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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
HEPRO III, Barcelona 2011
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
Accia
ri et
al.
2008
ApJ
690
, L73
Reshmi Mukherjee
W Comae
1ES 1218+304
B2 1215+305
FOV shows recent detection of B2 1215+303
Benbow et al. ICRC 2011
HEPRO III, Barcelona 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).
HEPRO III, Barcelona 2011
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.
HEPRO III, Barcelona 2011
VER J0521+211 VER J0648+152
1 period = 1 month = 1 dark run
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.
HEPRO III, Barcelona 2011
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
Reshmi Mukherjee HEPRO III, Barcelona 2011
Size of emission region constrained by shortest timescale of variab. RB<cδtvarD/(1+z)
Urry
& P
adov
ani 1
995
1 period = 1 month = 1 dark run
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
Reshmi Mukherjee HEPRO III, Barcelona 2011
Γbulk = 30 γmin = 6.104 γmax = 2.106 q=1.5 B=0.036
Every dark run in good agreement !
1 period = 1 month = 1 dark run
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
HEPRO III, Barcelona 2011
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
1 period = 1 month = 1 dark run
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
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
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)
HEPRO III, Barcelona 2011
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
HEPRO III, Barcelona 2011
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?
Reshmi Mukherjee HEPRO III, Barcelona 2011
J.Casares et al (MNRAS 360, 1105 (2005))
Stage et al. 2006
HMXB LS I+61o 303: VERITAS Follow up
Reshmi Mukherjee HEPRO III, Barcelona 2011
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
Reshmi Mukherjee HEPRO III, Barcelona 2011
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)
HEPRO III, Barcelona 2011
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)
HEPRO III, Barcelona 2011
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)
HEPRO III, Barcelona 2011
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)
HEPRO III, Barcelona 2011
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
HEPRO III, Barcelona 2011
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)
HEPRO III, Barcelona 2011
Abdo
et a
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Reshmi Mukherjee
VERITAS Observations Cygnus Region
HEPRO III, Barcelona 2011
E. A
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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
Reshmi Mukherjee HEPRO III, Barcelona 2011
VERITAS Observations Cygnus Region
E. A
liu fo
r th
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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
HEPRO III, Barcelona 2011
N. Otte for the VERITAS Collab. 3rd Fermi Symp. 2011 May
Reshmi Mukherjee
Crab: Latest Results VERITAS
HEPRO III, Barcelona 2011
N. Otte for the VERITAS Collab. 3rd Fermi Symp. 2011 May
Summary of Results
Reshmi Mukherjee HEPRO III, Barcelona 2011
(see: http//veritas.sao.arizona.edu)
made with TeVCat
Reshmi Mukherjee
Thanks
- to all my VERITAS colleagues
(veritas.sao.arizona.edu)
HEPRO III, Barcelona 2011
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