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A new theory on GRB


In a study of Arxiv , Hancock, Gaensler and Murphy doubt that a GRB is followed radio emission , but this would depend on the origin of gamma-ray burst. A new hypothesis that we can verify only continuing to GRBs study.

grb

 Source: www.nasa.gov

Who is interested in the gamma-ray bursts and follows the circular GCN (Gamma-ray Coordinates Network) knows that every gamma-ray burst detected by the telescope BAT ( Burst Alert Telescope) SWIFT follows the revelation by the telescope XRT (X-Ray Telescope), always on board SWIFT, luminescence X that can be more or less bright, can have or not episodes of restrike, but it is always characterized by a decrease of the flow that goes out in a matter of hours, days, weeks or months.

The non-detection of counterparty X is truly exceptional and almost always depends on the inability to focus a specific area of ​​the sky because it is too close to the Sun, the Moon, etc. All things considered, the probability that a gamma-ray burst has a counterpart X exceeds 95%, and then it is reasonable to assume that all bursts have a counterpart X. In parallel with the X-ray observations, SWIFT collects UV and optical images through a small optical telescope ultraviolet, called UVOT. However, the limited size of UVOT did not make the ideal tool to study the optical counterparts of GRBs and only the brightest optical flashes are revealed while all other, far more numerous , the GCN carry the phrase “no credible counterpart has been found” (by UVOT ) .

More fortunate in the hunt optical counterparts are much larger ground-based telescopes, and therefore more sensitive. Years of effort devoted to the automation of the operations of many telescopes allow you to make optical observations immediately after the detection of a GRB alert. This always best “readiness”, combined with the particular pains to try to aim SWIFT in areas accessible to observers on the ground, has increased over the years, the number of gamma-ray bursts detected by optical and now stands at around 70%. Experts point out that, when the optical observations from the ground begin within 4 hours of GRBs, the success rate is around 90%.

And on the radio? Readers of GCN know that the revelation of GRBs in radio is rarer and they are often reported upper limits. The revelations are not due to lack of interest by radio astronomers. Each gamma-ray burst detected by Swift and positioned with precision thanks to the image X is also being studied by radio telescopes.

It’s a problem of sensitivity? This is the question that placed Hancock, Gaensler and Murphy and their response (strangely) in the negative. They used data collected by the VLA 178 gamma-ray bursts by applying the technique of stacking. Working with the sum of all the images related to GRB unrevealed they realized that no effort could also make out a faint emission. It seems clear that there are two types of gamma-ray bursts: those who have radio emission and those who do not have it. It remains to understand what causes this different behavior. According to the authors, the difference is due to some intrinsic mechanism to the GRB engine that suppresses radio emission.

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