* Astronomy

Members Login
Username 
 
Password 
    Remember Me  
Home -> Astronomy News -> Galaxies -> Ark 564
Post Info TOPIC: Ark 564
Blobrana


L

Posts: 131433
Date:
UGC 12163
Permalink  
 

Title: The high-Eddington NLS1 Ark 564 has the coolest corona
Author: E. Kara, J. A. Garcia, A. Lohfink, A. C. Fabian, C. S. Reynolds, F. Tombesi, D. R. Wilkins

Ark 564 is an archetypal Narrow line Seyfert 1 that has been well observed in soft X-rays from 0.3-10 keV, revealing a steep spectrum, strong soft excess, iron K emission line and dramatic variability on the order of hours. Because of its very steep spectrum, observations of the source above 10 keV have been sparse. We report here on the first NuSTAR observation of Ark 564. The source was observed for 200 ks with NuSTAR, 50 ks of which were concurrent with Suzaku observations. NuSTAR and Suzaku observed a dramatic flare, in which the hard emission is clearly delayed with respect to the soft emission, consistent with previous detections of a low-frequency hard lag found in XMM-Newton data. The NuSTAR spectrum is well described by a low-temperature Comptonisation continuum (with an electron temperature of 15 ± 2 keV), which irradiates a highly ionised disc. No further relativistic broadening or ionized absorption is required. These spectral results show that Ark 564 has one of the lowest temperature coronae observed by NuSTAR to date. We discuss possible reasons for low-temperature coronae in high-Eddington sources.

Read more (458kb, PDF)



__________________
Blobrana


L

Posts: 131433
Date:
RE: Ark 564
Permalink  
 

Title: Discovery of Relativistic Outflow in the Seyfert Galaxy Ark 564
Authors: A. Gupta, S. Mathur, Y. Krongold, F. Nicastro

We present Chandra high energy transmission grating spectra of the narrow-line Seyfert-1 galaxy Ark 564. The spectrum shows numerous absorption lines which are well modelled with low velocity outflow components usually observed in Seyfert galaxies (Gupta et al. 2013). There are, however, some residual absorption lines which are not accounted for by low-velocity outflows. Here we present identifications of the strongest lines as K{\alpha} transitions of OVII(two lines) and OVI at outflow velocities of ~0.1c. These lines are detected at 6.9{\sigma}, 6.2{\sigma}, and 4.7{\sigma} respectively and cannot be due to chance statistical fluctuations. Photoionisation models with ultra-high velocity components improves the spectral fit significantly, providing further support for the presence of relativistic outflow in this source. Without knowing the location of the absorber, its mass and energy outflow rates cannot be well constrained; we find E\dot{E}(outflow)/L_{bo} ranging from < 0.001% to 60% using different assumptions. This is the first time that absorption lines with ultra-high velocities are unambiguously detected in the soft X-ray band. The presence of outflows with relativistic velocities in AGNs with Seyfert-type luminosities is hard to understand and provides valuable constraints to models of AGN outflows.

Read more (83kb, PDF)



__________________
Blobrana


L

Posts: 131433
Date:
Permalink  
 

Title: A Two-Phase Low-velocity Outflow in the Seyfert 1 Galaxy Ark~564
Authors: A. Gupta, S. Mathur, Y. Krongold, F. Nicastro

The Seyfert 1 galaxy Ark 564 was observed with Chandra high energy transmission gratings for 250 ks. We present the high resolution X-ray spectrum that shows several associated absorption lines. The photoionisation model requires two warm absorbers with two different ionisation states (logU=0.39±0.03 and logU=-0.99±0.13), both with moderate outflow velocities (~100 km s^-1) and relatively low line of sight column densities (logNH=20.94 and 20.11 cm^-2). The high ionisation phase produces absorption lines of OVII, OVIII, NeIX, NeX, MgXI, FeXVII and FeXVIII while the low ionisation phase produces lines at lower energies (OVI & OVII). The pressure--temperature equilibrium curve for the Ark 564 absorber does not have the typical "S" shape, even if the metallicity is super-solar; as a result the two warm-absorber phases do not appear to be in pressure balance. This suggests that the continuum incident on the absorbing gas is perhaps different from the observed continuum. We also estimated the mass outflow rate and the associated kinetic energy and find it to be at most 0.006% of the bolometric luminosity of Ark~564. Thus it is highly unlikely that these outflows provide significant feedback required by the galaxy formation models.

Read more (187kb, PDF)



__________________
Blobrana


L

Posts: 131433
Date:
Permalink  
 

Title: Spectral Optical Monitoring of the Narrow Line Seyfert 1 galaxy Ark 564
Authors: A.I. Shapovalova, L.C. Popovic, A.N. Burenkov, V.H. Chavushyan, D. Ilic, A. Kovacevic, W. Kollatschny, J. Kovacevic, N.G. Bochkarev, J.R. Valdes, J. Torrealba, J. Leon-Tavares, A. Mercado, E. Benitez, L. Carrasco, D. Dultzin, E. de la Fuente

We present the results of a long-term (1999--2010) spectral optical monitoring campaign of the active galactic nucleus (AGN) Ark 564, which shows a strong Fe II line emission in the optical. This AGN is a narrow line Seyfert 1 (NLS1) galaxies, a group of AGNs with specific spectral characteristics. We analyse the light curves of the permitted Ha, Hb, optical Fe II line fluxes, and the continuum flux in order to search for a time lag between them. Additionally, in order to estimate the contribution of iron lines from different multiplets, we fit the Hb and Fe II lines with a sum of Gaussian components. We found that during the monitoring period the spectral variation (F_max/F_min) of Ark 564 was between 1.5 for Ha to 1.8 for the Fe II lines. The correlation between the Fe II and Hb flux variations is of higher significance than that of Ha and Hb (whose correlation is almost absent). The permitted-line profiles are Lorentzian-like, and did not change shape during the monitoring period. We investigated, in detail, the optical Fe II emission and found different degrees of correlation between the Fe II emission arising from different spectral multiplets and the continuum flux. The relatively weak and different degrees of correlations between permitted lines and continuum fluxes indicate a rather complex source of ionisation of the broad line emission region.

Read more (204kb, PDF)



__________________
Page 1 of 1  sorted by
 
Quick Reply

Please log in to post quick replies.
Home -> Astronomy News -> Galaxies -> Ark 564


Create your own FREE Forum
Report Abuse 		Powered by ActiveBoard