During Phase I and Phase II of the CGRO‐mission, the quasar PKS 0528+134 was in the field of view of the COMPTEL instrument during several viewing periods. The quasar was detected by COMPTEL mainly at energies above 10 MeV. Below 10 MeV there is evidence for the source during some CGRO viewing periods, while below 3 MeV no signal is detected. The detections and non‐detections during different viewing periods follow the trend seen by EGRET, thereby indicating a time‐variable MEV‐flux of the quasar. The COMPTEL spectral results together with the simultaneously measured EGRET spectrum, indicate a spectral break in the upper part of the COMPTEL energy range at energies between 10 MeV and 30 MeV

Bennett, K

Bloemen, H

Collmar, W

Diehl, R

Hermsen, W

Lichti, G G

McConnell, Mark L

Ryan, James M.

Schonfelder, V

Stacy, G

Steinle, H

Strong, A W

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)1994Comptel observations of the quasar PKS0528+134W 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 CitationComptel observations of the quasar PKS 0528+134 Collmar, W. and Diehl, R. and Lichti, G. G. and Schönfelder, V. and Steinle, H.and Strong, A. W. and Bloemen, H. and Hermsen, W. and McConnell, M. and Ryan, J. and Stacy, J. G. and Bennett, K. and Williams, O.R. and Winkler, C., AIP Conference Proceedings, 304, 659-663 (1994), DOI:http://dx.doi.org/10.1063/1.45668AuthorsW Collmar, R Diehl, G G. Lichti, V Schonfelder, H Steinle, A W. Strong, H Bloemen, W Hermsen, 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/177Comptel observations of the quasar PKS 0528+134W. Collmar, R. Diehl, G. G. Lichti, V. Schönfelder, H. Steinle, A. W. Strong, H.Bloemen, W. Hermsen, M. McConnell, J. Ryan, J. G. Stacy, K. Bennett, O. R.Williams, and C. Winkler  Citation: AIP Conference Proceedings 304, 659 (1994); doi: 10.1063/1.45668 View online: http://dx.doi.org/10.1063/1.45668 View Table of Contents:http://scitation.aip.org/content/aip/proceeding/aipcp/304?ver=pdfcov Published by the AIP Publishing  Articles you may be interested in Comptel gammaray observations of the quasars CTA 102 and 3C 454.3 AIP Conf. Proc. 304, 644 (1994); 10.1063/1.45665  Simultaneous observations of the continuum emission of the quasar 3C 273 fromradio to γray energies AIP Conf. Proc. 304, 611 (1994); 10.1063/1.45659  MeV emission from the blackhole candidate GRO J0422+32 measured withCOMPTEL AIP Conf. Proc. 304, 197 (1994); 10.1063/1.45619  COMPTEL detection of the variable radio source GT 0236+610 AIP Conf. Proc. 304, 324 (1994); 10.1063/1.45581  Search for gammaray emission from AGN with COMPTEL AIP Conf. Proc. 280, 483 (1993); 10.1063/1.44271   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 18:01:18COMPTEL OBSERVATIONS OF THE QUASAR PKS 0528+134 W. Collmar, R. Diehl, G.G. Lichti, V. SchOnfelder, H. Steinle, A. W. Strong Max-Planck-Institut ftir extraterrestrische Physik, D-85740 Garching, FRG H. Bloemen, W. Hermsen SRON Leiden, P.B. 95(i)4, NL-2300 RA Leiden, The Netherlands M. McConnell, J. Ryan, J.G: Stacy University of New Hampshire, Durham NH 03824, USA K. Bennett, O.R. Williams, C. Winkler Astrophysics Division, ESTEC, NL-2200 AG Noordwijk, The Netherlands ABSTRACT During Phase I and Phase II of the CGRO-mission, the quasar PKS 0528+134 was in the field of view of the COMPTEL instrument during several viewing periods. The quasar was detected by COMPTEL ir~tinly at energies above 10 MeV. Below 10 MeV there is evidence for the source during some CGRO viewing periods, while below 3 MeV no signal is detected. The detections and non-detections during different viewing periods follow the trend seen by EGRET, thereby indicating a time-variable MeV-flux of the quasar. The COMPTEL spectral results together with the simultaneously measured EGRET spectrum, indicate a spectral break in the upper part of the COMPTEL energy range at energies between 10 MeV and 30 MeV. INTRODUCTION PKS 0528+134 was originally detected at ~/-ray energies (mainly above 100 MeV) by the EGRET experiment (Kanbach et al. 1991) during two CGRO pointings towards the galactic anticentre at the beginning of the mission (April and May 1991). Located in the same field as the well-known sources Crab and Geminga, this new T-ray source was identified with the radio source PKS 0528+134, and confirmed as a quasar, after positional analysis and after an optical spectrum revealed a redshift of 2.07 for this object (Hunter et al. 1993). A search in the COMPTEL data (0.75 - 30 MeV) for AGN detected by EGRET led to the discovery of PKS (i)528+134 also at low energy "y-rays (Collmar et al. 1993a). Preliminary results from the early viewing periods have been presented by Collmar et al. (1993b). In this paper we review the latest COMPTEL results on PKS 0525+134. Being work in progress (especially for the CGRO Phase II observations), the quantitative results should be considered as preliminary. OBSERVATIONS Up to the end of Phase II (August 1993) of the CGRO-mission, the quasar PKS 0528+134 (1: 191~ b: -11.~ was in the COMPTEL field of view several times. 9 1994 American Institute of Physics 659  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 18:01:18660 Quasar PKS 0528+134 During 5 viewing periods (VP) the source was located within 20 ~ of the COMPTEL pointing direction. The relevant data of these observations are given in Table I. For VP 2.5 (Target of Opportunity observation of the sun) no results have been derived yet (COMPTEL was operating in a special mode to detect solar neutrons). This observation period will be included in future work. Table I: COMPTEL observations ofPKS (i)528+128 (< 20 ~ pointing direction) VP Observation Observation Angular distance VP target Time Duration to point, direction (days) (o) 0 April 22 - May 7, 91 15 -8 CGRO verific.1 1 May 16 - May 30, 91 14 6.2 Crab pulsar 2.5 June 8 - June 15, 91 7 5.1 Sun, ToO a 213 March 23 - March 29, 93 6 9.0 Crab pulsar 221 May 13 - May 24, 93 11 6.3 Crab pulsar DATA ANALYSIS The COMPTEL data analysis package (COMPASS) includes for mapping and source analysis the Maximum-Entropy-Method (MEM) described by Strong et al. (1992) and the Maximum-Likelihood-Method (MLM) described by de Boer et al. (1992). Both methods can be used for the generation of skymaps, but - in the current setup of the COMPTEL data analysis ystem - source significances, fluxes and error regions are derived by the MLM. The COMPTEL data analysis for PKS 0528+134 is complicated by its proximity to the Crab (1: 184~ b:-5.~ The Crab is only 8 ~ away and is the brightest source in the COMPTEL energy range. Figure la shows a MLM-map of the Crab region in the 10- 30 MeV band. The image is clearly dominated by the Crab, though emission from PKS 0528+134 is also evident. The contour lines are elongated in direction of the Parkes quasar. From this figure it is apparent that a flux estimate for PKS 0528+134 can not simply be derived by reading off the relevant values from the map, because the two sources are not clearly resolved, and the Crab outshines the quasar by about a factor of 5 or more. For determination of the flux associated with the quasar, we have adopted the following procedure: emission models of the Crab and PKS 0528+134 have been generated by convolution of assumed (or known in case of Crab) source parameters with the COMPTEL response. These source models have been included into the null hypothesis of the likelihood fitting process so that their flux values are allowed to vary while their positions are kept fixed. This approach leads to a simultaneous determination of the Crab and PKS 0528+134 fluxes, together with the generation of an overall skymap with the two sources removed. We believe that this method should be best suited for this analysis. However, some systematic effects may still remain, and may possibly be larger at lower 1VP 0 was used for data analysis from April 28 to May 7, 1991 after COMPTEL had reached a stable observation configuration ~'arget of Opportunity observation  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 18:01:18W. Collmar et aL 661 energies, because the angular esolution is decreasing with energy (SchSnfelder et al. 1993), resulting in a broadening of the Crab signal. An investigation ofpossible systematic effects is in progress. In the present analysis only point spread functions assuming an E-2-power law spectrum for PKS 0528+134 have been applied. Though this may not correspond to the true spectral slope of the quasar, the impact of this specific choice on our flux estimates i  considered to be small. Fig. 1. Maximum-likelihood skymaps of the Crab region in the 10-30 MeV band from combined VP 0, 1,213. Fig. la shows the Crab and the evidence for PKS 0528+134. Crab dominates the map. The likelihood ratio contours tart at a value of 9 with a step of 5, and are cut off at a value of 54. Fig. lb shows the likelihood map of the same region with the Crab removed (a model of the Crab was included in the null hypothesis of the likelihood fitting procedure). The remaining feature is evidence for PKS 0528+134. RESULTS Four CGRO viewing periods have been analysed with respect o PKS 0528+134. Using a combination of data from VP 0, 1, and 213 (roughly 30 days of gross observation time), the quasar is detected by COMPTEL at energies above 10 MeV. Though masked by the nearby presence of the Crab, the 10-30 MeV skymap clearly reveals the source (Fig. 1). Applying the analysis method escribed above, a statistical detection significance of 3.3c~ is found. Below 10 MeV the combined skymaps yield no positive detection, though there is some evidence for emission in the 3-10 MeV band during two individual VP. In individual VP the main signal is also seen at energies above ll) MeV (e.g. during VP 0 and VP 1 at about he 2~ level each). Below 10 MeV the best evidence is found during VP 213 in the 3-10 MeV range. Figure 2 shows the 3-1(i) MeV skymap of VP 213 (Crab removed) giving evidence for PKS i)528+134 at a level of about 2.1~. For VP 221  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 18:01:18662 Quasar PKS 0528+134 only a "quick-look" analysis has been carried out to date. No evidence could be found for PKS 0528+134 in the different COMPTEL energy bands. ~ I I I I I I I I I f l r l~ l l~  i l l l i i  0 Crab 5- + PKS0528+134 ].5 -10 -15 200 o I I I I I I I I I I I I I I I I I I I I I I I I 195 190 185 180 175 Ga l .  Long i tude  Fig. 2.3-10 MeV likelihood map of the Crab region for VP 213. The Crab is removed. A 2.1 t~ excess at the position of PKS 0528+134 is visible. EGRET has detected this source during VP 0 and VP 1 (Kanbach et al. 1992). PKS 0528+134 was redetected by EGRET during VP 213 at a very high intensity level (Sreekumar et al. 1993). No evidence for PKS 11)528+134 could be found by EGRET during VP 221 (Nolan et al. 1993). The COMPTEL results for the individual VP follow the intensity behaviour of PKS 0528+134 as measured by EGRET. For the VP when the source is detected by EGRET (VP 0, VP 1, VP 213), there is also evidence in the COMPTEL data at a significance level of about 2t~ each. For VP 221 when PKS 0528+134 is not detected by EGRET; the COMPTEL data also do not show any hint for the source. So in general, COMPTEL measures the same intensity behaviour as EGRET, indicating a time-variable MeV-flux of the quasar. During VP 213 EGRET detects the source at its highest intensity level ever measured in 3'-rays. At energies above 100 MeV, PKS 0528+134 is as bright or even brighter than the Crab pulsar (Sreekumar et al. 1993). The COMPTEL flux results for VP 213 indicate that the quasar was also brightest in the COMPTEL energy during this viewing period. Unfortunately, this VP lasted only for 6 days resulting in enlarged statistical errors. It can be stated however, that in the COMPTEL energy range the source was weaker than the Crab pulsar. This fact indicates that during VP 213, PKS (i)528+134 had either a different spectrum than the Crab pulsar and/or a spectral break above the COMPTEL energy range has occured. In any case, a comparison of the EGRET and COMPTEL results of VP 213 will be very interesting. Figure 3 shows the COMPTEL and EGRET spectra of VP 1. The EGRET spectrum is from Hunter et al. (1993). The COMPTEL results together with the EGRET spectrum indicate a spectral break in the upper part of the COMPTEL energy range, probably at energies between 10 MeV and 30 MeV. EGRET spectra for other VP are not publicly available at the present time.  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 18:01:18W. Collmar et al. 663 A 10  2 lo~ <. 1~ 4 5- 1(~ 5 s 10 7 ~c~ 816 g 1-jo 10 - t  ' ' ' "1 '11  ' " ' "1  , r - l ,p l , ,  I ,~r r rH l~r -~ l~ \ ' ,  PKS 0528+134 \ I \ COMPTEL spectrum \ \ Obs. 1.0 T \\\ ~-~, \ +, \ gGRs.EiT.Ospect .... 1 10 10 2 10 3 ]0 4 Energy (MeV) Fig. 3. Contemporaneous COMPTEL and EGRET energy spectra of PKS(1528+134 during VP 1. The COMPTEL upper limits are 2c~. The EGRET spectrum is from Hunter et al. (1993). The dashed line represents the extrapolation of the EGRET spectrum throughout the COMPTEL energy range. The evidence for a spectral break is visible. SUMMARY The COMPTEL data of four CGRO viewing periods containing PKS (/528+134 within 20 ~ of the pointing direction have been analysed. The source was clearly detected with a significance of 3.3~ at energies above 10 MeV combining data of three VP. Below 10 MeV evidence for the source could be found only in the 3-111MeV band during VP 213 and VP {1 at a significance l vel of the order of 2~ and lcy, respectively. In general, the long term intensity bahaviour measured by COMPTEL follows the trend as seen by EGRET, thereby indicating a time-variable MeV-flux. Combining the EGRET and COMPTEL energy spectra for VP 1 (the only EGRET spectrum pubficly available at the present ime), a spectral break in the energy range between 10 MeV and 30 MeV is indicated. REFERENCES de Boer, H. et al 1992, in Data Analysis in Astronomy IV, eds. V. Di Ges~ et al. (New York: Plenum Press), 241 Colhnar, W. et al. 1993a, Proc. AIP Conference 280, 483 Collmar, W. et al. 1993b, Proc. XXIII 1CRC Calgary, Vol. 1,168 Hunter, S. D. et a1.1993, ApJ 409, 134 Kanbach, G. et al. 1991, IAU Circ. 5431 Nolan, P.L. et al. 1993, IAU Circ. 5802 SchSnfelder, V. et al. 1993, ApJS 86, 657 Sreekumar, P. et al. 1993, IAU Circ. 5753 Strong, A.W. et al 1992, in Data Analysis in Astronomy IV, eds. V. Di Ges?a et al. (New York: Plenum Press), 251  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 18:01:18

Comptel observations of the quasar PKS 0528+134

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Comptel observations of the quasar PKS 0528+134

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