Investigating the jet structure and its link with the location of the high-energy emitting region in radio-loud AGN

Transcription

1 Investigating the jet structure and its link with the location of the high-energy emitting region in radio-loud AGN Filippo D Ammando (INAF-IRA and DIFA Bologna) Monica Orienti (INAF-IRA) Marcello Giroletti (INAF-IRA) dammando@ira.inaf.it 1

2 Radio waves and gamma rays: an obvious couple synchrotron radio emission originates from relativistic electrons that can up-scatter photons to high energy: gamma-ray photon - leptonic models predict some connection between radio and gamma-ray emission low energy photon relativistic e - the blazar sequence was originally devised on the basis of the radio luminosity evidence or not of flux-flux, Lum-Lum correlations is a debated issue (e.g. Padovani et al. 1993, Stecker et al. 1993, Mücke et al. 1997, Ghirlanda et al. 2010) due to bias, variability, number of sources, etc. Donato et al. (2002) dammando@ira.inaf.it 2

3 EGRET Era Hartmann et al blazars detected by EGRET Mostly FSRQ (75% FSRQ, 25% BL Lacs) Only 3 tentative detections of radio galaxies: - Centaurus A - NGC 6251 (Mukherjee et al. 2002) - 3C 111 (Hartmann et al. 2008) Ghisellini et al dammando@ira.inaf.it 3

4 The Fermi Gamma-ray Space Telescope Large Area Telescope (LAT) 20% of the sky at any instant from 20 MeV to >300 GeV Gamma-ray Burst Monitor (GBM) entire unocculted sky transients from 8 kev to 40 MeV Launched from Cape Canaveral Air Station on 11 June 2008 nearly circular orbit 565 km, 25.6 dammando@ira.inaf.it 4

5 AGN in the Fermi Era 3 months LAT data 11 months LAT data 24 months LAT data Abdo et al Abdo et al Nolan et al dammando@ira.inaf.it 5

6 The Third LAT AGN Catalogue (3LAC) Ackermann et al. 2015, ApJ, 810, 14 BCU = Blazar candidates of uncertain type 48 months of LAT data 1591 (1444) sources with TS>25, b >10 (71% more than in 2LAC) 182 low-latitude AGN (24 FSRQ, 30 BL Lacs, 125 BCU, 3 non-blazar AGN) 467 FSRQ 632 BL Lacs 460 BCU (~50% new 3LAC sources) 32 non-blazar AGN dammando@ira.inaf.it 6

7 Cataloging Hard Sources Hard sources can be missed in the full-band catalog Angular resolution is very good Background is very low Source confusion mostly not an issue 3FGL 2FHL 7

8 New LAT > 10 GeV catalog 3FHL 3FHL 1556 sources at E >10 GeV in 84 months of Fermi-LAT data dammando@ira.inaf.it 8

9 The 3FHL Catalog 1556 sources: 79% extragalactic 8% Galactic 13% unassociated 1286 in 3FGL 133 in TeVCat 211 new sources (not in 1FHL/2FHL/3FGL/TeVCat) 16 with redshift > 2 dammando@ira.inaf.it 9

10 High-energy emission location WHERE? WHO? IR UV TORUS Sub-pc scale e.g. Ghisellini+98 UV from BLR BLR Sub-pc scale e.g. Sikora+09 Magnetic field reconnection pc scale IR from hot dust e.g. Sikora+09, Marscher+10 > 10 parsec e.g. Marscher 2012 Standing conical shock Credits: A. Marscher 10

11 PKS : a test case 2011 October 1-week time bins 2011 July dammando@ira.inaf.it 11

12 Multifrequency analysis of PKS Two major γ-ray flares were detected by Fermi-LAT in 2011 July and October rotation of about 380 of the optical polarization angle close in time with the 2011 July flare and no radio flare After 2011 September a huge radio outburst has been detected, first in the millimetre regime followed with some time delay at centimetre down to decimetre wavelengths. New jet component ejected Orienti, Koyama, D Ammando, et al. 2012, MNRAS, 428, 2418 dammando@ira.inaf.it 12

13 Time delays The shock scenario: Normalized at the 86-GHz values 1) growth stage at high frequencies, when the radiation is optically-thin; 2) plateau stage: the peak moves to lower frequencies but the maximum is almost constant; ) decay stage: the peak is lower w.r.t. the plateau stage dammando@ira.inaf.it 13

14 Multifrequency analysis of PKS Two major γ-ray flares were detected by Fermi-LAT in 2011 July and October rotation of about 380 of the optical polarization angle close in time with the 2011 July flare and no radio flare After 2011 September a huge radio outburst has been detected, first in the millimetre regime followed with some time delay at centimetre down to decimetre wavelengths. New jet component ejected Radio flare characterized by a rising and a decaying stage, in agreement with the formation of a shock and its evolution Orienti, Koyama, D Ammando, et al. 2012, MNRAS, 428, 2418 dammando@ira.inaf.it 14

15 The origin of the γ-ray emission The huge radio outburst detected since 2011 September reached its maximum in the millimeter close in time with the γ-ray flare of 2011 October, suggesting a common emitting region for these two events. If the onset of the mm flare is a consequence of a shock propagating along the jet, it turns out that the γ-ray emission may be on pc-scale distance from the central region : Δrproj ~ 0.6 pc Δtobs = 40 days βapp = 25.4c θ = 3 Δθ ~ 0.1 mas Δr ~ 10 pc This is consistent with what found by Marscher et al. (2010) for the γ-ray flare detected in 2009 March from the same source. dammando@ira.inaf.it 15

16 Multifrequency analysis of PKS Two major γ-ray flares were detected by Fermi-LAT in 2011 July and October rotation of about 380 of the optical polarization angle close in time with the 2011 July flare and no radio flare After 2011 September a huge radio outburst has been detected, first in the millimetre regime followed with some time delay at centimetre down to decimetre wavelengths. New jet component ejected Radio flare characterized by a rising and a decaying stage, in agreement with the formation of a shock and its evolution The July γ-ray flare may be due to the first perturbation occurring in the central region opaque to the radio emission. As it propagates it becomes visible at longer wavelengths. As it passes through a standing shock a second γ-ray flare is produced, while the shock becomes visible as a superluminal knot. Orienti, Koyama, D Ammando, et al. 2012, MNRAS, 428, 2418 dammando@ira.inaf.it 16

17 Parsec-scale jet kinematics of a sample of blazars Jorstad & Marscher analyzed the parsec-scale jet kinematics from 2007 June to 2013 January of a sample of γ-ray blazar with the VLBA at 43 GHz (52 prominent γ-ray flares and 240 features identified in the radio maps) 4C The γ-ray flares are contemporaneous with an increase of the flux in the 43 GHz VLBI core, which suggests that a disturbance propagating in the jet is necessary to produce a strong γ-ray event About 83% of the γ-ray flares occurred near the extrapolated time of the passage of superluminal knots through the VLBI core Approximately 65% of superluminal knots do not trigger prominent γ-ray events These results support the idea that the majority of strong γ-ray events originate close to the VLBI core seen on mm wave images, within the parsec-scale jet...but rapid variability has been observed in γ rays for FSRQ dammando@ira.inaf.it 17

18 Proper motion of γ-ray emitting NLSy1 With 6-epoch MOJAVE data for SBS we obtained an apparent velocity of the jet knot (9.3±0.6)c, suggesting the presence of boosting effect as well as in blazars. The time of ejection is T 0 = 24 August 2009, likely connected with a radio flare. No significant γ-ray activity was detected in that period. D Ammando et al. 2013b, MNRAS, 436, 191 Superluminal motion was detected also in 1H and PMN J (Lister et al. 2016). No superluminal motion was detected for the jet components of PKS A sub-luminal component was reported in Lister et al. (2016). D Ammando et al. 2013a, MNRAS, 433, 952 dammando@ira.inaf.it 18

19 NGC 1275: limb brightening From 1990s to 2013 the jet structure of NGC 1275 changed from ridge-brightening to limbbrightening. This change in apparent transverse structure might be caused by the change in the transverse velocity structure Nagai et al In the context of a structured jet, this transition may be related to the γ-ray time variability on the timescale of decades Dhawan et al dammando@ira.inaf.it 19

20 NGC 1275: LAT observations Kataoka et al Tavecchio & Ghisellini 2014 About an order of magnitude brighter than EGRET UL significant brightening on decade time scale Flux doubling on monthly time-scale: 0.1 pc jet emission region 20

21 Dissipation zone in M87: far away... After a huge flare, the unresolved and stationary knot HST-1 in M87 jet ejected superluminal blobs moving down the outflow Why does the HST-1 knot behave like a central engine? Is the gamma-ray emission produced in HST-1 as well? Cheung et al dammando@ira.inaf.it 21

22 ...or closer to the SMBH? The observed γ-rays may be instead produced in the innermost part of the M87 jet Acciari et al [HESS, MAGIC & VERITAS] 22

23 TeV flare from M87 in 2012 Hada et al A remarkable flux increase from the jet base (radio core) at 22 and 43 GHz coincident with the VHE enhancement Meanwhile, HST-1 was stable in radio => the 2012 VHE activity originates in the jet base, not HST-1 Fermi-LAT light curves basically stable up to 2012 February and no increase during the VHE activity dammando@ira.inaf.it 23

24 Unveiling the nature of the AGN PKS On pc-scales PKS shows a knotty structure similar to misaligned AGN (3C 120 and M87). The brightness profile along the jet axis decreases rapidly with increasing distance from the core, but it then steeply rises again at ~30 mas The core dominance and the γ-ray properties are similar to those estimated for other SSRQ and BLRG detected in γ-rays, suggesting an intermediate viewing dammando@ira.inaf.it 24

25 Nature of the source How to conciliate the knotty jet structure observed in radio with the high activity observed in γ rays? Emitting jet not closely aligned w.r.t to the line of sight. It is possible to model the SED of the γ-ray flare with a low Doppler factor as suggested in the past for this source? Structured jet with spine or layer region active in different epochs? RGs may/should be misaligned blazars low power FR I BL Lac high power FR II FSRQ SED modeling Spine dominated.. Blazar Layer dominated.. RG dammando@ira.inaf.it 25

26 Structured jet scenario for PKS Applying a structured jet model a viewing angle between 6 and 15 deg is preferred, with the rapid variability observed during γ-ray flares favouring a smaller angle. For relatively small angles the spine emission largely dominates the SED For larger angles the only suitable solution is that the low-energy bump is dominated by the synchrotron emission of the spine, and the IC bump by the IC emission of the layer dammando@ira.inaf.it 26

27 Concluding Remarks Although there are many constraints on the possible high-energy emission processes, there is no consensus on the location of the highenergy emitting region in radio-loud AGN The high-resolution multi-epoch radio data can unravel the jet velocity and its change along the flow, pinpointing not only the presence of propagating shock by tracking a fast moving knot, but also a stratified jet by detecting gradients in the brightness distribution and transition from edge-brightening to limb-brightening By analysing high-resolution VLBI observations of a sample of γ-ray emitting AGN, we will be able to discriminate between the different scenarios about the location of high-energy emission This will be an interesting topic for actual and future networks of radio telescopes in conjunction with the Fermi satellite and the upcoming Cherenkov Telescope Array dammando@ira.inaf.it 27

28 Thanks for your attention! 28

29 Back up slides 29

30 First all-sky census between 50 GeV and 2 TeV 2FHL includes 360 sources, with photons collected in 80 months using Pass 8 data The 2FHL catalogue contains 282 sources not detected by the IACTs The 2FHL catalogue contains 57 sources not included in the 3FGL and 48 never detected in γ rays 2FHL catalogue Ackermann et al. 2016, ApJS, 222, 5 dammando@ira.inaf.it 30

31 SED modelling of PKS The case for θ = 20 requires a large intrinsic luminosity. In that case the optical depth reaches 1 at about 1 GeV Once observed at a small angle, the SED obtained with θ = 15 does not resemble that of a blazar, in contrast to the unification scheme for radio galaxies and blazars dammando@ira.inaf.it 31