Origin of X-rays in blazars

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1 Origin of X-rays in blazars Greg Madejski, Stanford / KIPAC With much of the work presented here done by Amy Furniss, Masaaki Hayashida, Krzysztof Nalewajko, Marek Sikora, Jim Chiang, David Paneque, Mislav Balokovic, Francesco Borracci, Koji Noda, Gianpiero Tagliaferri, Tulia Sbarrato,

2 Two kinds of blazars Very coarsely, there are two general classes of blazars: Low-luminosity, w/ the two broad SED peaks at higher energies (UV/X-rays, & VHE γ-rays) High luminosity, with two SED peaks at lower energies (mm/ir, & MeV range) EXAMPLES: HBL blazar BL Lac object C454.3 blazar that flared (et al. and Horan 2009, Fermi coll. Paper) early in Fermi days (Abdo et al 2012)

3 Pre-Fermi view of Origin of X-rays in HBL (BL-Lac type) blazars X-rays are likely produced via synchrotron process, by the most energetic tail of the radiating particles The X-ray spectrum evolves in a predictable and expected manner (Takahashi et al. 96) This picture generally holds in the Fermi era, but with many updates owing to NuSTAR - more details in a few min SED of HBL-type blazar Mkn 421 (Macomb et al. 1995)

4 X-rays from FSRQ blazars in the EGRET era: archetypal GeV blazar 3C279 in 1996 (Data from Wehrle et al. 1998) * Correlated variability on day time scales is common (but poor sampling!) X-rays are just low energy tail of the inverse Compton emission peak - Probably incorrect

5 Two new kids on the block: Fermi and NuSTAR FERMI / LAT: Wide field of view allows monitoring of ~ 2 steradians of the sky Fermi-GLAST always points away from the Earth (good duty cycle) Energy range is ~ GeV, with the peak effective area of ~ 10,000 cm 2 - allows an overlap with TeV observatories; energy resolution is about 10% MOTIVATES MANY MULTI-BAND CAMPAIGNS!

6 Launched June 13, 2012 Focusing high energy X-ray telescope (3-79 kev) Low background ~100X sensitivity improvement over other instruments in this bandpass Harrison et al. 2013, ApJ, 770, 103 probe obscured AGN study the population of Galactic hard X-ray-emitting compact objects study the non-thermal radiation in young supernova remnants core-collapse supernovae in the Local Group observe blazars contemporaneously with ground-based radio, optical, and TeV telescopes, as well as with Fermi and Swift, to constrain the structure of AGN jets

7 HBL-type Blazars Observed by NuSTAR Generally in the context of MW campaigns NuSTAR MAGIC/VERITAS/HESS Swift Fermi Large Area Telescope Optical instruments OVRO/Metzahovi/f-Gamma Mrk 421 1ES PKS ES Mrk 501 (here Furniss et al. 2015)... Example of Swift and NuSTAR data for Mkn 501 (z = 0.03): Able to reconstruct full synchrotron peak with Swift XRT simultaneous observations: X-ray spectrum not a simple power law

8 Mkn 501: Finer temporal resolution VERITAS MAGIC Fermi NuSTAR Swift Optical F-GAMMA

9 Mkn 501 X-ray vs. VHE variability 10 simultaneous VHE/NuSTAR observations Thomson regime SSC emission predicts quadratic relationship between X-ray and VHE band SSC in Klein-Nishina regime predicts linear relationship between X-ray and VHE band Quadratic fit to the data is better than a linear fit based on χ 2 minimization

10 Mkn 421 (NuSTAR Fermi, optical, VHE γ-rays) Work in progress (Balokovic et al. 2015, but the X-ray TeV analysis suggests indicates linear correlation the scattering is likely in the Klein-Nishina regime in contrast to Mkn 501

11 First results for the Mkn 421 campaign Balokovic et al OBSERVATIONAL RESULTS (cont d): Spectrum variable: generally hardens as the source brightens Hard X-ray spectrum is gradually steepening power law (e-distribution?) NOT exp. cutoff No hard X-ray tail in NuSTAR (no onset of IC comp.) SUMMARY of X-ray related inferences for HBLs: The X-rays are the tail of the synchrotron emission picture seems to hold OK - But the new insight is that we don t see yet the cutoff of γ el distribution (> 10 6?) Future: analysis of the big 2013 flare in Mkn 421 (Furniss et al. 2016) 11

12 Switching gears to FSRQs: 3C 279 s light curve for 6 years - Aug. 08-Aug 14 >100 MeV"

13 Multi-band variability in Fermi days * Fermi motivates terrific multi-band light curves Search for coincidences / delays amongst various bands: optical and γ-rays closely correlated * Very important new hint: rotation of optical polarization angle, seen in BL Lac (Marscher), but clearly associated with the γ-ray flare in 3C279 (Abdo+ 2010; Hayashida+ 2012): 180 o in 20 days * Rotation of polarization angle: clear departure from simple axi-symmetry one possibility a curved jet - a quivering jet, presumably unstable, or jittered at its base (near the disk) might work as well Simplest but not unique interpretation: compact region containing accelerated particles propagates with jet s Lorentz factor Γ, the dissipation over a distance along the jet r = Γ 2 c Δt This is a large distance! parsecs from the black hole! Opt/γ-ray correlation clear, but X-rays not clearly correlated with any other band! Nature, vol436, 887 (2010) A.Young Γ jet Γ jet

14 Recent (2013/14) 3C279 multi-band light curve (A)! (B)"(C)! (D)" (A) and (C) are! with NuSTAR! R-band" SMARTS, Kanata" Swift-UVOT (V)" Pol. degree" Pol. angle" (R-band)" 120" PA 60" [deg]" 0" Kanata"

15 3C279 NuSTAR Spectrum * Important new result from joint fits of Swift and NuSTAR X-ray data: X-ray spectrum is not a simple power law * No simple explanation yet, but is this a signature of the low-e cutoff of electron energy distribution?

16 3C279 SED & conclusions - X-rays are not time-correlated with other bands!! - Swift+NuSTAR X-ray spectrum not a simple power law, gets softer with energy - X-ray spectrum does not extend into the γ-ray regime! - Does not look like the same component as γ-ray peak! - Could it be inverse Compton on the internal jet photons (=SSC)?! ""

17 Bright Swift-BAT blazars PKS and S Both were selected as NuSTAR targets because: Swift-BAT sources -> guaranteed high quality NuSTAR spectra Fermi-band emitters allowing broad broad-band modelling Located at an appreciable redshift (z > 2) At those redshifts, the syn & IC peaks move left NuSTAR samples rising part of the IC peak -> bright; Fermi LAT fainter One of the goals is to assess their contribution to the E>30 kev Cosmic X-ray Background Since blazars are variable on all timescales to study spectral variability we secured two ~40 ks NuSTAR snapshots for each for each source Optical data from REM were secured to be contemporaneous Paper led by Gianpiero Tagliaferri, Fermi data reduction by Masaaki

18 Fermi results: the light curves and spectra Fermi analysis done in a standard manner by Masaaki Hayashida, in similarity to the procedure for 3C279 OBSERVATIONAL RESULTS: Both sources reasonably bright, average flux ~ a few x 10-7 (E>100 MeV) Both sources are clearly variable in the γ-ray band 1-yr LAT indices somewhat softer than Γ=2.5 Each blazar was observed by NuSTAR twice marked with vertical lines LAT spectra consistent with power laws, 1-week spectra consistent w/1yr spectra 18

19 X-ray spectra from NuSTAR + Swift No rapid variability within each observation, but clear variability between observations (1 month & 4 months) Since the sources and spectra are variable, an accurate full-band X-ray spectrum requires simultaneous observations with NuSTAR + soft X-ray telescopes (Swift) Again a similar result to 3C279: spectra better described by a broken power-law model, softening towards higher energies 19

20 X-ray spectra in the context of previous observations X-ray spectra in the context of previous observations: clearly there is flux and X-ray spectral variability 20

21 Broad-band SEDs and modelling Modelling done with the standard Syn + External Radiation Compton models of Tavecchio & Ghisellini * Inferred values of Lorentz factors, ~ 15, agree with the previous estimates * Location of the dissipation region appears to be outside of the Broad Line Region but inside the IR-producing molecular torus Adding UVOT data allows estimate of the BH mass (both are ~ 4 x 10 9 M o ), L/L Edd ~ 0.3 It is possible to estimate the power of the jet vis-à-vis the accretion disk As is the case for 3C279: jet power is considerable, close to the power delivered via accretion

22 Life at high redshift: blazar B Quite high redshift! z ~ 5.2 Adding NuSTAR data strongly supports the blazar nature of the object Clear emission lines, allow an estimate of the isotropic luminosity, BH mass Synchrotron + IC modelling Implies Γ ~ 10

23 B : Conclusions The NuSTAR observations confirm that B is blazar, although with properties somewhat different than expected before: bent, or wiggling jet? Strong implications on cosmology (Γ 2 argument) ~ hundreds of black holes with mass ~ 10 9 M o so early on in the history of the Universe problem for evolution of BH?

24 Summary and new insights In Mkn 421, the X-ray TeV analysis suggests that the scattering is in the Klein-Nishina regime in contrast to Mkn 501 (bottom, where it is in Thomson regime 3C279 MW light curve Mkn 421: linear is better fit Origin of X-rays? Mkn 501: Quadratic appears to be a better fit