Powerful Gamma-Ray Burst Made Currents Flow in the Earth

Oct. 17, 2022: Astronomers have never seen anything quite like it. On Oct. 9, 2022, Earth-orbiting satellites detected the strongest gamma-ray burst (GRB) in modern history: GRB221009A. How strong was it? It caused electrical currents to flow through the surface of our planet. Dr. Andrew Klekociuk in Tasmania recorded the effect using an Earth Probe Antenna:

Note: Data from STIX have been flipped (increasing counts go down) to ease comparison of the two waveforms. NWC is a VLF transmitter in Australia.

The blue curve is a signal from Klekociuk’s antenna, which was sensing VLF (very low frequency) currents in the soil at the time of the blast. The orange curve shows the gamma-ray burst recorded by the high-energy STIX telescope on Europe’s Solar Orbiter spacecraft, one of many spacecraft that detected the event. The waveforms are a nearly perfect match.

“I am a climate scientist at the Australian Antarctic Division–that’s my day job,” says Klekociuk. “VLF is my hobby. I started doing VLF radio measurements in the 1970’s when I was in high school. This is the first time I have detected a gamma-ray burst.”

Klekociuk’s unusual “ham rig” uses Earth itself as a giant antenna. In his back garden there are two metal spikes stuck into the ground 75 meters apart. They are connected to a radio receiver via insulated buried wires. In recent years amateur radio operators have been experimenting with this weird kind of antenna to detect VLF radio signals circling our planet in the Earth-ionosphere waveguide. Earth’s crust forms one of the waveguide’s walls, allowing Earth Probe antennas to detect distant transmitters.

“During the gamma-ray burst I detected flickering from multiple stations,” says Klekociuk, who made this map showing transmission paths illuminated by the GRB:

NWC, VTX3, Mokpo and NML are VLF transmitters Klekociuk monitors using his Earth Probe Antenna. GRB effects were observed for all except NML, which was outside the radiation footprint.

Researchers have known since 1983 that gamma-ray bursts can ionize Earth’s atmosphere and, thus, disturb the great waveguide. This appears to be the first time anyone has recorded the effect using an Earth Probe Antenna.

The outburst on Oct. 9th shocked astronomers. Consider this tweet from Phil Evans of the University of Leicester in the immediate aftermath of the burst: “It’s bright. Really bright. Like, stupidly really bright.” Evans works with data from NASA’s Swift gamma-ray observatory, and the overflowing signal had apparently broken some of his plotting software.

Researchers have since pinpointed the burst. It came from a dusty galaxy 2.4 billion light years away, almost certainly triggered by a supernova explosion giving birth to a black hole. This is actually the closest GRB ever recorded, thus accounting for its extreme intensity.

The afterglow of GRB 221009A about an hour after it was first detected. Credit: NASA/Swift. [more]

“In our research group, we’ve been referring to this burst as the ‘BOAT’, or Brightest Of All Time, because when you look at the thousands of bursts gamma-ray telescopes have been detecting since the 1990s, this one stands apart,” says Jillian Rastinejad, an astronomer at Northwestern University who has been monitoring the burst’s afterglow using the Gemini South Telescope in Chile.

Meanwhile, other observers in the UK and Germany have also reported ionospheric disturbances resulting from the burst. They all used regular above-ground antennas.

2.4 billion light years away… Now that’s DXing.

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Lucy’s Super-Close Flyby on Earth

Oct. 15, 2022: Most spacecraft try to avoid hitting the atmosphere. Lucy is about to do it on purpose. On Oct. 16th, NASA’s Lucy spacecraft will skim Earth’s atmosphere, passing only 220 miles (350 kilometers) above our planet’s surface. Near closest approach over Australia it will be visible to the naked eye glowing almost as brightly as a 1st magnitude star.

This is a gravity assist maneuver–the first of three required for Lucy’s complicated mission to visit 8 different asteroids. The slingshot will give Lucy the energy it needs to fly towards the asteroid belt and, its ultimate destination, the orbit of Jupiter.

Named for a hominid fossil found in 1974 in Africa, Lucy is on a mission to study a completely different kind of relic: the Trojan asteroids. These are primitive leftovers from the formation of our solar system, collected into swarms around two of Jupiter’s Lagrange points. Sensors onboard the spacecraft will examine their appearance and composition, putting competing theories of planetary genesis to the test.

To reach the Trojans, Lucy must first return to Earth. Launched on Oct. 16, 2021, the spacecraft is coming home after exactly one year in space. Lucy’s trajectory will bring it deep into near Earth orbit, passing through a region full of Earth-orbiting satellites and debris. NASA will be ready to make last-minute adjustments to avoid collisions. The altitude is so low, the mission team had to include the effect of atmospheric drag when designing the flyby. Passing so close allows Lucy to extract maximum energy from Earth’s gravitational field.

On the left, the location in the sky where Lucy will first appear when it emerges from the Earth’s shadow for the Western United States. Red stars correspond to cities on the right.

Observers in western Australia will be the first to see Lucy. At around 10:55 UTC (6:55 p.m. local time) on Oct. 16th, the spacecraft will race overhead shining like a 1st or 2nd magnitude star. At the apex of its brightness, it will suddenly disappear into Earth’s shadow, vanishing at 11:02 UTC (7:02 p.m. local time).

Lucy will continue over the Pacific Ocean in darkness and emerge from the Earth’s shadow at 4:26 a.m. PDT (11:26 UTC). By that time it will have dimmed to 6th or 7th magnitude. Amateur astronomers in the western United States should be able to see Lucy using binoculars or a small telescope.

After the gravity assist, Lucy will recede from Earth, passing by the Moon and taking a few pictures before continuing out into interplanetary space. It might remain bright enough to see using backyard telescopes for more than 24 hours.

Want to see Lucy? You can spot the spacecraft using observing tips from the Southwest Research Institute. Ephemerides from JPL are recommended, too.

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