Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

More about that gamma burst (the brightest ever recorded)

  1. Oct 14, 2008 #1


    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    Gamma-Ray Burst at the extreme: "the naked-eye burst" GRB 080319B
    P.R. Wozniak, W.T. Vestrand, A.D. Panaitescu, J.A. Wren, H.R. Davis, R.R. White (Los Alamos National Laboratory)
    accepted for publication in Astrophysical Journal
    (Submitted on 14 Oct 2008)

    "On 19 March 2008, the northern sky was the stage of a spectacular optical transient that for a few seconds remained visible to the naked eye. The transient was associated with GRB 080319B, a gamma-ray burst at a luminosity distance of about 6 Gpc (standard cosmology), making it the most luminous optical object ever recorded by human kind. We present comprehensive sky monitoring and multi-color optical follow-up observations of GRB 080319B collected by the RAPTOR telescope network covering the development of the explosion and the afterglow before, during, and after the burst. The extremely bright prompt optical emission revealed features that are normally not detectable. The optical and gamma-ray variability during the explosion are correlated, but the optical flux is much greater than can be reconciled with single emission mechanism and a flat gamma-ray spectrum. This extreme optical behavior is best understood as synchrotron self-Compton model (SSC). After a gradual onset of the gamma-ray emission, there is an abrupt rise of the prompt optical flux suggesting that variable self-absorption dominates the early optical light curve. Our simultaneous multi-color optical light curves following the flash show spectral evolution consistent with a rapidly decaying red component due to large angle emission and the emergence of a blue forward shock component from interaction with the surrounding environment. While providing little support for the reverse shock that dominates the early afterglow, these observations strengthen the case for the universal role of the SSC mechanism in generating gamma-ray bursts."

    they give the luminosity distance as about 20 billion lightyears. (6 Gpc) comments?
    Last edited: Oct 14, 2008
  2. jcsd
  3. Oct 14, 2008 #2
    Well, certainly accents the need for a decent sized dedicated scope to point at these guys for followup spectra and imaging. LSST will pick them up, but there is no spectrograph on it. Most of the spectra of the GRB afterglows come from other observations on the bigger scopes getting interrupted to go after the afterglow. This is a problem as telescope time is precious, expensive, and extremely hard to get these days. A good 6.5m scope with a good spectrograph dedicated to go after transients when there are ones, and perhaps other deep surveying when not would be a winner for sure.
  4. Oct 14, 2008 #3


    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    just some random additional info:
    at the bottom of page 3, you see they found the redshift to be z = 0.937
    and they assumed standard cosmology (matter, cc, Hubble = 0.27, 0.73, 71 )
    so lets get the presentday distance
    putting 0.937 into Wright's calculator
    gives the same figure that they have for the luminosity distance (that is how you relate the observed flux watts/m^2
    to the flux at the source---the luminosity)

    and also it says the present distance to the object is 10.3 billion lightyears, and the light travel time was 7.5 billion years.
    Last edited: Oct 14, 2008
  5. Oct 14, 2008 #4
  6. Oct 15, 2008 #5
    Here’s some background on RAPTOR, SWIFT and Gamma Ray Bursts.




    In James Kaler’s book “Extreme Stars” he addresses what he labels Hypergiants. Normally large stars, like Red Supergiants (RSG) or Large Blue Variables (LBV) fuse hydrogen into heavier so called metallic elements like helium, carbon, nitrogen and oxygen. This fusion releases energy according to Einstein’s equation. This energy counteracts the enormous gravity of these giants to keep the star from collapsing totally. However, once iron is created at the core, this process stops. It takes more energy to fuse lighter elements into iron than is released by this process. At this point, the outer layers of the star collapse inward and bounce off the iron core, creating a shock wave ending in some form of nova. Depending on the force of the inward collapse, several outcomes can occur. If the iron core is squeezed to the point that the atom’s electrons are as tightly packed as is possible (called electron degeneracy), then a white dwarf star is the result. If the protons and electrons are crushed together into neutrons, then the star pretty much becomes an atomic nucleus the size of a city, called a neutron star. Finally, the core can become a singularity in a black hole.
    Hypergiant stars don’t follow this path. The core of a hypergiant is so compact that in addition to normal fusion, particle pairs are also created in abundance. At some critical point, particle-antiparticle pairs are annihilating at such a rate that the resulting gamma rays superheat the star’s core and it erupts (pair instability). The energy of this eruption tears the star apart from the core outwards. No core mass remains to implode into anything else. This is a candidate for the energy input that sparks the Synchrotron Self-Compton effect (SSC) mentioned in the above paper.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: More about that gamma burst (the brightest ever recorded)
  1. Gamma bursts (Replies: 13)

  2. Gamma Ray Bursts (Replies: 5)

  3. Gamma Ray Bursts (Replies: 7)