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

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 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 o n a I n s t i t u t e o f S c i e n c e a n d T e c h n o l o g y 2 U n i v e r s i d a d C o m p l u t e n s e d e Ma d r i d , G r u p o 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 o 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 o f T o k y o , I C R R 5 A P C , A s t r o P a r t i c l e e t C o s m o l o g i e , U n i v e r s i t é P a r i s D i d e r o t

THE CHERENKOV TELESCOPE ARRAY ● 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 T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017) 2

THE CHERENKOV TELESCOPE ARRAY CTA will greatly outperform current generation of IACT s ● T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017) 3

THE FERMI-LAT ● 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? T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017) 4

THE CHERENKOV TELESCOPE ARRAY CTA will greatly outperform current generation of IACT s ● 3FHL T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017) 5

THE CHERENKOV TELESCOPE ARRAY CTA will greatly outperform current generation of IACT s ● For the 3FHL future HAWC T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017) 6

FERMI-LAT 3FHL CATALOG 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) T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017) 7

SOURCE VHE EXTRAPOLATIONS T o 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 T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017) 8

SOURCE VHE EXTRAPOLATIONS T o 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 We assign a random redshift following each class distribution of known redshifts T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017) 9

SOURCE VHE EXTRAPOLATIONS T o handle the unknown spectrum above ~60 – 100 GeV ● We fjt spectra with difgerent functions + EBL attenuation – (Dominguez 2011) Power-law + EBL attenuation ● More optimistic extrapolation 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 ● T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017) 10

SOURCE VHE EXTRAPOLATIONS T o handle the unknown spectrum above ~60 – 100 GeV ● We fjt spectra with difgerent functions + EBL attenuation – (Dominguez 2011) PL + EBL Mrk 421 PKS 1101-536 Using naima: Bright source Faint source https://github.com/zblz/naima T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017) 11

SOURCE VHE EXTRAPOLATIONS T o handle the unknown spectrum above ~60 – 100 GeV ● We fjt spectra with difgerent functions + EBL attenuation – (Dominguez 2011) LP + EBL Mrk 421 PKS 1101-536 Using naima: Bright source Faint source https://github.com/zblz/naima T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017) 12

DETECTABILITY COMPUTATION 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/ ● T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017) 13

DETECTABILITY COMPUTATION 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 > 5 σ (ofg-to-on source exposure ratio of ● 5), excess > 10 and 5 times larger than 1% of the background T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017) 14

ACCESSIBLE EXTRAGAL. POPULATION Extragalactic source population accessible to CTA: ● Detectable sources Detected by by CTA current IACTs T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017) 15

ACCESSIBLE EXTRAGAL. POPULATION Extragalactic source population accessible to CTA: ● T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017) 16

ACCESSIBLE EXTRAGAL. POPULATION Extragalactic source population accessible to CTA: ● PLExp. 1 TeV 5 h obs. time T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017) 17

ACCESSIBLE EXTRAGAL. POPULATION Extragalactic source population accessible to CTA: ● PLExp. 1 TeV 20 h obs. time T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017) 18

ACCESSIBLE EXTRAGAL. POPULATION Detectable sources vs redshift ● Population of sources at large redshift, even in steady state, ● under conservative extrapolation schemes T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017) 19

CONCLUSIONS 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) T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017) 20

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ACCESSIBLE EXTRAGAL. POPULATION CTA easily detects 3FHL hardest sources ● Could there be a fainter/harder population of EHBLs, not ● detected by Fermi-LAT? T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017) 22

BLAZARS NOT DETECTED BY LAT? 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 T. Hassan – Extragalactic source population studies at VHE in the CTA era. (18 July 2017) 23