The COMPTEL data (∼0.7–30 MeV) were searched for emission from AGN. Four sources have been detected so far: the quasars 3C 273, 3C 279, PKS 0528+134, and the radio galaxy Centaurus A. 3C 273 and 3C 279 were detected in CGRO observation period 3 with quite different spectral shapes. There is also evidence for 3C 273 at a weak flux level in observation period 11. The quasar PKS 0528+134 was detected above 3 MeV as part of a search for AGN already observed by EGRET. Cen A was seen up to 3 MeV by combining data from different observation periods

Bennett, K

Bloemen, H

Collmar, W

de Vries, C

den Herder, J W

Diehl, R

Hermsen, W

Lichti, G G

McConnell, Mark L

Ryan, James M.

Schonfelder, V

Stacy, G

Steinle, H

Strong, A W

Swanenburg, B

Williams, O R

Winkler, C

English

UNH Scholars' Repository

University of New HampshireUniversity of New Hampshire Scholars' RepositorySpace Science Center Institute for the Study of Earth, Oceans, and Space(EOS)1993Search for gamma‐ray emission from AGN withCOMPTELW CollmarMax-Planck-Institut für extraterrestriche PhysikR DiehlMax-Planck-Institut für extraterrestriche PhysikG G. LichtiMax-Planck-Institut für extraterrestrische PhysikV SchonfelderMax-Planck-Institut für extraterrestrische PhysikH SteinleMax-Planck-Institut für extraterrestriche PhysikSee next page for additional authorsFollow this and additional works at: https://scholars.unh.edu/sscPart of the Astrophysics and Astronomy CommonsThis Conference Proceeding is brought to you for free and open access by the Institute for the Study of Earth, Oceans, and Space (EOS) at University ofNew Hampshire Scholars' Repository. It has been accepted for inclusion in Space Science Center by an authorized administrator of University of NewHampshire Scholars' Repository. For more information, please contact nicole.hentz@unh.edu.Recommended CitationSearch for gamma‐ray emission from AGN with COMPTEL Collmar, W. and Diehl, R. and Lichti, G. G. and Schönfelder, V. andSteinle, H. and Strong, A. W. and Bloemen, H. and den Herder, J. W. and Hermsen, W. and Swanenburg, B. N. and de Vries, C. andMcConnell, M. and Ryan, J. and Stacy, G. and Bennett, K. and Williams, O. R. and Winkler, C., AIP Conference Proceedings, 280,483-487 (1993), DOI:http://dx.doi.org/10.1063/1.44271AuthorsW Collmar, R Diehl, G G. Lichti, V Schonfelder, H Steinle, A W. Strong, H Bloemen, J W. den Herder, WHermsen, B Swanenburg, C de Vries, Mark L. McConnell, James M. Ryan, G Stacy, K Bennett, O R. Williams,and C WinklerThis conference proceeding is available at University of New Hampshire Scholars' Repository: https://scholars.unh.edu/ssc/184Search for gammaray emission from AGN with COMPTELW. Collmar, R. Diehl, G. G. Lichti, V. Schönfelder, H. Steinle, A. W. Strong, H.Bloemen, J. W. den Herder, W. Hermsen, B. N. Swanenburg, C. de Vries, M.McConnell, J. Ryan, G. Stacy, K. Bennett, O. R. Williams, and C. Winkler  Citation: AIP Conference Proceedings 280, 483 (1993); doi: 10.1063/1.44271 View online: http://dx.doi.org/10.1063/1.44271 View Table of Contents:http://scitation.aip.org/content/aip/proceeding/aipcp/280?ver=pdfcov Published by the AIP Publishing  Articles you may be interested in Gamma rays from active galactic nuclei AIP Conf. Proc. 280, 541 (1993); 10.1063/1.44325  High energy gammaray emission from active galactic nuclei observed by theenergetic gammaray experiment telescope (EGRET) AIP Conf. Proc. 280, 461 (1993); 10.1063/1.44319  Search for TeV gammaray emission from AGN’s using the Whipple imagingtelescope AIP Conf. Proc. 280, 508 (1993); 10.1063/1.44276  Monitoring the longterm behavior of active galactic nuclei using BATSE AIP Conf. Proc. 280, 473 (1993); 10.1063/1.44268  Initial results from COMPTEL—an overview AIP Conf. Proc. 280, 21 (1993); 10.1063/1.44123   This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at:http://scitation.aip.org/termsconditions. Downloaded to  IP:  132.177.229.79 On: Mon, 24 Nov 2014 18:14:33SEARCH FOR GAMMA-RAY EMISSION FROM AGN WITH COMPTELW. Collmar, R. Diehl, G.G. Lichti, V. Schönfelder, H. Steinle, A.W. StrongMax-Planck Institut für Extraterrestrische Physik, D/W-8046 Garching, GermanyH. Bloemen, J.W. den Herder, W. Hermsen, B.N. Swanenburg, C. de VriesSRON-Leiden, P.B. 9504, NL-2300 RA Leiden, The NetherlandsM. McConnell, J. Ryan, G. StacyUniversity of New Hampshire, Durham NH03824, USAK. Bennett, O.R. Williams, C. WinklerAstrophysics Division, ESTEC, 2200 AG Noordwijk, The NetherlandsABSTRACTThe COMPTEL data (^.„ 0.'"1-30 MeV) were searched for emission fromAGN. Four sources have been detected so far: the quasars 3C 273, 3C 279,PKS 0528+134, and the radio galaxy Centaurus A. 3C 273 and 3C 279 weredetected in CGRO observation period 3 with quite different spectral shapes.There is also evidence for 3C 273 at a weak flux level in observation period 11.The quasar PKS 0528+134 was cletected above 3 MeV as part of a search forAGN already observed by EGRET. Cen A was seen up to 3 MeV by combiningdata from different observation i>criods.INTRODUCTIONThe imaging Compton telescope COMPTEL is sensitive in the low en-ergy 7-ray range from about 0.7 MeV to 30 MeV. A detailed description of theCOMPTEL characteristics is given by Schönfelder et al'.COMPTEL's MeV energy range is particularly interesting for investiga-tions into the physics of AGN. Measurements in the neighbouring energy rangesindicate that some AGN might have their peak luminosity in this range and thatthere might be breaks in the spectra at MeV energies. Moreover, before COMP-TEL only three AGN were detected at MeV energies: NGC 4151 2 , MCG 8-11-1 3 ,and Cen A4 . Because each new detection increases our knowledge significantly,the COMPTEL data were searched for evidence of emission from AGN. Thepossibility of simultaneous mea.surements in neighbouring energy bands withCGRO would make AGN detections by COMPTEL even more valuable for theunderstanding of AGN physics.In this paper we report on the results of the search for y-ray emission fromAGN in the COMPTEL data. In particular, the search was dove for promisingobjects, with emphasis on AGN already detected by the EGRET experimentaboard CGRO. This paper represents a progress report with largely preliminaryresults. A more complete analysis for the different sources is underway.THE QUASARS 3C 273 AND 3C 279During the first year of its mission, the quasars 3C 273 and 3C 279 were© 1993 American Institute of Physics	 483 This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at:http://scitation.aip.org/termsconditions. Downloaded to  IP:  132.177.229.79 On: Mon, 24 Nov 2014 18:14:33484 Search for Gamma-Ray Emissionin the COMPTEL field of view twice: in the observation period 3 (tune 91)and 11 (October 91). In observation period 3, both quasars were detected byCOMPTEL, as already reportecd 5 . 3C 273 was detected mainly in the lowerpart of the COMPTEL energy range (1 - 10 MeV), while at the highest energies(10-30 MeV) only an upper limit could be derived. In contrast, 3C 279 wasdetected at the higher COMPTEL energies (3-30 MeV) while at lower energies(1-3 MeV) only an upper limit could be derived. In figure 1 the COMPTELuxes for the three energy interwals together with the spectral shapes measuredby EGRET and OSSE simultancously for 3C 273) are given for both quasars.The error bars on the C MPTEL spectral points are statistical only. For 3C 273the OSSE spectrum (photon index -1.8 6 ) is harder than the EGRET spectrum(photon index -2.47 ) indicating a break somewhere in the MeV region. TheCOMPTEL data are consistent with a spectral steepening around 1 MeV. For3C 279, EGRET and COMPTEL measurements together indicate a spectralbreak around 10 MeV5 .Figure 1. CGRO spectra of 3C 273 and 3C 279. a) Simultaneously(obs. 3) measured energy spectra of 3C 273 by OSSE 6 , COMPTELS ,and EGRET 7 . The lower COMPTEL spectral points are from Octo-ber 91 (obs. 11). b) Spectra of 3C 279. The OSSE spectral shape wasmeasured in September 91', COMPTEL in June 91 5 , and EGRETin June and October 91 8 .In observation period 11, the COMPTEL data show evidente for 3C 273at a weak flux level. The 1-3 MeV skymap of this region shows a feature witha significante of ti 4u (figure ^).  In the 3-10 MeV band a marginally significantfeature (^-, 2.4ar) appears. Both excesses are consistent with the location of 3C273. The derived flux level is r' 50% of that observed in observation period3 same upper limit for the 10-30 MeV band). The spectral points includingonly the statistical errors are also given in figure 1. A more detailed analysis isunderway. This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at:http://scitation.aip.org/termsconditions. Downloaded to  IP:  132.177.229.79 On: Mon, 24 Nov 2014 18:14:33W. Collmar et al. 485Figure 2. 1-3 MeV skymap of theVirgo region for observation pe-riod 11 (October 91). There isevidence (^„ 4ar) for 3C 273 at aweak flux level.Figure 3. Extrapolation of the measured EGRET AGN spectra (>100MeV) into the COMPTEL energy range. For clarity the flux is mul-tiplied by E2 . The horizontal lines indicate the conservative COMP-TEL 3a sensitivity limits' for the 4 standard energy* intervals assum-ing an E-2 power law spectrum.SEARCH FOR AGN DETECTED BY EGRETUp to now EGRET has announced the detection of 16 AGN 9 mainly atenergies above 100 MeV. For most of them spectral parameters are available.A search in the COMPTEL data for these AGN has been started. To selectthe promising candidates, the mcasured EGRET spectra were extrapolated intothe COMPTEL energy range for comparison with the conservative COMPTELsensitivity limits (figure 3).Besides 3C 273 and 3C 279 in observation period 3, there is only oneother promising candidate: the quasar PKS 0528+134. The extrapolation of This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at:http://scitation.aip.org/termsconditions. Downloaded to  IP:  132.177.229.79 On: Mon, 24 Nov 2014 18:14:33486 Search for Gamma-Ray Emissionthe measured EGRET spectrum passes well above the sensitivity limits for allfour COMPTEL standard energy intervals. A search for this quasar led to itsdetection during the CGRO validation period and also in the survey observationperiod 1. Skymaps for the energy ranges 3-10 MeV and 10-30 MeV from thegalactic anticentre region during 9 days of the CGRO validation period (April28 - May 7, 1991) are given in figure 4. A clear excess at the position of thequasar PKS 0528+134 is visible in both skymaps. Because of the very recentdetection of PKS 0528+134 and its proximity to the Crab (~ 8°), a precise fluxvalue has not yet been determined. A first estimate leads to a fiux level of theorder of 10%-20% of the Crab flux for both energy ranges. No obvious signalfrom this source could be found so far for energies below 3 MeV, indicating aspectral break. A detailed analysis of this source is in progress.Figure 4. Skymaps of the galactic anticentre (April 28 - May 7, 91) forthe energy ranges- 3-10 MeV (a) and 10-30 MeV (b). In both imagesthe Crab is saturated for botter visibility of the image structure atlower intensity levels. In both energy ranges an excess at the positionof the quasar PKS 0528+134 is visible.The search for other AGN measured by EGRET is currently being pursued.No other AGN have been detected by COMPTEL so far. The recent EGRETresult for the superluminal quasar CTA 102, having the softest spectrum 1 ° (pho-ton index -2.6) of all AGN detected by EGRET, makes this source a candidatefor COMPTEL.THE RADIO GALAXY CENTAURUS AThe CGRO observation period 12 (October 1991) was devoted to the skyregion containing the active radio galaxy Centaurus A (Cen A). Because CenA has been observed before at MeV energies4 , it was a prime candidate forCOMPTEL. Only an upper limit could be determined for observation period1211 . However, by combining the data of several pointings (Cen A was in theCOMPTEL field of view several times) Cen A was detected up to 3 MeV in This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at:http://scitation.aip.org/termsconditions. Downloaded to  IP:  132.177.229.79 On: Mon, 24 Nov 2014 18:14:33W. Collmar et al. 487the COMPTEL data. Evidence for the detection can be found in 12 . TheCOMPTEL spectral points, together with spectral results of other experimentsare shown in figure 5.100 r1Ó 11Ó21Ó3- 10 5.^i1Ó610-i- [Jbertini et al. 1989Gehrelss et al..1981''	 ^- von Ballmoos et al..1982+ 03SE, 1991 - 1st 6 Davst L	 Q OSSE, 1991 - laat 9 Days Figure 5. Spectral measurementsof Cen A (from 13 with COMP-TEL results added) . The COMP -TEL spectral points are derivedfrom a combination of several point-ings. The upper limits for thehigher energies are 2a.0.10	 1.00	 10.01 €Energy iMeV)J: SUMMARYBy searching the COMPTEL data for AGN in the energy range 0.7-30MeV, 4 different objects have been detected so far: the quasars 3C 273, 3C 279,PKS 0528+134, and the radio galaxy Cen A.The spectra of these objects are quite different. While two of them, 3C273 and Cen A, were detected at lower energies, the other two, 3C 279 and PKS0528+134 were only seen at higher energies, indicating a harder spectrum.The presented findings are promising for the future of the CGRO mission,especially because of the possibility of simultaneous spectral measurements overabout 5 decades in energy by the different CGRO experiments. This capabilitywill surely improve the understanding of the still enigmatic AGN engine.REFERENCES1. V. Schönfelder et al., Ap.J. Supp. (in press) (1992)2. F. Perotti et al.,, Ap.J. 247, L63 (1981)3. F. Perotti et al., Nature 292, 133 (1981)4. P. v. Balimoos et al., Ap.J. 312, 134 (1987)5. W. Hermsen et al., Astron. Astrophys. Supp. (in press) (1992)6. W.N. Johnson et al., these proceedings7. C. v. Montigny et al., Astron. Astrophys. Supp. (in press) (1992)8. D. Kniffen et al., Ap. J. submitted9. C. Fichtel et al., these proceedings10. P. Nolan et al., these proceedings11. H. Steinle et al., Advances in Space Research (in press) (1993)12. H. Bloemen et al., these proceedings13. W.N. Johnson et al., Astron. Astrophys. Supp. (in press) (1992) This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at:http://scitation.aip.org/termsconditions. Downloaded to  IP:  132.177.229.79 On: Mon, 24 Nov 2014 18:14:33

Search for gamma‐ray emission from AGN with COMPTEL

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