Photon Bath Research Articles

The Detection of the Diffuse Interstellar Bands in Dusty Starburst Galaxies

We report the detection of the Diffuse Interstellar Bands (``$DIBs$'') in the optical spectra of seven far-infrared-selected starburst galaxies. The $\lambda$6283.9 \AA and $\lambda$ 5780.5 \AA features are detected with equivalent widths of $\sim$ 0.4 to 1 \AA and 0.1 to 0.6 \AA respectively. In the two starbursts with the highest quality spectra (M82 and NGC2146), four other weaker $DIBs$ at $\lambda$ 5797.0 \AA, 6010.1 \AA, 6203.1 \AA, and 6613.6 \AA are detected with equivalent widths of $\sim$ 0.1 \AA. The region over which the $DIBs$ can be detected ranges from $\sim$ 1 kpc in the less powerful starbursts, to several kpc in the more powerful ones. The gas producing the $DIBs$ is more kinematically quiescent on-average than the gas producing the strongly-blueshifted $NaI\lambda\lambda$5890,5896 absorption in the same starbursts. We show that the $DIBs$ in these intense starbursts are remarkably similar to those in our Galaxy: the relative strengths of the features detected are similar, and the equivalent widths follow the same dependence as Galactic $DIBs$ on $E(B-V)$ and $NaI$ column density. While the ISM in starbursts is heated by a photon and cosmic ray bath that is $\sim$ 10$^3$ times more intense than in the diffuse ISM of the Milky Way, the gas densities and pressures are also correspondingly larger in starbursts. This ``homology'' may help explain the strikingly similar $DIB$ properties.

Compton-dragged Gamma-Ray Bursts Associated with Supernovae.

It is proposed that the gamma-ray photons that characterize the prompt emission of gamma-ray bursts are produced through the Compton-drag process, which is caused by the interaction of a relativistic fireball with a very dense soft photon bath. If gamma-ray bursts are indeed associated with supernovae, then the exploding star can provide enough soft photons for radiative drag to be effective. This model accounts for the basic properties of gamma-ray bursts, i.e., the overall energetics, the peak frequency of the spectrum, and the fast variability, with an efficiency that can exceed 50%. In this scenario, there is no need for particle acceleration in relativistic collisionless shocks. Furthermore, although the Poynting flux may be important in accelerating the outflow, no magnetic field is required in the gamma-ray production. The drag also naturally limits the relativistic expansion of the fireball to Gamma less, similar104.

Cancellation of Infrared Divergences at Finite Temperature

We consider a typical hard scattering process in a heat bath of photons and electrons at temperature,T, in finite temperature QED. We show that the infrared pieces of both the real and virtual parts of the cross section factorise; these can be exponentiated and cancel between each other to all orders in perturbation theory. Hence the Bloch–Nordsieck theorem remains valid for such processes at non-zero temperature as well. We use the technique of Grammer and Yennie to give a prescription for the extraction of the infrared divergent parts and for the form of the finite remainder. Symmetry arguments are used to show the finiteness of new terms arising in theT≠0 part of the computation.

Was The Electromagnetic Spectrum A Blackbody Spectrum In The Early Universe?

It is generally assumed that the electromagnetic spectrum in the primordial universe was a blackbody spectrum in vacuum. We derive the electromagnetic spectrum based on the fluctuation-dissipation theorem that describes the electromagnetic fluctuations in a plasma. Our description includes thermal and collisional effects in a plasma. The electromagnetic spectrum obtained differs from a blackbody spectrum in vacuum at low frequencies. In particular, concentrating on the primordial nucleosynthesis era, it has more energy than the blackbody spectrum for frequencies less than 3vpe to 6vpe, where vpe is the electron plasma frequency. [S0031-9007(97)04160-4] PACS numbers: 98.80. ‐ k, 52.25.Gj, 95.30.Qd, 98.70.Vc It is usually assumed in cosmology that the primordial plasma was a homogeneous plasma and that the electromagnetic field was a blackbody spectrum in vacuum. These assumptions are used, for example, in standard big bang nucleosynthesis calculations. Deviations from a blackbody spectrum in vacuum and a homogeneous plasma can affect primordial nucleosynthesis, and in this Letter we concentrate on this epoch. In the epoch of big bang nucleosynthesis, the Universe was a thermal bath of photons, electrons, positrons, baryons, and neutrinos. The usual treatment considers the Universe as a homogeneous plasma in thermal equilibrium and the electromagnetic field as a blackbody spectrum in vacuum. For example, in the energy density calculation, the energy density of the photons is given by the energy density of the blackbody spectrum in vacuum. In this manner, the primordial universe is treated as an ideal gas: collective effects are assumed to be

Self-consistent microscopic theory of fluctuation-induced transport.

A Maxwell's demon type "information engine" that extracts work from a bath is constructed from a microscopic Hamiltonian for the whole system including a subsystem, a thermal bath, and a nonequilibrium bath of phonons or photons that represents an information source or sink. The kinetics of the engine is calculated self-consistently from the state of the nonequilibrium bath, and the relation of this kinetics to the underlying microscopic thermodynamics is established.

Reaction rate in a heat bath

We show in detail how the presence of a heat bath of photons effectively gives charged particles in the final state of a decay process a temperature-dependent mass, and changes the effective strength of the force responsible for the decay. At low temperature, gauge invariance causes both these effects to be largely cancelled by absorption of photons from the heat bath and by stimulated emission into it, but at high temperature the temperature-dependent mass is the dominant feature.

Nuclear structure of 176Lu and its astrophysical consequences. II. 176Lu, a thermometer for stellar helium burning.

On the basis of the improved level scheme of $^{176}\mathrm{Lu}$ it is demonstrated that the stellar s-process production as well as the stellar beta decay rate of that nucleus depend strongly on temperature. This behavior results from the completely different half-lives of the ground state and the isomer; since these states are coupled by induced transitions in the hot stellar photon bath, the effective half-life of $^{176}\mathrm{Lu}$ is drastically reduced. The ${5}^{\mathrm{\ensuremath{-}}}$ state at 838.64 keV was identified as the most efficient mediating level. Consequently, $^{176}\mathrm{Lu}$ can no longer be considered as a chronometer for the age of the s process; instead, it can be interpreted as an s-process thermometer yielding a temperature range between 2.4\ifmmode\times\else\texttimes\fi{}${10}^{8}$ to 3.6\ifmmode\times\else\texttimes\fi{}${10}^{8}$ K.

Derivation of the master equation for the atomic density matrix for line polarization studies in the presence of magnetic field and depolarizing collisions in astrophysics

In this paper, we derive in a coherent manner, starting from the basic equations of evolution of a quantum mechanical system, the master equation for the density matrix of an atom interacting with a bath of perturbers (electrons, protons) and photons, in the presence of a weak magnetic field (in the domain of sensitivity to the Hanle effect: 0.1 ≲ ωLτ ≲ 10). This paper has been inspired by astrophysical purposes: the interpretation of line polarization induced by anisotropic excitation of the levels, eventually modified by the local magnetic field (the Hanle effect); the polarization can be due to scattering of the incident anisotropic radiation, as in solar prominences, or to impact polarization, as in solar flares. The physical conditions are then those of numerous astrophysical media: any directions of polarization and magnetic field, two-level atom approximation not valid, weak radiation field (so that the bare atom description is convenient), weak density of perturbers (so that the impact approximation is valid). The master equation is derived in the framework of the impact approximation, using the S-matrix formalism without perturbation development in a first step; the Hanle effect is included. The impact approximation leads to a decoupling of the interactions with the perturbers and with the radiation, which are then additive and can be treated independently. The perturbation development is introduced in a second step. The population and coherence transfer probabilities are then obtained for a polarized neutral atom interacting with collisional charged perturbers on the one hand, in the frame of the semi-classical perturbational theory, and on the other hand for a polarized atom interacting with an anisotropic and eventually polarized incident radiation. The linear polarization of the emitted radiation is studied in the following paper which is devoted to the derivation of the transfer equation for polarized radiation in the presence of a magnetic field.

Quantum electrodynamics based on self-fields: On the origin of thermal radiation detected by an accelerating observer

We continue with our series of papers concerning a self-field approach to quantum electrodynamics that is not second quantized. We use the theory here to show that a detector with a uniform acceleration {ital a} will respond to its own self-field as if immersed in a thermal photon bath at temperature {ital T}{sub {ital a}}={h bar}a/2{pi}kc. This is the celebrated Unruh effect, and it is closely related to the emission of Hawking radiation from the event horizon of a black hole. Our approach is novel in that the radiation field is classical and not quantized; the vacuum field being identically zero with no zero-point energy. From our point of view, all radiative effects are accounted for when the self-field of the detector, and not the hypothetical zero-point field of the vacuum, acts back on the detector in a quantum-electrodynamic analog of the classical phenomenon of radiation reaction. When the detector is accelerating, its transformed self-field induces a different back reaction than when it is moving inertially. This process gives rise to the appearance of a photon bath, but the photons are not real in the sense that the space surrounding the accelerating detector is truly empty of radiation, a factmore » that is verified by the null response of an inertially moving detector in the same vicinity. The thermal photons are in this sense fictitious, and they have no independent existence outside the detector.« less

Graviton emission by a thermal bath of photons.

The rate of emission of gravitons by a thermal bath of protons is calculated. Linearized quantum gravity is used to find the rate of graviton creation by thermal fluctuations of the photons. For the case of photons confined within a sphere of radius R and volume V at temperature T, the power radiated in gravitons is found to be P=(2.7\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}66}$ erg/s)(V/${\mathrm{cm}}^{3}$)(T/K${)}^{7}$ln(160RT/K/cm). If the thermal bath cools solely by emission of gravitons, the cooling time is of the order of \ensuremath{\tau}=(3\ifmmode\times\else\texttimes\fi{}${10}^{51}$ s) (1 K/T${)}^{3}$ln(160RT/K cm). Any region which has been cooling by graviton emission since the early Universe has a maximum temperature of 10 MeV at the present.

Nuclear excitation and stellar temperature

The chemical elements in nature are the products of stellar burning processes. If the underlying nuclear physics is sufficiently known, it may be possible to decipher the respective nucleosynthesis mechanisms, e.g. the production of the heavy elements by slow neutron capture (s-process). The observed abundance patterns can be strongly affected by temperature because beta decay rates and capture cross sections may become temperature dependent via significant population of excited nuclear states in the hot stellar photon bath; in turn, this allows derivation of estimates for the temperature. The status of such analyses is presented with particular emphasis on the example of 79Se. The results of the (empirical) classical model constitute important constraints for stellar models of helium burning zones in red giant stars. The long-lived radioisotope 176Lu represents a potential cosmic clock for the age of the s-process elements. For some time it is suspected that the decay of 176Lu was temporarily enhanced and that this clock is therefore misadjusted. In spite of several attempts, this enhancement is not yet understood quantitatively.

Quantum field theory at finite temperature: Renormalization and radiative corrections

We discuss radiative corrections and the renormalization prescription in finite-temperature quantum electrodynamics at the one-loop level. As an example we consider the Coulomb scattering of an electron on a heavy nucleus immersed in a heat bath of thermal photons. Temperature-dependent infrared divergences are shown to cancel in the corresponding cross section when allowing for soft, thermal bremsstrahlung as well as soft, thermal absorption processes. In the case of extreme-relativistic electrons, temperature-dependent mass singularities appear in the infrared-finite cross section. These singularities are shown to be cancelled by similar divergences in thermal emission and absorption processes.

Optical dephasing of impurities in organic and inorganic glasses. II. Coupling of an impurity to many two-level systems

The dephasing of optical impurities in glasses in analysed within a microscopic model, which was developed in part I of the present paper. Based on a many-body hamiltonian an ensemble of two-level systems (TLSs) interacting with a photon bath is used to describe the dynamics of the glass. The impurity is coupled to the TLSs. Equations of motion, derived for certain correlation functions, are solved approximately for the many-body problem to calculate the optical line shape within linear response theory. Discussing the obtained line shape expression we justify an averaging procedure for the description of the linewidth. Analytical as well as numerical linewidth calculations are presented. Several ways to explain the T 1.3 temperature dependence of linewidths observed experimentally are suggested, compared to each other and discussed.