Surveys above 10 keV represent one of the best resources to provide an unbiased census of the population of active galactic nuclei (AGNs). We present the results of 60 months of observation of the ...hard X-ray sky with Swift/Burst Alert Telescope (BAT). In this time frame, BAT-detected (in the 15-55 keV band) 720 sources in an all-sky survey of which 428 are associated with AGNs, most of which are nearby. Our sample has negligible incompleteness and statistics a factor of ~2 larger over similarly complete sets of AGNs. Our sample contains (at least) 15 bona fide Compton-thick AGNs and 3 likely candidates. Compton-thick AGNs represent ~5% of AGN samples detected above 15 keV. We use the BAT data set to refine the determination of the log N-log S of AGNs which is extremely important, now that NuSTAR prepares for launch, toward assessing the AGN contribution to the cosmic X-ray background. We show that the log N-log S of AGNs selected above 10 keV is now established to ~10% precision. We derive the luminosity function of Compton-thick AGNs and measure a space density of 7.9 super(+4.1) sub(- 2.9) x 10 super(-5) Mpc super(-3) for objects with a de-absorbed luminosity larger than 2 x 10 super(42) erg s super(-1). As the BAT AGNs are all mostly local, they allow us to investigate the spatial distribution of AGNs in the nearby universe regardless of absorption. We find concentrations of AGNs that coincide spatially with the largest congregations of matter in the local (< or =, slant85 Mpc) universe. There is some evidence that the fraction of Seyfert 2 objects is larger than average in the direction of these dense regions.
Hard X-ray observations are crucial to study the non-thermal jet emission from high-redshift, powerful blazars. We observed two bright z > 2 flat-spectrum radio quasars (FSRQs) in hard X-rays to ...explore the details of their relativistic jets and their possible variability. S50014+81 (at z = 3.366) and B0222+185 (at z = 2.690) have been observed twice by the Nuclear Spectroscopic Telescope Array (NuSTAR) simultaneously with Swift X-ray Telescope, showing different variability behaviors. We found that NuSTAR is instrumental to explore the variability of powerful high-redshift blazars, even when no gamma-ray emission is detected. The two sources have proven to have respectively the most luminous accretion disc and the most powerful jet among known blazars. Thanks to these properties, they are located at the extreme end of the jet-accretion disc relation previously found for gamma-ray detected blazars, to which they are consistent.
ABSTRACT We report the results of a multiband observing campaign on the famous blazar 3C 279 conducted during a phase of increased activity from 2013 December to 2014 April, including first ...observations of it with NuSTAR. The γ-ray emission of the source measured by Fermi-LAT showed multiple distinct flares reaching the highest flux level measured in this object since the beginning of the Fermi mission, with of 10−5 photons cm−2 s−1, and with a flux-doubling time scale as short as 2 hr. The γ-ray spectrum during one of the flares was very hard, with an index of , which is rarely seen in flat-spectrum radio quasars. The lack of concurrent optical variability implies a very high Compton dominance parameter . Two 1 day NuSTAR observations with accompanying Swift pointings were separated by 2 weeks, probing different levels of source activity. While the 0.5−70 keV X-ray spectrum obtained during the first pointing, and fitted jointly with Swift-XRT is well-described by a simple power law, the second joint observation showed an unusual spectral structure: the spectrum softens by at ∼4 keV. Modeling the broadband spectral energy distribution during this flare with the standard synchrotron plus inverse-Compton model requires: (1) the location of the γ-ray emitting region is comparable with the broad-line region radius, (2) a very hard electron energy distribution index , (3) total jet power significantly exceeding the accretion-disk luminosity , and (4) extremely low jet magnetization with . We also find that single-zone models that match the observed γ-ray and optical spectra cannot satisfactorily explain the production of X-ray emission.
Located at the center of the Perseus cluster, 3C 84 is an extremely bright and nearby radio galaxy. Because of the strong diffuse thermal emission from the cluster in X-rays, the detailed properties ...and the origin of a power-law component from the central active galactic nucleus (AGN) remains unclear in the source. We report here the first NuSTAR observations of 3C 84. The source was observed for 24.2 and 32 ks on 2018 February 1 and 4, respectively. NuSTAR observations spectrally decompose the power-law AGN component above 10 keV. The power-law component dominates the spectrum above 20 keV with a photon index ∼1.9 and an energy flux F20-30 keV = 1.0 × 10−11 erg cm−2 s−1, corresponding to an isotropic luminosity, L20-30 keV = 7.4 × 1042 erg s−1. We discuss possible emitting sites for the power-law component. The expected thermal emission from the accretion disk is not hot enough to account for the hard X-rays detected from the source. Similar X-ray and γ-ray photon indices and long-term flux variations, the absence of cutoff energy in the hard X-ray spectrum of the source, correlated hard X-ray flux and hardness ratio variations, and the similarity of optical-X-ray slope to blazar rather than Seyfert galaxies supports the hard X-ray power-law component originating from the jet.
A1689 is a galaxy cluster at z = 0.183 for which previous measurements of its mass by using various techniques gave discrepant results. We present a new detailed measurement of the mass with the data ...based on X-ray observations with the European Photon Imaging Camera aboard the XMM-Newton Observatory, determined by using an unparameterized deprojection technique. Fitting the total mass profile to a Navarro-Frenk-White model yields halo concentration c = 7.2image and r sub(200) = 1.13 plus or minus 0.21 h super(-1) Mpc, corresponding to a mass that is less than half of that found from gravitational lensing. Adding to the evidence of substructure from optical observations, X-ray analysis shows a highly asymmetric temperature profile and a nonuniform redshift distribution, implying large-scale relative motion of the gas. A lower than expected gas mass fraction f sub(gas) = 0.072 plus or minus 0.008 (for a flat lambda CDM cosmology) suggests a complex spatial and/or dynamical structure. We also find no sign of any additional absorbing component previously reported on the basis of the Chandra data, confirming the XMM-Newton low-energy response by using data from ROSAT.
We present time-resolved broadband observations of the quasar 3C 279 obtained from multi-wavelength campaigns conducted during the first two years of the Fermi Gamma-ray Space Telescope mission. ...While investigating the previously reported gamma -ray/optical flare accompanied by a change in optical polarization, we found that the optical emission appears to be delayed with respect to the gamma -ray emission by about 10 days. X-ray observations reveal a pair of "isolated" flares separated by ~90 days, with only weak gamma -ray/optical counterparts. The spectral structure measured by Spitzer reveals a synchrotron component peaking in the mid-infrared band with a sharp break at the far-infrared band during the gamma -ray flare, while the peak appears in the millimeter (mm)/submillimeter (sub-mm) band in the low state. Selected spectral energy distributions are fitted with leptonic models including Comptonization of external radiation produced in a dusty torus or the broad-line region. Adopting the interpretation of the polarization swing involving propagation of the emitting region along a curved trajectory, we can explain the evolution of the broadband spectra during the gamma -ray flaring event by a shift of its location from ~1 pc to ~4 pc from the central black hole. On the other hand, if the gamma -ray flare is generated instead at sub-pc distance from the central black hole, the far-infrared break can be explained by synchrotron self-absorption. We also model the low spectral state, dominated by the mm/sub-mm peaking synchrotron component, and suggest that the corresponding inverse-Compton component explains the steady X-ray emission.
ABSTRACT We report the first hard X-ray observations with NuSTAR of the BL Lac-type blazar PKS 2155-304, augmented with soft X-ray data from XMM-Newton and γ-ray data from the Fermi Large Area ...Telescope, obtained in 2013 April when the source was in a very low flux state. A joint NuSTAR and XMM spectrum, covering the energy range 0.5-60 keV, is best described by a model consisting of a log-parabola component with curvature and a (local) photon index 3.04 0.15 at photon energy of 2 keV, and a hard power-law tail with photon index 2.2 0.4. The hard X-ray tail can be smoothly joined to the quasi-simultaneous γ-ray spectrum by a synchrotron self-Compton component produced by an electron distribution with index p = 2.2. Assuming that the power-law electron distribution extends down to γmin = 1 and that there is one proton per electron, an unrealistically high total jet power of Lp ∼ 1047 erg s−1 is inferred. This can be reduced by two orders of magnitude either by considering a significant presence of electron-positron pairs with lepton-to-proton ratio , or by introducing an additional, low-energy break in the electron energy distribution at the electron Lorentz factor γbr1 ∼ 100. In either case, the jet composition is expected to be strongly matter-dominated.
Are Quasar Jets Dominated by Poynting Flux? Sikora, Marek; Begelman, Mitchell C; Madejski, Greg M ...
The Astrophysical journal,
05/2005, Volume:
625, Issue:
1
Journal Article
Peer reviewed
Open access
The formation of relativistic astrophysical jets is presumably mediated by magnetic fields threading accretion disks and central, rapidly rotating objects. As it is accelerated by magnetic stresses, ...the jet's kinetic energy flux grows at the expense of its Poynting flux. However, it is unclear how efficient the conversion from magnetic to kinetic energy is and whether there are any observational signatures of this process. We address this issue in the context of jets in quasars. Using data from all spatial scales, we demonstrate that in these objects the conversion from Poynting flux-dominated to matter-dominated jets is very likely to take place closer to the black hole than in the region where most of the Doppler-boosted radiation observed in blazars is produced. We briefly discuss the possibility that blazar activity could be induced by global MHD instabilities, e.g., via the production of localized velocity gradients that lead to dissipative events such as shocks or magnetic reconnection, in which acceleration of relativistic particles and production of nonthermal flares is taking place.
ABSTRACT Powerful blazars are flat-spectrum radio quasars whose emission is dominated by a Compton component peaking between a few hundred keV and a few hundred MeV. We observed two bright blazars, ...PKS 2149-306 at redshift z = 2.345 and S5 0836+710 at z = 2.172, in the hard X-ray band with the Nuclear Spectroscopic Telescope Array satellite. Simultaneous soft-X-rays and UV-optical observations were performed with the Swift satellite, while near-infrared (near-IR) data were obtained with the Rapid Eye Mount telescope. To study their variability, we repeated these observations for both sources on a timescale of a few months. While no fast variability was detected during a single observation, both sources were variable in the X-ray band, up to 50%, between the two observations, with larger variability at higher energies. No variability was detected in the optical/NIR band. These data, together with Fermi-Large Area Telescope, Wide-field Infrared Survey Explorer, and other literature data, are then used to study the overall spectral energy distributions (SEDs) of these blazars. Although the jet nonthermal emission dominates the SED, it leaves the UV band unhidden, allowing us to detect the thermal emission of the disk and to estimate the black hole mass. The nonthermal emission is well reproduced by a one-zone leptonic model by the synchrotron, self-Compton, and external Compton processes. Our data are better reproduced if we assume that the location of the dissipation region of the jet, Rdiss, is in between the torus and the broad-line region. The observed variability is explained by changing a minimum number of model parameters by a very small amount.
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