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.