scholarly journals The Nova V5584 Sgr: A Short Review

2015 ◽  
Vol 2 (1) ◽  
pp. 234-237
Author(s):  
R. Poggiani
Keyword(s):  
Short Review ◽  
Electromagnetic Spectrum ◽  
X Rays ◽  
Infrared Observations ◽  
X Ray ◽  
Sgr A

The nova V5584 Sgr was discovered during 2009 October. It has been monitored in different domains of the electromagnetic spectrum: optical, infrared and X-rays. The optical and infrared observations suggest that V5584 Sgr is a Fe II nova that formed dust. No X-ray emission was observed around the time of maximum.

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

2018 ◽  
Vol 610 ◽  
pp. A34 ◽  
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.

scholarly journals Non-equilibrium chemistry and destruction of CO by X-ray flares

2019 ◽  
Vol 486 (1) ◽  
pp. 1094-1122 ◽  
Author(s):  
Jonathan Mackey ◽  
Stefanie Walch ◽  
Daniel Seifried ◽  
Simon C O Glover ◽  
Richard Wünsch ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Thermal Evolution ◽  
Galactic Nuclei ◽  
Galactic Centre ◽  
X Rays ◽  
X Ray ◽  
Uv Emission ◽  
Sgr A ◽  
X Ray Binaries ◽  
Fractal Cloud

ABSTRACT Sources of X-rays such as active galactic nuclei and X-ray binaries are often variable by orders of magnitude in luminosity over time-scales of years. During and after these flares the surrounding gas is out of chemical and thermal equilibrium. We introduce a new implementation of X-ray radiative transfer coupled to a time-dependent chemical network for use in 3D magnetohydrodynamical simulations. A static fractal molecular cloud is irradiated with X-rays of different intensity, and the chemical and thermal evolution of the cloud are studied. For a simulated $10^5\, \mathrm{M}_\odot$ fractal cloud, an X-ray flux <0.01 erg cm−2 s−1 allows the cloud to remain molecular, whereas most of the CO and H2 are destroyed for a flux of ≥1 erg cm−2 s−1. The effects of an X-ray flare, which suddenly increases the X-ray flux by 105×, are then studied. A cloud exposed to a bright flare has 99 per cent of its CO destroyed in 10–20 yr, whereas it takes >103 yr for 99 per cent of the H2 to be destroyed. CO is primarily destroyed by locally generated far-UV emission from collisions between non-thermal electrons and H2; He+ only becomes an important destruction agent when the CO abundance is already very small. After the flare is over, CO re-forms and approaches its equilibrium abundance after 103–105 yr. This implies that molecular clouds close to Sgr A⋆ in the Galactic Centre may still be out of chemical equilibrium, and we predict the existence of clouds near flaring X-ray sources in which CO has been mostly destroyed but H is fully molecular.

scholarly journals V4046 Sgr: X-rays from accretion shock

2013 ◽  
Vol 9 (S302) ◽  
pp. 46-47
Author(s):  
C. Argiroffi ◽  
A. Maggio ◽  
T. Montmerle ◽  
D. Huenemoerder ◽  
E. Alecian ◽  
...  
Keyword(s):  
Tauri Star ◽  
X Rays ◽  
X Ray ◽  
Accretion Flows ◽  
T Tauri ◽  
Different Temperatures ◽  
Sgr A ◽  
Star Binary ◽  
Accretion Shock ◽  
Density Plasma

AbstractWe present results of the X-ray monitoring of V4046 Sgr, a close classical T Tauri star binary, with both components accreting material. The 360 ks long XMM observation allowed us to measure the plasma densities at different temperatures, and to check whether and how the density varies with time. We find that plasma at temperatures of 1–4 MK has high densities, and we observe correlated and simultaneous density variations of plasma, probed by O VII and Ne IX triplets. These results strongly indicate that all the inspected He-like triplets are produced by high-density plasma heated in accretion shocks, and located at the base of accretion flows.

scholarly journals Simultaneous Kepler/K2 and XMM-Newton observations of superflares in the Pleiades

2019 ◽  
Vol 622 ◽  
pp. A210 ◽  
Author(s):  
M. G. Guarcello ◽  
G. Micela ◽  
S. Sciortino ◽  
J. López-Santiago ◽  
C. Argiroffi ◽  
...  
Keyword(s):  
Time Evolution ◽  
Energy Budget ◽  
Solar Flares ◽  
Light Curves ◽  
Integrated Analysis ◽  
Electromagnetic Spectrum ◽  
The Sun ◽  
X Rays ◽  
X Ray ◽  
Different Ages

Context. Flares are powerful events ignited by a sudden release of magnetic energy which triggers a cascade of interconnected phenomena, each resulting in emission in different electromagnetic bands. In fact, in the Sun flares are observed across the whole electromagnetic spectrum. Multi-band observations of stellar flares are instead rare. This limits our ability to extend what we learn from solar flares to the case of flares occurring in stars with different properties. Aims. With the aim of studying flares in the 125-Myr-old stars in the Pleiades observed simultaneously in optical and X-ray light, we obtained new XMM-Newton observations of this cluster during the observations of Kepler K2 Campaign 4. The objective of this paper is to characterize the most powerful flares observed in both bands and to constrain the energy released in the optical and X-ray, the geometry of the loops, and their time evolution. We also aim to compare our results to existing studies of flares occurring in the Sun and stars at different ages. Methods. We selected bright X-ray/optical flares that occurred in 12 known members of the Pleiades from their K2 and XMM-Newton light curves. The sample includes ten K-M stars, one F9 star, and one G8 star. Flare average properties were obtained from integrated analysis of the light curves during the flares. The time evolution of the plasma in the magnetic loops is constrained with time-resolved X-ray spectral analysis. Results. Most of the flares studied in this work emitted more energy in optical than in X-rays, as in most solar flares, even if the Pleiades flares output a larger fraction of their total energy in X-rays than typical solar flares do. Additionally, the energy budget in the two bands is weakly correlated. We also found comparable flare duration in optical and X-rays and observed that rapidly rotating stars (e.g., with rotation period shorter than 0.5 days) preferentially host short flares. We estimated the slope of the cooling path of the flares in the log(EM)-vs.-log(T) plane. The values we obtained are affected by large uncertainties, but their nominal values suggest that the flares analyzed in this paper are mainly due to single loops with no sustained heating occurring during the cooling phase. We also observed and analyzed oscillations with a period of 500 s during one of the flares. Conclusions. The flares observed in the Pleiades can be classified as “superflares” based on their energy budget in the optical, and share some of the properties of the flares observed in the Sun, despite being more energetic. For instance, as in most solar flares, more energy is typically released in the optical than in X-rays and the duration of the flares in the two bands is correlated. We have attempted a comparison between the X-ray flares observed in the Pleiades and those observed in clusters with different ages, but to firmly address any evolutionary pattern of flare characteristics, similar and uniform multi-wavelength analyses on more complete samples are necessary.

scholarly journals Centaurus A: Hard X-ray and High-Energy Gamma-Ray Light Curve Correlation

Galaxies ◽  
2019 ◽  
Vol 7 (2) ◽  
pp. 44 ◽  
Author(s):  
Isak Davids ◽  
Markus Böttcher ◽  
Michael Backes
Keyword(s):  
Light Curve ◽  
High Energy ◽  
Electromagnetic Spectrum ◽  
X Rays ◽  
X Ray ◽  
Correlation Studies ◽  
High Energy Gamma ◽  
Energy Gamma ◽  
Γ Rays ◽  
Centaurus A

Centaurus A, powered by a 55 million solar mass supermassive black hole, has been intensively monitored in all accessible wavelength ranges of the electromagnetic spectrum. However, its very-high energy gamma ( γ ) ray flux (TeV photons), obtained from H.E.S.S. is relatively faint, hampering detailed light curve analyses in the most energetic energy band. Yet, the extensive long-term light curve data from Fermi-LAT and Swift-BAT (hard X-rays) allows for cross-correlation studies. We find a hint that X-ray emission from Centaurus A precedes the γ rays by 25 ± 125 days. If this lag is real and related to a γ γ absorption effect in the broad-line region (BLR) around the central source, we can constrain the size of the BLR using light-travel time arguments. These are first results of extended light curve correlation studies between high-energy γ rays and X-rays from Centaurus A.

scholarly journals The Origin of Flaring Activity in AE Aquarii

1995 ◽  
Vol 151 ◽  
pp. 272-275
Author(s):  
Nazar Ikhsanov
Keyword(s):  
Main Sequence ◽  
Compact Star ◽  
Compact Object ◽  
Electromagnetic Spectrum ◽  
Thermal Source ◽  
X Rays ◽  
Mass Ratio ◽  
X Ray ◽  
Γ Rays ◽  
Gas Accretion

AE Aqr is a close non-eclipsing binary system with an orbital period Porb ≈ 9.88 hr, eccentricity of the orbit e = 0.02 (Chincarini & Walker 1981) and a mass ratio q = 1.14 (Reinsch & Beuermann 1994), situated at the distance of ∼ 84 pc (Van Paradijs et al. 1989). The secondary is K3 red dwarf on or close to the main sequence (Bruch 1991). The primary cannot be observed directly. However, the stable photometric oscillations at a period of 33 s (and at half this period) in the optical (Patterson 1979), UV (Eracleous et al. 1994), X-rays (Patterson et al. 1980) and, probably, VHE γ-rays (Meintjes et al. 1992, Bowden et al. 1992) leave no doubt that the primary is a rapidly rotating magnetized compact object. The observed rate of deceleration of the primary rotation is Ṗ = 5.64 × 10−14 ss−1 (De Jager et al. 1994), and its mass is m1sin3i (0.56 ± 0.03) M⊙ (Reinsch & Beuermann 1994). The lack of eclipses allows to put a lower limit to the mass of the primary m1 ≥ 0.62M⊙.AE Aqr emits detectable radiation in all parts of the electromagnetic spectrum. In radio and γ-rays it is a powerful non-thermal source. However, in the optical, UV and X-rays the radiation is likely to be thermal and can be well explained by gas accretion onto a compact star (Patterson 1979, Patterson et al. 1980). The observed impulse profile of the pulsating component (Eracleous et al. 1994) looks similar to that of the accreting X-ray pulsars.

scholarly journals X-Ray Observations of the Galactic Centre

1989 ◽  
Vol 136 ◽  
pp. 567-580 ◽  
Author(s):  
G. K. Skinner
Keyword(s):  
Energy Range ◽  
High Energy ◽  
Point Sources ◽  
Galactic Centre ◽  
X Rays ◽  
Diffuse Emission ◽  
Variable Source ◽  
X Ray ◽  
Centre Region ◽  
Sgr A

Observations of the galactic centre region in the photon energy range 2–500 keV are reviewed. Point sources, transients, bursts and a patch of apparently diffuse emission ~1° in extent have all been observed. The relatively detailed information obtained with the Einstein observatory just above the bottom edge of the x-ray window is starting to be supplemented by observations at higher photon energies. Although there is known to be a strong, variable, source of high energy x-rays somewhere in the region there is little reason to associate it with Sgr A West, which is detectable, but relatively weak, in the energy range below 30 keV where detailed measurements have been possible.

Radium in Engineering Practice

1933 ◽  
Vol 124 (1) ◽  
pp. 305-332
Author(s):  
V. E. Pullin
Keyword(s):  
Gamma Ray ◽  
Harmful Effect ◽  
Engineering Practice ◽  
Electromagnetic Spectrum ◽  
X Rays ◽  
Ray Method ◽  
Metallic Structures ◽  
Good Definition ◽  
X Ray ◽  
Limited Function

Considerable advances have recently been made in nondestructive testing, and a new transportable X-ray laboratory is illustrated in the paper to show that X-rays have achieved a definite, if limited, function in this field. The paper is mainly devoted to a discussion of the properties of radium as a radiographic agent to show how it compares in value with the older X-ray method. The disintegration theory of radioactive materials is outlined and the relative wavelengths of various components of the so-called electromagnetic spectrum, used roughly to indicate their penetrating power, are given. The method of preparing radon is described as it has the great advantage that its use would afford an approximation to a point source of radiation. When employing one of the radium salts, the radium must be removed an appreciable distance from the sensitized film to obtain good definition, thus increasing the exposure time. Careful directions are given for the safe handling and storage of the element. The exposure camera in use in the Research Department, Woolwich, is described and curves are given indicating safe working distances for operators. Many experimental refinements making for clear radiography are mentioned. In the case of X-rays the effect of scattered radiation militates seriously against good results, whereas in gamma-ray photography there is practically no such harmful effect. Hence heavy irregular specimens may be radiographed by radium in perhaps one exposure. Exposure curves for radium, based upon experimental data obtained in the author's laboratory, are given. Owing to the general employment of photographic intensifying screens to shorten exposures, it is not possible to rely on calculations based on the inverse square law. The uses of X-rays and radium are compared and the particular advantages of radium illustrated by a large number of radiographs. X-rays have overwhelming advantages in the examination of metallic structures up to a thickness of about 3 inches. Radium, on the other hand, may be employed in the investigation of metals up to 8 inches or more in thickness.

scholarly journals Slugs and Snails and Puppy Dog Tails: jets from an unconventional angle

2014 ◽  
Vol 10 (S313) ◽  
pp. 199-207
Author(s):  
D. E. Harris
Keyword(s):  
Short Review ◽  
Active Galaxies ◽  
Electromagnetic Spectrum ◽  
Synchrotron Emission ◽  
X Rays ◽  
Current Experiment ◽  
Massive Black Holes ◽  
Extragalactic Jets ◽  
Inverse Compton ◽  
A Current

AbstractWe discuss some aspects of extragalactic jets originating from super massive black holes in the centres of active galaxies (and quasars). We start with a short review of sizes and flavors and then argue that the emission we detect across the electromagnetic spectrum does not come from the essence of the jet, but is rather a product of the jet. We go on to discuss some topics concerning synchrotron emission from jets, mainly aspects of knots. Finally we discuss the emission processes for the X-rays and describe a current experiment with LOFAR designed to test a requirement of inverse Compton models.

scholarly journals General relativistic MHD simulations of non-thermal flaring in Sagittarius A*

2021 ◽  
Author(s):  
K Chatterjee ◽  
S Markoff ◽  
J Neilsen ◽  
Z Younsi ◽  
G Witzel ◽  
...  
Keyword(s):  
Particle Acceleration ◽  
Near Infrared ◽  
Power Spectra ◽  
X Rays ◽  
Thermal Electron ◽  
X Ray ◽  
Particle Distributions ◽  
Accretion Flows ◽  
General Relativistic ◽  
Sgr A

Abstract Sgr A* exhibits regular variability in its multiwavelength emission, including daily X-ray flares and roughly continuous near-infrared (NIR) flickering. The origin of this variability is still ambiguous since both inverse Compton and synchrotron emission are possible radiative mechanisms. The underlying particle distributions are also not well constrained, particularly the non-thermal contribution. In this work, we employ the GPU-accelerated general relativistic magnetohydrodynamics (GRMHD) code H-AMR to perform a study of flare flux distributions, including the effect of particle acceleration for the first time in high-resolution 3D simulations of Sgr A*. For the particle acceleration, we use the general relativistic ray-tracing (GRRT) code BHOSS to perform the radiative transfer, assuming a hybrid thermal+non-thermal electron energy distribution. We extract ∼60 hr lightcurves in the sub-millimetre, NIR and X-ray wavebands, and compare the power spectra and the cumulative flux distributions of the lightcurves to statistical descriptions for Sgr A* flares. Our results indicate that non-thermal populations of electrons arising from turbulence-driven reconnection in weakly magnetised accretion flows lead to moderate NIR and X-ray flares and reasonably describe the X-ray flux distribution while fulfilling multiwavelength flux constraints. These models exhibit high rms per cent amplitudes, $\gtrsim 150{{\ \rm per\ cent}}$ both in the NIR and the X-rays, with changes in the accretion rate driving the 230 GHz flux variability, in agreement with Sgr A* observations.

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