The type Ia supernova SN 1998bu in M96 was observed by COMPTEL for a total of 88 days starting 17 days after the detection of the SN. A special mode improving the low-energy sensitivity was invoked. We obtained images in the 847 keV and 1238 keV lines of 56Co using an improved point-spread function for the low-energies. We do not detect SN1998bu. Sensitive upper limits at both energies constrain the standard supernova model for this event

Bennett, K

Bloemen, H

Collmar, W

Diehl, R

Georgii, R

Knodlseder, J

Lichti, G G

McConnell, Mark L

Pluschke, S

Ryan, James M.

Schonfelder, V

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)2000COMPTEL upper limits for the 56Co γ-rays fromSN1998buR GeorgiiMax-Planck-Institut für extraterrestricheS PluschkeMax-Planck-Institut für extraterrestrische PhysikR DiehlMax-Planck-Institut für extraterrestricheW CollmarMax-Planck-Institut für extraterrestriche PhysikG G. LichtiMax-Planck-Institut für extraterrestrische 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 upper limits for the 56Co γ-rays from SN1998bu Georgii, R. and Plüschke, S. and Diehl, R. and Collmar, W. and Lichti,G. G. and Schönfelder, V. and Bloemen, H. and Knödlseder, J. and McConnell, M. and Ryan, J. and Bennett, K., AIP ConferenceProceedings, 510, 49-53 (2000), DOI:http://dx.doi.org/10.1063/1.1303172AuthorsR Georgii, S Pluschke, R Diehl, W Collmar, G G. Lichti, V Schonfelder, H Bloemen, J Knodlseder, Mark L.McConnell, James M. Ryan, and K BennettThis conference proceeding is available at University of New Hampshire Scholars' Repository: https://scholars.unh.edu/ssc/135COMPTEL upper limits for the 56 Co γ-rays from SN1998buR. Georgii, S. Plüschke, R. Diehl, W. Collmar, G. G. Lichti, V. Schönfelder, H. Bloemen, J. Knödlseder, M.McConnell, J. Ryan, and K. Bennett  Citation: AIP Conference Proceedings 510, 49 (2000); doi: 10.1063/1.1303172 View online: http://dx.doi.org/10.1063/1.1303172 View Table of Contents: http://scitation.aip.org/content/aip/proceeding/aipcp/510?ver=pdfcov Published by the AIP Publishing  Articles you may be interested in γray flash from relativistic shock accelerated particles in the Hypernova environment AIP Conf. Proc. 801, 129 (2005); 10.1063/1.2141845  Sensitivity of VERITAS to microsecond γ-ray burst phenomena AIP Conf. Proc. 558, 574 (2001); 10.1063/1.1370826  COMPTEL time-averaged all-sky point source analysis AIP Conf. Proc. 510, 591 (2000); 10.1063/1.1303271  Reassessment of the 56 Co emission from SN 1991T AIP Conf. Proc. 410, 1084 (1997); 10.1063/1.54174  The Cosmic γ-ray Background from supernovae AIP Conf. Proc. 410, 1223 (1997); 10.1063/1.53933   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 15:20:15COMPTEL upper limits for the 56Co7-rays from SN1998buR. Georgii*, S. Pliischke*, R. Diehl*, W. Collmar*, G.G. Lichti*,V. Schonfelder*, H. BloeiW, J. Knodlseder*, M. McConnell",J. Ryanll and K. Bennett1'* Max-Planck-Institut fur extraterrestrische Physik, Postfach 1603, 85740 Garching, Germany^SRON, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands^CESR (CNRS/UPS), 9, av. du Colonel-Roche, 31028 Toulouse Cedex, FranceII Space Science Center, University of New Hampshire, Durham, NH 03824, USA^Astrophysics Division, ESTEC, ESA, 2200 AG Noordwijk, The NetherlandsAbstract. The type la supernova SN 1998bu in M96 was observed by COMPTELfor a total of 88 days starting 17 days after the detection of the SN. A special modeimproving the low-energy sensitivity was invoked. We obtained images in the 847keV and 1238 keV lines of 56Co using an improved point-spread function for the low-energies. We do not detect SN1998bu. Sensitive upper limits at both energies constrainthe standard supernova model for this event.INTRODUCTIONOn May 9.9 UT SN1998bu was discovered in M96 (NGC 3368) [14]. From wide-band spectrograms it was classified to be of the type la [1]. From a prediscoveryobservation [3] and an estimation for maximum blue light of tpmax — 10952.7 ±0.5TJD (i.e. May 19), P. Meikle [10] estimates the date of the explosion to be May 2.0± 1.0 UT (i.e. TJD 10935 ± 1). The Cepheid distance to M96 is about 11 Mpc.Observations of SNe in the optical and neighbouring bands concentrate on infor-mation on the light curves from such events. However, due to the creation of theoptical photons long after the initial explosion most information of the initial stateof a SN-explosion is lost. Therefore a distinction of the various SN-explosion scenar-ios via their optical light curves alone is very difficult. On the contrary, through theobservation of SN in the 7~ray line regime, information from much earlier states inthe explosion can be obtained. Considerable differences in the predicted spectra ofdifferent SN models, for example the He-Cap or detonation model, exist [6]. Theycan be used to discriminate between the models and to decide about the extend ofmixing in the SN-explosion.CP510, The Fifth Compton Symposium, edited by M. L. McConnell and J. M. Ryan© 2000 American Institute of Physics l-56396-932-7/00/$17.0049 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 15:20:15The sensitivity of existing 7~ray instruments, mainly the instruments on-boardCGRO (OSSE and COMPTEL), limits the observations of type la SN to suchevents which occur at distances well below 15 Mpc. Consequently, only one SNof type la, SN1991T, was marginally detected with COMPTEL [11]. SN1998buopens a second opportunity for line searches in SN, since according to some of themodels it should be observable with the sensitivities of COMPTEL and OSSE inthe Cepheid adopted distance of 11 Mpc.COMPTEL observations of SN1998bu started on TJD 10952, 17 days after theexplosion. Due to the late start of the observations and due to the low sensitivityof COMPTEL for low energies, we missed the decay of the 750 keV and 812 keVlines of 56Ni (r = 8.8 d). The observations were performed for a total of 88 dayswith the aim to detect the 847 keV and 1238 keV lines of the daughter nuclei 56Co(r = 112 d) .ANALYSIS AND RESULTSIn order to obtain a higher sensitivity at lower energies the observations wereperformed in the so-called "low mode", where the threshold of the D2 moduleswere considerably lowered (For a detailed description of COMPTEL see [12]). In the"low mode" most of the thresholds are well below 650 keV, the software thresholdin the standard COMPTEL analysis and show a considerable spread. Therefore ahomogeneous software threshold at this value for all D2 detectors is no longer agood choice, since we would lose low-energy sensitivity in those modules with lowthresholds. On the contrary the hardware thresholds of the Dl modules all lie in anarrow range below 50 keV, thus allowing to use this value as software threshold forall Dl detectors. Therefore the D2 modules were separated in groups with similarthresholds. A new point-spread function (PSF) was calculated, adding up theindividual PSFs for each of these groups weighted with the number of the membersin each group. Furthermore another PSF was derived from simulations whereeach module was simulated with its correct hardware threshold. The standardand the two new PSFs were then applied to 3 days worth of Crab low-mode datafortuitously collected during a observation of Geminga. Using the two new PSFswe clearly detect Crab with 5.1 a of 847 keV, compared to only 3.02 a with thestandard PSF. For the 1238 keV line the values are 1.6 a and 0.63 cr, respectively.This result reflects that most D2 modules are now sensitive below the standard650 keV software threshold used for the standard analysis, resulting in a largersensitivity for the 847 keV line. Since no major difference was found between theadded PSF and the simulated one, in the further analysis only the simulated PSFwas used, since it reflects the correct treatment of the threshold of each module.Unfortunately we are not able to make use of the full sensitivity gain in the 847keV line, due to the low threshold of some D2 modules, we start to see the 511keV line leading to a very high background. To eliminate this, two approaches arepossible, the spectral analysis and the imaging analysis.50 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 15:20:15FIGURE 1. Flux map of the SN1998bu region in 847 keV (left) and 1238 keV (right). The SNposition is marked by a diamond. The contour levels are in units of 10~8 photons/(cm2 sec). Thela contour level corresponds to 2900 for the left and 1600 for the right map, respectively.In the spectral analysis, a software cut at 600 keV in the D2 modules is usedto suppress the 511 keV line background. At the SN-position and at differentpositions on a grid around the SN position (the positions on the grid allow toobtain off-source spectra) residual spectra, using data from a 3° cone in the 3-dimensional data-space as a "source spectrum" and data from a 3° - 7° cone mantleas "background spectrum" are produced. Subsequently a template Gaussian, witha width corresponding to the instrumental energy resolution, is used to obtain lineintensities for both 7~ray lines at every position of the grid. Using this method,no significant difference between the source and the off-source positions can beseen. We derive 2cr upper limits in the following way: histograms for both linesusing the fitted intensities from all positions of the grid are derived. The width ofthe distribution is then interpreted as a measure of the statistical and systematicuncertainty of the method. Together with information on the exposure and theeffective area this yields a 2cr upper flux limit of 4.1 • 10~5 photons/(cm2 sec) forthe 847 keV line and 2.3 - 10~5 photons/(cm2 sec) for the 1238 keV line.In the imaging analysis a (p cut (see [12]) of 40° maximum is applied. Using thesimulated PSF and the (f> cut, the two maps for the two 7~ray energies (shown infigure 1) are produced using a maximum-likelihood method. Again it can clearlybe seen that there is no signal from the supernova. The 2cr upper limits can bederived as follows: From the histogram of all fluxes in the maps in figure 1 theFWHMs are determined, assuming a Gaussian distribution. Using the Bayesianmethod described in [4], which also accounts for the systematic and statisticaluncertainties, 2<j upper limits of 5.8 • 10~5 photons/(cm2 sec) for the 847 keV lineand of 3.2 • 10~5 photons/(cm2 sec) for the 1238 keV line are found.51 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 15:20:152a upper limit fromimaging analysisTJD TJDFIGURE 2. The model fluxes for the 847 keV (left) and for the 1238 keV (right) line for differentmodels versus time after the explosion. The upper row is for a distance of 11.3 Mpc, the lowerfor a distance of 9.9 Mpc.INTERPRETATION AND CONCLUSIONSFor the comparison of our upper limits, the distance to the SN plays a essentialrole. Interestingly the host galaxy M96 had already a HST-Cepheid-determinateddistance of 11.6 ± 0.9 Mpc [13], later revised to 11.3 ± 0.9 Mpc [5] , leavingSN1998bu as one of seven SN being observed in galaxies with a Cepheid distance.However, a distance determination based on Planetary Nebulae (PN) suggests adistance as close as 9.6 ± 0.6 Mpc [2]. This points to a distance which would becompatible with a Cepheid distance of 9.9 Mpc resulting from recently discussedcorrection in the distance ladder scale [9].In figure 2 expected model fluxes for a distance of 11.3 Mpc and 9.9 Mpc to M96are plotted versus the time after the explosion and are compared to the 2cr upperlimits obtained for both lines. The models are taken from Isern et al. [7] and fromKumagai et al. [8] and are scaled to the adopted distances. In figure 3 the expectedmaximal model fluxes are plotted versus distance in Mpc and are compared to theupper limit of the spectral analysis.From these figures it can be seen, that we can exclude the HeCD and the W7DTmodel for SN1998bu: the upper limits are below the peak flux for both lines anddistances. For the distance of 9.9 Mpc most other models would be inconsistent52 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 15:20:1511,0Distance in Mpc Distance in MpcFIGURE 3. The model fluxes for the 847 keV (left) and the 1238 keV line (right) versus distance.The horizontal solid line represents the spectral upper limits. The solid vertical lines show thetwo different Cepheid distances of 9.9 Mpc and 12.3 Mpc, respectively.with the 1238 keV measurement only, but be still marginally consistent with the 847keV flux. The deflagration model and the Sub-Chandrasekar model are consistentwith our line measurements for this distance.In summary we favour the deflagration model and the Sub-Chandrasekar modelfor SN 1998bu and regard the HeCD model as rather improbable (Otherwise theamount of 56Ni in the outer region of the progenitor CO-white dwarf should bemuch smaller then predicted by the current model). For detonation models asmaller mixing has to be assumed in order to be compatible with the results of theanalysis presented here.REFERENCES1. K. Ayani et al. and P. Meikle, IAU Circ. No, 6905, 1998.2. Feldmeier, J.J., Ciardullo, R. and Jacoby, G.H., Ap.J. 479, 231-243, 1997.3. Fraranda ,C. and Skiff, B.A., IAU Circ. No. 6905, 1998.4. Georgii et al., Proc. 2nd INTEGRAL workshop, ESA SP-382, 51-54, 1997.5. Hjorth, J. and Tanvir, N.R., Ap.J. 482, 68-74, 1997.6. Hoflich, P., Wheeler, J.C. and Khokhlov, A., APJ 492, 228-245, 1998.7. priv. communication.8. priv. communication.9. Manoz E. et al., astro-ph/9908140, 1999.10. Meikle, P. and Hernandez, M., astro-ph/990256, 1999.11. Morris, D.J. et al., Proc. of the 4th Compton Symposium, AIP Conf. proc. 410,1084-1088, 1997.12. Schonfelder et al., Ap.J. Suppl. Ser. 86, 657-692, 1993.13. Tanvir, N.R., Shanks, T., Ferguson, H.C. and Robinson, D.R.T., Nature 377, 27-31,1995.14. Villi, M., IAU Circ. No. 6899, 1998.53 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 15:20:15

COMPTEL upper limits for the 56Co γ-rays from SN1998bu

https://scholars.unh.edu/cgi/viewcontent.cgi?article=1134&context=ssc

COMPTEL upper limits for the 56Co γ-rays from SN1998bu

Abstract

Similar works

Full text

Available Versions

UNH Scholars' Repository