PoS(Integral08)007

INTEGRAL Studies of Nucleosynthesis Lines

M. Leising ∗†

Clemson UniversityE-mail: lmark@clemson.edu

R. Diehl ‡

Max Planck Institut für extraterrestrische Physik, Garching, GermanyE-mail: rod@mpe.mpg.de

The SPI Ge spectrometer on INTEGRAL continues to collect data on astrophysically-important

γ-ray lines from decays of26Al and 60Fe, and positron annihilation.44Ti decay lines from Cas

A have been observed with the IBIS imager, but the lack of other44Ti remnants is a mystery.

The26Al γ-ray line is now measured throughout the Galaxy, tracing the kinematics of interstellar

gas near massive stars, and highlighting regions of interest, such as groups of massive stars in

Cygnus and even more nearby regions, such as in Orion. The detection of60Fe radioactivity lines

at the level of 15% of the26Al flux presents a challenge both for measurement and explanation.

Positron annihilation emission from the nucleosynthesis regions within the Galactic plane appears

to be mainly from26Al and other supernova radioactivity, while the bulge region’s positron an-

nihilation brightness remains a puzzle. The continuing accumulation of large exposures to the

central Galaxy, and the anticipated continuing availability of INTEGRAL for rare nearby ex-

plosive events promise further improvements in our understanding of all these nucleosynthesis

sources.

7th INTEGRAL WorkshopSeptember 8-11 2008Copenhagen, Denmark

∗Speaker.†Supported by NASA‡from studies with SPI on INTEGRAL, supported by ESA and its member countries

c© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. http://pos.sissa.it/

PoS(Integral08)007

Gamma-Ray Lines M. Leising

1. Introduction

Setting the stage for INTEGRAL, the study of celestial nuclearγ-ray lines (apart from thenuclear contribution to the galactic positrons) began with theγ-ray spectrometer aboard the thirdHigh-Energy Astronomy Observatory (HEAO C-1). It detected the 1.809 MeV line of26Al decayin its two two-week scans along the galactic plane in 1979 and 1980 [1, 2]. The Solar Maxi-mum Mission Gamma-Ray Spectrometer’s exceptional stability and nearly a decade of trackingthe Sun around sky led to improved measurements of the26Al line [3, 4]. Both the HEAO C-1and SMM/GRS data set interesting upper limits with non-detections of line emission from44Ti and60Fe [1, 5]. The fortuitous SN 1987A provided an opportunity to study a core-collapse supernovaup close, and even though it could not be pointed at the supernova, the SMM/GRS was able to de-tect several lines of56Co decay [6, 7]. The lines emerged earlier than expected, indicating mixingof a few percent of the core radioactivity into the hydrogen envelope or beyond.

The next advances were provided by the Compton Gamma Ray Observatory. To studyγ-ray lines, it carried the Oriented Scintillation Spectrometer Experiment (CGRO/OSSE) and theCompton Telescope (CGRO/COMPTEL.) The CGRO/OSSE produced the first maps of the dif-fuse electron-positron annihilation radiation and measured57Co decay in SN 1987A [8]. TheCGRO/COMPTEL made the first map of the 1.809 MeV26Al decay photons (Fig.1) as well asmaps of diffuse continuum emission.

The currently operating INTEGRAL instruments SPI and IBIS both use code masks for imag-ing and background estimation. While not optimal for measuring diffuse emission, both provideunique capabilities. SPI provides an unprecedented combination of energy resolution and sensitiv-ity; IBIS angular resolution and sensitivity at hard X-ray energies. Both of these instruments aremaking significant contributions toγ-ray line studies, which we review below.

2. Diffuse Emission

2.1 26Al

Theγ-ray line from26Al radioactivity (τ=1.04 My, Eγ=1808.65 keV) may be considered themost direct proof of ongoing nucleosynthesis in the current epoch of the Galaxy’s evolution. Thehistory of26Al line observations up to the epoch of the Compton Observatory has been describedearlier [9]. 26Al production as imaged by COMPTEL (see Fig.1 [left]) occurs throughout theGalaxy, with apparent concentrations in regions hosting young and massive stars such as in Cygnus.The patchy distribution of26Al emission along the plane of the Galaxy could partly be instrumental,but argues for massive stars as dominant sources of Galactic26Al. This is consistent with estimatesfrom the ionizing radiation by those same stars [10]. Adopting plausible large-scale source distri-butions, the total amount of26Al in the Galaxy was estimated as 2–3 M�. Massive stars, throughcore-collapse supernovae and Wolf-Rayet phases, eject26Al into the interstellar medium, whereit decays to produce the observed emission. Typical ejection velocities are 1000 km s−1 or more.Ejecta are slowed by interaction with circumstellar and interstellar matter. Depending on whenthe 26Al is slowed, one would expect more or less Doppler broadening of the observed26Al line.Therefore, the26Al line provides a diagnostic of the mean environment around massive stars, which

2

PoS(Integral08)007

Gamma-Ray Lines M. Leising

Roland DiehlALMAP

CygnusCygnus

VelaVela

Inner GalaxyInner Galaxy

OrionOrion

ScoSco--CenCen

� ö � º�Á®ÝCÎ�Ç\º�¿�ö�^�ß���á=¿%ÎfÞGȦÆÏÆÏȦÔ8Á�º�¿ÀÔFÁ®ÝCÇÉÑ�ÎgÜ�ºF¿ÀºFÂ�ÇÉÈÀÂæô�¿+º�Á®Î Ù

1800 1805 1810 1815 1820Energy [keV]

0.0

0.2

0.4

0.6

0.8

Flu

x [1

0−4 p

h cm

−2 s

−1 k

eV−

1 rad

−1 ]

E=1808.92 (±0.06)FWHM=3.16 (±0.15)I=2.73 (±0.17)

1800 1805 1810 1815 1820Energy [keV]

0.0

0.2

0.4

0.6

0.8

Flu

x [1

0−4 p

h cm

−2 s

−1 k

eV−

1 rad

−1 ]

E=1809.03 (±0.08)FWHMSKY<1.3 (95%)I=2.93 (±0.15)

ÌIÍqÎJÏ.�JÏ èBô�ÎfÂ�ÇÏÍÉÊ®Þ ç�Î�ÍÉȦä Î�çQË+ÍÉÔ8Þ ÆÏÃ!Ò�ÞGÔ!ç�Îf¿�"®ÇÏÇÉȦÁ®Ý�Ê®ÆÏȦÁ�ÝîÇÉÑ�ÎCåaây¹�½eùaó��Uß�� á°¿}¹�º�»BȦÞCÊ�Þ ó}ÁÇÏÍÉÔ8ôÒ�ȦÞ�ºFÝFÎ8ö�ù¨Ñ�ÎC¿¦Î�Ë ÇF"#Ý8ÊBÍÉÎ�ÆÏÑ�Ô�ýsÆ\ÇÉÑ®Îß�� á=¿�¿¦ÈÀÁ�Î�"®ÇÏÇÉÎ�ç�ýsÈ¢ÇÉÑ_ºdÜ�ºFÊ�ÆÏÆÏÈÀºFÁ?Ó�ÇÉѮΠýsÈÀçBÇÉÑ[Ô�Ë�+�Ö!öÀÕfødÃ8Î>3 í�ð � #�¹�ïæã�Î�ÈÀÁ�Ý�ÂfÔ8Á�ÆÏȦÆ�ÇÉÎfÁÇ�ýsÈ¢ÇÉÑ[ȦÁ®Æ�ÇÏÍÉÊ�ÞGÎfÁÇкF¿e¿ÀȦÁ�ÎîýsÈÀçBÇÉÑ�ÆCº(ÍÉÔ8Ê�Á#ç]ÕFö عQÎ>3�öBù¨Ñ�ΰÍÉȦÝFÑ!Ç`"#Ý8ÊBÍÉÎ=ÆÏÑ�Ô�ýsƤÇÉѮΰ¿¦ÈÀÁ�Î�"�ÇÏÇÉÎ�çCýsÈ¢ÇÉÑQºyÂfÔFÞGô�Ô8ÆÏÈ¢ÇÉÎ\¿¦È¦Á®Î�¼ÅÆÏÑ®ºFô�Î\ÞGÔ!çBÎf¿#Ê�ÆÏÈÀÁ�ÝyÇÉÑ®ÎsÇÉÈÀÞGÎ�¼¾º�ä Î�ÍкFÝ8Îfç�ȦÁ�Æ�ÇÏÍÉÊ®ÞGÎfÁÇкF¿BÍÉÎfÆÏô�Ô8Á�ÆÏÎ�º�ƨȢÇÍÉÎfÆÏÊ®¿¢ÇÉÆaË ÍÉÔFÞ@ÂfÔ8ÆÏÞGȦÂ�¼�ÍкfÒ ç�ÎfÝ�Íк8箺(ÇÉȦÔ8Á�º�Á#ç�º�Á®Á®ÎfºF¿¦È¦Á®Ý8Æ=ç�ÊBÍÉȦÁ®Ý�ÇÉÑ�Î\ÇÉȦÞGÎ�ÔFË}ÔFÊ�ÍsÞGÎ�º�ÆÏÊ�ÍÉÎfÞGÎ�Á!Ç�Ó!Â�Ô8Á!ä Ô8¿¦ä ÎfçîýsÈ¢ÇÉÑ�ºGÜ�º�Ê®ÆÏÆÏÈÀºFÁ�ÍÉÎfôBÍÉÎfÆÏÎfÁÇÉȦÁ®ÝÇÉÑ®Î=ÂfÔ8ÆÏÞGȦÂCí�ȦÁÇÏÍÉȦÁ®ÆÏȦÂ(ï ß�� á°¿�¿¦ÈÀÁ�Î\ýsÈÀçBÇÉÑ%ö®ù¨Ñ�Î\¿Àº�ÇÏÇÉÎ�ÍsÈÀÆ¨Ë Ô8Ê�Á#çGÇÉÔ�ã�Î�í�/ Õ21 ÖCà Î>3gÓB×!-�ï�ö�é¤ÔFÇÉÑô"®ÇÉÆ`"®Á#ç ÇÉÑ#º(ǨÇÉÑ®Î=¿¦ÈÀÁ�Î�ȦÆaȦÁ!ÇÏÍÉȦÁ�ÆÏÈÀÂfºF¿¦¿¢Ò Á®º�ÍÏÍÉÔ�ýyö4�Î�ÍÉȦä Î�çÈÀÁ�Î��#ÊB»�Î�Æsº�ÍÉÎyÂfÔFÁ®ÆÏȦÆ�ÇÉÎfÁÇ=ºFÞGÔ8Á�Ý Î�º�Â�Ñ�Ô�ÇÉÑ®Î�Íæí�º�Á#ç º�ÍÉÎzEÊ®ÔFÇÉÎfçîȦÁ�Ê�Á®È¢ÇÉÆsÔF˨Õfë =�ñ ô�ÑQÂfÞ = ß=Æ = ¸sÍк8ç = ¸Ðï�ö

�=-B ?$Ð)*��E�'�) �4 ,�v�EM1 )+��)+,��,�)+-� %$�-8wQ4��B�Q���8�¾'f�){·,�E�1 EF$�&(-�*?E8$�H)+,�v%��$�D�E�E� *�1 �B"%$�)+D�1 E�,�-i�!1+,�E�'� %�!,�) 5BE�1q{ "?$ÐE_���B*%$�-�D�,��B)+ �E��) l��$É,�'�-� �-B��) &��B1+1q{��¾��-B'�E���EF5BEF1+-�*?E��Y3�� 5BEF1+EF �4!,�vYD%�B ���$FH�-B %&�E)+,l)+,M&(1 EF�!'],kv?�,Y,�v�-�$�Ei,�'f�B&(E rks t 1�$Ð-�"�'�&�EF$])+ @,kv�E�� �!1 �i��{B.��E(,f�!) 1+E��d$Ð,�"���) EF$�v%� 5�E�$kv�-3y ½�Z¡ ?�-D��1 $ÐE���E�'=E(,y�!1¾.?6�� �D�;ÔD��) E!v�1E�,O�!1¾.g6�� ��0D�î,kv%�!,O�B�Q-� �4U,kv%EYD�EF$Ð,d,�'f�B&�E�'f$�-8w r�sut 1 $�-B"�'f&(E8$�B'�E0�É6)�=,kv�EG) �w�'f�!'�E2��E���) $�$�)+-� d-8w¨3��!'�� ��"%$Ð,æ4B'f�!) %$�H#���!*%*?E��3y)+,kv ,kv�E��y>#õ�:FËi�,³&µÀõ�:@�B ��²�!'�) $Ð) �4|w�'�-B� 'f� ��) �,�)+5�E×v�E8�,��) �4Q-8w`��"%$É,æ�B'�-�"� ���&�1+"%$Ð,�EF'�$\- w����B$�$Ð) 5BEC$É,f�!'f$¶�Zõ\E� � %E(,Ð,yE�,y�B1�.6�� �B0���Ha�! ����¾/ �Q'f� ��) �,�)+-� i- w,w�'�E�E�EF1+E8&�,�'�-B ?$|�±w�'�E�E]�¨w�'�E�E[E���) $&�$�)+-� }H�õ\'�EF��$�$Ð,�'f�8v�1 "� �45�G-BD?$ÐEF'�5�E2� �!,Q'f� ��)+- w�'�E�ù®"�E� %&�)+E8$Q3y)À,�v,�v�Ez¼Hy t � $��,�E�1 1+)+,�E�H��!'�) $Ð) �4�w�'�-B� ,kv�E�)+-� �)q �) �4����B$�$Ð) 5BE!��$Ð,��B''f� ��) �,�)+-� ��B'�-�"� �������$�$�) 5BEG$É,f�!'y&(1 "%$Ð,�EF'�$F.;»�'�-B�|�B$Ð,�'�-B*;v5{�$Ð) &��B1�B'�4�"���E� ®,�$FH��B1 $�-d���B*%$C-8w=) ®,�EF'�$Ð,�EF1+1 �!'C4���$g) Ò��)�Ã�E�'�E� ®,#w�-B'���$$kv�-B"%1q��,�'f�B&(E°,kv�E�1 -�&��,�)+-� %$¤�! �� $Ð*%��&(EF��E� %$�)+,&{G-8w r�sut 1�$�-B"%'�&�EF$F.��¸D��y[-�1+E8&("�1 �!'y4®�B$�) $y-BD%$�E�'�5BE���,�v�'�-B"�4Dv��y>�1+) �E�EF��) $�$Ð) -B [�!,'f� ��) -¹w�'�E�ù®"�E� %&�)+E8$�H?�! ��Cv%��$yD�E�E� [���B*�*?E��O)+ ['f�,�v�E�'A}? �E�'�EF$��-�1+"�,�)+-� Ò�����B��ECE�,æ�!1¾.+H�6��BA�ó��! ��O/!7�7�6��(Ho�ux��\�!,�-B��) &zv5{���'�-B4�E� ���À³�� $k��{]$Ð"�'�5BE2{�$,v?� 5BEQD?EFE� M�B&F&("�� "�1 �!,�E����ÅEB. 4%.d��) &>��E!{Y�B ���e-#&>�#���! 62�D�B7���Ha�! ��Ñ�¨� ��&�-�$��Q) &���'f�){l) ®,�EF'���&�,�) -B ?$�3y)À,�v·) ��,�E�'f$É,�E�1 1 �B'�4®�B$�*�'�-���"?&(EF$�*�E� �E�,�'f�,�) �4�&(-� �,�)+ #"�"%�m4��!�����i��'f�){EF�Q) $�$Ð) -B 3Av�) &>v�v%�B$¤D�E�EF ���!*%*?E��î) �,�v�Ey:��¶µæ:��²$��5{�$�"�'�5BE!{���æ"� ®,�EF'æE(,g�B1�.�6�� �5ó8��.

»¤)+ ?�!1 1�{�H=�! ?�!1q{�,�) &F�!1æ��-���EF1 $×w�-B'�,�v�E½��) $É,�'�) D�"�,�)+-� v-8w r�s t 1$�-B"�'f&(E8$Àv%� 5�EîD�E�EF ]&(-� %$Ð,�'�"%&�,�E2��H�D%�B$�E2�Y-B Y�BD?-5�E��# �-3y1 E2��4�E- w�� �B1 ��&�,�) & $É,�'�"?&�,�"%'�E ) O)+,�$A��)�Ã�E�'�E� ®,g&(-���*?-� �E� ®,�$���µy-BD%)+ �E(,�B1�.�/!7�7 ¸D�(H!*�'�-B*�E�'�1�{�3\E�) 4 v®,�E��¹w�'�-�� �B$Ð,�'�-B*;v5{�$Ð) &��B1%�!'�4B"%�QEF ®,�$F.��0D�F�g-�"�D�1 E]��E]��*�-B �EF �,�) �B1Jw�"� %&�,�)+-� %$ô�Å)+ O4��B1 ��&�,�-�&�E� ®,�'�) &g'��D��) "%$�H�B ��[$�&F�!1 E�v�E�) 4 v®,��BD?-5�EC,kv�E0� �!1 �B&�,�) & *%1 �B �E���v?� 5BEGD�E�E� _&�-B ��$Ð,�'�"%&�,�E2��H!��$¤3=EF1+1��B$¤��-B'�E�$Ð-�*;v�) $É,�) &F�,�E�����-���E�1 $¤)+ ?&(1 "���) �4N�¨ó8�$�*�) '��B1¨$Ð,�'�"%&(,�"�'�E�&(-B��*�-B �EF ®,�$ �! ��]D�"�) 1*��)+ %4O-� Y,�v�E×��) $É,�'�) D�"��,�)+-� i- wzw�'�E�E�E�1 EF&(,�'�-B %$Q) ,�v�E�� �!1 �i��{²�B$N��EF'�) 5BE�� w�'�-B� *�"%1��$��!'���) $�*?EF'�$�) -B U��EF�B$�"�'�E���E� ®,f$��Z�¤�){#1+-�'��Â�=-B'>��EF$�6�� �D¸�He�B ���=-�'���E8$�� �e�8 F)+-�/!7�7�/ �(.���v%E $�&��B1+E,v�E�) 4 v®,�-8w r�s t 1}$Ð-�"�'�&�EF$�v%�B$D�E�EF Nw�-B"� ���,�- 1+) EgD�E(,É3\E�EF �,kv%E���-B1 EF&�"�1 �!'���) $k�|�Å�!D�-B"�,��!7�*%$���B ���,�v�E ,kv%) &>����) $k�½�Å�BD?-�"�,g7�. ¸i�f6#�®*�&2�(H�3y)+,kv�*�1 �!"%$�)+D%1+E 5�!1 "�EF$�B'�-�"� ���/!7B7 *�&!.

¼lEl&�-B��*%�!'�E r�s t 1C1 ) �E]$�*?E8&�,�'�����E(,�E�'��Q) �E���w�'�-B� ,kv�E8$ÐE��)�Ã�E�'�E� ®,g��-���E�1 $g�B ��O,�'f�B&�E�'f$�-8w r�s t 1¤$Ð-�"�'�&�EF$y) �,kv%E�� �!1 �i��{B.

»¤)�w�,�E�E� ×��)�Ã�E�'�E� ®,°$k��{¹��) $É,�'�) D�"�,�)+-� Q���B*%$�v%� 5�E\D�E�EF ��! %�B1�{5 �E���H�! �� 5�B'�) �,�)+-� %$�-B r�s t 1CD�'�)+4Dv®,� �E8$�$FH r�s t 1�1+) �EY&�E� ®,�'�-B)*�v�! ��3y)q��,kv�*%�!'f�!��E�,�E�'f$��!'�EC$kv�-3y O)+ C»¤)+4�"�'�E���.;��v�EG5�!'�) �!,�) -B %$\- w}�,Ð,�E2� r�s t 1�E���) $�$�)+-� *%�!'f�!��E(,�E�'f$¹w�-B'�,�v�E_) � �EF'a� �!1 �i��{ �B'�E�!1 1�&�-B %$�) $Ð,�EF ®,g3y)À,�v�) Y$É,f�,�) $Ð,�) &��B1e"� %&�E�'�,��B)+ ®,�) EF$F.�¼lE�"%$�E�,�v�E�) '$�&F�,�,�E�'s,�-GEF$Ð,�) ���,�Eæ��n�$k{#$Ð,�EF���,�) & oC"� ?&(E�'�,��B)+ ®,&{�H!3Av�) &>v�,�"�'� %$-B"�,æ��$#�¾/�É ���U7;É¢/ ��öY687p-E�(*;v[&(�v- r $ -�/�'f� ��-0/8H�6FA�7 ��É 7��M7;É 7 ��BE2�îH�7�É �:�V7;É x��·�BE2� w�-B'î,kv�E��%"���H¤&�E� ®,�'�-B)*��He�B ��U3y)*�#,kv²*?�i�'��B��E(,�EF'�$¶�Å3y)À,�vM62Æ_EF'�'�-B'�D%�B'�$>��H�$�E�*?�!'f�,�EF1�{�.

t $dD?E!w�-B'�E��Z��) E!v�1 E(,��!1¾.+H�/!7�7B0B����Hs3\E]&�-B #5BEF'Ð,�-�"�'d��E8�i�$Ð"%'�E�� r�s t 1�)+ ®,�E� %$�)À,&{�)+ ®,�-V�! KEF$Ð,�) ���,�EM- w ,�v�Er�J��� |�x������J~�[��� � r�swyx�}r|��J� )+ Q,kv%Ez� �!1 �i��{BH "%$�)+ %4��! ��B$�$Ð"���E��î4�E�-B��E�,�'�)��&��B1}$Ð-�"�'�&�E]�®��) $É,�'�) D�"�,�)+-� ���-���E�1},�-�E]�#,�'f�!*�-B1 �,�EG�B&('�-�$�$=,kv�EGEF ��,�) '�E|� �!1 �i��{Òw�'�-B� -B"%'Q) � �EF'��&� �!1 �i��{U �-�'����!1 )q F�,�)+-� ²-8wC$Ð"%&>v�O�Q-���EF1�H}��$���) $�&�"%$�$�E2�l�!D�-5BE�.o��v�) $ ) $ '�E2ù®"�) '�E��_D�EF&��B"%$�E ,�v�E�%"���,�-�����$�$y&�-B #5BEF'�$�) -B �'�E�1 )+E8$\-B rks t 1e$�-B"�'f&(E¶��) $É,f�! %&�EF$FH® %-!,��EF�B$�"�'�E2����)+'�EF&(,�1q{O) Y*%'�- ÄÉEF&�,�E2�_$k�5{[D�'�)+4Dv�,� �EF$�$z��) $Ð,�'�)+D%"�,�) -B ���!*%$F.C<#EF5BEF'��B1G,kv�'�E�E!����)+��E� ?$Ð) -B %�B1���) $Ð,�'�)+D�"�,�) -B ���-���E�1 $Y�B'�E�!*�*%1+) E2���B ���&�-B��*%�!'�E2�#v�EF'�E�HFE�. 4?.+H8�! �E!��*?-� �E� ®,�) �!1���) $�� ��-���E�1¾H�{nk{B-�"� �48�®��) $��po���-���EF1�H}�O4BEF-B��E(,�'�) &��B1�'�E�*%'�E8$ÐEF �,f�,�)+-� _D%�B$�E2�-B ���"?$É,CE���) $�$�)+-� }H?�B ��_��� "�1À,�)��Ï&(-���*?-� �E� ®,���-���EF1e) %&(1 "���) �4$Ð*%)+'f�!1����B'��@$Ð,�'�"%&(,�"�'�EF$s�B ��QD%�B$�E2�Q-� ��BD�"� ��%�! %&�EF$a- w�w�'�E�EyEF1+E8&��,�'�-B %$s)+ �) ®,�E�'f$Ð,�E�1 1 �!'°$�*%�B&�EB.8¼lEæ5�!'�{ $�&��B1+Ezv�E�) 4 v®,s*%�B'��B�QE�,�EF'�$-8wy,�v�E��B*�*�'�-B*�'�) �!,�Ed&�-B��*�-B �EF �,f$G,�-]�!1 $�-Y$É,�"���{U,�v�Ed1 �,�)À,�"���EE]�#,�EF ®, -8w�,�v�E r�s t 1\E���) $�$�) -B }.`³Ï ²�!1 1=��-���EF1 $FHe3\E�v%� 5�E�,�� �BE� ,kv�EÒ��) $É,f�! %&�EY-8wG,�v�El<�"� V,�-M,kv�E � �!1 �B&(,�) &_&(EF ®,�E�'��B$b��� 9A�..�a�®*�&�� rks t 1°���B$�$G$�E� %$�)À,�)+5�E�1q{ ��EF*?EF ���$G-� �����H�$����B1+1 E�'�� �3y)+1 1�4�1+-�D%�!1 1�{G'�E2��"%&(E�,�v�Eæ$Ð)q �E�- w?,�v�Ez� �!1 �i��{BH!�B ��Q'�E8$Ð"%1À,a) ,�v�E$Ð���B1+1 E�'æ�B�Q-�"� ®,y-8w r�sut 1?��.

��v�E � 5BE�'f�!4�E ��EF�B$�"�'�E2� rks t 1]�%"��u- w���/;É �2� 7;É¢/ ��ö6F7 -Y� *;v[&(� - r $ -�/ 'f� � -0/ w�-�'C,kv�E�) � �E�'�� �B1 �8��{�,kv#"%$C,�'f�! ?$&�1 �!,�E8$�) �,�-²�¾� �!1 �B&(,�) & rks t 1C����$�$�-8w×��/;É.ó¡�K7;É7ó8��¢{£ .F��v�Eù®"�-!,�E2� "� %&(EF'Ð,f�!) ®,&{ôv�E�'�E�)+ ?&(1 "���EF$sD?-B,kvQ,kv�Eæ$Ð,��!,�) $É,�) &F�!1�"� ?&(E�'k�,��B)+ ®,&{��B$\*�'�-B*?�!4��!,�E��0w�'�-��´,kv�E#}�,�,�) �4���E(,kv%-5�}H��! ���,kv�EG$k{#$��,�EF���!,�) &��B1�"� %&(EF'Ð,f�!) ®,&{×��E�'�)+5�E2��w�'�-�� 5�!'�) �!,�) -B %$��B�Q-� �4Q*�1 �B"��$Ð) D�1 E_'�E�*�'�EF$�E� ®,��!,�) -B %$�- wG,kv�E]$��5{���) $Ð,�'�) D�"�,�) -B v- w ,kv�E]E���) $��$Ð) -B �*%1+"%$\�!1+,�EF'� ?�,�) 5BE,¸i�®��)+��EF %$Ð) -B ?�!1 r�s t 1�$�-B"�'f&(EÀ��) $Ð,�'�)+D%"�,�) -B ��-5��E�1 $��Å$�E�E��B1 $�-×»¤)+4�"�'�E t x%. 6�) Y<#"�*�*%1+EF�QEF ®,��!1����,�EF'�) �!1 $y- w�g) E!v%1}E(,g�B1�.%/B7B7B0��D�(.

Figure 1: 26Al radioactivity from the Galaxy, as seen by the Compton Observatory and INTEGRAL. (Left:):The 26Al image from 9 years of sky survey with COMPTEL shows somewhat patchy emission along theplane of the Galaxy [13].(Right:): The26Al spectrum as measured by INTEGRAL/SPI shows the line to berather narrow [14, 15]

is rather unique: Such interstellar gas is dilute and ionized, so radiative effects are sparse; never-theless, this “hot phase” of the ISM has important implications for galactic structure and evolution.The GRIS balloone-borne Ge spectrometer instrument had reported such Doppler broadening [11],but the associated mean26Al nucleus velocities at the time of decay of about 500 km s−1 appearedto be implausibly large [12]. One of the main goals for INTEGRAL’s high-resolution Ge spec-trometer instrument SPI therefore was a clear spectroscopic measurement of the26Al line shape toassess the kinematics of26Al throughout the Galaxy.

The26Al line was found to be rather narrow with first observations of INTEGRAL [14], con-firming the measurement made with the Ge spectrometer on the RHESSI solar satellite [16]. Al-though the line was not clearly resolved, it appeared somewhat broadener than instrumental reso-lution, but far less than the 5.4 keV broadening of the earlier result [11]. Subsequent INTEGRALmeasurements added precision and spatial information on the26Al line parameters (Fig.2). Obser-vations of the inner Galaxy showed shifts in the line centroid, which plausibly followed the Dopplershifts expected from the large-scale galactic differential rotation [17]. With more data, line cen-troid determinations can be made for different viewing directions (Fig.2). Recent results suggestan asymmetry, with significantly-blueshifted26Al line emission towards the fourth quadrant of theGalaxy (i.e., negative longitudes). The value of the blue-shift appears on the high side of what isexpected from differential rotation, and may reflect peculiar bulk motion such as expected withinthe bar of the Galaxy. On the other hand, there are apparently no corresponding redshifts of the26Al line at correspondingly-positive longitude values, i.e. in the Galaxy’s first quadrant. In termsof 26Al emission, the inner Galaxy appears asymmetric; peculiar bulk motion could compensatefor differential large-scale rotation here, or the differences in inner spiral-arm structures may beresponsible for these results.

As the26Al signal weakens away from the inner Galaxy, it becomes more difficult to determineseparately the line shift and width per longitude bin. Analyzing 30-degree segments, it seems thattowards the Aquila direction (l' 25◦) the measured26Al line is broader than seen toward otherdirections. If one such region of a particularly young age (below about 5 Myrs) dominates the

3

PoS(Integral08)007

Gamma-Ray Lines M. Leising

0.0 0.5 1.0 1.5 2.0 2.5FWHM of Gaussian [keV]

99.7 %1.7 keV

95.4 %1.3 keV

68.3 %0.7 keV

0.0 0.5 1.0 1.5 2.0 2.5FWHM of Gaussian [keV]

0.0

0.2

0.4

0.6

0.8

1.0

1.2

prob

abili

ty d

ensi

ty [1

/keV

]

Õ�ë � ö � º�Á®ÝCÎ�Ç\º�¿�ö�^�ß���á=¿%ÎfÞGȦÆÏÆÏȦÔ8Á�º�¿ÀÔFÁ®ÝCÇÉÑ�ÎgÜ�ºF¿ÀºFÂ�ÇÉÈÀÂæô�¿+º�Á®Î

−60 −40 −20 0 20 40 60Galactic longitude [degree]

−1.5

−1.0

−0.5

0.0

0.5

1.0

1.5

Line

Ene

rgy

Shi

fts [k

eV]

−60 −40 −20 0 20 40 60Galactic longitude [degree]

0

1

2

3

4

5

6

Flu

x [1

0−4 p

h cm

−2 s

−1 r

ad−

1 ]

−40 −20 0 20 40Galactic longitude [degree]

1

2

3

4

5

FH

WM

[keV

]

ÌIÍqÎJÏiÐ�Ù�Ï�Ú�Û�Ü¥Ý ß�� á°¿%¿¦È¦Á®ÎyÎ�Á®Î�ÍÉÝ�Ò ÆÏÑ�È¢Ë ÇÉÆ°ºF¿¦Ô8Á�ÝCÇÉÑ®ÎyÜ�ºF¿ÀºFÂ�ÇÉȦÂæô®¿Àº�Á®Î í·°ø8ë ÷ /�G�/²øFë ÷ Ó#ýsÈ¢ÇÉÑ�¿¦Ô8Á�Ý8È¢ÇÉÊ#çBÎ�ã�ÈÀÁ�ýsÈÀç!ÇÉѮưÔFˤ×Fë ÷ Ó ß�� á=¿�ÆÏô�Î�Â�ÇÏÍÐºË ÍÉÔFÞVð�ÈÀÝFÊ�ÍÉÎ�98ï�ÍÉÎf¿Àº�ÇÉȦä ΤÇÉÔ°ÇÉѮΨ¿¦È¦Á®Î¨Â�ÎfÁÇÏÍÉÔ8ÈÀç�Ô�Ë#ÇÉѮΠß�� á=¿!¿¦ÈÀÁ�Î�í*"®ÇÏÇÉÎfçÎfÁ®Î�ÍÉÝFÒdÕ�Ø8ëFØBö ø Ù Ã Î�3yï�ö�Þ Íàß�ßEáãâpÝ ß�� á°¿�ÈÀÁÇÉÎfÁ�ÆÏÈ¢Ç¾Ò ç�ȦÆ�ÇÏÍÉȦã®ÊBÇÉÈÀÔFÁ�ºF¿¦ÔFÁ®ÝÇÉÑ®ÎsÜ�º�¿ÀºFÂ�ÇÉȦ°ô®¿ÀºFÁ�Îyí Ë ÍÉÔ8ÞVð�ȦÝFÊ�ÍÉÎfÆ�ØBÓ�9 ïC±8á=Æeº\ÂfÔFÞGô#º(ÍÉÈÀÆÏÔFÁ?Ó ß�� á=¿BȦÁ�¼ÇÉÎfÁ®ÆÏÈ¢Ç�Ò�ç�Î�ÍÉȦä Îfç�ã!Ò ÇÉÑ®ÎCåaây¹�½�ùaó��_ÈÀÞ�º�Ý8ȦÁ®ÝîȦÆ�º�¿ÀÆÏÔ ô®¿¦ÔFÇÏÇÉÎfç_í ÇÉÑ�ÎÆÏÔ8¿¦ÈÀçlÂfÊBÍÉä ÎJ±�箺�ÆÏÑ®Î�çY¿ÀȦÁ�Î�ºFÆGÇÉÑ®Î�º�ä Î�ÍкFÝ8Î�äFºF¿¦Ê�Î(ï�ö�ä ÛMå(å�Û�æ�Ý ß�� á=¿ð � #y¹;íÅÜ�º�Ê®ÆÏÆÏÈÀºFÁÒ"�ÇÏÇÉȦÁ®Ýï äFº�ÍÉÈÀº�ÇÉȦÔFÁMºF¿¦Ô8Á�Ý�ÇÉÑ®Î�Ü�º�¿ÀºFÂ�ÇÉȦÂd¿ÀÔFÁ®ÝFȦ¼ÇÉÊ#çBÎfÆfÓ�º=ãBÍÉÔ º8ç ß�� á=¿¿¦È¦Á®Î�Ë Î�º(ÇÉÊ�ÍÉΨȦÆ}ç�Î�ÇÉÎfÂ�ÇÉÎ�çæÇÉÔ(ý¨º�ÍÐçyÇÉѮΨ¿¦ÔFÁ®Ý8È¢ÇÉÊ®ç�ÎfÆ×Fë ÷ / G%/]Û8ë ÷ ö

Ð ���B$\,�v�E�$�&��!1 E '��D��) "%$y�! ��·v�EF)+4Dv®,�*?�!'f�!��E(,�E�'8. t 1+,�E�'� %�!,�) 5BE�1q{BH3\Eî"%$�E ���Q-���EF1�3Av%) &>v_) %&�1+"���EF$g,kv�E�$Ð*%)+'f�!1����B'��|$É,�'�"?&�,�"%'�E�- w,�v�E×� �!1 �i��{[�B$#��E�'�)+5�E2�YD�{��¤�){#1+-�' � �=-�'���EF$¹�É62�D� ¸���Ô�3=EQ"%$�E-� �1�{U,�v�E�) '�&(-���*?-� �E� ®,�$�w�-�'�,kv�E�) � �E�'×� �B1 �8�5{²�B �� ,kv�E[$�*�)��'f�!1G�!'���$�H�3y)+,kvK)*��E� ®,�) &��B1G$�&F�!1 E v�EF)+4Dv®,�*?�!'f�!��E(,�E�'8.¶�Å)+ �,kv%) $��-���E�1¾H�,kv�E·��E� %$�)+,&{]*�E�'�*?EF ���) &("�1 �!' ,�-_,kv�EC��) $��l) $¹��E8$�&�'�) D?E����$\$�EF&>v?� Ðpç[Ð � ���(.;³Ï O-B'>��E�'\,�-�� 5�-B)*�d�QD�) �B$�w�'�-�� D�'�)+4Dv®,y$�*�EF&() �!1'�E�4�)+-� %$�$Ð"%&>v��B$À��{#4B #"%$�Ë)�aEF1 �5Ë �\�B'�) %��H�3=E '�EF$Ð,�'�) &(,�,kv�) $y�! %�B1��{�$�) $C,�-·���!,��O3y)+,kv�) «Ç s�ÇdÇ@0�7DÕ��! ��]Ç u�Ç�Ç ¸B7DÕ!.�»¤)+4?.+6�6·�Å'�) 4 v®,��$kv�-3æ$G,�v�Ed5�B'�) �,�)+-� M-8wy1+-�48��1+)q�BEF1+)qv�-#-��U5�!1 "�EF$î3y)À,�v¾��)�Ã�EF'�EF �,$�&��B1+EÀv%E�) 4 v®,�$~w�-B'\D?-B,kv���-���EF1?,&{#*�EF$F.��gE�'�EBH�,kv�EC5�!1 "�EF$Iw�-B'=,kv�EE!�#*�-B %E� ®,�) �!1�����) $k�[��-5��E�1 $¶v%� 5BEQD?EFE� M$kv�)�w�,�E2�lD5{ K 6F0%H��B$�,kv�E$�*�) '��B1��Ï�!'�� ��-���E�1¤$�{�$Ð,�EF���!,�) &��B1+1q{�*%'�-5#)*��EF$æ��D?E�,Ð,�EF'#��EF$�&('�)+*��,�)+-� -8w -B"�'C���,f��.F¼v)À,�vUqg/a1+-�4 � D�E�) �4·�B$k{®��*�,�-!,�) &F�!1 1�{2a r��) $Ð,�'�)+D�"�,�E2�}H�3=E���EF'�) 5BEC�Q$�&��B1+E#v�EF)+4Dv�,�-8w\62¸�7 Õ / r �-Eè � *�&¹�Ð62Æd�~w�-B',�v�E r�s t 1?E���) $�$�)+-� Q) �,kv%Eæ)+ % �E�'�� �B1 ��&�,�) &A��) $k��H w�'�-��@,�v�Eg$�*�)+'f�!1

�!'��@��-���E�1�&(-B ?$É,�'��B)+ ®,�$F.8��v�) $s&(-� �}%'���$¨*�'�EF5#)+-�"%$s$�"%&>vQ$Ð,�"���)+E8$D%�B$�E2��-B ��y>#y����y:~�Ó���,f�C�Z��)+E2v�1}E(,g�B1�.�6�� ��AD��.

éWc0ê~m0®�®ÒÞ�hkâ�Þof%l«ë,j�f%n;áqmoÛ�pqj�f%Û��v�Ey$É,�"���{�- w%,�v�E rks t 1�1 )+ �Ey�B ��î)+,�$���E(,��B)+1 $¨) ¹��)�Ã�E�'�E� ®,a'�EF4B) -B %$-8w�,�v�EA� �!1 �i��{�) $¤-B �E=-8w�,�v�E\���B)+ 4B-®�!1 $}-8w%,kv�Ey<��I³}$�*�EF&�,�'�-���E]�,�EF'e-B �³&´,�y:��¶µ t �s.W�g$�)+ %4A}%5BE~{BEF�B'�$}-8w%<��I³o���!,��%H�3\E�}% �� ,�v�Erks t 1�$Ð) 4B ?�!18w�'�-B� ,�v�E=) � �EF'W� �B1 �8��{¹��Ç s�Ç5Ç�¸�7DÕ T Ç u�Ç5Ç 687DÕ2�}3y)+,kv�0v�) 4 v_$�)+4� �)�}�&��! ?&(EG-8w�ÅK/BA ƨ.���v�E rks t 10�%";�O) ®,�E�4�'��!,�E���-5�E�',kv�Eî)+ � %E�',� �B1 �8�5{d-8wA��/�É � � 7;É¢/ ��öl6F7�-Y�G*;v[&��b- r $.-0/g'��D��-�/) $\&(-� %$�) $Ð,�EF �,=3y)À,�v�-B"�'=-3y ��! ���-!,kv%E�'°E8�!'�1+) E�'=��EF�B$�"�'�E���E� ®,f$�H,kv�-�"�4 v $Ð) 4B �)�}?&F�! ®,�1q{�1 -3\E�'[,�v%�! �,�v�E·-B �E8$|w�'�-B�j��EF�B$�"�'�E]���E� ®,�$°3y)À,�v�)+ ?$É,�'�"���EF �,f$s3Av�) &>vNv%� 5�EæE�5�E� ���-B'�Eæ��-5��EF$Ð,=$Ð*?�i�,�) �!1�'�EF$�-B1 "�,�)+-� -� ,�v�Eæ$k��{�. �¤�8�#)+ %4�,�v�EÀ��) $É,f�! %&�Ey-8w�,kv�Eg<�"� �,�-,kv�EN� �!1 �B&(,�) & &�E� ®,�EF'C��$���� 9 A�..�N�#*�&BH�3=E�&(-� ®5�E�'�,g,�v�E ��E8�i�$Ð"%'�E�� r�s t 1��%"���,�-��×� �!1 �B&(,�) & r�s t 1}���B$�$�-8wA��/�É7ó$� 7;É7ó8�$¢r£ .¼]EQ&(-��Q*?�!'�E2�C��)�Ã�EF'�EF �,�*�1 �B"%$�)+D�1 E���-���E�1 $Aw�-�'æ,�v�Eî$k��{C��) $É,�'�)��D�"�,�)+-� �-8w r�s t 1�E���) $�$�)+-� ��! ��¶v�-3U)+,e���){C�8Ã�E8&�,},�v�E°4�1+-�D%�!1 rks t 1�%"��U��EF�B$�"�'�E���E� ®,8.o¼]EN}? ��l,kv%�!,���)�Ã�EF'�EF ®,î$��5{ ��) $Ð,�'�)+D%"�,�) -B ��-5��E�1 $¹��-Y �-B,�$�"�D%$Ð,��B �,�) �B1+1q{M�iÃ�EF&(, r�s t 1�) ®,�E� ?$Ð)+,&{²�! ��²1+) �E$�v?�!*�EF$#w�-B'C,�v�E�)+ ®,�E�4B'f�,�E2�Y)+ � %E�'�� �!1 �i��{�H��B ��]3=E0v%� 5�Eî"%$�E2�,kv�E�-BD%$�E�'�5BE��l5 �B'�) �,�)+-� %$�- w rks t 1=����$�$î5 �B1+"%EF$î,�-_E8$É,�)+���,�E��$�{�$Ð,�EF���!,�) &�"� %&�E�'�,��!) ®,&{BHB�D�;��E��Q,�- ,kv%Eg$É,f�,�) $Ð,�) &��B1�"� %&�E�'�,��!) ®,&{w�'�-��m,kv%E��Q-���EF1�}�,�,�) �4%H�,�-C{®) E�1*�],kv�Eb�C7�É.ób¢ £ "� %&�E�'�,��!) ®,&{ù®"�-!,�E2��.

��v�E rks t 1s1 )+ %E�&(E� ®,�'�-�)q�]E� �EF'�4D{Y�!*%*?E8�!'f$�D%1+"�E!��$kv�)�w�,�E��]'�E�1���,�)+5�E�,�-[,�v�Ed1 �!D�-B'f�,�-B'�{_5�!1 "�E�- w�6FAB7�A;É 0D���v7;É 7�óa��E!� )�wæ) ��,�EF4B'f�,�E��M-5BEF'�,�v�E�) � �EF'0� �B1 �8��{��Ð6FA�7 �;É 7��V7�É+6a�BE2�#��.W¼v)+,kv'�E!}% �E��M$Ð*%�!,�) �!1s'�EF$�-B1 "�,�)+-� ],�v�) $�,�"�'� ?$�-B"�,�,�-_D�E���-�$Ð,�1q{Ó��"�E,�-O�B$k{®����E(,�'�) &�D%"�1�����-!,�)+-� _3Av�) &>v_3\Eô}% ��]�!1 -B �4�,kv�EQ*�1 �! �E-8w},�v�E�� �!1 �i��{BH®�! ����,Ð,�'�) D�"�,�Eg,�- ��$�{#����E(,�'�) EF$=)+ �)+ � %E�'�$Ð*�) 'f�!1�!'���$î�! ��U,�-[,�v�E|� �!1 �i��{%¿ $GD?�!'8.�³Ï *?�!'�,�) &("�1 �!'8How�-B' ,kv%E�&(EF ��,�'f�!1¨1 -B �4�)À,�"���E�D�) Y,�-3\�B'���$g,kv%EN� �B1 ��&�,�) &×�=E� ®,�E�'8H?,�v�E�$Ð) 4B ?�!1) $°$É,�'�-� �4 E� �-�"�4 vQ,�-��B1+1 -3�w�-B's� 'f�,kv%E�'°$����!1 1�1+-� �4B)+,�"���Ey'��B �4BE)+ ®,�E�4B'f�,�)+-� }H!�! �� 3\E�}% ���� r�s t 1%1 )+ �E�&(E� ®,�'�-�)q�Q&(-� %$Ð) $Ð,�E� ®,s3y)+,kv,kv�Eg1 �BD?-�'��!,�-B'�{G5�!1 "�Eæ�! ��Q,kv#"%$a3y)+,kv�,�v�Eg�!D?$ÐEF %&(Ey- w�D�"%1��Q��-8�,�) -B i'�EF1 �!,�) 5BE�,�-Y,�v�E�<�"� }. t 1 $�-%H`v�E�'�E�,�v�E r�s t 1y1+) �E��!*�*�EF�B'�$�B$ ��-�$Ð,��� %�B'�'�-3�3y)À,�vM�! U"�*�*�E�'�1 ) �Q)+,�-8w 6B. ¸·�BE2�ø�¾/8Æd�(.���v�E��EF�B$�"�'�E2��1 ) �E�3y)*�#,�v�- w rks t 1Jw�'�-��´,kv�EC1 �!'�4BE]�Ï$�&��!1 Ey) �,�E�4�'��!,�E2�)+ % �E�'A� �!1 �i��{�3y)À,�v��B d"�*�*�E�'\1 )+��)+,�- w°6B. ¸���E!� ��/8Æd�°) $\&�-B %$�) $&�,�EF �,C3y)À,�vYE!�#*�EF&(,��!,�) -B %$Àw�'�-�� � �B1 ��&�,�) &G'�-!,f�,�)+-� _�! �����-���EF$Ð,)+ ®,�E�'f$É,�E�1 1 �B'�����E2��) "�� ,�"%'�D�"%1+EF %&(E��!'�-B"% ��[,�v�E�$Ð-�"�'�&�EF$�-8w rks t 1��,�"�'�D%"�1+EF ®,\5�E�1 -#&�)À,�)+E8$ÀÇ 6F0�7��#�´$ -�/!��.%>�"�'\1+) �E�3y)q�#,�vd'�EF$�"�1+,�$�!'�E=&�-B %$�) $Ð,�EF ®,¤3y)+,kvQ*�'�E�5#)+-�"%$�'�EF*?-�'Ð,f$�D5{ô��: t >z���Ê�Zy_� v�-B �E2{E(,=�B1�.?62��A�/ �(H µÀ��:=<�<5³A�¾<#��)À,�v�/!7�7 ¸D�(HD�"�,=,kv�Eæ5�E�'�{îD�'�-��D�Q1+) �E3y)À,�vV�M3y)*�#,kv Å ��É x �BE!�m'�E�*�-B'�,�E��·D�{��¶µA³Ð<Ñ��´g�){��UE�,��!1¾.62�D�B0D�C) $Q&(1 EF�!'�1q{]'�"�1 E2�M-�"�, D5{U-B"�'�<��I³G��E8�B$�"�'�EF��E� ®,�$a�ÀxDÆ$Ð) 4B %)�}?&F�! %&�E 1+EF5BE�1��(.

»�'�-B�m-�"�'G$É,�"���{_- w r�s t 1sEF��) $�$Ð) -B ])+ U$�*%�,�) �B1+1q{��¾'�EF$Ð,�'�) &(,�E��'�EF4B) -B %$��B1+-� �4î,�v�EG*�1 �! �EG- we,�v�E�� �!1 �i��{BH�3\E#}% ����ì rks t 1yD�'�)+4Dv®,� �E8$�$��!*%*?E8�!'f$Q��$�{#����E(,�'�) &×w�-�'�,kv�EO,É3\-U)+ � %E�'

ù®"%� ��'f�! ®,f$�H�3y)+,kv_�³�%";�O'f�,�)+-�-8w¨,�v�Eôx!,�v|ù�"?� ��'f�! ®,y,�-�,�v�E6F$Ð,y-8w�Å@6 É ¸��²7�É /·��»�) 4B"%'�EG0D�(.ì ��v�E rksut 1y1+) �EOE� �EF'�4D{M5�!'�)+E8$ &�1+E8�!'�1�{M�!1 -B %4_,kv%E|� �B1 ��&�,�) &*�1 �! �E���»¤)+4�"�'�Eî6F7D�.���î�Q) �-�'°'�E2��$kv�)�w�,#�¨ÅV7;É 6À�BE2�#��w�-B'°*�-�$��)À,�)+5�E�1 -B %4B)+,�"���E8$�HaD%"�,�$Ð) 4B �)�}?&F�! ®,QD%1+"�E8$�v%)�w�,½��Å 7�É x�qv7�É A�BE2�#�~w�-B'y �EF4��!,�) 5BE 1+-� �4B)+,�"���EF$F.ì ��v�E rks t 1�1+) �E�,�-3��!'>��$�,�v�EC��)+'�EF&(,�) -B i-8wC/B7DÕ Çís�Ç x®7DÕ$�v%-3æ$\�¹v�) ®,Aw�-B'æ�D�;��)+,�) -B %�B1�1+) �EGD�'�-��D��E� �) �4?.ì ��v�E�$�&F�!1 E v%E�) 4 v®,V-8w � �!1 �B&�,�) &]�¾*%1 �B �E r�s t 1_E���) $�$�)+-� ) $62¸�7 Õ / r �-Eè � *�&��Ð62Æd�(HJ��E�,�EF'���) �E2��,�-3\�B'��%$�,kv�E )+ % �E�'�� �!1 �i��{�CÇ sCÇ�Ç 0B7�Õ!��.

Figure 2: 26Al line details from INTEGRAL: (Left:) The probability distribution for additional broadeningof the26Al line, beyond the instrumental width [15]. (Right:) The26Al line centroid positions for differentdirections along the plane of the Galaxy show an expected blue-shift from large-scale galactic rotation in thefourth quadrant; a corresponding redshift in the first quadrant is not clear ([15]; see also [17]).

emission, a larger line width would be plausible, from increased turbulence of the ISM aroundgroups of massive stars. The integrated26Al signal observed with INTEGRAL now has reached asignificance (28σ ; [15]) similar to what COMPTEL obtained in its 9-year mission, making possibleimproved tests of kinematics of26Al nuclei at the time of their decay. The instrumental line widthof 3 keV FWHM limits such tests; moreover the periodic annealings and intervening cosmic-rayinduced 10% degradations of detector resolution result in a time-variable detector resolution overthe years of accumulated observations. Since these instrumental effects are well-calibrated, we cancompare the observed line shape to the expected one from instrumental properties, and parametrizethe difference in terms of an additional (assumed-Gaussian) astrophysical broadening. Fig2 (left)shows the probability distribution as obtained from this test. Clearly, there is no positive broadeningmeasured; the probability distribution peaks at small values near zero. Yet the shape, with anindicated plateau up to a few tenths of a keV, hints towards a small broadening of 0.3–0.4 keV,which would correspond to a velocity of 50 km s−1. The probability distribution provides a strictupper limit of 1.3 keV (at 95% probability) for additional broadening, which limits26Al velocitiesto less than 150 km s−1 on average. Note that this conversion to velocity limits assumes an isotropicand Gaussian distribution of velocities, such as expected from turbulence in the interstellar medium.Also, the underlying spectrum is obtained from integration over the entire inner Galaxy, which mayinclude regions of different intrinsic turbulence plus the bulk motion from the Galaxy’s differentiallarge-scale rotation. In summary, large kinematic broadening in the 100 km s−1 range such asdiscussed ten years ago are excluded, while INTEGRAL’s capability to measure velocities downalmost to average stellar velocities provides an interesting and unexpected perspective.

Clearly, the integration over many possibly unrelated source regions limits the impact of26Alresults obtained so far. Only in the Cygnus region may one safely assume a coherent and localizedsingle source region along the line of sight, which also has a strong26Al signal, on the order of 15σ[18]. However, the INTEGRAL exposure of the inner Galaxy now is approximately similar to theCOMPTEL all-sky survey (1991–2000). With similar spatial resolutions of INTEGRAL/SPI andCOMPTEL (2.7◦versus 3.6◦ FWHM, respectively), this allows study of specific regions of interestfor local line shape diagnostics, with years of INTEGRAL observations still to be analyzed, andstill to be acquired. The peculiar line width towards the Aquila region, and isolation of the26Al

4

PoS(Integral08)007

Gamma-Ray Lines M. Leising

signal from the nearby Sco-Cen association (distance 100–150 pc) are on the horizon. It will beimportant that such observations are taken under well-controlled background and spectral-responseconditions, so that instrumental limitations are minimized. The Orion region presents the mostnearby concentration of young massive stars at about 450 pc distance, well isolated on the skywith respect to other Galactic26Al sources, and marginally detected with COMPTEL (Fig.1) [19].Similar to Cygnus, or even better, is our knowledge about the stellar census of this region. But,being located towards the outer Galaxy with correspondingly lower space density of candidate hardX-ray sources, INTEGRAL’s observing program devoted just as much exposure to Orion so thatconfirmation or not of the weak COMPTEL26Al signal may be expected. These data are beinganalyzed, and a positive26Al detection would likely prompt more observations, for a determinationof bulk 26Al velocity of Orion. This is of interest because there is a large interstellar cavity in theforeground of the Orion26Al sources, which plausibly could cause deviations from spherically-symmetric26Al dispersion around its sources.

2.2 60Fe

Stellar nucleosynthesis models have shown that the long-livedγ-ray emitting radioactive iso-tope60Fe is synthesized within the convective envelopes of massive-stars. For stars exceding 8–10M�, these60Fe-rich ashes would be ejected in the terminal core-collapse supernova explosion. Thedetails are complex, and how shell burning regions develop and extinguish, and which neutron-producing reactions are important are uncertain. Yields of radioactive26Al and 60Fe are verysensitive to such detail, however [20]. Because of the dominant massive-star origin of26Al, theγ-ray flux ratio from the two isotopes constitutes an interesting global test of massive-star nucle-osynthesis models.

Following many reported non-detections and upper limits, a hint of60Fe γ-rays was foundwith RHESSI [21]. That signal corresponded to 16±5% of the26Al flux, consistent with earliertheoretical predictions of 15% [22]. Later studies of massive-star nucleosynthesis tended to predictlarger ratios of60Fe versus26Al, as progenitor evolution and wind models[23], as well as nuclear-reaction rates[24], were updated . Nucleosynthesis calculations [20, 24] generally still fall on thehigher side of the original prediction, but are consistent, given the substantial uncertainties in suchmodels. Uncertainties arise mainly from stellar structure, as establishment of suitable convective-burning regions is sensitive to stellar rotation, which in turn is affected by the mass loss historyduring evolution. Uncertainties on nuclear cross sections involve26Al destruction though n capture,and n-capture on unstable59Fe and on60Fe itself.

Confirmation of the RHESSI60Fe signal was reported from first-year INTEGRAL/SPI data[25], although features from a nearby instrumental line indicated systematics issues. In a recentanalysis of more data, a significant60Fe signal (at 5σ ) was found, with somewhat reduced sys-tematic effects from instrumental background. This underlying background is being investigated,specific signatures within the 19-detector Ge camera of SPI are being exploited to discriminateinternal versus celestialγ-rays on their respective modulation time scales. The INTEGRAL/SPIreported60Fe/26Al γ-ray flux ratio is now 0.14±0.06. Formally, there is agreement between obser-vations and models (see Fig.3), but more can be learned as uncertainties in each area are revisitedand re-assessed. We also hope to exploit INTEGRAL’s spatial resolution, towards determinationof spatially-resolved60Fe to26Al ratios. It seems feasible to obtain values for the different Galactic

5

PoS(Integral08)007

Gamma-Ray Lines M. Leising

Roland Diehl© INTEGRAL / SPI Team, 2007

W.Wang et al. , A&A (2007)

Roland DiehlNuclei in the Cosmos X, Mackinac Island, MI (USA), 31 Jul 2008

6060FeFe from Massive Stars: from Massive Stars: ObservationsObservations vs. Theoryvs. Theory

Current Models Agrees with Data on 60Fe/26Al γ-Ray Intensity RatioBut: Uncertainties are Substantial in Several Areas:

Assessments Needed:Stellar Models?Nuclear Physics?Gamma-Ray 60Fe Signal Origin?

latest FRANEC model (Limongi & Chieffi 2006)(stellar evolution & nucleosynthesis & IMF)

latest model Woosley et al 2007(stellar evolution & nucleosynthesis & IMF)

latest measurement (SPI)(Wang et al. 2007)

Timmes et al. 1995

Figure 3: (Left:) The 60Fe measurement with INTEGRAL . Superpositions of both lines of60Fe at theirnominal energies of 1173 and 1332 keV, respectively, show a weak signal from60Fe decay. (Right:) The setof 60Fe/26Al ratio measurements by different experiments and the ranges of current theoretical predictionsappear consistent. Deeper investigations of uncertainties in measurement and model may show if observa-tions are significantly lower than predictions.

quadrants, and the60Fe limit for the 26Al-bright Cygnus region will provide another interestingconstraint because, rather than being in steady state, here26Al from rather young massive-stargroups is observed.

3. Specific Sources

3.1 44Ti Supernova Remnants

Given a galactic supernova rate of 2–3 per century and a44Ti (44Ti τ=87y68,78keV

44Sc τ=5.7h1156keV

44Ca)yield of nearly 10−4 M� per event, it is reasonable to expect to find a few remnants in the innerGalaxy detectable at line flux levels near 10−4 cm−2 s−1. Increasingly sensitive searches foundnone there [26, 5], but the Cas A supernova remnant was detected in the 1.157 MeV line [27]. Thishas been confirmed by detections of the lower energy lines [28, 29], and now all flux measurementsare consistent with'2.5 10−5 cm−2 s−1. These verify the idea that44Ti is synthesized in the alpha-rich freezeout of nuclear statistical equilibrium, which occurs in material ejected by core-collapsesupernovae. Such observations might shed light on the role of asymmetries in the explosion and onthe mechanism of ejection. INTEGRAL/SPI attempts to do spectroscopy on the Cas A44Ti lines,with a chance to make use of simultaneous measurements of all three decay lines with the sameinstrument, so far yields only upper limits to the line fluxes. That for the 1.157 MeV line implies alower limit to the expansion velocity of∼ 500 km s−1 [30].

The lack of other detectable remnants is quite puzzling viewed in any of several ways. Starformation is concentrated in the inner Galaxy, and currentγ-ray line surveys [31] can detect typicalremnants at the distance of the galactic center for a few half-lives of44Ti, so the probability thatthe brightest remnant is in the outer Galaxy, at a distance of 3.4 kpc and of an age 320 years isvery improbable, assuming Cas A’s44Ti yield is not much different than the average. Apart fromCas A, current estimates of supernova rates and yields suggest that at least a few remnants should bedetected in the inner Galaxy at IBIS hard X-ray sensitivity [32], but even those rates and yields fallshort of the expected44Ca production rates required to explain the solar44Ca abundance [5, 22]. A

6

PoS(Integral08)007

Gamma-Ray Lines M. Leising

scenario that reproduces the solar abundance of44Ca, if made as44Ti, yields even more detectableremnants.

The solution of this puzzle is not clear. Perhaps supernova44Ti yields vary greatly, and theoutliers on the high side contribute most of the44Ti. However, Cas A, whose yield, 1.4 10−4

M� is higher than theoretical calculations, is not extreme enough. We would still require 1–2such supernovae per century, a few of which should be detectable. A plausible solution is thatmuch higher yield44Ti sources, which are very rare, e.g., He-triggered low-mass thermonuclearsupernovae [33], produce the time-averaged44Ca rate, but none has occurred in the Galaxay inrecent centuries. No such source has been recognized among extragalactic supernovae or galacticremnants. Such objects should be visible in the K X-rays of radioactive59Ni (τ =75 ky) decay [34]if they exist.

There is also evidence that44Ti is present in the ejecta of SN 1987A [35] at a mass somewhatless than that in Cas A. The impliedγ-ray line flux could be 3 10−6 ph cm−2 s−1, which is unde-tectable to current instruments, but could be measured by near-term instruments with hard X-rayoptics or much improved Compton telescopes.

3.2 Supernovae Ia and Novae

From general considerations, it was thought that the objects best studied byγ-ray lines wouldbe the profoundly thermonuclear objects, classical novae and Type Ia supernovae, rather than thecore-collapse supernovae for which the nuclear reactions are a side effect. However, we havedefinitively detected neither a nova nor a thermonuclear supernova. The reason is simply luck;none have occurred within the suitable volumes sampled by our instruments.

Type Ia supernovae are good standard candles because they are efficient thermonuclear bombs,producing typically 0.6 M� of 56Ni whose decay powers the visible display. Their kinetic energiesare high enough that theγ-ray escape is significant after one month. The best limit on56Co linesfrom a SN Ia was set by the SMM/GRS for the nearby SN 1986G, which found to have ejected lessthan 0.4 M� of 56Ni [36]. This was a somewhat under-luminous Type Ia, for which that56Ni massis not now thought to be extreme. The high-luminosity SN Ia prototype, SN 1991T, was the firstprospect for CGRO, but its distance of 13–14 Mpc meant that only upper limits were achieved [37,38], however one analysis method showed possible56Co line features [39]. SN 1998bu was onlyslightly closer, and also yielded only upper limits [40]. No SN Ia has been closer in the INTEGRALera, though SN 2003gs was observed early in the mission. No lines were seen. With recentlyobtained sensitivity to broad lines, SPI can detect typical SN Ia models in56Co lines to distance of6–7 Mpc, which occurs about once per twenty-five years. IBIS can possibly detect the 80–150 keVCompton continuum to distance of 9–10 Mpc, expected about once per decade.

Classical novae, envelope thermonuclear flashes on accreting white dwarfs, were long sus-pected to be brightγ-ray line sources [41, 42] Proton rich nuclei, includingγ-ray emitters22Naand 26Al and short-lived positron emitters13N and 18F, should be ejected, but yields are uncer-tain mainly because the underlying models are uncertain. Searches for22Na lines have so farproved fruitless, both blind and of nearby novae [1, 43, 44]. The nova contribution to the diffuse26Al emission is unknown, but is probably not dominant given the lack of26Al in the bulge. Theelectron-positron annihilation emission over the first hours after outburst would be an excellentdiagnostic of the burning and transport of envelope material. The models have become somewhat

7

PoS(Integral08)007

Gamma-Ray Lines M. Leising

more pessimistic in recent years [45]. As the onset of the runaway is unpredictable, a wide fieldmonitor with good background stability is essential. The FERMIγ-ray burst monitor (GBM) mightserve this purpose in the immediate future.

4. Summary

Gamma-ray lines from radioactive decay of cosmic nuclei have provided astrophysics withdirect proof of ongoing nucleosynthesis in the present-day universe. Although the number ofdifferent isotopes available for such study is limited, these provide key calibration points formodels of nucleosynthesis in stars and supernovae.44Ti is beginning to yield unique insights intothe interior processes of massive-star gravitational collapses, with potential further insight intoasymmetrical features such as jets, while corresponding measurements with Ni isotopes onthermonuclear supernova processes have not had the luck of a sufficiently nearby event. Diffuseγ-ray emission in the Galaxy from decay of radioactive26Al and 60Fe all provide tests of ourmodels of massive-star interior structure and nucleosynthesis. INTEGRAL measurements, inmost cases with just a few years of data, have advanced our understanding of each of these topics.It continues to provide a unique capability for study ofγ-ray line emission, which will not bereplaced in the foreseeable future.

References

[1] W. A. Mahoney, J. C. Ling, A. S. Jacobson and R. E. Lingenfelter,ApJ262(Nov., 1982) 742–+.

[2] W. A. Mahoney, J. C. Ling, W. A. Wheaton and A. S. Jacobson,ApJ286(Nov., 1984) 578–585.

[3] G. H. Share, R. L. Kinzer, J. D. Kurfesset. al., ApJ292(May, 1985) L61–L65.

[4] M. J. Harris, G. H. Share, M. D. Leisinget. al., ApJ362(Oct., 1990) 135–146.

[5] M. D. Leising and G. H. Share,ApJ424(Mar., 1994) 200–207.

[6] S. M. Matz, G. H. Share, M. D. Leisinget. al., Nature331(1988) 416–418.

[7] M. D. Leising and G. H. Share,ApJ357(July, 1990) 638–648.

[8] J. D. Kurfess, W. N. Johnson, R. L. Kinzeret. al., ApJ399(Nov., 1992) L137–L140.

[9] N. Prantzos and R. Diehl,Phys. Rep.267(Mar., 1996) 1–69.

[10] J. KnödlsederApJ510(Jan., 1999) 915–929.

[11] J. E. Naya, S. D. Barthelmy, L. M. Bartlettet. al., Nature384(Nov., 1996) 44–46.

[12] W. Chen, R. Diehl, N. Gehrelset. al., in The Transparent Universe(C. Winkler, T. J.-L. Courvoisierand P. Durouchoux„ eds.)vol. 382, pp. 105–+, 1997.

[13] S. Plüschke, R. Diehl, V. Schönfelderet. al., in Exploring the Gamma-Ray Universe(A. Gimenez,V. Reglero and C. Winkler„ eds.)vol. 459, pp. 55–58, Sept., 2001.

[14] R. Diehl, J. Knödlseder, G. G. Lichtiet. al., A&A 411(Nov., 2003) L451–L455[arXiv:astro-ph/0309097 ].

[15] W. Wang, M. G. Lang, R. Diehlet. al., A&A 496(Mar., 2009) 713–724 [0902.0211 ].

[16] D. M. SmithApJ589(May, 2003) L55–L58 [arXiv:astro-ph/0304508 ].

8

PoS(Integral08)007

Gamma-Ray Lines M. Leising

[17] R. Diehl, H. Halloin, K. Kretschmeret. al., Nature439(Jan., 2006) 45–47[arXiv:astro-ph/0601015 ].

[18] J. Knödlseder, M. Valsesia, M. Allainet. al., in 5th INTEGRAL Workshop on the INTEGRALUniverse(V. Schoenfelder, G. Lichti and C. Winkler„ eds.)vol. 552, pp. 33–+, Oct., 2004.

[19] R. DiehlNew Astronomy Review46 (July, 2002) 547–552.

[20] A. Chieffi and M. Limongi,New Astronomy Review46 (July, 2002) 459–462.

[21] D. M. Smith in5th INTEGRAL Workshop on the INTEGRAL Universe(V. Schoenfelder, G. Lichti andC. Winkler„ eds.)vol. 552, pp. 45–+, Oct., 2004.

[22] F. X. Timmes, S. E. Woosley, D. H. Hartmann and R. D. Hoffman,ApJ464(1996) 332–+.

[23] N. PrantzosA&A 420(June, 2004) 1033–1037 [arXiv:astro-ph/0402198 ].

[24] S. E. Woosley and A. Heger,Phys. Rep.442(Apr., 2007) 269–283 [arXiv:astro-ph/0702176 ].

[25] M. J. Harris, J. Knödlseder, P. Jeanet. al., A&A 433(Apr., 2005) L49–L52[arXiv:astro-ph/0502219 ].

[26] W. A. Mahoney, J. C. Ling, W. A. Wheaton and J. C. Higdon,ApJ387(1992) 314–319.

[27] A. F. Iyudin, R. Diehl, H. Bloemenet. al., A&A 284(1994) L1–L4.

[28] J. Vink, J. M. Laming, J. S. Kaastraet. al., ApJ560(Oct., 2001) L79–L82[arXiv:astro-ph/0107468 ].

[29] M. Renaud, J. Vink, A. Decourchelleet. al., ApJ647(Aug., 2006) L41–L44[arXiv:astro-ph/0606736 ].

[30] P. Martin, J. Knödlseder, J. Vinket. al., A&A in press(2009).

[31] M. Renaud, F. Lebrun, J. Balletet. al., in 5th INTEGRAL Workshop on the INTEGRAL Universe(V. Schoenfelder, G. Lichti and C. Winkler„ eds.)vol. 552, pp. 81–+, Oct., 2004.

[32] L.-S. The, D. D. Clayton, R. Diehlet. al., A&A 450(May, 2006) 1037–1050[astro-ph/0601039 ].

[33] S. E. Woosley, R. E. Taam and T. A. Weaver,ApJ301(Feb., 1986) 601–623.

[34] M. D. LeisingApJ563(2001) 185–190.

[35] P. Lundqvist, C. Kozma, J. Sollerman and C. Fransson,A&A 374(Aug., 2001) 629–637[arXiv:astro-ph/0105402 ].

[36] S. M. Matz and G. H. Share,ApJ362(Oct., 1990) 235–240.

[37] G. G. Lichti, K. Bennett, J. W. den Herderet. al., A&A 292(Dec., 1994) 569–579.

[38] M. D. Leising, W. N. Johnson, J. D. Kurfesset. al., ApJ450(Sept., 1995) 805–+.

[39] D. J. Morris, K. Bennett, H. Bloemenet. al., in AIP Conf. Proc. 410: Proceedings of the FourthCompton Symposium, pp. 1084–+, Nov., 1997.

[40] R. Georgii, S. Plüschke, R. Diehlet. al., A&A 394(Nov., 2002) 517–523.

[41] D. D. Clayton and F. Hoyle,ApJ187(Feb., 1974) L101+.

[42] M. D. Leising and D. D. Clayton,ApJ323(1987) 159–169.

[43] M. D. Leising, G. H. Share, E. L. Chupp and G. Kanbach,ApJ328(May, 1988) 755–762.

9

PoS(Integral08)007

Gamma-Ray Lines M. Leising

[44] A. F. Iyudin, K. Bennett, H. Bloemenet. al., A&A 300(Aug., 1995) 422–+.

[45] M. Hernanz, J. José, A. Cocet. al., ApJ526(1999) L97–L100.

[46] P. Martin and J. Vink,New Astronomy Review52 (Oct., 2008) 401–404.

[47] F. A. Harrison, F. E. Christensen, W. Craiget. al., Experimental Astronomy20 (Dec., 2005) 131–137.

[48] P. Ferrando, M. Arnaud, U. Brielet. al., Memorie della Societa Astronomica Italiana79 (2008) 19–+.

[49] M. Renaud, F. Lebrun, A. Decourchelleet. al., Memorie della Societa Astronomica Italiana79 (2008)50–+ [0709.2648 ].

10