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View Full Version : Could a nearby Earth-threatening GRB not even be possible?



Luckmeister
2009-Aug-01, 11:27 PM
From Wikipedia:


The sources of most GRBs are billions of light years away from Earth, implying that the explosions are both extremely energetic (a typical burst releases as much energy in a few seconds as the Sun will in its entire 10 billion year lifetime) and extremely rare (a few per galaxy per million years[1]).

This makes me wonder if GRB's might be the product of a much younger set of conditions in our universe. Can anyone point me to studies that address this possibility?

Luckmeister

m74z00219
2009-Aug-01, 11:42 PM
From Wikipedia:



This makes me wonder if GRB's might be the product of a much younger set of conditions in our universe. Can anyone point me to studies that address this possibility?

Luckmeister

I think you're right about it having something to do with the universe at a younger age. The reason being that population three stars (the first stars) were all exceedingly massive, so they tended to go out violently.

http://en.wikipedia.org/wiki/Population_III_stars

AndreasJ
2009-Aug-02, 12:49 PM
If "most" are from over a billion ly away, it would follow some are from within 1 billion ly, and therefore cosmologically recent - they went off in a universe much more like out own than like that of population III stars.

Luckmeister
2009-Aug-02, 06:13 PM
If "most" are from over a billion ly away, it would follow some are from within 1 billion ly, and therefore cosmologically recent - they went off in a universe much more like out own than like that of population III stars.


Yeah, "most" and "some" is not very definitive. That's why I'd like to see something more informative than what's said in Wikipedia -- and not all GRBs are alike in destructive potential.

Luckmeister

astromark
2009-Aug-03, 09:30 AM
Like a shock wave echo's across the galaxy Fortunatly it would seem that Gamma Ray Bursts are rare. Unfortunatly we as yet are not so sure we are not in danger from such... I seem to recall the observation of a 'unstable' end on view of a spiraling mass. Where a nova event could trigger a gama burst that could be looking us down the barrel... but do not worry about this or any other such event. THERE IS NOTHING WE CAN DO. Just look away and hope it will not happen. After all it has not happened yet has it...:)...
Regarding this topic and others like it... Ware your seat belt. Be careful driving. Eat seasonably...bla, bla, bla.... Do not worry about what you can not change.
The OP suggestion that this might have only be possible from a early super giant... but they are not all gone. are they ?

Cougar
2009-Aug-03, 02:04 PM
This makes me wonder if GRB's might be the product of a much younger set of conditions in our universe. Can anyone point me to studies that address this possibility?

Apparently it is not unreasonable (http://www.iop.org/EJ/article/0004-637X/529/2/635/39618.text.html) to think that the cosmological evolution of GRBs is roughly correlated with the star formation history of the universe, which this paper (http://arxiv.org/abs/astro-ph/0403293) suggests....




...peaked some 8 billion years ago, and then declined by a factor of around ten to its present value.

Tim Thompson
2009-Aug-05, 10:02 PM
This makes me wonder if GRB's might be the product of a much younger set of conditions in our universe. Can anyone point me to studies that address this possibility?
Aside from the well known thermonuclear (type Ia) and core collapse supernovae, there is a third class called pair instability supernovae (Fraley, 1968 (http://adsabs.harvard.edu/abs/1968Ap%26SS...2...96F)). Only super massive stars can experience this third class of supernova explosion. Like the type Ia supernovae, it leaves behind no collapsed remnant, and it is also the most energetic class of supernova explosion.

Since redshift 3, the cosmological star formation rate has dropped by about a factor of 100. So the early universe has a lot more super massive stars and should have a lot more GRBs; more long GRBs because there are more super massive stars to experience the hypernova explosions they are associated with, and more short GRBs because there are a lot more of the neutron star binaries that they are associated with. And indeed, that's what we see, more GRBs at higher redshifts (see Lloyd-Ronning, Fryer & Ramirez-Ruiz, 2002 (http://adsabs.harvard.edu/abs/2002ApJ...574..554L) who show a significant correlation between GRB luminosity and redshift; Feulner, et al., 2005 (http://adsabs.harvard.edu/abs/2005ApJ...633L...9F) who derive star formation rates out to redshift 5; Le & Dermer, 2007 (http://adsabs.harvard.edu/abs/2007ApJ...661..394L) who study the redshift distribution of GRBs and Yuksel, et al, 2008 (http://adsabs.harvard.edu/abs/2008ApJ...683L...5Y), who use high redshift GRBs to derive a high redshift star formation rate; in all cases the arXiv link leads to PDF copies of the papers, and in most cases you can also follow the links to find papers which cite these (and carry on or improve the results), and the earlier papers cited by these papers).

However, it is important to note that it is the mass of the progenitor star that drives the power of a GRB, and even in the current universe, we might expect to see a GRB since we do still have super massive stars. The lowest redshift GRB that I an aware of is GRB 980425, with redshift 0.0085 corresponding to a light travel time distance of 116,000,000 light years, not all that far away cosmologically speaking (about twice the distance to the Virgo Cluster, and considerably closer than either the Hercules or Coma galaxy clusters).

SN 2006gy is the most luminous supernova explosion observed so far, and is the first candidate for a pair instability supernova in the local universe (Smith, et al., 2007 (http://adsabs.harvard.edu/abs/2007ApJ...666.1116S), Woosley, Blinnikov & Heger, 2007 (http://adsabs.harvard.edu/abs/2007Natur.450..390W), Smith, 2008 (http://adsabs.harvard.edu/abs/2008AIPC..990..122S); in NGC 1260, about 240,000,000 light years away). This brings to mind the perilously short distance between Earth & Eta Carinae, and the question: Could Eta Carinae hit Earth with a GRB? The answer appears to be no, primarily because the axis of the system is pointing away from us, and a GRB is almost certainly collimated along the axis of symmetry (Thomas, et al., 2008 (http://adsabs.harvard.edu/abs/2008AsBio...8....9T)). But of course we don't know how many such super massive stars there really are in the Milky Way, or in the local universe. So we could still be in some cosmic danger, if we happen to be in the collimated line of sight.

Luckmeister
2009-Aug-06, 06:16 AM
Thanks Tim for the in-depth answer -- good links too.

Luckmeister

chornedsnorkack
2009-Aug-06, 08:14 AM
Aside from the well known thermonuclear (type Ia) and core collapse supernovae, there is a third class called pair instability supernovae (Fraley, 1968 (http://adsabs.harvard.edu/abs/1968Ap%26SS...2...96F)). Only super massive stars can experience this third class of supernova explosion. Like the type Ia supernovae, it leaves behind no collapsed remnant, and it is also the most energetic class of supernova explosion.

Since redshift 3, the cosmological star formation rate has dropped by about a factor of 100. So the early universe has a lot more super massive stars and should have a lot more GRBs; more long GRBs because there are more super massive stars to experience the hypernova explosions they are associated with, and more short GRBs because there are a lot more of the neutron star binaries that they are associated with.

So, precisely how do we know which supernovas cause GRB-s and which do not?

If GRB-s, like pulsars and active galactic nuclei/BL Lacertae objects/quasars/blazars are directional, is there any way of deciding whether a supernova caused a GRB in some other direction, or did not cause one at all?

If we look at the population of supernovae that caused GRB-s, and compare this with the population of supernovae that are not accompanied by GRB, is there any systematic difference? Specifically, can a GRB be caused by type II supernova, or only by type Ib/c supernova? (Likewise, what precisely do GRB progenitor stars look like?)

Now, while types II and Ib/c are caused by massive stars, type Ia supernovae are caused by binary white dwarfs. They are notorious for happening in elliptical galaxies and old globular clusters devoid of type II supernovae.

If short GRB-s are caused by decay of old binaries (in their case neutron star binaries rather than white dwarf binaries like type Ia), should they take place where type Ia supernovae also happen?

What does a neutron star merger look like from directions other than the GRB axis?


But of course we don't know how many such super massive stars there really are in the Milky Way, or in the local universe. So we could still be in some cosmic danger, if we happen to be in the collimated line of sight.
Indeed. Clarke Burst was +5,4, for about one minute, at 7,5 milliard lightyears. A similar GRB 2,5 million times closer, i. e. at 3000 lightyears (much farther than Betelgeuse and farther than belt of Orion or Deneb) would be 32 magnitudes brighter, at -26,6.

Tim Thompson
2009-Aug-06, 08:28 PM
So, precisely how do we know which supernovas cause GRB-s and which do not?
Well, the observational evidence suggests that only high energy supernovae (hypernovae) can be responsible for GRBs. Even allowing for GRB energy to be collimated in beams and not isotropic, the energy output is still quite high. We also now know that the optical and IR afterglow following GRBs is that of a non type-Ia supernova. See, for instance, Iwamoto, et al., 1998 (http://adsabs.harvard.edu/abs/1998Natur.395..672I); Galama, et al., 1998 (http://adsabs.harvard.edu/abs/1998Natur.395..670G); Nakamura, et al., 2001 (http://adsabs.harvard.edu/abs/2001ApJ...550..991N); Kawabata, et al., 2003 (http://adsabs.harvard.edu/abs/2003ApJ...593L..19K); Mazzali, et al., 2003 (http://adsabs.harvard.edu/abs/2003ApJ...599L..95M); Stanek, et al., 2005 (http://adsabs.harvard.edu/abs/2005ApJ...626L...5S); Mazzali, et al., 2006 (http://adsabs.harvard.edu/abs/2006ApJ...645.1323M). The association of GRBs specifically with pair instability supernovae is best illustrated by the papers I already referenced. But the association of long GRBs in general with supernovae & hypernovae, based on the GRB afterglow looks reliable.


If GRB-s, like pulsars and active galactic nuclei/BL Lacertae objects/quasars/blazars are directional, is there any way of deciding whether a supernova caused a GRB in some other direction, or did not cause one at all?
Maybe not. If we are not in the beam, we won't see the GRB. But we might see the effect of the GRB on the interstellar medium around the observed supernova and infer a GRB from that.


If we look at the population of supernovae that caused GRB-s, and compare this with the population of supernovae that are not accompanied by GRB, is there any systematic difference?
Same problem. How do you know that a supernova did not generate a GRB? What we do see is that the GRBs identified with a supernova are systematically identified with an exceptionally high energy event, which is in itself revealing.


Specifically, can a GRB be caused by type II supernova, or only by type Ib/c supernova? (Likewise, what precisely do GRB progenitor stars look like?)
I have only seen specific correlations with type Ib & Ic and the argument that a "bright" type II "cannot be ruled out".


If short GRB-s are caused by decay of old binaries (in their case neutron star binaries rather than white dwarf binaries like type Ia), should they take place where type Ia supernovae also happen?
I am unaware of any specific studies of a spatial correlation between GRBs & Type Ia SNe. However, Grindlay, Portegies-Zwart & McMillan, 2006 (http://adsabs.harvard.edu/abs/2006NatPh...2..116G) agrees with this scenario.


What does a neutron star merger look like from directions other than the GRB axis?
See Shibata, et al., 2005 (http://adsabs.harvard.edu/abs/2005PhRvD..71h4021S) and citations thereto. Neutron star merger simulations concentrate on modeling gravitational wave output. It appears to me that a merger would be underluminous and maybe even not visible at all over large distances if not seen along the beam. Perhaps and X-ray burst without optical counterpart. Turatto, et al., 1998 (http://adsabs.harvard.edu/abs/1998ApJ...498L.129T) report an exceptionally underluminous type II SN 1997D and argue that the low luminosity is due to the low mass of 56Ni in the ejecta. In a neutron star merger there is probably even less material, like 56Ni, to power an afterglow, and most of the prompt emission will be neutrinos (as is the case for all supernovae anyway). Most of the prompt electromagnetic photons will likely be X-rays and not visible light or longer wavelengths.


Indeed. Clarke Burst was +5,4, for about one minute, at 7,5 milliard lightyears. A similar GRB 2,5 million times closer, i. e. at 3000 lightyears (much farther than Betelgeuse and farther than belt of Orion or Deneb) would be 32 magnitudes brighter, at -26,6.
That's GRB 080319B (http://en.wikipedia.org/wiki/GRB_080319B), for those who don't recognize the reference. The reference is to Arthur C. Clarke, who died on March 19 2008, on which day SWIFT recorded 4 GRBs including GRB 080319B. It was the brightest GRB on record, visible to the naked eye under a dark sky, for about a minute, despite a light travel time distance of about 7,500,000,000 light years. As chornedsnorkack tells us, at 3000 light years it would have rivaled the Sun in visual brightness.

chornedsnorkack
2009-Aug-06, 10:11 PM
Well, the observational evidence suggests that only high energy supernovae (hypernovae) can be responsible for GRBs. Even allowing for GRB energy to be collimated in beams and not isotropic, the energy output is still quite high.


We have no idea about what the GRB energy is unless we know the beam width angle. (We can infer beam width for those pulsars that have interpulse.)



Same problem. How do you know that a supernova did not generate a GRB?
I said, "accompanied by" - I did not mention whether I meant accompanied by existing GRB or observable GRB. I did mean observable GRB.


What we do see is that the GRBs identified with a supernova are systematically identified with an exceptionally high energy event, which is in itself revealing.

I have only seen specific correlations with type Ib & Ic and the argument that a "bright" type II "cannot be ruled out".

Has a spectral confirmation of type II, IIb, Ib or Ic been made?


It appears to me that a merger would be underluminous and maybe even not visible at all over large distances if not seen along the beam. Perhaps and X-ray burst without optical counterpart. Turatto, et al., 1998 (http://adsabs.harvard.edu/abs/1998ApJ...498L.129T) report an exceptionally underluminous type II SN 1997D and argue that the low luminosity is due to the low mass of 56Ni in the ejecta. In a neutron star merger there is probably even less material, like 56Ni, to power an afterglow,
To the contrary, by my suspicion.

Ni 56 undergoes just 2 beta decays and releases a total of 5 MeV per 56 nucleons. Whereas neutron star decay should generate nuclei that are initially at neutron drip line and liable to undergo multiple and energetic beta decays at a wide range of half-lives.

and most of the prompt emission will be neutrinos (as is the case for all supernovae anyway).

I thought that in the core of a fresh neutron star deep in the middle of supernova, the extreme density and sustained high temperature should favour Urca process over thermal expansion and electromagnetic radiation. Whereas in the debris of a disrupted neutron star should more easily allow expansion and radiation.

astromark
2009-Aug-07, 02:00 AM
In the original post the suggestion that GRB might no longer be possible near to us. Thus we are in no danger. Wishful thinking and little proof of fact. Not that I do not like the argument. Its a good one. The record of such might even support this view.
Unfortunately I think its nieve to have such a view. Space is so big and we are so small. Impossible is like a challenge to the probability of improbability.. only I know what I mean... and Douglas Adams. Mark.