VERITAS Observations of Relativistic Jets -...

Reshmi Mukherjee HEPRO III, Barcelona 2011

VERITAS Observations of Relativistic Jets Reshmi Mukherjee1 for the VERITAS Collaboration 1Barnard 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: < 0.1o at 1 TeV, 0.14o at 200 GeV (68% values)

Reshmi Mukherjee

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)

HEPRO III, Barcelona 2011

Blazars Detected by VERITAS AGN Type z

Mkn 421 HBL 0.030

Mkn 501 HBL 0.034

1ES 2344+514 HBL 0.044

1ES 1959+650 HBL 0.047

W Comae IBL 0.102

RGB J0710+591* HBL 0.125

H 1426+428 HBL 0.129

1ES 1215+303 IBL 0.130

1ES 0806+524 HBL 0.138

1ES 0229+200 HBL 0.139

1ES 1440+122 IBL 0.162

RX J0648.7+1516 Blazar 0.179

1ES 1218+304 HBL 0.182

RBS 0413 HBL 0.190

1ES 0414+009 HBL 0.287

PG 1553+113 HBL 0.43 < z < 0.47

1ES 0502+675 HBL 0.341 ?

3C 66A IBL 0.444 ?

PKS 1424+240 IBL/HBL ?

VER J0521+211 Blazar ?

Key Science Project: Discovery, MWL & ToO observations ~400 hr/yr including moonlight data

  19 detections   10 discoveries

  ≥4 VHE intermediate BL Lacs

  Predominately nearby   - EBL horizon?

  Target selection   Mostly X-ray candidates   Now – Fermi-LAT motivated

  All LAT detected except 1ES0229+200

Reshmi Mukherjee

Blazar sequence – expanding on TeV source classes

Non-thermal, continuum spectra. Dramatic peak at γ-ray energies. Emission extends to GeV-TeV.

Absence of intrinsic γγ pair absorption beaming in blazars. High isotropic γ-ray luminosity ~ 1048erg/s Optical depth >> 1 γ-ray emission originates in strongly beamed sources.

Reshmi Mukherjee

Sambruna 1996; Fossati et al. 1998.

Sambruna 1996; Fossati et al. 1998.

  HBLs: νpk ~ 1016-18 Hz   IBLs: νpk ~ 1015-16 Hz   LBLs: νpk ~ 1013-15 Hz  “Extreme” HBLs > 1018 Hz

Blazars detected by Fermi

Non-HBLs – VERITAS:   W Comae   3C 66A   1ES 1215+303   1ES 1440+122


  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

  70% of excess from 4-night flare in 2008 March   275γ, 8.6σ; τ ≈1.3 ± 0.3 days, 9% CU

IBLs: VERITAS Discovery of W Com

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Reshmi Mukherjee

W Comae

1ES 1218+304

B2 1215+305

FOV shows recent detection of B2 1215+303

Benbow et al. ICRC 2011


Discoveries: Finding Blazars behind the Galactic plane

Reshmi Mukherjee

  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).


1 period = 1 month = 1 dark run

Blazars behind the Galactic plane

Reshmi Mukherjee

Identified as VHE candidates because of cluster of E>50 GeV (Fermi) photons at source position.

  γ-ray excess, 15.6 σ, 5% Crab   Position compatible with radio & X-ray source RGB J0521.8+2112   z unknown. Follow-up optical spectroscopy revealed continuum dominated spectrum, no absorption lines, typical of BL Lacs

  Unidentified radio & X-ray source RGB J0648+152 located 6o off the plane   VERITAS: 19 h in Mar-Apr10   γ-ray excess, 5.3 σ, 2% Crab   Follow-up optical spectroscopy at Lick: z=0.179.

E. Aliu et al. 2011, in prep.


VER J0521+211 VER J0648+152


Low-latitude blazar: RX J0648.7+1516

Reshmi Mukherjee

  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.


E. Aliu et al. 2011, in prep.

Blazar Models – What have we learnt with VERITAS?

Particle acceleration & radiation in blazar jets – Collimated ejection of plasma with bulk Lorentz factor >>1   Radiation – peaks in SED. Non-thermal synchrotron & IC (Ieptonic), or hadronic processes   Sources of soft photons: synchrotron self-Compton radiation, accretion disk photons, radiation scattered by BLR, …..

  Synchrotron & SSC flux: F ~ δ3+α   External Compton : F ~ δ4+2α

(δ = 1/[Γ(1-βcos θ)] Doppler factor)

  VERITAS data modeled using leptonic one-jet model (Boettcher & Chiang 2002)   Observed radiation originating from ultra-rel. e- in a spherical emission region (RB), moving at βΓc.

Relativistic jet outflow with Γ ≈ 10


  Size of emission region constrained by shortest timescale of variab. RB<cδtvarD/(1+z)

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HBLs: RGB J0710+591 Some examples of blazar modeling:

  “Extreme” HBL. Promising VHE candidate

  Redshift 0.125

  Useful for EBL studies

  VERITAS detection triggered observations at other wavelengths, including Fermi-LAT detection

  First Fermi-LAT source found with VHE guidance

V. Acciari et al. 2010, ApJL 715, L49

ΓHE = 1.46 ± 0.17stat ± 0.05sys ΓVHE = 2.69 ± 0.26stat ± 0.20sys


Γbulk = 30 γmin = 6.104 γmax = 2.106 q=1.5 B=0.036

Every dark run in good agreement !


TeV Blazars: Mrk 501

1997

2009

V. Acciari et al., (2010) arXiv:1012.2200

Reshmi Mukherjee

  Joint MWL campaign VERITAS/MAGIC, Fermi-LAT, Suzaku.   Large shift in synchrotron peak; little shift in IC peak. Both epochs well described by SSC model  X-ray data used to place limits on peak frequencies:

  230 keV (5.5 X 1019 Hz) – high   0.6 keV (0.6 X 1017 Hz) – low

  Shift in VHE peak not as dramatic -- Could be from onset of KN suppression -- KN effects become important above hν ~ mec2 in electron rest frame


Γbulk = 30 γmin = 1 γb = 3.105 γmax = 3.106 q=1.6 qb= 2.6

Also see Panequeʼs poster A43

SEDs: Constraints from MW Observations

Reshmi Mukherjee

Abdo et al. arXiv:1011.1053

High optical luminosity is expected to play a key role in providing the seed population for IC scattering.

Correlated MW observations of IBL 3C 66A


HBL 1ES 1218+304: Variable Emission   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)

V. Acciari et al. 2010, ApJL 709, L163

Reshmi Mukherjee

R ≤ ct δ/(1 + z)) For typical Doppler factors δ= 20 (Marscher 2006), R<0.01pc.

  long-term monitoring program   major flares in 2008 & 2010

  initiated large MWL efforts   spectral hardening with increasing flux

  high in VHE & X-ray since 11/09   35 h of data; ~400σ

  huge flare on Feb 17th 2010   variability on 5-10 min time scales   >10σ per 2 minute bin

ApJ submitted (2010)

TeV Blazar: Mrk 421


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

HEPRO III, Barcelona 2011 Also see M. Raueʼs talk & D.E. Harris A.23

Reshmi Mukherjee

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)


Galactic Science Program

  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 Edot/d2 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

Galactic sources of HE relativistic outflows


Mirabel 2006 Science

Stage et al. 2006

HMXB LS I+61o 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 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;   Different component than in TeV?


J.Casares et al (MNRAS 360, 1105 (2005))

Stage et al. 2006

HMXB LS I+61o 303: VERITAS Follow up


2008-2009: 37 h data, 3.3 σ, no detection Almost entire orbit covered

2009-2010: 18 h data, 0.8 σ, no detection Deep exposure near apastron

Acciari et al. 2011, ApJ arXiv: 1105.0449

Stage et al. 2006

HMXB LS I+61o 303: VERITAS Follow up


October 2010: periastron detection

5% of the Crab Nebula flux at E>300 GeV

Is this long term variability related to the

environment of the Be star?

Acciari et al. 2011, ApJ arXiv: 1105.0449

HESS J0632+057: a new binary?

Reshmi Mukherjee

HESS J0632+057: Only unidentified TeV source in Galactic plane that is point-like.

  Discovered by H.E.S.S. in 2004/2006 (Γ=2.53, F(>1 TeV) ~3% Crab.

  MWL follow-up shows a hard spectrum X-ray source & faint radio source coincident with a massive B0pe star (MWC148) (Hinton et al 2009).

  Faint point-like, variable radio source (<2ʼʼ extension, 0.2-0.4 mJy, Skilton et al 2009)

  Not detected by Fermi LAT

  No binary system identified (e.g. Aragona et al 2010)

  VERITAS non-detection 2006-2009, VERITAS detection in 2010. Implies variability.

  Variable X-ray emission measured by Swift. (Falcone et al 2010))

Hinton ApJL 690 (2009)

A new TeV binary system? Coincident with Be star MWC 148? (Hinton et al 2009). An unusual isolated massive star? (confined stellar wind, Townsend et al 2007)


XMM

TeV Variability

Reshmi Mukherjee

VERITAS Feb-Mar 2010

HESS/VERITAS. (in prep.)

 30 h in Dec 2006 - Jan 2009: not detected by VERITAS (ApJ 687 L94 (2009))   Excluded with ~4σ confidence that HESS J0632+057 is a steady gamma-ray emitter   H.E.S.S./VERITAS campaign in 2009/2010 (publication in prep)   8h in Oct 2009: no detection (UL~1.3% Crab)   20 h in Feb/March 2010: clear detection (7.5 σ, 1.5% Crab)   clearly variable in VHE gamma rays   is it a VHE binary? Need detection of orbital modulation (at any wavelength)


And finally…

Reshmi Mukherjee

  Swift X-ray monitoring establishes periodic behavior (T=320±5 days) (Bongiorno, 2011) Atel #3153   VERITAS observations Feb 7/8, 2011 triggered by X-ray activity (Atel #3152)  > 8σ, F (E> 300 GeV) ~ 4% Crab   Confirmed by MAGIC (Atel #3161)


Reshmi Mukherjee

Pulsar Wind Nebulae   Most of the rotational energy in pulsars is lost in the form of a particle wind made of electrons (leptonic accelerators?)   This wind form the PWN that shines at all wavelengths. Does CTA 1 emit from the shell? from the PWN? from both?

CTA 1 radio shell Age~13 kyr Dist=1.4±0.3 kpc Pulsar Ė=4.5x1035erg/s First pulsar discovered at GeV γ-rays by Fermi-LAT

(Gaensler & Slane, 2006, ARA&A, 44, 17)


Reshmi Mukherjee

The most recent: CTA 1

  Observations: 26.5 hrs between Oct 2010 and Jan 2011   Extended emission centered around the pulsar (7.3σ/6.2σ pre/post-trials significance)   Preliminary flux ~4% Crab - working on spectrum   Morphology clearly suggests young PWN   Properties of CTA 1 nicely fit in the middle of those of known TeV/X-ray PWN

Black Contours:1420 MHz show SNR shell Red Circle: Fermi pulsar Green : 3 to 7σ TeV contours


B. McArthur for the VERITAS Collab. 3rd Fermi Symp. 2011 May

Reshmi Mukherjee

Recent Studies of the Cygnus Region

  MGRO J2019+37:  ~80% Crab at 20 TeV (Abdo et al. 2007)

  Located towards the Cyg OB1 association   Coincident with two EGRET UIDs (3EG J2021+3716 & 3EG J2021+3616)   3EG J2016+3651=blazar B2013+370? (Mukherjee et al., 2000)

  3EG J2021+3716 = radio pulsar PSR J2021+3651 (Roberts et al., 2002)

  Both associations have been now confirmed with the LAT: 1FGL J2021.0+3651(pulsed) and 1FGL J2015.7+3708 (very variable, V=139) (Abdo et al., 2009)


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Reshmi Mukherjee

VERITAS Observations Cygnus Region


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VERITAS Observations:   75 hrs between May & December 2010   Point--‐like source detected coincident with the CTB 87 PWN. – VER J2016+372: 6.1σ F (E>1TeV) ~ 0.8% Crab Nebula. Can exclude at 99% level the blazar B 2013+370. – 1FGLJ2015.7+3708 is variable, likely assoc. with blazar.   GeV and TeV emission in this region seems to be of quiet different origin!   VER J2016+372 could contribute to the MGRO J2019+37


VERITAS Observations Cygnus Region

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  Broad emission region detected in extended source analysis   0.23° integration radius, 650 GeV threshold   Broad TeV Excess: 7.4 σ post   Coincides with MGRO J2019+37 (dashed ellipse).   Substructure and/or multiple sources? Under evaluation.

Reshmi Mukherjee NERQUAM, Yale 2011

  Remnant of historic supernova in 1054 A.D.   Dist ~ 2 kpc Period ~ 33 ms   Most energetic pulsar 4.6 x 1038 erg/s   One of the brightest GeV γ-ray pulsars   Powers the brightest TeV γ-ray source

The Crab pulsar

Break between few MeV and few GeV (exponential cutoff)

Acceleration regions (polar vs outer gap) and radiation mechanisms (curvature radiation) studied through the cutoff

MAGIC detection above 25 GeV suggested that emission comes from a region > 6 stellar radii ➔ outer gap scenarios favored

Reshmi Mukherjee

Crab: Latest Results VERITAS


N. Otte for the VERITAS Collab. 3rd Fermi Symp. 2011 May

Summary of Results


(see: http//veritas.sao.arizona.edu)

made with TeVCat

Reshmi Mukherjee

Thanks

- to all my VERITAS colleagues

(veritas.sao.arizona.edu)


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