Synchrotron Origin Research Articles

Detection of Optical Synchrotron Emission from the Radio Jet of 3C 279

We report the detection of optical and ultraviolet emission from the kiloparsec scale jet of the well-known quasar 3C~279. A bright knot, discovered in archival V and U band {\it Hubble Space Telescope} Faint Object Camera images, is coincident with a peak in the radio jet $\sim0.6\arcsec$ from the nucleus. The detection was also confirmed in Wide Field Planetary Camera-2 images. Archival Very Large Array and MERLIN radio data are also analyzed which help to show that the high-energy optical/UV continuum, and spectrum, are consistent with a synchrotron origin from the same population of relativistic electrons responsible for the radio emission.

The high energy gamma-ray emission expected from Tycho's supernova remnant

A nonlinear kinetic model of cosmic ray (CR) acceleration in supernova remnants (SNRs) is used to describe the properties of Tycho's SNR. Observations of the expansion characteristics and of the nonthermal radio and X-ray emission spectra, assumed to be of synchrotron origin, are used to constrain the overall dynamical evolution and the particle acceleration parameters of the system, in addition to what is known from independent estimates of the distance and thermal X-ray observations. It is shown that a very efficient production of nuclear cosmic rays, leading to strong shock modification, and a large downstream magnetic field strength μG are required to reproduce the observed synchrotron emission from radio to X-ray frequencies. This field strength is still well within the upper bound for the effective magnetic field, consistent with the acceleration process. The -decay γ-ray flux turns out to be somewhat greater than the inverse Compton (IC) flux off the Cosmic Microwave Background at energies below 1 TeV, dominating it strongly at 10 TeV. The predicted TeV γ-ray flux is consistent with but close to the very low upper limit recently obtained by HEGRA. A future detection at TeV would clearly indicate hadronic emission.

Proton-synchrotron radiation of large-scale jets in active galactic nuclei

I propose a new mechanism for explanation of nonthernal X-ray emission of large-scale AGN jets. Namely, I assume that this radiation has synchrotron origin emitted by extremely high energy protons, and discuss implications of this model for several prominent hot spots and knots resolved by Chandra in Pictor A, 3C 120, PKS 0637-752, 3C 273.

Optical synchrotron emission from the nuclei of FR I radio galaxies

We studied HST images of a complete sample of 33 FR I radio galaxies. Emission from an unresolved Central Compact Core (CCC) is detected in the great majority of the objects. CCC optical emission shows a striking correlation with the radio core fluxes, which extends over four decades with a slope of ∼1. This argues strongly for a non-thermal synchrotron origin of the CCCs, which would then dominate the nuclear emission both in the radio and in the optical bands. The high detection rate of CCCs sets strong constraints on the existence/geometry of any obscuring, optically thick structure (torus) in FR I. We also find evidence for a different behavior of low and high power objects belonging to our sample. CCC fluxes also represent upper limits to any unobscured thermal/disc emission, which translate into a fraction as small as ≲10 −7−10 −5 of the Eddington luminosity (for a 10 9 M ⊙ black hole).

Chandraobservations of the X-ray jet in 3C 66B

Our Chandra observation of the FRI radio galaxy 3C66B has resulted in the first detection of an X-ray counterpart to the previously known radio, infra-red and optical jet. The X-ray jet is detected up to 7 arcsec from the core and has a steep X-ray spectrum, alpha ~ 1.3 +/- 0.1. The overall X-ray flux density and spectrum of the jet are consistent with a synchrotron origin for the X-ray emission. However, the inner knot in the jet has a higher ratio of X-ray to radio emission than the others. This suggests that either two distinct emission processes are present or that differences in the acceleration mechanism are required; there may be a contribution to the inner knot's emission from an inverse-Compton process or it may be the site of an early strong shock in the jet. The peak of the brightest radio and X-ray knot is significantly closer to the nucleus in the X-ray than in the radio, which may suggest that the knots are privileged sites for high-energy particle acceleration. 3C66B's jet is similar both in overall spectral shape and in structural detail to those in more nearby sources such as M87 and Centaurus A.

Chandrafinds that X-ray jets are common in low-power radio galaxies

We present results for the first three low-power radio galaxi es from the B2 bright sample to have been observed with Chandra. Two have kpc-scale radio jets, and in both Chandra resolves jet X-ray emission, and detects soft X-ray core emission and an X-ray emitting galaxy-scale atmosphere of luminosity a few 10 41 ergs s 1 . These are the first detections of X-ray jets in low-power radio galaxies more distant than Cen A and M 87. The cooling time of the galaxy-scale gas implies mass infall rates of order on e solar mass per year. The gas pressure near the jets is comparable to the minimum pressure in the jets, implying that the X-ray emitting gas may play an important role in jet dynamics. The third B2 radio galaxy has no kpc-scale radio jet, and here only soft X-ray emission from the core is detected. The ratio of X-ray to radio flux is similar for the jets and cores, and the results favour a synchrotron origin for the emission. kpc-scale radio jets are detected i n the X-ray in � 7 ks exposures with Chandra more readily than in the optical via HST snapshot surveys.

TeV photons from gamma-ray bursts

We show that the massive production of ultra-energetic photons is unavoidable in cosmological Gamma-Ray Bursts (GRBs) as far as the synchrotron-self-Compton emission mechanism is assumed to be the main one. Using the primary result of our analisys — that the observed emission is of synchrotron origin — we derive information on the physical parameters of GRB emitting regions. The parameters found imply that at least few per cent of the energy initially deposited in sub-MeV domain is converted into ultra-energetic photons due to the inverse Compton scattering off electrons accelerated in relativistic shocks. Hence, GRBs should be the brightest sources in the corresponding spectral range, several orders of magnitude more luminous than active galactic nuclei. Taking into account angular resolution of Cherenkov telescopes, we expect that TeV gamma-ray flux from a typical GRB is comparable to the background. The energies of ultra-hard photons from GRBs typically exceed 1 TeV, in some cases approaching 100 TeV. Together with high luminosity and the possibility to carry out simultaneous observations at other wavelengths, this makes GRBs an ideal probes for the two-photon absorption by the infrared background radiation at high redshifts. The presented theory of ultra-hard GRB emission is necessary for the interpretation of new observations started at MILAGRO and planned by other groups.

Radio Emission from GRO J1655−40 during the 1994 Jet Ejection Episodes

We report multifrequency radio observations of GRO J1655-40 obtained with the Australia Telescope Compact Array, the Molonglo Observatory Synthesis Telescope and the Hartebeesthoek Radio Astronomy Observatory at the time of the major hard X-ray and radio outbursts in 1994 August-September. The radio emission reached levels of the order of a few Jy and was found to be linearly polarized by up to 10%, indicating a synchrotron origin. The light curves are in good agreement with those measured with the VLA, but our closer time sampling has revealed two new short-lived events and significant deviations from a simple exponential decay. The polarization data show that the magnetic field is well ordered and aligned at right angles to the radio jets for most of the monitoring period. The time evolution of the polarization cannot be explained solely in terms of a simple synchrotron bubble model, and we invoke a hybrid "core-lobe" model with a core which contributes both synchrotron and free-free emission and "lobes," which are classical synchrotron emitters.

Infrared synchrotron oscillations in GRS 1915+105

We report simultaneous observations of the black hole candidate X-ray transient GRS 1915+105 in the infrared (IR) at K and in the radio at 2 cm. Oscillations of period 26 min were observed in both wavebands, having (dereddened) peak–peak amplitudes of about 40 mJy and with the IR leading the radio by 7 min, or perhaps by 33 or 59 min. A synchrotron origin for the oscillations continues to seem very likely. We consider a range of problems raised by these observations, and briefly discuss the applicability of expanding-synchrotron source or conical jet models to the oscillations. Comparing simplistic estimates of the ejecta mass to the missing inner disc mass in the model of Belloni et al., we find that a significant fraction of the inner disc may be ejected during the oscillations.

Spatially Resolved Spectra of 3C Galaxy Nuclei

We present and discuss visible-wavelength long-slit spectra of four low-redshift 3C galaxies obtained with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope (HST). The slit was aligned with near-nuclear jetlike structure seen in HST images of the galaxies, to give unprecedented spatial resolution of their inner regions. In 3C 135 and 3C 171, the spectra reveal clumpy emission-line structures that indicate outward motions of a few hundred kilometers per second within a centrally illuminated and ionized biconical region. There may also be some low-ionization, high-velocity material associated with 3C 135. In 3C 264 and 3C 78, the jets have blue featureless spectra consistent with their proposed synchrotron origin. There is weak associated line emission in the innermost part of the jets with mild outflow velocity. These jets are bright and highly collimated only within a circumnuclear region of lower galaxy luminosity, which is not dusty. We discuss the origins of these central regions and their connection with relativistic jets.

Evidence for a Disk-Jet Interaction in the Microquasar GRS 1915+105

We report simultaneous X-ray and infrared (IR) observations of the Galactic microquasar GRS1915+105 using XTE and the Palomar 200-inch telescope on August 13-15, 1997 UTC. During the last two nights, the microquasar GRS 1915+105 exhibited quasi-regular X-ray/infrared (IR) flares with a spacing of $\sim 30$ minutes. While the physical mechanism triggering the flares is currently unknown, the one-to-one correspondence and consistent time offset between the X-ray and IR flares establish a close link between the two. At late times in the flares the X-ray and IR bands appear to ``decouple'', with the X-ray band showing large-amplitude fast oscillations while the IR shows a much smoother, more symmetrical decline. In at least three cases, the IR flare has returned to near its minimum while the X-rays continue in the elevated oscillatory state, ruling out thermal reprocessing of the X-ray flux as the source of IR flare. Furthermore, observations of similar IR and radio flares by Fender et al. (1997) imply that the source of the IR flux in such flares is synchrotron emission. The common rise and subsequent decoupling of the X-ray and IR flux and probable synchrotron origin of the IR emission is consistent with a scenario wherein the IR flux originates in a relativistic plasma which has been ejected from the inner accretion disk. In that case, these simultaneous X-ray/IR flares from a black-hole/relativistic-jet system are the first clear observational evidence linking of the time-dependent interaction of the jet and the inner disk in decades of quasar and microquasar studies.

Learning about Active Galactic Nucleus Jets from Spectral Properties of Blazars

We use multiwavelength spectra of core-dominated flat spectrum radio-loud quasars (FSRQs) to study properties of jets in active galactic nuclei. From a comparison of the predicted bulk Compton radiation with the observed soft X-ray fluxes, we find that these jets must be optically very thin. This eliminates the importance of such processes as Coulomb interactions, pair annihilation, and bremsstrahlung and determines the minimum distance from the black hole where a powerful jet can be fully developed (accelerated, collimated, and mass loaded). In the case of pair dominated jets, this distance is 100GMBH/c2. Further constraints on the parameters of a jet can be derived from luminosities and positions of spectral peaks of low-energy (IR/optical) and high-energy (γ-ray) radiation components, provided that both are produced by the same population of electrons. Whereas there appears to be a consensus about the synchrotron origin of the low-energy component, there is still debate about the mechanism of production of γ-rays. Most likely, they result from Comptonization of a soft radiation field by the same electrons that produce synchrotron radiation. Such a soft radiation field can be provided by the synchrotron process in a jet, by the accretion disk, and by a fraction of the disk radiation that is reprocessed/rescattered by emission line clouds, dust, and intercloud medium. We show that for FSRQs, the production of the high-energy radiation can be dominated by Comptonization of synchrotron radiation only for jets with moderate bulk Lorentz factors Γj (3) or if external radiation fields are much weaker than those observed in typical quasars. Furthermore, in synchrotron self-Compton (SSC) models, the relativistic plasma producing nonthermal radiation is constrained to be very weakly magnetized (B' < 0.01 gauss) and located at very large distances (r ~ 1019 cm). These can impose problems with jet confinement and with short observed timescale of variability. In the external radiation Compton (ERC) models, the magnetic fields are predicted to be much stronger (B' ~ 100 gauss), and nonthermal radiation can be produced very closely to the black hole (r ~ 1016 cm), which alleviates the problems with plasma confinement and short timescale variability. However, because of the close proximity to the black hole, the constraints imposed by the bulk Compton radiation imply that the plasma must be free of e+e- pairs. Finally, we discuss the difficulties that existing models have in explaining the sharp spectral breaks at MeV energies and postulate a hot version of the ERC scenario for the production of MeV peaks. We show that appropriate electron temperatures (kT ~ 100 MeV) to produce the luminosity peak at MeV energies by Comptonization of external UV radiation are achievable at subparsec distances only for proton-electron plasmas.

When Is BL Lac Not a BL Lac?

We have found broad Hα and Hβ line emission in spectra of BL Lacertae taken on 1995 May 21 and June 1: on those occasions BL Lac did not meet the defining criteria for the class named after it. The Hα line luminosity, ~2 × 1041 h-2 erg s-1 for H0 = 100 h km s-1 Mpc-1, is significantly above the detection threshold in older published spectra which do not show the line. Several possible explanations for the increase in broad line luminosity are discussed. The continuum was at the faint end of its commonly observed range: V ~ 16.0 on 1995 May 21. The polarization, measured on 1995 June 1, was also near the low end of the typical range in BL Lac: ~5.0% in PA ~ 22° near 7500 A, rising to ~6.1% in PA ~ 15° near 4900 A. Absorption features in the spectrum show the presence of the associated galaxy, but the light is still dominated by an underlying smooth continuum, the intrinsic shape of which is well approximated between 8000 and 4000 A by Fν ∝ ν-1.7, indicating a synchrotron origin. We confirm the narrow emission line redshift, z = 0.0686 ± 0.0004.

The ultraviolet-to-radio continuum of the ultraluminous galaxy IRAS F10214 + 4724

We present new observations and theoretical models for the continuous ultraviolet-to-radio spectrum of the ultraluminous protogalaxy candidate IRAS F 10214 + 4724. The radio spectrum at 1.49-8.44 GHz (consistent with a power law of slope 0.9 0.1) and the resolved nature of the radio source are compatible with a synchrotron origin of the radio radiation associated with a luminous starburst. The object has an exceptionally high ratio of far-infrared to radio emission, however, and this could imply that the starburst is unusually young. The submillimetre and far-infrared spectrum is modelled in terms of emission from both spherically symmetric dust clouds and an axially symmetric flared disc

Optical polarization of the crab-like supernova remnant 0540-693 in the Large Magellanic Cloud

view Abstract Citations (22) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Optical Polarization of the Crab-like Supernova Remnant 0540-693 in the Large Magellanic Cloud Chanan, Gary A. ; Helfand, David J. Abstract We have measured the linear optical (V band) polarization in the nebula surrounding the Large Magellanic Cloud pulsar 0540-693 and find a positive result (integrated over the nebula) of P = 5.6% +/- 1.0%, oriented at an angle 79^deg^ +/- 5^deg^ east of north. Our technique corrects for but does not determine the interstellar polarization, which may be of order 2%. This result is similar to the integrated optical polarization of the Crab Nebula and is strong confirmation of a synchrotron origin for the 0540 nebular emission. Publication: The Astrophysical Journal Pub Date: March 1990 DOI: 10.1086/168524 Bibcode: 1990ApJ...352..167C Keywords: Crab Nebula; Magellanic Clouds; Optical Polarization; Supernova Remnants; Emission Spectra; Linear Polarization; Probability Distribution Functions; Synchrotron Radiation; Astrophysics; GALAXIES: MAGELLANIC CLOUDS; NEBULAE: CRAB NEBULA; NEBULAE: INDIVIDUAL ALPHANUMERIC: SNR 0540-69.3; NEBULAE: SUPERNOVA REMNANTS; POLARIZATION; RADIATION MECHANISMS full text sources ADS | data products SIMBAD (4) NED (2)

Discovery of intergalactic radio emission in the Coma–A1367 supercluster

THE Coma cluster is a rich cluster of galaxies nested in an even larger supercluster of galaxies. The plane of the supercluster seems to be defined by the Coma cluster itself and another galaxy cluster, Abell 1367, which lies ∼40 Mpc farther west1, 2. The largest structures known are the giant voids and superclusters which are as large as 70h−175 Mpc (refs 3–5). The Coma cluster of galaxies seems to be located on the rim of a giant void6 in the three-dimensional distribution of galaxies. Here we describe the detection of faint, supercluster-scale radio emission at 326 MHz that extends between the Coma cluster of galaxies (Abell 1656) and the Abell 1367 cluster and which is apparently not associated with any individual galaxy system in the complex. The radiation's synchrotron origin implies the existence of a large-scale intercluster magnetic field with an estimated strength of 0.3–0.6 μG, which is remarkably strong. The synchrotron-emitting relativistic electrons cannot be older than a few times 108 yr, but we speculate that the magnetic field is the fossil of a pre-galactic primaeval field, which was amplified in the course of the formation of intergalactic voids and superclusters.

Simultaneous X-ray, ultraviolet, and optical observations of the BL Lacertae object PKS 2155-304

view Abstract Citations (62) References (38) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Simultaneous X-Ray, Ultraviolet, and Optical Observations of the BL Lacertae Object PKS 2155-304 Treves, A. ; Morini, M. ; Chiappetti, L. ; Fabian, A. ; Falomo, R. ; Maccagni, D. ; Maraschi, L. ; Tanzi, E. G. ; Tagliaferri, G. Abstract X-ray observations of PKS 2155-304, performed at nine epochs in 1983-1985 with the EXOSAT satellite, are reported. The source was observed quasi-simultaneously in the far-UV with IUE, and in the optical and infrared with ESO telescopes. X-ray light curves with 400 s time resolution are derived. On two occasions the flux showed a rapid regular rising with a doubling time ~ 1 hr. Spectral fits performed on X-ray data averaged over each observation yield the following results. The medium energy data (1-10 keV) are well fitted by single power laws plus absorption, with energy index between 1.5 and 2. Marginal evidence for an absorption edge at ~ 7 keV is found in the best exposed spectrum. If we combine the ME data with those obtained with the low energy telescope (0.1-2 keV), evidence for some spectral depression at ~ 1 keV is found. This may be modeled with an edge at 660+/-26 eV with optical depth τ = 1.8 +/- 0.2. The quasi-simultaneous ultraviolet and optical data allow the reconstruction of the energy distribution on several occasions. In all cases but one, the optical, UV, and X-ray intensities are correlated. However, the variability amplitudes decrease, and the time scales increase, with decreasing frequency. These results are indicative of a synchrotron origin for the X-rays and of distinct, but connected, emission regions for the X-ray, ultraviolet, and optical bands. Publication: The Astrophysical Journal Pub Date: June 1989 DOI: 10.1086/167532 Bibcode: 1989ApJ...341..733T Keywords: Bl Lacertae Objects; Light Curve; Ultraviolet Spectra; X Ray Sources; Exosat Satellite; Iue; Spectrum Analysis; Synchrotron Radiation; Temporal Resolution; Astrophysics; BL LACERTAE OBJECTS; GALAXIES: INDIVIDUAL ALPHANUMERIC: PKS 2155-304; X-RAYS: SOURCES; ULTRAVIOLET: SPECTRA full text sources ADS | data products SIMBAD (2) NED (2) MAST (1) INES (1)

Radio Studies of Extragalactic Supernovae

Some exploding stars (supernovae) are powerful emitters of centimeter radio radiation. Detailed observations have shown that these supernovae quickly become detectable in the radio range, first at shorter wavelengths (higher frequencies) and later at progressively longer and longer wavelengths (lower frequencies). This part of the phenomenon appears to be well explained by a monotonic decrease in the amount of ionized material surrounding the radio-emitting regions as the shock from the explosion travels outward. The radio emission itself is of a nonthermal, synchrotron origin, as is the case in most bright cosmic radio sources. Once the absorption effects become negligible, the radio intensity declines with time until reaching the detection limit of the telescope. Models suggest that the absorbing material originates in a dense wind of matter lost by the supernova progenitor star, or by its companion if it is in a binary system, in the last stages of evolution before the explosion. The synchrotron radio emission can be generated either externally by the shock wave from the explosion propagating through this same high density stellar wind or internally by a rapidly rotating neutron star, which is the collapsed core of the exploded star. Present results appear to favor the former model for at least the first several years after the supernova explosion, although the latter model remains viable.

Frequency-dependent polarization in blazars

It is argued that the observed properties of the intrinsically frequency-dependent polarization (FDP) in blazars suggest a one rather than a multi-component source model. Assuming a synchrotron origin of the emitted radiation, a well ordered magnetic field and a sharp break or cutoff in the electron distribution are both obligatory in such models; non-uniform pitch angle distribution or synchrotron losses enhance the resulting FDP. It is emphasized that the existence of such conditions in blazars finds observational support. Furthermore, a specific model is presented in order to illustrate the salient features of one-component models.

UBVRI observations of BL Lacertae objects

view Abstract Citations (53) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS UBVRI observations of BL Lacertae objects. Moles, M. ; Garcia-Pelayo, J. M. ; Masegosa, J. ; Aparicio, A. Abstract A total of 85 UBVRI observations of BL Lac objects is presented. For most of them, an average continuum can be traced by means of well-defined color indices. These continua are always well reproduced by power laws, strongly supporting the hypothesis of a synchrotron origin of the radiation output, as well as the conclusion that there is no dust in such objects. The analysis of the variability leads to a rough estimate of the value of the magnetic field, which is of the same order for all the objects, around 0.00003 G. The optical continua can be considered to correspond to the broken part of the synchrotron spectrum. Relativistic effects are needed in order to avoid the Compton paradox. Publication: The Astrophysical Journal Supplement Series Pub Date: June 1985 DOI: 10.1086/191040 Bibcode: 1985ApJS...58..255M Keywords: Astronomical Photometry; Bl Lacertae Objects; Color; Relativistic Effects; Synchrotron Radiation; Ubv Spectra; Astrophysics full text sources ADS | data products SIMBAD (18) NED (15)