Origin of cosmic gamma rays

An attempt is made to distinguish origin locations and dominant production mechanisms of cosmic gamma rays. The study adds to information about the cosmic ray progenitors, primarily electrons and protons of 10(^8) – 10(^10) eV. The disc longitude distribution for energies above 100 MeV is unfolded to give the Galactic gamma ray emissivity for radial symmetry or uniform emission along spiral sections. The correlation is reasonable with models based on the molecular hydrogen distribution. Inconsistency with spiral arm positions is found. The Galactic centre region, where gas density is high, is a probable example of a thick target region for gamma ray-producing cosmic rays. The emissivity under these conditions is calculated. To satisfy the proportion of the observed flux interpreted as coming from the Galactic centre region, a cosmic ray intensity greater than that locally is required. This supports a Galactic origin for the cosmic rays in question. The required injection rate is several hundreds of times the local value, and its relationship to magnetic field and gas density is examined. Contributions to the high latitude flux from the Galaxy and discrete extragalactic sources are calculated. It is shown that a large part may result from inverse Compton scattering of electrons diffusing away from the Galactic disc. The diffusion is modelled on the basis of other astro-physical data. With the Galaxy as a guide, and relating gamma ray emission to other properties, the contributions from external normal and radio galaxies are calculated. The total of all contributions is found to be a significant proportion of the observed flux, casting doubt on such cosmological models as are normalised to fit the entire measured spectrum in magnitude and shape. Radio galaxies may provide the bulk of the 1-10 MeV background if there is proportionality between their gamma ray and radio luminosities

The BL LAC phenomenon: X-ray observations of transition objects and determination of the x-ray spectrum of a complete sample of flat-spectrum radio sources

This report summarizes the activities related to two ROSAT investigations: (1) x-ray properties of radio galaxies thought to contain BL Lac type nuclei; and (2) x-ray spectra of a complete sample of flat-spectrum radio sources. The following papers describing the research are provided as attachments: Multiple X-ray Emission Components in Low Power Radio Galaxies; New X-ray Results on Radio Galaxies; Analysis Techniques for a Multiwavelength Study of Radio Galaxies; Separation of X-ray Emission Components in Radio Galaxies; X-ray Emission in Powerful Radio Galaxies and Quasars; Extended and Compact X-ray Emission in Powerful Radio Galaxies; and X-ray Spectra of a Complete Sample of Extragalactic Core-dominated Radio Sources

Beamed and Unbeamed X-ray Emission in FR1 Radio Galaxies

There is good evidence for X-ray emission associated with AGN jets which are relativistically boosted towards the observer. But to what jet radius does such X-ray emission persist? To attempt to answer this question one can look at radio galaxies; their cores are sufficiently X-ray faint that any unbeamed X-ray emission in the vicinity of the central engine must be obscured. The jets of such sources are at unfavourable angles for relativistic boosting, and so their relatively weak X-ray emission must be carefully separated from the plateau of resolved X-ray emission from a hot interstellar, intragroup, or intracluster medium on which they are expected to sit. This paper presents results arguing that jet X-ray emission is generally detected in radio galaxies, even those of low intrinsic power without hot spots. The levels of emission suggest an extrapolated radio to soft X-ray spectral index, alpha(sub tao x) of about 0.85 at parsec to perhaps kiloparsec distances from the cores

Galaxy gas ejection in radio galaxies: the case of 3C 35

We report results from XMM-Newton and Chandra observations of the nearby (z = 0.067) giant radio galaxy 3C 35. We find evidence for an X-ray emitting gas belt, orthogonal to and lying between the lobes of 3C 35, which we interpret as fossil-group gas driven outwards by the expanding radio lobes. We also detect weak emission from a second, more extended group-type environment, as well as inverse-Compton X-ray emission from the radio lobes. The morphological structure of the radio lobes and gas belt point to co-evolution. Furthermore, the radio source is powerful enough to eject galaxy-scale gas out to distances of 100kpc, and the ages of the two features are comparable (tsynch~140Myr, tbelt~80 Myr). The destruction of 3C 35's atmosphere may offer clues as to how fossil systems are regulated: radio galaxies need to be of power comparable to 3C 35 to displace and regulate fossil-group gas. We discuss the implications of the gas belt in 3C 35 in terms of AGN fuelling and feedback.Comment: 18 pages, accepted to MNRA

Interaction between the intergalactic medium and central radio source in the NGC 4261 group of galaxies

Using observations from the Chandra and XMM-Newton X-ray observatories, we examine the interaction between the intra-group medium and central radio source in the nearby NGC 4261 galaxy group. We confirm the presence of cavities associated with the radio lobes and estimate their enthalpy to be ~2.4x10^58 erg. The mechanical power output of the jets is >=10^43 erg/s, at least a factor of 60 greater than the cooling luminosity in the region the lobes inhabit. We identify rims of compressed gas enclosing the lobes, but find no statistically significant temperature difference between them and their surroundings, suggesting that the lobe expansion velocity is approximately sonic (Mach<=1.05). The apparent pressure of the radio lobes, based on the synchrotron minimum energy density argument, is a factor of 5 lower than that of the intra-group medium. Pressure balance could be achieved if entrainment of thermal gas provided additional non-radiating particles in the lobe plasma, but the energy required to heat these particles would be ~20 per cent. of the mechanical energy output of the radio source. NGC 4261 has a relatively compact cool core, which should probably be categorised as a galactic corona. The corona is capable of fuelling the active nucleus for considerably longer than the inferred source lifetime, but can be only inefficiently heated by the AGN or conduction. The expansion of the radio lobes has affected the structure of the gas in the galaxy, compressing and moving the material of the corona without causing significant shock heating, and expelling gas from the immediate neighbourhood of the jets. We discuss the possible implications of this environment for the duration of the AGN outburst, and consider mechanisms which might lead to the cessation of nuclear activity.Comment: Accepted for publication in MNRAS, 17 pages, 6 figure

New insights into the evolution of the FR I radio galaxy 3C 270 (NGC 4261) from VLA and GMRT radio observations

We present Giant Metrewave Radio Telescope (GMRT) 240 MHz observations of the nearby luminous FR I radio source 3C 270, in the group-central elliptical NGC 4261. Combining these data with reprocessed Very Large Array (VLA) 1.55 and 4.8 GHz observations, we produce spectral index maps that reveal a constant spectral index along the jets and a gradual steepening from the ends of the jets through the lobes towards the nucleus. A Jaffe & Perola (JP) model fitted to the integrated spectrum of the source gives an asymptotic low-frequency index of $\alpha_{inj}=0.53_{-0.02}^{+0.01}$, while JP models fitted to the observed spectral index trend along the lobes allow us to estimate radiative ages of $\sim29$ Myr and $\sim37$ Myr for the west and east lobes respectively. Our age estimates are a factor of two lower than the 75-Myr upper limit derived from X-ray data (O'Sullivan et al. 2011). We find unlikely the scenario of an early supersonic phase in which the lobe expanded into the ISM at approximately Mach 6 (3500 km s$^{-1}$), and suggest that either the source underwent multiple AGN outbursts with possible large changes in jet power, or possibly that the source age that we find is due to a backflow that transports young electrons from the jet tips through the lobes toward the nucleus relatively quickly. We calculate that in the lobes the energy ratio of non-radiating to radiating particles is $\sim4-24$ indicating significant gas entrainment. If the lobes are in pressure balance with their surroundings, the total energy required to heat the entrained material is $10^{58}$ erg, $\sim$40% of the total enthalpy of the lobes.Comment: 14 pages, 11 figures, 8 tables. Accepted for publication by MNRAS. Revised throughout in response to referee's comment