The gamma-ray emitting radio-loud narrow-line Seyfert 1 galaxy PKS 2004−447

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Citation of Original Publication

The gamma-ray emitting radio-loud narrow-line Seyfert 1 galaxy PKS 2004−447 - I. The X-ray View A. Kreikenbohm, R. Schulz, M. Kadler, J. Wilms, A. Markowitz, C. S. Chang, B. Carpenter, D. Elsässer, N. Gehrels, K. Mannheim, C. Müller, R. Ojha, E. Ros and J. Trüstedt A&A, 585 (2016) A91 DOI:


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As part of the TANAMI multiwavelength progam, we discuss new X-ray observations of the γ-ray and radio-loud narrow line Seyfert 1 galaxy (γ-NLS1) PKS 2004−447. The active galaxy is a member of a small sample of radio-loud NLS1s detected in γ-rays by the Fermi Large Area Telescope. It stands out for being the radio-loudest and the only southern-hemisphere source in this sample. We present results from our X-ray monitoring program comprised of Swift snapshot observations from 2012 through 2014 and two new X-ray observations with XMM-Newton in 2012. Supplemented by archival data from 2004 and 2011, our data set allows for a careful analysis of the X-ray spectrum and variability of this peculiar source. The (0.5–10) keV spectrum is described well by a power law (Γ ~ 1.6), which can be interpreted as non-thermal emission from a relativistic jet. The source exhibits moderate flux variability on timescales of both months and years. Correlated brightness variations in the (0.5–2) keV and (2–10) keV bands are explained by a single variable spectral component, such as the one from the jet. A possible soft excess seen in the data from 2004 cannot be confirmed by the new XMM-Newton observations taken during low-flux states. Any contribution to the total flux in 2004 is less than 20% of the power-law component. The (0.5–10) keV luminosities of PKS 2004−447 are in the range of (0.5−2.7) × 10⁴⁴ erg s⁻¹. A comparison of the X-ray properties among the known γ-NLS1 galaxies shows that in four out of five cases the X-ray spectrum is dominated by a flat power law without intrinsic absorption. These objects are moderately variable in their brightness, while spectral variability is observed in at least two sources. The major difference across the X-ray spectra of γ-NLS1s is the luminosity, which spans a range of almost two orders of magnitude from 10⁴⁴ erg s⁻¹ to 10⁴⁶ erg s⁻¹ in the (0.5–10) keV band.