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Gamma Ray Bursts (GRBs) are among the most energetic phenomena astronomers regularly observe. These events are triggered by massive explosions and a large amount of the energy if focused into narrow beams that sweep across the universe. These beams are so tightly concentrated that they can be seen across the visible universe and allow astronomers to probe the universe’s history. If such an event happened in our galaxy and we stood in the path of the beam, the effects would be pronounced and may lead to large extinctions. Yet one of the most energetic GRBs on record (GRB 080607) was shrouded in cloud of gas and dust dimming the blast by a factor of 20 – 200, depending on the wavelength. Despite this strong veil, the GRB was still bright enough to be detected by small optical telescopes for over an hour. So what can this hidden monster tell astronomers about ancient galaxies and GRBs in general?
GRB 080607 was discovered on June 6, 2008 by the Swift satellite. Since GRBs are short lived events, searches for them are automated and upon detection, the Swift satellite immediately oriented itself towards the source. Other GRB hunting satellites quickly joined in and ground based observatories, including ROTSE-III and Keck made observations as well. This large collection of instruments allowed astronomers, led by D. A. Perley of UC Berkley, to develop a strong understanding of not just the GRB, but also the obscuring gas. Given that the host galaxy lies at a distance of over 12 billion light years, this has provided a unique probe into the nature of the environment of such distant galaxies.
One of the most surprising features was unusually strong absorption near 2175 °A. Although such absorption has been noticed in other galaxies, it has been rare in galaxies at such large cosmological distances. In the local universe, this feature seems to be most common in dynamically stable galaxies but tends to be “absent in more disturbed locations such as the SMC, nearby starburst galaxies” as well as some regions of the Milky Way which more turbulence is present. The team uses this feature to imply that the host galaxy was stable as well. Although this feature is familiar in nearby galaxies, observing it in this case makes it the furthest known example of this phenomenon. The precise cause of this feature is not yet known, although other studies have indicated “polycyclic aromatic hydrocarbons and graphite” are possible suspects.
Earlier studies of this event have shown other novel spectral features. A paper by Sheffer et al. notes that the spectrum also revealed molecular hydrogen. Again, such a feature is common in the local universe and many other galaxies, but never before has such an observation been made linked to a galaxy in which a GRB has occurred. Molecular hydrogen (as well as other molecular compounds) become disassociated at high temperatures like the ones in galaxies containing large amounts of star formation that would produce regions with large stars capable of triggering GRBs. With observations of one molecule in hand, this lead Sheffer’s team to suspect that there might be large amounts of other molecules, such as carbon monoxide (CO). This too was detected making yet another first for the odd environment of a GRB host.
This unusual environment may help to explain a class of GRBs known as “subluminous optical bursts” or “dark bursts” in which the optical component of the burst (especially the afterglow) is less bright than would be predicted by comparison to more traditional GRBs.
Sources:
Monster in the Dark: The Ultra Luminous GRB 080706 and its Dusty Environment
The Discovery of Vibrationally-Excited H2 In the Molecular Cloud Near GRB 080706
It is interesting that gamma-ray bursts were detected serendipitously by the Vela satellites, which were built to detect covert nuclear weapon tests in space by the Soviet Union. The first detection of a GRB were made by the Vela 3 and Vela 4 satellites on July 2, 1967, at 14:19 UTC, but it was ignored because the operators at Los Alamos Scientific Laboratory were uncertain as to what had happened. Eventually, after the Los Alamos team continued to find inexplicable gamma-ray bursts in their data from additional satellites with better instruments, they determined that the sources of the GRBs had not been of terrestrial or solar origin. The discovery was then declassified and published in 1973 as an Astrophysical Journal article entitled “Observations of Gamma-Ray Bursts of Cosmic Origin”.
Oh, I almost forgot… at the first line, since the reference to gamma-ray bursts is plural, it should be the plural phenomena, not the singular “phenomenon”.
Also, at the penultimate paragraph, in the fifth line, disassociated is misspelled.
🙂
I see a bud leaf.
I’m a co-author on this paper!!!! Awesome!!!!
By the way, it’s true that the host is over 4 billion ly away, but that’s like saying San Francisco is over 500 miles from New York…
Thanks for the corrections Ivan. My spellcheck doesn’t know disassociated regardless of how I spell it and thanks to dyslexia, I have trouble catching extra floating letters like that.
Don: Based on the redshift listed in the most recent paper the distance according to my conversion was 4.1 Gly. I rounded down a little, but it’s not the understatement you imply unless my calculations were wrong. I’ll double check them in a bit.
So, dust shrouds, huh? I pick the PAH model for now, because it is more exciting.
@ Don: Congrats! Speak of chemical data with “outreach”. 😀
Me too! Isn’t it supposed to be mostly faces? This is more “budeidolia”.
The interstellar medium is believed to contain the majority of gaseous heavier elements then helium that freeze out onto dust grains, representing a significant total interstellar galactic mass. The identity of the carrier is still unknown although PAH and graphite is likely. Can the 2175 A absorption bump be the dust extinction signature of graphite dust, or carbon nanoparticles like recent buckyballs discovered, that are interacting with radiation? Carbon monoxide forms when ice absorbed on carbonaceous material is irradiated into polar CO- . Carbon the third most abundant element in the universe, is much heavier molecular weight then H and He, could explain the 90 percent dark matter gravity halo mass of galaxies, imo.
I see coniferous trees. I’m not a druggie. :d
Who made the pic? Some artist or telescope? Or both?
Was GRB created by a star. Couldn’t it be a black hole?
I see a double rainbow all the way! 🙂
Great article, Jon!
Implying we are? As a fact, the first time I saw the ikon was on a beer bottle. [Yes, it was that bad.]
Don: Thanks for the heads up on the distance. I redid my calculations and got a new distance of a bit over 12 Gly. That match up better with what you’d gotten?
Jon: Well, speaking of a “distance” is always a very hairy issue in cosmology. Assuming the standard First Year WMAP cosmological paramteres, Ned Wright’s Cosmology Calculator gives me a LOOKBACK TIME of 11.5 Gy for z = 3.036. I guess this is what you call “distance”. The actual luminosity distance is 85 Gly… (this is the distance the object has from us NOW).
Headroundu: It’s an artist’s impression. And the GRB was created by massive star that collapsed into a black hole.
“the spectrum also revealed molecular hydrogen. … this lead Sheffer’s team to suspect that there might be large amounts of other molecules, such as carbon monoxide (CO). ”
Do I remember correctly, that H2 is virtually undetectable and that CO is used as a marker, relying on the hypothesis that H2 always contains traces of CO?
What would be the meaning of that paragraph then?
Nice article John but ” this lead Sheffer’s team to suspect ” should be “this led…”, unless you are referring to the metal element 🙂
@Manu: Actually, it’s only cold H2 that’s basically invivisible and is traced by CO. These lines are vibration excitations, and they form a forest in the UV. See the figures in Sheffer’s work.
Hey Ivan, who cares about a few spelling errors? Get a life!
@Don Alexander: thanks a lot!