Gamma Ray Bursts

[Astronuc]

Gamma-ray bursts are short-lived bursts of gamma-ray photons, the most energetic form of light. At least some of them are associated with a special type of supernovae, the explosions marking the deaths of especially massive stars.

Lasting anywhere from a few milliseconds to several minutes, gamma-ray bursts (GRBs) shine hundreds of times brighter than a typical supernova and about a million trillion times as bright as the Sun, making them briefly the brightest source of cosmic gamma-ray photons in the observable Universe. GRBs are detected roughly once per day from wholly random directions of the sky.

http://imagine.gsfc.nasa.gov/docs/science/know_l1/bursts.html

Using Swift observations of prompt and afterglow emission to classify GRBs
http://arxiv.org/abs/astro-ph/0701811

We present an analysis of early BAT and XRT data for 107 gamma--ray bursts (GRBs) observed by the Swift satellite. We use these data to examine the behaviour of the X-ray light curve and propose a classification scheme for GRBs based on this behaviour. As found for previous smaller samples, the earliest X-ray light curve can be well described by an exponential which relaxes into a power law, often with flares superimposed. The later emission is well fit using a similar functional form and we find that these two functions provide a good description of the entire X-ray light curve. For the prompt emission, the transition time between the exponential and the power law gives a well-defined timescale, T_p, for the burst duration. We use T_p, the spectral index of the prompt emission, beta_p, and the prompt power law decay index, alpha_p to define four classes of burst: short, slow, fast and soft. Bursts with slowly declining emission have spectral and temporal properties similar to the short bursts despite having longer durations. Some of these GRBs may therefore arise from similar progenitors including several types of binary system. Short bursts tend to decline more gradually than longer duration bursts and hence emit a significant fraction of their total energy at times greater than T_p. This may be due to differences in the environment or the progenitor for long, fast bursts.

[Astronuc]

Gamma-Ray Bursts

http://heasarc.gsfc.nasa.gov/docs/objects/grbs/grbs.html

http://heasarc.gsfc.nasa.gov/docs/objects/grbs/grbs.html#Spectra

[Astronuc]

Some links to sites on Gamma Ray Bursts

http://www.batse.msfc.nasa.gov/events/5hgrbs/info/soc.html

http://www.mpe.mpg.de/~jcg/grbgen.html

Here you find some information on the results of GRBs which have been localized within a few hours to days to less than 1 degree by the following instruments and procedures: detection by the BeppoSAX GRBM and imaging in the BeppoSAX WFC; detection by BATSE and subsequent scanning observations by the RXTE/PCA; detection by BATSE and quasi-simultaneous localization by RXTE/ASM scans; triangulation by the Interplanetary Network (IPN); imaging by HETE and INTEGRAL.

http://space.mit.edu/HETE/Bursts/

http://gcn.gsfc.nasa.gov/gcn/hete_grbs.html

http://www.ssl.berkeley.edu/ipn3/masterli.html

[Astronuc]

http://www.nasa.gov/centers/goddard/news/topstory/2007/intergalatic_shot.html
GRB 070125

A team of astronomers has discovered a cosmic explosion that seems to have come from the middle of nowhere ? thousands of light-years from the nearest galaxy-sized collection of stars, gas, and dust. This "shot in the dark" is surprising because the type of explosion, a long-duration gamma-ray burst (GRB), is thought to be powered by the death of a massive star.

"Here we have this very bright burst, yet it's surrounded by darkness on all sides," says Brad Cenko of the California Institute of Technology, Pasadena, Calif., lead author of the team's paper, which has been accepted for publication in The Astrophysical Journal. "The nearest galaxy is more than 88,000 light-years away, and there's almost no gas lying between the burst and Earth."

The blast was detected on January 25, 2007, by several spacecraft of the Inter-Planetary Network. Observations by NASA's Swift satellite pinpointed the explosion, named GRB 070125 for its detection date, to a region of sky in the constellation Gemini. It was one of the brightest bursts of the year, and the Caltech/Penn State team moved quickly to observe the burst?s location with ground-based telescopes.

Using the team's robotic 60-inch telescope at Palomar Observatory in Calif., the astronomers discovered that the burst had a bright and fast-fading afterglow in visible light. This prompted them to observe the afterglow in detail with two of the world's largest telescopes, the 8-meter Gemini North telescope and 10-meter Keck I telescope, both near the summit of Hawaii's Mauna Kea.

  Pretty cool!  Very interesting that it appears outside the nearest known galaxy!

[alokmohan]

Alokmohan  back.web  slow.