• F. C. Odo

      Articles written in Journal of Astrophysics and Astronomy

    • Relativistic Beaming and Orientation Effects in BL Lacertae Objects

      F. C. Odo A. A. Ubachukwu A. E. Chukwude

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      We use the correlation between the core-to-lobe radio luminosity ratio (𝑅) and the linear size (𝐷) of a sample of BL Lacertae objects to investigate the relativistic beaming and radio source orientation paradigm for high peaked and low-peaked BL Lacs (X-ray and radio selected BL Lacs respectively) and to constrain relativistic beaming model for this extreme class of active galactic nuclei. We show that the 𝑅 - 𝐷 distributions of the BL Lac populations contradict blazar orientation sequence, with the X-ray selected BL Lacs (XBLs) being more consistent with the beaming and orientation model. On the premise that Fanaroff-Riley Type I radio galaxies are the unbeamed parent population of these objects, we derive the bulk Lorentz factor of the jets, 𝛾 ∼ 7-20 corresponding to a critical cone angle for optimum boosting, 𝜙c of ∼ 1° - 4°, while on average, these objects are inclined at 5° - 12° to the line-of-sight. The implications of these results for the blazar unification sequence are discussed.

    • On the Absence of Core Luminosity–Core-Dominance Parameter (𝑃C - 𝑅) Correlation in Radio Galaxies and BL Lacs

      J. A. Alhassan A. A. Ubachukwu F. C. Odo

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      We have presented an alternative interpretation for the absence of correlation in the relationship between the core radio power (𝑃C) and core-dominance parameter (𝑅) for a sample of BL Lacs and radio galaxies found in Fan & Zhang (Astron. Astrophys. 407, 899 (2003)). This is contrary to the predictions of the relativistic beaming and radio source orientation models in which the core luminosity is expected to be Doppler-boosted relative to the extended luminosity which is generally assumed to be isotropic. Our analysis of the 𝑃C - 𝑅 data indicates a strong luminosity selection effect (reminiscent of bright source samples due to Malmquist bias) in the sample. In particular, we showed that a strong 𝑃C - 𝑅 correlation exists above some redshift cut-off which may correspond to the flux limit of the sample used.

    • On Asymmetries in Powerful Radio Sources and the Quasar/Galaxy Unification

      C. I. Onah A. A. Ubachukwu F. C. Odo

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      We utilize the distributions of fractional separation difference (𝑥) as asymmetry parameter, linear size (𝐷) and core-to lobe luminosity ratio (𝑅) as orientation indicators, to investigate a consequence of radio source orientation and relativistic beaming effects in a sample of powerful non-symmetric extragalactic radio sources. In this scenario, radio sources viewed at small orientation angles to the line-of-sight are expected to show a high degree of asymmetry in observed radio structures due to relativistic beaming, with foreshortened projected linear sizes. A simple consequence of this is the 𝑥 - 𝐷 anti-correlation. Results show a tight correlation (𝑟 > 0.8) between the total and core radio luminosities and a clear 𝑥 - 𝐷 anti-correlation (𝑟 ∼ -0.5). The observed 𝑥 - 𝐷 anti-correlation is consistent with average orientation angle 𝜙 ≈ 48° and a maximum Lorentz factor 𝛾 ∼ 2 for the sample, with minimum angular separation of 26° between radio galaxies and quasars. However, there is no clear 𝑥 - 𝑅 correlation. While the results are consistent with quasar/galaxy unification via orientation, intrinsic asymmetry also seems to play a major role.

    • On the unified scheme for high-excitation galaxies and quasars in 3CRR sample


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      In this paper, we use the distributions of luminosity ($P$) and radio size ($D$) to re-examine the consistency of the unified scheme of high-excitation radio galaxies and quasars in the recently updated 3CRR sample. Based on a standard cosmology, we derive theoretically and show from observed data, the luminosity limit above which the 3CRR objects are well-sampled. We find, on average, a quasar fraction $\sim$0.44 and galaxy-to-quasar size ratio $\approx$2. Assuming a relativistic outflow of jet materials, we find a mean angle to the line of sight in the range 35$^{\circ} \leq \phi \leq 44^{\circ}$ for the quasars. On supposition of luminosity and orientation-dependent linear size evolution, expressed in a general functional form $D_{\rm (P,z,\phi)} \approx P^{\pm q}(1+z)^{−w} \sin \phi$, we show that above the flux detection threshold of the 3CRR sample, high-excitation galaxies and quasars undergo similar evolutionwith $q = −0.5$; $w = −0.27$ and luminosity independent evolution parameter $x = 2.27$, when orientation effect is accounted for. The results are consistent with orientation-based unified scheme for radio galaxies and quasars.

    • On the unified view of gamma-ray energy distribution of BL Lac objects and flat spectrum radio quasars

      F. C. ODO B. E. AROH

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      We study the distributions of $\gamma$-ray properties of a sample of $\gamma$-ray loud blazars taken from the third catalogue of blazars detected by Fermi-Large Area Telescope (Fermi-LAT).We compute the $\gamma$-ray dominance ($D_{\rm g}$) of the sample which includes 415 flat spectrum radio quasars (FSRQs) and 535 BL Lacertae objects (BL Lacs). We find that BL Lacs and FSRQs are highly dominated by $\gamma$-ray emission, which is consistent with diffuse high-energy neutrino flux associated with $\gamma$-ray loud blazars. The $\gamma$-ray dominance fairly scales with $\gamma$-ray luminosity ($r \sim +0.5$) in both BL Lacs and FSRQs, but shows little or no correlation ($r \leq 0.2$) with radio luminosity in either sample. BL Lacs and FSRQs occupy separate and parallel regions on the $D_{\rm g}$-luminosity plane. There is a fairly significant correlation ($r \sim 0.5$) between $\gamma$-ray dominance and frequency at synchrotron peak ($\nu_{\rm pk}$) in BL Lacs, which disappears in FSRQs. On the other hand, there is a tight correlation ($r \geq +0.8$) between $\gamma$-ray and radio luminosity with a smooth transition from BL Lacs at low luminosities to FSRQs at high luminosities. Nevertheless, the presence of few BL Lac-like FSRQs is noted. These results suggest that while there may be intrinsic differences between BL Lacs and FSRQs, some form of a unified scheme can also be relevant.

    • On the unified view of extragalactic sources based on their broadband emission properties

      E. U. IYIDA I. O. EYA F. C. ODO

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      Our understanding of the unification of jetted active galactic nuclei (AGNs) has advanced greatly as the size of extragalactic sources increased. In this paper, based on the large sample of radio sources, we compiled 680 blazars (279 flat spectrum radio quasars (FSRQs) and 401 BL Lacertae (BL Lacs)) from the 3FGL sample and 64 Seyfert galaxies (3 Narrow-line, 34 and 27 regular Seyfert 1 and Seyfert 2 respectively) from the INTEGRAL/IBIS survey to statistically test the relationship between Seyfert galaxies and the blazar samples of FSRQs and BL Lacs. We compute the synchrotron (SS), Compton (CS) and inverse Compton (IC) continuous spectra from the low energy components of radio to X-ray, radio to $\gamma$-ray and the high energy component of X-ray to $\gamma$-ray bands, respectively. Results show from the distributions of the continuous spectra that Seyfert galaxies form the tail of the distributions, suggestive of similar underlying history and evolution. A two-sampleKolmogorov–Smirnov (K–S) test of the continuous spectra showed that Seyfert galaxies differ from BL Lacs and FSRQs in the low energy components of the spectra, while there is no clear difference between them in the high energy component, which implies that high energy emissions in Seyfert galaxies, BL Lacs and FSRQs may be as a result of the same emission mechanism. There is a regular sequence of the distributions on SS–CS and IC–CS planes in each individual subsample. Linear regression analyses of our sample yield significant positive correlations ($r \geq 0.60$) between SS–CS and IC–CS data. This upturns into an anti-correlation ($r > -0.60$) in IC–SS data. These results are not only consistent with unified scheme for blazars but also show that Seyfertgalaxies can be unified with the classical radio-loud AGNs counterparts.

  • Journal of Astrophysics and Astronomy | News

    • Continuous Article Publication

      Posted on January 27, 2016

      Since January 2016, the Journal of Astrophysics and Astronomy has moved to Continuous Article Publishing (CAP) mode. This means that each accepted article is being published immediately online with DOI and article citation ID with starting page number 1. Articles are also visible in Web of Science immediately. All these have helped shorten the publication time and have improved the visibility of the articles.

    • Editorial Note on Continuous Article Publication

      Posted on July 25, 2019

      Click here for Editorial Note on CAP Mode

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