ITN: Unusual Pulsar Discovered

[CraigS]

Gamma and X-Ray emission detected from a weaker non-magnetic pulsar SGR 0418:

Mysterious pulsar with hidden powers discovered

We have now discovered bursts and flares, i.e. magnetar-like activity, from a new pulsar whose magnetic field is very low," said Dr Silvia Zane, from UCL's (University College London) Mullard Space Science Laboratory, and an author of the research.
…
"It is the very first time this has been observed and the discovery poses the question of where the powering mechanism is in this case.
…
A crucial question is how large an imbalance can be maintained between the surface and interior magnetic fields. SGR 0418 represents an important test case.
…
"If further observations by Chandra and other satellites push the surface magnetic field limit lower, then theorists may have to dig deeper for an explanation of this enigmatic object"

The issue challenging the model is the size differential between surface and internal magnetic field strengths.

Would be good to get the paper. Does anyone have access to the "Science Express" publication ?

Cheers

[CraigS]

Correction … (I found the paper) ..

The issue is the low surface dipolar magnetic field, B < 3 × 10∧13 Gauss (quite low - in the range of only a radio pulsar class).

In order for this object to emit bursts with such a low surface field, it is hypothesised that the magnetar activity is driven by the magnetic energy stored in the internal toroidal field. This component cannot be measured directly.

This large internal field could stress the crust and ultimately deforms/cracks the star surface layers, periodically allowing magnetic helicity to be transferred to the external field, thus causing the (repeated) short x-ray bursts, (period ∼9.1 s, slow pulsations with a variable pulse profile), and the overall magnetar-like activity.

Interesting ..

Cheers

[Jarvamundo (Alex)]

It is the very first time this has been observed and the discovery poses the question of where the powering mechanism is in this case.

heheh more surprises aye, we seem to have a relaxation oscillator being interrupted by inbound current... kinda what we were saying was going to happen?

The 'power' is not hidden deep within, it's being delivered externally from the incoming current from the galactic environment, to the star system. As the plasma spheres receive this current, critical limit will be met causing the double layers (capacitors) to release outbursts. The system is at the complete mercy of the electrical environment.

Or yes hey, maybe it's not a surge to a strobe light, maybe it's some other untestable property of our hypothetical 'neutron stars'.

[bojan]

Alex,
We all know what you are going to say when something like this appears in the press
But, just for a change, how about you give us a more serious comment - supported by some numbers.
Other wise reading your posts became a pretty boring chore...

For example, I simply can' see how you can just accept this
"As the plasma spheres receive this current, critical limit will be met causing the double layers (capacitors) to release outbursts. The system is at the complete mercy of the electrical environment..."
And you are just walking over my challenges to explain frequency stability of those systems (up to 10^-14 !!!!).
Not to mention that the behaviour of this "capacitor" of yours is very doubtful, assuming the stellar size of it.

[Jarvamundo (Alex)]

Originally Posted by bojan

Alex,
We all know what you are going to say when something like this appears in the press

Correct it's a qualitative prediction of the ES pulsar model... I'm not sold on the gravitational collapse theory, or neutron matter star theory, or now these new cracks that can appear to let the hidden magnetic dynamo out.

Just seems like were invoking alot of unverified phenomena with yet more adhock attachments. Epicycles.

To me the stability will be provided by a resonance of the electrical circuit, much like a tank circuit... Quantitative detail of frequency stability is something i'll explore further. I aknowledge this is the remaining key difficulty of yours i have not addressed in detail yet. These questions are valuable for me Bojan, i thank you for them.

now.. Double layers *do* store vast amounts of electrical energy, this has been empirically verified from lab to solar scales, so i have no concern there with cosmic scales of plasma double layers.

If you're happy with the gravitationally collapsed, hypothetical super dense matter, with rotational frequency 'glitch' star quakes, and now cracks that let the forever hidden dynamo out - model, then all the best to you.

Qualitatively an interrupted resonant electrical circuit is infinitely closer to verified empirical physical processes for me. This article is another example of these qualitative expectations, and i'm happy to explore a cosmology built from physical processes that do exist.

[CraigS]

Alex;

So, from the PU ‘Plasma Scaling’ link you sent the other day, it says:

The first thing to notice is that many cosmic phenomena cannot be reproduced in the laboratory because the necessary magnetic field strength is beyond the technological limits. Of the phenomena listed, (Ionosphere, Exosphere, Interplanetary space, Interstellar space, Intergalactic space, Solar Chromosphere & Corona), only the ionosphere and the exosphere can be scaled to laboratory size. Another problem is the ionization fraction. When the size is varied over many orders of magnitude, the assumption of a partially ionized plasma may be violated in the simulation.

So, according to PU, there are many, many aspects of Plasma laboratory modeling/testing which cannot be demonstrated in the lab.

From this, it would seem unlikely that you could demonstrate your pulsar model in a ‘scaled down’ version in the lab. The only option I can see for the Relaxation Oscillator hypothesis, is a purely theoretical approach, using physics and mathematical models …

Originally Posted by Jarvamundo

Double layers *do* store vast amounts of electrical energy, this has been empirically verified from lab to solar scales, so i have no concern there with cosmic scales of plasma double layers.

These two pieces of information seem to be at odds with each other when discussing Relaxation Oscillators emitting pulsar levels of radiation and exhibiting stabilities in the order of the magnitudes mentioned by Bojan. The leap between lab models and real-life pulsar phenomena would seem far from trivial.

Can you explain the discrepancy and fill in the blanks ?

Cheers

[bojan]

No way, Alex.
In the course of my work as RF engineer I simply know from 35+ years experience that NO tank circuity can provide such a stability - it never happened and it never will. And there are many good theoretical analysis available on many web pages and textbooks on this issue.
If a tank circuit is for you a good enough explanation for frequency stability, then I'm afraid I must say you don't know what you are talking about.

As I mentioned earlier (in another thread ? ) the most stable frequency-wise electronic oscillators have MECHANICAL control elements (crystals) which are stable enough and and have Q-factor high enough to provide reasonable stability. Atomic clocks are way better (and better than pulsars), but they are not electronics oscillators in principle..

Your relaxation oscillator (with discharge tube) is tens of orders on magnitude worse it terms of stability than quartz oscillators..

On the other hand, fast rotating object is a good explanation of such phenomena.. much, much better model than relaxation oscillator, anyway.

Of course, if we assume that pulsars are electronics oscillators.. with external power etc.. why not conclude immediately that they are actually beacons built by advanced civilisations.. to help their space fleet to navigate through Galaxy :-) (BTW, this may be helpful one day for humans as well.. and it won't matter if pulsars are artificial, or rotating or whatever their nature may be).

Now,double layers..
How the discharge can happen UNIFORMLY throughout the whole thing (of stellar size !!), and in REPEATABLE way, every time..(again, with (observed !!) accuracy better than 10^-13 !!!!!) Did you think about recovery process? How it is possible that it is so fast (milliseconds... and that could tell us also something about its size.. what do you think, how big (or small) this system is? ) ?

Discharge is VERY chaotic process.. just look at lightning. You never know when and where it will strike. Far from being repeatable.

Originally Posted by Jarvamundo

Correct it's a qualitative prediction of the ES pulsar model... I'm not sold on the gravitational collapse theory, or neutron matter star theory, or now these new cracks that can appear to let the hidden magnetic dynamo out.

Just seems like were invoking alot of unverified phenomena with yet more adhock attachments. Epicycles.

To me the stability will be provided by a resonance of the electrical circuit, much like a tank circuit... Quantitative detail of frequency stability is something i'll explore further. I aknowledge this is the remaining key difficulty of yours i have not addressed in detail yet. These questions are valuable for me Bojan, i thank you for them.

now.. Double layers *do* store vast amounts of electrical energy, this has been empirically verified from lab to solar scales, so i have no concern there with cosmic scales of plasma double layers.

If you're happy with the gravitationally collapsed, hypothetical super dense matter, with rotational frequency 'glitch' star quakes, and now cracks that let the forever hidden dynamo out - model, then all the best to you.

Qualitatively an interrupted resonant electrical circuit is infinitely closer to verified empirical physical processes for me. This article is another example of these qualitative expectations, and i'm happy to explore a cosmology built from physical processes that do exist.

[sjastro]

There is a simple way of refuting this relaxation oscillator nonsense, observation.

A relaxation oscillator or blinking star is emitting spherical radiation (ie radiation is being emitted in all directions), in a pulsar the beam of radiation is rotating around a perpendicular axis.

If the object in the Crab Nebula is a blinking star the spherical radiation will reflect off the surrounding dust and form light echoes.
http://en.wikipedia.org/wiki/Light_echo

No such phenomena is observed!!!

Regards

Steven

[bojan]

Good point. However...
A question from me now (I am now in Alex's mode ).
Instead of expected onion-shape [BTW, layers of light for millisecond pulsating are expected to be very thin (1 ms equals ~300km), objects that small are not observable from those distances],we should be able to see some sort of bright ring, where rotating beam is hitting the shell of previously ejected material from a progenitor star.
Would the bright rings observed at SN 1987A in LMC be a good explanation for this?

Originally Posted by sjastro

There is a simple way of refuting this relaxation oscillator nonsense, observation.

A relaxation oscillator or blinking star is emitting spherical radiation (ie radiation is being emitted in all directions), in a pulsar the beam of radiation is rotating around a perpendicular axis.

If the object in the Crab Nebula is a blinking star the spherical radiation will reflect off the surrounding dust and form light echoes.
http://en.wikipedia.org/wiki/Light_echo

No such phenomena is observed!!!

Regards

Steven

This is also a question/point for Alex: 300km = 1ms.
The size of millisecond relaxation oscillator can not be larger than 300km in diameter.
The discharge in any material starts at random place(s) and then it propagates from there with the speed lower than c.
The recovery is also random-chaotic process, it includes cooling (significant temperature drop, recombination...) and it takes much longer time than discharge.. (This is why UJT, SCR's, thyratrons, neon tubes and similar are such a lousy oscillators).

All this tells us a lot about sizes involved in the process.
I tried to put this bug in Alex's ear earlier. but he didn't react, so now I am more direct - millisecond pulsar simply MUST be a VERY compact object in astronomical terms, whatever it's nature may be.
Rotating neutron star with two beams is (again) much more plausible model, contrary to relaxation oscillator explanation which is just an interesting mind game played by bored (or frustrated) electronics engineers.

[CraigS]

Originally Posted by bojan

Good point. However...
A question from me now (I am now in Alex's mode ).
Instead of expected onion-shape [BTW, layers of light for millisecond pulsating are expected to be very thin (1 ms equals ~300km), object this small are not observable],we should be able to see some sort of bright ring, where rotating beam is hitting the shell of previously ejected material from a progenitor star.
Would the bright rings observed at SN 1987A in LMC be a good explanation for this?





This is also a question/point for Alex: 300km = 1ms.
The size of millisecond relaxation oscillator can not be larger than 300km in diameter.
I tried to put this bug in his ear earlier. but he didn't react, so now I am more direct - millisecond pulsar simply MUST be a VERY compact object in astronomical terms, whatever it's nature may be.
Rotating neutron star with two beams is (again) much more plausible model, contrary to relaxation oscillator explanation which is just an interesting mind game played by bored (or frustrated) electronics engineers.

The duration of the pulse (~1ms) is a function of the circuit tuning parameters. The physical size/geometry of the components, whilst related, doesn't directly correlate with the pulse duration. I'm not clear on what you're saying here.

Can you explain ?

Cheers

[bojan]

Originally Posted by CraigS

The duration of the pulse (~1ms) is a function of the circuit tuning parameters. The physical size/geometry of the components, whilst related, doesn't directly correlate with the pulse duration. I'm not clear on what you're saying here.

Can you explain ?

Cheers

Of course

What you are talking about is ideal circuit, with lumped elements - meaning, the component properties (capacitance, inductance, resistance etcetera ) are concentrated in infinitely small spaces.

However (what is often ignored by non-RF people) when you move to higher frequencies (or the size of the circuit becomes comparable to the 1/4 wavelength of the frequencies involved) we are dealing with circuit with distributed parameters.
In other words, the things become much more complicated, and the circuit components are no more simple - for example, you may find a capacitor is actually a weird combination of number of capacitances, inductances and resistors.. all that can be sometimes modelled by equivalent schematic, or, what is more practical, we just take s-parameters of the component, valid for certain frequency range, and we are not bothered with actual physical component (black box approach).

So, the duration of 1ms in a circuit 300km size is VERY significant. The circuit will behave completely different from small PCB on the bench, even if values are the same.

[CraigS]

Originally Posted by bojan

Of course

What you are talking about is ideal circuit, with lumped elements - meaning, the component properties (capacitance, inductance, resistance etcetera ) are concentrated in infinitely small spaces.

However (what is often ignored by non-RF people) when you move to higher frequencies (or the size of the circuit becomes comparable to the 1/4 wavelength of the frequencies involved) we are dealing with circuit with distributed parameters.
In other words, the things become much more complicated, and the circuit components are no more simple - for example, you may find a capacitor is actually a weird combination of number of capacitances, inductances and resistors.. all that can be sometimes modelled by equivalent schematic, or, what is more practical, we just take s-parameters of the component, valid for certain frequency range, and we are not bothered with actual physical component (black box approach).

And what you're saying is that the 'equivalent circuit' required to achieve stability at the ~1ms pulse frequency is far more complicated than the one Alex has forwarded us.

Let's not go further on this .. this is Alex's model, and be both know we could design it all for him. But as Steven (& Carl) have pointed out, there is no astronomical behavioural evidence to support the concept of active behaviour of 'electrical analogous components' (plasma double layer capacitors, etc) in the first place … I have pointed out that it cannot even be modelled in the lab, using the plasma scaling transformations developed by Alven etc .. you have pointed out that the stability of ROs is inadequate.

That should suffice.

Cheers

[bojan]

Originally Posted by CraigS

And what you're saying is that the 'equivalent circuit' required to achieve stability at the ~1ms pulse frequency is far more complicated than the one Alex has forwarded us.

Yes.
The frequency stability of RO is determined not only by equivalent circuit components values - which will always be idealised and, linear.

RO is non-linear circuit. and it's behaviour, among other things, depends also on physical processes going on in its components.
And that is so complicated sometimes, that it can't be properly modelled..

All that can be said about this here is that the expected frequency stability of the best possible RO (cosmic or the one on the test bench) is tens of orders of magnitude lower than those observed at pulsars (together with their 'star-quake' glitches included).

[sjastro]

Originally Posted by bojan

Good point. However...
A question from me now (I am now in Alex's mode ).
Instead of expected onion-shape [BTW, layers of light for millisecond pulsating are expected to be very thin (1 ms equals ~300km), objects that small are not observable from those distances],we should be able to see some sort of bright ring, where rotating beam is hitting the shell of previously ejected material from a progenitor star.

You would not be able to observe a light echo from a rotating beam. The echo is a function of the expanding wave front perpendicular to the observer, not the shape of the intervening matter.

A rotating beam sweeps out a disk. Since we can observe the pulsar, our line of sight corresponds to the edge of the disk. Hence we would not be see a light echo.

If on the other hand the pulsar is sending out spherically expanding wavefronts (pulses) then there exists a wavefront perpendicular to our line of sight. If there is matter between the observer and the pulsar, the size of the echo is a function of the distance travelled by the wavefront.

Would the bright rings observed at SN 1987A in LMC be a good explanation for this?

Malin's famous light echo rings of SN 1987A highlight the mechanism.
The two light echo rings correspond to the presence of two separate sheets of intervening matter. The larger ring is due to matter closer to Earth, the component of spherical wavefront perpendicular to the Earth has travelled further resulting in the larger ring.

Note the spherically expanding wavefront is due to the supernova blast itself. To date there is no evidence of a neutron star let alone a pulsar.

Regards

Steven

[bojan]

Originally Posted by sjastro

You would not be able to observe a light echo from a rotating beam. The echo is a function of the expanding wave front perpendicular to the observer, not the shape of the intervening matter.

A rotating beam sweeps out a disk. Since we can observe the pulsar, our line of sight corresponds to the edge of the disk. Hence we would not be see a light echo.

If on the other hand the pulsar is sending out spherically expanding wavefronts (pulses) then there exists a wavefront perpendicular to our line of sight. If there is matter between the observer and the pulsar, the size of the echo is a function of the distance travelled by the wavefront.

Well, that's my point: The distance between wave fronts of individual consecutive pulses is ~300km for 1millisecond flashes.
This can't possibly be detected.

Despite the fact that rotating beam forms a disk, I still think we should be able to see (in principle) an illuminated ring (or fragments of it), provided the rotating beam is hitting the inside of a slow expanding hollow spherical shell.

[sjastro]

Originally Posted by bojan

Well, that's my point: The distance between wave fronts of individual consecutive pulses is ~300km for 1millisecond flashes.
This can't possibly be detected.

It has nothing to do with the period of the pulses. It's the distance travelled by each individual pulse through a medium. Think of the pulse as a cone shape. The diameter of the cone represents the light echo. The longer the cone, the greater the distance travelled in the medium, the larger the light echo. The fact that there is a small period between each pulse is immaterial, the first pulse emitted forms the outer edge of the light echo. Each successive pulse will lead to a "filled in" light echo.
We don't observe such beasts.

Despite the fact that rotating beam forms a disk, I still think we would be able to see (in principle) an illuminated ring (or fragments of it), provided the rotating beam is hitting the inside of a slow expanding hollow spherical shell.

How can this be. The thickness of the disk is very small even after taking into account diffraction effects on the beam. As an observer in the plane of the disk, the best we can hope to see is a small illuminated region on either side of the pulsar, and that is not possible given it is well beyond the resolution of our telescopes.

Regards

Steven

[CraigS]

I'm having a lot of trouble trying to understand the baseline geometry of where both of you are coming from. (That might just be me, though). There's a good chance that you guys have different orientations in mind ?

Anyway, I've got a question ...

How do we know when we are looking at a pulsar, that we aren't seeing multiple light pulses per single revolution of the neutron ?
The assumption seems to be that the light beam has two poles (and presumably, we see only one of them because of our orientation to the beam).
Do we know for certain that there are only two poles ? If there were more, we'd see an increase in the pulse frequency.. leading to ever increasing theoretical rotation rates.

Cheers
PS: Like a big mirror ball flashing at you in a disco ?

[bojan]

Originally Posted by sjastro

It has nothing to do with the period of the pulses. It's the distance travelled by each individual pulse through a medium. Think of the pulse as a cone shape. The diameter of the cone represents the light echo. The longer the cone, the greater the distance travelled in the medium, the larger the light echo. The fact that there is a small period between each pulse is immaterial, the first pulse emitted forms the outer edge of the light echo. Each successive pulse will lead to a "filled in" light echo.
We don't observe such beasts.

Of course I do understand the concept..
I just tried to point out there is no way to distinguish between the train of pulses from one single long brightening (like in this example you gave us earlier - V838 Monocerotis. It could have been flashing very fast during the outburst, but the effect we have now would have been the same).

Originally Posted by sjastro

How can this be. The thickness of the disk is very small even after taking into account diffraction effects on the beam. As an observer in the plane of the disk, the best we can hope to see is a small illuminated region on either side of the pulsar, and that is not possible given it is well beyond the resolution of our telescopes.

Well, I do agree the intensity of such illuminated ring would be small.
That's why I sad:

Originally Posted by bojan

... I still think we would be able to see (in principle) an illuminated ring (or fragments of it).....

[CraigS]

Moving right along .. (feel free to continue the other conversation however, guys) ..

I found another recent (peer reviewed) paper which analyses the poloidal/toroidal field interaction wrt the oscillation emissions. These guys even propose to use the flare phenomenon from magnetars, as a way of probing the physics of the interior physics of Neutron Stars.

Neutron stars are notable for the extreme strength of their magnetic fields, with surface fields reaching ∼ 10∧15 G for magnetars and interior fields perhaps being an order of magnitude stronger still. We expect many aspects of neutron star (NS) physics to be influenced by their magnetic fields, but we still have limited understanding of the actual structure of these fields; there are still open questions concerning their strength in the stellar interior, the relative proportions of poloidal and toroidal components and the possible effect of superconductivity (among others). One particular motivation for improving modelling of NS magnetic fields is the observation of quasi-periodic oscillations (QPOs) in the aftermath of giant flares from magnetars; these provide the first direct evidence of NS oscillations and give us a potential probe of the interior physics of these stars.

They discuss the nature of magnetic instabilities and oscillations in magnetars and pulsars, and find an ‘Alfven mode’ which has a frequency comparable with observed magnetar QPOs.

Their modelled poloidal fields also exhibit instabilities, observable via oscillations. There is a balance which can be struck between poloidal/toroidal components to explain variations in oscillations.

They conclude with a proposal to study the stability and oscillation spectra of the modelled mixed-field configurations, in a future study, and compare these with real-life Neutron Star observations.

This appears to be the ‘state-of-the-art’ modelling wrt Neutron/ Pulsars/Magnetars and to my way of thinking, explains with an ever increasing better fit, the behaviours of these objects.

Interesting stuff.

Cheers

[CraigS]

Originally Posted by CraigS

How do we know when we are looking at a pulsar, that we aren't seeing multiple light pulses per single revolution of the neutron ?
The assumption seems to be that the light beam has two poles (and presumably, we see only one of them because of our orientation to the beam).
Do we know for certain that there are only two poles ? If there were more, we'd see an increase in the pulse frequency.. leading to ever increasing theoretical rotation rates.

Cheers
PS: Like a big mirror ball flashing at you in a disco ?

Having just done a scout around, I have a feeling that this possibility:

i) may not be needed to explain observations to date (in other words, a two pole light beam suffices in the presently accepted Pulsar model) and;

ii) if calculated spin rates (based on observations) ever exceed the theoretical spin maximum of ~1500 per sec they may then consider more exotic topologies.

Happy to be corrected on any of this, in going forward.

Cheers
PS: Are you losin it when you start to answer your own questions ?