1. GRB 090323 and GRB 090328 Two long high-energy GRBs detected by Fermi
Elisabetta Bissaldi
on behalf of the Fermi GBM and LAT collaborations
Max-Planck-Institut für extraterrestrische Physik (MPE - Garching) • Member of the Fermi GBM Team

2. Outline Overview of the two bursts: Main infos GBM detection
GRB
GRB
Open issues and conclusions
Main infos
GBM detection
ARR and LAT detection
Background issues
Time interval selection
Spectral analysis
Time-integrated
Time-resolved
LAT long-lived emission

3. GRB 090323 PRELIMINARY NaI 9 and NaI 11 50-300 keV Main infos:
GBM Trigger time: 00:02:42.63 UT on March 23, 2009
Triggered detectors: NaI 9 and NaI 11
Also seed in detectors NaI 6, 7, 8 and 10
Detected in BGO 1 up to 1.5 MeV
Autonomous repointing maneuver sent from GBM to LAT
LAT detection gives an improved localization
Follow-up by Swift in the X-ray and optical
Follow up by ground-based telescopes
Redshift measurement  z = 3.6 (Chornock et al., 2009)

4. GBM detectors
First quick-look data analysis of the NaI detectors ( keV band)
Temporal resolution:
Blue line: 1 s resolution
70 s, covering ~8 s pre-burst and ~60 s post-burst.
Black line: 8 s resolution n0 n1 n2 n3 n4 n5 n6 n7 n8 n9 na nb

5. Autonomous Repoint Request (ARR)
Actual orbit due to ARR
Planned orbit
The high energy emission detected by the LAT was made possible by the ARR sent from GBM
Otherwise GRB would have been out of FOV!
GRB
LAT 6 hour automated science processing 5

6. GBM orientation evolution
NaI 6
In GBM, the effect of the ARR is particularly visible after T0+60 s, where the detectors orientation changes with incredible rapidity, making the spectral analysis a delicate issue
Actual orbit
NaI 7
angle (deg)
NaI 9
ARR
NaI 11
Time since T0 (sec)

7. NaI background subtraction
8 – 900 keV
8 – 900 keV

8. Time interval selection
8 – 900 keV
For each time interval, because of the slewing due to the ARR, we need to select the best NaI detector combination!
T90 ~140 s
Fluence = (1.23 ± 0.02)E-04 erg/cm2
1-sec Peak Flux = 12.3 ± 0.4 ph/s/cm2

9. Spectral results interval c
8 – 900 keV
GBM only Band fit
Energy (keV)
Time resolved analysis
Epeak = keV alpha = ± beta =

10. Band parameter evolution
8 – 900 keV
Epeak
alpha
beta

11. GRB 090323 LAT afterglow LAT detections During GBM time: ~25 events
PRELIMINARY
PRELIMINARY
Binsize: 60 s
15 deg ROI
blue line: GRB within 98deg of Earth limb
black line: (SAA)
50MeV-300GeV
transient class
binsize: 50 s
LAT detections
During GBM time: ~25 events
Next 10 minutes: ~60 events
Extended emission (up to 1.7 ks): ~80 events

12. GRB 090328 NaI 6 and NaI 7 50-300 keV PRELIMINARY Main facts:
GBM Trigger time: 09:36:46.51 UT on March 28, 2009
Triggered detectors: NaI 6 and NaI 7
ARR
LAT detection gives an improved localization
Follow-up by Swift in the X-ray and optical
Follow-up by ground-based telescopes
Redshift measurement: z = (Cenko et al., 2009)
Radio afterglow detected with the VLA at 8.46 GHz (Frail et al. 2009)

13. Time interval selection
8 – 900 keV
T90~60s
Fluence = (5.2 ± 0.7)E-05 erg/cm2
1-sec Peak Flux = 22.6 ± 0.8 ph/s/cm2

14. Interval c GBM only Band fit 101 100 10-1 10-2 10-3 10-4 10-5
Epeak = 479 ± 58 keV alpha = beta =
Energy (keV)

15. Band parameter evolution

16. GRB 090328 LAT afterglow LAT high-energy detection
PRELIMINARY
PRELIMINARY
50MeV-300GeV
transient class
binsize: 50 s
Binsize: 60 s
15 deg ROI
blue line: GRB within 98deg of Earth limb
black line: (SAA)
LAT high-energy detection
During GBM time: ~18 events
Next 1.5 ks: ~100 events
Extended emission (6.8 ks): ~60 events

17. Conclusions Fermi analysis of two long bursts ~150 s and ~60 s in GBM
Detected to much longer time in the LAT
ARR enabled the detections of the extended emission
…Papers coming soon!

18. Backup slides

19. BGO detector BGO 1 0.15-0.40 MeV 0.40-0.85 MeV 0.85-1.5 MeV 1.5-3 MeV

20. 090323 GBM+LAT Band fit Epeak = 482 ±18 keV Alpha = -0.74 ± 0.02
Beta =

21. GBM+LAT Band+PL fit Epeak = 508 ± 33 alpha = -1.086 ± 0.020
beta = ± 0.15
G = ± 0.5

22. GBM+LAT Band+PL nFn GBM+LAT Band fit Epeak = 488 ± 31
alpha = ± 0.021
beta = ± 0.0
Energy (keV)
Energy (keV)

23. Fluence interval: 8-1000 keV
GBM T90 calculation
Fluence interval: keV
T50 ~ 56 s
T90 ~ 135 s
Fluence = (1.23 ± 0.02)E-04 erg/cm2
1-sec Peak Flux = 12.3 ± 0.4 ph/s/cm2
Time since T0 (sec)

24. Fluence interval: 8-1000 keV
GBM T90 calculation
Fluence interval: keV
T50 ~ 19 s
T90 ~ 61 s
Fluence = (5.2 ± 0.7)E-05 erg/cm2
1-sec Peak Flux = 22.6 ± 0.8 ph/s/cm2
Time since T0 (sec)

25. NaI trigger detectors combined
7-10 keV
10-22 keV
22-44 keV
44-95 keV
keV
keV
keV
keV
NaI 9 + NaI 11

26. BGO detector BGO 1 0.15-0.40 MeV 0.40-0.85 MeV 0.85-1.5 MeV 1.5-3 MeV

27. GBM detectors NaI 6 + NaI 7 BGO 1 7-10 keV 10-22 keV 22-44 keV
MeV
MeV
MeV
1.5-3 MeV
MeV
10-20 MeV
20-30 MeV
MeV
NaI 6 + NaI 7
BGO 1