Hey everyone,

since neither UT nor the BA have featured this so far, I wanted to give you a heads-up. It's also a shameless self-advertisement, as I'm co-author on the Castro-Tirado paper and actually did quite a bit of work for it...

As was recently reported on the ESO press release page, two papers have appeared in the newest issue of Nature magazine detailing observations of GRB0 070610/SWIFT J195509.6+261406. This source was first detected as a gamma-ray burst (GRB 070610) on the 10th of June 2007. As a GRB, it looks completely normal, both temporally and spectrally. But ground-based follow-up resulted in the detection of rapid, complex optical flares, leading to the source to be recognized as Galactic in origin. It increased the burst frequency, remained active for a few days and then diappeared completely.

The paper by Stefanescu et al. reports on observations at extremely high temporal resolution with the fibre-fed photon-counting device OPTIMA-Burst. These observations lead to the discovery of the flaring source, and show some of the powerful flares in exquisite (down to 0.1 seconds per point) time resolution. The structure is quite similar to the substructure seen in the gamma-ray and X-ray flares of magnetars like SGRs and AXPs.

Castro-Tirado et al. report on a broadband follow-up campaign, which tracked the source with multiple optical telescopes, discovering about 40 flares, measuring the distance to the source, showing that it was at best associated with a very low-mass star, and not detecting it at late times in X-rays. Some observational details can be found in the supplement, which should be free of charge.

First, I should say that I'm sorry for the following... As most of you will not have electronic access to Nature (not even our institute does, ahem...), here are the astro-ph versions:

http://arxiv.org/abs/0809.4231
http://arxiv.org/abs/0809.4043

BUT they represent only the submitted versions of the papers, which differ from the final versions in many details (the core results are of course identical, otherwise we would have hardly made it into Nature...), due to the lead authors following a rather obscure nature publishing policy...

Anyway, the situation is the following: The properties of the source are like none ever seen before. There is one earlier paper on the event, from Kasliwal et al., which tries to link it to superfast giant X-ray transients, but we show this interpretation has multiple problems. The magnetar interpretation presented in the two Nature papers is mainly the result from a process of elimination. Almost all objects that are somehow linked to normal stars (such as star + neutron star/black hole binaries with accretion processes) are ruled out by the rapid variability of the flares, the lack of any Halpha emission from the source, and the total lack of radio detections or a quiescent X-ray counterpart. An isolated neutron star seems the only remaining possibility, and there, it's the magnetars which give you the flares.

Normally, magnetars flare in the gamma- and X-ray regimes. This source, during Swift monitoring, presented one fast X-ray flare (alas, somehow the Swift observations never occured during ground-based optical observations and vice versa...) compared to over 40 optical outbursts, and was, after the initial GRB, totally quiet in gamma-rays. One point is, since typical SGRs and AXPs lie behind massive extinction in the Galactic plane, we don't know anything about their optical properties, so perhaps they are bursting at low energies all the time. Still, as long as no counterexample is found, SWIFT J1955 stands alone.

One intriguing speculation now is that that this source represents the transition phase from young magnetars like SGRs to Dim Isolated Neutron stars (DINs), of which several have been found at much closer distance by the HST. As they age and their magnetic fields go down, the energy regime of their eruptions is also reduced, from gamma-rays to optical flashes to radio emission. The exact nature of the optical flashes is also not yet understood, one speculation is that they are something like aurora, induced by ions travelling along extremely strong magnetic field lines.

So much for now, have away at a discussion (and I'm sure a bunch of ATM ideas will pop up really soon too...), we, therewhile, wait for another similar source or a re-activation of this one.

__________________
David Alexander Kann
PhD student
Thueringer Landessternwarte Tautenburg

Ignite our minds and let's burn brighter
These are the wonders at your feet
- Dark Tranquillity, The Wonders At Your Feet

Thanks Don! Excellent heads up. Nice work. No...Nice heads-up and excellent work!

If it wasn't for the clear local indices you have identified, is there anything about this that might have caused it to be considered a more distant event?

__________________
jwj

It's a big universe out there...is it really unwinding, really burning out?

Well, initially, I actually had my qualms about our distance determination. Originally, all we had was the X-ray measurment, and my colleagues argued: "The NH column density as derived by the XRT is the same as found in the HI maps from Kalberla et al., so the source must be in the galaxy." I was a bit flabbergasted about this, because actually, the correct interpretation is that it's BEHIND the galaxy!!

Then we got our own measurement in CO and HI, and the situation became much better. Now, the X-ray measurement is less than the total hydrogen column we measure, so there must be additional hyrdogen behind it, which places the source within the galaxy. But if you are a real nitpicker, you'll see we have two XRT measurements (don't ask me why or how, that was not my work...). If you take 7.2 +3 -2, the situation is reasonably clear in comparison to 14.1 +/- 2.0. But if you take the other measurement, 10 +4-3 - well, they overlap strongly within the error bars. Also, the red clump method just sets a LOWER limit on the distance.

So, if one is picky, one can still argue that the source might be behind, possibly even WAY behind the galaxy.

Back when I posted my first GCN on it being Galactic, none of these numbers were available to me, and I had not the foggiest notion of what the source might be. Still, I claimed it to Galactic, and I completely agree with my co-authors that it is.

First of all, it clearly is not a classic GRB. Nonewithstanding what some people claim, the GRB phenomenon is understood well enough that we can rule that out.

Secondly, the source is in the Galactic plane. Of course, every once in a while, we get real, extragalactic GRBs behind the plane, no wonder, gamma-rays don't care whit for extinction and GRBs are distributed isotropically in the sky, probably, every few hundred or thousand years, one occurs right behind the central black hole... But this is not a GRB, and a very rare object, which implies that the chances of it happening behind the plane by chance are very low.

Then there's the energetics argument. Even back then, it was clear that the source was flashing by maybe two magnitudes within a few minutes. Light travel time arguments show you that the source diameter is on the level of a giant star or smaller. Now, from Stefanescu et al, we have five magnitudes in 4 seconds!! Down goes the source size, and now it screams compact object. There is nothing in the knowledge of how normal stars behave that gives you such flashes. On the other hand, if you do have a compact object, there's a pretty good link between the emitted energy and the band that it's mostly emitted in. SGR hyperflares can easily be detected out to the Virgo galaxy cluster, and one has been found in Andromeda and one in M81, but these things occur in gamma-rays. At the time I wrote my GCN, I saw already that the source was not really active in the X-rays. So the energy being emitted is, relatively speaking, low. And such a source has to be pretty close by to be so bright, after all, recall that we are seeing it through several magnitudes of extinction, and later, flares were found that hit 14th magnitude, meaning they might reached 10th mag if the view was clear.

Then there's the VLT/NACO H band observation, which is really powerful. At the place of our flasher, we see NOTHING. Yes, the extinction a few mags, but that's not extremely high, and "a few mags" is in the optical, in the H band, it's not even one magnitude - slightly cloudy today, nothing more. And we see nothing. If this source was in a decently nearby galaxy, this galaxy would be huge and bright and visible at the very least in this image. But there is no galaxy. Compact objects are associated with massive star formation, for that, you need at least starbursting dwarf galaxies. Sure, there are a lot of GRB host galaxies that would have remained undetected even in this image, but these are out at redshift 1 and beyond. And nothing in the known universe can produce radiation like this and lie at such a distance. If we assume the lack of a galaxy indicates at least, say, redshift 0.5, then the optical flashes at peak outshine almost all quasars, and this can't be linked to the quasar phenomenon at all, because even OVV (Optically Violently Variable) quasars don't increase their optical luminosity by a factor of 100 in a few seconds, not to forget the fact that quasars are bright X-ray sources and brilliant in the radio range, and this thing was utterly radio-quiet.

So:
We have several really good measures that the source is at least 3-4 kpc away.
We have decent indications, but not more, that the source if still within the Galactic plane.
While the exact emission mechanism is still unclear, the spectral behaviour (strong in optical, weak in X-rays, nothing except at the start in gamma-rays, nothing in radio, and repeating very often) indicates that the emitted energies are not overwhelmingly large, so it can't be too far away.

So, at least if you think about it, no, it should be Galactic and not way beyond our galaxy.

Of course, I will not have the hubris to claim that we know everything. There might be some kind of process that creates emission like this (remember, we never got a spectrum of the flares themselves...) but at a vast energy level, somewhere way out there. This might be possible.

But I won't bet on it.

__________________
David Alexander Kann
PhD student
Thueringer Landessternwarte Tautenburg

Ignite our minds and let's burn brighter
These are the wonders at your feet
- Dark Tranquillity, The Wonders At Your Feet

Hi Don (David?)
Just like to add my thanks, having just finished an essay on GRB's and about to start another one on SGRs this is very timely! I was just wondering if this object is a transition between a magnetar and a DINS, would that represent the low-mag field or the slow-spin end of the magnetar spectrum (or both)?

cheers
Murray

I'd have to admit being a bit out of my depth here (and call me Alex).

I think the "both" is the best answer. During spin-down, the field also ever-so-slightly diffuses, mostly during such reconnection events which are discussed when it comes to the magnetar superflares. After such an event, the field reaches a new state, and, to my understanding, the field strength should be a bit reduced.

But please, better look for original literature on this, I'm much more a GRB than a magnetar person.

__________________
David Alexander Kann
PhD student
Thueringer Landessternwarte Tautenburg

Ignite our minds and let's burn brighter
These are the wonders at your feet
- Dark Tranquillity, The Wonders At Your Feet

Bit scary those Magnetars, causing day time
levels of ionisation in the atmosphere from
thousands of lightyears distance!

And I posted something about an unusual
aurora seen in the 1890's from several
English towns one evening. "like a lighthouse
beam across the sky several times a second"
was one eyewitness quote. Wow, a rotating
neutron star sending high energy photons?

Had my planisphere out trying to see where
Gemini and Geminga might be. A little bit
woo woo. But not much

Actually, it doesn't sound too outlandish...

Though I have two caveats: First point is, I know next to nothing about aurora physics, so it may be possible that the "relaxation time" is too long to allow such a high frequency auroral display. Secondly, typical magnetars rotate only once every few seconds, maybe ten times slower than what you report here (do you have a link, btw? It does sound interesting, a bit like the solar superstorm of 1859), but, of course, a really young one would be faster. So at least from my POV, the jury's out. Incidentally, the SGR 1806-20 hyperflare on 041227 happened when the magnetar was just a few degrees from the sun, so it barely changed the upper atmosphere which was at daytime levels anyway.

Incidentally^2, on 080822, a true new magnetar (SGR 0501+4516) was discovered, and just on Friday (081003), a known AXP (AXP 1E 1547.0-5408) emitted several SGR-like bursts and has now also been called SGR 1550-5418, though I don't know if that name will stick.

__________________
David Alexander Kann
PhD student
Thueringer Landessternwarte Tautenburg

Ignite our minds and let's burn brighter
These are the wonders at your feet
- Dark Tranquillity, The Wonders At Your Feet

It is on my grb idea thread back in 2005,sep.
This link might work,

Grb idea.


Sure some have looked at the subject.

Looking at the papers you quoted in the OP and one on DINS by Alper (A&SS 2007) it seems that DINS show a field strength a magnitude lower than typical magnetars and that all magnetars have fairly slow periods (a fact which I'd forgotten but is obvious since the spin-down rate is proportional to B!).

It seems a little too coincidental that we have SGRs, AXPs, DINS, RRATs and now this optical (and IR!) SWIFTy thing sitting in the same corner of the P-Pdot space. Its starting to look like a continuum with the peak frequency of the burst dependent on the magnetic field strength and with the size/ presence of a fall-back disk and the initial spin speed and spin-ups only complicating things a little.

If the DINs are supposed to be wandering close to the NS extinction line I reckon the rest of them are at least in the nursing home! Will probably need a lot more of each type detected to make it look convincing though, its a fairly small population to start making sweeping conclusions.

Fascinating stuff though, don't know why people get so hung up on black holes, neutron stars are much more interesting!