Gamma-ray Emission From Advection-Dominated Accretion Flows Around Black Holes: Application to the Galactic Center

We calculate the flux and spectrum of \gamma-rays emitted by a two-temperature advection-dominated accretion flow (ADAF) around a black hole. The \gamma-rays are from the decay of neutral pions produced through proton-proton collisions. We discuss both thermal and power-law distributions of proton energies and show that the \gamma-ray spectra in the two cases are very different. We apply the calculations to the \gamma-ray source, 2EG J1746-2852, detected by EGRET from the direction of the Galactic Center. We show that the flux and spectrum of this source are consistent with emission from an ADAF around the supermassive accreting black hole Sgr A^* if the proton distribution is a power-law. The model uses accretion parameters within the range made likely by other considerations. If this model is correct, it provides evidence for the presence of a two temperature plasma in Sgr A^*, and predicts \gamma-ray fluxes from other accreting black holes which could be observed with more sensitive detectors.Comment: 19 pages (Latex), 4 Figures. ApJ 486. Revised Tables and Figure

Are Particles in Advection-Dominated Accretion Flows Thermal?

We investigate the form of the momentum distribution function for protons and electrons in an advection-dominated accretion flow (ADAF). We show that for all accretion rates, Coulomb collisions are too inefficient to thermalize the protons. The proton distribution function is therefore determined by the viscous heating mechanism, which is unknown. The electrons, however, can exchange energy quite efficiently through Coulomb collisions and the emission and absorption of synchrotron photons. We find that for accretion rates greater than \sim 10^{-3} of the Eddington accretion rate, the electrons have a thermal distribution throughout the accretion flow. For lower accretion rates, the electron distribution function is determined by the electron's source of heating, which is primarily adiabatic compression. Using the principle of adiabatic invariance, we show that an adiabatically compressed collisionless gas maintains a thermal distribution until the particle energies become relativistic. We derive a new, non-thermal, distribution function which arises for relativistic energies and provide analytic formulae for the synchrotron radiation from this distribution. Finally, we discuss its implications for the emission spectra from ADAFs.Comment: 29 pages (Latex), 3 Figures. Submitted to Ap

Discovery of a Hard X-Ray Source, SAX J0635+0533, in the Error Box of the Gamma-Ray Source 2EG 0635+0521

We have discovered an x-ray source, SAX J0635+0533, with a hard spectrum within the error box of the GeV gamma-ray source in Monoceros, 2EG J0635+0521. The unabsorbed x-ray flux is 1.2*10^-11 erg cm^-2 s^-1 in the 2-10 keV band. The x-ray spectrum is consistent with a simple powerlaw model with absorption. The photon index is 1.50 +/- 0.08 and we detect emission out to 40 keV. Optical observations identify a counterpart with a V-magnitude of 12.8. The counterpart has broad emission lines and the colors of an early B type star. If the identification of the x-ray/optical source with the gamma-ray source is correct, then the source would be a gamma-ray emitting x-ray binary.Comment: Accepted to the Astrophysical Journal, 8 page

Etablierung der homöopathischen Mastitistherapie in einem biologisch-dynamisch wirtschaftenden Milcherzeugerbetrieb unter Berücksichtigung ökologischer, epidemiologischer und ökonomischer Gesichtspunkte.

6 Summary The dairy cow mastitis as a disease with an immense economic impact is widely spread in organic as well as in conventional farms. Due to the lack of alternatives to antibiotic treatment, most therapeutical measures are based on antibiotics even in organic farms and against common regulations. In contrary to these procedures the EU regulations (Council Regulation EC 1804/99)as well as the consumer’s anticipation demand the possibly lowest levels of residual charges of dairy products and environment. A two and a half year study in a bio-dyn dairy herd in Brandenburg (Germany) with 300 dairy cows suffering from udder health problems was conducted to evaluate if clinical mastitis in dairy cows is to control successfully with homeopathic remedies to minimize antibiotic treatment. To assess the efficacy of the homeopathic treatment the investigations are made using a double blind placebo controlled study design (RCCT). Using a predetermined treatment protocol and a certain diagnostic pattern to match right remedies in the sense of the homeopathic remedy pictures, the intention of the chosen treatment schedule was to provide a very transparent concept which can be used also by unexperienced veterinarians. For treatment of acute mastitis the following remedies were used: Phytolacca D6, Bryonia D6 , Echinacea D6 and Belladonna D6. Aconitum D6 was added in case of fever at the beginning of disease. Cases of chronical and subclinical mastitis were treated by Echinacea D6, Phytolacca D6 and Hepar sulfuris D8. In the first part of the study nearly all mastitis cases were treated only with homeopathics avoiding antibiotics strictly. The unsatisfying results in this part lead to a modification in the second part in which in case of certain infections (S.aureus, Sc.spp.) a limited use of antibiotics was admitted. Furthermore, selected udders with subclinical and chronical infections with these kind of bacteria were dried off antibiotically. Simultaneously the farmer was engaged to intensify the efforts to optimize preventive and environmental measures in the herd. In the second part of the study 126 cows (148 quarters) suffered from clinical mastitis (Verum: n=60; Placebo: n=66). The cure rates were nearly identical. In the whole population the clinical cure rate (CCR) immediately after treatment was 95%, 7 to 8 weeks after treatment 65%. The 107 clinically affected quarters which were infected by pathogenic bacteria showed a bacteriological cure rate (BCR) of 55% each and a complete bacterio-cytological cure rate (BCCR) of 35% and 40% after 4-5 weeks and 7-8 weeks after treatment, respectively. During the observation time of 8 weeks a total of 12 cows in each of the treatment groups produced a homologous recurrent infection. 6 cows in the verum group and 4 cows in the placebo group developed a new infection in one of the other quarters. The treatment results seems to be satisfying while the enhanced but still not optimized environmental conditions in the herd are possibly responsible for the high amount of new infections and recurrences. Looking at the results of the study at all, the use of antibiotics could be decreased by 75% due to the therapy management (in spite of the change of it because of unsatisfying results) in combination with preventive measures. Additionally the herd udder health could be increased. So the mean herd somatic cell count decreased by 75.000 somatic cells/ml to 165.000 somatic cells/ml. Furthermore, the milk yield increased by 250 kg to 6.500 kg/cow/year. The count of infections with S. aureus in the herd decreased dramatically. The decreasing input of antibiotics in mastitis therapy in the project farm lead to a decrease of 36.000 kg antibiotically loaded milk compared to a hypothetic conventional mastitis management. Furthermore, the omission of withdrawal times after homeopathic treatment resulted in a benefit of additional production milk of 25.000 kg. The antibiotics minimizing therapy concept of the second part of this investigation which could be evaluated under practice conditions can be recommended for other farms too if simultaneous herd prevention measures can be assured by the farm manager to ensure good preconditions for the convalescence of the cows. The cure rates after placebo are unexpected high. Due to these results it is profoundly debatable whether the strategies of conventional therapy of bovine mastitis are suitable to ensure herd udder health. It should be evaluated which part of the cure rate is amounted by self cure and which other factors have an effect on the healing. The nearly identical cure rates in both treatment groups do not allow the proof of homeopathic efficacy at all. Indeed, comparing the bacteriologically caused mastitis cases (107 quarters), there is a significantly higher cure rate in the verum group (p < 0.05)

Advection-Dominated Accretion Model of Sagittarius A*: Evidence for a Black Hole at the Galactic Center

Sgr A* at the Galactic Center is a puzzling source. It has a mass M=(2.5+/-0.4) x 10^6 solar masses which makes it an excellent black hole candidate. Observations of stellar winds and other gas flows in its vicinity suggest a mass accretion rate approximately few x 10^{-6} solar masses per year. However, such an accretion rate would imply a luminosity > 10^{40} erg/s if the radiative efficiency is the usual 10 percent, whereas observations indicate a bolometric luminosity <10^{37} erg/s. The spectrum of Sgr A* is unusual, with emission extending over many decades of wavelength. We present a model of Sgr A* which is based on a two-temperature optically-thin advection-dominated accretion flow. The model is consistent with the estimated mass and accretion rate, and fits the observed fluxes in the cm/mm and X-ray bands as well as upper limits in the sub-mm and infrared bands; the fit is less good in the radio below 86 GHz and in gamma-rays above 100 MeV. The very low luminosity of Sgr A* is explained naturally in the model by means of advection. Most of the viscously dissipated energy is advected into the central mass by the accreting gas, and therefore the radiative efficiency is extremely low, approximately 5 x 10^{-6}. A critical element of the model is the presence of an event horizon at the center which swallows the advected energy. The success of the model could thus be viewed as confirmation that Sgr A* is a black hole.Comment: 41 pages (Latex) including 6 Figures and 2 Tables. Final Revised Version changes to text, tables and figures. ApJ, 492, in pres

A luminosity constraint on the origin of unidentified high energy sources

The identification of point sources poses a great challenge for the high energy community. We present a new approach to evaluate the likelihood of a set of sources being a Galactic population based on the simple assumption that galaxies similar to the Milky Way host comparable populations of gamma-ray emitters. We propose a luminosity constraint on Galactic source populations which complements existing approaches by constraining the abundance and spatial distribution of any objects of Galactic origin, rather than focusing on the properties of a specific candidate emitter. We use M31 as a proxy for the Milky Way, and demonstrate this technique by applying it to the unidentified EGRET sources. We find that it is highly improbable that the majority of the unidentified EGRET sources are members of a Galactic halo population (e.g., dark matter subhalos), but that current observations do not provide any constraints on all of these sources being Galactic objects if they reside entirely in the disk and bulge. Applying this method to upcoming observations by the Fermi Gamma-ray Space Telescope has the potential to exclude association of an even larger number of unidentified sources with any Galactic source class.Comment: 18 pages, 4 figures, to appear in JPhys

MAGIC observations of very high energy gamma-rays from HESS J1813-178

Recently, the HESS collaboration has reported the detection of gamma-ray emission above a few hundred GeV from eight new sources located close to the Galactic Plane. The source HESS J1813-178 has sparked particular interest, as subsequent radio observations imply an association with SNR G12.82-0.02. Triggered by the detection in VHE gamma-rays, a positionally coincident source has also been found in INTEGRAL and ASCA data. In this Letter we present MAGIC observations of HESS J1813-178, resulting in the detection of a differential gamma-ray flux consistent with a hard-slope power law, described as dN/(dA dt dE) = (3.3+/-0.5)*10^{-12} (E/TeV)^{-2.1+/-0.2} cm^(-2)s^(-1)TeV^(-1). We briefly discuss the observational technique used, the procedure implemented for the data analysis, and put this detection in the perspective of multifrequency observations.Comment: Accepted by ApJ Letter

Constraints on the steady and pulsed very high energy gamma-ray emission from observations of PSR B1951+32/CTB 80 with the MAGIC Telescope

We report on very high energy gamma-observations with the MAGIC Telescope of the pulsar PSR B1951+32 and its associated nebula, CTB 80. Our data constrain the cutoff energy of the pulsar to be less than 32 GeV, assuming the pulsed gamma-ray emission to be exponentially cut off. The upper limit on the flux of pulsed gamma-ray emission above 75 GeV is 4.3*10^-11 photons cm^-2 sec^-1, and the upper limit on the flux of steady emission above 140 GeV is 1.5*10^-11 photons cm^-2 sec^-1. We discuss our results in the framework of recent model predictions and other studies.Comment: 7 pages, 7 figures, replaced with published versio

MAGIC upper limits on the very high energy emission from GRBs

The fast repositioning system of the MAGIC Telescope has allowed during its first data cycle, between 2005 and the beginning of year 2006, observing nine different GRBs as possible sources of very high energy gammas. These observations were triggered by alerts from Swift, HETE-II, and Integral; they started as fast as possible after the alerts and lasted for several minutes, with an energy threshold varying between 80 and 200 GeV, depending upon the zenith angle of the burst. No evidence for gamma signals was found, and upper limits for the flux were derived for all events, using the standard analysis chain of MAGIC. For the bursts with measured redshift, the upper limits are compatible with a power law extrapolation, when the intrinsic fluxes are evaluated taking into account the attenuation due to the scattering in the Metagalactic Radiation Field (MRF).Comment: 25 pages, 9 figures, final version accepted by ApJ. Changet title to "MAGIC upped limits on the VERY high energy emission from GRBs", re-organized chapter with description of observation, removed non necessaries figures, added plot of effective area depending on zenith angle, added an appendix explaining the upper limit calculation, added some reference

Discovery of Very High Energy gamma-rays from 1ES 1011+496 at z=0.212

We report on the discovery of Very High Energy (VHE) gamma-ray emission from the BL Lacertae object 1ES1011+496. The observation was triggered by an optical outburst in March 2007 and the source was observed with the MAGIC telescope from March to May 2007. Observing for 18.7 hr we find an excess of 6.2 sigma with an integrated flux above 200 GeV of (1.58$\pm0.32) 10^{-11}$ photons cm$^{-2}$ s$^{-1}$. The VHE gamma-ray flux is >40% higher than in March-April 2006 (reported elsewhere), indicating that the VHE emission state may be related to the optical emission state. We have also determined the redshift of 1ES1011+496 based on an optical spectrum that reveals the absorption lines of the host galaxy. The redshift of z=0.212 makes 1ES1011+496 the most distant source observed to emit VHE gamma-rays up to date.Comment: 4 pages, 6 figures, minor changes to fit the ApJ versio