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Dark Gamma Ray Bursts

An artist’s conception of the environment around GRB 020819B based on ALMA observations. The GRB occurred in an arm of a galaxy in the constellation of Pisces (The Fishes). GRBs are huge explosions of a star spouting high-speed jets in a direction toward the observer. In a complete surprise, less gas was observed than expected, and correspondingly much more dust, making some GRBs appear as “dark GRBs”.

Gamma-ray bursts (GRBs) are intense bursts of extremely high energy observed in distant galaxies — the brightest explosive phenomenon in the Universe. Bursts that last more than a couple of seconds are known as long-duration gamma-ray bursts (LGRBs) and are associated with supernova explosions — powerful detonations at the ends of the lives of massive stars.

In just a matter of seconds, a typical burst releases as much energy as the Sun will in its entire ten-billion-year lifetime. The explosion itself is often followed by a slowly fading emission, known as an afterglow, which is thought to be created by collisions between the ejected material and the surrounding gas. However, some gamma-ray bursts mysteriously seem to have no afterglow — they are referred to as dark bursts. One possible explanation is that clouds of dust absorb the afterglow radiation.

  • More information: here

Credit: Bunyo Hatsukade(NAOJ), ALMA (ESO/NAOJ/NRAO)

christinetheastrophysicist:

NASA’s Swift satellite has detected a sudden burst of energy coming from our neighboring galaxy M31, the Andromeda Galaxy. It is unclear exactly what this is at the moment, either a gamma ray burst (GRB) or an ultra-luminous x-ray source (ULX), but both outcomes are very exciting, especially since this occurred so close to us.

If this energetic source turns out to be a gamma ray burst, it was likely created from a collision of neutron stars. If an ultra-luminousx-ray source, the cause would be a black hole consuming matter.

There is a lot of discussion about this happening on Twitter right now. Check out #GRBm31 for what astronomers and astrophysicists are saying.

More unfolding news on this HERE and HERE!

Related: previous posts on Gamma Ray Bursts (GRBs).

Going Nova: Star Explosions Unleash Gamma-Ray Blasts

Gamma-rays, the most powerful form of light, may erupt from star explosions called novas surprisingly often, but the way these gamma-rays form remains a mystery, scientists say.

High-energy gamma-rays are typically associated with supernovas, the explosive deaths of stars. These explosions are bright enough to momentarily outshine their entire galaxies.

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Relativistic jets and the Collapsar model

Gamma-ray bursts (GRBs) were first detected by American nuclear detection surveillance satellites in the late 1960s. The Vela spacecraft series were designed to monitor world-wide compliance with the 1963 Nuclear Test Ban Treaty. The satellites detected no clandestine nuclear explosions, but they discovered something far more interesting: powerful bursts of gamma rays emanating from random directions in space. By analyzing the different arrival times of the bursts as detected by different satellites, scientists concluded that the sources of the bursts were cosmic and not terrestrial or solar. The discovery was declassified and published in 1973 as an Astrophysical Journal article entitled “Observations of Gamma-Ray Bursts of Cosmic Origin”. This alerted the astronomical community to the existence of gamma-ray bursts (GRBs), now recognized as the most violent events in the universe.

To this day GRBs remain one of the greatest mysteries of modern astronomy. We know that GRBs lasting less than 2 seconds (short GRBs) may originate from a variety of processes. There are several theories that explain how the energy from a gamma-ray burst progenitor is turned into radiation. One hypothesis describing how long gamma-ray bursts originate is called the “collapsar" model: gamma-rays are generated when massive, spinning stars collapse to form black holes and spew out powerful jets of plasma at nearly the speed of light.These stellar collapses (collapsars) are thought to be similar to supernovae, except that a jet is produced by the accretion of stellar material onto a compact object formed at the center of the collapsing star. These jets are called ‘relativistic jets' and they can transport the energy from the collapsed core to large distances. Inside the jet, the uneven distribution of temperature, density and pressure create internal shock waves that move inward and outward as faster regions within the jet collide with slower ones. The collisions between the fast-moving gas and its surroundings, as well as within the jet itself, create gamma rays. When the jet hits the surrounding interstellar medium it produces another shock wave. This causes particles to rapidly lose energy (fast cooling), due to the strong magnetic field in the GRB emission region, through a process known as synchrotron radiation. This phenomenon is observed as long gamma-ray bursts and it’s followed by a so-called “afterglow”, a slowly fading emission that can be seen at all wavelengths; starting with X-rays, followed by ultraviolet, visible and infrared light, and eventually radio waves.The afterglow can last for days or even weeks.

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Credit: NASA’s Goddard Space Flight Center

Massive Burst of Light Soon After Big Bang Just Reached Earth

Intense light from the enormous explosion of a star more than 12 billion years ago — shortly after the Big Bang — recently reached Earth and was visible in the sky. Known as a gamma-ray burst, light from the rare, high-energy explosion traveled for 12.1 billion years before it was detected and observed by a telescope, ROTSE-IIIb, owned by Southern Methodist University. SMU physicists report that their telescope was the first on the ground to observe the burst and to capture an image, said Farley Ferrante, a graduate student in SMU’s Department of Physics, who monitored the observations along with two astronomers in Turkey and Hawaii.

Recorded as GRB 140419A by NASA’s Gamma-ray Coordinates Network, the burst was spotted at 11 p.m. April 19 by SMU’s robotic telescope at the McDonald Observatory in the Davis Mountains of West Texas.

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Detection of the Cosmic Gamma Ray Horizon: Measures All the Light in the Universe Since the Big Bang

May 24, 2013 — How much light has been emitted by all galaxies since the cosmos began? After all, almost every photon (particle of light) from ultraviolet to far infrared wavelengths ever radiated by all galaxies that ever existed throughout cosmic history is still speeding through the Universe today. If we could carefully measure the number and energy (wavelength) of all those photons — not only at the present time, but also back in time — we might learn important secrets about the nature and evolution of the Universe, including how similar or different ancient galaxies were compared to the galaxies we see today.

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Something Exciting Is Happening in the Andromeda Galaxy

NASA’s Swift satellite has detected a sudden burst of energy coming from our neighboring galaxy M31, the Andromeda Galaxy. It is unclear exactly what this is at the moment, either a gamma ray burst (GRB) or an ultra-luminous x-ray source (ULX), but both outcomes are very exciting, especially since this occurred so close to us.

If this energetic source turns out to be a gamma ray burst, it was likely created from a collision of neutron stars. If an ultra-luminousx-ray source, the cause would be a black hole consuming matter.

There is a lot of discussion about this happening on Twitter right now. Check out #GRBm31 for what astronomers and astrophysicists are saying.

What is a Gamma Ray Burst?

We define a gamma-ray burst based on its observational properties: an intense flash of gamma rays, lasting anywhere from a fraction of a second to up to a few minutes.

Gamma-ray bursts have a few other common features. We believe them to be beamed - the energy does not escape from the explosion everywhere equally, but is focused into a narrow jet (or more likely, two oppositely-directed jets.) The burst itself is also normally followed by a much longer-lived (but also much fainter) signal, visible at optical and other wavelengths. This so-called “afterglow”, discovered only in the 1990s, allows us to pinpoint the origin of the GRB - something not possible from the short-lived gamma-ray signal alone.1

History

Cosmic gamma ray bursts (GRBs) were discovered by accident in the late 1960’s by satellites designed to detect gamma rays produced by atomic bomb tests on Earth. The GRBs appear first as a brilliant flash of gamma rays, that rises and falls in a matter of minutes. These bursts are often followed by afterglows at X-ray, optical and radio wavelengths.

A major leap forward in understanding the source of cosmic GRBs was made when the Burst and Transient Source Experiment (BATSE) was launched aboard the Compton Gamma Ray Observatory in 1991.

BATSE had an all-sky monitor that was capable of detecting a GRB virtually anywhere in the sky. Over a period of 9 years BATSE recorded thousands of GRBs, about 1 per day. Among other things, these results showed that the bursts occurred at random all over the sky. If the bursts were associated with objects in our Milky Way Galaxy, they would not show such a universal distribution. Rather, they would be concentrated along the plane of our galaxy like most of the matter in the Milky Way. The BATSE data was so good that it allowed astronomers to also rule out the possibility that the GRBs might be originating in the halo of our galaxy.2

GRB Progenitors

Black Holes

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The most powerful explosions in the universe are caused by the births of black holes rather than dense neutron stars called magnetars, new evidence confirms.4

White Dwarfs

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Very old compact stars called white dwarfs are known to flare as well, but the amount of energy is not enough to explain distant GRBs.  Other GRB progenitors include neutron stars (magnetar, pulsars or a hybrid), starquakes, cannonballs or strange stars (stars composed of strange matter).Wolf-Rayet stars have also been proposed.7

http://astro.berkeley.edu/research/grbs/grbinfo.html

http://chandra.harvard.edu/xray_sources/grb.html

https://en.wikipedia.org/wiki/File:BH_LMC.png

http://www.newscientist.com/article/dn19681-most-powerful-gammaray-bursts-linked-to-black-holes.html

https://en.wikipedia.org/wiki/File:Sirius_A_and_B_Hubble_photo.jpg

http://www.space.com/3724-alternative-theories-gamma-ray-bursts.html

http://cds.cern.ch/record/482530/files/0012512.pdf