#grbs

Gamma-Ray Bursts (GRBs)

Gamma-Ray Bursts (GRBs) are bursts of highly energetic gamma rays lasting from less than a second to several minutes – the blink of an eye on cosmological timescales. They are known to occur at huge distances from Earth, towards the limits of the observable Universe.

The VLT has observed the afterglow of a Gamma-Ray Burst that is the farthest known ever. With a measured redshift of 8.2, the light from this very remote astronomical source has taken more than 13 000 million years to reach us. It is thus seen when the Universe was less than 600 million years old, or less than five per cent its present age. It must have released 300 times as much energy in a few seconds as our Sun will in its entire lifetime of more than 10 000 million years. GRBs are therefore the most powerful explosions in the Universe since the Big Bang.

Researchers have tried to discover the nature of these explosions for a long time. Observations show that GRBs come in two types – short-duration (shorter than a few seconds), and long-duration – and it was suspected that two different kinds of cosmic event caused them.

In 2003, astronomers using ESO telescopes played a key role in linking long-duration GRBs with the ultimate explosions of massive stars, known as 'hypernovae'. By following the aftermath of an explosion for a whole month, they showed that the light had similar properties to that from a supernova, caused when a massive star explodes at the end of its life.

In 2005, ESO telescopes detected, for the first time, the visible light following a short-duration burst. By tracking this light for three weeks, astronomers showed that the short-duration bursts – unlike the long-duration ones – could not be caused by a hypernova. Instead, it is thought that they are caused by the violent mergers of neutron stars or black holes. 

Image credit: (NASA Cruz deWilde)

Nuevas evidencias revelan un misterioso fenómeno astronómico que desafía totalmente nuestra comprensión del universo ¡No podrás creer lo que los científicos han encontrado! El Misterioso Fenómeno Astronómico El Descubrimiento: Científicos de todo el mundo han detectado un fenómeno astronómico sorprendente que ha capturado la atención de la comunidad científica y del público en general. Enormes…

Otra misteriosa señal cósmica vuelve a sorprender a los astrónomos

ABC.es

Un misterioso y potentísimo «flashazo» de rayos X acaba de ser detectado por el equipo de investigadores que opera el observatorio Chandra

Localización de la enigmática fuente de rayos X – NASA/CXC/F. Bauer et al

El Universo está lleno de señales que los científicos, sencillamente, no alcanzan a comprender. Señales tan energéticas y potentes que pueden ser captadas desde la Tierra incluso…

New Post has been published on http://www.newsnish.com/technology/science/shocks-in-a-distant-gamma-ray-burst-help-reveal-two-general-types-of-grbs/

Shocks in a Distant Gamma-Ray Burst Help Reveal Two General Types of GRBs

Gamma ray bursts (GRBs)–flashes of high-energy light occur about once a day, randomly, from around the sky–are the brightest events in the known universe. While a burst is underway, it is many millions of times brighter than an entire galaxy.

Shocks in a Distant Gamma-Ray Burst Help Reveal Two General Types of GRBs

Astronomers are anxious to decipher their nature not only because of their dramatic energetics, but also because their tremendous brightness enables them to be seen across cosmological distances and times, providing windows into the young universe.

There appear to be two general types of GRBs: those associated with the deaths of massive stars, and ones believed to originate from the coalescence of two extreme objects (neutron stars or black holes) that had been orbiting each other in a binary system. In general the two types can be distinguished by the lengths of their bursts, the former lasting longer than a few seconds, while the latter are briefer.

Astronomers think that, despite the differences, both kinds of GRBs have hot discs accreting material leading to the production of bipolar jets of charged particles moving at relativistic speeds. In the standard model, shocks internal to the fireball produce the gamma-rays in the first (longer duration) case, while shocks from the jets’ interactions with the external medium produce the initial burst of gamma-rays in the second case.

Many details are similar in both scenarios, however, while some others vary according to the type, and astronomers have been trying to constrain these various parameters so that they can trace the origin of each GRB more precisely.

CfA astronomer Raffaella Margutti and her colleagues used several ground-based telescopes to follow-up a GRB event that went off in June of 2014, examining the afterglow from about three days after the detection to about one hundred and twenty days later. They conclude that the burst is associated with a massive star’s death (a supernova), but find that some of its emission apparently results from shocks external to the fireball as are seen in the less luminous class of GRBs.

The results are consistent with the predictions of supernova modeling, but the fact that this object spans both classes highlights the complexity of the sometimes-overlapping physical processes at work and the importance of observations at multiple wavelengths.

New Outburst From V404 Cygni

What looks like a shooting target is actually an image of nested rings of X-ray light centered on an erupting black hole. On June 15, NASA’s Swift satellite detected the start of a new outburst from V404 Cygni, where a black hole and a sun-like star orbit each other. Since then, astronomers around the world have been monitoring the ongoing light show.

On June 30, a team led by Andrew Beardmore…