second highest spin-down lumnosity (second only to the Crab pulsar). (Gupta et al., Curr. Sci, vol 89, p 853, 2005).
 yg1.jpg
  •  Variation of DM for PSR B2217+47 : GMRT has been used in simultaneous multi-frequency pulsar observation mode to obtain accurate estimates (~ 1 part in 10000 or better) of pulsar Dispersion Measures (DMs) at individual epochs, and to monitor the DM fluctuations on long time scales (of months). Shown here is a sample result for the variation of DM for the pulsar B2217+47, observed at the frequencies of 610 and 325 MHz, over a period of more than one year, starting from 8 Jan 2001. The error bars are 3-sigma values. (Ahuja et al., MNRAS, vol 357, p 1013, 2005).
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  •  Double Pulsar J0737-3039 : The illustration shows the first hint of temporal evolution in a crucial property of the 'double pulsar', J0737-3039, a unique system consisting of two orbiting pulsars, with pulsation periods of 23 milliseconds (A) and 2.8 seconds (B). The two profiles, taken with GMRT at 0.34 GHz at a time interval of 8 months in 2004, display the variation of the mean flux of the pulsar B near the orbital longitude 210 deg. The profile width are 44±4deg and 27±1deg for the Epoch 1 and Epoch 2, implying a rapid evolution of this general relativistic stellar binary. (Joshi, B.C., submitted to Elsevier Science)

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 Deep Fields 
  • Spitzer extragalactic First Look Survery (xFLS) field : A small portion of a deep survey of the Spitzer extragalactic First Look Survey (xFLS) field observed by the GMRT at 610 MHz. The resolution is about 5 arcsec, and the r.m.s. noise of about 30 microJy/beam. About 4 square degrees of this xFLS field have been observed, which will allow detailed studies of the sources from their radio and Spitzer IR observations.( Dave Green and Tim Garn, Cavendish Laboratory, Cambridge, U.K.)
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Sun and Solar wind 
  •  A 17 sec snapshot of noise storm sources in the solar corona at 09:04:04 UT on Aug 27, 2002 at 327 MHz. Left panel: Image using only GMRT visibilities. Middle panel: Image using only visibilities from the Nancay RadioHeliograph (NRH). Right panel: Image obtained by combining GMRT and NRH visibilities. Images like those in the right panel achieve a resolution of 49" and dynamic ranges between 250-320. (Claude Mercier, Prasad Subramanian, Alain Kerdraon, Monique Pick, S.Ananthakrishnan, P. Janardhan, 2005, A&A, in press.)
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  •  Top panel shows the soft X-ray light curves from GOES 10 satellite during the M2.8 flare on November 17, 2001; Lower left panel shows the simultaneous radio 'light curve' taken with GMRT at 1060 MHz; The Sun at 17 GHz imaged with the Nabeyama Radio Heliograph around the same time is shown in the lower right panel. The bright prominence seen on the eastern solar limb is the flaring region. (Prasad Subramanian, Ananthakrishnan, et al., Solar Physics, 2000).
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