Swift Observes An Unusual Bang In The Far Universe

Almost 40 years have passed since top secret nuclear weapon warning satellites accidentally discovered bursts of high energy gamma rays coming from space. Although many thousands of gamma ray bursts (GRBs) have since been detected, the origin and nature of these bursts is still not well understood.

One example of an unusual gamma ray burst occurred on 1 August 2005, when instruments on board the NASA-UK-Italy Swift spacecraft detected a bizarre GRB, which displayed unprecedented behaviour. Results based on the Swift data were presented yesterday at the RAS National Astronomy Meeting in Leicester by Massimiliano De Pasquale from Mullard Space Laboratory-UCL.

Gamma ray bursts take the form of a brilliant burst of radiation, followed by a slowly fading afterglow. This shallow decay in the X-ray and optical light curve usually lasts for several days after the high energy explosion.

Swift data have shown that, whatever the ‘central engine’ that powers the GRB may be, it does not switch off after a few seconds, but often produces fast flares of radiation and injects energy into the outflow for hours.

Scientists believe that most GRBs are thought to be the result of a black hole swallowing a large star. This process might take long enough to explain both the prompt emission of X-rays and gamma rays, the late flares and energy injection.

The remaining matter is launched outwards at a huge velocity, but the interstellar medium around the burst acts like a “brake” to this outflow, being heated in the process and producing the afterglow emission.

In the case of the August 2005 gamma ray burst, known as GRB050801 after its date of detection, there was a bright afterglow with a steady emission both in X-ray and optical wavelengths, without any initial, brilliant flare. This behaviour lasted for only 250 seconds after the end of the prompt emission, before the afterglow began the typical decline in brightness. This behaviour has never been observed before.

The flat emission both in X-ray and optical wavelengths gives some hints about the ‘central engine’ of this GRB.

“This feature might be explained if we assume that, rather than a black hole, the core of the star has shrunk its mass and its magnetic field into an object known as a magnetar,” said Massimiliano De Pasquale.

A magnetar is a form of neutron star, the remains of a collapsed star that was originally about 10 times more massive than the Sun. This extremely dense object typically has a radius of only 10 km but the same mass of the Sun.

Magnetars are thousands of times more magnetic than ordinary neutron stars, with a magnetic field 1,000 million million times stronger than the Earth’s. Only a few of these exotic objects are known.

“Such an object initially rotates very quickly, typically hundreds of times every second, but it slows down by irradiating its energy at the magnetic poles, like a lighthouse,” said De Pasquale. “This would keep the afterglow emission steady for a time scale similar to that observed for GRB 050801.

The joint analysis of data from the XRT and UVOT instruments on Swift has also allowed the team to determine the distance of GRB050801, which was previously unknown, by measuring the amount of light absorbed during its intergalactic travel en route to the Earth.

It turns out that the burst took place 9 billion light-years away, which means that the gamma rays, X-rays and light from the gamma ray burst were created and began their journey across the universe 4,500 million years before the Earth was born.

“The explosion produced the same amount of energy as the Sun produces during its entire lifetime of 10 billion years,” said Massimiliano De Pasquale.

Source: Royal Astronomical Society

Related stories:

Faint gamma-ray bursts do actually exist
(PhysOrg.com) -- Gamma-ray bursts, powerful glares of high-energy that wash through the Universe once every day or so are, for a brief time, the brightest objects in the gamma-ray sky. ESA’s Integral gamma-ray observatory has observed several low-luminosity gamma-ray bursts, confirming the existence of an entire population of weaker bursts hardly noticed so far.
Cosmic strings might emit cosmic sparks, answer cosmological questions
(PhysOrg.com) -- For astronomers, understanding what happened in the early moments of the universe could answer many questions in physics and astronomy. One possible player in the early universe is cosmic strings, which arise naturally in particle physics models. However, cosmic strings are quite strange hypothetical entities: they’re thinner than a proton, but can be as long as the universe. Cosmic strings might have formed as imperfections when the early universe was undergoing drastic phase changes.
A Star That Bursts, Blinks and Disappears
(PhysOrg.com) -- "Twinkle, twinkle little star" goes the nursery rhyme. Now, astronomers are reporting on a strange case where one of the littlest of stars "twinkled" with gamma rays, X-rays, and light -- and then vanished.
GLAST Burst Monitor Team Hard at Work Fine Tuning Instrument and Operations
(PhysOrg.com) -- While only on orbit for 40 days and still in the process of a two-month checkout, NASA's Gamma-ray Large Area Telescope (GLAST) has already detected 12 powerful gamma-ray bursts, an encouraging harbinger of good things to come for this mission. The gamma-ray bursts were detected by the GLAST Burst Monitor (GBM), one of two instruments on the spacecraft.
NASA GLAST Burst Monitor Powers Up Successfully
NASA’s GLAST Burst Monitor (GBM) Instrument Operations Center in Huntsville, Ala., the focal point for observing gamma ray bursts, was alive with energy as scientists gathered to witness instrument activation the evening of June 25. The GBM team linked in with GLAST mission operations at NASA’s Goddard Space Flight Center in Greenbelt, Md., by teleconference and studied a big screen projecting spacecraft information live.
Excitement Builds as GLAST Readies Its Gamma-ray Vision
Scientists around the world are excited about all the things that the Gamma-ray Large Area Space Telescope, or GLAST, is going to uncover after it launches on June 5 from Cape Canaveral Air Force Station, Fla.
Swift satellite catches first 'normal' supernova in the act of exploding
Thanks to a fortunate observation with NASA's Swift satellite, astronomers, for the first time, have caught a normal supernova at the moment of its birth--the first instant when an exploding star begins spewing its energy into space, transforming into a supernova that during its brief lifetime will shine brighter than billions of stars combined.
Powerful antenna attached to NASA's GLAST satellite
The powerful antenna system that will enable NASA's Gamma-ray Large Area Telescope (GLAST) to communicate with stations on Earth has been successfully connected to the spacecraft in the Astrotech payload processing facility near NASA's Kennedy Space Center, Fla.

News discussion:

Space & Earth science news