CGRO-COMPTEL measures gamma-ray burst positions, time-histories and spectra in the 0.1–30 MeV energy range, in both imaging “telescope” and single detector “burst spectroscopy” mode. GRB 990123, one of the most recent bright bursts seen by COMPTEL, was caught in the optical while the gamma-ray emission was ongoing. The burst spectral shape can be characterized by a peak in ν−Fν just below 1 MeV and a power-law tail above(photon index∼−2.4,) and flattening below. There is also spectral evolution by downward movement of the peak and/or softening of the power laws. We present light-curves, time resolved spectra and an image map for this burst

Bennett, K

Collmar, W

Connors, A

Hermsen, W

Kippen, R M

Kolaczyk, E

Kuiper, L

McConnell, Mark L

Miller, R S

Ryan, James M.

Schonfelder, V

Williams, O R

Winkler, C

Young, C A

English

University of New Hampshire

University of New Hampshire
University of New Hampshire Scholars' Repository
Space Science Center Institute for the Study of Earth, Oceans, and Space(EOS)
2000
Spectra of a recent bright burst measured by
CGRO-COMPTEL: GRB 990123
C A. Young
University of New Hampshire - Main Campus
A Connors
Eureka Scientific
K Bennett
ESTEC
W Collmar
Max-Planck-Institut für extraterrestriche Physik
W Hermsen
Space Research Organization of the Netherlands (SRON)
See next page for additional authors
Follow this and additional works at: https://scholars.unh.edu/ssc
Part of the Astrophysics and Astronomy Commons
This 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 of
New Hampshire Scholars' Repository. It has been accepted for inclusion in Space Science Center by an authorized administrator of University of New
Hampshire Scholars' Repository. For more information, please contact nicole.hentz@unh.edu.
Recommended Citation
Spectra of a recent bright burst measured by CGRO-COMPTEL: GRB 990123 Young, C. A. and Connors, A. and Bennett, K. and
Collmar, W. and Hermsen, W. and Kippen, R. M. and Kolaczyk, E. D. and Kuiper, L. and McConnell, M. and Miller, R. and Ryan, J. M.
and Schönfelder, V. and Williams, O. R. and Winkler, C., AIP Conference Proceedings, 526, 170-174 (2000), DOI:http://dx.doi.org/
10.1063/1.1361528
Authors
C A. Young, A Connors, K Bennett, W Collmar, W Hermsen, R M. Kippen, E Kolaczyk, L Kuiper, Mark L.
McConnell, R S. Miller, James M. Ryan, V Schonfelder, O R. Williams, and C Winkler
This conference proceeding is available at University of New Hampshire Scholars' Repository: https://scholars.unh.edu/ssc/123
Spectra of a recent bright burst measured by CGRO-COMPTEL: GRB 990123
C. A. Young, A. Connors, K. Bennett, W. Collmar, W. Hermsen, R. M. Kippen, E. D. Kolaczyk, L. Kuiper, M.
McConnell, R. Miller, J. M. Ryan, V. Schönfelder, O. R. Williams, and C. Winkler 
 
Citation: AIP Conference Proceedings 526, 170 (2000); doi: 10.1063/1.1361528 
View online: http://dx.doi.org/10.1063/1.1361528 
View Table of Contents: http://scitation.aip.org/content/aip/proceeding/aipcp/526?ver=pdfcov 
Published by the AIP Publishing 
 
Articles you may be interested in 
Power density spectra of gamma-ray bursts 
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X-ray excesses in GRB spectra 
AIP Conf. Proc. 526, 175 (2000); 10.1063/1.1361529 
 
Study of the characteristics of GRB energy spectra 
AIP Conf. Proc. 526, 160 (2000); 10.1063/1.1361526 
 
Gamma-ray burst spectroscopy 
AIP Conf. Proc. 526, 115 (2000); 10.1063/1.1361518 
 
Testing the intrinsic randomness in the angular distributions of gamma-ray bursts 
AIP Conf. Proc. 526, 102 (2000); 10.1063/1.1361516 
 
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132.177.229.79 On: Mon, 24 Nov 2014 14:31:02
Spectra of a Recent Bright Burst 
Measured by 
CGRO-COMPTEL:GRB 990123 
C. A. Young’, A. Connors 2, K. Bennett3, W. Collmar4, 
W. Hermsen5, R. M. Kippen’, E. D. Kolaczyk7, L. Kuiper5, 
M. McConnell’, R. Miller’, J. M. Ryan’, V. Sch6nfelder4, 
0. R. Williams3, and C. Winkler3 
‘Space Science Center, University of New Hamphsire, Durham NH, USA 
‘Eureka Sci en tific 
3 Astrophy sits, Division, ESTEC, NL-2200 AG Noordwijk, NL 
4Max-Planc k-Institut fur Extraterrestrische Physik, D-85740 Garching, FRG 
5 SRON- Utrecht, Sorbonnelaan 2, NL-3584 Utrecht, NL 
6 CSPAAR, University of Alabama in Huntsville, Huntsville AL, USA 
’ Departme nt of Mathematics and Statistics, Boston University, Boston MA, USA 
Abstract. CGRO-COMPTEL measures gamma-ray burst positions, time-histories 
and spectra in the 0.1-30 MeV energy range, in both imaging “telescope” and single 
detector “burst spectroscopy” mode. GRB 990123, one of the most recent bright 
bursts seen by COMPTEL, was caught in the optical while the gamma-ray emission 
was ongoing. The burst spectral shape can be characterized by a peak in v - FV just 
below 1 MeV and a power-law tail above (photon index N -2.4), and flattening below. 
There is also spectral evolution by downward movement of the peak and/or softening 
of the power laws. We present light-curves, time resolved spectra and an image map 
for this burst. 
INTRODUCTION 
GRB 990123 is the only gamma-ray burst to be simultaneously observed in opti- 
cal wavelengths. The Burst and Transient Source Experiment (BATSE) on CGRO 
triggered the Compton Telescope (COMPTEL) on CGRO at 35216.121 s UT on 
23 January 1999 (BATSE trigger #7343). The burst was located at a zenith angle 
(w.r.t. CGRO and COMPTEL) pointing of 58.4”. The gamma-ray emission lasted 
for about 100 s with the > 1 MeV emission seen by COMPTEL most significant be- 
tween 18 s and 46 s after the BATSE trigger. The Robotic Optical Transient Search 
Experiment (ROTSE) detected optical emission during and after the gamma-ray 
emission. ROTSE made 6 measurements starting 22.2 s after the BATSE trigger. 
CP526, Gamma-Ray Bursts: Sh Huntsville Symposium, edited by R. M. Kippen, et al. 
0 2000 American Institute of Physics l-56396-947-5/00/$17.00 
170 
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132.177.229.79 On: Mon, 24 Nov 2014 14:31:02
10” ARM 
-7-30 MeV 
FIGURE 1. GRB 990123 (BATSE 
#7343) in the COMPTEL low (0.2-1.6 
MeV) and high (0.6-11 MeV) range 
burst mode, plus the 0.7-30 MeV tele- 
scope mode light-curves. The ROTSE 
m, are indicated with the telescope 
mode. 
3.52x lo* 3,53x10* 3.54x lo* 
Time (seconds U-T.) 
COMPTEL detected the second and third peaks of GRB 990123 in both its imag- 
ing telescope (“double scatter”; 0.75-30 MeV) and non-imaging burst-spectroscopy 
(“burst mode”; 0.3-1.5 MeV and 0.6-10 MeV; see Schijnfelder et al. 1993) modes. 
Telescope position constraints were broadcast (via GCN/BACODINE) about 10 
minutes after burst onset and preliminary light-curves were posted soon thereafter 
(Young et al. 1999; Connors et al. 1999). 
In the imaging telescope mode, COMPTEL provides detailed information on 
individual time-tagged photons with i ms time resolution. Because of the small 
effective area and limited telemetry of the telescope mode, however, only ~200 
burst events were recorded. In spectroscopy mode the effective area was roughly 
two orders of magnitude greater, and the dead time was negligible. The COMPTEL 
light-curves are displayed in Fig. 1. 
TELESCOPE MODE 
The spectra from the two modes were handled differently. For the 0.75-30 MeV 
telescope data, one selects only events whose event circle falls within a certain angle 
of the source position ( “angular resolution measure”, or ARM; Schiinfelder et al. 
1993), both reducing background and providing a nearly diagonal response (e.g., 
Kippen et al. 1998). For the telescope spectrum displayed in Fig. 2, a 10” ARM limit 
was used. The 32.768 s integration interval of (35229.452 s, 35262.22 s) was chosen 
b,ot h to cover all the significant gamma-ray emission and to allow an accurate live 
time calculation. The background data were taken 15 orbits prior to the burst (see 
Kippen et al. 1998). The data were fit to a simple power-law via a forward folding 
technique. The best-fit is 2.0 & 0.4(E/l MeV) -3*33*0*4 photons/cm2-s-MeV, giving 
a total fluence of (0.98 If O.5)x1O-4 ergs/cm2 (0.75-30 MeV). However, a turnover 
at or below 1 MeV is also consistent with the telescope data. 
171 
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132.177.229.79 On: Mon, 24 Nov 2014 14:31:02
FIGURE 2. The best-fit power-law 
spectrum is 2.0 III 0.4(E/l MeV)-3-33*o.4 
photons/cm”-s-MeV, giving a total flu- 
ence of (0.98 III 0.5)x10m4 ergs/cm” 
(0.75-30 MeV). However, a turnover at 
or below 1 MeV is also consistent with 
these telescope data. 
BURST MODE 
The single detector count spectra obtained in “spectroscopy mode” ‘were pro- 
cessed as follows: the background was estimated from a spectrum of 140 s duration 
starting 202 s prior to the BATSE trigger (at 35216 s). Eight high range detector 
(0.6-10.0 MeV) spectra (4 s integration time each) covering a 32 s time interval 
(35230.2 s, 35262.3 s), were background subtracted and summed. The spectral fit- 
ting of these time-averaged data was performed by convolving a trial photon spec- 
trum with the detector response matrix to produce a count spectrum. We used a x2 
statistic to compare the model spectrum with the data. We first assumed a single 
power law for the spectrum between 0.9 and 5.0 MeV. As shown in Fig. 1 there is 
no significant signal above 4 MeV. The best fit parameters for the single power law 
in this energy range are: normalization = (1.37 III 0.10) photons/[cm2-set-MeV] at 
1 MeV; and index = (-2.63~tO.16). The fluence (0.9-5 MeV, 32 set) is 7.86 x 10B5 
erg/cm2. We note a clear break (Briggs et al. 1999) in the spectrum below 0.9 MeV, 
where the spectrum becomes flatter. Also, preliminary analysis of the low range 
(0.3-1.5 MeV) spectroscopy data covering the same 32 s time interval indicates a 
single power law with index -2.0. 
Due to evidence for spectral evolution (Briggs et al. 1999) with a break in COMP- 
TEL’s energy range, one goal of this analysis was to produce time resolved spectra 
of this burst. Traditional spectral analysis techniques (like those applied above) 
use a parametric approach assuming a particular model and approximately account 
for the Poisson nature of the data using x2 type approximations or data transfor- 
mations. These techniques thus require high statistics and so don’t allow for fine 
time binning of our data. We have begun the implementation of a newly developed 
technique that addresses some of these shortcomings enabling the use of finer time 
resolution. Nowak and Kolaczyk (1999) have presented a method for deconvolv- 
ing spectra that is both non-parametric and explicitly handles Poisson data. We 
172 
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132.177.229.79 On: Mon, 24 Nov 2014 14:31:02
period 1 
I 
u U aa 
va 
s 
i,
e 
period 2 
% 
P 
iz 
%= 
:i”- I 
hl u lu 
period 3 
~ I 
u U IU 
period 4 
~ I
U U w 
period 5 
~ 
1 U w 
/\ 
period 6 
i I 
U U lu 
FIGURE 3. Time resolved Y - FV 
spectra of 6 consecutive 4 s interval- 
s of GRB 990123, showing qualitative 
evidence for spectral evolution. The 
deconvolution was performed using a 
non-parametric approach. 
Deconvolved Photon Energy MeV 
divided the low and high range burst data into seven 4 s time intervals. Using 
this non-parametric technique we deconvolved these spectra with the instrumen- 
t response. Though only preliminary, Fig. 3 shows qualitative spectral structure 
consistent with the previous analysis with a spectral break below 1 MeV. The time 
periods displayed don’t show any spectral evolution but they are consistent with 
the comparable times shown in Briggs et al. (1999). ' 
IMAGE MAP 
GRB 990123 was so bright in MeV gamma-rays that COMPTEL was able to 
image it in a 10 sigma detection. (The preliminary COMPTEL detection, broadcast 
about 11 minutes after the BATSE trigger, was 8.2 sigma.) Fig. 4 shows the 
combined COMPTEL and BATSE 1, 2, and 3 sigma location contours. The IPN, 
BeppoSAX X-ray, prompt Optical (ROTSE), fading optical, and radio counterpart 
locations are included on the map. 
CONCLUSIONS 
For GRB 990123, observed in the optical during the gamma-ray emission, one 
notes that the optical flux peaks after the brightest gamma-ray portion and is not 
a simple extrapolation of the MeV flux. Some have noted this may be a signature 
of self-absorption; while others suggest this shows the optical to have come from 
a separate component (Briggs et al. 1999). Traditional analysis techniques show 
consistent results for the burst and telescope data from COMPTEL. A preliminary 
non-parametric analysis is consistent with other methods and shows qualitative 
173 
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132.177.229.79 On: Mon, 24 Nov 2014 14:31:02
20 10 -10 -20 
(Systomatl6 umlx lnaludad - IPN, B!WC, optreal. &IO powhons ovdad) 
I tw1. cy)tem* 6mJ I - -ltcm* bd 
----w------- -------Bs--- ------------ ------------ 
. ( -Q7& -QfMJ ( 231.37. 44.761 bppS&t-yl 
01 -477. -Qcs] (231.s 4&m noTsc‘lmdud 
al MQ -1 tuaro. w1)Jolrp1f--n 
+I -Qn. -Q=l iu1-4 +cnlwwm-e 
FIGURE 4. The combined 
COMPTEL and BATSE Huntsville 
1, 2 and. 3 sigma location contours 
(systematic uncertainties included), 
along with the IPN timing arc (Hur- 
ley, Feroci et al GCN 222), and in- 
dications of the BeppoSAX X-ray, 
prompt optical (ROTSE), fading op- 
tical, and radio counterparts. 
evidence for a spectral break just under 1 MeV. Further investigation of this new 
technique will allow for quantitative results. 
ACKNOWLEDGMENTS 
The COMPTEL project is supported in part through NASA grant NAS 5-26646, 
DARA grant 50 QV 90968, and the Netherlands Organization for Scientific Re- 
search (NWO). AC is supported in part through the hospitality of Wellesley Col- 
lege and NASA grant NAG5-7984. MM is supported in part through NASA grant 
NAG5-7829. 
REFERENCES 
1. Akerlof, C. W., et al., GCN 205 (1999). 
2. Briggs, M. S., et al., ApJ 524, 82 (1999). 
3. Connors, A., et al., GCN 230, 237 (1999). 
4. Hurley, K., et al., GCN 222 (1999). 
5. Kippen, R. M., et al., A&. Space Res. 22 (7), 1097-1100 (1998). 
6. Loredo, T. J., in Statistical Challenges in Modern Astronomy, eds. G. J. Babu & 
E. D. Fiegelson, Springer-Verlag, New York, 1999. 
7. Nowak, R. D., Kolaczyk, E. D., IEEE Trans. Inform. Theory, Sept. (1999). 
8. Schiinfelder, V., et al., ApJS 86, 629 (1993). 
174 
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132.177.229.79 On: Mon, 24 Nov 2014 14:31:02


Spectra of a recent bright burst measured by CGRO-COMPTEL: GRB 990123

UNH Scholars' Repository

University of New HampshireUniversity of New Hampshire Scholars' RepositorySpace Science Center Institute for the Study of Earth, Oceans, and Space(EOS)2000Spectra of a recent bright burst measured byCGRO-COMPTEL: GRB 990123C A. YoungUniversity of New Hampshire - Main CampusA ConnorsEureka ScientificK BennettESTECW CollmarMax-Planck-Institut für extraterrestriche PhysikW HermsenSpace Research Organization of the Netherlands (SRON)See 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 CitationSpectra of a recent bright burst measured by CGRO-COMPTEL: GRB 990123 Young, C. A. and Connors, A. and Bennett, K. andCollmar, W. and Hermsen, W. and Kippen, R. M. and Kolaczyk, E. D. and Kuiper, L. and McConnell, M. and Miller, R. and Ryan, J. M.and Schönfelder, V. and Williams, O. R. and Winkler, C., AIP Conference Proceedings, 526, 170-174 (2000), DOI:http://dx.doi.org/10.1063/1.1361528AuthorsC A. Young, A Connors, K Bennett, W Collmar, W Hermsen, R M. Kippen, E Kolaczyk, L Kuiper, Mark L.McConnell, R S. Miller, James M. Ryan, V Schonfelder, O R. Williams, and C WinklerThis conference proceeding is available at University of New Hampshire Scholars' Repository: https://scholars.unh.edu/ssc/123Spectra of a recent bright burst measured by CGRO-COMPTEL: GRB 990123C. A. Young, A. Connors, K. Bennett, W. Collmar, W. Hermsen, R. M. Kippen, E. D. Kolaczyk, L. Kuiper, M.McConnell, R. Miller, J. M. Ryan, V. Schönfelder, O. R. Williams, and C. Winkler  Citation: AIP Conference Proceedings 526, 170 (2000); doi: 10.1063/1.1361528 View online: http://dx.doi.org/10.1063/1.1361528 View Table of Contents: http://scitation.aip.org/content/aip/proceeding/aipcp/526?ver=pdfcov Published by the AIP Publishing  Articles you may be interested in Power density spectra of gamma-ray bursts AIP Conf. Proc. 526, 205 (2000); 10.1063/1.1361535  X-ray excesses in GRB spectra AIP Conf. Proc. 526, 175 (2000); 10.1063/1.1361529  Study of the characteristics of GRB energy spectra AIP Conf. Proc. 526, 160 (2000); 10.1063/1.1361526  Gamma-ray burst spectroscopy AIP Conf. Proc. 526, 115 (2000); 10.1063/1.1361518  Testing the intrinsic randomness in the angular distributions of gamma-ray bursts AIP Conf. Proc. 526, 102 (2000); 10.1063/1.1361516   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 14:31:02Spectra of a Recent Bright Burst Measured by CGRO-COMPTEL:GRB 990123 C. A. Young’, A. Connors 2, K. Bennett3, W. Collmar4, W. Hermsen5, R. M. Kippen’, E. D. Kolaczyk7, L. Kuiper5, M. McConnell’, R. Miller’, J. M. Ryan’, V. Sch6nfelder4, 0. R. Williams3, and C. Winkler3 ‘Space Science Center, University of New Hamphsire, Durham NH, USA ‘Eureka Sci en tific 3 Astrophy sits, Division, ESTEC, NL-2200 AG Noordwijk, NL 4Max-Planc k-Institut fur Extraterrestrische Physik, D-85740 Garching, FRG 5 SRON- Utrecht, Sorbonnelaan 2, NL-3584 Utrecht, NL 6 CSPAAR, University of Alabama in Huntsville, Huntsville AL, USA ’ Departme nt of Mathematics and Statistics, Boston University, Boston MA, USA Abstract. CGRO-COMPTEL measures gamma-ray burst positions, time-histories and spectra in the 0.1-30 MeV energy range, in both imaging “telescope” and single detector “burst spectroscopy” mode. GRB 990123, one of the most recent bright bursts seen by COMPTEL, was caught in the optical while the gamma-ray emission was ongoing. The burst spectral shape can be characterized by a peak in v - FV just below 1 MeV and a power-law tail above (photon index N -2.4), and flattening below. There is also spectral evolution by downward movement of the peak and/or softening of the power laws. We present light-curves, time resolved spectra and an image map for this burst. INTRODUCTION GRB 990123 is the only gamma-ray burst to be simultaneously observed in opti- cal wavelengths. The Burst and Transient Source Experiment (BATSE) on CGRO triggered the Compton Telescope (COMPTEL) on CGRO at 35216.121 s UT on 23 January 1999 (BATSE trigger #7343). The burst was located at a zenith angle (w.r.t. CGRO and COMPTEL) pointing of 58.4”. The gamma-ray emission lasted for about 100 s with the > 1 MeV emission seen by COMPTEL most significant be- tween 18 s and 46 s after the BATSE trigger. The Robotic Optical Transient Search Experiment (ROTSE) detected optical emission during and after the gamma-ray emission. ROTSE made 6 measurements starting 22.2 s after the BATSE trigger. CP526, Gamma-Ray Bursts: Sh Huntsville Symposium, edited by R. M. Kippen, et al. 0 2000 American Institute of Physics l-56396-947-5/00/$17.00 170  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 14:31:0210” ARM -7-30 MeV FIGURE 1. GRB 990123 (BATSE #7343) in the COMPTEL low (0.2-1.6 MeV) and high (0.6-11 MeV) range burst mode, plus the 0.7-30 MeV tele- scope mode light-curves. The ROTSE m, are indicated with the telescope mode. 3.52x lo* 3,53x10* 3.54x lo* Time (seconds U-T.) COMPTEL detected the second and third peaks of GRB 990123 in both its imag- ing telescope (“double scatter”; 0.75-30 MeV) and non-imaging burst-spectroscopy (“burst mode”; 0.3-1.5 MeV and 0.6-10 MeV; see Schijnfelder et al. 1993) modes. Telescope position constraints were broadcast (via GCN/BACODINE) about 10 minutes after burst onset and preliminary light-curves were posted soon thereafter (Young et al. 1999; Connors et al. 1999). In the imaging telescope mode, COMPTEL provides detailed information on individual time-tagged photons with i ms time resolution. Because of the small effective area and limited telemetry of the telescope mode, however, only ~200 burst events were recorded. In spectroscopy mode the effective area was roughly two orders of magnitude greater, and the dead time was negligible. The COMPTEL light-curves are displayed in Fig. 1. TELESCOPE MODE The spectra from the two modes were handled differently. For the 0.75-30 MeV telescope data, one selects only events whose event circle falls within a certain angle of the source position ( “angular resolution measure”, or ARM; Schiinfelder et al. 1993), both reducing background and providing a nearly diagonal response (e.g., Kippen et al. 1998). For the telescope spectrum displayed in Fig. 2, a 10” ARM limit was used. The 32.768 s integration interval of (35229.452 s, 35262.22 s) was chosen b,ot h to cover all the significant gamma-ray emission and to allow an accurate live time calculation. The background data were taken 15 orbits prior to the burst (see Kippen et al. 1998). The data were fit to a simple power-law via a forward folding technique. The best-fit is 2.0 & 0.4(E/l MeV) -3*33*0*4 photons/cm2-s-MeV, giving a total fluence of (0.98 If O.5)x1O-4 ergs/cm2 (0.75-30 MeV). However, a turnover at or below 1 MeV is also consistent with the telescope data. 171  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 14:31:02FIGURE 2. The best-fit power-law spectrum is 2.0 III 0.4(E/l MeV)-3-33*o.4 photons/cm”-s-MeV, giving a total flu- ence of (0.98 III 0.5)x10m4 ergs/cm” (0.75-30 MeV). However, a turnover at or below 1 MeV is also consistent with these telescope data. BURST MODE The single detector count spectra obtained in “spectroscopy mode” ‘were pro- cessed as follows: the background was estimated from a spectrum of 140 s duration starting 202 s prior to the BATSE trigger (at 35216 s). Eight high range detector (0.6-10.0 MeV) spectra (4 s integration time each) covering a 32 s time interval (35230.2 s, 35262.3 s), were background subtracted and summed. The spectral fit- ting of these time-averaged data was performed by convolving a trial photon spec- trum with the detector response matrix to produce a count spectrum. We used a x2 statistic to compare the model spectrum with the data. We first assumed a single power law for the spectrum between 0.9 and 5.0 MeV. As shown in Fig. 1 there is no significant signal above 4 MeV. The best fit parameters for the single power law in this energy range are: normalization = (1.37 III 0.10) photons/[cm2-set-MeV] at 1 MeV; and index = (-2.63~tO.16). The fluence (0.9-5 MeV, 32 set) is 7.86 x 10B5 erg/cm2. We note a clear break (Briggs et al. 1999) in the spectrum below 0.9 MeV, where the spectrum becomes flatter. Also, preliminary analysis of the low range (0.3-1.5 MeV) spectroscopy data covering the same 32 s time interval indicates a single power law with index -2.0. Due to evidence for spectral evolution (Briggs et al. 1999) with a break in COMP- TEL’s energy range, one goal of this analysis was to produce time resolved spectra of this burst. Traditional spectral analysis techniques (like those applied above) use a parametric approach assuming a particular model and approximately account for the Poisson nature of the data using x2 type approximations or data transfor- mations. These techniques thus require high statistics and so don’t allow for fine time binning of our data. We have begun the implementation of a newly developed technique that addresses some of these shortcomings enabling the use of finer time resolution. Nowak and Kolaczyk (1999) have presented a method for deconvolv- ing spectra that is both non-parametric and explicitly handles Poisson data. We 172  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 14:31:02period 1 I u U aa va s i,e period 2 % P iz %= :i”- I hl u lu period 3 ~ I u U IU period 4 ~ IU U w period 5 ~ 1 U w /\ period 6 i I U U lu FIGURE 3. Time resolved Y - FV spectra of 6 consecutive 4 s interval- s of GRB 990123, showing qualitative evidence for spectral evolution. The deconvolution was performed using a non-parametric approach. Deconvolved Photon Energy MeV divided the low and high range burst data into seven 4 s time intervals. Using this non-parametric technique we deconvolved these spectra with the instrumen- t response. Though only preliminary, Fig. 3 shows qualitative spectral structure consistent with the previous analysis with a spectral break below 1 MeV. The time periods displayed don’t show any spectral evolution but they are consistent with the comparable times shown in Briggs et al. (1999). ' IMAGE MAP GRB 990123 was so bright in MeV gamma-rays that COMPTEL was able to image it in a 10 sigma detection. (The preliminary COMPTEL detection, broadcast about 11 minutes after the BATSE trigger, was 8.2 sigma.) Fig. 4 shows the combined COMPTEL and BATSE 1, 2, and 3 sigma location contours. The IPN, BeppoSAX X-ray, prompt Optical (ROTSE), fading optical, and radio counterpart locations are included on the map. CONCLUSIONS For GRB 990123, observed in the optical during the gamma-ray emission, one notes that the optical flux peaks after the brightest gamma-ray portion and is not a simple extrapolation of the MeV flux. Some have noted this may be a signature of self-absorption; while others suggest this shows the optical to have come from a separate component (Briggs et al. 1999). Traditional analysis techniques show consistent results for the burst and telescope data from COMPTEL. A preliminary non-parametric analysis is consistent with other methods and shows qualitative 173  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 14:31:0220 10 -10 -20 (Systomatl6 umlx lnaludad - IPN, B!WC, optreal. &IO powhons ovdad) I tw1. cy)tem* 6mJ I - -ltcm* bd ----w------- -------Bs--- ------------ ------------ . ( -Q7& -QfMJ ( 231.37. 44.761 bppS&t-yl 01 -477. -Qcs] (231.s 4&m noTsc‘lmdud al MQ -1 tuaro. w1)Jolrp1f--n +I -Qn. -Q=l iu1-4 +cnlwwm-e FIGURE 4. The combined COMPTEL and BATSE Huntsville 1, 2 and. 3 sigma location contours (systematic uncertainties included), along with the IPN timing arc (Hur- ley, Feroci et al GCN 222), and in- dications of the BeppoSAX X-ray, prompt optical (ROTSE), fading op- tical, and radio counterparts. evidence for a spectral break just under 1 MeV. Further investigation of this new technique will allow for quantitative results. ACKNOWLEDGMENTS The COMPTEL project is supported in part through NASA grant NAS 5-26646, DARA grant 50 QV 90968, and the Netherlands Organization for Scientific Re- search (NWO). AC is supported in part through the hospitality of Wellesley Col- lege and NASA grant NAG5-7984. MM is supported in part through NASA grant NAG5-7829. REFERENCES 1. Akerlof, C. W., et al., GCN 205 (1999). 2. Briggs, M. S., et al., ApJ 524, 82 (1999). 3. Connors, A., et al., GCN 230, 237 (1999). 4. Hurley, K., et al., GCN 222 (1999). 5. Kippen, R. M., et al., A&. Space Res. 22 (7), 1097-1100 (1998). 6. Loredo, T. J., in Statistical Challenges in Modern Astronomy, eds. G. J. Babu & E. D. Fiegelson, Springer-Verlag, New York, 1999. 7. Nowak, R. D., Kolaczyk, E. D., IEEE Trans. Inform. Theory, Sept. (1999). 8. Schiinfelder, V., et al., ApJS 86, 629 (1993). 174  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 14:31:02

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Spectra of a recent bright burst measured by CGRO-COMPTEL: GRB 990123

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