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DECADAL VERITAS OBSERVATIONS OF LS I +61 303: DETECTION OF TEV EMISSION AROUND ENTIRE ORBIT Payel Kar, David Kieda, & The VERITAS Collaboration ICRC 2017, Bexco, Busan Korea 12-20 July 2017 OUTLINE OF THE TALK An Outline of VERITAS

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DECADAL VERITAS OBSERVATIONS OF LS I +61° 303: DETECTION OF TEV EMISSION AROUND ENTIRE ORBIT

Payel Kar, David Kieda, & The VERITAS Collaboration ICRC 2017, Bexco, Busan Korea 12-20 July 2017

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Payel Kar Decadal VERITAS Observation

  • f LS I +61° 303 | ICRC 2017

OUTLINE OF THE TALK

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▸ An Outline of VERITAS Observatory & TeV Binaries ▸ LS I +61 303 system ▸ Phase based flux analysis and discovery of quiescent

emission

▸ Spectral Energy Distribution in different parts of the orbit ▸ Pulsar Flip-Flop Model ▸ Conclusions

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Payel Kar Decadal VERITAS Observation

  • f LS I +61° 303 | ICRC 2017

VERITAS OBSERVATORY

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▸ 4 Imaging Atmospheric

Cherenkov Telescopes in AZ, US

▸ Fully Operational since Sep 2017 ▸ Energy Range 85GeV to > 30TeV ▸ Field of View 3.5° ▸ Angular resolution ~0.1° ▸ Sensitivity: 5σ detection of 1%

Crab in <25h

▸ Upgrades: T1 relocation, mirror

alignment, trigger, PMTs, etc.

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Payel Kar Decadal VERITAS Observation

  • f LS I +61° 303 | ICRC 2017

TEV BINARIES: MODELS & MOTIVATIONS

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Microquasar Pulsar + Be Star Pulsar + Massive Star

▸ All gamma ray binaries are not TeV binaries, Only

5 out of >120 HMXB gamma rays >100 GeV

▸ They could be pulsar wind or accretion powered,

microquasar gamma-ray emitter yet to be confirmed

▸ Varibility patterns generally depends on orbital

periods

▸ Other variability patterns also present, micro

flares, periodic flares, multi-year cycles etc.

▸ Influence of stellar winds on variability patterns (?) ▸ Are there more in our galaxy or nearby ?

Mirabel, I.F. Science 312, 1759 (2006) 


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Payel Kar Decadal VERITAS Observation

  • f LS I +61° 303 | ICRC 2017

LS I +61° 303 : ORBITAL PARAMETERS

Relative Orbit of Compact Object Apastron (when farthest away) Periastron (closest approach) Center of Mass

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Disc of Be Star

Sierpowska-Bartosik et al. 2009 ApJ 693.1462S

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Payel Kar Decadal VERITAS Observation

  • f LS I +61° 303 | ICRC 2017

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LS I +61° 303 : PREVIOUSLY BY VERITAS

  • 2009-2010 no TeV detection near apastron

2010 TeV detection in singe orbit near periastron passage Flaring activity in 2011 (15% of Crab), in 2014 (30% of Crab)

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Payel Kar Decadal VERITAS Observation

  • f LS I +61° 303 | ICRC 2017

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LS I +61° 303 : VERITAS OBSERVATION SET

1518 m

6.2σ

2305 m

3.8σ

1207 m

0.7σ

933 m

4.6σ

1551 m

14.0σ

490 m

6.5σ

522 m

5.6σ

1746 m

21.4σ

1137 m

16.0σ

703 m

12.4σ

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Payel Kar Decadal VERITAS Observation

  • f LS I +61° 303 | ICRC 2017

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4% 7% 14% 23% 13% 4% 10% 10% 5% 8%

Overlaid on J. Casares,et al., MNRAS, 360 (2005), pp. 1105–1109

▸ Φ0= MJD 43366.275 ▸ 10 phase bins ▸ Bin width ΔΦ =0.1 ▸ >5σ in 9 of 10 bins

DATA IN EACH BIN

LS I +61° 303 : PHASE BINED ANALYSIS

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Payel Kar Decadal VERITAS Observation

  • f LS I +61° 303 | ICRC 2017

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4% 7% 14% 23% 13% 4% 10% 10% 5% 8%

DATA IN EACH BIN

▸ ~3% Crab quiescent emission ▸ TeV outburst near apastron passage ▸ Limited exposure UL in 1 phase ▸ Highly variable VHE emission

LS I +61° 303 : PHASE BINED FLUX

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Payel Kar Decadal VERITAS Observation

  • f LS I +61° 303 | ICRC 2017

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LS I +61° 303 : SPECTRAL ENERGY DISTRIBUTIONS

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Payel Kar Decadal VERITAS Observation

  • f LS I +61° 303 | ICRC 2017

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LS I +61° 303 : SPECTRAL ENERGY DISTRIBUTIONS

H.E.S.S. COLLABORATION ICRC 2015

  • G. MAIER, VERITAS COLLABORATION

ICRC 2017

LS 5039 HESS J0632+057

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Payel Kar Decadal VERITAS Observation

  • f LS I +61° 303 | ICRC 2017

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  • Ejector Phase: EM pressure expelled

relativistic particles is high, sweep away the surrounding matter beyond capture radius

  • Propeller Phase: Outward EM pressure

is balanced with the inward pressure from the surrounding medium. No Accretion but matter gathers around the magnetosphere

  • LS I +61 303 flip-flop along the orbit

between E-P

  • Ejector during TeV outburst near

apastron

  • Rest Propeller
  • Microquasar & Colliding Wind pulsar

models could explain with modifications.

LS I +61° 303 : A NEUTRON STAR MODEL

  • R. Zamanov, et al. 2nd National Conference on Astrophysics of Compact Objects, Sept. 2001, p. 50
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Payel Kar Decadal VERITAS Observation

  • f LS I +61° 303 | ICRC 2017

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LS I +61° 303 : SUMMARY

  • 10y of observations, 240h of data
  • LS I +61 303 flip-flop along the orbit, Ejector during TeV
  • utburst near apastron, Propeller for rest of the orbit
  • Quiescent TeV emission at for Propeller
  • TeV outbursts for Ejector
  • Spectral studies along the orbit
  • Microquasar & Colliding Wind pulsar models could

explain with modifications.