Bump Component Research Articles

Spectral energy distribution template of redshift-zero AGN and the comparison with that of quasars

Spectral energy distributions (SEDs) of the central few tens of parsecs of some of the nearest active galactic nuclei [AGN] have been used to construct a genuine redshift-zero SED template [1]. This paper presents the comparison between this redshift-zero template and those of the radio loud and radio quiet quasar templates by [2]. Despite the four orders of magnitude difference in power between the redshift-zero AGNs, mostly Seyfert galaxies, and that of quasars, they all show a remarkable similarity. The distinction relays on the importance of the so-called blue bump component – emission from the accretion disk - which is absent in Seyfert type 2, mildly present in Seyfert type 1, seen in full realm in quasars. Conversely, the characteristic red bump component - dust reprocessed emission in the IR - is present in all cases. The difference between the three AGN classes can be ascribed in terms of central dust obscuration and progressive view angle of the nuclear core.

X-rays as the dominant excitation mechanism of [Fe ii] and H2 emission lines in active galaxies

We investigate the excitation mechanisms of near-infrared [Fe ii] and H2 emission lines observed in Active Galactic Nuclei (AGNs). We built a photoionization model grid considering a two-component continuum, one accounts for the Big Bump component peaking at 1Ryd and another represents the X-ray source that dominates the continuum emission at high energies. Photoionization models considering as ionizing source a spectral energy distribution obtained from photometric data of the Sy 2 Mrk 1066 taken from the literature were considered. Results of these models were compared with a large sample of observational long-slit and Integral field Unit (IFU) spectroscopy data of the nuclear region for a sample of active objects. We found that the correlation between the observational [Fe ii]{\lambda}1.2570 {\mu}m/Pa{\beta} vs. H2{\lambda}2.1218 {\mu}m/Br{\gamma} is well reproduced by our models as well as the relationships that involve the H2 emission line ratios observed in the spectroscopic data.We conclude that the heating by X-rays produced by active nuclei can be considered a common and very important mechanism of excitation of [Fe ii] and H2.

Analysis of inclusive(d,xp)reactions on nuclei from9Be to238U at 100 MeV

Inclusive proton emissions from deuteron-induced reactions on ${}^{9}$Be, ${}^{12}$C, ${}^{27}$Al, ${}^{58}$Ni, ${}^{93}$Nb, ${}^{181}$Ta, ${}^{208}$Pb, and ${}^{238}$U at an incident energy of 100 MeV are analyzed using the continuum discretized coupled-channels theory for the elastic-breakup process and the Glauber model for the neutron-stripping process in order to investigate deuteron-breakup processes over a wide range of target mass numbers. The effects of Coulomb interactions are taken into account to give a proper description of proton emissions at forward angles. Moreover, the phenomenological moving-source model is used to estimate evaporation and preequilibrium components in inclusive $(d,\phantom{\rule{-0.16em}{0ex}}xp)$ spectra. The calculation reproduces fairly well a prominent bump observed around half the incident energy in experimental $(d,\phantom{\rule{-0.16em}{0ex}}xp)$ spectra for light and medium nuclei at forward angles of less than 20${}^{\ensuremath{\circ}}$ whereas the calculation underestimates the bump component as the target atomic number increases. The underestimation is likely due to the fact that the eikonal approximation used in the Glauber model becomes worse due to strong Coulomb interactions. It is shown that the Glauber-model calculation for the neutron-stripping process leads to an improvement of this discrepancy by substituting the eikonal phase shift for the quantum phase shift given by the optical-model calculation.

The dust-eliminated shape of quasar spectra in the near-infrared: a hidden part of the big blue bump

The near-infrared shape of the big blue bump component in quasar spectra has till now been essentially unknown. It usually cannot be observed directly, due to the strong hot dust emission that dominates quasar spectra longward of ∼1 μm. However, this is quite an important part of the spectrum theoretically. At least bare-disc models provide quite a robust prediction for the overall continuum shape in the near-infrared. Self-gravity should become important in the outer, near-infrared-emitting regions of the putative disc, possibly leaving a signature of disc truncation in the near-infrared. We propose here that this important part of the spectrum can be revealed for the first time by observing polarized flux from normal quasars. At least in some polarized quasars, the emission lines are all unpolarized and so the polarized flux should originate interior to the broad-line region, and therefore also interior to the dust-emitting region. This can then be used to eliminate the dust emission. We present the results of near-infrared polarimetry for three such quasars (Ton202,4C 37.43 and B2 1208+32). The data for Ton202 have the highest signal-to-noise ratio, and the near-infrared polarized flux in this case is measured to have quite a blue shape, F v ν +0.42±0.29 , intriguingly consistent with the simple multitemperature blackbody, bare-disc prediction of ν +1/3 . All these data, although still with quite low signal-to-noise ratio for the other two objects, demonstrate the unique potential of the technique with future better data. We also present similar data for other quasars and radio galaxies, and briefly discuss the nature of the polarization.

High-resolution single-pulse studies of the Vela pulsar

We present high-resolution multi-frequency single-pulse observations of the Vela pulsar, PSR B0833 − 45, aimed at studying micro-structure, phase-resolved intensity fluctuations and energy distributions at 1.41 and 2.30 GHz. We find micro-structure in about 80 per cent of all pulses independent of observing frequency. The width of a micro-pulse seems to depend on its peak flux density, whilst quasi-periodicities observed in micro-pulses remain constant. The width of the micro-pulses may decrease with increasing frequency, but confirmation is needed at higher frequencies. The fraction of pulses showing quasi-periodic micro-pulses may become smaller at higher frequencies. We show that the micro-pulse width in pulsars has a period dependence which suggests a model of sweeping micro-beams as the origin of the micro-pulses. Like individual pulses, the micro-pulses of Vela are highly elliptically polarized. There is a strong correlation between Stokes parameters V and I in the micro-structure. We do not observe any micro-pulses where the handedness of the circular intensity changes within a micro-pulse, although flips within a pulse are not uncommon. We show that the V/I distribution is Gaussian with a narrow width and that this width appears to be constant as a function of pulse phase. The phase-resolved intensity distributions of I are best fitted with log-normal statistics. Extra emission components, i.e. ‘bump’ and ‘giant micro-pulses’, discovered by Johnston et al. at 0.6 and 1.4 GHz are also present at the higher frequency of 2.3 GHz. The bump component seems to be an extra component superposed on the main pulse profile but does not appear periodically. The giant micro-pulses are time-resolved and have significant jitter in their arrival times. Their flux density distribution is best fitted by a power-law, indicating a link between these features and ‘classical’ giant pulses as observed for the Crab pulsar (PSR B0531 + 21), PSR B1937 + 21 and PSR B1821 − 24. We find that Vela contains a mixture of emission properties representing both ‘classical’ properties of radio pulsars (e.g. micro-structure, high degree of polarization, S-like position angle swing, orthogonal modes) and features which are most likely related to high-energy emission (e.g. extra profile components, giant micro-pulses). It hence represents an ideal test case to study the relationship between radio and high-energy emission in significant detail.

150 keV Emission from PKS 2149−306 withBEPPOSAX

A BeppoSAX observation of the z = 2.34 quasar PKS 2149-306 produced a strong signal in the high-energy PDS instrument up to a maximum observed energy of nearly 50 keV, 150 keV in the quasar frame. The BeppoSAX spectrum spans almost three decades (0.3-150 keV, quasar frame) and shows an extremely hard (α = 0.4 ± 0.05) X-ray spectrum above 3 keV (comparable to XJB the X-ray background slope), and either a softer (α = 1.0) low-energy component, or an ionized absorber at zero redshift. No evidence is seen of an Fe-K emission line (EW 120 keV (quasar frame). The SED of PKS 2149-306 shows two peaks at ~1012±0.5 Hz and ~1021±1.0 Hz (~0.3 mm and ~4 MeV), strongly resembling a low-energy cut off BL Lac object (LBL). The ratio of the two peaks shows an extreme Compton dominance (CD = 1.4 ± 0.4), as in flat-spectrum radio quasars (FSRQs). The presence of an additional optical/UV big bump component may provide photons that cool the jet, suppressing the radio emission.

The ultraviolet spectrum of the narrow-line Seyfert 1 galaxy RE J1034+396

RE J1034+396 has one of the hottest big blue bumps of any Seyfert 1 (kTBB∼120 eV) and thus provides a valuable insight into the physics in the nuclei of active galaxies. In this paper, we present UV spectroscopy of RE J1034+396, taken with the Faint Object Spectrograph on the Hubble Space Telescope. With a spectral resolution of ∼1–2 A FWHM and a typical signal-to-noise ratio of ∼15 per diode, this is one of the first detailed UV spectra of an object in the narrow-line Seyfert 1 (NLS1) class. The spectrum probes the physics and kinematics of the high-ionization and coronal line gas, and the strength and form of the big blue bump component in the UV. We detect many emission lines, including Lyα, C ivλ1549, He iiλ1640, C iii] λ1909 and Mg iiλ2798. We also identify a feature at 2647 A (in the rest frame) with highly ionized iron ([Fe xi] λ2649); a line of the same species ([Fe xi] λ7892) has also been seen in the optical spectrum. The velocity widths of the UV lines are relatively narrow (FWHM<2000 km s−1), although C ivλ1549 appears to have a broad underlying component with a FWHM typical of quasars (∼5500 km s−1). The FWHM are similar to those of the optical lines, which suggests that all line emission in RE J1034+396, i.e. including that of high- and low-ionization species and the forbidden lines, may be dominated by an intermediate-velocity (FWHM∼1000 km s−1), intermediate-density (log Ne ∼ 7.5 cm−3) region of gas. The slope of the UV continuum (αuv∼0.9) is soft (i.e. red) relative to quasars and the UV to soft X-ray flux ratio is unusually low (the 0.2 keV/1200 A flux ratio is 1/200), implying that the big blue bump component is very weak in the UV. The present-epoch UV to soft X-ray continuum is consistent with earlier data, demonstrating that this extreme big blue bump component is also very stable, unlike many other NLS1s which show extreme patterns of variability.

The ultraviolet spectrum of the narrow-line Seyfert 1 galaxy RE J1034+396

RE J1034+396 has one of the hottest big blue bumps of any Seyfert 1 (kTBB∼120 eV) and thus provides a valuable insight into the physics in the nuclei of active galaxies. In this paper, we present UV spectroscopy of RE J1034+396, taken with the Faint Object Spectrograph on the Hubble Space Telescope. With a spectral resolution of ∼1–2 A FWHM and a typical signal-to-noise ratio of ∼15 per diode, this is one of the first detailed UV spectra of an object in the narrow-line Seyfert 1 (NLS1) class. The spectrum probes the physics and kinematics of the high-ionization and coronal line gas, and the strength and form of the big blue bump component in the UV. We detect many emission lines, including Lyα, C ivλ1549, He iiλ1640, C iii] λ1909 and Mg iiλ2798. We also identify a feature at 2647 A (in the rest frame) with highly ionized iron ([Fe xi] λ2649); a line of the same species ([Fe xi] λ7892) has also been seen in the optical spectrum. The velocity widths of the UV lines are relatively narrow (FWHM<2000 km s−1), although C ivλ1549 appears to have a broad underlying component with a FWHM typical of quasars (∼5500 km s−1). The FWHM are similar to those of the optical lines, which suggests that all line emission in RE J1034+396, i.e. including that of high- and low-ionization species and the forbidden lines, may be dominated by an intermediate-velocity (FWHM∼1000 km s−1), intermediate-density (log Ne ∼ 7.5 cm−3) region of gas. The slope of the UV continuum (αuv∼0.9) is soft (i.e. red) relative to quasars and the UV to soft X-ray flux ratio is unusually low (the 0.2 keV/1200 A flux ratio is 1/200), implying that the big blue bump component is very weak in the UV. The present-epoch UV to soft X-ray continuum is consistent with earlier data, demonstrating that this extreme big blue bump component is also very stable, unlike many other NLS1s which show extreme patterns of variability.

Dense, thin clouds and reprocessed radiation in the central regions of active galactic nuclei

The primary radiation generated in the central continuum-forming region of Active Galactic Nuclei can be reprocessed by very dense, small-scale clouds that are optically-thin to Thomson scattering. In spite of the extreme conditions expected to prevail in this innermost, central environment, the radiative clouds can survive and maintain cool temperatures relative to the ambient emitting region by means of magnetic confinement. Motivated by these ideas, we present a detailed quantitative study of such clouds, explicitly describing the physical properties they can attain under thermal and radiative equilibrium conditions. We also discuss the thermal stability of the gas in comparison to that of other reprocessing material thought to reside at larger distances from the central source. We construct a model to predict the emergent spectra from a source region containing dense clouds which absorb and reemit the primary radiation generated therein. Our predicted spectra show the following two important results: (i) the reprocessed flux emitted at optical/UV energies is insufficient to account for the blue bump component in the observed spectra; and (ii) the amount of line radiation that is emitted is at least comparable to (and in many cases dominates) the continuum radiation. The lines are extremely broad and tend to accumulate in the extreme ultraviolet, where they form a peak much more prominent than that which is observed in the optical/UV. This result is supported by current observations, which indicate that the spectral energy distribution of radio-quiet AGN may indeed reach a maximum in the EUV band.

Double-peaked Balmer line emission in the radio-quiet AGN RX J1042 + 1212

We present optical and X-ray spectra of a radio-quiet X-ray selected AGN, RX J1042+1212 ($z$=0.271). The Halpha and Hbeta emission lines are very broad (with full widths at half maximum of ~10000 km s-1) and have double-peaked profiles. Such features are rarely observed in AGN in general but are even more unusual in radio-quiet objects. The analysis of the ROSAT PSPC data reveals a non-varying, unabsorbed spectrum with an energy spectral index, alphax=1.2 and little or no emission from a soft X-ray excess. The slope of the optical spectrum is similar, alphaopt=1.0, and is consistent with an extrapolation of the X-ray spectrum, suggesting that the same power-law continuum may dominate throughout and that the big blue bump component is relatively weak. We look for a link between these various properties and investigate models of double-peaked Balmer line emission in AGN. An accretion disc origin is unlikely in RX J1042+1212 as this model predicts that lines emitted by a disc should have a net gravitational redshift (both Halpha and Hbeta have a net blueshift). Emission from two broad line regions, each gravitationally bound to one component of a supermassive black hole binary, is a possibility if the two components are similar in size and nature. Alternatively, the lines (or at least the narrow peaks of the lines) may be produced by a double-sided jet or bipolar flow.

The Soft X-ray Excesses Observed by ROSAT

The properties of the soft X-ray excesses of bright Seyfert 1 galaxies and Quasars are described using the observations obtained with the PSPC (0.1–2.4 keV) detector of the XRT telescope aboard ROSAT during the ROSAT all sky survey (RASS). The sample consists of 58 Seyfert 1 type AGN detected with more than 300 counts during the RASS and observed at least once with IUE.The soft X-ray photon indices of our sample members range from 1.6 to 3.4 in a wide distribution (&lt; Γ &gt; = 2.50, σ = 0.48). The width of the distribution is considerably larger than the mean statistical uncertainty on the individual spectral slopes (σ = 0.33). Excepting for IC 4329A and Mrk 766, the mean contribution of absorbing cold matter intrinsic to the Seyfert galaxies of our sample to the absorbing column density is less than 1020cm−2. In IC 4329A and Mrk 766 intrinsic absorbtion is observed at soft X-ray. Both sources are also strongly reddened by dust.An excess of soft X-ray flux is detected in 90% of the sources above the exptrapolation of the hard X-ray power law. It can be shown that the PSPC spectral slope is a measure of the strength of the soft X-ray excess. If the reddened sources are excluded, a correlation appears between the strength of the ultraviolet blue bump and the soft X-ray photon index (figure 1). The ratio of the ultraviolet to infrared fluxes and the ultraviolet spectral slope are also related to the strength of the blue bump. The observations are compatible with a model where most of the spectral variations arising among the sources studied are driven by the strength of the bump component, which varies by a factor of 100 from object to object. A bump model consisting of a power law with a high energy cutoff at 80 eV can fit most of the sources. In any case, the spectral energy distribution of the ultraviolet to soft X-ray bump is characterised by vFv(1375 Å) = (1–5) ∫ε &gt; 150eVFεdε.