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

Abstract

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) × 10 44 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 10 44 erg s −1 to 10 46 erg s −1 in the (0.5-10) keV band.

A Panchromatic View of Relativistic Jets in Narrow-Line Seyfert 1 Galaxies

“…On the contrary, a relatively hard X-ray spectrum was detected in the Swift/XRT observations of SBS 0846+513 [12,21], PMN J0948+0022 [22,23,29], 1H 0323+342 [24], PKS 1502+036 [25,30], and PKS 2004−447 [31,32]. This suggests a significant contribution of inverse Compton radiation from a relativistic jet in X-rays, similar to what is found for FSRQ (e.g., [33]).…”

“…On the contrary, the X-ray spectra of PKS 2004−447 collected in May and October 2012 are well reproduced by a single power-law with a hard photon index (Γ X ∼1.7) and no significant soft X-ray excess [31,32]. The XMM-Newton spectrum of PKS 1502+036 collected in 2012 was quite well fit by a simple power-law model, although some residuals are observed at low and high energies.…”

Multi-wavelength properties of radio-loud Narrow-line Seyfert 1 galaxies

“…Deep X-ray spectroscopy with the X-ray observatories XMM-Newton, Suzaku, and NuSTAR of selected sources has revealed that most radio-loud NLS1 galaxies studied thus far show significant soft X-ray emission components, that are most plausibly related to the accretion disc (e.g., [50], [36], [58], [29], [114], [110], [147], [54], [89], [85], [55], [91]; Fig. 4b), but apparently absent in a few cases, at least at some epochs (PKS2004-447: [110], [83]; SDSSJ2118-0732: [146]).…”

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

“…The observations reported in this series were conducted as part of the TANAMI 2 multiwavelength programme (Ojha et al 2010;Kadler et al 2015) that monitors γ-ray loud AGNs south of −30 • declination. In a separate paper (Kreikenbohm et al 2016, hereafter Paper I), we discussed X-ray observations with XMM-Newton and Swift, finding a flat blazar-like power law and moderate variability on time scales down to months with an observed luminosity of (0.7-2.6) ×10 44 erg/s. In this paper, we present the first Very-Long-Baseline Interferometry (VLBI) image for PKS 2004−447 at 8.4 GHz (the highest radio frequency VLBI image of the source in the literature so far), as well as the first long-term simultaneous multi-frequency radio monitoring with ATCA.…”