Time Lags in Narrow-Line Seyfert 1 Galaxies and the Origin of Their Soft Excess Emission (original) (raw)

On the origin of the featureless soft X-ray excess emission from the Seyfert 1 galaxy ESO 198-G24

Monthly Notices of the Royal Astronomical Society, 2014

We present medium and high resolution X-ray spectral study of a Seyfert 1 galaxy ESO 198-G24 using a long (∼ 122 ks) XMM-Newton observation performed in February 2006. The source has a prominent featureless soft X-ray excess below 2 keV. This makes the source well suited to investigate the origin of the soft excess. Two physical modelsblurred reflection, and optically thick thermal Comptonization in a warm plasma, describe the soft-excess equally well resulting in similar fits in the 0.3 − 10 keV band. These models also yield similar fits to the broad-band UV (Optical Monitor) and X-ray data. XMM-Newton observations performed in 2000, 2001 and 2006 on this source show flux variability. From 2001 to 2006, the UV flux increased by ∼ 23% while the 2 − 10 keV X-ray flux as well as the soft-excess flux decreased by ∼ 20%. This observation can be described in the blurred reflection scenario by a truncated accretion disk whose inner-most radius had come closer to the blackhole. We find that the best-fit inner radius of the accretion disk decreases from R in = 4.93 +1.12 −1.10 R G to R in < 2.5R G from 2001 to 2006. This leads to an increase in the UV flux and compressing the corona, leading to reduction of the powerlaw flux and therefore the soft-excess. The blurred reflection model seems to better describe the soft-excess for this source.

The contribution of narrow-line Seyfert 1 galaxies to the soft X-ray background

New Astronomy Reviews, 2000

T he contribution of N arrow-Line Seyfert 1 galaxies to the soft X-ray background G .H asi nger a I.Lehm ann a; b M .Schm i dt c J. E.G unn d D. P.Schnei der b R .G i acconi e J.Tr um per f G .Zam orani g a A strophysikal isches InstitutPotsdam ,A n der Sternwarte 16,D-14482 Potsdam , G erm any b D epartm ent ofA stronom y & A strophysics,525 D avey Lab,T he Pennsyl vania State U niversity,

Narrow-line Seyfert 1 galaxies at hard X-rays★

Monthly Notices of the Royal Astronomical Society, 2011

Narrow Line Seyfert 1 (NLSy1) galaxies are a peculiar class of type 1 AGN (BLSy1). The X-ray properties of individual objects belonging to this class are often extreme and associated with accretion at high Eddington ratios. Here we present a study on a sample of 14 NLSy1 galaxies selected at hard X-rays (> 20 keV) from the fourth INTEGRAL/IBIS catalogue. The 20-100 keV IBIS spectra show hard X-ray photon indeces flatly distributed (Γ 20−100keV ranging from ∼ 1.3 to ∼ 3.6) with an average value of <Γ 20−100keV > = 2.3±0.7, compatible with a sample of hard X-ray BLSy1 average slope. Instead, NLSy1 show steeper spectral indeces with respect to BLSy1 when broad-band spectra are considered. Indeed, we combine XMM-Newton and Swift/XRT with INTEGRAL/IBIS data sets to obtain a wide energy spectral coverage (0.3-100 keV). A constraint on the high energy cut-off and on the reflection component is achieved only in one source, Swift J2127.4+5654 (E cut−of f ∼ 50 keV, R=1.0 +0.5 −0.4 ). Hard X-ray selected NLSy1 do not display particularly strong soft excess emission, while absorption fully or partially covering the continuum is often measured as well as Fe line emission features. Variability is a common trait in this sample, both at X-ray and at hard X-rays. The fraction of NLSy1 in the hard X-ray sky is likely to be ∼ 15%, in agreement with estimates derived in optically selected NLSy1 samples. We confirm the association of NLSy1 with small black hole masses with a peak at 10 7 M ⊙ in the distribution, however hard X-ray NLSy1 seem to occupy the lower tail of the Eddington ratios distribution of classical NLSy1.

An absorption origin for the soft excess in Seyfert 1 active galactic nuclei

Monthly Notices of the Royal Astronomical Society, 2007

The soft excess seen in the X-ray spectra of many active galactic nuclei (AGN) can be well modelled by reflection from a partially ionized accretion disc. However, this often requires extreme parameters, both in terms of the underlying space-time and the reflection geometry, and requires that the disc is far from hydrostatic equilibrium. An alternative model uses similarly partially ionized, velocity smeared material but from an accretion disc wind seen in absorption. We explicitly compare these two models for the origin of the soft excess using XMM-Newton data for PG QSOs and narrow-line Seyfert 1 galaxies (NLS1s). We find that while reflection and absorption give comparably good fits to the data, the absorption model allows a much clearer correspondence with the stellar mass black holes. All the objects are high mass accretion rate AGN, so should be analogous to the high/soft and very high states in black hole binaries. The intrinsic spectral indices derived from the absorption model are all consistent with a oneto-one mapping between spectral state and AGN type, with the NLS1s having softer spectra corresponding to the very high state, while the broad-line AGN have = 2 as expected for the high/soft state. By contrast, a few AGN have intrinsically hard spectra with the reflection model. While this supports an absorption interpretation of the soft excess, we note that the required Gaussian velocity dispersion of 0.2c (corresponding to an outflow velocity 0.4c) is too fast for a radiatively driven accretion disc wind and instead requires that the material is entrained in a magnetic outflow (jet). We also use the simultaneous optical monitor data to derive the ratio of disc to total accretion power which is another tracer of spectral state in X-ray binaries. This does not always show that the disc in NLS1s contributes less than 80 per cent of the total power, as expected for a very high state. We suggest that this is an artefact of the standard disc models used to determine the disc luminosity in our fits. The disc seen in the very high state of black hole binaries is often observed to be distorted from the standard shape, and a similar effect in NLS1s could recover the one-to-one mapping between black hole binary spectral state and AGN type.

Extended hard-X-ray emission in the inner few parsecs of the Galaxy

Nature, 2015

The Galactic Centre hosts a puzzling stellar population in its inner few parsecs, with a high abundance of surprisingly young, relatively massive stars bound within the deep potential well of the central supermassive black hole, Sagittarius A* (ref. 1). Previous studies suggest that the population of objects emitting soft X-rays (less than 10 kiloelectronvolts) within the surrounding hundreds of parsecs, as well as the population responsible for unresolved X-ray emission extending along the Galactic plane, is dominated by accreting white dwarf systems 2-5. Observations of diffuse hard-X-ray (more than 10 kiloelectronvolts) emission in the inner 10 parsecs, however, have been hampered by the limited spatial resolution of previous instruments. Here we report the presence of a distinct hard-X-ray component within the central 4 3 8 parsecs, as revealed by subarcminute-resolution images in the 20-40 kiloelectronvolt range. This emission is more sharply peaked towards the Galactic Centre than is the surface brightness of the soft-X-ray population 5. This could indicate a significantly more massive population of accreting white dwarfs, large populations of lowmass X-ray binaries or millisecond pulsars, or particle outflows interacting with the surrounding radiation field, dense molecular material or magnetic fields. However, all these interpretations pose significant challenges to our understanding of stellar evolution, binary formation, and cosmic-ray production in the Galactic Centre. The Galactic Centre region is dense with X-ray-emitting objects 6 ; it contains the supernova remnant Sagittarius (Sgr) A East, the colliding stellar winds surrounding Sgr A*, the hot plasma of the Sgr A East plume, dozens of magnetic X-ray filaments, and thousands of resolved 7 and unresolved point sources that constitute the Galactic ridge X-ray emisison 3-5,8. In hard X-rays, the INTEGRAL satellite has detected emission centred within 19 of the Galactic Centre 9. However, the spatial resolution of INTEGRAL's IBIS coded aperture mask (129) has motivated speculation that the emission results not from a single object, but from a collection of the many surrounding X-ray sources 3. The NuSTAR X-ray observatory 10 , which has an effective area extending from 3 to 79 keV and an angular resolution of 180 (equivalent to 0.7 pc at the Galactic Centre), viewed the Galactic Centre for a total of 281 ks in July, August and October of 2012. The image of the central 12 pc 3 12 pc of the Galaxy (Fig. 1) in the 20-40 keV energy band reveals for the first time a faint diffuse emission that is peaked at the Galactic Centre and extends along the Galactic plane. The image is dominated by this feature, whose spectrum and localization within several parsecs of Sgr A* distinguish it from other unresolved X-ray emission in the Galaxy, and which has no obvious correlation with radio images of the dense molecular gas of the circumnuclear disk 11 or the dust and gas of Sgr A West 12. The features prominent in soft-X-ray images no longer visibly contribute, with the exception of bright pointlike emission from the pulsar wind nebula G359.9520.04 13 and fainter emission from the X-ray filament G359.9720.038 14 and the Cannonball 15 neutron star.

1H0419-577: a ``two-state'' soft X-ray Seyfert galaxy

Astronomy and Astrophysics, 1998

In this paper we report on the first simultaneous optical and X-ray (Beppo-SAX) observations of the radio-quiet AGN 1H0419-577. The optical spectrum clearly leads us to classify this source as a Seyfert 1. The X-ray spectrum is, however, somewhat at odds with this classification: a simple flat (Γ ∼ 1.55) and featureless power-law is a good description of the whole 1.8-40 keV spectrum, even if the upper limit to a broad iron line is not very tight. An analysis of a still unpublished ROSAT observation of the same target reveals that the soft X-ray spectrum has undergone a transition from a steep (Γ = 2.5) to a flat (Γ = 1.55) state, at least in the 0.7-2 keV band. If this difference is due to a remarkably variable soft excess, it is unlikely that a single component is responsible for the optical/UV/soft X-ray spectral distribution. The hypothesis that the difference is due to a change in the primary X-ray continuum and its implications for current Comptonization models are discussed.

XMM-Newton long-look observation of the narrow line Seyfert 1 galaxy PKS 0558-504

Astronomy and Astrophysics, 2010

Context. PKS 0558-504 has been observed repeatedly by XMM-Newton as a calibration and performance verification (PV) target.In this work, we present results from the spectral analysis of a long XMM-Newton observation of the radio loud Narrow Line Seyfert 1 galaxy PKS 0558-504. Aims. To study the soft excess component in this object, the spectral variations it exhibits in both the hard and soft X-ray bands, and their correlation. Methods. We used mainly the PN data, and we fitted various spectral models to the time average spectra of the individual orbits as well as the spectra from data segments of shorter duration. We also used the RGS data to search for signs of a warm absorber in the source. Results. The source is highly variable, on all sampled time scales. We did not observe any absorption features in either the soft or hard band. We found weak evidence for the presence of an iron line at ∼ 6.8 keV, which is indicative of emission from highly ionized iron. The 2-10 keV band spectrum of the source is well fitted by a simple power law model, whose slope steepens with increasing flux, similar to what is observed in other Seyferts as well. The soft excess is variable both in flux and shape, and it can be well described by a low-temperature Comptonisation model, whose slope flattens with increasing flux. Finally, the soft excess flux variations are moderately correlated with the hard band variations, and we found weak evidence that they are leading them by ∼ 20 ksec. Conclusions. Our results rule out a jet origin for the bulk of the X-ray emission in this object. We found no signals of a warm absorber. The observed hard band spectral variations suggest intrinsic continuum slope variations, caused by changes in the "heating/cooling" ratio of the hot corona. The low-temperature Comptonising medium, responsible for the soft excess emission, could be a hot layer in the inner disc of the source, which appears due to the fact that the source is accreting at a super-Eddington rate. The soft excess flux and spectral variations could be caused by random variations of the accretion rate.