1. OBSERVATIONS OF AGNs USING PACT (Pachmarhi Array of Cherenkov Telescopes) Debanjan Bose (On behalf of PACT collaboration) “The Multi-Messenger Approach To High Energy Gamma Ray Sources” July 4 -July 7, Barcelona, Spain

2. Active Galactic Nuclei AGNs dominate extra-galactic astronomy by virtue of their great luminosities A super massive black hole at the centre surrounded by an accretion disk A strong jet of relativistic particles emanates perpendicular to the plane of the accretion disk Blazars are a class of AGN with jet along the line of sight

3. B L Lac objects or Blazars  Variable at all wavelengths  SEDs are characterised by two humps  Divided into two sub-classes HBL and LBL  VHE flares are generally well correlated with X-ray flare

4. Pachmarhi Array of Cherenkov Telescopes Pachmarhi located in central India, 22º28' N 78º25' E altitude ~ 1075m 24 telescopes spread over an area of 80m  100m Each telescope has 7 para-axially mounted parabolic mirrors of diameter 0.9m, f/d ~ 1 A fast photo-tube (EMI9807B) of 2" diameter at the focus of every mirror A coincidence of 4 out of 6 telescopes in a sector generates trigger For each trigger TDC (timing) and ADC (photon density) informations are recorded Energy threshold of PACT ~ 750 GeV

5. Pachmarhi Array of Cherenkov Telescopes Pachmarhi located in central India, 22º28' N 78º25' E altitude ~ 1075m 24 telescopes spread over an area of 80m  100m Each telescope has 7 para-axially mounted parabolic mirrors of diameter 0.9m, f/d ~ 1 A fast photo-tube (EMI9807B) of 2" diameter at the focus of every mirror A coincidence of 4 out of 6 telescopes in a sector generates trigger For each trigger TDC (timing) and ADC (photon density) informations are recorded Energy threshold of PACT ~ 750 GeV

6. Pachmarhi Array of Cherenkov Telescopes Pachmarhi located in central India, 22º28' N 78º25' E altitude ~ 1075m 24 telescopes spread over an area of 80m  100m Each telescope has 7 para-axially mounted parabolic mirrors of diameter 0.9m, f/d ~ 1 A fast photo-tube (EMI9807B) of 2" diameter at the focus of every mirror A coincidence of 4 out of 6 telescopes in a sector generates trigger For each trigger TDC (timing) and ADC (photon density) informations are recorded Energy threshold of PACT ~ 750 GeV

7. OBSERVATION LOG Mkn 421 Z=0.030 Mkn 501 Z=0.034 ON 231 Z=0.102 1ES1426+42 8 Z=0.129 20003510. 710. -- 20011960. -- 20021860. 510. -- 1520. 20031770. 840. 510. 570. 20042270. 780. 550. 870. 2005 930. -- 960. Observation duration (mins.) year

8. ANALYSIS OF PACT DATA Arrival direction of a shower is determined by reconstructing the shower front using the relative arrival time of cherenkov shower at each telescope The Cherenkov front is fitted with a plane, normal to this plane gives the direction of shower axis Space angle between the direction of shower axis and direction of source is obtained for events with  8 telescopes Space angle distributions of source and background runs are compared over same zenith angle range

9. ANALYSIS OF PACT DATA Background space angle distributions are normalized w.r.t Source distribution by comparing shape in 2.5º to 6.5 º window, since no γ-rays are expected in that region γ-ray signal is obtained as excess of source events over background events in 0º to 2.5º region as No. of γ-rays Where c is a constant

10. Mkn 421  First blazar detected at TeV energies by WHIPPLE in 1992  This is also the closest (z=0.031)  Quite often it goes into flaring state  Flare in TeV energies mostly associated with flare in X-ray energies

11. Mkn 421  First blazar detected at TeV energies by WHIPPLE in 1992  This is also the closest (z=0.031)  Quite often it goes into flaring state  Flare in TeV energies mostly associated with flare in X-ray energies PACT ASM on board RXTE

12. Mkn 421 Time average flux combining all data obtained using PACT during 2000-2005 is 4.45(  1.9)  10 -12 photons cm -2 s -1 above 1.2 TeV 2001

13. Multiwavelength Campaign 2003 for Mkn421 26 th February to 5 th March there was a multiwavelength campaign between X-ray and γ-ray Source was in quiet state PACT data was not so useful X-ray data taken by RXTE satellite has been analysed

14. Analysis of PCA data For timing analysis FTOOLS and XRONOS has been used

15. Analysis of PCA data  Spectral data analysed using XSPEC  Model used : power law with exponential cutoff  Best fit parameters for combined spectra N H ~ 1.38  10 20 cm -2  ~ 2.39 (  0.03) E cutoff ~ 23.9 (  2.4) keV  Systematic error assumed was 1%

16. Multiwavelength Campaign 2003 for Mkn421 26 th February to 5 th March there was a multiwavelength campaign between X-ray and γ-ray Source was in quiet state PACT data was not so useful X-ray data taken by RXTE satellite has been analysed NIR data - Gurushikhar Observatory, Mount Abu, India Radio data at 22 and 37 Ghz – Metsähovi radio telescope

17. Multiwavelength Campaign 2003 for Mkn421 radio NIR X-ray

18. Multiwavelength Campaign 2003 for Mkn421 radio NIR X-ray One zone SSC model :  =14, B=0.4G, R=0.7  10 16 cm, w e =0.06 erg cm -3, E b =10.34, E min =6.5, E max =11.22, p 1 =2.05, p 2 =3.6 (Krawczynski et al 2004)

19. Multiwavelength Campaign 2003 for Mkn421 radio NIR X-ray PACT One zone SSC model :  =14, B=0.4G, R=0.7  10 16 cm, w e =0.06 erg cm -3, E b =10.34, E min =6.5, E max =11.22, p 1 =2.05, p 2 =3.6 (Krawczynski et al 2004)

20. Multiwavelength Campaign 2003 for Mkn421

21. SED of Mkn421 during flare in 2001 Mkn421 was in very active state in early months of 2001 We have analysed the RXTE data taken in March - April Optical data (V-band) was taken by WEBT collaboration, using KVA-telescope on La Palma Radio data was taken by Metsähovi radio telescope

22. SED of Mkn421 during flare in 2001 radio optical X-ray One zone SSC model :  =15.2, B=0.12G, R=15  10 16 cm, w e =0.023 erg cm -3, E b =11.0, E min =6.5, E max =11.6, p 1 =2.0, p 2 =3.0 Solid - 2001 Dotted - 2003

23. Spectral Index vs Flux 2003 2001 Spectra hardens as flux increases

24. Other Blazars In 1997 huge flare was detected from Mkn501 by other experiment During PACT observations from 2000-2005 Mkn501 was in low state We have estimated 3  upperlimit 1997

25. Other Blazars In 1997 huge flare was detected from Mkn501 by other experiment During PACT observations from 2000-2005 Mkn501was in low state We have estimated 3  upperlimit 1ES1426+428 is a distant blazar, needs very long observation

26. Other Blazars In 1997 huge flare was detected from Mkn501 by other experiment During PACT observations from 2000-2005 Mkn501was in low state We have estimated 3  upperlimit 1ES1426+428 is a distant blazar, needs very long observation ON231, LBL type, no experiment has detected significant excess above 100 GeV

27. Conclusions Sensitivity of PACT is not good enough to detect blazars in reasonable time when they are not in active state Out of 4 blazars for Mkn421 we have estimated average integral flux and for others we have given upperlimits γ-ray and X-ray seems to be correlated, during flare energy spectrum hardens as flux increases One-zone SSC model can not fit the measured fluxes at radio and optical wavelengths, introduction of additional zone improves the fit significantly More sensitive detectors are needed like HAGAR to detect faint sources

28. High Altitude GAmma Ray (HAGAR) Observatory  A 7 telescopes array is coming up at Hanle in Himalayas altitude 4.3 km

29. High Altitude GAmma Ray (HAGAR) Observatory  A 7 telescopes array is coming up at Hanle in Himalayas altitude 4.3 km  Lateral spread is less, near shower core density is 4-5 times higher compare to sea level PACT HAGAR

30. High Altitude GAmma Ray (HAGAR) Observatory  A 7 telescopes array is coming up at Hanle in Himalayas altitude 4.3 km  Lateral spread is less, near shower core density is 4-5 times higher compare to sea level  Low atmospheric attenuation : @ Hanle 14% @ sea level 50%  Energy Threshold : 60 GeV ; sensitivity better than PACT 60 GeV

31. High Altitude GAmma Ray (HAGAR) Observatory  A 7 telescopes array is coming up at Hanle in Himalayas altitude 4.3 km  Lateral spread is less, near shower core density is 4-5 times higher compare to sea level  Low atmospheric attenuation : @ Hanle 14% @ sea level 50%  Energy Threshold : 60 GeV ; sensitivity better than PACT

32. High Altitude GAmma Ray (HAGAR) Observatory  A 7 telescopes array is coming up at Hanle in Himalayas altitude 4.3 km  Lateral spread is less, near shower core density is 4-5 times higher compare to sea level  Low atmospheric attenuation : @ Hanle 14% @ sea level 50%  Energy Threshold : 60 GeV ; sensitivity better than PACT

33. Thank you !!

34. SSC parameters for optical 2001 :  =14, B=0.055G, R=1.6  10^17 cm, we =0.00019 erg cm^(-3), Eb=10., Emin=6.5, Emax=11., p1=2.05, p2=3.4 SSC parameters for radio 2001 :  =14, B=0.003G, R=8  10^17 cm, we =0.000020 erg cm^(-3), E(b)=11, Emin=6.5, Emax=11.5, p1=2.05, p2=3.4 SSC parameters for radio 2003 :  =14, B=0.003G, R=8  10^17 cm, we =0.000015 erg cm^(-3), E(b)=11, Emin=6.5, Emax=11.5, p1=2.05, p2=3.4 SSC parameters for optical 2003 :  =14, B=0.055G, R=1.6  10^17 cm, we =0.00017 erg cm^(-3), Eb=10., Emin=6.5, Emax=11., p1=2.05, p2=3.4

35. SED of Mkn421 for 2001