Long-Term X-ray Spectral Variability of AGN

Transcription

1 Long-Term X-ray Spectral Variability of AGN Sam Connolly Ian McHardy, Chris Skipper, Dimitrios Emmanoulopoulos, Tom Dwelly University of Southampton Jet Triggering Mechanisms in Black Hole Sources TIFR, Mumbai 2016

2 Active Galactic Nuclei: X-Ray Emission Flux = Log Flu AE -Γ x Log Energy X- Rays X-Ray Corona (electrons) UV/Optical Accretion Disc Black Hole

3 Softer when Brighter AGN Photon Index Flux (2-10 kev, erg cm -2 s -1 ) Sobolewska & Papadakis 2009 Positive correlation between photon index and accretion rate Higher accretion rate leads to greater supply of optical seed photons, cooling the corona and increasing the photon index.

4 Black Hole X-ray Binaries Photon Index Wu & Gu 2008 Log L X ( kev) / L Softer when brighter at high Eddington ratio Harder when brighter at low Eddington ratio

5 Harder when Brighter Behaviour in Samples of AGN Gu & Cao 2009 Photon Index Photon Index Log L Bol / L edd (L bol /L X = 16) Constantin et al Shemmer et al. Log L Bol / 2006 L

6 NGC 7213 Harder when brighter behaviour in a single AGN Hardness Ratio (5-10/2-4 kev) Photon Index Cout Rate (2-10 kev, counts Flux (2-10 kev, x erg cm -2 s -1 ) s -1 ) Only previous example of this behaviour in a single AGN Emmanoulopoulos et al. 2012

7 Swift/Palomar AGN: Hardness Ratios Hardness Ratio Hard Count Rate 24 Swift AGN taken from the Palomar Sample Connolly et al (submitted)

8 Swift/Palomar AGN: Hardness Ratios Hardness Ratio Hard Count Rate 24 Swift AGN taken from the Palomar Sample Connolly et al (submitted)

9 Swift/Palomar AGN: Hardness Ratios Hardness Ratio Hard Count Rate 24 Swift AGN taken from the Palomar Sample Connolly et al (submitted)

10 Swift/Palomar AGN: Hardness Ratios Hardness Ratio Hard Count Rate 24 Swift AGN taken from the Palomar Sample Connolly et al (submitted)

11 Photon Index-Luminosity Correlations Photon Index Flux (2-10 kev, x erg cm -2 s -1 ) 12 Swift AGN with sufficient data for flux-binned spectral fitting Connolly et al (submitted)

12 Comparison to accretion rate Photon Index Log L X, (2-10 kev) / L Data compared to the fitx of Constantin and Shemmer to samples of LLAGN Connolly et al (submitted)

13 Harder when Brighter Behaviour in Samples of AGN Gu & Cao 2009 Photon Index Photon Index Log L Bol / L edd (L bol /L X = 16) Constantin et al Shemmer et al. Log L Bol / 2006 L

14 Comparison to accretion rate Photon Index Log L X, (2-10 kev) / L Data compared to the fitx of Constantin and Shemmer to samples of LLAGN Connolly et al (submitted)

15 Advection Dominated Accretion Flow X-Rays X-Ray Corona UV/Optical Accretion Disc Black Hole

16 Advection Dominated Accretion Flow X-Rays X-Ray Corona UV/Optical Accretion Disc Black Hole ADAF

17 Advection Dominated Accretion Flow ADAF models predict harder-when-brighter behaviour (e.g. Esin et al. 1997) Increase in accretion rate injects energy into e - population in the ADAF This leads to more high-energy synchrotron/bremsstrahlung seed photons and a harder Compton-scattered X-ray spectrum

18 Jets: Harder-when-Brighter Behaviour in Blazars 1ES , Krawczynski Photon Index Count Rate (10 kev, kev -1 cm -2 s -1 ) Synchrotron Self-Compton leads to an anticorrelation between accretion rate and photon index LLAGN much weaker, unlikely to be main cause of spectral behaviour

19 Absorption Driven Variability Many AGN are known to have highly variable absorption (e.g. NGC 1365, NGC 4395, Mkn 335 Risaliti et al 2002, 2013, Iwasawa 2005)

20 Absorption Driven Variability Many AGN are known to have highly variable absorption (e.g. NGC 1365, NGC 4395, Mkn 335 Risaliti et al 2002, 2013, Iwasawa 2005) Most previous spectral studies concentrate on shorttimescale changes, caused by local variations in absorption, as opposed to global changes

21 Absorption Driven Variability Many AGN are known to have highly variable absorption (e.g. NGC 1365, NGC 4395, Mkn 335 Risaliti et al 2002, 2013, Iwasawa 2005) Most previous spectral studies concentrate on shorttimescale changes, caused by local variations in absorption, as opposed to global changes The Swift archive contains long-term spectral data on many AGN

22 AGN Geometry Based on Urry & Padovani 1995

23 AGN Geometry Based on Urry & Padovani 1995 & Elvis 2000

24 NGC 1365 Long-Term kev Swift Lightcurve NGC 1365 Mkn 335 LX /L MJD Each data point is a separate Swift spectrum

25 NGC 1365 Long-Term kev Swift Lightcurve Hardness Ratio (H-S/H+S) NGC 1365 Mkn 335 MJD Each data point is a separate Swift spectrum

26 NGC 1365 Hardness Ratio vs flux SOFT Hardness Ratio HARD HARD Count Rate Softens at the highest fluxes, as commonly seen in the 2-10 kev band Hardens rapidly at very low fluxes, not previously seen in AGN: - Previously seen in an XRB (Kulkers 1998) Connolly et al. 2014, 2015

27 NGC 1365 Spectral Variability Low Flux Spectrum Simple power law Excess at high energies

28 NGC 1365 Spectral Variability High Flux Spectrum Absorbed power law combined with a weaker unabsorbed component

29 NGC 1365 Spectral Variability

30 NGC 1365 Spectral Variability

31 NGC 1365 Spectral Variability

32 NGC 1365 Spectral Variability

33 NGC 1365 Spectral Variability

34 NGC 1365 Spectral Variability

35 Spectral Modelling Connolly et al Assuming a constant spectral index, the best fitting model has 2- components: 1) Lower luminosity, unabsorbed power law 2) Higher luminosity, absorbed power law, for which N H varies inversely with luminosity Varying Γ gives a similar fit, however the range in Γ is much larger than expected from Comptonisation models ( ). Variation cannot be due to ionisation only

36 Normalisation of Absorbed Powerlaw vs Absorbing Column Connolly et al Absorbing column decreases as normalisation of absorbed power law increases Pearson s rank order value 0.98 Absorbed power law normalisation intrinsic luminosity

37 Normalisations of Absorbed vs Unabsorbed components Connolly et al Strong correlation, approximately linear relationship

38 Elvis wind model (2000) The wind launch radius higher for greater luminosities Launch angle smaller for greater luminosities Depending on inclination, absorbing material could move out of the line of sight at higher luminosities.

39 Elvis wind model (2000) The wind launch radius higher for greater luminosities Launch angle smaller for greater luminosities Depending on inclination, absorbing material could move out of the line of sight at higher luminosities.

40 Mkn 335 Spectral Variability

41 Mkn 335 Spectral Variability

42 Mkn 335 Spectral Variability

43 Mkn 335 Spectral Variability

44 The Varying Wind Model

45 The Varying Wind Model

46 Conclusions The long-term spectral variability of NGC 1365 is best described by a changing absorbing column negatively correlated with luminosity This might be explained by an absorbing wind whose launch radius increases with increasing luminosity. Mkn 335 may show similar behaviour at low luminosities. 18 new LLAGN found to be harder when brighter At least 5 show a Γ-luminosity anticorrelation Could be caused by ADAF and/or Jets Supports the theory that LLAGN are analogous to the low-hard state in BHXRBs For more info see Connolly et al. 2014, 2015 (submitted):