Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userFast quasi-periodic oscillations in the eclipsing polar VV Puppis from VLT and XMM-Newton observations
88
0
0.0
(
0
)
Added by
J. M. Bonnet-Bidaud
Publication date
2019
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
We present high time resolution optical photometric data of the polar VV Puppis obtained simultaneously in three filters (u, HeII $lambda$4686, r) with the ULTRACAM camera mounted at the ESO-VLT telescope. An analysis of a long 50 ks XMM-Newton observation of the source, retrieved from the database, is also provided. Quasi-periodic oscillations (QPOs) are clearly detected in the optical during the source bright phase intervals when the accreting pole is visible, confirming the association of the QPOs with the basis of the accretion column. QPOs are detected in the three filters at a mean frequency of $sim$ 0.7 Hz with a similar amplitude $sim$ 1%. Mean orbitally-averaged power spectra during the bright phase show a rather broad excess with a quality factor Q= $ u$/$Delta u$ = 5-7 but smaller data segments commonly show a much higher coherency with Q up to 30. The XMM (0.5--10 keV) observation provides the first accurate estimation of the hard X-ray component with a high kT $sim$ 40 keV temperature and confirms the high EUV-soft/hard ratio in the range of (4--15) for VV Pup. The detailed X-ray orbital light curve displays a short $Delta phi simeq 0.05$ ingress into self-eclipse of the active pole, indicative of a accretion shock height of $sim$ 75 km. No significant X-ray QPOs are detected with an amplitude upper limit of $sim$30% in the range (0.1--5) Hz. Detailed hydrodynamical numerical simulations of the post-shock accretion region with parameters consistent with VV Pup demonstrate that the expected frequencies from radiative instability are identical for X-rays and optical regime at values $ u$ $sim$ (40--70) Hz, more than one order magnitude higher than observed. This confirms previous statements suggesting that present instability models are unable to explain the full QPO characteristics within the parameters commonly known for polars.
rate research
Read More
Quasi-periodic oscillations (QPOs) of a few seconds have been detected in some Polars, the synchronised subclass of cataclysmic systems containing a strongly magnetised white dwarf (WD) which accretes matter from a red dwarf companion. The QPOs are thought to be related to instabilities of a shock formed in the accretion column, close to the WD photosphere above the impact region. We present optical observations of the polar V834 Centauri performed with the fast ULTRACAM camera mounted on the ESO-VLT simultaneously in three filters (u, He II 4686A, r) to study these oscillations and characterise their properties along the orbit. Fast Fourier transforms and wavelet analysis have been performed and the mean frequency, rms amplitude, and coherence of the QPOs are derived; a detailed inspection of individual pulses has also been performed. The observations confirm the probable ubiquity of the QPOs for this source at all epochs when the source is in a high state, with observed mean amplitude of 2.1 percent (r), 1.5 percent (He II), and 0.6 percent (u). Trains of oscillations are clearly observed in the r light curve and can be mimicked by a superposition of damped sinusoids with various parameters. The QPO energy distribution is comparable to that of the cyclotron flux, consistent for the r and He II filters but requiring a significant dilution in the u filter. New 1D hydrodynamical simulations of shock instabilities, adapted to the physical parameters of V834 Cen, can account for the optical QPO amplitude and X-ray upper limit assuming a cross section of the accretion column in the range (4-5) E14 cm2. However, the predicted frequency is larger than the observed one by an order of magnitude. This shortcoming indicates that the QPO generation is more complex than that produced in a homogeneous column and calls for a more realistic 3D treatment of the accretion flow in future modelling.
We present XMM-Newton observations of the eclipsing polar EP Dra which cover nearly 3 binary orbital cycles. The X-ray and UV data show evidence for a prominent dip before the eclipse which is due to the accretion stream obscuring the accretion region. The dip ingress is rapid in hard X-rays suggesting there is a highly collimated core of absorption. We find that a different level of absorption column density is required to match the observed count rates in different energy bands. We propose that this is due to the fact that different absorption components should be used to model the reprocessed X-rays, the shocked X-ray component and the UV emission and explore the affect that this has on the resulting fits to the spectrum. Further, there is evidence that absorption starts to obscure the softer X-rays shortly after the onset of the bright phase. This suggests that material is threaded by an unusually wide range of magnetic field lines, consistent with the suggestion of Bridge et al. We find that the period is slightly greater than that determined by Schwope & Mengel.
We report on the discovery of mHz quasi-periodic oscillations (QPOs) from the high mass X-ray binary (HMXB) IGRJ19140+0951, during a 40 ks XMM-Newton observation performed in 201 5, which caught the source in its faintest state ever observed. At the start of the observation, IGRJ19140+0951 was at a low flux of 2$times$10$^{-12}$~erg~cm$^{-2}$~s$^{-1}$ ( 2-10 keV; L$_{rm X}$=3$times$10$^{33}$~erg~s$^{-1}$ at 3.6 kpc), then its emission rised reaching a flux 10 times higher, in a flare-like activity. The investigation of the pow er spectrum reveals the presence of QPOs, detected only in the second part of the observation, with a strong peak at a frequency of 1.46$pm{0.07}$~mHz, together with higher harm onics. The X-ray spectrum is highly absorbed (N$_{rm H}$=$10^{23}$~cm$^{-2}$), well fitted by a power-law with a photon index in the range 1.2-1.8. The re-analysis of a Chandra archival observation shows a modulation at 0.17+/-0.05mHz, very likely the neutron star spin period (although a QPO cannot be excluded). We discuss the origin of the 1.46 mHz QPO in the framework of both disc-fed and wind-fed HMXBs, favouring the quasi-spherical accretion scenario. The low flux observed by XMM-Newton leads to about three orders of magnit ude the source dynamic range, overlapping with the one observed from Supergiant Fast X-ray Transients (SFXTs). However, since its duty cycle is not as low as in SFXTs, IGRJ19140 +0951 is an intermediate system between persistent supergiant HMXBs and SFXTs, suggesting a smooth transition between these two sub-classes.
We study the Rossby wave instability model of high-frequency quasi-periodic oscillations (QPO) of microquasars. We show ray-traced light curves of QPO within this model and discuss perspectives of distinguishing alternative QPO models with the future Large Observatory For X-ray Timing (LOFT) observations.
XMM-Newton has observed the X-ray sky since early 2000. The XMM-Newton Survey Science Centre Consortium has published catalogues of X-ray and ultraviolet sources found serendipitously in the individual observations. This series is now augmented by a catalogue dedicated to X-ray sources detected in spatially overlapping XMM-Newton observations. The aim of this catalogue is to explore repeatedly observed sky regions. It thus makes use of the long(er) effective exposure time per sky area and offers the opportunity to investigate long-term flux variability directly through the source detection process. A new standardised strategy for simultaneous source detection on multiple observations is introduced. It is coded as a new task within the XMM-Newton Science Analysis System and used to compile a catalogue of sources from 434 stacks comprising 1,789 overlapping XMM-Newton observations that entered the 3XMM-DR7 catalogue, have a low background and full-frame readout of all EPIC cameras. The first stacked catalogue is called 3XMM-DR7s. It contains 71,951 unique sources with positions and parameters such as fluxes, hardness ratios, quality estimates, and information on inter-observation variability. About 15% of the sources are new with respect to 3XMM-DR7. Through stacked source detection, the parameters of repeatedly observed sources can be determined with higher accuracy than in the individual observations. The method is more sensitive to faint sources and tends to produce fewer spurious detections. With this first stacked catalogue we demonstrate the feasibility and benefit of the approach. It supplements the large data base of XMM-Newton detections by additional, in particular faint, sources and adds variability information. In the future, the catalogue will be expanded to larger samples and continued within the series of serendipitous XMM-Newton source catalogues.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
