27 research outputs found
Chandra's X-ray study confirms that the magnetic standard Ap star KQ Vel hosts a neutron star companion
KQ Vel is a peculiar A0p star with a strong surface magnetic field of about
7.5 kG. It has a slow rotational period of nearly 8 years. Bailey et al. (2015)
detected a binary companion of uncertain nature, and suggested it could be a
neutron star or a black hole. In this Letter we analyze X-ray data obtained by
the Chandra telescope to ascertain information about the stellar magnetic field
and interaction between the star and its companion. We confirm previous X-ray
detection of KQ Vel with a relatively large X-ray luminosity of 2\times 10^{30}
erg/s. X-ray spectra suggest the presence of hot gas at > 20MK and, possibly,
of a non-thermal component. X-ray light curves are variable, but better quality
data are needed to determine periodicity if any. We interpret X-ray spectra as
a combination of two components: the non-thermal emission arising from the
aurora on the A0p star and the hot thermal plasma filling the extended shell
surrounding the "propelling" neutron star. We explore various alternatives, but
a hybrid model involving the stellar magnetosphere along with a hot shell
around the propelling neutron star seems most plausible. We speculate that KQ
Vel was originally a triple system, and the Ap star is a merger product. We
conclude that KQ Vel is an intermediate-mass binary consisting of a strongly
magnetic main sequence star and a neutron star.Comment: accepted to A&AL. 8 pages including the appendix where the formalism
describing the X-ray emission from a hot shell around a propelling neutron
star in settling accretion regime is presente
NuSTAR observations of the supergiant X-ray pulsar IGR J18027-2016: accretion from the stellar wind and possible cyclotron absorption line
We report on the first focused hard X-ray view of the absorbed supergiant system IGR J18027−2016 performed with the Nuclear Spectroscopic Telescope Array observatory. The pulsations are clearly detected with a period of P_(spin)=139.866(1) s and a pulse fraction of about 50–60 per cent at energies from 3 to 80 keV. The source demonstrates an approximately constant X-ray luminosity on a time-scale of more than dozen years with an average spin-down rate of P ≃ 6x10^(-10) s s^(-1). This behaviour of the pulsar can be explained in terms of the wind accretion model in the settling regime. The detailed spectral analysis at energies above 10 keV was performed for the first time and revealed a possible cyclotron absorption feature at energy ∼23 keV. This energy corresponds to the magnetic field B ≃ 3x10^(12) G at the surface of the neutron star, which is typical for X-ray pulsars
Constraints on the massive graviton dark matter from pulsar timing and precision astrometry
The effect of a narrow-band isotropic stochastic GW background on pulsar
timing and astrometric measurements is studied. Such a background appears in
some theories of gravity. We show that the existing millisecond pulsar timing
accuracy () strongly constrains possible observational
consequences of theory of massive gravity with spontaneous Lorentz braking
\cite{dtt:2005}, essentially ruling out significant contribution of massive
gravitons to the local dark halo density. The present-day accuracy of
astrometrical measurements () sets less stringent
constraints on this theory.Comment: 4 pages, 1 figure; changes in content, references added, accepted for
publication in PR
NuSTAR observations of the supergiant X-ray pulsar IGR J18027-2016: accretion from the stellar wind and possible cyclotron absorption line
We report on the first focused hard X-ray view of the absorbed supergiant system IGR J18027−2016 performed with the Nuclear Spectroscopic Telescope Array observatory. The pulsations are clearly detected with a period of P_(spin)=139.866(1) s and a pulse fraction of about 50–60 per cent at energies from 3 to 80 keV. The source demonstrates an approximately constant X-ray luminosity on a time-scale of more than dozen years with an average spin-down rate of P ≃ 6x10^(-10) s s^(-1). This behaviour of the pulsar can be explained in terms of the wind accretion model in the settling regime. The detailed spectral analysis at energies above 10 keV was performed for the first time and revealed a possible cyclotron absorption feature at energy ∼23 keV. This energy corresponds to the magnetic field B ≃ 3x10^(12) G at the surface of the neutron star, which is typical for X-ray pulsars
Galactic Binary Gravitational Wave Noise within LISA Frequency Band
Gravitational wave noise associated with unresolved binary stars in the
Galaxy is studied with the special aim of determining the upper frequency at
which it stops to contribute at the rms noise level of the proposed space-born
interferometer (LISA). The upper limit to this background is derived from the
statistics of SN Ia explosions, part of which can be triggered by binary white
dwarf coalescences. The upper limiting frequency at which binary stochastic
noise crosses LISA rms sensitivity is found to lie within the range 0.03-0.07
Hz, depending on the galactic binary white dwarf coalescence rate. To be
reliably detectable by LISA, the energy density of relic cosmological
background per logarithmic frequency interval should be
Omega_{GW}h_{100}^2>10^{-8} at f>0.03 Hz.Comment: 16 pages with 1 eps figure, aasms4.sty, to appear in the ApJ vol. 494
February 20, 1998 issu
The 5 hr pulse period and broadband spectrum of the Symbiotic X-ray Binary 3A 1954+319
We present an analysis of the highly variable accreting X-ray pulsar 3A
1954+319 using 2005-2009 monitoring data obtained with INTEGRAL and Swift. This
considerably extends the pulse period history and covers flaring episodes in
2005 and 2008. In 2006 the source was identified as one of only a few known
symbiotic X-ray binaries (SyXBs), i.e., systems composed of a neutron star
accreting from the inhomogeneous medium around an M-giant star. The extremely
long pulse period of 5.3 hr is directly visible in the 2008 INTEGRAL-ISGRI
outburst light curve. The pulse profile is double peaked and generally not
significantly energy dependent although there is an indication of possible
softening during the main pulse. During the outburst a strong spin-up of -1.8
10^(-4) hr hr^(-1) occurred. Between 2005 and 2008 a long-term spin-down trend
of 2.1 10^-5 hr hr^(-1) was observed for the first time for this source. The
3-80 keV pulse peak spectrum of 3A 1954+319 during the 2008 flare could be well
described by a thermal Comptonization model. We interpret the results within
the framework of a recently developed quasi-spherical accretion model for
SyXBs.Comment: 5 pages, 4 figures, published in The Astrophysical Journal Letter
Advances in Understanding High-Mass X-ray Binaries with INTEGRAL and Future Directions
High mass X-ray binaries are among the brightest X-ray sources in the Milky Way, as well as in nearby Galaxies. Thanks to their highly variable emissions and complex phenomenology, they have attracted the interest of the high energy astrophysical community since the dawn of X-ray Astronomy. In more recent years, they have challenged our comprehension of physical processes in many more energy bands, ranging from the infrared to very high energies. In this review, we provide a broad but concise summary of the physical processes dominating the emission from high mass X-ray binaries across virtually the whole electromagnetic spectrum. These comprise the interaction of stellar winds with the high gravitational and magnetic fields of compact objects, the behaviour of matter under extreme magnetic and gravity conditions, and the perturbation of the massive star evolutionary processes by presence in a binary system. We highlight the role of the INTEGRAL mission in the discovery of many of the most interesting objects in the high mass X-ray binary class and its contribution in reviving the interest for these sources over the past two decades. We show how the INTEGRAL discoveries have not only contributed to significantly increase the number of high mass X-ray binaries known, thus advancing our understanding of the population as a whole, but also have opened new windows of investigation that stimulated the multi-wavelength approach nowadays common in most astrophysical research fields. We conclude the review by providing an overview of future facilities being planned from the X-ray to the very high energy domain that will hopefully help us in finding an answer to the many questions left open after more than 18 years of INTEGRAL scientific observations.The INTEGRALteams in the participating countries acknowledge the continuous support from their space agencies and funding organizations: the Italian Space Agency ASI (via different agreements including the latest one, 2019-35HH, and the ASIINAF agreement 2017-14-H.0), the French Centre national d’études spatiales (CNES), the Russian Foundation for Basic Research (KP, 19-02-00790), the Russian Science Foundation (ST, VD, AL; 19-12-00423), the Spanish State Research Agency (via different grants including ESP2017-85691-P, ESP2017-87676-C5-1-R and Unidad de Excelencia MarÃa de Maeztu – CAB MDM-2017-0737). IN is partially supported by the Spanish Government under grant PGC2018-093741-B-C21/C22 (MICIU/AEI/FEDER, UE). LD acknowledges grant 50 OG 1902
Gravitational Wave Astronomy: in Anticipation of First Sources to be Detected
The first generation of long-baseline laser interferometric detectors of
gravitational waves will start collecting data in 2001-2003. We carefully
analyse their planned performance and compare it with the expected strengths of
astrophysical sources. The scientific importance of the anticipated discovery
of various gravitatinal wave signals and the reliability of theoretical
predictions are taken into account in our analysis. We try to be conservative
both in evaluating the theoretical uncertainties about a source and the
prospects of its detection. After having considered many possible sources, we
place our emphasis on (1) inspiraling binaries consisting of stellar mass black
holes and (2) relic gravitational waves. We draw the conclusion that
inspiraling binary black holes are likely to be detected first by the initial
ground-based interferometers. We estimate that the initial interferometers will
see 2-3 events per year from black hole binaries with component masses
10-15M_\odot, with a signal-to-noise ratio of around 2-3, in each of a network
of detectors consisting of GEO, VIRGO and the two LIGOs. It appears that other
possible sources, including coalescing neutron stars, are unlikely to be
detected by the initial instruments. We also argue that relic gravitational
waves may be discovered by the space-based interferometers in the frequency
interval 2x10^{-3}-10^{-2} Hz, at the signal-to-noise ratio level around 3.Comment: latex, 100 pages, including 20 postscript figures. Small typos
corrected, references adde