arXiv subjects

S. Fabrika

Publications and source records attributed to S. Fabrika.

53 records · Page 3Linked to original sources

arXiv2006

Spectroscopy of Optical Counterparts of Ultraluminous X-ray Sources

Here we present the results of panoramic and long-slit observations of eight ULX nebular counterparts held with the 6m SAO telescope. In two ULXNe we detected for the first time signatures of high excitation ([OIII]5007 / Hβ> 5). Two of the ULXs were identified with young (T ~ 5-10 Myr) massive star clusters. Four of the eight ULX Nebulae (ULXNe) show bright high-excitation lines. This requires existence of luminous (~ 10^{38} .. 10^{40} erg/s) UV/EUV sources coinciding with the X-ray sources. Other 4 ULXNe require shock excitation of the gas with shock velocities of 20-100km/s. However, all the studied ULXN spectra show signatures of shock excitation, but even those ULXNe where the shocks are prevailing show presence of a hard ionizing source with the luminosity at least ~10^{38} erg/s. Most likely shock waves, X-ray and EUV ionization act simultaneously in all the ULXNe, but they may be roughly separated in two groups, shock-dominated and photoionization-dominated ULXNe. The ULXs have to produce strong winds and/or jets powering their nebulae with \~10^{39} erg/s. Both the wind/jet activity and the EUV source needed are consistent with the suggestion that ULXs are high-mass X-ray binaries with the supercritical accretion disks of the SS433 type.

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arXiv2006

Observation Campaign of SS 433 in April 2006

A radio-IR-optical-X-ray observation campaign of SS 433 has been performed in April 2006, when the jet axis is almost perpendicular to the line of sight. Five flares have been detected during the campaign by radio monitoring observation with RATAN-600. The X-ray astronomical satellite Suzaku observed the source in and out of eclipse. In the X-ray data out of eclipse, the flux shows a significant variation with a time scale of hours. The source seems to be in the active state during the campaign. The observation logs and preliminary results are presented.

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arXiv2006

The supercritical accretion disk in SS433 and ultraluminous X-ray sources

SS433 is the only known persistent supercritical accretor, it may be very important for understanding ultraluminous X-ray sources (ULXs) located in external galaxies. We describe main properties of the SS433 supercritical accretion disk and jets. Basing on observational data of SS433 and published 2D simulations of supercritical accretion disks we estimate parameters of the funnel in the disk/wind of SS 433. We argue that the UV radiation of the SS433 disk (~50000 K, ~10^{40}erg/s) is roughly isotropic, but X-ray radiation (~10^7 K, ~10^{40}erg/s) of the funnel is midly anisotropic. A face-on SS433 object has to be ultraluminous in X-rays (10^{40-41}erg/s). Typical time-scales of the funnel flux variability are estimated. Shallow and very broad (0.1-0.3c) and blue-shifted absorption lines are expected in the funnel X-ray spectrum.

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arXiv2006

The Optical Counterpart of an Ultraluminous X-ray Source NGC6946 ULX-1

We present a study of a peculiar nebula MF16 associated with an Ultraluminous X-ray Source NGC6946 ULX-1. We use integral-field and long-slit spectral data obtained with the 6-m telescope (Russia). The nebula was for a long time considered powered by strong shocks enhancing both high-excitation and low-excitation lines. However, kinematical properties point to rather moderate expansion rates (V ~ 100-200 km/s). The total power of the emission-line source exceeds by one or two orders of magnitude the power observed expansion rate can provide, that points towards the existence of an additional source of excitation and ionization. Using CLOUDY96.01 photoionization code we derive the properties of the photoionizing source. Its total UV/EUV luminosity must be about 10^{40} erg/s.

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arXiv2006

Diagnostics of the black hole candidate SS433 with the RXTE

We present our analysis of the extensive monitoring of SS433 by the RXTE observatory collected over the period 1996-2005. The difference between energy spectra taken at different precessional and orbital phases shows the presence of strong photoabsorption (N_H>10^{23}cm^{-2}) near the optical star, probably due to its powerful, dense wind. Therefore the size of the secondary deduced from analysis of X-ray orbital eclipses might be significantly larger than its Roche lobe size, which must be taken into account when evaluating the mass ratio from analysis of X-ray eclipses. Assuming that a precessing accretion disk is geometrically thick, we recover the temperature profile in the X-ray emitting jet that best fits the observed precessional variations in the X-ray emission temperature. The hottest visible part of the X-ray jet is located at a distance of l_0/a~0.06-0.09, or ~2-3*10^{11}cm from the central compact object, and has a temperature of about T_{max}~30 keV. We discovered appreciable orbital X-ray eclipses at the ``crossover'' precessional phases (jets are in the plane of the sky, disk is edge-on), which under model assumptions put a lower limit on the size of the optical component R/a>0.5 and an upper limit on a mass ratio of binary companions q=M_x/M_{opt}<0.3-0.35, if the X-ray opaque size of the star is not larger than 1.2R_{Roche, secondary}.

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arXiv2006

Diagnostics of SS433 with the RXTE

We present analysis of extensive monitoring of SS433 by the RXTE observatory collected over the period 1996-2005. The difference between energy spectra taken at different precessional and orbital phases shows the presence of a strong photoabsorption near the optical star, probably due to its powerful dense wind. Assuming that a precessing accretion disk is thick, we recover the temperature profile in the X-ray emitting jet that best fits the observed precessional variations of the X-ray emission temperature. The hottest visible part of the X-ray jet is located at a distance of $l_0/a\sim0.06-0.09$, or $\sim2-3\times10^{11}$cm from the central compact object and has a temperature of about $T_{\rm max}\sim30$ keV. We discovered appreciable orbital X-ray eclipses at the ``crossover'' precessional phases (jets are in the plane of the sky, disk is edge-on) which put a lower limit on the size of the optical component $R/a\ga0.5$ and an upper limit on a mass ratio of binary companions $q=M_{\rm x}/M_{\rm opt}\la0.3-0.35$. The size of the eclipsing region can be larger than secondary's Roche lobe because of substantial photoabsorption by dense stellar wind. This must be taken into account when evaluating the mass ratio from analysis of X-ray eclipses.

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arXiv2006

A search for kilogauss magnetic fields in white dwarfs and hot subdwarf stars

We present new results of a survey for weak magnetic fields among DA white dwarfs with inclusion of some brighter hot subdwarf stars. We have detected variable circular polarization in the Halpha line of the hot subdwarf star Feige 34 (SP: sdO). From these data, we estimate that the longitudinal magnetic field of this star varies from -1.1 +/- 3.2 kG to +9.6 +/- 2.6 kG, with a mean of about +5 kG and a period longer than 2 h. In this study, we also confirm the magnetic nature of white dwarf WD1105-048 and present upper limits of kilogauss longitudinal magnetic fields of 5 brightest DA white dwarfs. Our data support recent finding that 25% of white dwarfs have kilogauss magnetic fields. This frequency also confirms results of early estimates obtained using the magnetic field function of white dwarfs.

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arXiv2006

Intergal field spectroscopy survey of classical LBV stars in M33

Five well-known LBV stars in M33 were observed with the Multi-Pupil Fiber Spectrograph (MPFS) on the 6-m Russian telescope. We observed LBVs varA, varB, varC, var2 and var83. In three of them, var2, var83, varB, large-scale nebulae were found with sizes from 15 pc and larger. The nebula shapes are complex, like one-side tails or conical nebulae. They all are related to their LBV stars. In var2 and var83 stars we found radial velocity gradients 15-30 km/s across their nebulae. The stars varA and varC do not show extended nebulae, but nebular lines are certainty present in their spectra.

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arXiv2006

Enigma of ultraluminous X-ray sources may be resolved by 3D-spectroscopy (MPFS data)

The ultraluminous X-ray sources (ULXs) were isolated in external galaxies for the last 5 years. Their X-ray luminosities exceed 100-10000 times those of brightest Milky Way black hole binaries and they are extremely variable. There are two models for the ULXs, the best black hole candidates. 1. They are supercritical accretion disks around a stellar mass black hole like that in SS433, observed close to the disk axes. 2. They are Intermediate Mass Black Holes (of 100-10000 solar masses). Critical observations which may throw light upon the ULXs nature come from observations of nebulae around the ULXs. We present results of 3D-spectroscopy of nebulae around several ULXs located in galaxies at 3-6 Mpc distances. We found that the nebulae to be powered by their central black holes. The nebulae are shocked and dynamically perturbed probably by jets. The nebulae are compared with SS433 nebula (W50).

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arXiv2006

Integral Field Spectroscopy of a peculiar Supernova Remnant MF16 in NGC6946

We present a study of a peculiar Supernova Remnant MF16, associated with the Ultraluminous X-ray Source (ULX) NGC6946 ULX-1. Observations were taken with the MultiPupil Fiber Spectrograph (MPFS) with 6-m telescope on January 2005. The nebula is found to be highly asymmetric, one of the parts being much denser and colder. The two-component structure of the emission lines and radial velocity gradient argue for a non-spherical nebula, expanding with a velocity of about 100 km/s. Neither shock models nor the X-ray emission can adequately explain the actual emission line spectrum of MF16, so we suggest an additional ultraviolet source with a luminosity of about 10E40 erg/s. We confirm coincidence of the ULX with the central star, and identify radio emission observed by VLA with the most dense part of the nebula.

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arXiv2005

Properties of SS433 and ultraluminous X-ray sources in external galaxies

We suggest that the ultraluminous X-ray sources located in external galaxies (ULXs) are supercritical accretion disks like that in SS433, observed close to the disk axis. We estimate parameters of the SS433 funnel, where the relativistic jets are formed. Emergent X-ray spectrum in the proposed model of the multicolor funnel (MCF) is calculated. The spectrum can be compared with those of ULXs. We predict a complex absorption-line spectrum with broad and shallow K$α$/Kc blends of the most abundant heavy elements and particular temporal variability. Another critical idea comes from observations of nebulae around the ULXs. We present results of 3D-spectroscopy of nebulae of two ULXs located in Holmberg II and NGC6946. In both cases the nebula is found to be powered by the central black hole. The nebulae are compared with SS433 nebula (W50).

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arXiv2005

Crowded field 3D spectroscopy of LBV candidates in M33

We present integral field spectroscopy of the LBV candidate stars B416 and v532 in the local group galaxy M33. B416 is surrounded by an elongated ring-like nebula, which has a projected radius of 20x30 pc. From the datacube we create ionization and radial velocity maps of the nebula. The excitation of the gas decreases towards the outer part of the ring, while the inner part of the nebula is filled with a more excited gas. In the EW direction the ring is seen to expand with a maximum projected velocity amplitude of about 40 km/s. The eastern part approaches the observer. We estimate the nebula dynamical lifetime 8*10E5 years. It could be a residual MS bubble, which indicates a main-sequence or pre-LBV status of the star. We classify B416 as an "iron star" or B[e]-supergiant. In v532 an elongated nebula has been marginally detected. The total projected size of the nebula along the main axis is 30 pc, and the total radial velocity gradient is 44+/-11 km/s. v532 exhibits both strong photometric and spectral variability. At the time of our observations it was in an intermediate brightness state with a rich nitrogen spectrum. We classify v532 as an LBV, showing LBV <-> Ofpe/WN transitions. We stress the importance of integral field spectroscopy as the optimal technique for studying nebulae and the evolution of LBV-like stars in nearby galaxies.

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arXiv2005

Broad band variability of SS433: Accretion disk at work?

We present broad band power spectra of variations of SS433 in radio, optical and X-ray spectral bands. We show that at frequencies lower than 1e-5 Hz the source demonstrates the same variability pattern in all these bands. The broad band power spectrum can be fitted by one power law down to frequencies ~1e-7 Hz with flattening afterwards. Such a flattening means that on time scales longer than ~1e7 sec the source variability becomes uncorrelated. This naturally leads to the appearance of quasi-poissonian flares in the source light curve, which have been regularly observed in radio and optical spectral bands. The radio flux power spectrum appears to have a second break at Fourier frequencies ~1e-5 Hz which can be caused by the smearing of the intrinsic radio variability on timescale of the light-crossing time of the radio emitting region. We find a correlation of the radio and optical fluxes of SS433 and the radio flux is delayed by about ~2 days with respect to the optical one. Power spectra of optical and X-ray variabilities continue with the same power law from 1e-7 Hz up to ~0.01-0.05 Hz. The broad band power spectrum of SS433 can be interpreted in terms of self-similar accretion rate modulations in the accretion disk proposed by Lyubarskii (1997) and elaborated by Churazov et al. (2001). We discuss a viscous time-scale in the accretion disk of SS433 in implication to the observed broad band power spectrum.

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arXiv2004

Integral field spectroscopy of the ultraluminous X-ray source Holmberg II X-1

We present optical integral field observations of the H II region containing the ultraluminous X-ray source Holmberg II X-1. We confirm the existence of an X-ray ionized nebula as the counterpart of the source due to the detection of an extended He II (4686A) region (21 x 47 pc) at the Chandra ACIS-S position. An extended blue objects with a size of 11 x 14 pc is coincident with the X-ray/He II region, which could indicate either a young stellar complex or a cluster. We have derived an X-ray to optical luminosity ratio of Lx/Lb>170, and presumable it is Lx/Lb~300-400 using the recent HST ACS data. We find a complex velocity dispersion at the position of the ULX. In addition, there is a radial velocity variation in the X-ray ionized region found in the He II emission of +-50 km/s on spatial scales of 2-3 arcsec. We believe that the putative black hole not only ionizes the surrounding HII gas, but also perturbs it dynamically (via jets or the accretion disk wind). The spatial analysis of the public Chandra ACIS-S data reveals a point-like X-ray source and marginal indication of an extended component (<<15 % of the total flux). The XMM-Newton EPIC-PN spectrum of HoII X-1 is best fitted with an absorbed power-law in addition to either a thermal thick plasma or a thermal thin plasma or a multi-colour disk black body (MCD). In all cases, the thermal component shows relatively low temperatures (kT~0.14-0.22 keV). Finally we discuss the optical/X-ray properties of HoII X-1 with regards to the possible nature of the source.

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arXiv2004

First simultanous X-ray and optical observations of rapid variability of supercritical accretor SS433

We present results of first simultaneous optical and X-ray observations of peculiar binary system SS433. For the first time, chaotic variability of SS433 in the optical spectral band (R band) on time scales as small as tens of seconds was detected. We find that the X-ray flux of SS433 is delayed with respect to the optical emission by approximately 80 sec. Such a delay can be interpreted as the travel time of mass accretion rate perturbations from the jet base to the observed X-ray emitting region. In this model, the length of the supercritical accretion disk funnel in SS433 is ~1e12 cm.

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arXiv2002

The central region in SS433 supercritical disk and origin of flares

Mean orbital light curves of SS433 in different precessional phases are analysed for active and passive states separately. In passive states the mean brightness depends strongly on the disk orientation, the star is fainter by a factor about 2.2 in the disk edge-on positions. In active states the brightness does not depend significantly on the precessional phase. We suggest that in active states hot gas cocoons surrounding the inner jets grow and can not be shielded by the disk rim in the edge-on phases. Brightest optical flares are clear separated in two groups in orbital phases, it is considered as indication of orbital eccentricity. Bright flares prefer specific precession and nodding phases, it favours the slaved disk model and the flares as disk perturbations by a torque applied to outer parts of the accretion disk.

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arXiv2001

Face-on SS433 stars as a possible new type of extragalactic X-ray sources

The SS433 objects is a well-known source of relativistic jets, which are formed in supercritical accretion disk. It is very probable that the disk has polar channels and their radiation is collimated (the photocones). The face-on SS433 object can appear as beamed ultra-bright (and highly variable) X-ray source, L_x = 10^39 - 10^42 erg/s. We discuss properties of these hypothetical objects and their frequency expected in galaxies. We describe a search for such objects using the ROSAT ASS Bright Source Catalog and Faint Source Catalog (99528 point-like sources) and the RC3 catalog (16741 spiral and irregular galaxies). Among in total 418 positive correlations in all types of galaxies we find that in S and Irr galaxies 142 sources are unknown as AGNs. We isolated by visual inspection 37 clear non-nuclear, 43 probably non-nuclear and 35 probably nuclear sources. The last two classes certainly contain many unknown AGNs. The sources of the 1-st class have X-ray luminosities mainly 10^39 - 3 10^41 erg/s. Their observed frequency is about 4% - 5% per S/Irr galaxy, what is in agreement with expected frequency of face-on SS433 stars. The only way to recognize such stars is their expected violent variability in X-rays.

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