GMRT vital in understanding gravitational wave event

Manasi Saraf Joshi
Thursday, 21 December 2017

Team from Nat’l Centre for Radio Astrophysics studies aftermath of event through radio waves

Pune: For the first time, Giant Metrewave Radio Telescope (GMRT) has been successful in understanding what exactly happened when two neutron stars collided, creating the gravitational wave noted during the LIGO-Virgo experiment in August this year.

Poonam Chandra, astronomer at the National Centre for Radio Astrophysics (NCRA), Pune, who is part of the team, said, “For the first time, gravitational waves from a neutron star merger were detected and the electromagnetic counterpart from this merger has been detected. In this historical feat, GMRT has the credit to detect it at the lowest frequency ever. It is a proud moment for Indian astronomy.”

Speaking to Sakal Times, Prof Yashwant Gupta from GMRT (Khodad) said, “When this event of happened in August, a huge amount of energy was released and this energy comes out in different forms. Sometimes it comes out like a jet shooting from one direction, or sometimes like a strong jet hitting a material. When it is impeded with an equally strong object, the jet gets defused.”

He added, “Scientists were trying to decipher the kind of explosion it was and whether it was like a jet or a defused mushroom. Here, the radio frequency played a major role in understanding the event.”

“Although the event was over by then, the way the cooling of an object happens for a long time, radiations were emitted from it. The radiations were still emitting after 30 to 50 days and through radio signals, the scientists studied the nature and frequency of it,” said Prof Gupta.

“With help of the radio telescope we tried to understand the mystery of such events, besides getting a better understanding of such events and physics,” he said, adding that they are still studying its signalling.

Radio wavelength increasing
† A team of scientists from Caltech and other institutions reported that the signal at radio wavelengths continues to brighten more than 100 days after the August 17 event.
† These radio observations indicate that a superfast jet, launched from the two neutron stars as they collided, is slamming into surrounding material and creating a slower-moving, billowy cocoon. “We think the jet is dumping its energy into the cocoon,” said Gregg Hallinan, an assistant professor of astronomy at Caltech.
† The findings were made at the lowest sub-GHz frequencies with the GMRT in Pune, India along with the Karl G Jansky Very Large Array in New Mexico, and the Australia Telescope Compact Array.
† The radio emission, detected 16 days after the August 17 event and still measurable as of December 2, tells a different story. If the jet had been fast and beam-like, the radio light would have weakened with time, as the jet lost energy. The fact that the brightness of the radio light is increasing suggests the presence of a cocoon that is choking the jet. The reason is complex, but it has to do with the fact that the slower moving, wider-angle material of the cocoon gives off more radio light than the faster-moving,sharply focused jet material.
† The possibility that a cocoon was involved in the August 17 event was originally proposed by Caltech’s Mansi Kasliwal, assistant professor of astronomy, and colleagues. She and her team from the NSF-funded Global Relay of Observatories Watching Transients Happen (GROWTH) project observed the event at multiple wavelengths.

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