GRB 230805B

S. B. Cenko (GSFC), A. D'Ai (INAF-IASFPA),
V. D'Elia (SSDC & INAF-OAR), J.D. Gropp (PSU), J. A. Kennea (PSU),
H. A. Krimm (NSF), N. P. M. Kuin (UCL-MSSL), S. Laha (GSFC/UMBC) and
M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 11:23:51 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 230805B (trigger=1183217).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 207.747, +31.185 which is 
   RA(J2000) = 13h 50m 59s
   Dec(J2000) = +31d 11' 05"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex
structure with a duration of about 60 sec.  The peak count rate
was ~1300 counts/sec (15-350 keV), at ~5 sec after the trigger. 

The XRT began observing the field at 11:27:03.3 UT, 192.3 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 207.74281,
31.19102 which is equivalent to:
   RA(J2000)  = 13h 50m 58.28s
   Dec(J2000) = +31d 11' 27.7"
with an uncertainty of 1.9 arcseconds (radius, 90% containment). This
location is 25 arcseconds from the BAT onboard position, within the BAT
error circle. This position may be improved as more data are received;
the latest position is available at https://www.swift.ac.uk/sper. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (1.41 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.6
(+2.86/-2.45) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 858 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of
the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. 
The 8'x8' region for the list of sources generated on-board covers 100% of the
XRT error circle. The list of sources is typically complete to about 18 mag. No
correction has been made for the expected extinction corresponding to E(B-V) of
0.014. 

Burst Advocate for this burst is S. B. Cenko (brad.cenko AT nasa.gov). 
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/)

V. Lipunov, V.Kornilov, E.Gorbovskoy, K.Zhirkov, N.Tyurina, P.Balanutsa, A.Kuznetsov, D. Vlasenko, 
G.Antipov, D.Zimnukhov, V.Senik, E.Minkina, A.Chasovnikov, V.Topolev, D.Kuvshinov,  D.Cheryasov, Ya.Kechin
(Lomonosov Moscow State University, SAI, Physics Department),

R. Podesta, C.Lopez, F. Podesta, C.Francile 
(Observatorio Astronomico Felix Aguilar OAFA),

R. Rebolo, M. Serra 
(The Instituto de Astrofisica de Canarias),

D. Buckley 
(South African Astronomical Observatory),

O.A. Gres, N.M. Budnev
(Irkutsk State University, API),

L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez 
(INAOE, Guillermo Haro Astrophysics Observatory),

A. Tlatov, D. Dormidontov 
(Kislovodsk Solar Station of the Pulkovo Observatory),

A. Gabovich, V.Yurkov 
(Blagoveschensk Educational State University)


MASTER-SAAO robotic telescope  (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)  located in South Africa (South African Astronomical Observatory) was pointed to the Swift GRB 230805B ( S. B. Cenko et al., GCN 34339
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 ) errorbox  19680 sec after notice time and 19762 sec after trigger time at 2023-08-05 16:53:13 UT, with upper limit up to  16.6 mag. Observations started at twilight.  The observations began at zenith distance = 66 deg. The sun  altitude  is -10.7 deg. 

The galactic latitude b = 76 deg., longitude l = 52 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=2250484

We obtain a following upper limits.  

Tmid-T0  |          Site       |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________

   19853 |         MASTER-SAAO |   C |   180 | 16.6 |        
Filter C is a clear (unfiltred) band. 


The observation and reduction will continue. 
The message may be cited.

A. S. Moskvitin (SAO RAS) and V. P. Goranskij (SAI MSU) report
on behalf of a larger collaboration.

We observed the field of the GRB 230805B (Cenko et al., GCNC #34339)
with the 1-m telescope of SAO RAS Zeiss-1000 equipped with the
Multi-Mode Photometer-Polarimeter (MMPP). We obtained 4 x 300 sec.
exposures in Rc band on August 5, 17:50:15--18:11:48 UT.

Within the XRT error circle we marginally detected a single object
(possible OT) with coordinates (Epoch = 2000.0):
R.A. = 13:50:58.2, Dec. = +31:11:28.6 (+/- 0".5)
and brightness about R = 22.7 +/- 0.3 (t_mid - t0 = 6.61 hours).

This preliminary photometry is based on the nearby SDSS stars;
magnitudes are converted using Lupton (2005) equations.

A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAR), T. Sbarrato (INAF-OAB),
S. Dichiara (PSU), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), J.P.
Osborne (U. Leicester), K.L. Page (U. Leicester) and P.A. Evans report
on behalf of the Swift-XRT team:

We have analysed 6.0 ks of XRT data for GRB 230805B, from 210 s to 25.0
ks after the  BAT trigger. The data are entirely in Photon Counting
(PC) mode. The best available XRT position  (using the promptly
downlinked event data, the XRT-UVOT alignment and matching UVOT field
sources to the USNO-B1 catalogue) is RA, Dec = 207.74271, 31.19102
which is equivalent to:

RA (J2000): 13 50 58.25
Dec(J2000): +31 11 27.7

with an uncertainty of 1.9 arcsec (radius, 90% confidence).

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=3.7 (+0.9, -0.4). At T+650 s  the decay
flattens to an alpha of -0.22 (+0.72, -0.08) before breaking again at
T+4027 s to a final decay with index alpha=1.7 (+0.6, -0.5).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.76 (+0.26, -0.24). The
best-fitting absorption column is  8.9 (+7.5, -6.2) x 10^20 cm^-2, in
excess of the Galactic value of 1.4 x 10^20 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 3.8 x 10^-11 (4.4 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     8.9 (+7.5, -6.2) x 10^20 cm^-2
Galactic foreground: 1.4 x 10^20 cm^-2
Excess significance: 2.0 sigma
Photon index:	     1.76 (+0.26, -0.24)

If the light curve continues to decay with a power-law decay index of
1.7, the count rate at T+24 hours will be 5.6 x 10^-4 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.1 x
10^-14 (2.5 x 10^-14) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01183217.

This circular is an official product of the Swift-XRT team.

D. B. Malesani (Radboud Univ. and DAWN/NBI) and T. Pursimo (NOT) report on behalf of a larger collaboration:

We observed the location of GRB 230805B (Cenko et al., GCN 34339
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 ) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations were secured in the r and z bands. An object with position consistent with the one reported by Moskvitin & Goranskij (GCN 34343
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 ) is well detected in our data. Based on nearby stars from the Gaia catalog, we measure the following J2000 coordinates, with an error of ~0.3":

RA  = 13:50:58.23
Dec = +31:11:28.6

At a mean epoch 2023 Aug 5.91 UT (10.4 hr after the trigger), we measure a preliminary magnitude (calibrated against nearby Pan-STARRS point-like sources) r = 23.5 +- 0.15 AB. Compared to the measurement by Moskvitin & Goranskij (GCN 34343
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 ), our magnitude value provides 2-sigma evidence for fading, consistent with afterglow behavior.

Y.-D. Hu, I. Perez-Garcia, E. Fernandez-Garcia, A. J. Castro-Tirado, M.D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy and F. J. Aceituno (IAA-CSIC), P. J. Meintjes and H. Van Heerden (UFS, SouthAfrica), A. Martin-Carrillo and L. Hanlon (UCD, Ireland), M. Gritsevich (Univ. of Helsinki) and C. J. Perez del Pulgar (UMA), on behalf of a larger collaboration, report:

Following the detection of GRB 230805B by Swift (Cenko et al. GCNC 34339), the BOOTES-6/DPRT 0.6m robotic telescope at Boyden Observatory in Maselspoort (South Africa) automatically observed the GRB location starting on Aug. 05, 17:15 UT (~ 5.9 h after trigger). No new optical source is detected on the co-added image (7 x 60 s, clear filter) within the enhanced Swift/XRT error region (D'Ai et al. GCNC 34345) down to 19.9 mag.

We also triggered the 1.5m telescope at Observatorio de Sierra Nevada in Granada (Spain), starting on Aug. 05, 20:30 UT (~ 9.1 h after trigger). At the position of the suggested optical afterglow reported by Moskvitin and Goranskij (GCNC 34343) we found a faint optical source for which we preliminary measure I = 22.9+/-0.4 (on a 12 x 150s co-added image), consistent with the fading reported by Malesani and Pursimo in the r-band (GCNC 34346).

We thank both the staff at Boyden and Sierra Nevada Observatories for their excellent support.

U.Quadri and  L.Strabla (Bassano Bresciano Astronomical Observatory),
in a large collaboration with:
M.G. Dainotti (National Astronomical Observatory of Japan), 
Y. Niino (Tokyo University, Institute of Astronomy), 
K. Kalinowski (Aarhus University, Department of Physics and Astronomy),
B. De Simone (Universita' degli Studi Di Salerno)
report: 

We imaged the field of GRB 230805B detected by SWIFT(trigger 1183217)
with the robotic telescope of (IAU station 565) Bassano Bresciano 
Observatory, Italy. Member of: 
AAVSO - American Association of Variable Star Observers.
UAI/SSV - Unione Astrofili Italiani/sezione stelle variabili.
GAC - Gruppo Astrofili Cremonesi.

The observations started 8.74 hour after the GRB trigger, At the end of twilight 
with our Newton telescope D=250 mm F/D=4.8.

Weather conditions were good.

We co-added 4 series of 20 exposures of 60 sec each.

Start T0+      End T0+     CR lim
8.74 hour   10.00 hour      19.5

CR is unfiltered with R zero point

We did not found any optical counterpart in the error box of the XRTcandidate.
S. B. Cenko (GSFC) et al. GCN 34339
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Magnitudes were estimated with the USNO-B1.0 cat. and 
are not corrected for galactic dust extinction.

Reference:
http://www.osservatoriobassano.org/GRB.asp

The message may be cited.

GRB 230805B: Swift/UVOT Upper Limits

S. J. LaPorte (PSU) and S. B. Cenko (GSFC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 230805B
196 s after the BAT trigger (Cenko et al., GCN Circ. 34339
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 ).
No optical afterglow consistent with the XRT position
(Evans et al., GCN Circ. 34345
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 )
is detected in the initial UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first
finding chart (FC) exposure and subsequent exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white_FC           196          345          147         >20.2
u_FC               354          604          246         >19.5
white              196         1878          284         >20.7
v                  683         1927          135         >19.0
b                  610         1854          136         >20.4
u                  354         1829          363         >19.6
w1                 732         1804          117         >19.4
w2                1014         1730           58         >18.8

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.014 in the direction of the burst
(Schlegel et al. 1998).

J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester) 
report on behalf of the Swift-XRT team.

Using 3447 s of XRT Photon Counting mode data and 3 UVOT
images for GRB 230805B, we find an astrometrically corrected X-ray
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 207.74318, +31.19135 which is equivalent
to:

RA (J2000): 13h 50m 58.36s
Dec (J2000): +31d 11' 28.8"

with an uncertainty of 2.1 arcsec (radius, 90% confidence).

This position may be improved as more data are received. The latest
position can be viewed at http://www.swift.ac.uk/xrt_positions. Position
enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans
et al. (2009, MNRAS, 397, 1177).

This circular was automatically generated, and is an official product of the
Swift-XRT team.

D. Turpin (CEA Paris-Saclay), C. Adami (LAM), B. Schneider (MIT),
E. Le Floc'h, D. Götz, F. Schüssler (CEA Paris-Saclay), A. de Ugarte Postigo (OCA/CNRS),
S. Basa (LAM), S. D. Vergani (GEPI, Obs. de Paris), report on behalf
of a larger collaboration:

We observed the field of GRB 230805B (Cenko et al., GCN 34339
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 ; D'Ali et al.,
GCN 34345
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 ; LaPorte et al., GCN 34251
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 ; Osborne et al. GCN 34353
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 )
using the T193cm telescope at Observatoire de Haute-Provence (France)
equipped with the MISTRAL spectro-imager. In 5 exposures, obtained
in the r-band (5x600s) from 2023 05 August 20:36:08 UT to
21:34:34 UT (mid-time ~9.69h after trigger) under poor seeing conditions,
we do not detect any source at the position reported by
Moskvitin et al., GCN 34343
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 ; Malesani et al., GCN 34346
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 ; Hu et al., GCN 34347
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down to the following 5-sigma limit:

r > 21.5 mag (AB)

The photometric calibration was performed using nearby stars from
the PanSTARRS catalog and the magnitude is not corrected for Galactic
extinction.

We acknowledge the excellent support from Observatoire de Haute-Provence,
in particular Jean Balcaen for the MISTRAL observations and
the SOPHIE observer Lisa Altinier. 

J.Mangan (CNRS/IJCLab) and C. Meegan (UAH) report on behalf of the Fermi GBM Team:

"At 11:23:33.59 UT on 05 August 2023, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 230805B (trigger 712927418 / 230805475),
which was also detected by Swift BAT (S. B. Cenko et al. 2023, GCN 34339
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 ).
The Fermi GBM on-ground location is consistent with the Swift BAT position.

The angle from the Fermi LAT boresight at the GBM trigger time is 48 degrees.

The GBM light curve consists of multiple emissions
with a duration (T90) of about 60 s (50-300 keV).
The time-averaged spectrum from T0-0 s to T0+60.5 s is best fit by
a simple power law function with index -1.4 +/- 0.03

The event fluence (10-1000 keV) in this time interval is
(4.8 +/- 0.3)E-6 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+-0.1 s in the 10-1000 keV band
is 2.3 +/- 0.2 ph/s/cm^2.

The spectral analysis results presented above are preliminary; 
final results will be published in the GBM GRB Catalog: 
https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html
 
For Fermi GBM data and info, please visit the official Fermi GBM Support Page: 
https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"

N. Higuchi, I. Takahashi, M. Sasada, M. Niwano, S. Sato, S. Hayatsu, R. Hosokawa, H. Seki, H. Takei, Y. Yatsu (Tokyo Tech) and N. Kawai (Riken) report on behalf of the MITSuME collaboration:

We observed the field of GRB 230805B (Cenko et al. GCN Circular #34339
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 ) with the optical three color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50 cm telescope Akeno. 

The observation started at 2023-8-05 11:25:51 UT (120 seconds after the Swift/BAT trigger). We stacked the images with good conditions. We did not detect any uncatalogued sources within the error region (Osborne et al. GCN Circular #34353
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 ). We obtained the 5-sigma limits of the stacked images as follows.

T0+[sec] | MID-UT | T-EXP[sec] | 5-sigma limits
------------------------------------------------------------------------------------------------
1117 | 2023-08-05 11:42:28 | 240.0 | g'>18.5, Rc>18.5, Ic>17.9
4357 | 2023-08-05 12:36:28 | 840.0 | g'>18.9, Rc>19.0, Ic>18.5
------------------------------------------------------------------------------------------------
T0+ : Elapsed time after the burst
T-EXP: Total Exposure time

We used the PS1 catalog for flux calibration. The catalog magnitudes in PS1 g, r and i bands were converted to our g', Rc and Ic band magnitudes following Tonry et al. (2012), Table 6. The magnitudes are expressed in the AB system. The images were processed in real-time through the MITSuME GPU reduction pipeline (Niwano et al. 2021, PASJ, Vol.73, Issue 1, Pages 4-24; https://github.com/MNiwano/Eclaire).

P. K. Navaneeth (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:

Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long GRB 230805B which was also detected by Swift-BAT (Cenko et al., GCN Circ. 34339
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 ), and Fermi-GBM (Mangan et al., GCN Circ. 34357
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 ).

The source was detected in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2023-08-05 11:23:33.50 UTC. The measured peak count rate associated with the burst is 165 (+36, -38) counts/s above the background in the combined data of three quadrants (out of four), with a total of 1304 (+507, -508) counts. The local mean background count rate was 337 (+1, -2) counts/s. Using cumulative rates, we measure a T90 of 54 (+27, -25) s. 

The source was also detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range.

CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project.

CZTI GRB detections are reported regularly on the payload site at: 
http://astrosat.iucaa.in/czti/?q=grb

Giulio Scarfì (Gruppo Astronomia Digitale - Iota Scorpii Observatory, La
Spezia,
Italy)
in a large collaboration with:
M.G. Dainotti (National Astronomical Observatory of Japan),
Y. Niino (Tokyo University, Institute of Astronomy),
K. Kalinowski (Aarhus University, Department of Physics and Astronomy),
B. De Simone (Universita' degli Studi Di Salerno)
Unione Astrofili Italiani (UAI)
report:

We imaged the field of GRB 230805B detected by SWIFT(trigger 11:23:51 UT)
with the telescope GSO 16” of Iota Scorpii Observatory, La Spezia Italy

Member of:

UAI/SSV - Unione Astrofili Italiani/sezione stelle variabili, GRB section.
GAD - Gruppo Astronomia Digitale.

The observations started 550 min after the GRB trigger, at the end of
twilight,
with a Ritchey Cretien D=406 mm with reducer F/D=6,15.
Weather conditions were very good.

We co-added 6 exposures of 300 sec each.


Start T0+      End T0+       R lim
550 min        581 min         20


We did not found any optical counterpart in the error box of the XRT
candidate.
Page et al. GCN 34339
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Magnitudes were estimated with the Gaia EDR3 cat. and
are not corrected for galactic dust extinction. 20.0

Reference:
https://www.parcodellestelle.com/

The message may be cited.

H. A. Krimm (NSF), S. D. Barthelmy (GSFC),
S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa),
C. B. Markwardt (GSFC),D. M. Palmer (LANL),
T. Parsotan (GSFC/UMBC), T. Sakamoto (AGU),
M. Stamatikos (OSU) (i.e. the Swift-BAT team):

Using the data set from T-40 to T+200 sec from the recent telemetry
downlink,
we report further analysis of BAT GRB 230805B (trigger #1183217)
(Cenko et al., GCN Circ. 34339
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 ).  The BAT ground-calculated position is
RA, Dec = 207.738, 31.190 deg which is
   RA(J2000)  =  13h 50m 57.2s
   Dec(J2000) = +31d 11' 23.0"
with an uncertainty of 2.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 41%.

The BAT  light curve shows a complex structure with a duration of ~ 100 sec.
T90 (15-350 keV) is 93.77 +- 18.83 sec (estimated error including
systematics).

The time-averaged spectrum from T-21.60 to T+103.27 sec is best fit by a
simple
power-law model.  The power law index of the time-averaged spectrum is
1.36 +- 0.20.  The fluence in the 15-150 keV band is 1.9 +- 0.2 x 10^-06
erg/cm2.
The 1-sec peak photon flux measured from T-17.66 sec in the 15-150 keV band
is 1.2 +- 0.3 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level.

The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/1183217/BA/