Hard Tail Research Articles

Hard X-ray spectral properties and discovery of narrow annihilation line in the spectrum of Nova Muscae

The observations of X-ray Nova in Musca (GRS1124-684) by two coded mask telescopes on board GRANAT observatory provided spectral data in broad 3 – 1300 keV band. During these observations, spanned over a ∼year, the Nova was detected in a three apparently different spectral states, corresponding to different epochs of the soft X-ray light curve: (1) A spectrum with two distinct components (soft, below ∼ 8 keV and hard power law tail with slope ∼ 2.5, detected up to ∼ 300 keV). The soft emission changed gradually with characteristic decay time around 30 days, while power law component exhibited strong variability on the time scales of several hours and decreased much more slowly. (2) A soft spectrum (without hard power law tail), observed during the “kick” of the soft X-ray light curve. (3) A hard power law spectrum with slope ∼ 2.2. Thus, while the 3 – 300 keV luminosity decreased by more than order of magnitude, the source passed through all spectral states known for galactic black hole candidates (Cyg X-1, GX339-4, 1E1740.7-2942, GRS1758-258 etc.).On January 20–21 1991, the SIGMA telescope aboard GRANAT detected a relatively narrow variable emission line near 500 keV (Fig.1,2) with net flux ≈ 6 · 10−3phot/s/cm2, most probably related with electron-positron annihilation processes, occurring in the source /1–4/. Additional excess above power law continuum, centered around ∼ 200 keV, was found during this observation.

ROSAT observations of pulsed soft X-ray emission from PSR 1055-52

Utilizing the position-sensitive proportional counter and the high-resolution imager aboard the orbiting X-ray observatory ROSAT, we have detected pulsations at the radio period from the pulsar PSR 1055-52. The pulse shapes are energy-dependent and show a transition at about 0.5 keV where the phase angle of the pulse peak changes by about -120 deg and the pulsed fraction increases from 11 percent to 63 percent toward larger energies. Simple spectral models are found to be unsatisfactory, while multicomponent models, such as a soft blackbody and hard power-law tail, yield better fits to the pulse-height data. The hard power-law tail is consistent with the extension of the recently reported EGRET results and may indicate a common emission mechanism for the X-ray through GeV gamma-ray regime. The soft blackbody component with T(infinity) = (7.5 +/- 0.6) x 10 exp 5 K, if interpreted as the initial cooling of a neutron star, is consistent with standard cooling models and does not require the presence of exotic components.

Annihilation radiation from a power-law distributed electron-positron plasma on the ground Landau level: the case of low magnetic fields

Intensity, polarization, and cooling rate of the two-photon annihilation radiation are studied in detail in the case of one-dimensional power-law distributions of electrons and positrons, assuming that they occupy the ground Landau level in a strong magnetic fieldB∼1010–1012 G. Simple analytical expressions for limiting cases are obtained and results of numerical calculations of radiation characteristics are presented. Power-lawe ± distributionsη ± ∝ e ± are shown to generate power-law spectra of the annihilation radiation atE≫mc 2 andE≪mc 2, with indices depending on the direction of radiation. The annihilation spectra at ϑ=0 show the largest blue-shifts of their maxima and the hardest high-energy tailsI(E≫mc 2, ϑ=0)∝E −(k−1). The blue-shifts reduce, and the hard tials steepen, with increasing ϑ. At ϑ>(2mc 2/E)1/2 the slopes of the high-energy tails rapidly transform to that at ϑ=π2,I(E≫mc 2, ϑ=π/2)∝E −(2k+3). The direction-integrated spectraS(E) also display the power-law tials at low and high energies,S(E≫mc 2)∝E −(k+1). The total annihilation rate and energy losses decrease with decreasingk, being higher than for the isotropice ± power-law distributions at the samek. The radiation is linearly polarized in the plane formed by the magnetic field and wave-vector. The polarization degreeP is maximum atE≫mc 2:P max≃0.6 for ϑ=π/2. Annihilation features and power-law-like hard tails observed in many gamma-ray burst spectra may be associated with the annihilation radiation of the magnetized power-law distributed plasma near neutron stars. Comparison of the observed and theoretical spectra allows one to estimate the power-law index of thee − e +-distribution and the gravitational redshift factor in the radiating region.

Hybrid accretion disks in active galactic nuclei. I - Structure and spectra

A unified treatment is presented of the two distinct states of vertically thin AGN accretion disks: a cool (about 10 to the 6th K) optically thick solution, and a hot (about 10 to the 9th K) optically thin solution. A generalized formalism and a new radiative cooling equation valid in both regimes are introduced. A new luminosity limit is found at which the hot and cool alpha solutions merge into a single solution of intermediate optical depth. Analytic solutions for the disk structure are given, and output spectra are computed numerically. This is used to demonstrate the prospect of fitting AGN broadband spectra containing both the UV bump as well as the hard X-ray and gamma-ray tail, using a single accretion disk model. Such models are found to make definite predictions about the observed spectrum, such as the relation between the hard X-ray spectral index, the UV-to-X-ray luminosity ratio, and a feature of about 1 MeV.

A jet model for a very high state of GX 339 - 4

A jet model is proposed which explain results derived by Ginga observation of GX 339 {minus} 4 in its very high state. Specifically, the model can explain: (1) the possible existence of large Compton clouds of 1-billion-cm size; (2) the independent change of the soft and hard components in the long term; (3) the rapid variability of the hard tail component in the short term; and (4) the possible existence of absorbing matter around the compact star. 25 refs.

Compton reflection and the variable X-ray spectrum of NGC 5548

Spectral analysis of EXOSAT and Ginga observations of the Seyfert galaxy NGC 5548 has revealed a complex form. At least four components, a steep non-thermal power law, an iron line, a hard tail and a soft emission component, have been identified in the 0.05-20 keV range. The soft component arises from thermal emission by optically thick material. Hard X-ray illumination of this material gives rise to the hard tail, by continuum Compton reflection, and the bulk of the iron line, via fluorescence. Varying relative levels of the power law and reflected continua result in apparent spectral index variations. Spectral and temporal considerations lead to the conclusion that the material lies close to the central energy source.

Nucleotide sequence of cDNA and primary structure for hard tail growth hormone

Full-length cDNA for hard tail growth hormone (htGH) has been cloned, and the nucleotide and deduced amino acid sequences have been analyzed. htGH is composed of 188 amino acid residues, and it shows 79, 74, 72, 59, 56, 37, 33 and 30% identity of amino acid with yellow tail, tuna, sea bream, flounder, salmon, blue shark, bullfrog and human GHs, respectively.

Hard X-rays from Coma Cluster region

A high-energy nonthermal component in the 18-130 keV energy band was detected by balloon-borne observations of the region containing the Coma Cluster of galaxies. The emitted photon spectrum is well-described by a single power law of photon index -1.77 and an intensity of 8.9 x 10 to the -5th photons/sq cm/s/KeV at 50 keV. The emission supports the presence of a hard tail, and could be due to the inverse Compton mechanism of relativistic electrons permeating the cluster off the 2.7 K background radiation or the presence in the field of an active galactic nucleus. 30 refs.

An evolving relativistic jet model for the BL Lacertae object Markarian 421

Coordinated observations of the nearby BL Lacertae object Mrk 421 obtained during May 1980, January 1984 and March 1984, are described. These observations give a time-frozen picture of the continuous spectrum of Mrk 421 at X-ray, ultraviolet, optical, and radio wavelengths. The observed spectra have been fitted to an inhomogeneous relativistic jet model described by Hutter and Mufson. The studies show that it is difficult to describe the data by a single jet whose properties vary as a function of time in a self-consistent manner unless the flat spectrum, hard X-ray tail present in January 1984 is due to an additional short-lived component of emission. These jet models are compared with homogeneous, spherically symmetric, synchrotron self-Compton models for this source.

MINIJETS: ORIGIN AND USEFULNESS

As the energy is increased, minijet production provides a steadily-increasing fraction of the total cross section in hadron-hadron collisions. We argue that, rather than being a new phenomenon, this is the result of the hard tail of soft diffractive events becoming increasingly prominent. We discuss the production of multiple minijets, and point out the interest of searching for minijet events in deep inelastic lepton scattering at HERA. Consequences for charm production are considered.

Simultaneous X-ray and optical observations of GX 339-4 in an X-ray high state

Optical emission, soft X-rays, and hard X-rays have been observed simultaneously from the black hole candidate GX 3339-4 in a typical high state. Each of these components is interpreted as arising from a characteristic region of the accretion disk. Considered as a black hole, GX 339-4 lacks the variable 2 keV blackbody component that would be emitted from the 'solid' surface of a neutron star in the low-mass neutron star binaries. The X-ray emission in the high state is therefore extremely soft and stable in time. The intermediate disk region is optically thick and geometrically thin. The observed soft X-ray component with a 'disk blackbody' spectrum comes from this region. The innermost disk region is dynamically unstable due to the effect of general relativity and possibly due to radiation pressure. This region is responsible for the generation of the hard X-ray tail through Comptonization.

New synchrotron luminosity distance limit for the 1979 March 5 gamma-ray event

New synchrotron luminosity estimates are provided for the March 5, 1979 gamma-ray event, based on the lack of low-frequency self-absorption cutoff. This leads to distance limits much lower than 55 kpc for a neutron-star emission area even in the most conservative case. The source is likely Galactic. If in addition the thermal self-Compton interpretation is invoked for the hard tail above 300 keV in the burst spectrum, then the source distance lies in the range 0.1-2 kpc for extreme ranges of the neutron-star emission area. This result strongly impacts current observational programs for this source.

A simple and accurate cryosurgical tool for the treatment of benign skin lesions: the "hard tail" dip-stick.

Although widely used, cryosurgery with liquid nitrogen still has its difficulties. Too often, large swabs sprayers, and cryoprobes damage surrounding skin. Small swabs are inadequate because of their limited "reservoir" capacity. This article describes a new tool, namely the "hard tail" dip-stick, which has been devised in an attempt to avoid these inadequacies.

The X-ray spectrm of the Coma Cluster of galaxies

The HEAO 1 A-2 and OSO 8 observations of the Coma Cluster of galaxies in the 2-60 keV energy band are presented. The spectrum is not well fitted by an isothermal bremsstrahlung model with an Fe line. To model the spectrum more accurately, we have performed fits of polytropic models and find that the gas is well fitted by an equation of state with polytropic index ranging between 1.38 and 1.6. This analysis reduces the total cluster mass by a factor of 3-5 below the optically derived virial mass. Using the best-fitting parameters, the gas is found to be a significant fraction (25 percent) of the total cluster mass. The Fe K-alpha line blend is strongly detected, from which we infer 0.18-0.36 solar abundance in the X-ray emitting gas. The Fe K-beta line blend is also weakly detected. The spectrum is not consistent with the existence of a hard X-ray tail at the flux level reported by Bazzano el al. (1984). In addition, the HEAO I scanning mode data place strong constraints on possible contaminating sources in the region surrounding Coma.

Solution of the Percus-Yevick equation in the coexistence region of a simple fluid

There has been much recent interest in the behavior of integral-equation theories for the distribution functions of a fluid near the critical point and in the two-phase region. For most systems, implementation of these theories necessitates numerical solution of the integral equations. However, for two examples, the adhesive hard sphere fluid in the Percus-Yevick approximation and the hard sphere plus Yukawa tail model in the mean spherical approximation, analytical solutions of the Ornstein-Zernike equation are available. In this work we consider the comparison of results obtained via numerical methods with the analytical solution of the Percus-Yevick equation for the adhesive hard sphere fluid. This complements a recent study by us of the mean spherical approximation for the hard sphere plus Yukawa tail fluid. This allows us to examine carefully how errors arise in the numerical solutions. We examine the accuracy of numerical calculations of the critical exponents as well as the interpretation of solutions obtained in the coexistence region. We discuss the implications of this work for applications to more realistic potentials where only numerical solutions are available.

X-ray spectral variability of 3C273

3C273 has been monitored by EXOSAT over the period December 1983 to June 1984 in 4 observations. In the December observation the flux was high and the spectrum showed a power law index of 1.5 changing to 0.9 at~8 keV. In subsequent observations the flux dropped to~40% of its original value and the hard tail disappeared. In the last observation the LE flux increased by a factor of 2 with no accompanying ME flux increase.

Hard X-ray observation of galactic X-ray sources

A large (1455 cm 2) hard X-ray telescope was successfully launched aboard a stratospheric balloon on October 4, 1980. During this flight four galactic X-ray sources were observed, namely the transient recurrent X-ray pulsar A0535+26, the Crab Nebula, Cygnus X-1 and X Persei. Here we report the results on the latter two sources. From Cygnus X-1 we measured a photon flux in the band 30 to 200 keV, of 3.5 × 10 −2 photons cm −2 which is 6.5 times lower than that recieved from the source in a “low” intensity state in the same energy band. In addition, the photon spectrum in the same energy band was very soft and consistent with a power law with photon index α = 2.71 ± 0.14. Even if a simultaneous observation of the source at lower energies was not available, our data strongly suggest that we observed the source during a “high” intensity state. We report also positive detection in the band 30 to 200 keV of the low luminosity X-ray pulsar X Persei. In its spectrum we confirm the presence of a hard X-ray tail consistent with a power law (photon index α = 2.17 ± 0.42).

Observations of a hard X-ray component in the spectrum of Nova Ophiuchi

view Abstract Citations (30) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observations of a hard X-ray component in the spectrum of Nova Oph. Wilson, C. K. ; Rothschild, R. E. Abstract The spectrum and time variation of Nova Ophiuchi (H1705-25) in the 10-200 keV range as measured by the UCSD/MIT instruments aboard HEAO 1 during the period 1977 August 25 to September 28 are reported. The composite curve is best fitted by a kT = 2 keV thin thermal bremsstrahlung model below 10 keV and a separate hard X-ray component fitted equally well by a power-law component with photon index 2.19 + or - 0.06 or a kT = 32.1 + or - 2.4 keV thermal bremsstrahlung model. This is the first observation of a hard tail in the spectrum of a transient X-ray source with sufficient statistical significance to allow a detailed study of its spectral and temporal variability. It is found that the intensity variations of the high-energy X-rays are consistent with the variability at lower energies (3-6 keV), but no hard X-ray spectral index variability is found on time scales from 2 days to 2 weeks. The results can be interpreted as due to accretion onto a neutron star (or possibly onto a black hole) that may also be surrounded by an extended corona. Publication: The Astrophysical Journal Pub Date: November 1983 DOI: 10.1086/161483 Bibcode: 1983ApJ...274..717W Keywords: Binary Stars; Neutron Stars; Novae; Stellar Mass Accretion; X Ray Sources; Black Holes (Astronomy); Bremsstrahlung; Heao 1; Light Curve; Ophiuchi Clouds; Stellar Spectra; Thermal Radiation; X Ray Spectra; Astrophysics full text sources ADS | data products SIMBAD (4)

X-Ray Observations of Active Galactic Nuclei

HEAO 1 A2 and Einstein SSS spectral observations of Seyfert galaxies and BL Lac objects suggest that in both cases, the X-ray emission is due to relativistic particles. The five BL Lac objects have very soft spectra and at higher energies (above 10 keV) may have hard tails. Combining our X-ray data with radio, infrared, optical, and ultraviolet observations, we can fit the BL Lac spectra with the familiar synchrotron self-Compton model if we allow for relativistic beaming (Urry and Mushotzky 1982, Urry et al. 1982). We show that Doppler beaming of an underlying (Seyfert-like) source population flattens the observed luminosity function, and we emphasize that the relative numbers of BL Lacs and quasars in given spectral intervals are strong functions of selection effects, the degree of Doppler beaming, and the form of the intrinsic luminosity function.

Transport of neutrinos, radiation and energetic particles in accretion flows

The equations describing the transport of suprathermal charged particles, electromagnetic radiation and neutrinos across accretion flows onto compact objects are solved analytically, the effects of shocks in the flow being included. These solutions are used in discussing three illustrative astrophysical examples: acceleration of cosmic rays, generation of spectral continua in quasars and the effect of neutrinos during the collapse of supernova precursors. The main results are: (а) Accretion flows with shocks accelerate cosmic rays very efficiently up to the highest energies. (b) The emergent spectra of electromagnetic radiation from such flows reproduce the observed spectra of quasars from infrared to the hard X-ray region. (c) The neutrinos in the collapsing cores of red giants develop a very hard non-thermal tail in their distribution facilitating the rebound of the gravitational collapse leading to the supernovae.