Intrinsic Temperatures Research Articles

High Brightness Temperatures in IDV Sources

High brightness temperatures are a characteristic feature of IntraDay Variability (IDV) of extragalactic radio sources. Recent studies of the polarization properties of some IDV sources (e.g., 1150+812, PKS 0405-385 and 0716+714) have shown that these sources harbor several compact IDV components with angular sizes of ∼10-30µas and very high polarizations (of up to ∼50%-70%). These results indicate the possibility of the existence of uniform magnetic fields in the IDV components. We investigate the incoherent synchrotron and self- Compton radiation of an anisotropic distribution of relativistic electrons which spin around the magnetic field lines at small pitch angles. The brightness temperature limit caused by second-order Compton losses is discussed and compared to the brightness temperatures derived from energyequipartitionarguments.It is found that anisotropic distributions of elec- trons moving in ordered magnetic fields can raise the equipartition and Compton brightness temperatures by a factor of up to ∼3-5. This would remove some of the difficulties in the interpretation of extremely high intrinsic brightness temperatures of > 10 12 K (or apparent brightness temperatures of ∼ 10 14 K with a Doppler factor of ∼30).

Intrinsic Properties of the Magnetically Collimated H2O Maser Jet of W43A

Water maser polarization observations in the precessing jet of W43A have revealed that it is magnetically collimated. Here we present a detailed description of the physical properties of the water maser environment in the jet. We discuss the maser saturation level and beaming angle as well as the intrinsic temperatures and densities. Additionally, we show that the polarization angle of the strongest red-shifted maser feature undergoes a fast rotation of 90 degrees across the maser. Along with the variation of linear polarization fraction, this strongly supports the current theoretical description of maser linear polarization.

Intrinsic Brightness Temperatures of AGN Jets

We present a new method for studying the intrinsic brightness temperatures of the parsec-scale jet cores of Active Galactic Nuclei (AGN). Our method uses observed superluminal motions and observed brightness temperatures for a large sample of AGN to constrain the characteristic intrinsic brightness temperature of the sample as a whole. To study changes in intrinsic brightness temperature, we assume that the Doppler factors of individual jets are constant in time as justified by their relatively small changes in observed flux density. We find that in their median-low brightness temperature state, the sources in our sample have a narrow range of intrinsic brightness temperatures centered on a characteristic temperature, T_int = 3 x 10^10 K, which is close to the value expected for equipartition, when the energy in the radiating particles equals the energy stored in the magnetic fields. However, in their maximum brightness state, we find that sources in our sample have a characteristic intrinsic brightness temperature greater than 2 x 10^11 K, which is well in excess of the equipartition temperature. In this state, we estimate the energy in radiating particles exceeds the energy in the magnetic field by a factor of ~ 10^5. We suggest that the excess of particle energy when sources are in their maximum brightness state is due to injection or acceleration of particles at the base of the jet. Our results suggest that the common method of estimating jet Doppler factors by using a single measurement of observed brightness temperature and/or the assumption of equipartition may lead to large scatter or systematic errors in the derived values.

Polarimetric Observations of 15 Active Galactic Nuclei at High Frequencies: Jet Kinematics from Bimonthly Monitoring with the Very Long Baseline Array

We present total and polarized intensity images of 15 active galactic nuclei obtained with the Very Long Baseline Array at 7 mm wavelength at 17 epochs from 1998 March to 2001 April. At some epochs the images are accompanied by nearly simultaneous polarization measurements at 3 mm, 1.35/0.85 mm, and optical wavelengths. Here we analyze the 7 mm images to define the properties of the jets of two radio galaxies, five BL Lac objects, and eight quasars on angular scales 0.1 mas. We determine the apparent velocities of 106 features in the jets. For many of the features we derive Doppler factors using a new method based on a comparison of the timescale of decline in flux density with the light-travel time across the emitting region. This allows us to estimate the Lorentz factors (Γ), intrinsic brightness temperatures, and viewing angles of 73 superluminal knots, as well as the opening angle of the jet for each source. The Lorentz factors of the jet flows in the different blazars range from Γ ~ 5 to 40 with the majority of the quasar components having Γ ~ 16–18, while the values in the BL Lac objects are more uniformly distributed. The brightest knots in the quasars have the highest apparent speeds, while the more slowly moving components are pronounced in the BL Lac objects. The quasars in our sample have similar opening angles and marginally smaller viewing angles than the BL Lacs. The two radio galaxies have lower Lorentz factors and wider viewing angles than the blazars. Opening angle and Lorentz factor are inversely proportional, as predicted by gasdynamical models. The brightness temperature drops more abruptly with distance from the core in the BL Lac objects than in the quasars and radio galaxies, perhaps owing to stronger magnetic fields in the former resulting in more severe synchrotron losses of the highest energy electrons. In nine sources we detect statistically meaningful deviations from ballistic motion, with the majority of components accelerating with distance from the core. In six sources we identify jet features with characteristics of trailing shocks that form behind the primary strong perturbations in jet simulations. The apparent speeds of these components increase with distance from the core, suggestive of acceleration of the underlying jet.

Cyclotron Maser Emission from Blazar Jets?

We consider the production of electron cyclotron maser emission by low-density, highly magnetized plasmas in relativistic jets. The population inversion required to drive cyclotron maser instability could occur in localized, transient sites where hydromagnetic instabilities, shocks, and/or turbulence lead to magnetic mirroring along current-carrying flux tubes. The maser is pumped by the conversion of kinetic and magnetic energy into work as electrons are accelerated into the maser by the parallel electric field that develops as a result of the mirror. We estimate the maximum brightness temperatures TB that can be obtained in a single maser site and in an array of many masers operating simultaneously, under conditions likely to apply in blazar jets. Synchrotron absorption, by relativistic electrons within the jet, presents the largest obstacle to the escape of the maser radiation and may render most of it invisible. However, we argue that a high brightness temperature could be produced in a thin boundary layer outside the synchrotron photosphere, perhaps in the shear layer along the wall of the jet. Induced Compton scattering provides additional constraints on the maximum brightness temperature of a masing jet. We suggest that recent observations of diffractive scintillation in the blazar J1819+3845, indicating intrinsic brightness temperatures greater than 1014 K at 5 GHz, may be explained in terms of cyclotron maser emission. High-TB maser emission from blazar jets may extend to frequencies as high as ~100 GHz, with the maximum possible TB scaling with frequency roughly ∝ ν-1. Less massive relativistic jet sources, such as microquasars, are even better candidates for producing cyclotron maser emission, primarily in the infrared and optical bands.

Sensitive VLBI Observations of thez[FORMULA][F]=4.7[/F][/FORMULA] QSO BRI 1202-0725

We present sensitive phase-referenced VLBI results on the radio continuum emission from the z=4.7 double source BRI 1202-0725. The observations were carried out at 1425 MHz using the Very Long Baseline Array (VLBA), the phased Very Large Array (VLA), and the Green Bank Telescope (GBT). Our sensitive VLBI images of BRI 1202-0725 at 0.25 x 0.14 arcsec resolution show a continuum structure in each of its two components. Fitting Gaussian models to these continuum structures yield total flux densities of 315 +/- 38 and 250 +/- 39 microJy, for the northern and the southern components, respectively. The estimated intrinsic brightness temperatures of these continuum structures are about 2 x 10^4 K. Neither component is detected at the full VLBI resolution (29 mas x 7 mas), with a 4 sigma point source upper limit of 40 microJy/beam, or an upper limit to the intrinsic brightness temperature of 6.7 x 10^5 K. The highest angular resolution with at least a 4sigma detection is about 85 mas. At this resolution, the images reveal a single continuum feature in the northern component of BRI 1202-0725, and two continuum features in the southern component, separated by 320 mas. This is similar to the structures seen in the high resolution images of the CO emission. The extent of the observed continuum sources at 1.4 GHz and the derived brightness temperatures are consistent with nuclear starbursts. Moreover, the absence of any compact high-brightness temperature source suggests that thereis no radio-loud AGN in BRI 1202-0725.

Effect of the inclusion of PEG on the solid‐state properties and drug release from polylactic acid films and microcapsules

AbstractThe use of poly(lactic acid) (PLA) for controlled drug delivery applications was limited by unfavorable physical properties such as hydrophobicity, high intrinsic crystallinity, low permeability, and high glass transition temperatures. This research used polyethylene glycols (PEGs) of varying molecular weights (300–18,500 g/mol) and concentrations (0–50% w/w) to modify the permeability, intrinsic crystallinity, glass transition temperature, residual solvent levels, and release of a model drug, 5‐flurouracil (5FU), from monolithic films and microcapsules fabricated with PLA. The films were fabricated by solvent casting from methylene chloride. The microcapsules were formed by a coacervation method by using a methylene chloride/hexane solvent/nonsolvent system. Compared to PLA films, all PLA : PEG films showed the following: (1) a glass transition temperature between 40 and 55°C, (2) 5–8% lower residual solvent levels, and (3) enhanced permeability to 5FU. These results suggested that the incorporation of PEG improves the physical properties of PLA films to enable fabrication of controlled release delivery systems. Similar to the films, incorporation of PEG also enhanced the permeability of PLA microcapsules to 5FU. However, high intrinsic crystallinity, dual endothermal character for PLA melting, and significant burst release of 5FU in PLA : PEG microcapsules may limit their development for controlled drug delivery applications. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2025–2030, 2004

Sub‐Milliarcsecond Imaging of Quasars and Active Galactic Nuclei. III. Kinematics of Parsec‐scale Radio Jets

We report the results of a 15 GHz (2 cm) multi-epoch VLBA program, begun in 1994 to study the outflow in radio jets ejected from quasars and active galaxies. The observed flow of 208 distinct features measured in 110 quasars, active galaxies, and BL Lac objects shows highly collimated relativistic motion with apparent transverse velocities typically between zero and about 15c, with a tail extending up to about 34c. Within individual jets, different features appear to move with a similar characteristic velocity which may represent an underlying continuous jet flow, but we also see some stationary and even apparently inward moving features which co-exist with the main features. Comparison of our observations with published data at other wavelengths suggests that there is a systematic decrease in apparent velocity with increasing wavelength, probably because the observations at different wavelengths sample different parts of the jet structure. The observed distribution of linear velocities is not consistent with any simple ballistic model. Either there is a rather broad range of Lorentz factors, a significant difference between the velocity of the bulk relativistic flow and the pattern speed of underlying shocks, or a combination of these options. Assuming a ballistic flow, comparison of observed apparent velocities and Doppler factors computed from the time scale of flux density variations is consistent with a steep power law distribution of intrinsic Lorentz factors, an isotropic distribution of orientations of the parent population, and intrinsic brightness temperatures about an order of magnitude below the canonical inverse Compton limit. It appears that the parent population of radio jets is not dominated by highly relativistic flows (abridged).

Molecular Gas and Dust atz = 2.6 in SMM J14011+0252: A Strongly Lensed Ultraluminous Galaxy, Not a Huge Massive Disk

We used the IRAM interferometer to detect CO (3-2), CO (7-6), and 1.3 mm dust continuum emission from the submillimeter galaxy SMM J14011+0252 at z = 2.6. Contrary to a recent claim that the CO was extended over 66 (57 kpc), the new data yield a size of 2''× ≤ 05 for the CO and the dust. Although previous results placed the CO peak in a region with no visible counterpart, the new maps show that the CO and dust are centered on the J1 complex seen on K-band and optical images. We suggest that the CO is gravitationally lensed not only by the foreground cluster A1835 but also by an individual galaxy on the line of sight. Comparison of measured and intrinsic CO brightness temperatures indicates that the CO size is magnified by a factor of 25 ± 5. After correcting for lensing, we derive a true CO diameter of ~008 (700 pc), consistent with a compact circumnuclear disk of warm molecular gas similar to that in Arp 220. The high magnification means that the true size, far-IR luminosity, star formation rate, CO luminosity, and molecular gas mass are all comparable with those in present-epoch ultraluminous IR galaxies, not with a huge, massive, early-universe Galactic disk.

Sub-milliarcsecond Imaging of Quasars and Active Galactic Nuclei. II. Additional Sources

We report further results from our imaging survey at 15 GHz (λ = 2 cm) with the Very Long Baseline Array (VLBA). This paper presents single-epoch images for 39 sources, bringing the total number of objects in the sample to 171. Our sample is representative of a complete unbiased sample, and it will be used for statistical analysis of source properties. We compare the observed brightness temperatures derived from our VLBA observations with those derived from total intensity variations at 22 and 37 GHz. These are consistent with intrinsic brightness temperatures in the range 10^(10)–10(12) K. We also present three new spectroscopic redshift values: z = 0.517 ± 0.001 for 0026+346, z = 1.591 ± 0.003 for 0727-115, and z = 0.2016 ± 0.0004 for 1155+251.

High-Resolution Imaging of Molecular Line Emission from High-Redshift QSO[CLC]s[/CLC

We present moderate- (1'') and high-resolution (02) observations of the CO (2–1) emission at 43 GHz and radio continuum emission at 1.47 GHz from the z = 4.7 QSO BRI 1202-0725 and the z = 4.4 QSO BRI 1335-0417 using the Very Large Array. The moderate-resolution observations show that in both cases the CO emission is spatially resolved into two components separated by 1'' for BRI 1335-0417 and 4'' for BRI 1202-0725. The high-resolution observations show that each component has substructure on scales ∼02–05, with intrinsic brightness temperatures ≥20 K. The CO ladder from (2–1) up to (7–6) suggests a high kinetic temperature for the gas (Tkin ≃ 70 K) and a high column density [N(H2) ≃ 1024 cm-2]. In both sources the continuum-to-line ratio is LFIR/L ≃ 335. All these characteristics (brightness temperature, excitation temperature, column density, and continuum-to-line ratio) are comparable to conditions found in low-redshift, ultraluminous nuclear starburst galaxies. We find that the CO-emitting regions in BRI 1202-0725 and BRI 1335-0417 must be close to face-on in order to avoid having the gas mass exceed the gravitational mass, implying perhaps unreasonably large rotational velocities. While this problem is mitigated by lowering the CO luminosity–to–H2 mass conversion factor (X), the required X values become comparable to, or lower than, the minimum values dictated by optically thin CO emission. We considered the possibility of magnification by gravitational lensing in order to reduce the molecular gas masses.

The effect of formation redshifts on the cluster mass-temperature relation

I employ an ensemble of hydrodynamical simulations and the xspec mekal emission model to reproduce observable spectral and flux-weighted temperatures for 24 clusters. Each cluster is imaged at 16 points in its history, which allows the investigation of evolutionary effects on the mass—temperature relation. In the zero-redshift scaling relations, I find no evidence for a relationship between cluster temperature and formation epoch for those clusters that acquired 75 per cent of their final mass since a redshift of 0.6. This result holds for both observable and intrinsic intracluster medium temperatures, and implies that halo formation epochs are not an important variable in analysis of observable cluster temperature functions.

Rapid polarization variations at 20 cm in 0917+624

The intraday variations (IDV hereafter) of the total and the polarized flux density observed at 20 cm in 0917+624 (in May 1989) are analysed. It is shown that the IDV can be interpreted in terms of refractive interstellar scintillation. The observed variations are dominated by one scintillating component with a timescale $\tau\approx0.6$ days and a scintillation index $m\approx0.04$. In addition, one more scintillating component with a shorter timescale and a smaller scintillation index is needed to improve the fit to the observed Q - and U -light curves. The relationship between the scintillating components and the VLBI components are also discussed. It is shown that Doppler beaming of the 20 cm scintillating components with a Lorentz factor $\stackrel {> }{_\sim}$ 7 may be needed to reduce their intrinsic brightness temperatures significantly below the inverse-Compton limit.

In-Flight Main Beam Reconstruction for Planck-LFI

In-flight measurements of the shape of the antenna main beam is a crucial input to the data analysis pipeline of each high resolution Cosmic Microwave Background (CMB) anisotropy experiment. We study the main beam reconstruction achievable by the PLANCK Low Frequency Instrument (LFI) through the observation of external planets. Although were strict our analysis to the 30 GHz LFI channel, the method can be easily extended to all the PLANCK frequency channels and to other CMB anisotropy experiments. We show that it is possible to fit the time ordered data from the external planets (mainly Jupiter and Saturn) to obtain an accurate, robust, simple and fast reconstruction of the main beam properties under very general conditions, almost independently of the calibration accuracy. In addition, we find that a bivariate Gaussian approximation of main beam shapes represents a significant improvement with respect to asymmetric representation. The impact of the most relevant systematic effects is also addressed. We demonstrate that by combining the recovery of the maximum signal at the planet transit with accurate in-flight calibration, it is possible to measure the intrinsic planet temperatures at millimetric wavelengths with < 1% accuracy. This work is based on PLANCK-LFI activities.

Hawking radiation in string theory and the string phase of black holes

The quantum string emission by black holes is computed in the framework of the ``string analog model'' (or thermodynamical approach), which is well suited to combine quantum-field theory (QFT) and string theory in curved backgrounds (particularly here, as black holes and strings possess intrinsic thermal features and temperatures). The QFT-Hawking temperature ${T}_{H}$ is upper bounded by the string temperature ${T}_{S}$ in the black hole background. The black hole emission spectrum is an incomplete gamma function of ${(T}_{H}\ensuremath{-}{T}_{S}).$ For ${T}_{H}\ensuremath{\ll}{T}_{S},$ it yields the QFT-Hawking emission. For ${T}_{H}\ensuremath{\rightarrow}{T}_{S},$ it shows that highly massive string states dominate the emission and undergo a typical string phase transition to a microscopic ``minimal'' black hole of mass ${M}_{\mathrm{min}}$ or radius ${r}_{\mathrm{min}}$ (inversely proportional to ${T}_{S})$ and string temperature ${T}_{S}.$ The string back reaction effect [self-consistent black hole solution of the semiclassical Einstein equations with mass ${M}_{+}$ (radius ${r}_{+})$ and temperature ${T}_{+}]$ is computed. Both the QFT and string black hole regimes are well defined and bounded: ${r}_{\mathrm{min}}&lt;~{r}_{+}&lt;~{r}_{S},{M}_{\mathrm{min}}&lt;~{M}_{+}&lt;~M,{T}_{H}&lt;~{T}_{+}&lt;~{T}_{S}.$ The string ``minimal'' black hole has a life time ${\ensuremath{\tau}}_{\mathrm{min}}\ensuremath{\simeq}{(k}_{B}c/G\ensuremath{\Elzxh}){T}_{S}^{\ensuremath{-}3}.$

Dense Cores Mapped in Ammonia: A Database

We present a database of 264 cores mapped in the (J,K) = (1,1) and (2,2) lines of NH3. We list the core gas properties?peak positions, total ammonia column densities, intrinsic line widths, kinetic temperatures, volume densities, core sizes, aspect ratios, and velocity gradients, as well as the properties of associated young stellar objects (YSOs)?associated IRAS sources along with their luminosities and core-YSO distances, outflow velocities, and SIMBAD and cluster associations. We also present the results of our statistical analysis and enumerate important pairwise correlations among the various gas and YSO properties. The results indicate that the association of stellar clusters with star-forming cores has a greater impact on their properties than does the presence of associated YSOs within these cores, although the latter influence is also statistically significant. In other words, the difference in core properties (nonthermal line widths, kinetic temperatures, and core sizes) between cores with and without associated YSOs is less significant when compared with the difference in these properties between cores with and without cluster associations. Furthermore, core gas and YSO properties show a significant dependence on the star-forming region in which the core is located. For instance, cores in Orion have larger line widths, higher kinetic temperatures, and larger sizes compared with cores in Taurus. Similarly, YSOs in Orion are more luminous than those in Taurus. These cluster and regional dependencies seem important enough that they ought to be accounted for in any self-consistent theory of star formation. Finally, the ratio of starless to stellar cores is too small (8:12 in Taurus, 2:41 in Orion A) to be consistent with ambipolar diffusion timescales that predict ratios as high as 3-30. This result is true even for regions that are known to be well surveyed and not to suffer from significant sample biases.

Radio-frequency amplifier with tenth-kelvin noise temperature based on a microstrip direct current superconducting quantum interference device

A dc superconducting quantum interference device (SQUID) with a resonant microstrip input and a cooled heterostructure field-effect transistor as a postamplifier is used as a radio-frequency amplifier in the frequency range 90–500 MHz. At liquid He3 temperatures, gains of 24 and 20 dB and intrinsic noise temperatures of 0.06±0.02 and 0.12±0.10 K were achieved at 89.6 and 438 MHz, respectively. The system noise temperature at 438 MHz was also estimated from the Nyquist noise produced by a resonant circuit coupled to the input of the microstrip SQUID.

Red supergiants in the LMC - III: luminous F and G stars

New BVRI observations for 40 and spectrophotometric measurements for 3 F to G LMC supergiant candidates (and 3 galactic F to G supergiants) are presented. The errors of the BVRI data are 0.01 to 0.03 mag in most cases. The wavelength range of the spectra is 3400 to 6400 Å, their resolution 10 Å. The mean error of the fluxes is 0.03 mag. Spectral indices measuring the strengths of the Hβ, Hγ, Hδ, NaD and CaII H+K lines, the CHα0 and CNβ0 bands, of the Balmer jump and the slope of the continuum redwards are discussed as measures of effective temperature and luminosity on the basis of galactic stars with accurate MK types and parallaxes. The Hγ line and the continuum gradient are very good temperature criteria, the CHα0 band and especially the Balmer jump for luminosity. The luminosity classification given for F to G supergiant candidates in the LMC in the literature is often doubtful. 5 of the 3 stars observed spectrophotometrically turn out to be probably galactic foreground dwarfs on the basis both of the Balmer jump and the comparison of their flux distributions with synthetic ones based on the Kurucz model atmospheres. Surface gravities derived purely on the basis of flux distributions and such ones given by models of stellar evolution agree with each other for dwarfs and giants only. For supergiants the former are about 1.0 dex higher than the latter. As a consequence effective temperatures and metallicities given by these two methods deviate from each other for such stars, too. The intrinsic colours and temperatures of galactic and LMC supergiants do not differ. With absolute magnitudes up to -9.6 mag the upper luminosity limit in the LMC does not exceed that in the Galaxy, where Ia-0 supergiants have MV of up to -9.5 mag. The metallicities of the supergiants show a rather large scatter. Nevertheless the mean metallicities of 0.0 ± 0.09 dex for the Galaxy and -0.6 ± 0.10 dex for the LMC agree well with other observations.

Total Flux Density Variations in Extragalactic Radio Sources. I. Decomposition of Variations into Exponential Flares

We show that 22 and 37 GHz total flux density variations in compact extragalactic radio sources can to a good accuracy be modeled by superposition of a small number of flare components. Both the rise and the decay of these flares are exponential, with a characteristic decay timescale 1.3 times longer than the rise timescale. The properties of the individual model flares derived from these flux decompositions are in agreement with data obtained from VLBI observations of the corresponding new shock components. The total flux density decompositions can be used to search correlations between radio and other regimes, to calibrate and to interpret VLBI observations, and to derive physical parameters of the shocks. In particular, the associated brightness temperatures of the flares can be used to estimate the amount of Doppler boosting in each source and, using additional VLBI data, to derive the intrinsic brightness temperatures, the Lorentz factors and the viewing angles of the sources.

Structure and Properties of AGN Cores from VLBI and Total Flux Density Variations

AbstractBy combining VLBI and total flux density data it is possible to get an indirect “look” at the innermost, unresolved core regions of AGN and to estimate physical parameters such as the intrinsic brightness temperatures, Lorentz factors and viewing angles, unobtainable by either VLBI or multi-frequency flux monitoring alone.