Gamma-ray Burst 060923C

(All information courtesy of the instrument teams.)

Previous IAU Circulars

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Results of Observations

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 23 Sep 06 13:34:42 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     230711,   Seg_Num: 0
GRB_RA:          346.127d {+23h 04m 30s} (J2000),
                 346.212d {+23h 04m 51s} (current),
                 345.491d {+23h 01m 58s} (1950)
GRB_DEC:          +3.942d {+03d 56' 32"} (J2000),
                  +3.979d {+03d 58' 43"} (current),
                  +3.672d {+03d 40' 21"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       0 [cnts]    Image_Peak=1676 [image_cnts]
TRIGGER_DUR:     88.000 [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:        14001 TJD;   266 DOY;   06/09/23
GRB_TIME:        48782.53 SOD {13:33:02.53} UT
GRB_PHI:          65.47 [deg]
GRB_THETA:        36.88 [deg]
SOLN_STATUS:     0x13
RATE_SIGNIF:     0.00 [sigma]
IMAGE_SIGNIF:    11.45 [sigma]
MERIT_PARAMS:     +1  +0  +0  +6  +1  +1  +0  +0 +96  +1 
SUN_POSTN:       180.35d {+12h 01m 25s}   -0.15d {-00d 09' 13"}
SUN_DIST:        165.36 [deg]   Sun_angle= -11.1 [hr] (East of Sun)
MOON_POSTN:      190.60d {+12h 42m 23s}   -6.19d {-06d 11' 33"}
MOON_DIST:       155.62 [deg]
MOON_ILLUM:      1 [%]
GAL_COORDS:       79.10,-49.61 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      348.78,  9.10 [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.  
COMMENTS:        This trigger occurred at longitude,latitude = 153.99,11.15 [deg].

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 23 Sep 06 13:36:56 UT
NOTICE_TYPE:     Swift-XRT Image
TRIGGER_NUM:     230711,   Seg_Num: 0
GRB_RA:          346.1173d {+23h 04m 28.1s} (J2000),
                 346.2029d {+23h 04m 48.6s} (current),
                 345.4813d {+23h 01m 55.5s} (1950)
GRB_DEC:          +3.9251d {+03d 55' 30.3"} (J2000),
                  +3.9615d {+03d 57' 41.2"} (current),
                  +3.6552d {+03d 39' 18.7"} (1950)
GRB_ERROR:       5.4 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       41 [cnts]
IMG_START_DATE:  14001 TJD;   266 DOY;   06/09/23
IMG_START_TIME:  48985.95 SOD {13:36:25.95} UT,   203.4 [sec] since BAT Trigger Time
CENTROID_X:      259.05,  raw= 259  [pixels]
CENTROID_Y:      401.40,  raw= 401  [pixels]
ROLL:            284.55 [deg]
GAIN:            1
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   241.86
GRB_POS_XRT_Z:   -99.59
IMAGE_URL:       sw00230711000msxps_rw.img
SUN_POSTN:       180.36d {+12h 01m 25s}   -0.15d {-00d 09' 15"}
SUN_DIST:        165.36 [deg]   Sun_angle= -11.1 [hr] (East of Sun)
MOON_POSTN:      190.61d {+12h 42m 27s}   -6.20d {-06d 12' 05"}
MOON_DIST:       155.59 [deg]
MOON_ILLUM:      1 [%]
GAL_COORDS:       79.07,-49.62 [deg] galactic lon,lat of the burst
ECL_COORDS:      348.76,  9.09 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 23 Sep 06 13:36:58 UT
NOTICE_TYPE:     Swift-XRT Processed Image
TRIGGER_NUM:     230711,   Seg_Num: 0
GRB_RA:          346.1173d {+23h 04m 28.1s} (J2000),
                 346.2029d {+23h 04m 48.6s} (current),
                 345.4813d {+23h 01m 55.5s} (1950)
GRB_DEC:          +3.9251d {+03d 55' 30.3"} (J2000),
                  +3.9615d {+03d 57' 41.2"} (current),
                  +3.6552d {+03d 39' 18.7"} (1950)
GRB_ERROR:       5.4 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       41 [cnts]
IMG_START_DATE:  14001 TJD;   266 DOY;   06/09/23
IMG_START_TIME:  48985.95 SOD {13:36:25.95} UT,   203.4 [sec] since BAT Trigger Time
CENTROID_X:      259.05,  raw= 259  [pixels]
CENTROID_Y:      401.40,  raw= 401  [pixels]
ROLL:            284.55 [deg]
GAIN:            1
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   241.86
GRB_POS_XRT_Z:   -99.59
IMAGE_URL:       sw00230711000msxps_rw.img
SUN_POSTN:       180.36d {+12h 01m 25s}   -0.15d {-00d 09' 15"}
SUN_DIST:        165.35 [deg]   Sun_angle= -11.1 [hr] (East of Sun)
MOON_POSTN:      190.61d {+12h 42m 27s}   -6.20d {-06d 12' 05"}
MOON_DIST:       155.59 [deg]
MOON_ILLUM:      1 [%]
GAL_COORDS:       79.07,-49.62 [deg] galactic lon,lat of the burst
ECL_COORDS:      348.76,  9.09 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Processed Image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 23 Sep 06 13:37:27 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     230711,   Seg_Num: 0
GRB_RA:          346.127d {+23h 04m 30s} (J2000),
                 346.212d {+23h 04m 51s} (current),
                 345.491d {+23h 01m 58s} (1950)
GRB_DEC:          +3.942d {+03d 56' 32"} (J2000),
                  +3.979d {+03d 58' 43"} (current),
                  +3.672d {+03d 40' 21"} (1950)
GRB_DATE:        14001 TJD;   266 DOY;   06/09/23
GRB_TIME:        48782.53 SOD {13:33:02.53} UT
TRIGGER_INDEX:   20000
GRB_PHI:          65.47 [deg]
GRB_THETA:        36.88 [deg]
DELTA_TIME:      0.00 [sec]
TRIGGER_DUR:     88.000 [sec] 
SOLN_STATUS:     0x13
RATE_SIGNIF:     0.00 [sigma]
IMAGE_SIGNIF:    11.45 [sigma]
LC_URL:          sw00230711000msb.lc
SUN_POSTN:       180.36d {+12h 01m 26s}   -0.15d {-00d 09' 15"}
SUN_DIST:        165.36 [deg]   Sun_angle= -11.1 [hr] (East of Sun)
MOON_POSTN:      190.62d {+12h 42m 28s}   -6.20d {-06d 12' 12"}
MOON_DIST:       155.59 [deg]
MOON_ILLUM:      1 [%]
GAL_COORDS:       79.10,-49.61 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      348.78,  9.10 [deg] ecliptic lon,lat of the burst (or transient)
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.  
COMMENTS:        This trigger occurred at longitude,latitude = 153.99,11.15 [deg].

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 23 Sep 06 13:36:55 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     230711,   Seg_Num: 0
GRB_RA:          346.1173d {+23h 04m 28.1s} (J2000),
                 346.2029d {+23h 04m 48.6s} (current),
                 345.4813d {+23h 01m 55.5s} (1950)
GRB_DEC:          +3.9251d {+03d 55' 30.3"} (J2000),
                  +3.9615d {+03d 57' 41.2"} (current),
                  +3.6552d {+03d 39' 18.7"} (1950)
GRB_ERROR:       5.4 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       8.46e-10 [erg/cm2/sec]
GRB_SIGNIF:      6.40 [sigma]
IMG_START_DATE:  14001 TJD;   266 DOY;   06/09/23
IMG_START_TIME:  48985.95 SOD {13:36:25.95} UT,   203.4 [sec] since BAT Trigger Time
TAM[0-3]:        327.65 237.18 261.31 243.35
AMPLIFIER:       2
WAVEFORM:        134
SUN_POSTN:       180.36d {+12h 01m 25s}   -0.15d {-00d 09' 15"}
SUN_DIST:        165.36 [deg]   Sun_angle= -11.1 [hr] (East of Sun)
MOON_POSTN:      190.61d {+12h 42m 27s}   -6.20d {-06d 12' 04"}
MOON_DIST:       155.59 [deg]
MOON_ILLUM:      1 [%]
GAL_COORDS:       79.07,-49.62 [deg] galactic lon,lat of the burst
ECL_COORDS:      348.76,  9.09 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.

GCN Circular #5591
M. Stamatikos (NASA/ORAU), S. D. Barthelmy (GSFC), D. N. Burrows (PSU), M. Capalbi (ASDC), M.L. Conciatore (ASDC), C. Guidorzi (Univ Bicocca&INAF-OAB), S. T. Holland (GSFC/USRA), J. A. Kennea (PSU), F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL), M. Perri (ASDC), T. Sakamoto (NASA/ORAU), D. E. Vanden Berk (PSU) and H. Ziaeepour (UCL-MSSL) report on behalf of the Swift Team:
At 13:33:02 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 060923C (trigger=230711). Swift slewed immediately to the burst. The BAT on-board calculated location is RA,Dec 346.127, +3.942 {23h 04m 30s, +03d 56' 32"} (J2000) with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). This is an image-trigger (88 sec), and as such, the BAT TDRSS lightcurve does not show significant activity.
The XRT began observing the field at 13:36:25 UT, 203 seconds after the BAT trigger. XRT found a bright, fading, uncatalogued X-ray source located at RA(J2000) = 23h 04m 28.1s, Dec(J2000) = +03d 55' 30.3", with an estimated uncertainty of 8.1 arcseconds (90% confidence radius). This location is 70 arcseconds from the BAT on-board position, within the BAT error circle. The initial flux in the 2.5s image was 8.5e-10 erg/cm2/s (0.2-10 keV).
There is a 4th magnitude star 12 arcmin from the XRT error circle. Therefore, UVOT will not and can not observe this burst.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 23 Sep 06 13:55:52 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     230711,   Seg_Num: 0
GRB_RA:          346.1195d {+23h 04m 28.6s} (J2000),
                 346.2051d {+23h 04m 49.2s} (current),
                 345.4835d {+23h 01m 56.0s} (1950)
GRB_DEC:          +3.9264d {+03d 55' 35.0"} (J2000),
                  +3.9628d {+03d 57' 45.9"} (current),
                  +3.6565d {+03d 39' 23.4"} (1950)
GRB_ERROR:       6.1 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       2.50e-11 [erg/cm2/sec]
GRB_SIGNIF:      5.00 [sigma]
IMG_START_DATE:  14001 TJD;   266 DOY;   06/09/23
IMG_START_TIME:  48985.94 SOD {13:36:25.94} UT,   203.4 [sec] since BAT Trigger Time
TAM[0-3]:        327.61 237.19 261.35 242.66
AMPLIFIER:       2
WAVEFORM:        134
SUN_POSTN:       180.37d {+12h 01m 28s}   -0.16d {-00d 09' 33"}
SUN_DIST:        165.35 [deg]   Sun_angle= -11.1 [hr] (East of Sun)
MOON_POSTN:      190.75d {+12h 43m 00s}   -6.28d {-06d 16' 30"}
MOON_DIST:       155.45 [deg]
MOON_ILLUM:      1 [%]
GAL_COORDS:       79.08,-49.62 [deg] galactic lon,lat of the burst
ECL_COORDS:      348.77,  9.09 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        TAM values are not valid.

GCN Circular #5592
K. Torii (Osaka U.) reports on behalf of the ART collaboration:
The error region of GRB 060923C (Stamatikos et al. GCN 5591) was observed with the ART-3 telescopes in Toyonaka, Osaka.
Preliminary analysis does not reveal an optical afterglow candidate brighter than R~15 at 6 minutes after the trigger.
GCN Circular #5593
A. Gomboc (University of Ljubljana), C. Guidorzi (Univ Bicocca & INAF-OAB), A. Melandri, I.A. Steele, R.J. Smith, C.G. Mundell, A. Monfardini, D. Carter, S. Kobayashi, D. Bersier, M. Bode (Liverpool JMU), P. O'Brien, E. Rol, N. Bannister (Leicester) report:
The 2m Faulkes North Telescope (Hawaii) automatically reacted to the Swift burst GRB060923C (trigger 230711, Stamatikos et al. GCN 5591).
Observations started about 4.2 min after the trigger time and were performed in R and i' bands. From the stacked images we do not detect any new source down to:
```
Filter  Start(min from GRB)   End(min from GRB)   TotExp(s)      Lim
---------------------------------------------------------------------
R       4.22                   20.00                220          19.0
i'      6.52                   22.70                220          17.5
----------------------------------------------------------------------
```
GCN Circular #5594
A. Melandri (Liverpool JMU), C. Guidorzi (Univ Bicocca & INAF-OAB), A. Gomboc (University of Ljubljana), I.A. Steele, R.J. Smith, C.G. Mundell, A. Monfardini, D. Carter, S. Kobayashi, D. Bersier, M. Bode (Liverpool JMU), P. O'Brien, E. Rol, N. Bannister (Leicester) report:
The 2m Faulkes Telescope South (Siding Spring, Australia) automatically reacted to the Swift burst GRB 060923C (trigger 230711, Stamatikos et al., GCN 5591).
Observations were performed in the R-band. From t=19.38 min to t=20.27 min (after the burst event) a 3x10s stacked image gives a limiting magnitude R > 19.5 inside the XRT error circle (Stamatikos et al. GCN 5591).
This message can be cited.
GCN Circular #5596
M.Zhai, L.P. Xing, Y.L. Qiu, J.Y. Wei, J.Y. Hu, J.S. Deng and W.K. Zheng on behalf of EAFON report:
We have imaged the field of GRB 060923C with the TNT 0.8m telescope at Xinglong Observatory.The first image was taken at 13:36:37 UT, 215s after the burst. A series of White and R band images were obtained. No new source were detected in our combined images down to:
```
Filter Mid_Time(s)  3 sigma limit
---------------------------------
White    487          19.2
 R        1210          20.0
```
This message may be cited.
GCN Circular #5598
A. Rau (Caltech), E.O. Ofek (Caltech) and D.B. Fox (Penn State) report on behalf of a larger collaboration:
We imaged the position of GRB060923C (Stamatikos et al., GCN 5591) on UT 2006 Sep 23.58 (30 minutes post trigger) with the Low Resolution Imager and Spectrograph at Keck-I. Observations were performed at high airmass (3.1).
Within the XRT error circle, we detect a single point-like object, with I~21 mag, at coordinates:
R.A. 23:04:28.4, Dec. +03:55:29 (J2000)
We note that this source is marginally detected in the Palomar Optical Sky Survey (DSS) at a similar brightness.
GCN Circular #5600
S. D. Barthelmy (GSFC), L. Barbier (GSFC), J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), D. Hullinger (BYU-Idaho), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC) on behalf of the Swift-BAT team:
Using a partial data set from T-119 to T+183 sec from recent telemetry downlinks, we report further analysis of BAT GRB 060923C (trigger #230711) (Stamatikos, et al., GCN Circ. 5591). The BAT ground-calculated position is RA,Dec = 346.123, 3.963 deg {23h 4m 29.4s, 3d 57' 47.4"} (J2000) +- 2.2 arcmin, (radius, sys+stat, 90% containment). The partial coding was 17%.
With only a partial data set downlinked (there is a gap in the data between T+51 to +62 sec), the mask-weighted lightcurve has a single long emision from T+0 to T+110 sec.
The lower limit to the fluence in the 15-150 keV band is 1.3 +- 0.2 x 10^-6 erg/cm2. We repeat that there is an 11-sec gap in the data in the middle of this burst used for this analysis.
When the full data set is downlinked, we will report the usual numbers.
GCN Circular #5601
M. Perri, M. Capalbi, M.L. Conciatore (ASDC), D.N. Burrows (PSU) and M. Stamatikos (NASA/ORAU) report on behalf of the Swift XRT team:
We have analysed the first four orbits of Swift XRT data on the BAT GRB 060923C (Stamatikos, et al., GCN Circ. 5591). A 5.5 ks Photon Counting mode image provides a refined XRT position:
```
RA(J2000)  =  23h 04m 28.49s
Dec(J2000) = +03d 55' 26.6"
```
with an uncertainty of 5.9" (90% containment). This is 2.4' away from the center of the BAT refined position (Barthelmy et al., GCN Circ. 5600) and 6.9" away from the first XRT position quoted in GCN Circ. 5591 (Stamatikos, et al.). This position lies 2.8" from the object reported by Rau et al. (GCN Circ. 5598).
The 0.3-10 keV X-ray light curve from T+212 s to T+13 ks can be fit by a broken power law model with temporal break at T+780s (+/-120s) and decay indices -3.4 (+/-0.2) and -0.6 (+/-0.2) before and after the break, respectively.
The X-ray spectrum covering the time period from T+212s to T+275s is well fit by an absorbed power-law with a photon index of 1.85 (+/-0.13) and a column density consistent with the Galactic value in the direction of the burst (5.3e20 cm**-2).
Assuming the X-ray emission continues to decline at the same rate, we predict a 0.3-10 keV XRT count rate of ~0.01 count/s at T+24hr, which corresponds to an observed 0.3-10 keV flux of ~5e-13 erg/cm**2/s.
This circular is an official product of the Swift XRT Team.
GCN Circular #5604
Stefano Covino (INAF/OABr), Daniele Malesani (SISSA/ISAS), and Gianpiero Tagliaferri (INAF/OABr), report on behalf of the MISTICI collaboration:
We imaged the field of GRB 060923C (Stamatikos et al., GCN 5591) on 2006 Sep 24 from 3:39 to 4:16 UT with the ESO VLT+ISAAC in the J band under good seeing conditions.
Within the refined XRT error circle (Perri et al., GCN 5601) we detect three sources with the following positions (RA, DEC, J2000) and magnitudes:
```
    A:    23:04:28.40, +03:55:29.1    19.23 +- 0.03
    B:    23:04:28.31, +03:55:29.0    22.87 +- 0.12
    C:    23:04:28.18, +03:55:28.5    21.33 +- 0.07
```
Source C could be extended. Absolute magnitudes are calibrated with respect to two 2MASS stars in the field. The reported errors are only statistical; the absolute calibration error may be of the order of ~0.15 mag. At this stage, we cannot say whether any of these sources is related to GRB 060923C. A finding chart is posted at the followin URL:
http://www.sissa.it/~malesani/GRB/060923C/finder_ISAAC.jpg
Source A has been reported by Rau et al. (GCN 5598) and could also be marginally visible in the DSS.
We acknowledge support from the ESO observing staff at Paranal, in particular Christophe Dumas and Emmanuel Jehin.
This message may be cited.
GCN Circular #5606
S.Maeno, E.Sonoda, M.Yamauchi (University of Miyazaki)
We have observed the field covering the error circle of GRB 060923C (GCN 5591) with the unfiltered CCD camera on the 30-cm telescope at University of Miyazaki. The observation was started 15:01:30 UT on Sep. 23.
We have compared our data of 30 sec exposures with the USNO-A2.0 catalog, there is no new source at the position reported by GCN 5591.
```
The upper limit is as follows:
--------------------------------------------------------------
Start(UT)	End(UT)	    Num. of frames	Limit (mag.)	
--------------------------------------------------------------
15:01:30	15:32:39	17		~17.5
---------------------------------------------------------------
```
GCN Circular #5607
D.B. Fox (Penn State) reports on behalf of a larger collaboration:
"We have imaged the XRT position of GRB060923C (Stamtikos et al., GCN 5591) in the K-band with Gemini-North + NIRI on two occasions with mean epochs of 05:39 UT and 08:34 UT, respectively, on 24 Sep 2006. We detect the (I-band) source of Rau et al. (GCN 5598; hereafter source "A") as well the additional (J-band) sources "B" and "C" of Covino et al. (GCN 5604). At both epochs, these are the only sources consistent with the XRT localization.
Although we lack an absolute photometric calibration at this time, we observe a relative decline of Source B by ~0.4 mag in K-band between these two epochs. The magnitudes of Sources A and C are not observed to vary, being consistent across our two epochs to within 0.1 mag.
Noting as well the indication for Source A in the DSS (GCN 5598), and that Source C is clearly extended in our images, we suggest that Source B is the afterglow of GRB060923C. In this case, the absence of detectable afterglow light in the early Keck+LRIS I-band images may indicate a high-redshift origin or high line-of-sight extinction for this burst."
GCN Circular #5608
T.Uehara, I.Takahashi, K.Yoshida, A.Kobayashi, D.Oyamada, Y.E.Nakagawa, S.Sugita, K.Yamaoka, A.Yoshida (AGU) report:
We have observed the feild of GRB060923C (Stamatikos et al. GCN 5591) from 13:35:46 (UT) with 0.3m AROMA robotic telescope with R-band filter at Aoyama Gakuin University.
Although the weather condition was not good, we have taken 60 frames of image with 20s exposure each. The photometric calibration was made by first 5 and every 20 frames by comparing with USNO A2.0 stars in the same field. No new source was found. The 3 sigma limiting magnitude of each combined image is as below.
```
number       mean           time since     limiting magnitude
of frames    time (UT)      GRB (s)        in R (3 sigma)
========================================================================
5            13:36:39          217                 15.4
20           13:40:20          436                 15.8
20           13:54:06          1264                16.8
20           14:10:26          2244                17.5
```
GCN Circular #5609
Paolo D'Avanzo (INAF-OABr), Stefano Covino (INAF-OABr), Daniele Malesani (SISSA/ISAS), and Gianpiero Tagliaferri (INAF-OABr), report on behalf of the MISTICI collaboration:
We imaged again the field of GRB 060923C (Stamatikos et al., GCN 5591) on 2006 Sep 25 from 0:51 to 1:36 UT with the ESO VLT+ISAAC in the J band. Seeing conditions were comparable to our previous observation (Covino et al., GCN 5604).
With respect to the first epoch of imaging, we detect sources A and C, with the same brightness. Source B has faded significantly and is barely detectable. Image subtraction performed with ISIS also confirms the fading.
We therefore fully confirm the identification by Fox (GCN 5607) of source B as the afterglow of GRB 060923C.
We acknowledge support from the ESO observing staff at Paranal.
This message may be cited.
GCN Circular #5610
P. Chandra (UVA/NRAO) and D. A. Frail (NRAO) report on behalf of the Caltech-NRAO-Carnegie GRB Collaboration:
"We observed the field centered on the BAT position of the Swift burst GRB 060923C (GCN#5591) using the VLA at a frequency of 8.46 GHz and starting at 6.02 UT on Sept 25, about 2 days after the burst. There is no detection of the GRB with 2-sigma upper limit of 100 microJy.
The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc."
GCN Circular #5611
T. Sakamoto (GSFC/ORAU), L. Barbier (GSFC), S. D. Barthelmy (GSFC), J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), D. Hullinger (BYU-Idaho), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC) on behalf of the Swift-BAT team:
Using the data set from T-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 060923 (trigger #230711) (Stamatikos, et al., GCN Circ. 5591; Barthelmy, et al., GCN Circ 5600). The BAT ground-calculated position is RA,Dec = 346.122, 3.943 deg {23h 4m 29.3s, 3d 56' 33.8"} (J2000) +- 2.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 17%.
The mask-weighted lightcurve has a single long emision from T+0 to T+110 sec. T90 (15-350 keV) is 76 +- 2 sec (estimated error including systematics). The long duration and smooth profile of the lightcurve suggest, but do not prove, that this is a high redshift burst.
The time-averaged spectrum from T+6.8 to T+90.7 is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.27 +- 0.24. The fluence in the 15-150 keV band is 1.6 +- 0.2 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T+27.54 sec in the 15-150 keV band is 1.0 +- 0.4 ph/cm2/sec. All the quoted errors are at the 90% confidence level.
GCN Circular #5648
G. Kornienko, A. Erofeeva (UAPhO), A.Pozanenko (IKI), V.Rumyantsev (CrAO) on behalf of larger GRB follow up collaboration report:
We observed the error box of GRB060923C (Stamatikos et al., GCN 5591) with 0.4m telescope of Ussuriysk Astrophysical Observatory in R-band starting Sep.23 (UT) 13:51:55. We do not detect the optical transient detected by Fox (GCN 5607). Upper limits of the first image (exposure 60 s) and combined image (exp. 10x60 s) are based on USNOA2.0:
```
Mid time,    Exposure,   Limiting mag (3 sigma)
(UT)           (s)

Sep. 23.5781     1x60        16.0
Sep. 23.5829    10x60        17.3
```
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Jochen Greiner, last update: 28-Sep-2006 [Disclaimer]