Thanks!

With that, the meeting is over. Thanks are due to our intrepid bloggers: René Breton, Fotis Gavriil, Sebastien Guillot, Christian Haakonsen, Jason Hessels and Anna Watts. They did an outstanding job of giving you the quick punchline on the talks.

Ramanpreet Kaur : Chandra and XMM-Newton observations of 7 enigmatic faint persistently slow pulsators

The author presented the analysis of two (out of seven) faint slow pulsators with period greater than 150 sec, precluding that they belong to the HMXB, LMXB or IP (intermediate polar) class. Using XMM and Chandra, spectral, timing and positional data were obtained in order to classify the source. The first source, SAX J2324.4-6200, is most probably a Be/X-ray source (HMXB) based on the X-ray spectrum or an very uncommon LMXB. The second slow pulsator, SAX J1452.8-4959 shows no pulsation and have a very faint counterpart, suggesting a possible LMXB or IP classification. However, the timing analysis is uncertain, indicating that the source could be of a different class (e.g CV, background AGN, ...). The X-ray to optical/IR flux ratio for these sources is not known yet.

Ignacio Negueruela: Multiwavelength observations of HMXBs: Constraints on the accretion environment of neutron stars

Most HMXBs are X-ray pulsars, and strong magnetic fields somehow inhibit jet formation, so no radio emission is detected. The nature of the donor determines the main properties of the HMXB, and low resolution spectroscopy in the optical, or IR (if optically obscured), is used to characterise the donor. High quality spectra are needed to determine luminocity class and mass loss rate, but this is difficult (especially in IR) as large telescopes are needed.

In some HMXBs, the orbital parameters can be determined. For SMC X-1, the neutron star mass is quite robustly shown to be less than 1.2 solar masses, in line with a general trend of neutron stars in HMXBs being less massive than those in LMXBs (though mass errors are large, and the sample small). The mass of the donor star in 4U1700-37 is measured to be 58 solar masses, so it appears that not all massive stars form black holes. The neutron star in this HMXB is found to be 2.4 solar masses, though the errors are large.

Lara Sidoli: Transient outburst mechanisms

Supergiants Fast X-ray Transients (SFXTs) present short transient X-ray emissions (first observed: XTE J1739) associated with OB supergiant companions and have a high dynamical range of luminosity between outbursts and quiescent phases. Different mechanisms are evoked to explain the short outbursts. The most obvious one involved a spherically symmetric clumpy wind from the companion. Observations of IGR J11215 suggested a different mechanism involving an equatorial disk wind from the supergiant. Finally, the third mechanism involves an outburst being driven by a magnetic barrier in which the wind accretion is prevented by a high magnetic field (magnetar-like) and a long spin period. More data are still required and the present monitoring campaign with Swift should address what mechanism is best suited to explain the different behaviors observed among the SFXTs population.

Teo Muñoz-Darias: Bowen Blend Echo-tomography of Neutron Star LMXBs

Teo gave an overview of a technique which picks out reprocessed emission lines (the Bowen blend) from the irradiated companion star in a neutron star binary. The continuum emission, by contrast, is swamped by the contribution from the disk. Using simultaneous X-ray/optical observations you can look for delayed echoes of X-ray variability. The time delays then tell you about the properties of the binary system as a function of orbital phase. The group are currently writing up an analysis of 4U 1636-536 (for which, fortuitously, they observed 3 reprocessed X-ray bursts), to complement an analysis of Sco X-1 published last year. In both cases the observed delays are consistent with reprocessing from the companion star for the Bowen blend lines, and the accretion disk for the continuum.

Piergiorgio Casella: Discovery of two intermittent accreting millisecond X-ray pulsars

There are a total of 8 known millisecond X-ray pulsars, which is fewer than expected from the hundreds of candidate LMXBs. A detailed search of the entire RXTE archive revealed intemittent millisecond X-ray pulsations from Aql X-1 (550Hz) and SAX J1748.9-2121 (442Hz). In the case of Aql X-1 the pulsations were only seen in 0.01% of total observation time, which indicates that longer observations may reveal millisecond pulsations in several sources where none are presently detected.

Diego Altamirano: "Millihertz quasi-periodic oscillations and their relation with Type-I X-ray Bursts: an intimate relation?"

Diego discussed whether there is a strong link between the mHz QPOs seen in some LMXBs and the occurence of Type I X-ray bursts. Until now we haven't been able to predict X-ray bursts, the recurrence time of which depend on a lot of unknown parameters. However, mHz QPOs, sometimes drifting in frequency, disapear just before an X-ray burst. This is the first time that something in the persistent emission seems to predict an X-ray burst (though mHz QPOs are not always seen before a burst). It appears that one won't see a burst unless the frequency of the mHz QPO drops below some threshold (9mHz appears to be the "magic number" in e.g. 4U1636-53). How do we interpret this? It could possibly be due to marginally stable burning.

Are mHz QPOs a new way to study X-ray bursts and changes in spectral states? Why is 9mHz the "magic number" and why there is frequency drift remains unknown.

Robert Hynes: Multiwavelength Observations of Neutron Star Transients

Rob took us away from the X-ray, and discussed the ways in which observations in the radio, IR, optical and UV are helping us to figure out the physics of neutron star binaries. Such multi-wavelength studies are building up evidence for the presence of jets, and innovative techniques like Doppler tomography and echo-mapping are generating new constraints on binary properties including neutron star mass and the size of the orbit. He also presented exciting new evidence for optical mHz Quasi-Periodic Oscillations in 4U 0614+09 - a phenomenon that has previously only been observed in 4U 1626-67. Wrapping up, he pointed out that most multi-wavelength work so far has focused on the persistent systems. There is a lot of work to be done to extend these studies to the transient systems.

Coming Talks: New Afternoon Schedule for Saturday July 19

All times are Eastern Daylight Time.

Tatehiro Mihara	Cyclotron line studies of the X-ray binary pulsars	2:00p
Lara Sidoli	Transient outburst mechanisms	2:30p
Shin Watanabe	X-ray spectroscopy of NS environments in HMXBs	3:00p
Ignacio Negueruela	Multiwavelength observations of HMXBs: Constraints on the accretion environment of neutron stars	4:00p
Ramanpreet Kaur	Chandra and XMM-Newton observations of 7 enigmatic faint persistently slow pulsators	4:30p
Dae-Sik Moon	Space Mid-Infrared Spectroscopy for Understanding the Evolution of Highly-Obscured Neutron Star X-ray Binaries	4:45p
Meeting Closed

At COSPAR: International X-ray Observatory

In discussions with Mariano Mendez and Luigi Piro, they mentioned the following:

ESA has decided that XEUS as proposed is too expensive, and it has been dropped from the ESA long-range plan. NASA and ESA have met over the past few days, and have agreed to jointly explore an international X-ray observatory, which would replace Con-X and XEUS; the agreement for doing so has been written up, and it is expected to be signed today.

Michiel van der Klis: Accreting millisecond X-ray pulsars

Accreting millisecond X-ray pulsars (AMPs) are predicted by the recycling scenario but were unsuccessfully detected in the early searches (with EXOSAT) due to an insufficient timing resolution. RXTE allowed the detection of the first AMP: SAX J1808.4. Now, 10 AMPs are known (including some intermittent and some sporadic) with frequencies between 182 and 600 Hz. Their spectral energy distribution is quite hard and indicates Compton scattering shock interactions. In addition, we observed smooth sinusoidal pulse profiles. However, the pulse shape sometimes changes (e.g. for SAX J1808).

Intermittent and sporadic pulsars can provides clues to why most NS-LMXBs do not show AMPs behaviors. This can be explained by several reasons: a relatively low mass accretion rate, a weak B-field, scattering, a wandering hot spot, ... AMPs also allow for high precision timing and calculation of orbital ephemerids (although complicated by a pulse changes and a short detectability). Moreover, we observe an important phase residual (not fully understood) suggesting possible torque or propeller effects.

The author presented results from SAX J1808 (long term spin down, change in the orbital period) and finished with a quick overview of burst oscillations and kHz QPOs.

Anna Watts: "Type I bursts and burst oscillations"

Anna reviewed the X-ray bursts which are observed from roughly half the known NS LMXBs. There is a rich variety of phenomena observed in these bursts, and new types of bursts are still emerging (e.g. burst triplets). These new types of bursts are revealing new burning regimes. However, there is still no satisfactory explanation for the burst oscillations, which are confidently observed in 12 sources. These burst oscillations show great variety in behaviour from source to source, which makes it difficult to provide a singular explanation.

Coming Talks: Saturday July 19

Last day of talks for session E11. All times are Eastern Daylight Time.

Anna Watts	Type I bursts and burst oscillations	9:30a
Michiel van der Klis	Accreting millisecond X-ray pulsars	10:00a
Mariano Mendez	Aperiodic variability in low-mass X-ray binaries	10:30a
Robert Hynes	Multiwavelength Observations of Neutron Star Transients	11:30a
Diego Altamirano	Millihertz quasi-periodic oscillations and their relation with Type-I X-ray Bursts: an intimate relation?	12:00p
Piergiorgio Casella	Discovery of two intermittent accreting millisecond X-ray pulsars	12:15p
Teo Muñoz-Darias	Bowen Blend Echo-tomography of Neutron Star LMXBs	12:30p
A. Nepomuk Otte	Detection of the Crab pulsar above 25 GeV with the MAGIC telescope	12:45p
Tatehiro Mihara	Cyclotron line studies of the X-ray binary pulsars	2:00p
Lara Sidoli	Transient outburst mechanisms	2:30p
Ignacio Negueruela	Multiwavelength observations of HMXBs: Constraints on the accretion environment of neutron stars	5:00p
Shin Watanabe	X-ray spectroscopy of NS environments in HMXBs	5:30p
Ramanpreet Kaur	Chandra and XMM-Newton observations of 7 enigmatic faint persistently slow pulsators	6:00p
Dae-Sik Moon	Space Mid-Infrared Spectroscopy for Understanding the Evolution of Highly-Obscured Neutron Star X-ray Binaries	6:15p

Benjamin Owen: How LIGO can follow up high-energy observations of young neutron stars

Ben discussed LIGO's attempts to do searches for gravitational wave emission from isolated spinning neutron stars, where the position is known but where you have to search over an unknown spin frequency. The poster child source for this type of search is Cas A. LIGO are interested in targeting (a) isolated non-pulsing neutron stars (like some of the CCOs), (b) as yet unseen neutron stars in pulsar wind nebulae/small supernova remnants, (c) massive star-forming regions in which a lot of neutron stars might be born, and (d) globular cluster cores. He also advertised the upcoming LIGO/Neutron Star astronomer meeting to be held in January 2009.

In Montreal: Fireworks at La Ronde

La Ronde amusement park is host of the Loto-Quebec's International Fireworks Competition. Events are on Wednesdays and Saturdays at 10 pm (rain or shine), with competitors representing a different country each time. This Saturday, July 19, will feature Howard & Sons Pyrotechnics Australia. You may buy a ticket and go watch the fireworks on site, but I would rather suggest you just walk East on Ste-Catherine Street to Papineau Street near the Jacques-Cartier Bridge (it's a nice ~15 minutes walk from the Palais des Congres area) and the whole street is blocked to cars from St-Denis Street. Follow this link to see some gorgeous pictures from this year's previous events.

Jonathan Arons: Beam Filamentation Instability of Interacting Current Sheets in Striped Relativistic Winds: The Origin of Low Sigma?

According to models, pulsar wind nebula behave as if the wind is weakly magnetized at termination shock. For the aligned rotator, the current sheet is flat and along the equator. In reality, pulsars are oblique rotators. The current sheet of such a pulsar travels away with the wind outflow and has a more complicated "wavy" or "striped" topology. One has to find a way of dissipating the striped sheets as they travel away in order to obtain a low magnetization at the termination shock. You may imagine these striped sheets as parallel slabs having anti-parallel magnetic fields, which generate, in the highly magnetized plasma in between, a current flow. Plausible magnetization dissipation mechanisms are investigated within this framework.

George Pavlov: Central Compact Objects in Supernova Remnants

George reviewed the status of observations of Compact Central Objects (CCOs) - radio and gamma-ray quiet X-ray sources that are found close to the center of supernova remnants. Evidence is emerging that at least two of them are 'antimagnetars' (gamnetars?) - neutron stars that are born spinning slowly but with unusually low magnetic fields compared to most radio pulsars. The youngest of the CCOs (in the Cas A supernova remnant) seems to be different - and could well be a quiescent magnetar. Single temperature blackbody spectral fits for this object suggest a very small radius (which might imply that it is a quark star). More complex spectral fits involving two components with different temperatures, however, can give an acceptable fit to a neutron star equation of state. Ultimately phase-coherent timing analysis (with XMM/Chandra), and the detection and modeling of spectral lines, are the best way to figure out the nature of these objects.

Patrick Slane: Observations of pulsar wind nebulae

Pat discussed the geometry of pulsar wind nebulae (PWN), such as their jet and torus structure. The jets, for example, are due to the the fact that the wind termination shock is farther from the pulsar at equator than along the axis. The pulsar dumps energetic particles into the PWN. Where the synchrotron lifetime of the particles is comparable to the age of the supernova, a break appears in the spectrum. Energetic electrons produce both the synchrotron and inverse Compton (IC) emission observed in PWN. By measuring both emission mechanisms, using gamma-ray and X-ray observations, one can constrain the magnetic field of the nebula. The interaction between the PWN and its surrounding supernova remnant may explain why PWN seem distorted. Because PWN evolve within a supernova remnant a reverse shock "slams" into the PWN. Turbulent and asymmetric structures are due to this reverse shock. This may explain why TeV sources are offset from pulsars.

Roberto Turolla: "Surface emission from isolated neutron stars"

Roberto Turolla discussed the various exciting prospects, as well as the complications, in theoretically understanding the surface emission from isolated neutron stars. Whether these have an atmosphere or not is crucial for understanding their emission, but remains unknown.
One would expect there to be an atmosphere, but then why do we see a BB in the X-rays? The seven XDINSs, also known as the "magnificent seven" are still radio quiet (see results/poster by Joshi et al.). Finding more sources is crucial.

David Kaplan: "Optical/IR/UV Observations of Isolated Neutron Stars"

David nicely showed how optical/IR/UV observations are providing unique information about neutron star spectral energy distributions and energetics. These objects are hard to observe (B magnitudes of 25-28), but this is still very worthwhile. So far, 6 isolated neutron stars have optical counterparts. Optical/IR/UV have in fact given very strong evidence that INSs are indeed neutron stars. A major outstanding issue is the "optical excess" (X-ray determined blackbody does not fit well at longer wavelengths). Also, it is still unknown whether the optical or UV is pulsed. Can we constrain atmospheric models using these multi-wavelength data?

Frank Haberl: X-ray observations of Isolated Neutron Stars

The author presented a global view of X-ray observations of neutrons stars and the possible information that one can deduce from them. Evidence of multicomponent Xray spectra and pulsation of the Xray flux are evidence for a non-uniform temperature on the surface of the neutron star. Three middle aged pulsars (The three musketeers) present two thermal components (from the surface and a hot spot) and a power-law component (most probably coming from the magnetosphere). Pulse phase spectroscopy from Chandra and XMM showed that the hot and the cold blackbody components are not in phase.

XMM observations of the 7 known isolated neutron stars showed that they do not have pure blackbody spectra, indicating absorption features (even multiple lines). Several origins for those lines were mentioned, e.g. Cyclotron resonance, atomic lines transitions (Hydrogen). Those isolated neutron stars also provide a unique ways of measuring their magnetic fields using 2 independent method (magnetic dipole breaking and proton cyclotron absorption). Observations of RX J0720.4-3125 put forward the evidence for precession of the neutron star and the evidence of 2 polar caps.

Finally, the author showed with cooling curves analysis the evidence of magnetic field decay. The main conclusion from this presentation is that a NS model with a uniform temperature and a dipolar magnetic field is far too simple.

Valery Suleimanov: Models of magnetized neutron stars atmospheres

New model atmospheres for high magnetic fields (>10^12 G) have been computed for fully ionized hydrogen and helium atmospheres, and for partially ionized hydrogen amospheres. It was found that the inclination of the magnetic field was unimportant, but that vacuum polarization significantly affected the spectra in the case of large fields (polarization is important because magnetic fields introduce angle and polarization dependence in the opacities). Most of the resulting spectra have absobtion features due to proton cyclotron lines.

Silvia Zane: A resonant cyclotron scattering model for the soft X-ray spectra of magnetar candidates (Talk given by Roberto Turolla)

The goal of providing the model presented here is to explain why the 0.5-10 keV emission is well represented by a Blackbody + power law component. The main idea suggests that the magnetic field is twisted inside the object. This required a supporting current that could be the cause of the X-ray luminosity increase that we observe, the cause of spectral hardening and of spin down torque increase. The resonant cyclotron scattering model developed can be applied to all magnetars (2 tabulated models available for XSPEC). Further investigation of the effects of QED cross section are required to take into account ultra-relativistic electrons. In addition, the author evoked the need to understand the cause of long term variability of AXPs and the high energy tail observed. Finally, the issue of a possible external field also have to be investigated.

A. Nepomuk Otte: Detection of the Crab pulsar above 25 GeV with the MAGIC telescope

The Crab pulsar was detected with ~6 sigma significance at >25GeV using MAGIC. Detection of the Crab has been called the holy grail of ground based gamma ray astronomy, since sensitivity below 100GeV is very difficult to achieve using the air Cherenkov detectors. The interpulse amplitude was larger than the main pulse, indicating that the interpulse has a much harder spectrum than the main pulse.

At COSPAR: Mission updates

We've just heard that RXTE is likely to be extended to August 2009 - unfortunately not long enough for full overlap with LIGO's next science run, but long enough to give some overlap with GLAST. In Session E15 we heard about exciting new mission proposals including AXTAR (an advanced X-ray timing mission), NICE (which aims to explore neutron star properties), and GEMS (investigating gravity and extreme magnetism) - but the big topic was the possible merger of Constellation-X and XEUS.

Mike Muno: Massive Stars and Magnetars

Mike Muno cites Heger et al (2003), which claimed neutron stars can form from stars with initial masses > 25 solar masses, if they have high (i.e. solar) metalicities. But there's scant data supporting this. Muno's serendipitous discovery of a magnetar in Westerlund 1 (which has ~100 stars with M>35 Msun; age 3.6 Myr) supports this. Two other magnetars (SGR 1806-20 and SGR 1900+14) may also be associated with young clusters (and so, have massive star progenitors).

Muno recently searched 506 Chandra and 441 XMM observations near the galactic plane for new magnetars with 5<P<30 sec, finding none. With the known objects, he places a "standard AXP" birth rate of 0.003-0.016/yr; and estimates there are 59(+92,-32) total "standard AXPs" in the galaxy. For transient AXPs, the birth rate is 0.008-0.06/yr, and a total number of ~600 in the galaxy. At least 10% of neuron stars are born as magnetars. New transient magnetar searches are needed to firm these uncertain numbers.

Coming Talks: Friday July 18

Scheduled talks, times are Eastern Daylight Time

Mike Muno	Magnetars and Massive Stars	9:30a
Silvia Zane	A resonant cyclotron scattering model for the soft-ray spectra of magnetar candidates	10:30a
Valery Suleimanov	Models of magnetized neutron stars atmospheres	10:45a
Frank Haberl	X-ray observations of Isolated Neutron Stars	11:30a
David Kaplan	Optical/IR Observations of Isolated Neutron Stars	12:00p
Roberto Turolla	Surface emission from isolated neutron stars	12:30p
Elena Amato	Pulsar Wind nebulae: Theoretical Overview	2:00p
Patrick Slane	Observations of pulsar wind nebulae	2:30p
Rino Bandiera	On the peculiar shapes of some pulsar bow-shock nebulae	3:00p
Ingo Buesching	Cooling flows in Pulsar Wind Nebulae	3:15p
George Pavlov	Central Compact Objects in Supernova Remnants	5:00p
Jonathan Arons	Beam Filamentation Instability of Interacting Current Sheets in Striped Relativistic Winds: The Origin of Low Sigma?	5:30p
Ocker De Jager	Probing the birth periods and pair production multiplicities of neutron stars through multiwavelength observations of their wind nebulae.	5:45p
Nobuyuki Kawai	Jets and tori of a young pulsar PSR B1509-58	6:00p
Benjamin Owen	How LIGO can follow up high-energy observations of young neutron stars	6:15p

Andreas Reisenegger: Neutron star magnetic fields: a theoretical perspective

Neutron star matter is stably stratified by a composition gradient, i.e. is not a barotropic fluid, and the magnetic fields are weak (the fluid pressure is about 7 orders of magnitude greater than the magnetic pressure for magnetar strength fields). Stable hydromagnetic equilibria appear to exist, where the stable stratification plays an important role. Erosion of this stratification through beta decays or ambipolar diffusion (relative motion of charged particles and neutrons) allows magnetic field evolution.

David Eichler: A model for the large amplitude QPO luminosity variation in the tail of SGR giant flares

We heard some discussion earlier in the session about the seismic vibrations that have been detected in the aftermath of giant flares from magnetars. One of the big questions relating to the oscillations (which allow us to do seismology and study the interior of the stars) is how a vibration of the stellar surface can generate varying X-ray emission. Particularly challenging for theorists are the high amplitudes of the variations in the X-ray emission. These are far too large to be explained by physical motions of the star's crust (it would be ripped apart) - so you need some kind of amplification mechanism. David Eichler presented a new model that may resolve this problem. The model relies on the fact that torsional oscillations of the crust (twisting motions) will also force the magnetic field to twist and oscillate. The associated currents drive variations in density; resonant cyclotron upscattering then operates, with varying optical depth, to generate high amplitude variable X-ray emission. The nice thing about the model is that you don't need large amplitude crust movements to get much larger amplitude variations in the X-ray. David also pointed out that the energy deposited in the crust as the oscillations dissipate energy could be responsible for the observed afterglows.

Joseph Gelfand: Radio Emission from the Magnetar SGR 1806-20 Giant Flare

The 2004 Decemeber 27 giant flare from SGR 1900+14 was the most energetic giant flare ever observed. The radio light curve had a t^-1.5 to ^ 2.2 dependence 9 to 25 days after the event. After that it had a t^-3 dependence. The source rebrightened 25 to 35 days later. After 35 days the flux decreased as t^-1. The radio spectrum had an average spectral index of -0.7+/-0.3. This is what is expected from shock heated electrons. In the first few days after the event, not much motion was observed in the position of the radio nebula; however, 9 to 31 days later, constant proper motion was observed at 1/2 of the expansion rate. This motion was observed along the major axis. No coherent motion 31 days later. All these results were found via modeling the UV data. The emission seems to be a one-sided outflow. He interprets this behaviour as being due to the giant flare ejecting material into the surroundings. The collision compressed ejecta into a thin shell. What is the ejecta? Either the ejection of a magnetic flux loop or baryons ablated off the surface of the neutron star. Both give ejecta mass of 10^24.5 g.

Peter den Hartog: Different spectral components revealed in the high-energy pulse profiles of Anomalous X-ray Pulsars

4 AXPs have been detected above 10 keV, 3 with INTEGRAL and 1 with the High Energy X-ray Timing Experiment (HEXTE) aboard the Rossi X-ray Timing Explorer (RXTE). For AXPs 4U 0142+61 and 1 RXS J1708-40 he finds peak energies of 279 keV and 287 keV respectively. Pulsed emission from 1 RXS J1708-40 is observed upto 270 keV. Broadband phase resolved spectroscopy of this source revealed that different components of its pulse profile vary with energy. In only 0.1 in pulse phase the spectrum of the source goes from very hard to very soft. He concludes that the pulsed spectra of AXPs are much more complex than previously thought. Many spectral components are required to explain the pulse shapes of these sources. These observations can be used to test the geometries of the magnetospheres of these sources. If you would like a copy of Peter's thesis, email him at Hartog@sron.nl.

Fotis Gavriil: Review of Magnetar X-ray Observations

Fotis Gavriil gave a summary of X-ray (and some other wavelength!) observations of magnetars, which are neutron stars with extremely strong magnetic fields. There are now 4 confirmed Soft Gamma Repeaters (SGRs), with 1 candidate, and 10 confirmed Anomalous X-ray Pulsars (AXPs), with 1 candidate. Three of the confirmed sources, and one of the candidates, are associated with supernova remnants, implying that they are young stars. For an up to date summary of all known magnetars see this website.

Fotis gave a nice overview of all of the great things that we have learned about magnetars from X-ray observations with RXTE, including the persistent pulsations, the short repeating X-ray flares, the rare giant gamma-ray flares, and their long-term X-ray outbursts. Of particular interest is the high level of flux variability, and changes in pulse profile. Both types of source also show major timing noise (particularly the SGRs), and glitches have now been detected in all of the AXPs for which coherent timing is available. With regard to the short X-ray flares, he noted that the AXPs burst less often but can have much longer bursts (minutes as opposed to less than a second for the SGRs). He made a special point about the common statement that SGR bursts are more energetic, noting that this could just be because the SGRs are more prolific bursters, since high energy bursts are rarer.

Fotis also discussed in detail the emerging connections between the high field radio pulsars (one of which has now been found to show magnetar like X-ray flares) and the magnetars (some of which show transient radio pulsations). He argued that we now seem to be seeing a continuum of behavior, and pointed out that the high magnetic field radio pulsars have not been observed in X-ray very often, so we may have missed other transient magnetar like episodes. Something for future missions!

Wrapping up, he posed a number of questions for the future. How are magnetars born? What is the reason for their inherent variability? How common are they in the Galaxy? What is the source for their high energy emission? What is the connection between the magnetars and the rotation powered radio pulsars? And do other young, highly magnetized rotation powered pulsars exhibit magnetar like behavior?

Rino Bandiera: On the peculiar shapes of some pulsar bow-shock nebulae

Balmer lines, in particular Halpha are excellent tracers of bow-shock nebula. The "Guitar" nebula contains a fast moving pulsar moving toward the head of the Guitar. The field in X-rays contains a strange linear feature oriented about 120 degrees away from the pulsar's proper motion direction. The energetics of the pulsar spin-down does not seem to explain this elongated feature. He proposes the magnetic flux tubes of the ISM are directed along the direction of this feature. In this region, the gyration radius of electrons is comparable to the bow-shock size, and hence higher energy electrons would diffuse out the shock.

Yuri Lyubarsky: Theoretical overview of magnetars

The strong magnetic fields (~10^15 G) in magnetars feed many types of activity, and the emission from magnetars is powered by the field rather than by rotation or accretion. By restricting electron motion, the magnetic fields also suppress the radiation cross-section, thus allowing large super-Eddington luminocities.

A 10^46 erg giant flare was seen from the magnetar SGR 1806-20 on Dec. 27th 2004, which provides a useful test of magnetar theory. Despite being ~100 times brighter than other flares from this source, the energy in the pulsating tail was similar to that of other flares. This is thought to be because the energy in the tail is set by the storage capacity in the magnetosphere, which mostly depends on the magnetic field. Mass ejection was also detected in connection with the giant flare, by resolving the ejected cloud using radio interferometry. Further, QPOs were detected in the tail of the giant flare.

QPOs open for the possibility of NS seismology. Intermittent QPOs can probe (perhaps) shear modes in the NS crust, while low frequency (~20Hz) QPOs can probe the Alfven speed in the core. Magnetic fields couple the crust to the core on timescales of 0.01-0.1s, and this must be considered when interpreting QPOs.

The trapped fireball model predicts frequency dependent radiation cross-section, and this produes a flat spectrum below BB peak. One should attempt to fit this to the spectrum of sources which have previously been fitted with a BB plus power law spectrum.

The magnetar paradigm for SGRs and AXPs is now unquestioned, and high quality spectral data require sophisticated models of the radiation transfer. X-ray polarimitry would be a great help, but is presently unavailable.

In Montreal: My personal restaurants address book

As I am a local, I thought it would be interesting to share my personal restaurants address book. I hope this will inspire you...

Au Pied De Cochon: Quebec modern "terroir" food. This place is absolutely unique...
Located on Duluth street, east form St-Denis.

Steak et Frites (bring your own wine):
3 locations: L'hotel W (downtown), St-Paul street, Laurier street (Cote-des-Neiges and Parc)

M. Burger: Very innovative, "customizable" burgers
Located on Drummond, north from Maisoneuve.

For Grec food, the place to be is Duluth street, east from St-Denis. Several "bring your own wine" places.

Little Italy neighborhood is located around the Jean-Talon metro station (orange line). It's not downtown but it's the place to be for great Italian food (St-Laurent, corner Jean-Talon).

For some great Cuisine Francaise restaurants, I suggest to go on Rachel Street, east from St-Denis. Several "bring your own wine", very classy but affordable (CAN$ 20-30) restaurants (especially when you bring your wine). The "917" and "Poisson Rouge" are particularly recommended.

Last, not the least: Poutine! You have to try it, it's a local, greasy meal unique to Quebec. I suggest "La Banquise" corner Rachel and Papineau. See more at Montreal Poutine.

Jason Hessels: Uncovering the population of nearby neutron stars at low radio frequencies

Looking for nearby pulsars

• Look for pulsars at distances below 2 kpc.
  
• Get luminosity distributions.
• Since they're close, they can easily be follow up at other wavelengths.
• Look for pulsars at low frequencies. Low dispersion measurement (DM) sources easy to distinguish from noise. Low frequencies have not been exploited. Unfortunately, these sources will have many dispersion trials.

Galactice Plane Survey with the Green Bank Telescope (GBT)

• GBT survey at 350-MHz. Look for pulsars and radio transients. Sensitive to Low DM sources. The entire Northern Galactic Plane has been covered. 33 new pulsars so far! Examples of sources discovered because of low frequency observing:

1. PSR J0243+62 discovered in a single pulse search. P=592 ms. At a distance of 400 kpc. Very low luminosity L400~0.2 mJy kpc^2.
   
2. PSR J0054+66 also identified in a single pulse search. P=1.39 s. D~ 1kpc.

• GBT350 discoveries show there are still many nearby intermittent sources.
• These are the types of sources that the LOw Frequency ARray (LOFAR) will find.

Pulsars with LOFAR

• 30-80 MHz.
• 2x24 High band antennae (HBA) tiles.
• 96 Low Band Antennae (LBA) tiles.
• Ideal for surveying the local Galaxy for pulsars.
• Single pulses from B0329+54 found "blindly" using just 6 LOFAR HBA tiles.
• Simulations show that there is the potential to find +1000 new pulsars.
• LOFAR will be online soon and will provide unparalleled sensitivity.
  

Maxim Lyutikov: Crab giant pulses at sub-nanosecond resolution: quantitative model of non-trivial spectrum

A model for the emission of giant pulses from the Crab pulsar is proposed by Lyutikov and is based on anomalous cyclotron resonance on the ordinary modes. His main conclusions are: 1. giant pulses come from closed field lines; 2. giant pulses are seen by chance, i.e. produced in narrow emission windows; 3. closed field lines are not dead, but populated by plasma with n >> n_{GJ}; 4. Earth analogues: magnetosperic hiss, roars.

Rene Breton: "New test of gravity using eclipses in the double pulsar PSR J0737-3039A/B"

Rene Breton showed how he and collaborators have used the eclipses of pulsar A in the double pulsar system to perform a new test of gravity:

• Double pulsar system is observed almost edge on (i ~ 89 deg): eclipses of pulsar A by the magnetosphere of B.
• Eclipses last for ~30 seconds, no strong frequency dependence.
• Can see modulation during the eclipse at the spin rate of pulsar B.
• Synchrotron absorbtion in the magnetosphere of pulsar B.
• "rotating doughnut" model, very sensitive to the geometry of the system.
• Very good evidence for dipolar magnetic field.
• Kramer et al. 2006: measured 5 relativistic effects from pulsar timing (most precise test of GR in the strong-field regime)
• Breton et al. 2008 in Science: Eclipse profile changing with time: precession of pulsar B's spin axis measured: 4.77+0.66 deg/yr (consistent with GR prediction)

Some very nice movies showing this result are available here.

Vyacheslav Zavlin: Pulsar high energy emission: Soft X-rays

This presentation was a broad overview of soft x-ray emission from pulsars/NSs. Observations of NSs in the soft X-ray band are important since the bulk of the flux from NSs falls in this range and since some NSs/pulsars have still not been detected outside this range. Both thermal and non-thermal emission can be observed. The thermal emission, due to internal heat (or from a small hot spot), is ideal to constrain the equation of state. It is important to note that a blackbody interpretation of the thermal radiation implies an emission area much smaller than with a H-atmosphere interpretation. The non-thermal emission can be due to the magnetosphere, pulsar wind nebula, or inter-binary shocks. Young objects (~1 kyr) are dominated by non-thermal emission, while middle-aged and old pulsar (>1 Gyr) are dominated by thermal radiation, from the surface and hot polar caps respectively. The author presented different objects that have been observed in different wavelength bands (Vela, PSR J0538+2817, Geminga, ...). In most cases,  polar caps (thermal emission) were (very likely) detected. However, non-thermal emission can be used in many cases to explain the X-ray emission. Finally, regarding the cooling models of pulsars/NSs, we notice large difference in the cooling curve whether or not proton superfluidity is included in the model.

Matthew Baring: Theoretical Perspectives on Non-Thermal Pulsar Emission

At present, there are over 1700 radio pulsars, around 30 optical pulsars, over 60 X-ray pulsars, and 7 gamma ray pulsars known. The main focus of this talk was how to distinguish between the polar cap and outer gap emission models, in particular how to do this using the 30MeV to 300GeV capabilities of the newly launched GLAST telescope.
The predicted populations of pulsars detectable with GLAST differ depending on whether one uses a polar cap model or an outer gap model. If pulsar emission originates from a polar cap, one expects 150-200 new pulsars detected with GLAST, while one expects 300-800 new pulsar detections if the emission originates from around the surface, as in the outer gap model.
The predicted spectrum of the Vela pulsar differs in the two models, and simulations indicate that GLAST should be able to resolve this difference.
In general, the polar cap model predicts that the highest detectable energies from pulsars decrease with increasing magnetic field, while the outer gap model predicts increasing maximum energy with increasing magnetic field. The present data cannot rule out either model on this basis, but GLAST data may be able to do so.
In the future, polarimetry in X-ray and soft gamma ray bands would be valuable in constraining pulsar emission mechanisms, by distinguishing between synchrotron and curveature polarization throgh the polarization swing profiles.

Ben Stappers: "Pulsar radio emission: overview of observational status"

• Better chance of finding drifting subpulses at longer observing wavelengths? (Weltevrede et al. 2006, 2007). Drifting a general property of radio emission from neutron stars?

• "swooshes": epsiodic emission in "new" region (pulse phase) turns on when the "normal" emission turns off. Hard to reconcile with carousel model.
• "flaring": similar to "swooshing" phenomenon, occasional bright pulses at different pulse longitudes.
  
• "RRAT-alogue" (catalogue of known RRATs): more than 24 RRATs now known (11 presented in original McLaughlin et al. paper). New, very nearby RRATs being found.
  
• Some RRATs show bursts of several pulses, closely spaced: "bursters".
  
• Four "intermittent pulsars" (e.g. PSR B1931+24) now known. Switch on/off on timescales of weeks to months and show different Pdot when on/off.
• Very high degree of modulation in single pulses of radio-emitting magnetar XTE J1810-197.
• Is there a continuum of processes across the different "off" states from the single/few pulse nulls, extreme nullers, RRATs, and intermittent pulsars?
  

Coming Talks: Thursday, July 17

Talks scheduled for July 17th (times are Eastern Daylight Time):

Ben Stappers	Pulsar radio emission: overview of observational status	9:30a
Matthew Baring	Theoretical Perspectives on Non-Thermal Pulsar Emission	10:00a
Willem Hermsen	Non-thermal high-energy emission from radio pulsars: observational status prior to the GLAST era.	10:30a
Vyacheslav Zavlin	Pulsar high-energy emission: soft X-rays	11:30a
Alberto Pellizzoni	Recent pulsar results from AGILE	12:00p
Rene Breton	New Test of Gravity Using Eclipses in the Double Pulsar PSR J0737-3039A/B	12:30p
Alice Harding	Multiwavelength Emission From Pulsar Slot Gaps	12:45p
Maxim Lyutikov	Crab giant pulses at sub-nanosecond resolution: quantitative model of non-trivial spectrum	2:00p
Jason Hessels	Uncovering the population of nearby neutron stars at low radio frequencies	2:15p
Yuri Lyubarsky	Theoretical overview of magnetars	2:30p
Fotis Gavriil	Review of Magnetar X-ray Observations	3:00p
Diego Götz	INTEGRAL and Magnetars: a hard X-ray approach to extreme neutron stars	5:00p
Peter Den Hartog	Different spectral components revealed in the high-energy pulse profiles of Anomalous X-ray Pulsars	5:30p
Joseph Gelfand	Radio Emission from the Magnetar SGR 1806-20 Giant Flare	5:45p
David Eichler	A model for the large amplitude QPO luminosity variation in the tail of SGR giant flares	6:00p
Andreas Reisenegger	Neutron star magnetic fields: a theoretical perspective	6:15p

In Montreal: Fantasia Film Festival

For those looking for something to do in the evenings, I highly recommend the Fantasia Film Festival, which is currently happening in and around Concordia University in the downtown area. This is Montreal's premiere alternative film festival. Sunday night I saw "Be a Man! Samurai School" (a comedy?), and I can definitely recommend it. The director was on hand and gave us an impressive martial arts display.

At COSPAR: About E15 (tuesday morning)

During the first talk this morning, S. Bhattacharya claimed that the spin frequency of NS must be measured simultaneously with the radius and the mass in order to constrain the EoS. Does anyone has a comment about that ? Is it really crucial to measure the spin frequency ?

Another comment that I would like to make concerns a question following the talk by R. Wijnands. He expressed doubts about the qLMXBs nature of those objects detected in GC since they have been observed in outbursts. I find it a quite interesting opinion, however, I don't think that we should exclude those objects from being quiescent accreting neutron stars. Only a few qLMXBs are known in globular clusters and for a several years only. The quiescent period can last more than 10 years in some cases of known field qLMXBs therefore I believe that time will tell whether or not they are transient objects and if they will go through an outburst stage.

At COSPAR: EoS Introduction (E15)

Here is a quick summary of this morning's session.

Peter Jonker presented how to observationally constrain the EoS of neutron stars and also talked about the cooling of neutron stars. He briefly mentioned the upcoming Galactic Belt Survey, a series of observation with Chandra covering a total of 6x1 arcmin in order to find more X-ray transient near the galactic plane. Overall, I found that it was an excellent presentation outlining the crucial points of LMXBs observations and quoting several well-known objects like 4U 1608-52, Cen X-4, the long duration transient KS 1731-260, or the very faint transient SAX J1808.4-3657.

This was then followed by a talk by Pawel Haensel presenting the theory behind all this. As accreting matter compresses the inner crust, material gets out of equilibrium and electron capture/neutron emission occur, releasing 1.5-2 MeV per accreted nucleon. He also talked about the timescales involved.

Finally, Nathalie Degenaar gave a very interesting talk about very faint X-ray transients with outburst luminosities as low as 10^34 erg/s. In two case, a faint burst was happening followed by a Type 1 X-ray burst suggesting right away that this small burst could be a precursor to the Type 1 burst.

Tomorrow's half day session will be fully dedicated to the methods of constraining the EoS using accreting neutron stars. I am looking forward to the presentation by R. Wijnands, N. Webb, and P. Ray.

Welcome!

Welcome to the blog for:

Astrophysical Studies of Neutron Stars from Multiwavelengths Observations
COSPAR 2008, Session E11
Thursday July 17 - Saturday July 19
Montreal, Canada

In recent years, we have seen tremendous progress in the field of neutron star research, primarily enabled by multi-wavelength timing, imaging and spectroscopic observations with both ground and space-based observatories. Along with ground-based radio, optical and infra-red telescopes, an array of X-ray and Gamma ray observatories -- such as RXTE, INTEGRAL, Chandra, XMM-Newton and SWIFT -- with broad ranging timing, spectral and imaging capabilities has opened a new era of multi-wavelength investigations. Multi-wavelength observations of the different manifestations of neutron stars like radio pulsars, magnetars, isolated neutron stars etc. offer the opportunity to investigate a wide range of astrophysical problems including the extremes of gravity, density and magnetic field. At the COSPAR assembly in Montreal, 2008, we will have an opportunity to bring together researchers from diverse fields and gauge direction of future neutron star research with existing and coming observatories, such as GLAST and ASTROSAT.


With our intrepid team of live-bloggers, we'll be bringing you the short story on talks given during the E11 sessions, looks forward towards coming sessions, hold discussions on topics needing clarity, and provide useful local information for those who are physically in Montreal for the meeting.

Look for the science talk live-blogging -- short descriptions of science talks given during the E11 sessions, posted immediately after the talks themselves. This is a great place to make comments, particularly if you are not in Montreal for the conference.

Watch for "In Montreal" -- postings about goings-on in the city while COSPAR is in session.

And our "At COSPAR" postings will focus on events which will be of special interest to readers of this blog, especially regarding neutron stars outside the E11 scientific session.