# Gamma-Ray Burst Aimed Directly at Earth

A massive gamma-ray burst detected last March, believed to be the brightest ever seen, turns out to have been aimed directly at the Earth. A narrow jet that drove material toward us at 99.99995 of the speed of light is revealed in the data, itself wrapped within a somewhat slower and wider jet. The best estimates are that an alignment like this occurs only once every ten years. Says Paul O’Brien (University of Leicester, and a member of the team working on the Swift satellite):

“We normally detect only the wide jet of a GRB as the inner jet is very narrow, equivalent to not much more than 1/100th the angular size of the full Moon. It seems that to see a very bright GRB the narrow jet has to be pointing precisely at the Earth. We would expect that to happen only about once per decade. On March 19th, we got lucky.”

It could be said that any information we get about GRBs is in a sense lucky, given how tricky are the constraints for observing them. And indeed, another GRB just degrees away from this one was already under observation when the big blast went off, making it hard to miss. But wherever the GRB, the Swift satellite is making it possible to gather data from it, finding the original explosion and quickly alerting optical telescopes on Earth — so that they can begin observing within minutes. In this case, the blast was so intense that it temporarily blinded Swift’s X-Ray Telescope and UltraViolet/Optical Telescope, and its visible light was quickly being examined by wide-field cameras in Chile.

Image: This artist’s concept shows the “naked-eye” GRB close up. Observations suggest material shot outward in a two-component jet (white and green beams). Credit: NASA/Swift/Mary Pat Hrybyk-Keith and John Jones.

All of this gives us the opportunity to study a GRB from gamma-ray to radio wavelengths, examining what happened to one massive star that exhausted its fuel. GRB 080319B seized the attention of the world when it became clear that the burst was actually bright enough to be visible to the unaided eye, cresting at a magnitude of 5.3 even though the star that spawned it was located over 7.5 billion light years away. The bright afterglow is the result of the gas jets muscling out from the collapsing stellar core, striking gas the star had previously shed and heating it.

The paper is Racusin et al., “GRB 080319B: A Naked-Eye Stellar Blast from the Distant Universe,” slated for publication in Nature tomorrow and available here.

Addendum: Interesting comment by Alex Filippenko (UC Berkeley) in a just arrived news release (not yet up on the Berkeley site): If the supernova that produced this GRB were located 6000 light years from us, the event would have appeared as bright as the Sun. Filippenko calls it “…the most powerful event ever seen in human existence.”

Comments on this entry are closed.

• James M. Essig September 10, 2008, 20:05

Hi Paul;

My God! As bright as the Sun at 6,000 light-years.

My brother John and I work in the field of solar concentrators, albeit, non-precise ones for solar cooking and other purposes requiring concentrated solar energy. At 600 light-years, because of the inverse square law of beam cross-section, the concentration of supernova energy would be equal to 100 Suns. My brother John and I where able to ignite firewood in about 5 to 10 seconds under approximately 80 Suns concentration as well as overcook fresh refrigerated steaks in about 5 minutes. At 60 light-years, the concentration would be 10,000 Suns or equal to a blackbody emitter at 3,000 K to 4,000 K or greater depending on the absorptivity of the surface for which such radiant energy flux impinges. This is the equivalent of full exposure to an oxy-acetylene blow torch which can cut through the most refractive alloys in common use in industry.

Now if we could only duplicate such energy sources in distant future cosmic or at least stellar scale engineering projects, we could for all practical purposes have unlimited gamma factor interstellar travel.

Thanks;

Jim

• Bart Colombo September 10, 2008, 21:42

I’ve heard that GRB’s are unlikey to occur in our galaxy due to its metal content. Anyone have any information on this?

• Benjamin September 11, 2008, 2:33

I’m less optimistic than James about the wattage you’d get at close range. I wouldn’t want one of these GRBs to go off anywhere near Earth, and if one did, we would be effectively wiped out, as James’ numbers show: 600 light years in all directions is a huge volume, and if we would get 100 suns power at that distance, I’d hate to think what that would do to us down here on earth, let alone the satellites we have in orbit or any other space-based systems, or for instance the prospect of damaging our energy supplies by overloading solar collectors. Would this be strong enough to burn or kill unprotected humans? If so, add half the Earth’s population to that total.

Now if you get to 60 light years, which still encompasses a vast number of celestial objects, going on James’ calculation again, I can’t see any life in the solar system surviving. I’m curious in a morbid sort of way as to whether anything could survive on the other side of the planet, if one half was irradiated to the point of ionisation.

Here’s an idea for a science fiction story: a GRB occurs at an intermediate distance, enough to sterilise any life exposed but not strong enough to cause great physical damage to the Earth. This is bad enough. What is especially interesting is that it is eclipsed by the Moon, leading to a nice round part of the earth escaping its worst effects.

I’d imagine that anyone who was particularly religious in this region would immediately see this as a miracle showing that they are right, and the other major religions, whose populations are presumably devastated, are definitively proven wrong. The survivors of the rest of the world – people who were more resilient, had better medicine, were indoors at the time, et cetera – would feel resentful to the point of genocide towards those who were saved by the eclipse.

• Ronald September 11, 2008, 5:11

@James: apart from the fact that such a GRB doesn’t last very long. A continuously burning bright (giant) star, such as O giant, might serve your purposes much better.

• James M. Essig September 11, 2008, 8:41

Hi Folks;

Benjamin; A catastrophic gamma ray burst would indeed make an outstanding science fiction story or even a great movie. To the best of my knowledge, Hollywood has never done such a movie.

Ronald; an O giant star could make an exellent source for dive and fry solar sails and as a beam generator power source since O giants last for atleast 5 million to 10 million years.

Thanks;

Jim

• James M. Essig September 11, 2008, 11:30

Hi Benjamin;

The one solar luminosity at 6,000 light years I presume applies to the optical light generated by the supernova. I presume that the high energy photon flux for gamma rays could be much higher perhaps destroying all mamalian organisms or other animal life forms on the side of the planet that was blasted by the jet/burst. High energy gamma rays can produce high energy muons by reacting with the upper atmosphere of Earth like planets wherein the end result can be lethal radiation doses reaching to a depth of dozens of meters below ground.

Either way, GRB 080319B was a real bad boy.

Thanks;

Jim

• ljk September 11, 2008, 19:32

http://www.skyandtelescope.com/news/home/28244844.html

Hubble Finds a Mystery Object

Posted by Alan MacRobert, September 11, 2008

Don’t get the idea that we’ve found every kind of astronomical object there is in the universe. In a paper to appear in the Astrophysical Journal, astronomers working on the Supernova Cosmology Project report finding a new kind of something that they cannot make any sense of.

Now you don’t see it, now you do. Something in Bootes truly in the middle of nowhere — apparently not even in a galaxy — brightened by at least 120 times during more than three months and then faded away. Its spectrum was like nothing ever seen, write the discoverers, with “five broad absorption bands between 4100 and 6500 Angstroms and a mostly featureless continuum longward of 6500 Angstroms.” Even the cause of the spectral features is unknown.

K. Barbary and others

http://media.skyandtelescope.com/images/What-Was-It.jpg

The project used the Hubble Space Telescope to monitor very distant galaxy clusters for supernovae. On February 21, 2006, in the direction of a far-away cluster in Bootes named CL 1432.5+3332.8 (redshift 1.112, distance 8.2 billion light-years), Hubble began seeing something brighten. It continued brightening for about 100 days and peaked at 21st magnitude in two near-infrared colors. It then faded away over a similar timescale, until nothing was left in view down to 26th magnitude. The object brightened and faded by a factor of at least 120, maybe more.

The mystery object did not behave like any known kind of supernova. It is not even in any detectable galaxy. “The shape of the light curve is inconsistent with microlensing,” say the researchers. They recorded three spectra of it — and its spectrum, they write, “in addition to being inconsistent with all known supernova types, is not matched to any spectrum in the Sloan Digital Sky Survey database” of vast numbers of objects. “We suggest that the transient may be one of a new class.”

What’s its distance? That would certainly be a first step to figuring it out, but only the broadest constraints can be put on its distance. Its lack of parallax motion means that it can’t be closer than about 130 light-years, and a lack of cosmic hydrogen absorption in its spectrum means that it can’t be farther than 11 billion light-years. That leaves a lot of leeway.

Here is the group’s paper with all the details. The lead author is Kyle Barbary (University of California at Berkeley):

http://arxiv.org/PS_cache/arxiv/pdf/0809/0809.1648v1.pdf

• Ron S September 11, 2008, 21:24

A few points, though I haven’t checked any references so this is off the cuff. Hopefully I’m not too wrong on these:

– I am pretty sure James is right, that the GRB is much brighter (higher energy content) at shorter wavelengths than at visible wavelengths. Thus the potential damage is quite high in comparison to a normal stellar spectrum.

– The radiation profile of the GRB is like a thin, 3D figure-8, with a beamwidth of about 0.4 degrees, somewhat similar to quasar jets. I believe this is inferred, not measured (may not even be possible to measure directly), by statistically estimating the number. Basically, counting all the GRBs over a time interval and then counting the number with the beam directed at us, thus getting a rough idea of the solid angle of the beam. Also since we don’t quite know how far away this GRB is (see ljk’s comment), but if you assume it is at a far distance, similar to all GRBs, the brightness of this one implies the emissions are beamed. Then the zone of ‘sterilization’ is not spherical, but rather more shaped like the (narrow) radiation pattern.

– If GRBs are homogeneously located throughout the universe (in both space and time) their occurrence would increase by the square of distance from us. I’m not sure but I believe it’s been shown that their distribution doesn’t follow this pattern; there is a sharp drop (even cut-off) at shorter distances. That implies GRBs were more common when the universe was younger, and now are either rare or extinct. No way to say for sure without knowing the actual mechanism of the GRB. I believe there are as yet only educated guesses.

• ljk January 27, 2009, 11:42

Naked-eye optical flash from GRB 080319B: Tracing the decaying neutrons in the outflow

Authors: Yi-Zhong Fan, Bing Zhang, Da-Ming Wei

(Submitted on 14 Jan 2009)

Abstract: For an unsteady baryonic gamma-ray burst (GRB) outflow, the fast and slow proton shells collide with each other and produce energetic soft gamma-ray emission. If the outflow has a significant neutron component, the ultra-relativistic neutrons initially expand freely until decaying at a larger radius.

The late time proton shells ejected from the GRB central engine, after powering the regular internal shocks, will sweep these $\beta-$decay products and give rise to very bright UV/optical emission. The naked-eye optical flash from GRB 080319B, an energetic explosion in the distant universe, can be well explained in this way.

Comments: 4 pages, accepted for publication in Phys. Rev. D as a Rapid Communication

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Journal reference: Phys.Rev.D79:021301,2009

DOI: 10.1103/PhysRevD.79.021301

Cite as: arXiv:0901.2128v1 [astro-ph.HE]

Submission history

From: Fan Yizhong [view email]

[v1] Wed, 14 Jan 2009 21:27:44 GMT (8kb)

http://arxiv.org/abs/0901.2128

• ljk February 20, 2009, 22:55

NASA Science News for February 20, 2009

NASA’s Fermi Gamma-ray Space Telescope has detected a record-setting gamma-ray burst with the greatest total energy and fastest motions ever seen.

FULL STORY at

• ljk June 24, 2009, 15:53

Analysis of the Prompt Optical Emission of the Naked-Eye GRB 080319B

Authors: C. Bartolini, G. Greco, A. Guarnieri, A. Piccioni, G. Beskin, S. Bondar, S. Karpov, E. Molinari

(Submitted on 23 Jun 2009)

Abstract: We present the observed/intrinsic optical parameters and the variability analysis of the Naked-Eye Burst, GRB 080319B, observed by the TORTORA wide-field optical monitoring system. The event is extreme not only in observed properties but also intrinsically: it is the most luminous event ever recorded at optical wavelengths. The temporal properties suggest short-lived periodic activities of the internal engine. This is the fastest optically variable source detected at cosmological distances.

Comments: 4 pages, 1 figure, proceeding of the “Neutron Stars and Gamma-Ray Burst, Recent Developments and Future Directions” conference, Egypt, March 30 – April 4, 2009

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Cite as: arXiv:0906.4144v1 [astro-ph.HE]

Submission history

From: Giuseppe Greco [view email]

[v1] Tue, 23 Jun 2009 00:51:47 GMT (80kb)

http://arxiv.org/abs/0906.4144

• ljk January 23, 2011, 2:28

Origin of the bright prompt optical emission in the naked eye burst

Authors: R. Hascoët (1 and 2), F. Daigne (1 and 2), R. Mochkovitch (1 and 2) ((1) UPMC Univ Paris 06, UMR 7095, Institut d’Astrophysique de Paris (2) CNRS, UMR 7095, Institut d’Astrophysique de Paris)

(Submitted on 20 Jan 2011)

Abstract: The huge optical brightness of GRB 080319B (the “Naked Eye Burst) makes this event really challenging for models of the prompt GRB emission. In the framework of the internal shock model, we investigate a scenario where the dominant radiative process is synchrotron emission and the high optical flux is due to the dynamical properties of the relativistic outflow: if the initial Lorentz factor distribution in the jet is highly variable, many internal shocks will form within the outflow at various radii. The most violent shocks will produce the main gamma-ray component while the less violent ones will contribute at lower energy, including the optical range.

Comments: 3 pages, 1 figure, proceedings of the conference “Deciphering the Ancient Universe with Gamma-Ray Bursts”, Kyoto, Japan. Editors: N. Kawai, S. Nagataki

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Cite as: arXiv:1101.3952v1 [astro-ph.HE]

Submission history

From: Romain Hascoet [view email]

[v1] Thu, 20 Jan 2011 16:37:09 GMT (99kb)

http://arxiv.org/abs/1101.3952