GMRT Report

The upgraded GMRT moves to the near final release:

The work on the upgrade of the GMRT has come close to the final release. For the GMRT observing cycle #34 (starting from April 2018), the upgraded GMRT (uGMRT) is being made available with all the four main receiver bands — Band-2 (120-250 MHz), Band-3 (250-500 MHz), Band-4 (550-850 MHz) and Band-5 (1000-1450 MHz) — populated on all the 30 antennas. Whereas Band-2 is released in a shared risk mode, all the other bands are available in the regular release mode. These are accompanied by a 30 antenna, 400 MHz bandwidth back-end that can implement a full Stokes interferometer for up to 16384 spectral channels, and a 4 beam pulsar receiver with incoherent array and phased array options, and a real-time 200 to 400 MHz bandwidth coherent dedispersion system for each beam.

Proposals for the GMRT observing cycle 34, submitted in January 2018, have reached an all time high of 110 submissions, with a record oversubscription factor of 2.8. The proposals for the uGMRT systems already outnumber those for the legacy GMRT systems, which is very promising. We expect some exciting new science results from this cycle of observations !

Sample early results with the uGMRT:

Meanwhile, results have already started flowing from the uGMRT systems. A few representative samples are as follows :

(i) The accompanying figure shows the first new pulsar discovered with the uGMRT operating at Band-3 (250-500 MHz) in the incoherent array mode, as part of a pilot for a proposed all-sky pulsar survey with the uGMRT. This first discovery is a pulsar with a period of 442.5 millisec and a dispersion measure of 69.1 parsec/cc, and shows up clearly in the search data (as seen in the accompanying figure) and follow-up observations have confirmed this discovery. This early discovery augurs well for the potential of finding many new pulsars with the improved sensitivity of the uGMRT. (figure courtesy of Y. Gupta and collaborators)

Figure 1: First new pulsar discovered with the uGMRT operating at Band-3 (250-500 MHz). This pulsar has a period of 442.5 millisec and a dispersion measure of 69.1 parsec/cc.

(ii) The uGMRT is being used at L-band for highly sensitive studies of the Extended Groth Strip as part of a search for redshifted HI 21-cm and radio continuum emission from star-forming galaxies. The accompanying figure shows a preliminary image made over just 100 MHz (1300-1400 MHz) of the full band uGMRT system. The RMS noise is 5 microJy/Bm, making this the deepest GMRT image so far, and also one of the deepest images from any radio telescope. We are eagerly awaiting the results from the full bandwidth analysis for theseobservations for an even more sensitive result. (courtesy A. Bera, N. Kanekar, N. Chengalur, NCRA).

Figure 2: Deep imaging results using just 100 MHz (1300-1400 MHz) of the full band uGMRT system. The RMS noise is 5 microJy/Bm, making this the deepest GMRT image so far.

The GMRT helps shed light on the first multi-messenger GW170817 neutron star merger event:

The first ever detection of gravitational waves from a neutron star merger event (GW170817) truly heralded the beginning of an exciting new era of multi-messenger astronomy. Amongst the host of observatories that followed up this GW event over different parts of the electromagnetic spectrum, the uGMRT with its unique low frequency detections of the source, has played an important role in constraining the models for the structure of this event. The accompanying plot (from Hallinan et al 2017) shows the detections with the uGMRT at low frequencies, which have allowed the authors to infer the details of the cocoon model for this event. Follow-up observations of this source with the uGMRT are continuing, and are expected to yield additional insights into the evolution of this enigmatic event.

Figure 3: Radio detection of GW 170817, the neutron star merger event, at low radio frequencies with the uGMRT.


Report provided by Tirthankar Roy Choudhury