EXTRAGALACTIC SOURCE POPULATION STUDIES AT VERY HIGH ENERGIES IN - - PowerPoint PPT Presentation

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EXTRAGALACTIC SOURCE POPULATION STUDIES AT VERY HIGH ENERGIES IN THE CHERENKOV TELESCOPE ARRAY ERA T. Hassan 1 , A. Dominguez 2 , J. Lefaucheur 3 , D. Mazin 4 , S. Pita 5 , A. Zech 3 , for the CTA Consortium 1 I n s t i t u t d e F i

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SLIDE 1

EXTRAGALACTIC SOURCE POPULATION STUDIES AT VERY HIGH ENERGIES IN THE CHERENKOV TELESCOPE ARRAY ERA

  • T. Hassan1, A. Dominguez2, J. Lefaucheur3, D. Mazin4, S. Pita5,
  • A. Zech3, for the CTA Consortium

1

I n s t i t u t d e F i s i c a d ’ A l t e s E n e r g i e s ( I F A E ) , T h e B a r c e l

  • n

a I n s t i t u t e

  • f

S c i e n c e a n d T e c h n

  • l
  • g

y

2

U n i v e r s i d a d C

  • m

p l u t e n s e d e Ma d r i d , G r u p

  • d

e A l t a s E n e r g í a s ( G A E )

3

L U T H , O b s e r v a t

  • r

e d e P a r i s , P S L R e s e a r c h U n i v e r s i t y , C N R S

4

U n i v e r s i t y

  • f

T

  • k

y

  • ,

I C R R

5

A P C , A s t r

  • P

a r t i c l e e t C

  • s

m

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  • g

i e , U n i v e r s i t é P a r i s D i d e r

  • t
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SLIDE 2

THE CHERENKOV TELESCOPE ARRAY

  • T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017)

2

  • The next generation of VHE gamma-ray detectors
  • 4 decades of energy range: ~20 GeV → ~ 300 T

eV

  • Layout of IACT

s of 3 difgerent sizes

  • Full sky coverage: two sites, one in each hemisphere
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SLIDE 3

THE CHERENKOV TELESCOPE ARRAY

  • T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017)

3

  • CTA will greatly outperform current generation of IACT

s

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SLIDE 4

THE FERMI-LAT

  • T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017)

4

  • Surveys the whole sky every 3 hours
  • Recently released the 3FHL catalog
  • Out of 7 years of Pass 8 data
  • 1556 sources above 10 GeV

(1231 extragalactic)

  • Only 72 of these sources detected

by current IACT

  • s. What about CTA?
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SLIDE 5

THE CHERENKOV TELESCOPE ARRAY

  • T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017)

5

  • CTA will greatly outperform current generation of IACT

s

3FHL

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SLIDE 6

THE CHERENKOV TELESCOPE ARRAY

  • T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017)

6

  • CTA will greatly outperform current generation of IACT

s

3FHL HAWC

For the future

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SLIDE 7

FERMI-LAT 3FHL CATALOG

  • T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017)

7

  • Given the low energy threshold of CTA (~20 GeV), the 3FHL

is the best available sample of persistent sources detectable by CTA

  • 79% of extragalactic sources (1231), 43% of these with

known redshift (526)

  • The main two problems to extrapolate their spectra to VHE:

–

57% of unknown redshift → unknown EBL absorption

–

Unknown intrinsic spectrum above ~60 – 100 GeV (limited by Fermi-LAT efgective area)

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SLIDE 8

SOURCE VHE EXTRAPOLATIONS

  • T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017)

8

  • T
  • handle the unknown redshift of 57% of 3FHL extragalactic

sources

–

We do not know their redshift, but we know their class From the extragalactic sources with known redshift

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SLIDE 9

SOURCE VHE EXTRAPOLATIONS

  • T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017)

9

  • T
  • handle the unknown redshift of 57% of 3FHL extragalactic

sources

–

We do not know their redshift, but we know their class We assign a random redshift following each class distribution of known redshifts From the extragalactic sources with known redshift

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SLIDE 10

SOURCE VHE EXTRAPOLATIONS

  • T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017)

10

  • T
  • handle the unknown spectrum above ~60 – 100 GeV

–

We fjt spectra with difgerent functions + EBL attenuation (Dominguez 2011)

  • Power-law + EBL attenuation
  • Power-law with exp. cutofg at 1/(1+z) T

eV + EBL attenuation

  • Broken Power-law + EBL attenuation

(if Γ > 2 → Γ = 2.5 above 100/(1+z) GeV )

  • Log-Parabola + EBL attenuation

More optimistic extrapolation

slide-11
SLIDE 11

SOURCE VHE EXTRAPOLATIONS

  • T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017)

11

  • T
  • handle the unknown spectrum above ~60 – 100 GeV

–

We fjt spectra with difgerent functions + EBL attenuation (Dominguez 2011) Mrk 421 PKS 1101-536 PL + EBL Bright source Faint source

Using naima: https://github.com/zblz/naima

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SLIDE 12

SOURCE VHE EXTRAPOLATIONS

  • T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017)

12

  • T
  • handle the unknown spectrum above ~60 – 100 GeV

–

We fjt spectra with difgerent functions + EBL attenuation (Dominguez 2011) Mrk 421 PKS 1101-536 LP + EBL

Using naima: https://github.com/zblz/naima

Bright source Faint source

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SLIDE 13

DETECTABILITY COMPUTATION

  • T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017)

13

  • Internal CTA performance IRFs were used to estimate source

detectability

  • Three difgerent software packages were tested, providing

consistent estimations

  • CTAmacros: https://github.com/cta-observatory/ctamacros
  • Gammapy: https://github.com/gammapy/gammapy
  • GAEtools: http://eprints.ucm.es/35143/
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SLIDE 14

DETECTABILITY COMPUTATION

  • T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017)

14

  • Internal CTA performance IRFs were used to estimate source

detectability

  • Three difgerent software packages were tested, providing

consistent estimations

  • Only sources culminating at less than 50 deg away from zenith

at each site were considered (using IRFs at 20 and 40 deg)

  • A source is detectable if S > 5σ (ofg-to-on source exposure ratio of

5), excess > 10 and 5 times larger than 1% of the background

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SLIDE 15

ACCESSIBLE EXTRAGAL. POPULATION

  • T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017)

15

  • Extragalactic source population accessible to CTA:

Detectable sources by CTA Detected by current IACTs

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SLIDE 16
  • T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017)

16

  • Extragalactic source population accessible to CTA:

ACCESSIBLE EXTRAGAL. POPULATION

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SLIDE 17

ACCESSIBLE EXTRAGAL. POPULATION

  • T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017)

17

  • Extragalactic source population accessible to CTA:
  • PLExp. 1 TeV

5 h obs. time

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SLIDE 18

ACCESSIBLE EXTRAGAL. POPULATION

  • T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017)

18

  • Extragalactic source population accessible to CTA:
  • PLExp. 1 TeV

20 h obs. time

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SLIDE 19
  • T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017)

19

  • Detectable sources vs redshift
  • Population of sources at large redshift, even in steady state,

under conservative extrapolation schemes

ACCESSIBLE EXTRAGAL. POPULATION

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SLIDE 20

CONCLUSIONS

  • T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017)

20

  • This kind of studies show the potential of future CTA Key

Science Projects and dedicated proposals

  • CTA will dramatically increase the number of detectable

blazars in their steady state, measuring their spectra over 4 decades in energy, in a wide range of redshifts (z ~ 1.5, not considering fmaring states)

  • Not only the study of AGN physics, also fundamental science

topics will benefjt from the detection of these sources (EBL, LIV, ALPs, IGMF ...)

  • CTA might be able to access new populations of EHBLs, not

detectable by Fermi-LAT (BZCAT)

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SLIDE 21

21

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SLIDE 22
  • T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017)

22

  • CTA easily detects 3FHL hardest sources
  • Could there be a fainter/harder population of EHBLs, not

detected by Fermi-LAT?

ACCESSIBLE EXTRAGAL. POPULATION

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SLIDE 23

BLAZARS NOT DETECTED BY LAT?

  • T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017)

23

  • There might be a hidden population of EHBLs
  • Nearly 50% of BZCAT

BL Lacs not detected by Fermi-LAT

  • EHBLs are faint in the

HEs, and would not be detectable by LAT

  • They are faint objects,

but CTA may be able to detect a signifjcant fraction