- GCN/BACODINE POSITION NOTICE
TITLE: GCN/SWIFT NOTICE
NOTICE_DATE: Wed 24 Aug 05 23:21:55 UT
NOTICE_TYPE: Swift-BAT GRB Position
TRIGGER_NUM: 151905, Seg_Num: 0
GRB_RA: 12.237d {+00h 48m 57s} (J2000),
12.312d {+00h 49m 15s} (current),
11.573d {+00h 46m 17s} (1950)
GRB_DEC: +22.592d {+22d 35' 31"} (J2000),
+22.623d {+22d 37' 22"} (current),
+22.320d {+22d 19' 10"} (1950)
GRB_ERROR: 4.00 [arcmin radius, statistical only]
GRB_INTEN: 0 [cnts] Image_Peak=2020 [image_cnts]
TRIGGER_DUR: 64.000 [sec]
TRIGGER_INDEX: 20000 E_range: 15-50 keV
BKG_INTEN: 0 [cnts]
BKG_TIME: 0.00 SOD {00:00:00.00} UT
BKG_DUR: 0 [sec]
GRB_DATE: 13606 TJD; 236 DOY; 05/08/24
GRB_TIME: 83536.30 SOD {23:12:16.30} UT
GRB_PHI: -22.48 [deg]
GRB_THETA: 32.54 [deg]
SOLN_STATUS: 0x13
RATE_SIGNIF: 0.00 [sigma]
IMAGE_SIGNIF: 8.76 [sigma]
MERIT_PARAMS: +1 +0 +0 +6 +1 -1 -1 +0 +64 +1
SUN_POSTN: 153.87d {+10h 15m 29s} +10.81d {+10d 48' 30"}
SUN_DIST: 129.65 [deg]
MOON_POSTN: 38.77d {+02h 35m 04s} +17.62d {+17d 37' 05"}
MOON_DIST: 25.30 [deg]
MOON_ILLUM: 67 [%]
GAL_COORDS: 122.18,-40.28 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS: 20.22, 15.94 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS: SWIFT-BAT GRB Coordinates.
COMMENTS: This is an image trigger. (The RATE_SIGNIF & BKG_{INTEN, TIME, DUR} are undefined.)
COMMENTS: A point_source was found.
COMMENTS: This does not match any source in the on-board catalog.
COMMENTS: This does not match any source in the ground catalog.
COMMENTS: This is a GRB.
- red DSS finding chart
ps-file
- GCN/SWIFT NOTICE
TITLE: GCN/SWIFT NOTICE
NOTICE_DATE: Wed 24 Aug 05 23:22:16 UT
NOTICE_TYPE: Swift-BAT GRB Lightcurve
TRIGGER_NUM: 151905, Seg_Num: 0
GRB_RA: 12.237d {+00h 48m 57s} (J2000),
12.312d {+00h 49m 15s} (current),
11.573d {+00h 46m 17s} (1950)
GRB_DEC: +22.592d {+22d 35' 31"} (J2000),
+22.623d {+22d 37' 22"} (current),
+22.320d {+22d 19' 10"} (1950)
GRB_DATE: 13606 TJD; 236 DOY; 05/08/24
GRB_TIME: 83536.30 SOD {23:12:16.30} UT
TRIGGER_INDEX: 20000
GRB_PHI: -22.48 [deg]
GRB_THETA: 32.54 [deg]
DELTA_TIME: 0.00 [sec]
TRIGGER_DUR: 64.000 [sec]
LC_URL: sw00151905000msb.lc
SUN_POSTN: 153.87d {+10h 15m 29s} +10.81d {+10d 48' 30"}
SUN_DIST: 129.65 [deg]
MOON_POSTN: 38.77d {+02h 35m 04s} +17.62d {+17d 37' 05"}
MOON_DIST: 25.30 [deg]
MOON_ILLUM: 67 [%]
GAL_COORDS: 122.18,-40.28 [deg] galactic lon,lat of the pointing direction
ECL_COORDS: 20.22, 15.94 [deg] ecliptic lon,lat of the pointing direction
COMMENTS: SWIFT-BAT GRB Lightcurve.
COMMENTS:
COMMENTS: The next comments were copied from the BAT_POS Notice:
COMMENTS: This is an image trigger.
COMMENTS: A point_source was found.
COMMENTS: This does not match any source in the on-board catalog.
COMMENTS: This does not match any source in the ground catalog.
COMMENTS: This is a GRB.
- GCN notice #3865
J. Gorosabel, V. Casanova, R. Garrido, A.J. Castro-Tirado,
M. Jelinek, de Ugarte Postigo, (IAA-CSIC), report:
We have carried out R-band observations starting at 23:49 UT
(~37 min after the GRB) with the 1.5m OSN telescope. A visual
comparison reveals an object placed at:
RA(J2000) = 00:48:56.1
DEC(J2000)= 22:36:32
not present on the DSS. A finding chart will be shortly available
at http://www.dsri.dk/~jgu/grb050824/FCs/osn.R.gif
The object has a magnitude of R~18. Further observations would
be required to confirm whether the object is fading."
- GCN notice #3866
S. Campana (INAF-OAB), S. Barthelmy (GSFC), D. Burrows (PSU),
J. Cummings (GSFC/NRC), N. Gehrels (GSFC), S. Hunsberger (PSU),
M. Ivanushkina (PSU), F. Marshall (GSFC), D. Palmer (LANL),
G. Tagliaferri (INAF-OAB),
on behalf of the Swift team:
At 23:12:16 UT, Swift-BAT triggered and located GRB050824 (trigger=151905).
This was a 64-sec image trigger. The spacecraft did not automatically slew
due to proximity to the moon (25 degrees). Hence there will be no immediate
results from XRT or UVOT. However, a TOO is being planned for this target.
The BAT on-board calculated location is RA,Dec 12.237d,+22.592d
{00h 48m 57s,+22d 35' 31"} (J2000), with an uncertainty of 3 arcmin
(radius, 90% containment, stat+sys). The BAT light curve shows a broad peak
from T+30 to T+70 sec. The emission is present only in the 15-50 keV band.
The peak count rate was ~500 counts/sec (15-50 keV) at ~40 seconds
after the trigger. At this early stage of the analysis we think this is
likely a GRB, as there is no known gamma-ray source at this location
in the SIMBAD database and the galactic latitude is -40 degrees.
- GCN notice #3867
B. E. Schaefer (Louisiana State), Fang Yuan (U Mich), and K. Alatalo
(Berkeley) report on behalf of the ROTSE collaboration:
ROTSE-IIIc, located at the H.E.S.S. site at Mt. Gamsberg, Namibia,
responded to GRB 050824 (Swift trigger 151905), producing images beginning
7.1 s after the GCN notice time. An automated response took the first
image at 23:22:02.1 UT, 585.8 s after the burst, under good conditions
although with the gibbous Moon only 25 degrees away. We took 10 5-sec, 10
20-sec and 130 60-sec eposures. These unfiltered images are calibrated
relative to USNO A2.0 (R).
ROTSE-IIId, located at the Turkish National Observatory at Bakirlitepe,
Turkey, also responded, producing images beginning 5.8 s after the GCN
notice time. An automated response took the first image at 23:22:00.8 UT,
584.5 s after the burst, under good conditions (but again, with the
gibbous Moon nearby). We took 10 5-sec, 10 20-sec and 80 60-sec eposures.
These unfiltered images are also calibrated relative to USNO A2.0 (R).
Comparison to the DSS (second epoch) reveals no new sources within the
3-sigma error circle, for both single images and coadding into sets of 10.
Individual images have limiting magnitudes ranging from 15.4-17.0; we set
the following specific limits.
ROTSE start UT end UT t_exp(s) mlim t_start-tGRB(s) Coadd?
--------------------------------------------------------------------------
III-c 23:22:02.1 23:23:27.1 85 17.3 585.8 Y
III-c 23:23:27.7 23:28:21.7 294 18.2 671.4 Y
III-d 23:22:00.8 23:24:20.8 140 17.4 584.5 Y
III-d 23:24:21.5 23:29:20.5 299 17.9 725.2 Y
In particular, we do not see the new source described by Gorosabel et al.
(GCN 3865), with this source being near or below our detection threshold.
- GCN notice #3869
V. Lipunov, V.Kornilov, A.Krylov, N.Tyurina, A.Belinski,
E.Gorbovskoy, D.Kuvshinov, G.Borisov, V.Vladimirov, G.Antipov, Krushinski V.
Sternberg Astronomical Institute, Moscow Union "Optic"
MASTER (http://observ.pereplet.ru)
responded to GRB 050824 (Swift trigger
151905) (see GCN3869). The first image was 764 sec after
SWIFT GRB050824 detection under the not very good weather
condition (Moon light).
We see OT-candidate proposed by J. Gorosabel (GCN 3865) with m = 17.9
(unfiltered, close to R, exp. 45 sec) on 2-3 sigma level.
Our m = 0.89R + 0.11B (R & B from USNO A).
UT (start) After GRB time m
23 25 00 764s 17.9 45 sec
23 31 44 19.5min - 28.5 min 18.3 summ of 9 images
23 42 07 29.8min - 36.7 min 19.4 summ of 7 images
The calibration will be continued.
The JPG-image of the summ will be available at
http://observ.pereplet.ru/images/GRB050824/1.jpg
This work is supported by RFFI 04-02-16411 grant.
This message can be cited.
Mailto: lipunov@sai.msu.ru
- GCN notice #3870
V. Lipunov, V.Kornilov, A.Krylov, N.Tyurina, A.Belinski,
E.Gorbovskoy, D.Kuvshinov, G.Borisov, V.Vladimirov, G.Antipov, Krushinski V.
Sternberg Astronomical Institute, Moscow Union "Optic"
MASTER (http://observ.pereplet.ru) responded to GRB 050824 (Swift trigger
151905) (see GCN3869). The first image was 764 sec after
SWIFT GRB050824 detection under the not very good weather
condition (Moon light).
We see OT-candidate proposed by J. Gorosabel (GCN 3865) with m = 17.9
(unfiltered, close to R, exp. 45 sec) on 2-3 sigma level.
Our m = 0.89R + 0.11B (R & B from USNO A).
UT (start) After GRB time m
23 25 00 764s 17.9 45 sec
23 31 44 19.5min - 28.5 min 18.3 summ of 9 images
23 42 07 29.8min - 36.7 min 19.4 summ of 7 images
The calibration will be continued.
The JPG-image of the summ will be available at
http://observ.pereplet.ru/images/GRB050824/1.jpg
This work is supported by RFFI 04-02-16411 grant.
This message can be cited.
Mailto: lipunov@sai.msu.ru
- GCN notice #3871
H. Krimm (GSFC/USRA), L. Barbier (GSFC), S. Barthelmy (GSFC),
J. Cummings (GSFC/NRC), K. Gendreau (GSFC), D. Hullinger (GSFC/UMD),
E. Fenimore (LANL), N. Gehrels (GSFC), C. Markwardt (GSFC/UMD),
P. Meszaros (PSU), D. Palmer (LANL), A. Parsons (GSFC),
T. Sakamoto (GSFC/NRC), G. Sato (ISAS), J. Tueller (GSFC)
on behalf of the Swift-BAT team:
Using the full data set from the recent telemetry downlink, we
report further analysis of Swift-BAT GRB 050824 (trigger #151905)
(Campana, et al., GCN 3866). The ground-analysis position is
RA,Dec 12.256 +22.618 (J2000) with an uncertainty of 3 arcmin
(radius, 90%, stat+sys). This is 1.9 arcmin from the onboard
position and 1.4 arcmin from the optical candidate reported by
Gorosabel et al. in GCN Circ. 3865.
The light curve shows a single peak with slow rise and slow decay.
T90 is 25 +- 5 seconds. Fitting a simple power law over the
interval from T+38 to T+64 sec, the photon index is 2.7 +/- 0.4
with a fluence of 2.3 +/- 0.5 x 10^-7 erg/cm^2 in the 15-150 keV
band (90% c.l). The peak flux in a 1-second wide window starting
at T+53 sec is 0.5 +/- 0.2 ph/cm^2/sec (15-150 keV).
The original GCN Notices were delayed in transmission to the ground
by 500 sec due to the burst happening during a telemetry downlink
session when the TDRSS real-time messages are held in a buffer until
the end of the downlink.
- GCN notice #3872
S. Campana (INAF-OAB), V. Mangano (INAF-IASF Palermo), G. Chincarini
(INAF-OAB &
Uni. Bicocca), G. Tagliaferri (INAF-OAB), D.N. Burrows (PSU), L.
Cominsky (Sonoma
State U.) and J. Norris (GSFC) report on behalf of the Swift XRT team:
We have analyzed the Swift XRT data from the first orbit observation of
GRB 050824
(Campana et al., GCN3866). The new refined coordinates are:
RA(J2000) = 0h48m56.05s
Dec(J2000) = +22:36:28.5
This position is 59 arcseconds from the BAT position given in GCN3866
(and 83
arcsec from the refined BAT position, Krimm et al. GCN3871) and 3.4
arcsec from
the suggested optical counterpart (Gorosabel et al., GCN3865).
We estimated an uncertainty of 6.8 arcseconds radius (90% confidence
level, throughout
the circular). A second fainter X-ray source is located 2.5 arcmin from
the suggested
afterglow position (and further away from the BAT refined position).
The 0.5-10 keV light curve XRT started 2005-08-25 UT00:53:45, 6089
seconds after
the BAT trigger, following an uploaded TOO since Swift did not
automatically
slewed on source (due to the Moon constraint). At the moment we have
data from
one Swift orbit. During the first orbit we accumulated 1346 seconds of
good data.
The afterglow candidate is detected with a count rate of (4.1+/-1.1)x10^-2
counts/second (55 total counts). We found no indication of count rate decay.
The number of counts is too low to perform a full spectral analysis.
Fixing the column density to the Galactic value (3.6x10^20 cm-2) a
preliminary
spectral fit to the PC data gives a spectral power law photon index of
2.6+/-0.6
in the 0.5-10 keV band. The average unabsorbed 0.5-10 keV flux is about
(1.2+/-0.7)E-12 erg cm-2 s-1.
- GCN notice #3874
GRB 050824: Spectroscopic redshift from the VLT
J. P. U. Fynbo, B. L. Jensen, J. Sollerman, J. Hjorth,
D. Watson, K. Pedersen, P. Jakobsson, J. M. Castro Cer=F3n
(DARK Cosmology Centre/Niels Bohr Institute), Javier Gorosabel
(IAA-CSIC) report:
"Using FORS2 on the ESO Very Large Telescope (VLT) we have obtained
spectra of the afterglow of GRB 050824 (GCN 3865, 3866) on 2005,
Aug 25.4 UT. We detect [OII], [OIII], H-beta, and [NeIII] in emission
and MgII in absorption, corresponding to a redshift of z=0.83.
We acknowledge excellent support from the Paranal staff, especially
Emmanuel Jehin."
- GCN notice #3875
P. B. Cameron (Caltech) and D. A. Frail (NRAO) report on behalf of a
larger collaboration:
"We have undertaken VLA observations at a frequency of 8.46 GHz toward
GRB 050824 (GCN 3866) on August 25.32 UT. No radio afterglow is
detected. At the position of the optical afterglow (GCN 3865) the
point-source limit is 44 +/- 50 microJy. No further observations are
planned.
The National Radio Astronomy Observatory is a facility of the National
Science Foundation operated under cooperative agreement by Associated
Universities, Inc."
- GCN notice #3876
D. Hohman (Stone Edge Observatory, NY) reports on behalf of
the AAVSO International High Energy Network on optical observations
of the Swift burst GRB050824 (Campana et al., GCN3866).
Images taken with a 20cm SCT and Ic filter with midpoint time
of 050825 0530UT (6.3hrs after the burst) do not show
any object at the candidate afterglow location by Gorosabel
et al. (GCN3865) down to the DSS-2 N-plate limit (about I=18).
The full report is given below.
The AAVSO thanks the Curry Foundation for support of the
AAVSO International High Energy Network.
---------------------------
Report filed on Thu Aug 25 08:37:34 2005:
Name: Dennis Hohman
email: dhohman@txrx.com
Observer: HDF
Site: Stone Edge Observatory
Location: Orchard Park, NY
LatitudeLongitude:
Elevation: 275 meters
Scope: SCT 20 cm
ScopeFocalRatio: F5.9
CCDVendor: ST7XME
CCDDetector: KAF402E
CCDSize: 752x512
CCDPixelScale: 1.5
CCDFOV: 13x19 arc min
Object: 050824
ObsDate: 08/25/05
ObsMidPointTime: 05:30
TimePerFrame: 240 sec
NumberOfFrames: 13
Filters: I
Processing: Flats/Darks/coadd
Seeing: 4 - 4.5
LimitingMag:
Sky: Clear
afterglowmag:
afterglowerr:
compstars:
Report: Full error circle covered. No new object to the limit of the POSS2/UKSTU IR plate.
comments:
A FITS image has been uploaded to
ftp://ftp.aavso.org/grb/DennisHohman_050824_2453608.02609_.fits
- GCN notice #3877
S. Campana (INAF-OAB), A. Moretti (INAF-OAB), V. Mangano (INAF-IASF
Palermo), D.N. Burrows (PSU), report:
We have analyzed 13 ks of Swift XRT data of GRB 050824
(Campana et al., GCN3866).
The 0.2-10 keV light curve XRT (started 6089 seconds after the BAT
trigger) now shows an indication of a temporal decay with a power
law index of -0.4+/-0.2 (90% confidence level).
The power law fit is better than a constant fit at a 3.3 sigma
level (F-test). This indicates that the source suggested in the
previous XRT circular (Campana et al., GCN3872) is the X-ray
afterglow of GRB050724.
The 307 photons in the 0.3-10 keV evergy band were also used for
spectral analysis. We fixed the column density to the Galactic value
(3.6x10^20 cm-2) and added a free local absorption at z=0.83 (Fynbo
et al., GCN3874) plus a power law. We found an accepetable model
(chi2_red=1.01) with a NH_loc=(1.7+/-1.3)x10^21 cm-2 and a power
law photon index of 2.0+/-0.2 (90% confidence level).
- GCN notice #3878
The Swift Ultra-Violet/Optical Telescope (UVOT) observations began at
00:53:49 UT, 1.8 hrs after the BAT trigger. UVOT detects a fading source at a
position consistent with that reported by Gorosabel et al. (GCN 3865) in 5
of its 6 filters. The magnitudes or 3-sigma upper limit in the first
exposure taken in each filter are as follows:
Filter Mid Time (hrs) Exp (s) Mag/3-sig UL
V 1.8 109 20.02+/-0.39
B 5.1 305 20.88+/-0.36
U 3.6 217 19.55+/-0.32
W1 9.5 205 19.85+/-0.33
M2 11.7 121 19.34+/-0.36
W2 12.3 1457 > 20.79
The afterglow has faded below 2-sigma above background 11hrs after the
burst trigger in all filters apart from the V and U, where it is still
detected at the 2.3-sigma and >3-sigma level, respectively.
The magnitudes have not been corrected for extinction. These magnitudes
are based on preliminary zero-points, measured in orbit, and will require
refinement with further calibration.
- GCN notice #3880
P. Schady (MSSL/PSU), R. Fink (GSFC), M. Ivanushkina (PSU), S. Holland
(GSFC/USRA), K. McGowen (MSSL), N. Gehrels (GSFC) on behalf of the Swift
UVOT team
CORRECTION: The mid time and exposure durations previously reported for
observations made by Swift/UVOT of GRB050824 are incorrect (Schady et al.
GCN 3878). The correct times are given below.
The Swift Ultra-Violet/Optical Telescope (UVOT) observations began at
00:53:49 UT, 1.8 hrs after the BAT trigger. UVOT detects a fading source
at a
position consistent with that reported by Gorosabel et al. (GCN 3865) in 5
of its 6 filters. The magnitudes or 3-sigma upper limit in the first
exposure taken in each filter are as follows:
Filter Mid Time (hrs) Exp (s) Mag/3-sig UL
V 1.8 900 20.02+/-0.39
B 5.1 900 20.88+/-0.36
U 3.6 545 19.55+/-0.32
W1 3.4 900 19.85+/-0.33
M2 2.1 532 19.34+/-0.36
W2 7.8 1457 > 20.79
The afterglow has faded below 2-sigma above background 11hrs after the
burst trigger in all filters apart from the V and U, where it is still
detected at the 2.3-sigma and >3-sigma level, respectively.
The magnitudes have not been corrected for extinction. The reddening in
this direction is E_{B-V} = 0.04mag. These magnitudes are based on
preliminary zero-points, measured in orbit, and will require refinement
with further calibration.
- GCN notice #3883
V. Lipunov, V.Kornilov, A.Krylov, N.Tyurina, A.Belinski,
E.Gorbovskoy, D.Kuvshinov, G.Borisov, V.Vladimirov, G.Antipov, Krushinski V.
Sternberg Astronomical Institute, Moscow Union "Optic"
MASTER (http://observ.pereplet.ru)
responded to GRB 050824 (Swift trigger
151905) (see GCN3869). The first image was 764 sec after
SWIFT GRB050824 detection under the Moon light.
We see OT-candidate proposed by J. Gorosabel (GCN 3865).
Our m = 0.89R + 0.11B (R & B from USNO A2).
We made new reduction and confirm previous our OT-decay result (GCN3870):
New reduction give next results about OT:
UT After GRB m error expotime
mean time
23 25 00 788s >17.8 45 s
23 25 00 - 23 47 55 24.0 min 18.6 +-0.3 15x30 s
23 49 00 - 00 09 35 47.0 min 19.4 +-0.3 15x30 s
The JPG-images available at
http://observ.pereplet.ru/images/GRB050824/1.jpg
This work is supported by RFFI 04-02-16411 grant.
This message can be cited.
Mailto: lipunov@sai.msu.ru
- GCN notice #3886
V. Lipunov, V.Kornilov, N.Tyurina, A.Belinski,
E.Gorbovskoy, D.Kuvshinov
Sternberg Astronomical Institute, Moscow Union "Optic"
We have analysed all photometric points obtained during first 2 hours (see
picture http://observ.pereplet.ru/images/GRB050824/2.jpg ) from ROTSE
(GCN Circ 3867), MASTER (GCN Circ 3883), J. Gorosabel et al. (GCN Circ
3865) and Swift UVOT(GCN Circ 3880) in similar colors .
The upper limits of ROTSE and MASTER for 500-750 sec (GRB time) are in
agreement. Both instrumental systems are more or less similar.
There is some contradiction with J. Gorosabel et al. (GCN 3865) and
MASTER data (GCN Circ 3880) for 24 - 47 minutes.
But there is no error bar in J. Gorosabel et al.(GCN 3865).
The SWIFT UVOT V-band is most closed to MASTER in color sense.
If we include only 2 MASTER points and Swift UVOT V-point we can obtain
next power low:
m = 2.1(+-0.2) log (t) + 19.5 ,
t in hours. This corresponds to usual flux power law
F ~ t^-0.9
However there is strong contradiction with ROTSE (11 min) uper limit and
J. Gorosabel et al. (GCN 3865) point.
JPG-images are available at
http://observ.pereplet.ru/images/GRB050824/2.jpg
This work is supported by RFFI 04-02-16411 grant.
This message can be cited.
Mailto: lipunov@sai.msu.ru
- GCN notice #3890
G. Crew, G. Ricker, J-L. Atteia, N. Kawai, D. Lamb, and S. Woosley, on
behalf of the HETE Science Team;
M. Arimoto, T. Donaghy, E. Fenimore, M. Galassi, C. Graziani,
J. Kotoku, M. Maetou, M. Matsuoka, Y. Nakagawa, T. Sakamoto, R. Sato,
Y. Shirasaki, M. Suzuki, T. Tamagawa, K. Tanaka, Y. Yamamoto,
and A. Yoshida, on behalf of the HETE WXM Team;
N. Butler, J. Doty, G. Prigozhin, R. Vanderspek, J. Villasenor,
J. G. Jernigan, A. Levine, G. Azzibrouck, J. Braga, R. Manchanda,
and G. Pizzichini, on behalf of the HETE Operations and HETE
Optical-SXC Teams;
M. Boer, J-F Olive, J-P Dezalay, and K. Hurley, on behalf of the HETE
FREGATE Team;
report:
The FREGATE instrument onboard HETE also detected the Swift burst GRB
050824 (Campana, et al., GCN 3866) as an untriggered event (U11648)
with a significance of 6 sigma. The direction to the burst source was
about 50 degrees from the instrument boresight, placing it outside the
WXM and SXC fields-of-view.
We have analyzed the spectrum of the event. A power-law (PL) fit to
the full FREGATE energy range (6-400 keV) yields a best-fit power-law
index of 2.35 +0.88/-0.48 (90% CL), consistent with the PL index
reported by the Swift BAT team (Krimm et al., GCN 3871). Assuming the
best-fit PL index, the value of the fluence ratio S(2-30)/S(30-400) is
2.7. GRB 050824 is thus an X-Ray Flash.
A PL fit restricted to photons with energy above 20 keV yields a
best-fit PL index of 3.29 +2.50/-1.36 (90% CL). This steepening of
the PL index suggests that the spectrum is representable by a Band
model with a value of E_peak near or below the low end of the FREGATE
energy range, so that the PL fit to the full energy range represents
an average of the contributions from the high- and low-energy parts of
the Band model.
Because of the low S/N of the event, a PL times exponential fit and a
Band-function fit are not statistically preferred over the simple PL
model. Nonetheless, in order to constrain E_peak, we have performed a
"constrained-Band model" analysis of the spectrum (see Sakamoto et al.,
ApJ 602, 875), and find E_peak < 12.7 keV (90% CL).
FREGATE light curve data and plots will be available soon at the
following URL: http://space.mit.edu/HETE/Bursts/U11648.
- GCN notice #3897
D. Sharapov, G. Abdullaeva, M. Ibrahimov (MAO), A.Pozanenko (IKI),
V.Rumyantsev (CrAO) on behalf of larger GRB follow up collaboration report:
We observed the field of OT (GCNs 3865, 3868, 3880) of GRB050824 (GCN
3866) with 1.5m telescope of Maidanak Astronomical Observatory. A set of R
images were taken between (UT) 21:27 - 22:01, on August 25.
We do not detect the OT in a stacked image. Based on USNO A2.0 nearby
stars we estimate limiting magnitude (3 sigma) of the stacked image (6x300
s) as R ~ 22.0. Detailed calibration of the stacked image is underway.
This message may be cited.
- GCN notice #3907
J. P. Halpern (Columbia U.) and N. Mirabal (U. Michigan) report on behalf of
the MDM Observatory GRB follow-up team:
"We observed the Swift GRB 050824 afterglow (Gorosabel et al., GCN #3865)
in the R band on five consecutive nights using the MDM 1.3m telescope.
Photometry was established using two Landolt standard-star fields on one
photometric night. From 5.6 to 12.6 hours, the decay is consistent with
a power law of index -0.55+/-0.05, which extrapolates well to the MASTER
photometry at 24 and 47 minutes (Lipunov et al., GCN #3883). This decay
index is similar to that seen in the Swift XRT light curve, -0.4+/-0.2
(Campana et al., CGN #3877), immediately preceding the MDM observations.
An unobserved inflection in the optical light curve then occurs, and from
1.3 to 4.4 days the decay index is -0.43+/-0.04. Our final measured point
is R=22.18+/-0.06 on Aug. 29.32.
Images and light curves are posted at
http://www.astro.columbia.edu/~jules/grb/050824/
This message may be cited."
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