VERITAS Observations of Relativistic Jets Reshmi Mukherjee 1 for the - PowerPoint PPT Presentation

VERITAS Observations of Relativistic Jets 
 Reshmi Mukherjee 1 for the VERITAS Collaboration 1 Barnard College, Columbia University  Sensitivity improvement: 1% Crab in ~25 hr Sensitive energy range: 100 GeV to 30 TeV  Spectral reconstruction: begins at ~150GeV. Energy resolution: ~15% - 20%  Angular resolution: < 0.1 o at 1 TeV, 0.14 o at 200 GeV (68% values) Reshmi Mukherjee HEPRO III, Barcelona 2011

Outline  Highlights from the Extragalactic Program  TeV Blazar Sample  Modeling blazar SEDs  M87  Galactic sources of HE relativistic outflows  Gamma-ray binaries  Pulsar wind nebulae (PWN) Reshmi Mukherjee HEPRO III, Barcelona 2011

Blazars Detected by VERITAS AGN Type z Mkn 421 HBL 0.030 Key Science Project: Discovery, Mkn 501 HBL 0.034 MWL & ToO observations 1ES 2344+514 HBL 0.044 ~400 hr/yr including moonlight data 1ES 1959+650 HBL 0.047 W Comae IBL 0.102 RGB J0710+591* HBL 0.125  19 detections H 1426+428 HBL 0.129  10 discoveries 1ES 1215+303 IBL 0.130 1ES 0806+524 HBL 0.138  ≥ 4 VHE intermediate BL Lacs 1ES 0229+200 HBL 0.139 1ES 1440+122 IBL 0.162  Predominately nearby RX J0648.7+1516 Blazar 0.179  - EBL horizon? 1ES 1218+304 HBL 0.182 RBS 0413 HBL 0.190  Target selection 1ES 0414+009 HBL 0.287 Mostly X-ray candidates  PG 1553+113 HBL 0.43 < z < 0.47  Now – Fermi-LAT motivated 1ES 0502+675 HBL 0.341 ?  All LAT detected except 1ES0229+200 3C 66A IBL 0.444 ? PKS 1424+240 IBL/HBL ? VER J0521+211 Blazar ? Reshmi Mukherjee

Blazar sequence – expanding on TeV source classes Non-thermal, continuum spectra. Sambruna 1996; Fossati et al. 1998. Dramatic peak at γ -ray energies. Emission extends to GeV-TeV. Blazars detected by Fermi  HBLs: ν pk ~ 10 16-18 Hz  IBLs: ν pk ~ 10 15-16 Hz Sambruna 1996;  LBLs: ν pk ~ 10 13-15 Hz Fossati et al. 1998.  “Extreme” HBLs > 10 18 Hz Non-HBLs – VERITAS:  W Comae  3C 66A Absence of intrinsic γγ pair absorption  beaming in blazars.  1ES 1215+303 High isotropic γ -ray luminosity ~ 10 48 erg/s  Optical depth >> 1  γ -ray emission originates in strongly beamed sources.  1ES 1440+122 Reshmi Mukherjee HEPRO III, Barcelona 2011

IBLs: VERITAS Discovery of W Com  Intermediate-peaked (IBL).  First IBL to be detected > 200 GeV  Strong flare 2008 March (ATel 1422)  2008 Jan – Apr: ~5 σ in ~40 hr observations Acciari et al. 2008 ApJ 690, L73 B2 1215+305 1ES 1218+304 FOV shows recent detection of B2 1215+303 W Comae  70% of excess from 4-night flare in Benbow et al. ICRC 2011 2008 March  275 γ , 8.6 σ ; τ ≈ 1.3 ± 0.3 days, 9% CU Reshmi Mukherjee HEPRO III, Barcelona 2011

Discoveries: Finding Blazars behind the Galactic plane  A number of unidentified Fermi sources are expected to be blazars behind the Galactic plane.  VHE telescopes are a good tool for identifying blazars at low latitudes (better localization, higher sensitivity to flux variability). Reshmi Mukherjee HEPRO III, Barcelona 2011

Blazars behind the Galactic plane Identified as VHE candidates because of cluster of E>50 GeV (Fermi) photons at source position. 1 period = 1 month = 1 dark run VER J0648+152 VER J0521+211  Unidentified radio & X-ray source RGB  γ -ray excess, 15.6 σ , 5% Crab  Position compatible with radio & X-ray J0648+152 located 6 o off the plane  VERITAS: 19 h in Mar-Apr10 source RGB J0521.8+2112  z unknown. Follow-up optical spectroscopy  γ -ray excess, 5.3 σ , 2% Crab revealed continuum dominated spectrum, no  Follow-up optical spectroscopy at Lick: absorption lines, typical of BL Lacs z=0.179. E. Aliu et al . 2011, in prep. Reshmi Mukherjee HEPRO III, Barcelona 2011

Low-latitude blazar: RX J0648.7+1516 E. Aliu et al . 2011, in prep. 1 period = 1 month = 1 dark run  Follow-up optical spectroscopy at the Shane 3m telescope at Lick Observatory.  The obtained results reveal a continuum dominated spectrum typical of BL Lac- type blazars.  Observed absorption lines are compatible with z= 0.179. Reshmi Mukherjee HEPRO III, Barcelona 2011

Blazar Models – What have we learnt with VERITAS? Particle acceleration & radiation in blazar jets – Relativistic jet outflow with Γ ≈ 10 Collimated ejection of plasma with bulk Lorentz factor >>1  Radiation – peaks in SED. Non-thermal synchrotron & IC (Ieptonic), or hadronic processes Urry & Padovani 1995  Sources of soft photons: synchrotron self- Compton radiation, accretion disk photons, radiation scattered by BLR, …..  Synchrotron & SSC flux: F ~ δ 3+ α  External Compto n : F ~ δ 4+2 α ( δ = 1/[ Γ (1 - β cos θ )] Doppler factor)  VERITAS data modeled using leptonic one-jet model (Boettcher & Chiang 2002)  Size of emission region  Observed radiation originating from ultra-rel. constrained by shortest timescale of e - in a spherical emission region (R B ), moving variab. R B <c δ t var D/(1+z) at β Γ c. Reshmi Mukherjee HEPRO III, Barcelona 2011

HBLs: RGB J0710+591 Some examples of blazar modeling: 1 period = 1 month = 1 dark run V. Acciari et al . 2010, ApJL 715, L49  “Extreme” HBL. Promising VHE candidate  Redshift 0.125  Useful for EBL studies Γ bulk = 30 γ min = 6.10 4 γ max = 2.10 6  VERITAS detection triggered q=1.5 B=0.036 observations at other wavelengths, including Fermi -LAT detection Γ HE = 1.46 ± 0.17 stat ± 0.05 sys  First Fermi-LAT source Γ VHE = 2.69 ± 0.26 stat ± 0.20 sys found with VHE guidance Reshmi Mukherjee HEPRO III, Barcelona 2011

TeV Blazars: Mrk 501 V. Acciari et al ., (2010) arXiv:1012.2200  Joint MWL campaign 1 period = 1 month = 1 dark run VERITAS/MAGIC, Fermi-LAT, Suzaku. 1997  Large shift in synchrotron peak; little shift in IC peak. Both epochs well described by SSC model  X-ray data used to place limits 2009 on peak frequencies:  230 keV (5.5 X 10 19 Hz) – high  0.6 keV (0.6 X 10 17 Hz) – low  Shift in VHE peak not as Γ bulk = 30 dramatic -- Could be from onset of KN γ min = 1 γ b = 3.10 5 γ max = 3.10 6 suppression q=1.6 q b = 2.6 -- KN effects become important Every dark run in good agreement ! above h ν ~ m e c 2 in electron rest frame Also see Paneque ʼ s poster A43 HEPRO III, Barcelona 2011 Reshmi Mukherjee

SEDs: Constraints from MW Observations Correlated MW observations of IBL 3C 66A High optical luminosity is expected to play a key role in providing the seed population for IC scattering. Abdo et al. arXiv:1011.1053 Reshmi Mukherjee

HBL 1ES 1218+304: Variable Emission 1 period = 1 month = 1 dark run  Redshift 0.182  Hard intrinsic spectrum Γ ≤ 1.5  Flare Jan 25 – Feb 5, 2009: 7% Crab to 20% Crab  ~1 day variability time scale challenges kiloparsec jet model of hard-spectrum emission ( Boettcher et al. 2008) R ≤ ct δ /(1 + z)) For typical Doppler factors δ = 20 (Marscher 2006) , R<0.01pc. V. Acciari et al . 2010, ApJL 709, L163 Reshmi Mukherjee

TeV Blazar: Mrk 421  long-term monitoring program ApJ submitted (2010)  major flares in 2008 & 2010 i nitiated large MWL efforts  spectral hardening with increasing flux   high in VHE & X-ray since 11/09 35 h of data; ~400 σ   huge flare on Feb 17th 2010 variability on 5-10 min time scales  >10 σ per 2 minute bin  Reshmi Mukherjee HEPRO III, Barcelona 2011

M87 – Radio Galaxy – 2008 Flare  Location of TeV γ - ray emission??  TeV: night-by-night averaged VHE light curve in 2008. Strong variability resulted in the detection of at least 2 flares  X-ray: Chandra core and HST-1 knot  VLBA: 43 GHz observations of nucleus, peak and flux integrated along the jet -- radio flux of the unresolved core risng.  Temporal coincidence of TeV & radio flares indicates they are related. Wagner et al. 2009 Also see M. Raue ʼ s talk & D.E. Harris A.23 HEPRO III, Barcelona 2011

Outline  Highlights from the Extragalactic Program  TeV Blazar Sample  Modeling blazar SEDs  M87  Galactic sources of HE relativistic outflows  Gamma-ray binaries  Pulsar wind nebulae (PWN) Reshmi Mukherjee HEPRO III, Barcelona 2011

Galactic Science Program Galactic sources of HE relativistic outflows Mirabel 2006 Science  Pulsar Wind Nebulae (pointed observations) o TeV emission from nebulae of energetic young pulsars. Large fraction of Galactic TeV sources. . o TeV PWNe associated with high E dot /d 2 pulsars.  TeV observations of binaries: o Binaries are the only variable Galactic TeV sources. o TeV emission probes the highest energy particles accelerated. May provide the keys to an understanding of astrophysical jets. o Two Scenarios: Microquasar: gamma-rays are produced in a radio-emitting jet o Pulsar Binary : particles accelerated in the shock produced by the interaction of the pulsar wind and the wind of the companion Reshmi Mukherjee HEPRO III, Barcelona 2011

HMXB LS I+61 o 303  Compact object orbiting a Be companion star  26.5 day, inclined orbit, e=0.54, circumstellar disk  Extended radio structure; microquasar? (but radio images shows orbital Stage et al. 2006 morphology change)  Strong VHE emission only near apastron: 15-20% of Crab Nebula Flux (MAGIC/VERITAS)  GeV emission peaks near periastron; 6 GeV cut-off; orbital modulation; orbit-to-orbit variations; J.Casares et al (MNRAS 360, 1105 (2005))  Different component than in TeV? Reshmi Mukherjee HEPRO III, Barcelona 2011