M. Hayashida

Broad-line Radio Galaxies Observed with Fermi-LAT: The Origin of the GeV γ-Ray Emission

We report on a detailed investigation of the γ-ray emission from 18 broad line radio galaxies (BLRGs) base d on two years ofFermi Large Area Telescope (LAT) data. We confirm the previously re po ted detections of 3C 120 and 3C 111 in the GeV photon energy range; a detailed loo k at the temporal characteristics of the observedγ-ray emission reveals in addition possible flux variability in both sources. No statistically significant γ-ray detection of the other BLRGs was however found in the con sidered dataset. Though the sample size studied is small, what appears to differentiate 3C 111 and 3C 120 from the BLRGs not yet detected in γrays is the particularly strong nuclear radio flux. This findi g, together with the indications of the γ-ray flux variability and a number of other arguments presented, indi cate that the GeV emission of BLRGs is most likely dominated by the beamed radiation of relativistic jets obse rved at intermediate viewing angles. In this paper we also analyzed a comparison sample of high accretion-rate Se yfert 1 galaxies, which can be considered radioquiet counterparts of BLRGs, and found none were detected in γ-rays. A simple phenomenological hybrid model applied for the broad-band emission of the discussed r adio-loud and radio-quiet type 1 active galaxies suggests that the relative contribution of the nuclear jets to he accreting matter is ≥ 1% on average for BLRGs, whilst ≤ 0.1% for Seyfert 1 galaxies. Subject headings: radiation mechanisms: non-thermal — galaxies: active — gal axies: individual (3C 111, 3C 120) — galaxies: jets — gamma rays: galaxies — X-rays: gala xiesWe report on a detailed investigation of the γ-ray emission from 18 broad-line radio galaxies (BLRGs) based on two years of Fermi Large Area Telescope data. We confirm the previously reported detections of 3C 120 and 3C 111 in the GeV photon energy range; a detailed look at the temporal characteristics of the observed γ-ray emission reveals in addition possible flux variability in both sources. No statistically significant γ-ray detection of the other BLRGs was found, however, in the considered data set. Though the sample size studied is small, what appears to differentiate 3C 111 and 3C 120 from the BLRGs not yet detected in γ-rays is the particularly strong nuclear radio flux. This finding, together with the indications of the γ-ray flux variability and a number of other arguments presented, indicates that the GeV emission of BLRGs is most likely dominated by the beamed radiation of relativistic jets observed at intermediate viewing angles. In this paper we also analyzed a comparison sample of high-accretion-rate Seyfert 1 galaxies, which can be considered radio-quiet counterparts of BLRGs, and found that none were detected in γ-rays. A simple phenomenological hybrid model applied for the broadband emission of the discussed radio-loud and radio-quiet type 1 active galaxies suggests that the relative contribution of the nuclear jets to the accreting matter is ≥1% on average for BLRGs, whereas it is ≤0.1% for Seyfert 1 galaxies.

Prospects for Indirect Dark Matter Searches with the Cherenkov Telescope Array (CTA)

The Cherenkov Telescope Array (CTA) will have a unique chance of discovery for a large range of masses in Weakly Interacting Massive Particles models of dark matter. The principal target for dark matter searches with CTA is the centre of the Galactic Halo. The best strategy is to perform CTA observations within a few degrees of the Galactic Centre, with the Galactic Centre itself and the most intense diffuse emission regions removed from the analysis. Assuming a cuspy dark matter density profile for the Milky Way, 500 hours of observations in this region provide sensitivities to and below the thermal cross-section of dark matter annihilations, for masses between a few hundred GeV and a few tens of TeV; therefore CTA will have a significant chance of discovery in some models. Since the dark matter density in the Milky Way is far from certain in the inner kpc region, other targets are also proposed for observation, like ultra-faint dwarf galaxies such as Segue 1 with 100 hours per year proposed. Beyond these two observational targets, further alternatives, such as Galactic dark clumps, will be considered closer to the actual date of CTA operations. Sensitivity predictions for dark matter searches are given on the various targets taking into account the latest instrument response functions expected for CTA together with a discussion on the systematic uncertainties from the backgrounds.

SUZAKU WIDE BAND ANALYSIS OF THE X-RAY VARIABILITY OF TeV BLAZAR Mrk 421 IN 2006

We present the results of X-ray observations of the well-studied TeV blazar Mrk 421 with the Suzaku satellite in 2006 April 28. During the observation, Mrk 421 was undergoing a large flare and the X-ray flux was variable, decreasing by ∼ 50 %, from 7.8 × 10 -10 to 3.7 × 10 -10 erg s -1 cm -2 in about 6 hours, followed by an increase by ∼ 35 %. Thanks to the broad bandpass coupled with high-sensitivity of Suzaku, we measured the evolution of the spectrum over the 0.4‐60 keV band in data segments as short as ∼ 1 ksec. The data show deviations from a simple power law model, but also a clear spectral variability. The time-resolved spectra are fitted by a synchrotron model, where the observed spectrum is due to a exponentially cutoff power law distribution of electrons radiating in uniform magnetic field; this model is preferred over a broken power law. As another scenario, we separate the spectrum into “steady” and “variable” components by subtracting the spectrum in the lowest-flux period from those of other data segments. In this context, the difference (“variable”) spectra are all well described by a broken power law model with photon index ∼ 1.6, breaking at energy ǫbrk ≃ 3 keV to another photon index ∼ 2.1 above the break energy, differing from each other only by normalization, while the spectrum of the “steady” component is best described by the synchrotron model. We suggest the rapidly variable component is due to relatively localized s hock (Fermi I) acceleration, while the slowly variable (“steady”) component is due to the superposition of shocks located at larger distance along the jet, or due to other acceleration process, such as the stochastic acceler ation on magnetic turbulence (Fermi II) in the more extended region. Subject headings:acceleration of particles — BL Lacertae objects: individual (Mrk 421) — galaxies: jets — X-rays: galaxies

The First MAXI/GSC Catalog in the High Galactic-Latitude Sky

AbstractWe present the first unbiased source catalog of the Monitor of All-sky X-ray Image (MAXI) mission athigh Galactic latitudes (|b|>10 ◦ ), produced from the first 7-month data (2009 September 1 to 2010 March31) of the Gas Slit Camera in the 4–10 keV band. We develop an analysis procedure to detect faint sourcesfrom the MAXI data, utilizing a maximum likelihood image fitting method, where the image response,background, and detailed observational conditions are taken into account. The catalog consists of 143X-ray sources above 7 sigma significance level with a limiting sensitivity of ∼ 1.5×10 −11 ergs cm −2 s −1 (1.2 mCrab) in the 4–10 keV band. Among them, we identify 38 Galactic/LMC/SMC objects, 48 galaxyclusters, 39 Seyfert galaxies, 12 blazars, and 1 galaxy. Other 4 sources are confused with multiple objects,and one remains unidentified. The log N - log S relation of extragalactic objects is in a good agreementwith the HEAO-1 A-2 result, although the list of the brightest AGNs in the entire sky has significantlychanged since that in 30 years ago.Key words:catalogs — surveys — galaxies: active — X-rays: galaxies1. INTRODUCTIONAll-sky X-ray surveys are powerful tools to investigatethe whole populations of active and hot phenomena inthe universe at the brightest flux end. The strong X-ray emitters include Galactic objects such as active stars,SNRs, pulsars, CVs, low mass and high mass X-ray bi-naries (with a neutron star or a black hole as the pri-mary), and extragalactic objects, mainly active galacticnuclei (AGNs; Seyfert galaxies and blazars) and clustersof galaxies. The source catalog consisting of a statisticallywell-defined sample detected from an unbiased survey isa primary product on which many subsequent studies arebased. For extragalactic populations, in particular, theseresults define the “local” sample in the present universe,the end point of their cosmological evolution. Thus, toestablish the statistical properties of bright X-ray sourcesusing the best quality data over the entire sky has alwaysbeen a key issue in high energy astrophysics.Past all-sky X-ray surveys indeed brought valuable in-formation on the X-ray source populations. In the softX-ray band, the ROSAT mission conducted an all-sky sur-vey in the 0.1–2.4 keV band, producing the ROSAT All-Sky Survey (RASS) Bright Source Catalog (BSC; Voges

The Most Intensive Gamma-Ray Flare of Quasar 3C 279 with the Second-Order Fermi Acceleration

The very short and bright flare of 3C 279 detected with Fermi-Large Area Telescope in 2013 December is tested by a model with stochastic electron acceleration by turbulences. Our time-dependent simulation shows that the very hard spectrum and asymmetric light curve are successfully reproduced by changing only the magnetic field from the value in the steady period. The maximum energy of electrons drastically grows with the decrease of the magnetic field, which yields a hard photon spectrum as observed. Rapid cooling due to the inverse-Compton scattering with the external photons reproduces the decaying feature of the light curve.The inferred energy density of the magnetic field is much less than the electron and photon energy densities. The low magnetic field and short variability timescale are unfavorable for the jet acceleration model from the gradual Poynting flux dissipation.

Revisit of Local X-Ray Luminosity Function of Active Galactic Nuclei with the MAXI Extragalactic Survey

We construct a new X-ray (2--10 keV) luminosity function of Compton-thin active galactic nuclei (AGNs) in the local universe, using the first MAXI/GSC source catalog surveyed in the 4--10 keV band. The sample consists of 37 non-blazar AGNs at

MAXI INVESTIGATION INTO THE LONG-TERM X-RAY VARIABILITY FROM THE VERY-HIGH-ENERGY γ-RAY BLAZAR Mrk 421

z=0.002-0.2

First Results from NuSTAR Observations of Mkn 421

, whose identification is highly (

The first MAXI/GSC catalog in the high-Galactic latitude sky

>97%

Blazar Spectra with Hard-sphere-like Acceleration of Electrons

) complete. We confirm the trend that the fraction of absorbed AGNs with