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Fraser
2004-Oct-01, 05:43 PM
SUMMARY: Supernovae are easy to see - after they've gone off. But it's impossible to find the stars beforehand, so you can study their final moments. Astronomers think they've found a warning sign that a star is about to explode: X-ray flashes. NASA's High-Energy Transient Explorer (HETE-2) has spotted three different powerful blasts of x-ray radiation over the last few weeks, and if astronomers' models hold true, these are precursors to much more powerful gamma-ray bursts, which have been linked with supernovae. Many telescopes around the world will be studying the regions that these x-ray flashes happened, hoping to catch a supernova in the act of exploding.

What do you think about this story? Post your comments below.

om@umr.edu
2004-Oct-01, 05:46 PM
That's great news, Fraser.

We desperately need some indication of an impending supernova explosion.

This may help us understand these events.

With kind regards,

Oliver
http://www.umr.edu/~om

dave_f
2004-Oct-01, 05:53 PM
Originally posted by fraser@Oct 1 2004, 05:43 PM
Many telescopes around the world will be studying the regions that these x-ray flashes happened, hoping to catch a supernova in the act of exploding.
Do we know how far away these things are? Are they in our galaxy, or are they pointing somewhere else?

lswinford
2004-Oct-01, 08:00 PM
Yep, I too was wondering (possibly wondering if I missed seeing it in the article) if it might be close enough and in a part of they sky where we might see it. :)

(Someone recently, I think it was a galaxy collision article, asked about "ringside seats." In this case, I hope its not in our close "neighborhood" and certainly not with one of those jets pointed our way. They tell me that if a neutron bomb explodes, one of those wonderful little devices designed to maybe break some windows but leave cities intact while killing all the inhabitants, it will make no noise--because everyone close enough to hear its sound would be dead. A supernova gamma burst that were too close would kill all its potential spectators :blink: )

jonfr
2004-Oct-01, 08:07 PM
Does anyone know what star they are speaking about ?
I've really like to know...

TuTone
2004-Oct-01, 08:17 PM
That would be something else to see one explode. :mellow:

antoniseb
2004-Oct-01, 08:26 PM
Originally posted by jonfr@Oct 1 2004, 08:07 PM
Does anyone know what star they are speaking about ?
This will not be a star in our galaxy. There will not be a visually bright new star from this. If I read the charts right, it was somewhere near the Aries/Taurus boundary, not too far from the Pleides.

Here's a link to more raw data:

HETE/Bursts/GRB040924 (http://space.mit.edu/HETE/Bursts/GRB040924)

jonfr
2004-Oct-01, 08:42 PM
Originally posted by antoniseb+Oct 1 2004, 08:26 PM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (antoniseb @ Oct 1 2004, 08:26 PM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin-jonfr@Oct 1 2004, 08:07 PM
Does anyone know what star they are speaking about ?
This will not be a star in our galaxy. There will not be a visually bright new star from this. If I read the charts right, it was somewhere near the Aries/Taurus boundary, not too far from the Pleides.

Here&#39;s a link to more raw data:

HETE/Bursts/GRB040924 (http://space.mit.edu/HETE/Bursts/GRB040924) [/b][/quote]
I still think that it is going to be an light show... :rolleyes:

antoniseb
2004-Oct-01, 08:50 PM
Originally posted by jonfr@Oct 1 2004, 08:42 PM
I still think that it is going to be an light show...
Based on the optical show put on by GRB030329, which was 3 times brighter in X-rays and gamma rays, I&#39;d guess that this one will be a 14th or 15th magnitude supernova. If you have a good sized telescope, you&#39;ll be able to find the host galaxy and watch it brighten and fade. Actually odds are, you will only see it fading.

StarLab
2004-Oct-02, 12:22 AM
Has the time until the supernova been predicted?

antoniseb
2004-Oct-02, 01:24 AM
Originally posted by StarLab@Oct 2 2004, 12:22 AM
Has the time until the supernova been predicted?
It should be about another week.

Don Alexander
2004-Oct-02, 05:19 PM
Hello, everybody&#33;

I&#39;m working on a diploma thesis on Gamma-Ray Bursts and their environment, so I might be the next-best thing to an expert within this forum. ;-}

I&#39;ve got some things to say, also about the press release, so bear with me, if you are interested.

First off, there seems to a misconception concerning Gamma-Ray Bursts and supernovae. When a very massive star (a so-called Wolf-Rayet star, like Gamma^2 Velorum) explodes as a Type Ib/c supernova (this weird designation is historical and comes from the hydrogen-deficient spectrum - this is actually like a Type II SN), it can trigger a GRB. If it rotates fast enough, polar jets will be produced and tear the star apart. We only see the GRB if we look exactly at one of the poles of this star.

When matter collides within these ultra-relativistic jets (this is several Earth masses moving at 99.9999% light speed), it produces gamma-rays - this is the GRB we see. Furthermore, when the jet collides with interstellar matter, the shocks glow brightly with synchroton radiation - this is the so-called optical afterglow, which is not the supernova&#33; The afterglow starts off extremely bright while the gamma-rays are still being emitted, and then loses brightness quickly.

Behind the jet, the remnants of the star expand as a supernova, and the decay of radioactive nuclei leads to the supernova light. As with all other SN, this light rises slowly, and peaks after about two weeks.

The SN happens at the same time as the GRB, but it is not visible because it&#39;s light curve rises very slowly, okay? A GRB does not tell you that a SN will happen here, it has already happened - but its maximum brightness is still a while off.

So. These explosions are at cosmological distances. GRB 030329 was at a redshift of 0.1685, that is about two BILLION light years away. The was the closest "classical" GRB. GRB 031203 (lately in the news, for example on the Chandra website and here, of course) was at redshift 0.105, that&#39;s still 1.6 billion light years away. It seems to have been a spherical, sub-energetic event. It had no real afterglow, but a bright supernova - it peaked at magnitude 18.3 in R, but was dimmed by almost two mags because of Galactic extinction.

These supernova are not bright and completely beyond visual detection by amateur telescopes&#33; A large scope (say, 16 inches or more) and a long CCD exposure may catch one. So no light show.

XRF 040912 has NOT been localized well. Two Chandra observations revealed 22 X-Ray sources within the HETE error circle, one of them decayed significantly. The Magellan telescope also detected a fading optical source - but these were DIFFERENT objects. So no one knows if the origin of this XRF has been found, and you have to have an exact localization to study the SN.

The XRF 040916 optical afterglow was found by Subaru, and it was quite faint. Hardly any one followed up this event.

The afterglow of GRB 040924 was extremely faint, already 18th magnitude 15 minutes after the burst, and a day later, it was beyond reach of everything but large scientific telescopes (23rd magnitude). This is actually good news, as a faint afterglow promises a well-detectable SN.

All three bursts do not have redshift determinations. There is a so-called pseudo-z, derived from gamma-ray data alone, but is has never been tested - optimistically, it could be a factor 2 off.

XRF 040912 (pseudo-z = 2.2) and XRF 040916 (pseudo-z 3.5) are likely way too far away for any detectable SN - the farthest one discovered, associated with GRB 021211, lies just beyond redshift 1 - this peaked at magnitude 24&#33;

So forget these two, I don&#39;t see a conflict&#33;

GRB 040924 has a pseudo-z of 0.57, shows no signs of high extinction within its host galaxy, and thus is a perfect target for a supernova search, that is true. But I have no knowledge that anyone is actually making an effort, and I am part of a large GRB collaboration - so no scientists scrambling.

Some more comments on the press release:

No matter what Ricker says, HETE is NOT working flawlessly&#33;&#33;&#33; This year has been extremely deficient of well-localized bursts, these three in so short a time span is a complete anomaly. 2002 and 2003 were much better. Every scientist not on the HETE team will tell you this.

Just to specify "location" - most initial HETE error circles are about the size of the full moon&#33; Not much compared to the complete sky, but the field of view of most large telescopes is much smaller. Perfect is a quick Chandra or XMM-Newton follow up, if they detect an X-Ray afterglow, it will be localized within arcseconds.

X-Ray flashes are NOT closer to Earth&#33;&#33;&#33; There is one confirmed XRF redshift, XRF 020903 (the first one with a discovered afterglow) - it lies at z = 0.251, not far in terms of GRBs, but more distant than 030329 and 031203. And look at the pseudo-z of these two recent bursts.

The second XRF with an afterglow, XRF 030723, was very well studied (though no redshift has been determined), and it showed an extreme late bump that is most probably a supernova - so I must contradict Woosley (quite a heresy...).

It is just plain WRONG that GRB 040924 is the fastest response ever. GRB 990123 was observed by Compton GRO, it sent a localization out 4 seconds after the onset of the burst, and the ROTSE I robotic telescope started observations 6 seconds later.

What most probably is correct is that the afterglow discovery by Fox & Moon was sent out faster than any other, even before HETE Ground Analysis confirmed that this is a real GRB (and not a cosmic ray hit).

So, enough for today, if anyone has questions, I&#39;ll try to answer them.

David Alexander Kann
Thueringer Landessternwarte Tautenburg

om@umr.edu
2004-Oct-02, 05:28 PM
Thanks, Don.

Is x-ray radiation a precursor to gamma-ray bursts and to supernova explosions?

Oliver
http://www.umr.edu/~om

antoniseb
2004-Oct-02, 07:01 PM
Originally posted by Don Alexander@Oct 2 2004, 05:19 PM
I&#39;ve got some things to say, also about the press release
Thanks Don, it is always good to get a realistic look at how some of these things are going. Hopefully Swift will give significantly more data than HETE II. I&#39;d been keeping an eye on the bursts recorded by HETE II, and was surprised that we weren&#39;t seeing nearly the one per day that the nuclear monitoring satelites of the sixties reported. This tells me a little bit about why.

Don Alexander
2004-Oct-02, 08:12 PM
Some answers:

X-rays are electromagnetic radiation, but more energetic. It&#39;s all the same stuff (photons), but depending on its energy, it has different names. In order of rising energy, they are:

radio (with lots of subdivisions), sub-millimiter (microwaves), far infrared, mid infrared, near infrared ("heat"), optical (light), ultraviolet, X-rays, gamma rays.

A nuclear physicist would tell you that gamma radiation is line radiation emitted by atomic nuclei, but we astrophysicists just call everything beyond X-rays gamma rays. By the way, the dividing are a little fuzzy, of course.

X-ray flashes are called thus because their peak energy lies in the X-ray band, not like the "harder" gamma rays.

By the way, the "millisecond" bursts mentioned in the press release are very probably due to the merger of neutrons stars, or neutron stars with black holes, so no supernovae there - no afterglow has ever been discovered, either. Spectrally, they are even harder than "collapsar" GRBs. Working on those will be my doctorate thesis...



Yes, Swift will be every GRB guys dream - and nightmare. Right now, good locations are so rare that we go for everything we can get. Swift will make triage necessary, everything that is just mediocre will just drop by the wayside.

And the Vela satellites did definitly NOT detect one GRB a day - they were very insensitive, only seeing "monsters" comparable to GRB 030329 or GRB 990123. This number comes from the BATSE detector on Compton, which detected 2704 bursts in less than ten years.

David Alexander Kann
Thueringer Landessternwarte Tautenburg

Guest_Don
2004-Oct-03, 01:26 PM
Originally posted by Don Alexander@Oct 2 2004, 08:12 PM
Some answers:

X-rays are electromagnetic radiation, but more energetic. It&#39;s all the same stuff (photons), but depending on its energy, it has different names. In order of rising energy, they are:

radio (with lots of subdivisions), sub-millimiter (microwaves), far infrared, mid infrared, near infrared ("heat"), optical (light), ultraviolet, X-rays, gamma rays.

A nuclear physicist would tell you that gamma radiation is line radiation emitted by atomic nuclei, but we astrophysicists just call everything beyond X-rays gamma rays. By the way, the dividing are a little fuzzy, of course.

X-ray flashes are called thus because their peak energy lies in the X-ray band, not like the "harder" gamma rays.

By the way, the "millisecond" bursts mentioned in the press release are very probably due to the merger of neutrons stars, or neutron stars with black holes, so no supernovae there - no afterglow has ever been discovered, either. Spectrally, they are even harder than "collapsar" GRBs. Working on those will be my doctorate thesis...



Yes, Swift will be every GRB guys dream - and nightmare. Right now, good locations are so rare that we go for everything we can get. Swift will make triage necessary, everything that is just mediocre will just drop by the wayside.

And the Vela satellites did definitly NOT detect one GRB a day - they were very insensitive, only seeing "monsters" comparable to GRB 030329 or GRB 990123. This number comes from the BATSE detector on Compton, which detected 2704 bursts in less than ten years.

David Alexander Kann
Thueringer Landessternwarte Tautenburg
At 4am this morning, 3rd Oct. I noticed a very bright star when looking esat from the south coast of england. It was brighter than anything else in the sky and could even bee seen through cloud when most of the other stars were obscured. I am new to astronomy and wondered if this could be one of the supernova or just a bright star. Any suggestions

Tinaa
2004-Oct-03, 01:43 PM
I&#39;ll bet that was the planet Venus you saw. Venus rises in the east and is the bightest object in the sky, minus the moon of course.

Guest
2005-Jul-02, 11:53 AM
new supernova SN 2005cs just exploded in to view in M51 or the "Whirlpool Galaxy"

Planetwatcher
2005-Jul-03, 08:38 AM
What makes me wonder is more along the line of the speeds of which certain forms of radiation is travelling.

I don&#39;t think Xrays travel as fast as light, and I believe that Gamma rays are even slower.
So unless there is a significant amount of lead time between the gamma and Xray bursts and the visual observation, and especially if the star observed is more distant, we could have missed the visual observation, and am receiving the gamma and Xray bursts, years, centuries, or even milliniums after the supernoves occured.

CharlesBell
2005-Jul-09, 05:20 PM
If supernovae are interesting to you, you can see what is happening right now at the web page:


Best supernovae site on the internet maintained by David Bishop (http://www.supernovae.net)


The Latest Supernovae discoveries (http://www.supernovae.net/snimages/)



SN2005cs in M51 Whirlpool Galaxy discovered June 27, 2005 by amateur Wolfgang Kloehr (Germany) (http://www.supernovae.net/sn2005/sn2005cs.html)


Recent Supernovae (http://cfa-www.harvard.edu/iau/lists/RecentSupernovae.html)