On Friday 6 July 2018 at 10:25 am (CEST), ASTRON’s Low Frequency Array (LOFAR) automatically responded to a transient astronomical event for the first time. A bright burst of gamma-rays was detected by a NASA satellite and an urgent message was sent to observatories on the ground. Within a few minutes, LOFAR stopped what it was doing and started a new observation of the exploding astrophysical object. This LOFAR rapid response mode is important to help identify the sources of mysterious short-duration astronomical events.

Published by the editorial team, 11 July 2018

Transient astronomical events are phenomena in the sky that last only a short amount of time, from milliseconds to hours. Examples of these events are gamma-ray bursts, or fast radio bursts. Gamma-ray bursts are extremely energetic explosions that have been associated with the supernova explosions of the most massive stars and the merger of a neutron star with another neutron star or a black hole. But it is unknown what engine is powering these massive outbursts; a black hole or a neutron star.

“When some objects explode, we think there may be low frequency radio emission associated with them,” says astronomer Antonia Rowlinson from ASTRON and the University of Amsterdam. “We know that there are a lot of interesting sources, such as gamma-ray bursts, flare stars and X-ray binaries, that are detected by other facilities. It is not known what they do at low radio frequencies as deep, rapid observations have not been taken.”


LOFAR stations in Exloo, the Netherlands. Credit: ASTRON



Rapid observations of the transient sky can open up a new window of discovering space. Therefore, a new rapid response mode was recently installed at LOFAR. LOFAR has unique sensitivity and excellent localization capabilities that enables astronomers to chase after faint sources and possibly detect new radio sources at the position of gamma-ray bursts. This would help identify what the engine behind the gamma-ray bursts is.

“The LOFAR rapid response mode enables LOFAR to react quickly to alerts”, Rowlinson explains. “When LOFAR receives an alert, and the proposal outranks the current observation, the current observation is stopped and the new observation takes over. So the telescope stops what it's doing to look at a new exploding astrophysical object. This typically takes 5 minutes but we hope to be faster in the future. This is a brand-new mode and onFriday it completed its first successful trigger.”

At the moment, the LOFAR transients team is processing the observation of the gamma-ray burst of Friday 6 July, called GRB 180706A, which was detected by NASA’s Neil Gehrels Swift Observatory. From now on, it is expected that LOFAR will trigger on new transient events every month. These observations may hold invaluable clues to show us what is happening during those mysterious phenomena in space.

Featured image courtesy of NASA/Swift/Cruz deWilde

Text by Iris Nijman


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