New X-ray detections of known Wolf-Rayet stars*

Abstract Using xmm-Newton, we undertook a dedicated project to search for X-ray bright wind-wind collisions in 18 WR+OB systems. We complemented these observations with Swift and Chandra datasets, allowing for the study of two additional systems. We also improved the ephemerides, for these systems displaying photometric changes, using TESS, Kepler, and ASAS-SN data. Five systems displayed a very faint X-ray emission (log [LX/LBOL] < −8) and three a faint one (log [LX/LBOL] ∼ −7), incompatible with typical colliding wind emission: not all WR binaries are thus X-ray bright. In a few other systems, X-rays from the O-star companion cannot be excluded as being the true source of X-rays (or a large contributor). In two additional cases, the emission appears faint but the observations were taken with the WR wind obscuring the line-of-sight, which could hide a colliding wind emission. Clear evidence of colliding winds was however found in the remaining six systems (WR 19, 21, 31, 97, 105, 127). In WR 19, increased absorption and larger emission at periastron are even detected, in line with expectations of adiabatic collisions.

Glimpses of the past activity of Sgr A★ inferred from X-ray echoes in Sgr C

10.1051/0004-6361/201731864 ◽

2018 ◽

Vol 610 ◽

pp. A34 ◽

Cited By ~ 6

Author(s):

D. Chuard ◽

R. Terrier ◽

A. Goldwurm ◽

M. Clavel ◽

S. Soldi ◽

...

Keyword(s):

Monte Carlo ◽

Black Hole ◽

Monte Carlo Model ◽

Line Of Sight ◽

X Rays ◽

X Ray ◽

Supermassive Black Hole ◽

The Past ◽

Sgr A ◽

Past Activity

Context. For a decade now, evidence has accumulated that giant molecular clouds located within the central molecular zone of our Galaxy reflect X-rays coming from past outbursts of the Galactic supermassive black hole. However, the number of illuminating events as well as their ages and durations are still unresolved questions. Aims. We aim to reconstruct parts of the history of the supermassive black hole Sgr A★ by studying this reflection phenomenon in the molecular complex Sgr C and by determining the line-of-sight positions of its main bright substructures. Methods. Using observations made with the X-ray observatories XMM-Newton and Chandra and between 2000 and 2014, we investigated the variability of the reflected emission, which consists of a Fe Kα line at 6.4 keV and a Compton continuum. We carried out an imaging and a spectral analysis. We also used a Monte Carlo model of the reflected spectra to constrain the line-of-sight positions of the brightest clumps, and hence to assign an approximate date to the associated illuminating events. Results. We show that the Fe Kα emission from Sgr C exhibits significant variability in both space and time, which confirms its reflection origin. The most likely illuminating source is Sgr A★. On the one hand, we report two distinct variability timescales, as one clump undergoes a sudden rise and fall in about 2005, while two others vary smoothly throughout the whole 2000–2014 period. On the other hand, by fitting the Monte Carlo model to the data, we are able to place tight constraints on the 3D positions of the clumps. These two independent approaches provide a consistent picture of the past activity of Sgr A★, since the two slowly varying clumps are located on the same wavefront, while the third (rapidly varying) clump corresponds to a different wavefront, that is, to a different illuminating event. Conclusions. This work shows that Sgr A★ experienced at least two powerful outbursts in the past 300 yrs, and for the first time, we provide an estimation of their age. Extending this approach to other molecular complexes, such as Sgr A, will allow this two-event scenario to be tested further.

X-rays from colliding winds in massive binaries

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317001028 ◽

2016 ◽

Vol 12 (S329) ◽

pp. 359-360

Author(s):

Yaël Nazé ◽

Gregor Rauw

Keyword(s):

High Resolution ◽

Mass Loss ◽

Strong Shock ◽

Stellar Mass ◽

Stellar Winds ◽

X Rays ◽

Current Generation ◽

X Ray ◽

AbstractIn a massive binary, the strong shock between the stellar winds may lead to the generation of bright X-ray emission. While this phenomenon was detected decades ago, the detailed study of this emission was only made possible by the current generation of X-ray observatories. Through dedicated monitoring and observations at high resolution, unprecedented information was revealed, putting strong constraints on the amount and structure of stellar mass-loss.

Long-term soft and hard X-ray investigation of the colliding wind WN+O binary WR 25

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz1447 ◽

2019 ◽

Vol 487 (2) ◽

pp. 2624-2638 ◽

Cited By ~ 1

Author(s):

Bharti Arora ◽

J C Pandey ◽

M De Becker

Keyword(s):

Thermal Emission ◽

Plasma Temperature ◽

Background Level ◽

Archival Data ◽

X Rays ◽

X Ray ◽

Upper Limits ◽

Post Shock ◽

ABSTRACT We investigated the long-term behaviour in X-rays of the colliding wind binary WR 25, using archival data obtained with Suzaku, Swift, XMM–Newton, and NuSTAR spanning over ∼16 yr. Our analysis reveals phase-locked variations repeating consistently over many consecutive orbits, in agreement with an X-ray emission fully explained by thermal emission from the colliding winds in the 208-d orbit. We report on a significant deviation of the X-ray flux with respect to the 1/D trend (expected for adiabatic shocked winds) close to periastron passage. The absence of a drop in post-shock plasma temperature close to periastron suggests this break in trend cannot be explained in terms of reduced pre-shock velocities in this part of the orbit. Finally, NuSTAR data reveal a lack of hard X-ray emission (above 10.0 keV) above the background level. Upper limits on a putative non-thermal emission strongly suggest that the sensitivity of present hard X-ray observatories is not sufficient to detect non-thermal emission from massive binaries above 10 keV, unless the wind kinetic power is large enough to significantly feed particle acceleration in the wind–wind interaction.

Search for non-thermal X-ray emission in the colliding wind binary Cygnus OB2 #8A

10.1051/0004-6361/201936735 ◽

2020 ◽

Vol 636 ◽

pp. A109 ◽

Cited By ~ 1

Author(s):

E. Mossoux ◽

J. M. Pittard ◽

G. Rauw ◽

Y. Nazé

Keyword(s):

Thermal Emission ◽

Broad Band ◽

X Rays ◽

X Ray ◽

Inverse Compton Scattering ◽

Thermal Radio Emission ◽

Shock Region ◽

Inverse Compton ◽

First Time ◽

Aims. Cyg OB2 #8A is a massive O-type binary displaying strong non-thermal radio emission. Owing to the compactness of this binary, emission of non-thermal X-ray photons via inverse Compton scattering is expected. Methods. We first revised the orbital solution for Cyg OB2 #8A using new optical spectra. We then reduced and analysed X-ray spectra obtained with XMM-Newton, Swift, INTEGRAL, and NuSTAR. Results. The analysis of the XMM-Newton and Swift data allows us to better characterise the X-ray emission from the stellar winds and colliding winds region at energies below 10 keV. We confirm the variation of the broad-band light curve of Cyg OB2 #8A along the orbit with, for the first time, the observation of the maximum emission around phase 0.8. The minimum ratio of the X-ray to bolometric flux of Cyg OB2 #8A remains well above the level expected for single O-type stars, indicating that the colliding wind region is not disrupted during the periastron passage. The analysis of the full set of publicly available INTEGRAL observations allows us to refine the upper limit on the non-thermal X-ray flux of the Cyg OB2 region between 20 and 200 keV. Two NuSTAR observations (phases 0.028 and 0.085) allow us to study the Cyg OB2 #8A spectrum up to 30 keV. These data do not provide evidence of the presence of non-thermal X-rays, but bring more stringent constraints on the flux of a putative non-thermal component. Finally, we computed, thanks to a new dedicated model, the anisotropic inverse Compton emission generated in the wind shock region. The theoretical non-thermal emission appears to be compatible with observational limits and the kinetic luminosity computed from these models is in good agreement with the unabsorbed flux observed below 10 keV.

Lifting the curtain: The Seyfert galaxy Mrk 335 emerges from deep low-state in a sequence of rapid flare events

10.1051/0004-6361/202039098 ◽

2020 ◽

Vol 643 ◽

pp. L7

Author(s):

S. Komossa ◽

D. Grupe ◽

L. C. Gallo ◽

P. Poulos ◽

D. Blue ◽

...

Keyword(s):

Active Galactic Nuclei ◽

Spectral Energy Distribution ◽

Galactic Nuclei ◽

Seyfert Galaxy ◽

Optical Emission ◽

Line Of Sight ◽

Spectral Energy ◽

X Rays ◽

X Ray ◽

Partial Covering

Context. The narrow-line Seyfert 1 galaxy Mrk 335 was one of the X-ray brightest active galactic nuclei, but it has systematically faded since 2007. Aims. We report the discovery with Swift of a sequence of bright and rapid X-ray flare events that reveal the emergence of Mrk 335 from its ultra-deep multiyear low state. Methods. Results are based on our dedicated multiyear monitoring of Mrk 335 with Swift. Results. Unlike other bright active galactic nuclei, the optical–UV is generally not correlated with the X-rays in Mrk 335 on a timescale of days to months. This fact either implies the absence of a direct link between the two emission components; or else implies that the observed X-rays are significantly affected by (dust-free) absorption along our line of sight. The UV and optical, however, are closely correlated at the 99.99% confidence level. The UV is leading the optical by Δt = 1.5 ± 1.5 d. The Swift X-ray spectrum shows strong deviations from a single power law in all brightness states of the outbursts, indicating that significant absorption or reprocessing is taking place. Mrk 335 displays a softer-when-brighter variability pattern at intermediate X-ray count rates, which has been seen in our Swift data since 2007 (based on a total of 590 observations). This pattern breaks down at the highest and lowest count rates. Conclusions. We interpret the 2020 brightening of Mrk 335 as a decrease in column density and covering factor of a partial-covering absorber along our line of sight in the form of a clumpy accretion-disk wind that reveals an increasing portion of the intrinsic emission of Mrk 335 from the disk and/or corona region, while the optical emission-line regions receive a less variable spectral energy distribution. This then also explains why Mrk 335 was never seen to change its optical Seyfert type (not “changing look”) despite its factor ∼50 X-ray variability with Swift.

A deep X-ray view of the bare AGN Ark 120

10.1051/0004-6361/201731290 ◽

2018 ◽

Vol 609 ◽

pp. A42 ◽

Cited By ~ 29

Author(s):

D. Porquet ◽

J. N. Reeves ◽

G. Matt ◽

A. Marinucci ◽

E. Nardini ◽

...

Keyword(s):

Spectral Analysis ◽

Active Galactic Nuclei ◽

Galactic Nuclei ◽

Line Of Sight ◽

Constant Density ◽

High Flux ◽

X Rays ◽

X Ray ◽

Intrinsic Absorption ◽

The Continuum

Context. The physical characteristics of the material closest to supermassive black holes (SMBHs) are primarily studied through X-ray observations. However, the origins of the main X-ray components such as the soft X-ray excess, the Fe Kα line complex, and the hard X-ray excess are still hotly debated. This is particularly problematic for active galactic nuclei (AGN) showing a significant intrinsic absorption, either warm or neutral, which can severely distort the observed continuum. Therefore, AGN with no (or very weak) intrinsic absorption along the line of sight, so-called “bare AGN”, are the best targets to directly probe matter very close to the SMBH. Aims. We perform an X-ray spectral analysis of the brightest and cleanest bare AGN known so far, Ark 120, in order to determine the process(es) at work in the vicinity of the SMBH. Methods. We present spectral analyses of data from an extensive campaign observing Ark 120 in X-rays with XMM-Newton (4 × 120 ks, 2014 March 18–24), and NuSTAR (65.5 ks, 2014 March 22). Results. During this very deep X-ray campaign, the source was caught in a high-flux state similar to the earlier 2003 XMM-Newton observation, and about twice as bright as the lower-flux observation in 2013. The spectral analysis confirms the “softer when brighter” behavior of Ark 120. The four XMM-Newton/pn spectra are characterized by the presence of a prominent soft X-ray excess and a significant Fe Kα complex. The continuum is very similar above about 3 keV, while significant variability is present for the soft X-ray excess. We find that relativistic reflection from a constant-density, flat accretion disk cannot simultaneously produce the soft excess, broad Fe Kα complex, and hard X-ray excess. Instead, Comptonization reproduces the broadband (0.3–79 keV) continuum well, together with a contribution from a mildly relativistic disk reflection spectrum. Conclusions. During this 2014 observational campaign, the soft X-ray spectrum of Ark 120 below ~0.5 keV was found to be dominated by Comptonization of seed photons from the disk by a warm (kTe ~ 0.5 keV), optically-thick corona (τ ~ 9). Above this energy, the X-ray spectrum becomes dominated by Comptonization from electrons in a hot optically thin corona, while the broad Fe Kα line and the mild Compton hump result from reflection off the disk at several tens of gravitational radii.

X-ray emission from the solar wind

Symposium - International Astronomical Union ◽

10.1017/s0074180900004617 ◽

1970 ◽

Vol 37 ◽

pp. 408-412

Author(s):

E. Boldt ◽

A. Klimas ◽

G. Sandri

Keyword(s):

Solar Wind ◽

Mean Free Path ◽

Ecliptic Plane ◽

Line Of Sight ◽

Astronomical Unit ◽

The Sun ◽

X Rays ◽

Electron Collisions ◽

X Ray ◽

Recent Developments

Recent developments have made it possible to detect cosmic X-rays with energies as low as several hundred eV. Several measurements of the diffuse X-radiation in this range have been reported (Baxter et al., 1969; Bowyer et al., 1968; Henry et al., 1968). In this note we investigate the possibility that these observers have detected X-radiation emitted by the solar wind. We conclude that they probably have not. However, we also find that bremsstrahlung may be detectable from a region of the sky near the sun. If this measurement is possible, it would represent an important method for determining some characteristics of the solar wind away from the ecliptic plane of the solar system. Even though the mean free path for electron collisions is large compared with the astronomical unit, the collision frequency, electron density, and energy released per encounter are sufficient to yield detectable soft X-radiation for lines of sight close to the sun. We have estimated the expected X-ray intensity in the vicinity of the earth on the basis of two models of the solar wind flow pattern; in the first, the flow is radial in all directions away from the sun, and in the second, the flow is confined to a disc of uniform thickness near the ecliptic. In both cases, we neglect temperature gradients for the electrons and compute the total flux received from interplanetary plasma along the line of sight. Most of the received intensity comes from the segment of the line of sight which is nearest the sun. The results are insensitive with respect to the position of the boundary of the solar cavity. Accordingly, we neglect the boundary and consider an infinitely large solar cavity.

The environment of the wind–wind collision region of η Carinae

10.1051/0004-6361/201731841 ◽

2018 ◽

Vol 610 ◽

pp. A37 ◽

Cited By ~ 5

Author(s):

C. Panagiotou ◽

R. Walter

Keyword(s):

Good Accuracy ◽

Complex Geometry ◽

Line Of Sight ◽

X Rays ◽

Telescope Array ◽

X Ray ◽

Collision Zone ◽

Collision Region ◽

Shock Fronts ◽

The Continuum

Context. η Carinae is a colliding wind binary hosting two of the most massive stars and featuring the strongest wind collision mechanical luminosity. The wind collision region of this system is detected in X-rays and γ-rays and offers a unique laboratory for the study of particle acceleration and wind magneto-hydrodynamics. Aim. Our main goal is to use X-ray observations of η Carinae around periastron to constrain the wind collision zone geometry and understand the reasons for its variability. Methods. We analysed 10 Nuclear Spectroscopic Telescope Array (NuSTAR) observations, which were obtained around the 2014 periastron. The NuSTAR array monitored the source from 3 to 30 keV, which allowed us to grasp the continuum and absorption parameters with very good accuracy. We were able to identify several physical components and probe their variability. Results. The X-ray flux varied in a similar way as observed during previous periastrons and largely as expected if generated in the wind collision region. The flux detected within ~10 days of periastron is lower than expected, suggesting a partial disruption of the central region of the wind collision zone. The Fe Kα line is likely broadened by the electrons heated along the complex shock fronts. The variability of its equivalent width indicates that the fluorescence region has a complex geometry and that the source obscuration varies quickly with the line of sight.

X-Ray and UV Emission from VV Puppis

Highlights of Astronomy ◽

10.1017/s1539299600005785 ◽

1983 ◽

Vol 6 ◽

pp. 653-653

Author(s):

J. Patterson ◽

K. Beuermann ◽

G. Fabbiano ◽

D.Q. Lamb ◽

J. C. Raymond ◽

...

Keyword(s):

Small Region ◽

Light Curves ◽

Line Of Sight ◽

X Rays ◽

Magnetic Pole ◽

X Ray ◽

Opposite Case ◽

Uv Emission ◽

Optical Light Curve ◽

The Mean

We have discovered hard and soft X-ray emission from W Puppis, the last of the four classical AM Her stars to be detected in X-rays. The orbital light curves in both soft and hard X-rays are in excellent agreement with the mean optical light curve, indicating that essentially all of the accretion luminosity originates from a very small region at the white dwarf’s magnetic pole. An X-ray dip occurs once per binary period, when the magnetic pole lies closest to our line of sight, and is probably due to absorption. The X-ray data and optical spectroscopy constrain fairly well the geometry of the system, dictating an inclina-tion angle i < 70º and a mass for the white dwarf in excess of 1.1 Mʘ. X-ray and UV observations constrain the temperature of the soft X-ray component to lie in the range 20–45 eV, while the hard X-ray component has a temperature in excess of 6 keV. The observed flux of soft X-rays is much larger than that of hard X-rays. However, when the energy band-passes of the observations are taken into account, the ratio of the soft and hard X-ray luminosities Ls/Lh = 0.5-50. The ratio is unity for Tbb = 30 eV and Tbr = 50 keV; ifc is smaller if Tbb and/or Tbr are larger and is larger in the opposite case. These results, taken together with those for AM Her using the Einstein OGS, suggest that the famous “soft X-ray problem” in the AM Her stars may have gone away.

A deep X-ray view of the bare AGN Ark 120

10.1051/0004-6361/201834448 ◽

2019 ◽

Vol 623 ◽

pp. A11 ◽

Cited By ~ 11

Author(s):

D. Porquet ◽

C. Done ◽

J. N. Reeves ◽

N. Grosso ◽

A. Marinucci ◽

...

Keyword(s):

Inclination Angle ◽

Spectral Energy Distribution ◽

Relativistic Effects ◽

Black Body ◽

Line Of Sight ◽

Spectral Signature ◽

Spectral Energy ◽

X Rays ◽

X Ray ◽

Convolution Model

Context. The spin of supermassive black holes (SMBH) in active galactic nuclei (AGN) can be determined from spectral signature(s) of relativistic reflection such as the X-ray iron Kα line profile, but this can be rather uncertain when the line of sight intersects the so-called warm absorber and/or other wind components as these distort the continuum shape. Therefore, AGN showing no (or very weak) intrinsic absorption along the line-of-sight such as Ark 120, a so-called bare AGN, are the ideal targets for SMBH spin measurements. However, in our previous work on Ark 120, we found that its 2014 X-ray spectrum is dominated by Comptonisation, while the relativistic reflection emission only originates at tens of gravitational radii from the SMBH. As a result, we could not constrain the SMBH spin from disc reflection alone. Aims. Our aim is to determine the SMBH spin in Ark 120 from an alternative technique based on the global energetics of the disc-corona system. Indeed, the mass accretion rate (Ṁ) through the outer disc can be measured from the optical-UV emission, while the bolometric luminosity (Lbol) can be fairly well constrained from the optical to hard X-rays spectral energy distribution, giving access to the accretion efficiency η = Lbol/(Ṁc2) which depends on the SMBH spin. Methods. The spectral analysis uses simultaneous XMM-Newton (OM and pn) and NuSTAR observations on 2014 March 22 and 2013 February 18. We applied the OPTXCONV model (based on OPTXAGNF) to self consistently reproduce the emission from the inner corona (warm and hot thermal Comptonisation) and the outer disc (colour temperature corrected black body), taking into account both the disc inclination angle and relativistic effects. For self-consistency, we modelled the mild relativistic reflection of the incident Comptonisation components using the XILCONV convolution model. Results. We infer a SMBH spin of 0.83+0.05−0.03, adopting the SMBH reverberation mass of 1.50 × 108 M⊙. In addition, we find that the coronal radius decreases with increasing flux (by about a factor of two), from 85+13−10Rg in 2013 to 14 ± 3 Rg in 2014. Conclusions. This is the first time that such a constraint is obtained for a SMBH spin from this technique, thanks to the bare properties of Ark 120, its well determined SMBH reverberation mass, and the presence of a mild relativistic reflection component in 2014 which allows us to constrain the disc inclination angle. We caution that these results depend on the detailed disc-corona structure, which is not yet fully established. However, the realistic parameter values (e.g. Lbol/LEdd, disc inclination angle) found suggest that this is a promising method to determine spin in moderate-Ṁ AGN.