Evidence Of Non-thermal Emission Research Articles

A search for non-thermal radio emission from jets of massive young stellar objects

Massive young stellar objects (MYSOs) have recently been shown to drive jets whose particles can interact with either the magnetic fields of the jet or ambient medium to emit non-thermal radiation. We report a search for non-thermal radio emission from a sample of 15 MYSOs to establish the prevalence of the emission in the objects. We used their spectra across the L-, C- and Q-bands along with spectral index maps to characterise their emission. We find that about 50% of the sources show evidence for non-thermal emission with 40% showing clear non-thermal lobes, especially sources of higher bolometric luminosity. The common or IRAS names of the sources that manifest non-thermal lobes are; V645Cyg, IRAS 22134+5834, NGC 7538 IRS 9, IRAS 23262+640, AFGL 402d and AFGL 490. All the central cores of the sources are thermal with corresponding mass-loss rates that lie in the range 3X10^{-7} to 7X10^{-6} solar masses per year. Given the presence of non-thermal lobes in some of the sources and the evidence of non-thermal emission from some spectral index maps, it seems that magnetic fields play a significant role in the jets of massive protostars. Also noted is that some of the sources show evidence of binarity and variability.

The Oldest X‐Ray Supernovae: X‐Ray Emission from 1941C, 1959D, and 1968D

We have studied the X-ray emission from four historical Type II supernovae (the newly recovered 1941C in NGC 4136 and 1959D in NGC 7331; and 1968D and 1980K in NGC 6946), using Chandra ACIS-S imaging. In particular, the first three are the oldest ever found in the X-ray band, and provide constraints on the properties of the stellar wind and circumstellar matter encountered by the expanding shock at more advanced stages in the transition toward the remnant phase. We estimate emitted luminosities ≈5 × 1037 erg s−1 for SN 1941C, ~a few × 1037 erg s−1 for SN 1959D, ≈2 × 1038 erg s−1 for SN 1968D, and ≈4 × 1037 erg s−1 for SN 1980K, in the 0.3-8 keV band. X-ray spectral fits to SN 1968D suggest the presence of a harder component, possibly a power law with photon index ≈2, contributing ≈1037 erg s−1 in the 2-10 keV band. We speculate that it may be evidence of nonthermal emission from a Crab-like young pulsar.

γ-rays and neutrinos

Cosmic rays are particles which originate from space and impinge on the earth's atmosphere with energies spanning over fourteen orders of magnitude. Despite first discovered almost hundred years ago, the origin of cosmic rays is still not completely unveiled. At very high energies (above 1015 eV) the composition and the spectral behavior are not fully assessed; the sources are not yet unambiguously identified as well and unclear are the underlying acceleration mechanisms. Strong indications are however provided by the evidence of non-thermal emission from several objects, which suggest acceleration of particles in plasma shock waves in the proximity of violent astrophysical environments. With the operation of a new generation of imaging Cherenkov telescopes, enormous progress has been achieved in the last years in the discovery of sources of high energy γ-rays. If originated in the decay of neutral pions, the observed γ-rays can represent the fingerprint of cosmic ray sources. In most cases, however, the observed electromagnetic emission can be attributed to other mechanisms. The discovery of high energy neutrinos of cosmic origin would instead provide an unambiguous signature for acceleration of hadrons, but no indication of cosmic neutrino signals has been collected so far. Here we review the success achieved during the latest years in observing the γ-ray imprint of the universe and the perspectives of opening a new observational window with the establishment of neutrino astrophysics.

An XMM-Newton study of the sub-structure in M 87's halo

The high signal to noise and good point spread function of XMM have allowed the first detailed study of the interaction between the thermal and radio emitting plasma in the central regions of M87. We show that the X-ray emitting structure, previously seen by ROSAT, is thermal in nature and that the east and southwest extensions in M87's X-ray halo have a significantly lower temperature (kT= 1.5 keV) than the surrounding ambient medium (kT= 2.3 keV). There is little or no evidence for non-thermal emission with an upper limit on the contribution of a power law component of spectral index flatter than 3 being less than 1% of the flux in the region of the radio lobes.

High resolution radio images of the symbiotic system R aquarii

We present MERLIN images of the symbiotic system R Aquarii obtained at 1.7 and 5 GHz. We identify the emission from the binary system and derive a mass loss rate for the Mira that is commensurate with that in typical Miras. We show that variations in the radio emission over the last decade are consistent with the jet model for the system originally presented by Solf (1992). In addition, we calculate the spectral index distribution and find that there is no evidence of non-thermal emission.

Aperture synthesis observations at 80 MHz of the Galactic center region - Possible evidence for Seyfert-like activity

view Abstract Citations (25) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Aperture synthesis observations at 80 MHz of the galactic center region : possible evidence for Seyfert-like activity. Larosa, T. N. ; Kassim, N. E. Abstract 80 MHz aperture synthesis observations of the Galactic center region made with the Clark lake TPT array are presented. The sources G 1.05 - 0.1, G 0.9 + 0.1, and G 0.16 - 0.15 were detected in emission. The detection of G 0.16 - 0.15, coincident with the southeastern part of the continuum arc feature, is evidence of nonthermal emission in this region of the arc. Several H II regions also appear in absorption against the nonthermal Galactic background. In addition a strong unidentified extended nonthermal source located approximately 34 arcmin from the Galactic center was detected. Although no direct evidence for the distance to this object is currently available, the properties of this source are very similar to those exhibited by radio lobes observed in the nuclei of Seyfert galaxies as reported by Wilson in 1981 and later papers. However, the possibility that this object is a Galactic SNR with an unusually step spectrum cannot be ruled out. Publication: The Astrophysical Journal Pub Date: December 1985 DOI: 10.1086/184571 Bibcode: 1985ApJ...299L..13L Keywords: Galactic Nuclei; Milky Way Galaxy; Radio Astronomy; Radio Galaxies; Seyfert Galaxies; Synthetic Apertures; Absorption Spectra; Astronomical Maps; Astronomical Spectroscopy; Data Reduction; H Ii Regions; Nonthermal Radiation; Astrophysics full text sources ADS | data products SIMBAD (4)

Microwave, ultraviolet, and soft X-Ray observations of hale region 16898

Hale region 16898 was observed by the Westerbork Synthesis Radio Telescope at 6 cm and by the Ultraviolet Spectrometer and Polarimeter and the X-Ray Spectrometer on the Solar Maximum Mission satellite. Optical pictures of the same active region were taken at Sacramento Peak, Big Bear, and Meudon Observatories. The radio emission mechanisms are identified by comparing radio data with ultraviolet and soft X-ray data. The height of the radio sources and the magnetic field strength at that height are deduced. A radio source above a large sunspot shows a crescent shaped depression of circular polarization and a high brightness temperature. The emission mechanism is identified as gyroresonance at the second and the third harmonic layers and it is found that the second harmonic layer, where the magnetic field strength is 900 G, must be in the corona. An extended loop-like source connecting the leading and the following part of the active region as well as the sources associated with small spots are mainly due to thermal free-free emission by hot and dense plasma which is also observed in ultraviolet and soft X-ray radiation. The calculated radio brightness temperature, using the physical parameters deduced from the ultraviolet and soft X-ray line intensities, agrees with the observed brightness temperature. The height of the low brightness temperature sources above the small spots is 6000 ± 3000 km and that above the large spot is less than 3000 km: the source above the large spot does not show any shift relative to the sunspot due to the projection effect. Very strong radio emission was found which was associated with the merging of a group of small spots into the large sunspot. In the same day, warm (≤ 106 K) and dense matter was present above the large spot. Evidence for nonthermal emission is presented.

Nonthermal radio observations of the major planets

Seventeen years of observations have shown that Jupiter is a complex and intriguing source of emission over the entire radio spectrum accessible from the ground. The observations indicate the presence of intense radiation belts and a strong magnetic field inclined to the axis of rotation. At decametric wavelengths, several remarkably powerful sources are correlated with the rotation of the planet and the orbital motion of the satellite Io. Longer-term variations of these sources may be associated with the sunspot cycle, with Jupiter's orbital motion, or with changes in the internal structure of the planet. There is at most marginal evidence of nonthermal emission from Saturn, and as yet no evidence for such radiation from Uranus or Neptune.

X-Ray Emissions from Solar Flares and from Celestial Sources

One of the interesting questions in solar X-ray astronomy is the question as to whether the hard X-ray emission which occurs during major solar flares is a thermal or nonthermal phenomenon. The evidence for non-thermal emission has been based in large measure on a balloon-borne experiment by Peterson and Winckler, which constituted the first detection of high energy flare X-rays. In the Peterson-Winckler experiment, the incident solar X-rays were measured by both an ion chamber and a Geiger counter photometer, and from the ratio of responses, the hardness character of the incident X-rays was reduced. It was concluded that the observed result could have been explained in terms of the sudden non-thermal production of a group of electrons with energy of the order of 500 kilovolts.