Gamma-ray Burst 081024B

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN NOTICE

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Fri 24 Oct 08 21:23:03 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      45
TRIGGER_NUM:     246576161
GRB_RA:          317.883d {+21h 11m 32s} (J2000),
                 317.984d {+21h 11m 56s} (current),
                 317.313d {+21h 09m 15s} (1950)
GRB_DEC:         +20.683d {+20d 40' 60"} (J2000),
                 +20.720d {+20d 43' 11"} (current),
                 +20.478d {+20d 28' 40"} (1950)
GRB_ERROR:       19.97 [deg radius, statistical only]
GRB_INTEN:       411 [cnts/sec]
DATA_SIGNIF:     7.30 [sigma]
INTEG_TIME:      0.128 [sec]
GRB_DATE:        14763 TJD;   298 DOY;   08/10/24
GRB_TIME:        76960.86 SOD {21:22:40.86} UT
GRB_PHI:         140.00 [deg]
GRB_THETA:        15.00 [deg]
HARD_RATIO:      0.22
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      78%  GRB
2nd_MOST_LIKELY:  16%  Cyg X-1
DETECTORS:       1,0,0, 0,0,0, 1,1,0, 1,0,0, 0,0,
SUN_POSTN:       209.67d {+13h 58m 41s}  -12.11d {-12d 06' 42"}
SUN_DIST:        111.20 [deg]   Sun_angle= -7.2 [hr] (East of Sun)
MOON_POSTN:      164.44d {+10h 57m 46s}   +3.99d {+03d 59' 20"}
MOON_DIST:       144.17 [deg]
MOON_ILLUM:      16 [%]
GAL_COORDS:       69.06,-18.47 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      327.91, 35.00 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.

GCN NOTICE

TITLE:          GCN/INTEGRAL NOTICE
NOTICE_DATE:    Fri 24 Oct 08 21:23:25 UT
NOTICE_TYPE:    INTEGRAL SPI ACS Trigger
TRIGGER_NUM:    5368,   Sub_Num: 0
GRB_INTEN:      9.09 [sigma]
GRB_TIME:       76959.26 SOD {21:22:39.26} UT
GRB_DATE:       14763 TJD;   298 DOY;   08/10/24
COMMENTS:       INTEGRAL SPI_ACS GRB Trigger.
COMMENTS:
ftp://isdcarc.unige.ch/arc/FTP/ibas/spiacs/2008-10-24T21-22-39.1375-27467-00007-0.lc

GCN Circular #8407
Nicola Omodei (INFN Pisa), on behalf of the Fermi-LAT Collaboration
The Fermi LAT telescope detected an increased count rate at 2008/10/24 (21:22:41), associated with a GRB detected also by the Fermi GBM (Trigger number:246576161). The location of the GRB reported by Fermi LAT data ground analysis is: Ra=322.9, Dec=21.204 which corresponds to
```
Ra (J2000) = 21:31:36.00
Dec (J200) = 21:12:14.4
```
within a statistical uncertainty of 0.16 degrees (68% containment radius). The emission from this point source was seen up to 3 GeV, in the first 5 seconds after the trigger.
The Fermi LAT point of contact for this burst is Nicola Omodei (nicola.omodei@pi.infn.it).
The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden. This message can be cited.
GCN Circular #8408
Valerie Connaughton and Michael Briggs (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 21:22:40.86 UT on 24 October 2008, the Fermi Gammay-Ray Burst Monitor (GBM) triggered on GRB 081024B (trigger 246576161 / 081024.891). The calculated location is consistent with the Fermi LAT-detected GRB reported by N. Omodei in GCN Circular 8407.
This GRB was about 800 ms long with 2 main peaks. The first peak lasted 200 ms and its spectrum is best fit using a power-law index with an exponential cutoff. The power-law index is -0.70 =B1 0.13, and the cutoff energy, parameterized as EPeak, is 1583 =B1 520 keV. The seond peak lasted 600 ms and is best fit by a power-law spectrum with an index of -1.28 =B1 0.04.
The fluence between 50 and 300 keV of this short burst is 3.4 =B1 0.1 x 10-7 erg/cm2, with a peak flux measured over a 64 ms timescale of of 4.2 =B1 0.2 photons/cm2/sec. Between 15 and 150 keV the 64 ms peak flux is 7.4 =B1 0.4 photons/cm2/sec.
The analysis results presented above are preliminary and further analysis is being performed; the final results will be published in the GBM GRB Catalog."
GCN Circular #8410
C. Guidorzi, R. Margutti, J. Mao (INAF-OAB) report on behalf of the Swift-XRT team:
Swift began observing the field of the Fermi-LAT GRB 081024B (Omodei et al., GCN Circ. 8407) 70.3 ks after the trigger. In 9.9 ks of Photon Counting mode data, we detect three uncatalogued sources within the Fermi-LAT error circle at the following positions:
```
Source 1:
RA(J2000):   21 31 47.85
Dec(J2000): +21 08 33.7
with an uncertainty of 6.6 arcsec.

Source 2:
RA(J2000):   21 31 37.22
Dec(J2000): +21 16 32.1
with an uncertainty of 5.4 arcsec.

Source 3:
RA(J2000):   21 31 29.26
Dec(J2000): +21 16 43.3
with an uncertainty of 5.5 arcsec.
```
Uncertainty radii are given at 90% containment. All of the sources have count rates of ~1.3e-3 counts/s during this observation.
It is not possible to determine whether these sources are fading given the current statistics.
This circular is an official product of the Swift-XRT team.
GCN Circular #8413
P. Schady (MSSL/UCL) and C. Guidorzi (INAF-OAB) report on behalf of the Swift UVOT team.
The Swift UltraViolet/Optical Telescope (UVOT) began observations of Fermi-LAT GRB 081024B (Omodei et al., GCN Circ. 8407) 70.3 ks after the trigger.
Source 1 and Source 2 in GCN Circ. 8410 (Guidorzi et al.) are outside the UVOT field of view, and no new source is detected at the position of Source 3 (GCN Circ 8410; Guidorzi et al.) down to the following 3 sigma upper limits:
```
Filter   Tstart(dys)  Exp(s)  3-sigma UL
v         1.215        885     > 20.33
b         0.824        864     > 21.26
u         0.814        2641    > 21.42
uvw1      0.894        1531    > 21.07
uvm2      0.883        2548    > 21.36
uvw2      1.163        1201    > 21.07
```
The values quoted above are on the UVOT Photometric System (Poole et al, 2008, MNRAS 383,627). They are not corrected for the expected Galactic extinction corresponding to a reddening of E(B-V)=0.07 mag in the direction of the burst (Schlegel et al. 1998).
GCN Circular #8416
C. Guidorzi and R. Margutti (INAF-OAB) report on behalf of the Swift-XRT team:
Swift re-observed the field of the Fermi-LAT GRB 081024B (Omodei et al., GCN Circ. 8407) 127 ks after the burst. From 13.5 ks of Photon Counting mode data, we found that sources 1 and 3 mentioned in our previous report (Guidorzi et al. GCN Circ. 8410) are still detected with a count rate compatible with being constant between the two observations. Although source 2 is no longer detected, we estimate that the fading is not statistically significant yet. Further data will allow us to determine the possible fading.
This circular is an official product of the Swift-XRT team.
GCN Circular #8417
S. B. Cenko (UC Berkeley) and M. M. Kasliwal (Caltech) report on behalf of a larger collaboration:
We have imaged the error circle of the short duration GRB081024B (Omodei, GCN 8407; Connaughton and Briggs, GCN 8408) with the Large Format Camera mounted on the Palomar 200 inch Hale telescope. Images were taken in the Sloan r' and i' filters at a mean epoch of approximately Oct 26.1 (~ 30 hours after the burst).
We detect several sources inside or near the potential X-ray afterglow (XRT Source 2; Guidorzi, Margutti, and Mao, GCN 8410; Guidorzi and Margutti, GCN 8416). Calibrating with respect to several nearby objects in the USNO-B1 catalog, we note the following positions and magnitudes for the four nearest sources:
```
O1 -  RA: 21:31:36.95   Dec: +21:16:35.4 (J2000.0)
      R = 20.6 mag

O2 -  RA: 21:31:37.63   Dec: +21:16:33.0 (J2000.0)
      R = 22.6 mag

O3 -  RA: 21:31:37.42   Dec: +21:16:36.4 (J2000.0)
      R = 23.4 mag

O4 -  RA: 21:31:37.32   Dec: +21:16:25.1 (J2000.0)
      R = 22.6 mag
```
We estimate the astrometric precision for each source is 0.5" in each coordinate. The photometric precision for the above reported magnitudes is likely large (~ 0.3 mag) due to both zeropoint uncertainty and bandpass differences. The limiting magnitude of our co-added image is approximately R > 23.5 mag.
We note that source O1 appears to be present in the DSS plates of this field. Additionally, source 02 is clearly extended. None of the objects show evidence for variability over the (limited) duration of our observations.
An image of the field is posted at:
http://www.srl.caltech.edu/~cenko/public/grb081024b.jpg
Further observations to search for variability are encouraged.
GCN Circular #8422
We observed the LAT error circle of the Fermi-LAT (Omodei, GCN 8407) and Fermi-GBM (Connaughton and Briggs, GCN 8408) detected short/hard GRB 081024B with the TLS Tautenburg 1.34m Schmidt telescope in full frame mode (field of view 42' x 42'), covering the complete error circle to about 2 sigma confidence level. We obtained 24 x 300 sec images in the Rc band under good observing conditions, at mid-time 0.88644 days after the GRB.
We report the following analysis of the three XRT sources (Guidorzi et al., GCN 8410), of which source 1 and 3 seem to remain constant (Guidorzi & Margutti, GCN 8416), whereas source 2 may be fading and thus represent the X-ray afterglow of GRB 081024B:
Source 1: We find a relatively bright stellar object which is clearly visible in the DSS.
Source 3: We find a moderately faint stellar object which is under the DSS limit.
Source 2: We detect all four objects reported by Cenko & Kasliwal (GCN 8417). Source O3 is close to the detection limit, implying that it is ~ Rc > 23.5, similar to that of the P200 image.
We use several nearby, isolated USNOB1.0 stars to determine the image zero point. We find that the zero point error is 0.04 magnitudes from four stars, better than the pessimistic estimation (0.3 magnitudes) of Cenko & Kasliwal (which also includes bandpass differences). Photometry was done using a 7 pixel aperature (matched to the typical seeing) on sources O1 and O4 (which are reasonably isolated). For sources O2 (close to a bright star) and O3 (close to O2), we used a 3 pixel aperature and used two bright, isolated stars to compute the aperature correction (a factor of 2).
We derive the following magnitudes for the four sources (in brackets, we give the magnitudes of Cenko & Kasliwal):
O1 (bright, stellar): Rc = 20.55 +/- 0.04 (20.6)
O2 (extended in P200): Rc = 22.25 +/- 0.10 (22.6)
O3 (faint): Rc = 23.48 +/- 0.34 (23.4)
O4 (faint, stellar): Rc = 22.53 +/- 0.16 (22.6)
All sources except O2 agree well with the P200 magnitudes obtained 0.36 days later, to within +/- 0.08 magnitudes despite the multiple differences (comparison stars, bandpass, etc.). Only source O2 is brighter, by ~ 0.35 magnitudes. While the source is close to a bright (~ magnitude of O1) star, which may contaminate the photometry even in the reduced aperature, O2 is clearly brighter in our image than O4, whereas they have identical magnitudes (as reported by Cenko & Kasliwal) in the P200 images. Since Cenko & Kasliwal report this source to be extended, this may indicate that we are seeing the optical afterglow as well as the underlying host galaxy of GRB 081024B. Still, caution is advised.
This GRB is of special interest. It is the first Fermi-detected short/hard GRB reported so far, and possibly the first one with a detection at >> 1 GeV (the very bright GRB 930131, the "Superbowl Burst", was only detected to ~ 1 GeV by CGRO EGRET, Sommer et al. 1994, ApJL, 422, L63), and, similar to GRB 930131 and also the AGILE-Grid-detected long GRB 080514B (Guiliani et al. 2008, A&A, in press), emission is seen for several seconds longer than at lower energies. Therefore, additional deep follow-up and spectroscopy of extended source O2 is highly encouraged. Further observations at TLS are planned (to perform image subtraction) in case we ever see the stars again.
This message may be cited.
GCN Circular #8423
D. A. Kann, S. Schulze and C. Hoegner (TLS Tautenburg) report:
We observed the LAT error circle of the Fermi-LAT (Omodei, GCN 8407) and Fermi-GBM (Connaughton and Briggs, GCN 8408) detected short/hard GRB 081024B with the TLS Tautenburg 1.34m Schmidt telescope in full frame mode (field of view 42' x 42'), covering the complete error circle to about 2 sigma confidence level. We obtained 24 x 300 sec images in the Rc band under good observing conditions, at mid-time 0.88644 days after the GRB.
We report the following analysis of the three XRT sources (Guidorzi et al., GCN 8410), of which source 1 and 3 seem to remain constant (Guidorzi & Margutti, GCN 8416), whereas source 2 may be fading and thus represent the X-ray afterglow of GRB 081024B:
Source 1: We find a relatively bright stellar object which is clearly visible in the DSS.
Source 3: We find a moderately faint stellar object which is under the DSS limit.
Source 2: We detect all four objects reported by Cenko & Kasliwal (GCN 8417). Source O3 is close to the detection limit, implying that it is ~ Rc > 23.5, similar to that of the P200 image.
We use several nearby, isolated USNOB1.0 stars to determine the image zero point. We find that the zero point error is 0.04 magnitudes from four stars, better than the pessimistic estimation (0.3 magnitudes) of Cenko & Kasliwal (which also includes bandpass differences). Photometry was done using a 7 pixel aperature (matched to the typical seeing) on sources O1 and O4 (which are reasonably isolated). For sources O2 (close to a bright star) and O3 (close to O2), we used a 3 pixel aperature and used two bright, isolated stars to compute the aperature correction (a factor of 2).
We derive the following magnitudes for the four sources (in brackets, we give the magnitudes of Cenko & Kasliwal):
O1 (bright, stellar): Rc = 20.55 +/- 0.04 (20.6)
O2 (extended in P200): Rc = 22.25 +/- 0.10 (22.6)
O3 (faint): Rc = 23.48 +/- 0.34 (23.4)
O4 (faint, stellar): Rc = 22.53 +/- 0.16 (22.6)
All sources except O2 agree well with the P200 magnitudes obtained 0.36 days later, to within +/- 0.08 magnitudes despite the multiple differences (comparison stars, bandpass, etc.). Only source O2 is brighter, by ~ 0.35 magnitudes. While the source is close to a bright (~ magnitude of O1) star, which may contaminate the photometry even in the reduced aperature, O2 is clearly brighter in our image than O4, whereas they have identical magnitudes (as reported by Cenko & Kasliwal) in the P200 images. Since Cenko & Kasliwal report this source to be extended, this may indicate that we are seeing the optical afterglow as well as the underlying host galaxy of GRB 081024B. Still, caution is advised.
This GRB is of special interest. It is the first Fermi-detected short/hard GRB reported so far, and possibly the first one with a detection at >> 1 GeV (the very bright GRB 930131, the "Superbowl Burst", was only detected to ~ 1 GeV by CGRO EGRET, Sommer et al. 1994, ApJL, 422, L63), and, similar to GRB 930131 and also the AGILE-Grid-detected long GRB 080514B (Guiliani et al. 2008, A&A, in press), emission is seen for several seconds longer than at lower energies. Therefore, additional deep follow-up and spectroscopy of extended source O2 is highly encouraged. Further observations at TLS are planned (to perform image subtraction) in case we ever see the stars again.
We are indebted to Antonio de Ugarte Postigo for pointing out the suspicious lack of authors in the first version.
This message may be cited.
GCN Circular #8444
Y. Hanabata, T. Uehara, T. Takahashi, Y. Fukazawa, C. Kira (Hiroshima U.), T. Enoto, K. Nakazawa, K. Makishima (Univ. of Tokyo), S. Sugita, K. Yamaoka (Aoyama Gakuin U.), M. Ohno, M. Kokubun, M. Suzuki, T. Takahashi (ISAS/JAXA), Y.E. Nakagawa, T. Tamagawa (RIKEN), M. Tashiro, Y. Terada, Y. Urata, A. Endo, K. Onda, N. Kodaka, K. Morigami, T. Sugasahara, W. Iwakiri (Saitama U.), E. Sonoda, M. Yamauchi, H. Tanaka, R. Hara, N. Ohmori (Univ. of Miyazaki), S. Hong (Nihon U.), on behalf of the Suzaku WAM team, report:
The short/hard GRB081024B (Fermi-LAT detected ; Omodei GCN8407, Fermi-GBM triggered ; Connaughton and Briggs, GCN 8408) triggered the Suzaku Wide-band All-sky Monitor (WAM) which covers an energy range of 50 keV - 5 MeV at 21:22:40.526 UT (=T0).
The observed light curve shows double-peaked structure with a duration (T90) of about 0.4 second. The fluence in 100 - 1000 keV was 2.7(+0.7, -1.0) X 10^-7 erg/cm^2. The peak flux within 0.5 second was 1.1(+0.3, -0.5) photons/cm^2/s in the same energy range.
Preliminary result shows that even at least 2 MeV photons have been detected, and the time-averaged spectrum from T0 to T0+0.5s is well fitted by a single power-law with a photon index of 1.24(+0.25, -0.19) (chi^2/d.o.f = 12.3/14). All the quoted errors are at statistical 90% confidence level, in which the systematic uncertainties are not included.
The light curves for this burst are availabel at: http://www.astro.isas.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/trig/grb_table.html
GCN Circular #8451
P. Chandra (RMC), S. B. Cenko (Berkeley), D. A. Frail (NRAO) and F. Harrison (Caltech) report on behalf of a larger GRB Collaboration:
"We used the Very Large Array to observe the Fermi-LAT detected short hard burst GRB 081024B (GCN 8407) at a frequency of 8.46 GHz on 2008 Oct. 28.99 UT. The VLA field of view was centered at RA: 21:31:37.63 Dec: +21:16:33.0 (J2000.0) for the observation. We don't see any radio source in the VLA field of view. The map rms is 38 uJy.
The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc."
GCN Circular #8454
C. Guidorzi, J. Mao, R. Margutti (INAF-OAB) on behalf of the Swift-XRT team report:
Swift-XRT re-observed the field of the Fermi-LAT and Fermi-GBM GRB 081024B (Omodei et al. GCN Circ. 8407; Connaughton et al GCN Circ. 8408) from 2.75 to 6.1 days after the burst with a net exposure of 13 ks. We combined this with our previous observation (Guidorzi et al. GCN Circ. 8416) for a resulting net exposure of 27 ks. Source 2 identified in our earliest report (Guidorzi et al. GCN Circ. 8410) as the only possibly fading source within the LAT error circle (GCN 8416) and possibly associated with the variable optical object O2 (Cenko & Kasliwal GCN Circ. 8417; Kann et al. GCN Circ. 8423), was finally detected with an average rate of (7.4 +- 2.2)e-4 counts/s from 1.5 to 6.1 days. From the comparison with the first observation (GCN 8410), in which the count rate was estimated to be (1.58 +- 0.54)e-3 counts/s, we estimate the probability of a constant rate source of 12%. We also derived an upper limit to the possible power-law decay index of alpha<0.8 from ~1 to ~5e5 s (90% confidence). Therefore, at the moment we cannot confirm source 2 as the X-ray afterglow candidate.
Further Swift-XRT observations are planned in order to clarify this issue.
This circular is an official product of the Swift-XRT team.
GCN Circular #8456
T. Fatkhullin, A. Moskvitin (SAO-RAS Niznij Arkhyz), A.J. Castro-Tirado (IAA-CSIC Granada), on behalf of a larger collaboration, report:
"We observed the field of the short duration GRB081024B (Omodei, GCNC 8407; Connaughton and Briggs, GCNC 8408) in the Rc-band with the 6-m telescope of the SAO RAS in Caucasus. In total two runs were performed starting on 28 Oct 2008 (20:16 UT) and 29 Oct. 2008 (15:22 UT). Integration times were 24 and 14 min respectively. Using SExtractor software (Bertin & Arnouts 1996, A&AS 117, 393) and source "O1" (Cenko & Kasliwal GCNC 8417; Kann et al. GCNC 8423) as a reference star, we estimated the following magnitudes of the sources within the XRT error box:
```
         28 Oct.                     29 Oct.
O1: Rc = 20.55 +/- 0.04      Rc = 20.55 +/- 0.04    (from GCN 8423)
O2: Rc = 22.62 +/- 0.06      Rc = 22.65 +/- 0.06    (within 3.6 arcsec aperture)
O3: Rc = 23.19 +/- 0.15      Rc = 23.18 +/- 0.10    (within 3.6 arcsec aperture)
O4: Rc = 22.46 +/- 0.06      Rc = 22.53 +/- 0.06    (within 3.6 arcsec aperture)
```
The second epoch image (29 Oct.) shows that extended object "O2" as noted from Palomar 200 inch Hale telescope observations (Cenko & Kasliwal GCNC 8417) is most likely superposition of two objects. These objects seem also to be extended in our image. we conclude that all four sources showed no variability during the time interval covered by our observations (including source "O2", whose magnitude is comparable to the one reported by Cenko & Kasliwal). As it is already mentioned by Guidorzi et al. (GCNC 8454) by means of Swift/XRT observations, we can not confirm that the source "O2" is fading in brightness, i.e. its relation to GRB081024B. This second epoch image can be retrieved via anonymous FTP: ftp://ftp.sao.ru/pub/grb/GRB081024B/GRB081024B_BTA_2nd_epoch.jpg"
This message can be cited.
GCN Circular #8513
C. Guidorzi (INAF-OAB) on behalf of the Swift-XRT team reports:
Swift-XRT re-observed the field of the Fermi-LAT and Fermi-GBM GRB 081024B (Omodei et al. GCN Circ. 8407; Connaughton et al GCN Circ. 8408) from 13.1 to 15.1 days after the burst with a net exposure of 9.8 ks.
We compared this with our previous observations (Guidorzi et al. GCN Circ. 8410, 8416, 8454). We still detect source 2, identified in our first observation (Guidorzi et al. GCN Circ. 8410), with a count rate of (1.1 +- 0.4)e-3 count/s, which is compatible with a constant rate source throughout the entire XRT observations. We also derived an upper limit to the possible power-law decay index of alpha<0.4 from ~1e5 to ~1.3e6 s (90% confidence). We conclude that source 2, initially proposed as possibly associated with GRB 081024B (Guidorzi et al. GCN Circ. 8416, 8454), is not the corresponding X-ray afterglow.
This circular is an official product of the Swift-XRT team.
GCN Report 178.1
GCN_Report 178.1 has been posted: http://gcn.gsfc.nasa.gov/reports/report_178_1.pdf by C. Guidorzi at INAF-OAB titled: "Final Swift report on Fermi-GBM GRB 081024B"
1002.0228 from 2 Feb 10
Masanori Ohno et al.: Fermi-LAT observations of GRBs with weak LAT emission
We present the analysis results of three Gamma-Ray Bursts (GRBs) detected by the Gamma-ray Burst Monitor (GBM) and the Large Area Telescope (LAT) onboard Fermi: the two long GRB 080825C and GRB 090217, and the first short burst with GeV photons GRB 081024B. The emission from GRB 081024B observed by the LAT above 100 MeV is delayed with respect to the GBM trigger, and significantly extends after the low-energy episode. Some hints for spectral hardening was observed in this burst as well as in GRB 080825C, possibly related to a separate and harder component showing up at late times. Conversely, GRB 090217 does not exhibit any noticeable feature. Together with the other bright LAT detected bursts (e.g. GRB 080916C and GRB 090510), these observations help to classify the GRB properties and give new insight on the acceleration mechanisms responsible for their emission at the highest energies.
1002.3205 from 18 Feb 10
Fermi LAT Collaboration et al.: Fermi detection of delayed GeV emission from the short GRB 081024B
We report on the detailed analysis of the high-energy extended emission from the short Gamma-Ray Burst (GRB) 081024B, detected by the Fermi Gamma-ray Space Telescope. Historically, this represents the first clear detection of temporal extended emission from a short GRB. The light curve observed by the Fermi Gamma-ray Burst Monitor lasts approximately 0.8 seconds whereas the emission in the Fermi Large Area Telescope lasts for about 3 seconds. Evidence of longer lasting high-energy emission associated with long bursts has been already reported by previous experiments. Our observations, together with the earlier reported study of the bright short GRB 090510, indicate similarities in the high-energy emission of short and long GRBs and open the path to new interpretations.

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Jochen Greiner, last update: 02-Feb-2010 [Disclaimer]