Publications (65)
Discovery of a flux-related change of the cyclotron line energy in Her X-1
R. Staubert, N. I. Shakura, K. Postnov +5
We present the results of ten years of repeated measurements of the Cyclotron Resonance Scattering Feature (CRSF) in the spectrum of the binary X-ray pulsar Her X-1 and report the…
The second data release from the European Pulsar Timing Array: IV. Implications for massive black holes, dark matter and the early Universe
J. Antoniadis, P. Arumugam, S. Arumugam +111
The European Pulsar Timing Array (EPTA) and Indian Pulsar Timing Array (InPTA) collaborations have measured a low-frequency common signal in the combination of their second and fir…
Probing stellar winds and accretion physics in high-mass X-ray binaries and ultra-luminous X-ray sources with LOFT
M. Orlandini, V. Doroshenko, L. Zampieri +28
This is a White Paper in support of the mission concept of the Large Observatory for X-ray Timing (LOFT), proposed as a medium-sized ESA mission. We discuss the potential of LOFT f…
Spectroscopic Searches for Evolutionary Orbital Period Changes in WR+OB Binaries: The case of CQ Cep and CX Cep
I. Shaposhnikov, A. Cherepashchuk, A. Dodin +1
We present the results of spectroscopic observations of two eclipsing WR+OB-type systems - CQ Cep and CX Cep, performed in 2020-2023 with a low-resolution slit spectrograph TDS ($Î…
Variable precession of the neutron star in Her X-1
R. Staubert, D. Klochkov, K. Postnov +3
We present evidence for an identical behavior of the precession of the accretion disk and that of the neutron star (NS) in Her X-1, based on investigating the well established 35 d…
Elusive hot stripped helium stars in the Galaxy I. Evolutionary stellar models in the gap between subdwarfs and Wolf-Rayet stars
L. Yungelson, A. Kuranov, K. Postnov +3
Stellar evolution theory predicts the existence of He-core remnants of the primary components of intermediate-mass close binaries that lost most of their H/He envelopes due to the…
Does the neutron star in Her X-1 really show free precession?
R. Staubert, D. Klochkov, D. Vasco +4
The accreting X-ray pulsar Her X-1 shows two types of long-term variations, both with a period of 35 days: 1) A modulation of the flux with a ten day long Main-On and a 5 d long Sh…
Wind accretion in symbiotic X-ray binaries
K. Postnov, N. Shakura, A. González-Galán +7
The properties of wind accretion in symbiotic X-ray binaries (SyXBs) consisting of red-giant and magnetized neutron star (NS) are discussed. The spin-up/spin-down torques applied t…
Diagnostics of the black hole candidate SS433 with the RXTE
E. Filippova, M. Revnivtsev, S. Fabrika +2
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 p…
NuSTAR rules out a cyclotron line in the accreting magnetar candidate 4U2206+54
J. M. Torrejón, P. Reig, F. Fürst +3
Based on our new NuSTAR X-ray telescope data, we rule out any cyclotron line up to 60 keV in the spectra of the high mass X-ray binary 4U2206+54. In particular, we do not find any…
Quenching of the accretion disk strong aperiodic variability at the magnetospheric boundary
M. Revnivtsev, E. Churazov, K. Postnov +1
We study power density spectra (PDS) of X-ray flux variability in binary systems where the accretion flow is truncated by the magnetosphere. PDS of accreting X-ray pulsars where th…
Pulse phase and precession phase resolved spectroscopy of Her X-1: studying a representative Main-On with RXTE
D. Vasco, R. Staubert, D. Klochkov +3
We performed a detailed pulse phase resolved spectroscopy of the accreting binary X-ray pulsar Her X-1 in the energy range 3.5-75 keV and have established pulse phase profiles for…
The pre-outburst flare of the A 0535+26 August/September 2005 outburst
I. Caballero, A. Santangelo, P. Kretschmar +11
We study the spectral and temporal behavior of the High Mass X-ray Binary A 0535+26 during a `pre-outburst flare' which took place ~5 d before the peak of a normal (type I) outburs…
Effect of post-recombination accretion on primordial binary black hole mergers within virialized dark matter halos
A. Konovalov, K. Postnov
Gravitational waves from binary black hole mergers remain among primary sources for ground-based and space laser interferometers. Primordial binary black holes (PBHs) can form bina…
NuSTAR observation of the Supergiant Fast X-ray Transient IGR J11215-5952 during its 2017 outburst
L. Sidoli, K. Postnov, A. Tiengo +4
We report on the results of a NuSTAR observation of the Supergiant Fast X-ray Transient pulsar IGRJ11215-5952 during the peak of its outburst in June 2017. IGRJ11215-5952 is the on…
Globular Cluster Seeding by Primordial Black Hole Population
A. Dolgov, K. Postnov
Primordial black holes (PBHs) that form in the early Universe in the modified Affleck-Dine (AD) mechanism of baryogenesis should have intrinsic log-normal mass distribution of PBHs…
Variable neutron star free precession in Hercules X-1 from evolution of RXTE X-ray pulse profiles with phase of the 35-day cycle
K. Postnov, N. Shakura, . R. Staubert +3
Accretion of matter onto the surface of a freely precessing NS with a complex non-dipole magnetic field can explain the change of X-ray pulse profiles of Her X-1 observed by RXTE w…
The Galactic LMXB Population and the Galactic Centre Region
S. Sazonov, A. Paizis, A. Bazzano +21
Seventeen years of hard X-ray observations with the instruments of the INTEGRAL observatory, with a focus on the Milky Way and in particular on the Galactic Centre region, have pro…
First simultanous X-ray and optical observations of rapid variability of supercritical accretor SS433
M. Revnivtsev, R. Burenin, S. Fabrika +6
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 ba…
INTEGRAL study of temporal properties of bright flares in Supergiant Fast X-ray Transients
L. Sidoli, A. Paizis, K. Postnov
We have characterized the typical temporal behaviour of the bright X-ray flares detected from the three Supergiant Fast X-ray Transients showing the most extreme transient behaviou…
Peculiarities in the orbital and precessional variability of SS433 from INTEGRAL observations
A. Cherepashchuk, R. Sunyaev, S. Molkov +3
Based on multiyear INTEGRAL observations of SS433, a composite IBIS/ISGRI 18-60 keV orbital light curve is constructed around zero precessional phase . It shows a pecul…
The appearance of magnetospheric instability in flaring activity at the onset of X-ray outbursts in A0535+26
K. Postnov, R. Staubert, A. Santangelo +3
We argue that X-ray flaring variability observed in the transient X-ray pulsar A 0535+26 is due to low-mode magnetospheric instability. This instability develops at the onset of ac…
Cyclotron lines in highly magnetized neutron stars
R. Staubert, J. Trümper, E. Kendziorra +10
Cyclotron lines, also called cyclotron resonant scattering features (CRSF) are spectral features, generally appearing in absorption, in the X-ray spectra of objects containing high…
Low-frequency spectra of neutron star + OB supergiant binaries: Does wind density drive persistent and flaring modes of accretion?
J. van den Eijnden, L. Sidoli, M. DÃaz Trigo +10
Neutron star high-mass X-ray binaries are well-studied in wavebands between the infrared and hard X-rays. Their low-frequency millimeter and radio properties, on the other hand, re…
Diagnostics of SS433 with the RXTE
E. Filippova, M. Revnivtsev, S. Fabrika +2
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 precessio…
A 0535+26 in outburst: magnetospheric instabilities and accretion geometry
I. Caballero, U. Kraus, K. Postnov +4
The Be/X-ray binary A 0535+26 showed a normal (type I) outburst in August/September 2005, which reached a maximum X-ray flux of 400mCrab in the 5-100keV range. The outburst was obs…
A propelling neutron star in the enigmatic Be-star ~Cassiopeia
K. Postnov, L. Oskinova, J. M. Torrejón
The enigmatic X-ray emission from the bright optical star, Cassiopeia, is a long-standing problem. Cas is known to be a binary system consisting of a Be-type star and a l…
A thousand looks at X Persei: X-ray spectroscopy at high time resolution
G. Sanjurjo-FerrÃn, J. M. Torrejón, J. J. Rodes-Roca +3
X Persei is a classical Be/X-ray binary composed of an O9.5III-B0V Be-type star and a neutron star (NS). The NS exhibits coherent pulsations with a spin period of ~837 s, orbiting…
Peculiar nature of hard X-ray eclipse in SS433 from INTEGRAL observations
A. Cherepashchuk, K. Postnov, E. Antokhina +1
The analysis of INTEGRAL observations (2003-2008) of superaccreting galactic microquasar SS433 at precessional phases with the maximum disk opening angle is carried out. The shape…
Searches for signatures of ultra-light axion dark matter in polarimetry data of the European Pulsar Timing Array
N. K. Porayko, P. Usynina, J. Terol-Calvo +74
Ultra-light axion-like particles (ALPs) can be a viable solution to the dark matter problem. The scalar field associated with ALPs, coupled to the electromagnetic field, acts as an…
Observational evidence for a changing tilt of the accretion disk with respect to the orbital plane in Her X-1 over its 35 day cycle
D. Klochkov, N. Shakura, K. Postnov +3
Analysis and interpretation of the Her X-1 X-ray light curve obtained with the ASM onbord RXTE over the period 1996 February to 2004 September is presented. We report that the feat…
Swift/BAT measurements of the cyclotron line energy decay in the accreting neutron star Her X-1: indication of an evolution of the magnetic field?
D. Klochkov, R. Staubert, K. Postnov +3
Context: The magnetic field is a crucial ingredient of neutron stars. It governs the physics of accretion and of the resulting high-energy emission in accreting pulsars. Studies of…
Long-term change in the cyclotron line energy in Hercules X-1
R. Staubert, D. Klochkov, J. Wilms +5
Aims. We investigate the long-term evolution of the Cyclotron Resonance Scattering Feature (CRSF) in the spectrum of the binary X-ray pulsar Her X-1 and present evidence of a true…
X-ray emission from magnetized neutron star atmospheres at low mass accretion rates. I. Phase-averaged spectrum
E. Sokolova-Lapa, M. Gornostaev, J. Wilms +12
Recent observations of X-ray pulsars at low luminosities allow, for the first time, to compare theoretical models for the emission from highly magnetized neutron star atmospheres a…
Spectroscopic Searches for Evolutionary Orbital Period Changes in WR+OB Binaries: the case of V444 Cyg
I. Shaposhnikov, A. Cherepashchuk, A. Dodin +1
We present the results of new photometric and spectroscopic observations of WN5+O6 binary V444 Cyg and a detailed analysis of extant spectroscopy and photometry. Using elements of…
Spins of black holes in coalescing compact binaries
K. Postnov, A. Kuranov, N. Mitichkin
Modern astrophysical methods of determination of spins of rotating stellar-mass black hole in close binaries and of supermassive black holes in active galactic nuclei are briefly d…
Two ~35 day clocks in Her X-1: evidence for neutron star free precession
R. Staubert, D. Klochkov, K. Postnov +3
We present evidence for the existence of two ~35 day clocks in the Her X-1/HZ Her binary system. ~35 day modulations are observed 1) in the Turn-On cycles with two on- and two off-…
NuSTAR observations of the supergiant X-ray pulsar IGR J18027-2016: accretion from the stellar wind and possible cyclotron absorption line
A. Lutovinov, S. Tsygankov, K. Postnov +3
We report on the first focused hard X-ray view of the absorbed supergiant system IGRJ18027-2016 performed with the NuSTAR observatory. The pulsations are clearly detected with a pe…
Detecting the intrinsic X-ray emission from the O-type donor star and the residual accretion in a Supergiant Fast X-ray Transient during its faintest state
L. Sidoli, K. Postnov, L. Oskinova +4
We report on the results of an XMM-Newton observation of the Supergiant Fast X-ray Transient (SFXT) IGR J08408-4503 performed in June 2020. The source is composed by a compact obje…
Wind Accretion - Observations Vs Theory
N. Shakura, K. Postnov
The theory of quasi-spherical subsonic accretion onto magnetized rotating neutron star is reviewed. Different regimes of quasi-spherical accretion onto a neutron star: supersonic (…
AX J1910.7+0917: the slowest X-ray pulsar
L. Sidoli, G. L. Israel, P. Esposito +2
Pulsations from the high mass X-ray binary AXJ1910.7+0917 were discovered during Chandra observations performed in 2011 (Israel et al. 2016). We report here more details on this di…
Pulse period evolution of GX 1+4
A. González-Galán, E. Kuulkers, P. Kretschmar +4
We report on the long-term evolution of the spin period of the symbiotic X-ray pulsar GX 1+4 and a possible interpretation within a model of quasi-spherical accretion. New period m…
Quasi-spherical accretion in X-ray pulsars
K. Postnov, N. Shakura, A. Kochetkova +1
Quasi-spherical accretion in wind-fed X-ray pulsars is discussed. At X-ray luminosities <4 10^{36} erg/s, a hot convective shell is formed around the neutron star magnetosphere, an…
On the nature of `off' states in slowly rotating low-luminosity X-ray pulsars
N. Shakura, K. Postnov, L. Hjalmarsdotter
We elaborate on a recently proposed model for subsonic quasi-spherical accretion onto slowly rotating pulsars, in which accretion is mediated through a hot quasi-static shell above…
Origin of bright flares in SFXTs
K. Postnov, N. Shakura, L. Sidoli +1
In the settling accretion theory, which is applicable to quasi-spherical accreting slowly rotating magnetized neutron stars with X-ray luminosity ~erg/…
Quasi-periodic flares in EXO 2030+375 observed with INTEGRAL
D. Klochkov, C. Ferrigno, A. Santangelo +5
Context: Episodic flaring activity is a common feature of X-ray pulsars in HMXBs. In some Be/X-ray binaries flares were observed in quiescence or prior to outbursts. EXO 2030+375 i…
Quasi-spherical accretion in low-luminosity X-ray pulsars: Theory vs. observations
K. Postnov, N. Shakura, A. Kochetkova +1
Quasi-spherical subsonic accretion can be realized in slowly rotating wind-fed X-ray pulsars (XPSRs) at X-ray luminosities <4 10^{36} erg/s. In this regime the accreting matter set…
A viscous-convective instability in laminar Keplerian thin discs. II. Anelastic approximation
N. Shakura, K. Postnov
Using the anelastic approximation of linearised hydrodynamic equations, we investigate the development of axially symmetric small perturbations in thin Keplerian discs. The sixth-o…
A search for the presence of magnetic fields in the two Supergiant Fast X-ray Transients IGR J08408-4503 and IGR J11215-5952
S. Hubrig, L. Sidoli, K. Postnov +4
A significant fraction of high-mass X-ray binaries are supergiant fast X-ray transients (SFXTs). The prime model for the physics governing their X-ray behaviour suggests that the w…
On the nature of the break in the X-ray luminosity function of low-mass X-ray binaries
M. Revnivtsev, K. Postnov, A. Kuranov +1
We analyze a flux-limited sample of persistent and bright (with 2-10 keV fluxes exceeding 1.4e-10 erg/s/cm2) low-mass X-ray binaries (LMXBs) in our Galaxy. It is demonstrated that…
Broad band variability of SS433: Accretion disk at work?
M. Revnivtsev, S. Fabrika, P. Abolmasov +6
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 sa…
Long-term developments in Her X-1: Correlation between the histories of the 35 day turn-on cycle and the 1.24 sec pulse period
R. Staubert, S. Schandl, D. Klochkov +3
We have studied the long-term (1971-2005) behaviour of the 1.24 sec pulse period and the 35 day precession period of Her X-1 and show that both periods vary in a highly correlated…
Evidence of Compton cooling during an X-ray flare supports a neutron star nature of the compact object in 4U1700-37
M. Martinez-Chicharro, J. M. Torrejón, L. Oskinova +5
Based on new Chandra X-ray telescope data, we present empirical evidence of plasma Compton cooling during a flare in the non pulsating massive X-ray binary 4U1700-37. This behaviou…
Theory of quasi-spherical accretion in X-ray pulsars
N. Shakura, K. Postnov, A. Kochetkova +1
A theoretical model for quasi-spherical subsonic accretion onto slowly rotating magnetized neutron stars is constructed. In this model the accreting matter subsonically settles dow…
Spin period evolution of the X-ray pulsar GX 1+4
A. González-Galán, E. Kuulkers, P. Kretschmar +4
We report on the long-term evolution of the spin period of the symbiotic X-ray pulsar GX 1+4 and a possible interpretation within a model of quasi-spherical accretion. New period m…
The first mm detection of a neutron star high-mass X-ray binary
J. van den Eijnden, L. Sidoli, M. Diaz Trigo +9
Neutron stars accreting from OB supergiants are often divided between persistently and transiently accreting systems, called Supergiant X-ray Binaries (SgXBs) and Supergiant Fast X…
Continuous monitoring of pulse period variations in Her X-1 using Swift/BAT
D. Klochkov, R. Staubert, K. Postnov +2
Context: Monitoring of pulse period variations in accreting binary pulsars is an important tool to study the interaction between the magnetosphere of the neutron star and the accre…
Spin period evolution of GX 1+4
A. González-Galán, E. Kuulkers, P. Kretschmar +4
We aim both to complement the existing data on the spin history of the peculiar accreting X-ray pulsar GX 1+4 with more past and current data from BeppoSAX, INTEGRAL, and Fermi and…
Solving puzzles of GW150914 by primordial black holes
S. Blinnikov, A. Dolgov, N. K. Porayko +1
The black hole binary properties inferred from the LIGO gravitational wave signal GW150914 posed several serious problems. The high masses and low effective spin of black hole bina…
Monitoring of pulse period in Her X-1 with Swift/BAT: evidence of mass ejection
D. Klochkov, R. Staubert, K. Postnov +2
Monitoring of pulse period variations in accreting binary pulsars is an important tool to study the interaction between the magnetosphere of the neutron star and the accretion disk…
Probing the nature of the X-ray source IGR J16327-4940 with Chandra
L. Sidoli, V. Sguera, K. Postnov +3
We report on the results of a Chandra observation of the source IGRJ16327-4940, suggested to be a high mass X-ray binary hosting a luminous blue variable star (LBV). The source fie…
A precessing warped accretion disk around the X-ray pulsar Her X-1
D. Klochkov, N. Shakura, K. Postnov +2
We have performed an analysis and interpretation of the X-ray light curve of the accreting neutron star Her X-1 obtained with the ASM RXTE over the period 1996 February to 2004 Sep…
INTEGRAL observations of Her X-1
D. Klochkov, R. Staubert, K. Postnov +6
Aims: We investigate the X-ray spectral and timing properties of the accreting X-ray pulsar Her X-1 observed with the INTEGRAL satellite in July-August 2005. Methods: The data anal…
Variable pulse profiles of Her X-1 repeating with the same irregular 35d clock as the turn-ons
R. Staubert, D. Klochkov, D. Vasco +4
The accreting X-ray pulsar Her X-1 shows two types of long-term variations, both with periods of ~35 days: 1) Turn-on cycles, a modulation of the flux}, with a ten-day long Main-On…
Luminosity-dependent changes of the cyclotron line energy and spectral hardness in Cep X-4
V. Vybornov, D. Klochkov, M. Gornostaev +5
X-ray spectra of accreting pulsars are generally observed to vary with their X-ray luminosity. In particular, the hardness of the X-ray continuum is found to depend on luminosity.…