VERITAS Observations of LS I 61 303

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VERITAS Observations of LS I 61 303

• Andrew W. Smith
• Argonne National Laboratory

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V.E.R.I.T.A.S.The Very Energetic Radiation
Imaging Telescope Array System
Instrument ? Four 12-m telescopes ? 500-pixel
cameras (3.5 FoV) ? FLWO, Mt. Hopkins, Az (1268
m)
Specifications ? Energy threshold 150 GeV ?
Source location lt 0.05 ? Energy resolution
10-20
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VERITAS
energy range 100 GeV to gt30 TeV
(spectral reconstruction starts at 150 GeV)
energy resolution 15 at 1 TeV peak
effective area 100,000 m2 angular
resolution 0.1 deg at 1 TeV, 0.14 deg at 200 GeV
(68 values) source location accuracy 90
arcseconds point source sensitivity 1
Crab in lt 50h, 10 in 45 min observation
time per year 750 hours non-moonlight, 100 hours
moonlight
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The VERITAS Catalogc. 2000
Pulsar Wind Nebula
Blazars
Starburst Galaxy!
Supernova Remnants
X-ray Binary
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LS I 61 303
-High Mass X-ray Binary System -2 kpc
distance -Pairing of Massive Be Star Compact
Object (unknown) -26.5 day orbit
Be Star
BH/NS
P26.5 day
Earth
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LS I 61 303
Radio Outbursts near apastron, 4yr modulation
TeV Activity detected by MAGIC/VERITAS around
apastron passage
High X-ray activity throughout orbit (strongest
at apastron, secondary near periastron)
Be Star
BH/NS
P26.5 day
Earth
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-Microquasar Accretion driven jet electrons
upscatter photons -Binary Pulsar Shock driven
electrons upscatter photons -Many variations in
both models clumpy winds, absorption.....need MW
observations to detail emission evolution
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2006-2007
Strong Detection around apastron
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2007-2008
Borderline detection around apastron, hint of
signal near periastron
5s
3.5s
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2008-2009
No Significant Signal detected!
All data 3s
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All Data 2006-2009
Apastron
Preliminary
Phases 0.9-0.5
Phases 0.5-0.9
10s
4.5s(pre-trial)
Preliminary
Preliminary
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Multi-Wavelength

• VERITASSwiftRXTE

-X-ray/TeVNo clear correlation/lack thereof
evident
2006
2007
-Need simultaneous, long term data to show
rigorously!
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MAGIC Collaboration ICRC 2009
-10 simulataneous X-ray/TeV points -Claim
discovery of Tev/X-ray Correlation and
demonstration that TeV/X-ray population is the
same
-Correlation co-efficient of 0.81, chance
probability of 5e-3 (2.8s).
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Multi-Wavelength w Fermi (before ICRC....)
VERITAS
Fermi
Detects the source continuously Emission peaks at
periastron
no detection during Fermi strong emission
Fermi
Misleading......but still interesting
Fermi
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Fermi (ICRC 2009)
No sign of spectral variability,
GeV-gtTeV not connected? Life just
got more complicated....
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Summary of Observations

• -TeV emission variable, peaks at apastron,
  evidence for weak signal near periastron.

-X-ray/TeV campaigns inconclusive- need long
term, well sampled data to derive statistically
viable conclusion
-GeV/TeV campaigns- Fermi possibility of
periastron emission may point to strong role of
absorption, different GeV/TeV spectral components?
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Possible Explanations for TeV

• -Binary Pulsar model Crushed B-field at
  periastron-less TeV emission due to synchrotron
  losses

-TeV emission peaks near apastron, cometary radio
emission (seen in VLBA)
Dhawan, 2006
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Possible Explanations for TeV

• -Microquasar model Accretion, jet power peaks at
  periastron, but TeV strongly absorbed- need to
  simultaneously measure spectra........

TeV
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Conclusions

• -The more we learn, less we know- how does GeV
  connection fit into models?
• -LS I 61 303 is a very complex (and local)
  laboratory for the study of astrophysical
  processes (accretion, ejection, shock physics,
  absorption?
• -If absorption is key player, possible to
  indirectly study stellar environments of massive
  stars....
• -Further observations upcoming- VERITASFermi in
  Fall (Fermi GI proposal approved) other
  observatories possible.....