Advanced search for the extension of unresolved TeV sources with - - PowerPoint PPT Presentation

Markus Holler for the H.E.S.S. Collaboration ICRC 2017 Busan, 15th July 2017

Advanced search for the extension of unresolved TeV sources with H.E.S.S.

• M. Holler . Extension of unresolved TeV sources with H.E.S.S. . ICRC . 15th July 2017

Advanced Extension Measurements

■ New, more realistic simulation

approach (poster GA, contrib. 755)

▪ Simulating each observation run of a

data set

▪ Using actual observation and

instrument conditions

■ Run MC analysis on given data set

with corresponding analysis settings and assumed source spectrum

■ Use Sherpa for the extension fit

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Quantity Type (per pixel, telescope, or for array) Active IACTs

• Telescope Tracking

array Source Position array Optical Efficiency ε telescope Transparency Coefficient array Camera Focus telescope Trigger Settings telescope Live-Time fraction telescope Broken Pixels pixel PMT Gain pixel Hi-Lo Ratio pixel Flatfield Coefficient pixel Night-Sky Background pixel Pointing Uncertainties telescope

• M. Holler . Extension of unresolved TeV sources with H.E.S.S. . ICRC . 15th July 2017

Tests on Point-Like Sources

■ Focus on highly significant (> 100σ)

sources with large S/B ratio

▪ PKS 2155-304: large, diverse data set ▪ Markarian 421: extreme zenith angle

(θ > 61°)

■ Other sources tested as well, with

identical outcome

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• M. Holler . Extension of unresolved TeV sources with H.E.S.S. . ICRC . 15th July 2017

PKS 2155-304

■ Detection significance: 125σ ■ S/B ratio: 6.9 ■ Source appears point-like ■ Extension upper limits

(2D Gaussian width):

▪ 13.7’’ (1σ) ▪ 23’’ (3σ)

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• M. Holler . Extension of unresolved TeV sources with H.E.S.S. . ICRC . 15th July 2017

Markarian 421

■ Detection significance: 196σ ■ S/B ratio: 35 ■ No hints of systematics despite

extremely large zenith angle

■ Extension upper limits

(2D Gaussian width):

▪ 23.4’’ (1σ) ▪ 33.5’’ (3σ)

■ Factor of ~ 3 below the currently

most constraining size limit of any TeV source!

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• M. Holler . Extension of unresolved TeV sources with H.E.S.S. . ICRC . 15th July 2017

Checking Unresolved Sources

■ New quality of extension measurements in

VHE gamma-ray astronomy

■ Search for extensions well below instrument

PSF possible, down to ≤ 40’’

■ Several to be checked, up to now one

studied in detail

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• M. Holler . Extension of unresolved TeV sources with H.E.S.S. . ICRC . 15th July 2017

Checking Unresolved Sources

■ New quality of extension measurements in

VHE gamma-ray astronomy

■ Search for extensions well below instrument

PSF possible, down to ≤ 40’’

■ Several to be checked, up to now one

studied in detail

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• M. Holler . Extension of unresolved TeV sources with H.E.S.S. . ICRC . 15th July 2017

Checking Unresolved Sources

■ New quality of extension measurement in

VHE gamma-ray astronomy

■ Search for extensions well below instrument

PSF possible, down to ≤ 40’’

■ Several to be checked, up to now one

studied in detail

■ Limits on the Crab Nebula up to now:

▪ < 1.5’ for E < 10 TeV (HEGRA) ▪ < 2.2’ for E > 500 GeV (MAGIC I)

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Albert et al. (2008)

• M. Holler . Extension of unresolved TeV sources with H.E.S.S. . ICRC . 15th July 2017

Crab Nebula, E > 700 GeV

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■ Detection significance

137σ

■ S/B ratio 58 ■ Highly incompatible with

point-source PSF

• M. Holler . Extension of unresolved TeV sources with H.E.S.S. . ICRC . 15th July 2017

Measuring the Crab Extension

■ Quote: Do your crabs measure

up? Even the most careful measurement is only as good as the gauge you use... and an inaccurate gauge can result in a steep fine for keeping undersize

• crabs. Gauges can be inaccurate

for a number of reasons.

■ Ok fine, we now believe our

gauge… and use Sherpa for the measurement itself (convolving PSF with different 2D Gaussian widths and checking LogLikelihood)

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greatcrabgear.com

• M. Holler . Extension of unresolved TeV sources with H.E.S.S. . ICRC . 15th July 2017

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■ Extension TS = 83 (~ 9σ) ■ Best-fit Gaussian width:

(52.2 ± 2.9stat ± 7.8sys)’’

• M. Holler . Extension of unresolved TeV sources with H.E.S.S. . ICRC . 15th July 2017

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H.E.S.S. Crab ICRC 2017

• M. Holler . Extension of unresolved TeV sources with H.E.S.S. . ICRC . 15th July 2017

MWL Comparison

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• M. Holler . Extension of unresolved TeV sources with H.E.S.S. . ICRC . 15th July 2017

MWL Comparison

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• M. Holler . Extension of unresolved TeV sources with H.E.S.S. . ICRC . 15th July 2017

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X-rays VHE UV

• M. Holler . Extension of unresolved TeV sources with H.E.S.S. . ICRC . 15th July 2017

Energy Dependency

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• M. Holler . Extension of unresolved TeV sources with H.E.S.S. . ICRC . 15th July 2017

Model vs. Data

■ Used updated model from Kennel

& Coroniti, assuming magnetisation parameter of 0.01

■ rTS = 0.15 pc (in line with newer

measurements)

■ Observed extension can be well

reproduced

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• M. Holler . Extension of unresolved TeV sources with H.E.S.S. . ICRC . 15th July 2017

Conclusions

■ Reached new quality of extension

measurements in VHE gamma-ray astronomy

■ Crab Nebula resolved at VHE energies

for the first time

■ Gaussian width: (52.2 ± 2.9stat ± 7.8sys)’’ ■ TeV IC nebula larger than synchrotron

X-ray one

■ arXiv identifier: 1707.04196

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• M. Holler . Extension of unresolved TeV sources with H.E.S.S. . ICRC . 15th July 2017

Backup

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• M. Holler . Extension of unresolved TeV sources with H.E.S.S. . ICRC . 15th July 2017

Likelihood Profiles

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• M. Holler . Extension of unresolved TeV sources with H.E.S.S. . ICRC . 15th July 2017

Year-by-Year Stability

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• M. Holler . Extension of unresolved TeV sources with H.E.S.S. . ICRC . 15th July 2017

Termination Shock Radius

■ Inner ring corresponding to ~ 15.6

arcsec (see e.g. Ng. & Romani 2007)

■ For an assumed distance of 2 kpc:

rTS = 0.15 pc

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