The γ‐ray telescope COMPTEL onboard GRO has so far located 6 gamma‐ray bursts which occurred in its ∼1 sr field of view. The positions of the sources were derived by the maximum‐entropy method. Systematic and statistical uncertainties for the four strongest bursts are approximately 1° to 2° and can be reduced in future analysis

Bennett, K

Bloemen, H

Busetta, M

Collmar, W

Connors, A

de Vries, C

deBoer, H

den Herder, J W

Diehl, R

Hermsen, W

Kippen, R M

Kuiper, L

Lichti, G G

Lockwood, J

McConnell, Mark L

Morris, D

Much, R

Ryan, James M.

Schonfelder, V

Stacy, G

Steinle, H

Strong, A W

Swanenburg, B

Varendorff, M

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)1991COMPTEL images locations of gamma‐ray burstsM VarendorffMax-Planck-Institut für extraterrestrische PhysikK BennettESTECH deBoerSRONM BusettaESTECH BloemenSpace Research Organization of the NetherlandsSee 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 images locations of gamma‐ray bursts Varendorff, M. G. and Bennett, K. and de Boer, H. and Busetta, M. and Bloemen, H.and Collmar, W. and Connors, A. and Diehl, R. and den Herder, J. W. and Hermsen, W. and Kippen, M. and Kuiper, L. and Lichti, G.and Lockwood, J. and McConnell, M. and Morris, D. and Much, R. and Ryan, J. and Schönfelder, V. and Stacy, G. and Steinle, H. andStrong, A. W. and Swanenburg, B. N. and de Vries, C. and Winkler, C., AIP Conference Proceedings, 265, 77-81 (1991),DOI:http://dx.doi.org/10.1063/1.42782AuthorsM Varendorff, K Bennett, H deBoer, M Busetta, H Bloemen, W Collmar, A Connors, R Diehl, J W. denHerder, W Hermsen, R M. Kippen, L Kuiper, G G. Lichti, J Lockwood, Mark L. McConnell, D Morris, RMuch, James M. Ryan, V Schonfelder, G Stacy, H Steinle, A W. Strong, B Swanenburg, C de Vries, and CWinklerThis conference proceeding is available at University of New Hampshire Scholars' Repository: https://scholars.unh.edu/ssc/189COMPTEL images locations of gammaray burstsM. G. Varendorff, K. Bennett, H. de Boer, M. Busetta, H. Bloemen, W. Collmar, A.Connors, R. Diehl, J. W. den Herder, W. Hermsen, M. Kippen, L. Kuiper, G. Lichti,J. Lockwood, M. McConnell, D. Morris, R. Much, J. Ryan, V. Schönfelder, G. Stacy, H. Steinle, A. W. Strong, B. N. Swanenburg, C. de Vries, and C. Winkler  Citation: AIP Conference Proceedings 265, 77 (1991); doi: 10.1063/1.42782 View online: http://dx.doi.org/10.1063/1.42782 View Table of Contents:http://scitation.aip.org/content/aip/proceeding/aipcp/265?ver=pdfcov Published by the AIP Publishing  Articles you may be interested in Spectral evolution of gammaray bursts AIP Conf. Proc. 265, 169 (1991); 10.1063/1.42820  BATSE observations of gammaray bursts AIP Conf. Proc. 265, 13 (1991); 10.1063/1.42813  OSSE observations of cosmic gammaray bursts AIP Conf. Proc. 265, 32 (1991); 10.1063/1.42804  Gamma ray burst source locations with the Ulysses/Compton/PVO Network AIP Conf. Proc. 265, 72 (1991); 10.1063/1.42781  Gammaray bursts observed by the watch experiment AIP Conf. Proc. 265, 53 (1991); 10.1063/1.42778   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 18:24:24COMPTEL IMAGES LOCATIONS OF GAMMA-RAY BURSTS M. G. Varendorff 1, K. Bennett 4, H. de Boer 2, M. Busetta 4, H. Bloemen 2, W. Collmar 1 A. Connors 3, R. Diem 1, j. W. den Herder 2, W. Hermsen 2, M. Kippen 3, L. Kuiper 2, G. Lichti 1, j. Lockwood 3, M. McConnell 3, D. Mor- ris 3, R. Much 1, j. Ryan 3, V. SchSnfelder 1, G. Stacy 3, H. Steinle 1, A. W. Strong 1, B. N. Swanenburg 2, C. de Vries 2, C. Winkler 4 1 Max-Planck Institut f/Jr extraterrestrische Physik, 8046 Garching, F.R.G. 2 Laboratory for Space Research Leiden, 2300 RA Leiden, The Netherlands 3 University of New Hampshire, Durham, NH 03824, U.S.A. 4 Space Science Department of ESA, ESTEC, 2200 AG Noordwijk, The Nether- lands ABSTRACT The ")'-ray telescope COMPTEL onboard GRO has so far located 6 gamma- ray bursts which occured in its ,,~ 1 sr field of view. The positions of the sources were derived by the maximum-entropy method. Systematic and statistical un- certainties for the four strongest bursts are approximately 1 ~ to 2 ~ and can be reduced in future analysis. INTRODUCTION The imaging 7-ray telescope COMPTEL is one of four instruments on board NASA's Gamma Ray Observatory (GRO), which was launched by the space shuttle Atlantis on April 5, 1991. In the first year of the mission COMP- TEL will perform a survey of the whole sky in the energy range from 1 MeV to 30 MeV with an energy resolution of 5% to 10% FWHM and an angular resolution of about 1 ~ to 2 ~ (la), depending on the gamma-ray energy. A de- scription of COMPTEL's burst detection capabilities together with results from GRB910503 is given by Winkler et al. 1 A detailed escription of the instrument and its technical properties is given by SchSnfelder et al. 2 COMPTEL has two different capabilities for burst measurements. First, the telescope itself for imag- ing of bursts in the 1 sr field of view and second two quasi omni-directional burst detectors for derivation of spectra from all detected bursts. The burst trigger function is performed by BATSE for all GRO instruments. During the first months of the mission, COMPTEL has detected many gamma-ray bursts. Most of them are not in the field of view, so only spectral information in the energy range 0.1 MeV to 10 MeV is available. For those, in its field of view, COMPTEL can provide images in the energy range from about 1 to 30 MeV. This is the first time that positions of gamma-ray bursts at MeV energies are determined by one single instrument. In this paper we report on the first results of the stronger bursts in the field of view. ANALYS IS  METHOD With present Compton telescopes no simple imaging of the sky is pos- sible. The source distribution in the sky has to be derived by combining the 9 1992 American Institute of Physics 77  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 18:24:2478 COMPTEL Images and Locations information provided by the measured events together with the response of the instrument. At present, three different methods are used by the COMPTEL team. These are the maximum-likelihood method, the angular resolution mea- sure (ARM) method, and the maximum-entropy method. The likelihood method searches for a best fit of a model sky to the data, after convolution with the in- srumental response. The ARM-method does not require detailed knowledge of the response; the distribution of events in a one-dimensional projection of the data space is determined (the so called ARM-distribution 3) for different trial source positions. A peak near the zero-point of this distribution with the angu- lar width of the point spread function indicates the presence of a source at the trial position. In this paper results of the maximum-entropy method are presented. For this analysis the software package MEMSYS 2 from Maximum-Entropy Data Consultants Ltd. was used. A detailed explanation of the method is given by Skilling and Bryan. 4 The application to this Compton telescope is discussed by Strong et al. 5 Only the main characteristics of this method are described here. A distribution of sources on an 'input' sky is searched, which matches the data after convolution with the point spread function and fullfills the maximum- entropy criterion. This criterion determines the smoothest qnput' sky which deviates, after convolution, not more than one standard deviation from the data. This method requires a detailed knowledge of the point spread function of the instrument. The telescope response to a gamma-ray point source can be described in the simplest way in a three-dimensional data space, defined by the scatter direction (X, r and the Compton scatter angle ~ (see Figure 1). X Figure 1. Three-dimensional data space. Each detected photon is represented by one point in this three-dimensional data space. In the idealised case, in which the scattered gamma-ray is totally absorbed in the lower detector, the pattern of all data points resulting from a point source with coordinates (Xo, r lies on a cone in the (X, r ~)-space, where the cone apex is at (Xo, r and the cone semi-angle is 45 ~ For real measurements, this cone mantle is blurred due to measurement uncertainties and especially due to incomplete absorption in the lower detector.  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 18:24:24M.G. Varendorff 79 RESULTS Up to now 6 gamma-ray bursts in the field of view have been analyzed. A list of these bursts including onset times and preliminary locations are given in Table I. Four of these bursts (GRB 910425, GRB 910503, GRB 910601 and GRB 910814) are strong events with about 100 counts. The time profile of GRB 910503 is given by Winkler et al. 1 The time profiles of GRB 910425, GRB 910601 and GRB 910814 are shown in Figure 2. These bursts have also been observed by ULYSSES, enabling the determi- nation of 'triangulation circles.' COMPTEL images together with these circles are shown in Figure 3. An image of GRB 910503 is given by Winkler et al. 1 At the moment, both the statistical and the systematic uncertainties in the posi- tions of the four strongest bursts are about 1 ~ to 2 ~ The statistical errors for the positions of the two weaker bursts are not determined, but are evidently larger than for the stronger bursts. SO u 4e  e 5e 40 !0  SO 40 20 tO GRB 910425 Lime r  GRB 910501 . i  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  I -  HOSe OreOe 6TS~O emmo m t ime I J l  GRB 910814 il ;~ ,In l i4. i o~oe eg~e le$oo i)e31e le4eo ,~ .  i , )  Figure 2. Time profiles of GRB 910425, GRB 910601 and GRB 910814.  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 18:24:2480 COMPTEL Images and Locations Figure 3. Maximum-entropy images of GRB 910425, GRB 910601, GRB 910627, and GRB 910814. The other two gamma-ray bursts (GRB 910609 and GRB 910627) are weaker events with _< 30 counts in the data. The statistical error of the position of these bursts is not yet estimated, but according to the smaller number of counts, it is larger than for the stronger bursts. The first burst GRB 910609 has only 6 counts, but all 6 events fell into a 14 ms time interval. The rate of background at this time is at about one event per second. According to BATSE measurements (private communication), this burst is 63 ~ away from the zenith of the instrument and is a strong event, which extends into the MeV-range. The nominal field of view of COMPTEL has a radius of -,~ 30 ~ around the zenith. At the position of 63 ~ from zenith the sensitivity of the telescope is very low and the standard response is not applicable to the data. As a result the position derived has a large systematic error >__ 10 ~ The second weak burst GRB 910627 was also bserved by Uly, se, and the  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 18:24:24M. G. Varendorff 81 COMPTEL image (Figure 3) is in good agreement with the triangulation circle, although the image is based on only 30 events. Table I. Burst onset t imes and locations. Date gal. Longitude gal. Latitude Triangulation 910425 910503 910601 910609* 910627 910814 Seconds 2268 229. 25455 171. 69736 72.5 2909 240. 16159 318. 69275 95. -20. 7. --5. -10. 59. -28. yes yes yes no yes yes * big systematic error in position. SUMMARY While COMPTEL images per se do not significantly improve the chances of finding counterparts, in combination with Ulysses or PVO timing data 'finding charts' are developed with small image dimensions (e.g., 1 ~ x I t for GRB 910503). This is a powerful tool in the search for suitable counterparts which may lead eventually to solving the GRB mystery. REFERENCES 1. C. Winkler et al., these proceedings. 2. V. SchSnfelder etal., IEEE Trans. Nucl. Sci. NS -31 ,766 (1984). 3. J. W. den Herder et al., "Compteh instrument description and performance," presented at the Second GRO Science Workshop, Annapolis, MD (1991). 4. J. Skilling and R. K. Bryan, "Maximum-entropy image reconstruction: gen- eral algorithm," MNRAS 211,111 (1984). 5. A. W. Strong etal., Proc. XXI Intl. Cosmic Ray Conf., Adelaide 4, 154 (1990). ACKNOWLEDGEMENT We are grateful to the Ulysses team for providing us the Ulysses arrival times of GRB 910425, GRB 910503, GRB 910601, GRB 910627 and GRB 910814. Furthermore we thank the BATSE team for the burst triggers.  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 18:24:24

COMPTEL images locations of gamma‐ray bursts

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COMPTEL images locations of gamma‐ray bursts

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