Gamma-ray Burst 081028

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Tue 28 Oct 08 00:27:24 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     332851,   Seg_Num: 0
GRB_RA:          121.890d {+08h 07m 34s} (J2000),
                 122.005d {+08h 08m 01s} (current),
                 121.240d {+08h 04m 58s} (1950)
GRB_DEC:          +2.311d {+02d 18' 40"} (J2000),
                  +2.285d {+02d 17' 06"} (current),
                  +2.457d {+02d 27' 25"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       0 [cnts]    Image_Peak=6719 [image_cnts]
TRIGGER_DUR:     128.000 [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:        14767 TJD;   302 DOY;   08/10/28
GRB_TIME:        1500.79 SOD {00:25:00.79} UT
GRB_PHI:          25.47 [deg]
GRB_THETA:        21.20 [deg]
SOLN_STATUS:     0x13
RATE_SIGNIF:     0.00 [sigma]
IMAGE_SIGNIF:    17.95 [sigma]
MERIT_PARAMS:     +1  +0  +0  +7  +1  +5  +0  +0  +1  +0 
SUN_POSTN:       212.68d {+14h 10m 43s}  -13.17d {-13d 10' 25"}
SUN_DIST:         91.18 [deg]   Sun_angle= 6.0 [hr] (West of Sun)
MOON_POSTN:      200.49d {+13h 21m 57s}  -13.69d {-13d 41' 29"}
MOON_DIST:        79.38 [deg]
MOON_ILLUM:      1 [%]
GAL_COORDS:      219.73, 17.96 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      123.60,-17.49 [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 = 119.48,4.65 [deg].

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Tue 28 Oct 08 00:28:53 UT
NOTICE_TYPE:     Swift-XRT Image
TRIGGER_NUM:     332851,   Seg_Num: 0
GRB_RA:          121.8953d {+08h 07m 34.8s} (J2000),
                 122.0100d {+08h 08m 02.4s} (current),
                 121.2449d {+08h 04m 58.7s} (1950)
GRB_DEC:          +2.3086d {+02d 18' 30.9"} (J2000),
                  +2.2826d {+02d 16' 57.3"} (current),
                  +2.4544d {+02d 27' 15.6"} (1950)
GRB_ERROR:       4.7 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       132 [cnts]
IMG_START_DATE:  14767 TJD;   302 DOY;   08/10/28
IMG_START_TIME:  1691.47 SOD {00:28:11.47} UT,   190.7 [sec] since BAT Trigger Time
CENTROID_X:      300.43,  raw= 300  [pixels]
CENTROID_Y:      294.22,  raw= 294  [pixels]
ROLL:            103.16 [deg]
GAIN:            2
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   -8.90
GRB_POS_XRT_Z:   -4.40
IMAGE_URL:       sw00332851000msxps_rw.img
SUN_POSTN:       212.68d {+14h 10m 43s}  -13.17d {-13d 10' 26"}
SUN_DIST:         91.17 [deg]   Sun_angle= 6.0 [hr] (West of Sun)
MOON_POSTN:      200.50d {+13h 22m 00s}  -13.70d {-13d 41' 48"}
MOON_DIST:        79.38 [deg]
MOON_ILLUM:      1 [%]
GAL_COORDS:      219.74, 17.96 [deg] galactic lon,lat of the burst
ECL_COORDS:      123.61,-17.49 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Tue 28 Oct 08 00:29:01 UT
NOTICE_TYPE:     Swift-XRT Processed Image
TRIGGER_NUM:     332851,   Seg_Num: 0
GRB_RA:          121.8953d {+08h 07m 34.8s} (J2000),
                 122.0100d {+08h 08m 02.4s} (current),
                 121.2449d {+08h 04m 58.7s} (1950)
GRB_DEC:          +2.3086d {+02d 18' 30.9"} (J2000),
                  +2.2826d {+02d 16' 57.3"} (current),
                  +2.4544d {+02d 27' 15.6"} (1950)
GRB_ERROR:       4.7 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       132 [cnts]
IMG_START_DATE:  14767 TJD;   302 DOY;   08/10/28
IMG_START_TIME:  1691.47 SOD {00:28:11.47} UT,   190.7 [sec] since BAT Trigger Time
CENTROID_X:      300.43,  raw= 300  [pixels]
CENTROID_Y:      294.22,  raw= 294  [pixels]
ROLL:            103.16 [deg]
GAIN:            2
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   -8.90
GRB_POS_XRT_Z:   -4.40
IMAGE_URL:       sw00332851000msxps_rw.img
SUN_POSTN:       212.68d {+14h 10m 43s}  -13.17d {-13d 10' 26"}
SUN_DIST:         91.17 [deg]   Sun_angle= 6.0 [hr] (West of Sun)
MOON_POSTN:      200.50d {+13h 22m 00s}  -13.70d {-13d 41' 49"}
MOON_DIST:        79.38 [deg]
MOON_ILLUM:      1 [%]
GAL_COORDS:      219.74, 17.96 [deg] galactic lon,lat of the burst
ECL_COORDS:      123.61,-17.49 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Processed Image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Tue 28 Oct 08 00:28:43 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     332851,   Seg_Num: 0
GRB_RA:          121.8953d {+08h 07m 34.87s} (J2000),
                 122.0100d {+08h 08m 02.40s} (current),
                 121.2449d {+08h 04m 58.77s} (1950)
GRB_DEC:          +2.3086d {+02d 18' 30.9"} (J2000),
                  +2.2826d {+02d 16' 57.3"} (current),
                  +2.4544d {+02d 27' 15.6"} (1950)
GRB_ERROR:       4.8 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       5.50e-09 [erg/cm2/sec]
GRB_SIGNIF:      11.48 [sigma]
IMG_START_DATE:  14767 TJD;   302 DOY;   08/10/28
IMG_START_TIME:  1691.47 SOD {00:28:11.47} UT,   190.7 [sec] since BAT Trigger Time
TAM[0-3]:        327.64 237.21 261.41 243.58
AMPLIFIER:       2
WAVEFORM:        134
SUN_POSTN:       212.68d {+14h 10m 43s}  -13.17d {-13d 10' 26"}
SUN_DIST:         91.17 [deg]   Sun_angle= 6.0 [hr] (West of Sun)
MOON_POSTN:      200.50d {+13h 22m 00s}  -13.70d {-13d 41' 46"}
MOON_DIST:        79.38 [deg]
MOON_ILLUM:      1 [%]
GAL_COORDS:      219.74, 17.96 [deg] galactic lon,lat of the burst
ECL_COORDS:      123.61,-17.49 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        The XRT position is 0.34 arcmin from the BAT position.  
COMMENTS:        The object found at this position is either a very bright burst or a cosmic ray hit.  
COMMENTS:        Examine the XRT Image to differentiate (CRs are much more compact); see examples at:  
COMMENTS:        http://www.swift.psu.edu/xrt/XRT_Postage_Stamp_Image_Photo_Gallery.htm .

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Tue 28 Oct 08 00:30:03 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     332851,   Seg_Num: 0
GRB_RA:          121.890d {+08h 07m 34s} (J2000),
                 122.005d {+08h 08m 01s} (current),
                 121.240d {+08h 04m 58s} (1950)
GRB_DEC:          +2.311d {+02d 18' 40"} (J2000),
                  +2.285d {+02d 17' 06"} (current),
                  +2.457d {+02d 27' 25"} (1950)
GRB_DATE:        14767 TJD;   302 DOY;   08/10/28
GRB_TIME:        1500.79 SOD {00:25:00.79} UT
TRIGGER_INDEX:   20000
GRB_PHI:          25.47 [deg]
GRB_THETA:        21.20 [deg]
DELTA_TIME:      0.00 [sec]
TRIGGER_DUR:     128.000 [sec] 
SOLN_STATUS:     0x13
RATE_SIGNIF:     0.00 [sigma]
IMAGE_SIGNIF:    17.95 [sigma]
LC_URL:          sw00332851000msb.lc
SUN_POSTN:       212.68d {+14h 10m 43s}  -13.17d {-13d 10' 27"}
SUN_DIST:         91.18 [deg]   Sun_angle= 6.0 [hr] (West of Sun)
MOON_POSTN:      200.51d {+13h 22m 03s}  -13.70d {-13d 42' 02"}
MOON_DIST:        79.40 [deg]
MOON_ILLUM:      1 [%]
GAL_COORDS:      219.73, 17.96 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      123.60,-17.49 [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 = 119.48,4.65 [deg].

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Tue 28 Oct 08 00:31:57 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     332851,   Seg_Num: 0
POINT_RA:        121.895d {+08h 07m 35s} (J2000)
POINT_DEC:        +2.311d {+02d 18' 38"} (J2000)
POINT_ROLL:      103.157d
IMG_START_DATE:  14767 TJD;   302 DOY;   08/10/28
IMG_START_TIME:  1701.11 SOD {00:28:21.11} UT,   200.3 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        4.706
N_STARS:         95
X_OFFSET:        456 [pixels]
Y_OFFSET:        584 [pixels]
X_MAX:           1415 [pixels]
Y_MAX:           1543 [pixels]
DET_THRESH:      18
PHOTO_THRESH:    10
SL_URL:          sw00332851000msufc0200.fits
SUN_POSTN:       212.68d {+14h 10m 43s}  -13.17d {-13d 10' 29"}
SUN_DIST:         91.17 [deg]   Sun_angle= 6.1 [hr] (West of Sun)
MOON_POSTN:      200.53d {+13h 22m 06s}  -13.71d {-13d 42' 26"}
MOON_DIST:        79.41 [deg]
MOON_ILLUM:      1 [%]
GAL_COORDS:      219.74, 17.96 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      123.61,-17.48 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Tue 28 Oct 08 00:32:37 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     332851,   Seg_Num: 0
POINT_RA:        121.895d {+08h 07m 35s} (J2000)
POINT_DEC:        +2.311d {+02d 18' 38"} (J2000)
POINT_ROLL:      103.157d
IMG_START_DATE:  14767 TJD;   302 DOY;   08/10/28
IMG_START_TIME:  1701.11 SOD {00:28:21.11} UT,   200.3 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        4.706
N_STARS:         95
X_OFFSET:        456 [pixels]
Y_OFFSET:        584 [pixels]
X_MAX:           1415 [pixels]
Y_MAX:           1543 [pixels]
DET_THRESH:      18
PHOTO_THRESH:    10
SL_URL:          sw00332851000msufc0200.fits
SUN_POSTN:       212.68d {+14h 10m 43s}  -13.18d {-13d 10' 29"}
SUN_DIST:         91.17 [deg]   Sun_angle= 6.1 [hr] (West of Sun)
MOON_POSTN:      200.53d {+13h 22m 08s}  -13.71d {-13d 42' 34"}
MOON_DIST:        79.41 [deg]
MOON_ILLUM:      1 [%]
GAL_COORDS:      219.74, 17.96 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      123.61,-17.48 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Source List.  
COMMENTS:        All 4 attachments are included.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Tue 28 Oct 08 00:33:29 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     332851,   Seg_Num: 0
POINT_RA:        121.895d {+08h 07m 35s} (J2000)
POINT_DEC:        +2.311d {+02d 18' 38"} (J2000)
ROLL:            103.157d
IMG_START_DATE:  14767 TJD;   302 DOY;   08/10/28
IMG_START_TIME:  1701.11 SOD {00:28:21.11} UT,   200.3 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     246846504
X_OFFSET:        815 [pixels]
Y_OFFSET:        899 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       975
Y_GRB_POS:       1059
BINNING_INDEX:   1
IM_URL:          sw00332851000msuni0200.fits
SUN_POSTN:       212.68d {+14h 10m 44s}  -13.18d {-13d 10' 30"}
SUN_DIST:         91.17 [deg]   Sun_angle= 6.1 [hr] (West of Sun)
MOON_POSTN:      200.54d {+13h 22m 09s}  -13.71d {-13d 42' 45"}
MOON_DIST:        79.42 [deg]
MOON_ILLUM:      1 [%]
GAL_COORDS:      219.74, 17.96 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      123.61,-17.48 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Image.  
COMMENTS:        The GRB Position came from the XRT Position Command.  
COMMENTS:        The image has 2x2 binning (compression).

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Tue 28 Oct 08 00:33:54 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     332851,   Seg_Num: 0
POINT_RA:        121.895d {+08h 07m 35s} (J2000)
POINT_DEC:        +2.311d {+02d 18' 38"} (J2000)
ROLL:            103.157d
IMG_START_DATE:  14767 TJD;   302 DOY;   08/10/28
IMG_START_TIME:  1701.11 SOD {00:28:21.11} UT,   200.3 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     246846504
X_OFFSET:        815 [pixels]
Y_OFFSET:        899 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       975
Y_GRB_POS:       1059
BINNING_INDEX:   1
IM_URL:          sw00332851000msuni0200.fits
SUN_POSTN:       212.68d {+14h 10m 44s}  -13.18d {-13d 10' 30"}
SUN_DIST:         91.17 [deg]   Sun_angle= 6.1 [hr] (West of Sun)
MOON_POSTN:      200.54d {+13h 22m 10s}  -13.71d {-13d 42' 50"}
MOON_DIST:        79.42 [deg]
MOON_ILLUM:      1 [%]
GAL_COORDS:      219.74, 17.96 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      123.61,-17.48 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Image.  
COMMENTS:        The GRB Position came from the XRT Position Command.  
COMMENTS:        The image has 2x2 binning (compression).  
COMMENTS:        If you have elected to receive attachments:  
COMMENTS:        The uvot_sources_image.fits.gz file does not exist; skipping the attachment.

GCN Circular #8421
C. Guidorzi (INAF-OAB), W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester), J. R. Cummings (NASA/UMBC), N. Gehrels (NASA/GSFC), S. T. Holland (CRESST/USRA/GSFC), E. A. Hoversten (PSU), K. L. Page (U Leicester), D. M. Palmer (LANL), T. Sakamoto (NASA/UMBC), M. Stamatikos (NASA/ORAU) and T. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team:
At 00:25:00 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 081028 (trigger=332851). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 121.890, +2.311 which is
```
   RA(J2000) = 08h 07m 34s
   Dec(J2000) = +02d 18' 40"
```
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). Although this is a BAT image trigger, the BAT light curve showed at least two slowly rising and falling peak structure with a duration of about 250 sec. The peak count rate of the first peak was ~600 counts/sec (15-350 keV), at ~70 sec after the trigger. The second peak was comparable in size peaking at ~210 sec.
The XRT began observing the field at 00:28:11.5 UT, 190.7 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 121.8953, +2.3086 which is equivalent to:
```
   RA(J2000)  = 08h 07m 34.87s
   Dec(J2000) = +02d 18' 30.9"
```
with an uncertainty of 4.8 arcseconds (radius, 90% containment). This location is 20 arcseconds from the BAT onboard position, within the BAT error circle. No event data are yet available to determine the column density using X-ray spectroscopy.
The initial flux in the 2.5 s image was 5.50e-09 erg cm^-2 s^-1 (0.2-10 keV).
UVOT took a finding chart exposure of nominal 150 seconds with the White (160-650 nm) filter starting 200 seconds after the BAT trigger. No afterglow candidate has been found in the initial data products. Image catalog data are not available at this time. 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 0.03.
Burst Advocate for this burst is C. Guidorzi (cristiano.guidorzi AT brera.inaf.it). 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/too.html.)
GCN Circular #8424
C. Clemens, S. Loew and J. Greiner (all MPE Garching) report on behalf of the GROND team:
We observed the field of GRB 081028 (Swift trigger 332851; Guidorzi et al., GCN #8421) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2 m ESO/MPI telescope at La Silla Observatory (Chile).
Observations started at 06:19 UT on October 28th, 2008, 5.8 hr after the GRB trigger, and are continuing. They were performed at an average seeing of 1.4" and at an average airmass of 2.4.
We found a single point source within the 4.8" Swift-XRT error circle reported by Guidorzi et al. (GCN #8421) at
```
RA (J2000.0) = 08h 07m 34.73s
DEC (J2000.0) = +02d 18' 29.1''
```
with an uncertainty of 0.5".
Based on the first 4.4 min of total exposures in g'r'i'z' and 4.0 min in JHK, we estimate preliminary magnitudes (all in AB system) of
```
g' ~ 19.9 mag,
r' ~ 19.3 mag,
i' ~ 19.2 mag,
z' ~ 19.1 mag,
J ~ 19.0 mag,
H ~ 18.7 mag and
K ~ 19.0 mag
```
with typical errors of +/- 0.1 in g'r'i'z' and +/- 0.15 in JHK. Given magnitudes are calibrated against SDSS as well as 2MASS field stars.
The object is seen in g' band, implying a redshift smaller than 3.5 and no statement about variability can be made at this point.
Please note, that no correction for the Galactic foreground extinction corresponding to a reddening of E_(B-V)= 0.03 mag in the direction of the burst (Schlegel et al. 1998) has been applied.
GCN Circular #8425
G. Olofsson (Stockholm), Johan P. U. Fynbo (DARK/NBI), and P. Jakobsson (Univ. Iceland) report:
We observed the field of GRB 081028 (Guidorzi et al., GCN 8421) with the NOT equipped with PolCor. Observations started on 2008 Oct 28, around 6 UT (more accurate information will follow).
At a position consistent with the X-ray error circle, we detect a bright object at the following coordinates:
```
RA(J2000) = 08:07:34.721
Dec(J2000) = +02:18:29.03
```
Given the small field of view, only four stars are available for astrometry. Assuming R = 15.7 for the USNO star at RA=08:07:33.70, Dec = +02:18:39.9, we compute R ~ 19.2 for the afterglow.
Our astrometry and photometry are consistent with those reported by Clemens et al. (GCN 8424). The object is not visible in the DSS nor in the SDSS, hence we are confident it is the afterglow of GRB 081028.
A finding chart is available on request.
GCN Circular #8426
Gendre, B (LAM-OAMP), Klotz, A. (CESR-OMP), Boer M. (OHP), Atteia J.L. (LATT-OMP) report:
We imaged the field of GRB 081028 detected by SWIFT (trigger 332851) with the TAROT robotic telescope (D=25cm) located at the Calern observatory, France.
The observations started 566.4s after the GRB trigger (423.2s after the notice). The elevation of the field increased from 16 degrees above horizon and weather conditions were very poor.
The first useful image started 4054.0 s after the notice. We co-added all exposure between 4054 and 6499 seconds. At the position reported by Clemens et al. (GCN 8424) and Olofsson et al. (GCN 8425), we do not detect any transient source, with a limit of R ~ 17.4. We do not detect any other source not present in the DSS.
Magnitudes were estimated with the nearby USNO-B1 stars and are not corrected for galactic dust extinction.
This message may be cited.
GCN Circular #8427
P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) report on behalf of the Swift-XRT team.
Using 5305 s of XRT Photon Counting mode data and 8 UVOT images for GRB 081028, 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 = 121.8948, +2.3083 which is equivalent to:
```
RA (J2000): 08h 07m 34.76s
Dec (J2000): +02d 18' 29.8"
```
with an uncertainty of 1.5 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 http://www.swift.ac.uk/xrt_positions/Goad.pdf), the current algorithm is an extension of this method.
This circular was automatically generated, and is an official product of the Swift-XRT team.
GCN Circular #8428
S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC), C. Guidorzi (INAF-OAB), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL), T. Sakamoto (GSFC/UMBC), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. N. Ukwatta (GWU) (i.e. the Swift-BAT team):
Using the data set from T-239 to T+963 sec from recent telemetry downlinks, we report further analysis of BAT GRB 081028 (trigger #332851) (Guidorzi, et al., GCN Circ. 8421). The BAT ground-calculated position is RA, Dec = 121.893, 2.305 deg, which is
```
   RA(J2000)  =  08h 07m 34.4s 
   Dec(J2000) = +02d 18' 16.8" 
```
with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment). The partial coding was 85%.
The mask-weighted light curve shows two main peaks and a tail. The first peak starts at ~T+20 sec, peaks at ~T+80 sec, and falls to a minumum betwen the two peaks at ~T+140 sec. The second peak peaks at ~T+220 sec. There is a tail out to approximately T+400 sec. T90 (15-350 keV) is 260 +- 40 sec (estimated error including systematics).
The time-averaged spectrum from T+29.3 to T+441.5 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 1.25 +- 0.38, and Epeak of 58 +- 23 keV (chi squared 57.6 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 3.7 +- 0.2 x 10^-6 erg/cm2 and the 1-sec peak flux measured from T+211.74 sec in the 15-150 keV band is 0.5 +- 0.1 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.84 +- 0.09 (chi squared 63.9 for 57 d.o.f.). 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/332851/BA/
GCN Circular #8429
C. Guidorzi, R. Margutti, J. Mao (INAF-OAB) on behalf of the Swift-XRT team report:
We have analysed the first 6 orbits of Swift-XRT data obtained for GRB 081028 (Guidorzi et al., GCN Circ. 8421), covering 650 s of Windowed Timing and 12.5 ks of Photon Counting (PC) mode data, between 197 s and 29 ks after the trigger. The UVOT-enhanced XRT position was given by Evans et al. in GCN Circ. 8427.
The light-curve shows a very complex evolution. In the first orbit data, covered entirely in WT mode, from 200 to 300 s it can be fit with a power law decay with an index of ~0.5. This temporally coincides with the decay of the second peak observed by BAT, which peaked at 220 s (Barthelmy et al. GCN Circ. 8428). Afterwards, there is flaring activity up to 400 s. From 400 to 700 s the afterglow undergoes a steep decay with a power-law index of 3.4, followed by a large flare with a peak rate of ~30 counts/s and lasting longer than 150 s. First orbit data stopped during the peak of this flare. From 4.1 to 8 ks the curve exhibits a steep decay with a power-law index of 3.8 +- 1.2 and the count rate drops to a value of ~5e-2 counts/s, after which it experiences a long rebrightening (at least up to 29 ks) with flaring activity, reaching a peak count rate of ~0.3 counts/s.
During the first orbit, the WT data spectrum undergoes a significant hard-to-soft evolution, with Gamma changing from 1 to 3. A WT spectrum extracted during the steep decay from 400 to 700 s can be modelled with an absorbed power-law, with Gamma = 2.51 +- 0.07 and NH = (8.0 +- 1.1)e20 cm^-2, in excess of the Galactic column in this direction of 4.0e20 cm^-2. The observed (unabsorbed) flux over this time interval is 7.8e-10 (1.1e-9) erg cm^-2 s^-1. A PC spectrum extracted from 5.0 to 23.2 ks can be modelled with an absorbed power-law, with Gamma = 2.25 +- 0.16 and NH = (9.3 +- 3.4)e20 cm^-2. The observed (unabsorbed) flux over this time interval is 7.3e-12 (1.0e-11) erg cm^-2 s^-1.
Presently, given the ongoing flaring behaviour, we cannot provide a reliable projection of the count rate over the next hours.
The results of the xrt automatic analysis are available at http://www.swift.ac.uk/xrt_products/00332851.
This is an official product of the Swift-XRT team.
GCN Circular #8430
P. Schady (MSSL-UCL) and C. Guidorzi (INAF-OAB) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 081028 201s after the BAT detection (Guidorziet al., GCN Circ. 8421). No source is detected in any of the individual or coadded exposures in any of the UVOT filters at the XRT position (GCN Circ. 8427), or at the position of the reported optical counterpart (GCN Circ. 8424, GCN Circ. 8425). The 3 sigma upper limits at the position of the optical counterpart for the first white finding chart (fc) and in consequent co-added observations are reported below (where T_start and T_stop represent the elapsed time since the BAT trigger in seconds).
```
Filter  T_start(s) T_stop(s)  Exp(s)   3 sigma Upper Limit
white     201           350           146         > 20.95
white     481           846            58           > 20.05
v             357          722            58           > 18.50
b             456          821            58           > 19.33
u             432          796            58           > 18.98
uvw1      407         771             58           >19.01
uvm2      382         746             58           >18.70
uvw2      506          868            55           >19.01
```
The above magnitudes are not corrected for the Galactic extinction corresponding to a reddening of E(B-V) = 0.03 mag (Schlegel et al., 1998, ApJS, 500, 525). The photometry is on the UVOT photometric system described in Poole et al. (2008, MNRAS, 383,627).
GCN Circular #8431
P. Schady (MSSL-UCL) and C. Guidorzi (INAF-OAB) report on behalf of the Swift/UVOT team:
Further to the UVOT observations of GRB 081028 reported in GCN Circ. 8430 (Schady et al.), we report an afterglow detection at the position of the optical counterpart (GCN Circ. 8424, GCN Circ. 8425) in later UVOT observations, from 10,000s after the BAT trigger. This is suggestive of a re-brightening of the afterglow consistent with the time of the brightening observed in the XRT light curve (Guidorzi et al., GCN Circ. 8429). The afterglow is detected in the v, b and u-band filters. The detection of the afterglow in the u-filter suggests a photometric upper limit on the redshift of z < ~2.3.
The magnitudes of the afterglow and 3-sigma upper limits are reported below:
```
Filter Tstart(s)   Tstop(s)    Exp(s)    Magnitude/3-sig UL
v      4050        5684        393.2       > 20.13
v      10740       28995      1770.3      20.23 +/- 0.19

b      4870        6504        393.3      > 20.79
b      17436       35567      1433.5     20.19 +/- 0.14

u      4665        6299        393.2      > 20.53
u      16524       34778      2539.8     21.21+/- 0.26

uvw1   4460        6094        393.2      > 20.61
uvw1   15618      33865       2656.7      > 21.89

uvm2   4255        5889        393.2      > 20.51
uvm2   21399      29784       2428.5      > 21.66

uvw2   5281         5480       196.6      >  20.23
uvw2   29001      28082       1771.2      >  20.61
```
The above magnitudes are not corrected for the Galactic extinction corresponding to a reddening of E(B-V) = 0.03 mag (Schlegel et al., 1998, ApJS, 500, 525). The photometry is on the UVOT photometric system described in Poole et al. (2008, MNRAS, 383,627).
GCN Circular #8434
E. Berger, R. Foley (Harvard), R. Simcoe (MIT), and J. Irwin (U. Michigan) report:
"We observed the optical afterglow (GCNs 8424, 8425, 8430) of GRB 081028 (GCN 8421) with the Magellan Echellette Spectrograph (MagE) on the Magellan/Clay 6.5-m telescope starting on 2008 Oct. 28.326 UT for a total integration time of 1800 sec. We find a wide range of absorption features (including Ly-alpha, SII, NV, SiIV, CIV, FeII, etc.) at a redshift of z=3.038, which we interpret as the redshift of the GRB. In addition, we find several intervening CIV and MgII absorbers."
GCN Circular #8442
C. Clemens, T. Kruehler and J. Greiner (all MPE Garching) report on behalf of the GROND team:
We observed the field of GRB 081028 for a second time at 07:45 UT on October 29th, 2008, 31.3 hr after the GRB trigger with 460 s of total exposures in g'r'i'z' and 480 s in JHK. Observations were performed at an average seeing of 1.3" and at an average airmass of 1.5.
We still detect the bright afterglow within the refined 1.5'' Swift-XRT error circle (Evans et al., GCN #8427) with the following preliminary magnitudes (all in AB system) of
```
g' ~ 21.26 mag,
r' ~ 20.49 mag,
i' ~ 20.24 mag,
z' ~ 19.99 mag and
J  ~ 19.6 mag
```
with statistical errors of +/- 0.05 in g'r'i'z' and +/- 0.1 in J. Given magnitudes are calibrated against SDSS as well as 2MASS field stars.
These measurements demonstrate a strong fading of the source compared to our first epoch observations (Clemens et al., GCN #8424). We therefore confirm this to be the afterglow of GRB 081028.
No correction for the Galactic foreground extinction corresponding to a reddening of E_(B-V)= 0.03 mag in the direction of the burst (Schlegel et al. 1998) has been applied.
GCN Circular #8455
V. Rumyantsev, V. Biryukov (CrAO), A. Pozanenko (IKI) report on behalf of larger GRB follow-up collaboration:
We observed the error box of Swift GRB 081028 (Guidorzi et al., GCN 8421) in R and I bands on Oct. 28, and BVRI on Oct. 29-31 with Shajn telescope of CrAO. The observations started on Oct. 28 00:40:56 (UT), i.e. ~16 minutes after burst onset. We clearly detect the afterglow (Clemens et al., GCN 8424, Olofsson et al., GCN 8425) in initial images. Preliminary photometry of combined images of Oct. 28 based on USNO-B1.0 0923-0196037 star RA (J2000) = 08:07:36.55, Dec. (J2000) = +02:18:29.4, and assuming R2=15.89 I=15.45 is following:
```
T0+     Filter, Exposure, mag.,     err.
(d)             (s)
0.0206  R       23x60     21.62 +/- 0.07
0.0415  I       30x60     21.32 +/- 0.09
0.0640  I       30x60     21.43 +/- 0.09
0.0865  I       30x60     21.20 +/- 0.08
0.1091  I       30x60     20.66 +/- 0.05
```
Our photometry confirms re-brightening of the optical afterglow (Schady & Guidorzi, GCN 8431) with sharp rise and maximum after ~9400 s which is consistent with the time of the brightening observed in the XRT light curve (Guidorzi et al., GCN 8429).
A finding chart of initial combined image in R can be found at http://grb.rssi.ru/GRB081028/
GCN Circular #8499
A. A. Miller, B. E. Cobb, J. S. Bloom, D. A. Perley (UC Berkeley), D. Starr (UCB, LCOGT) report:
We observed the optical afterglow of GRB 081028 (Clemens et al., GCN 8424, Olofsson et al., GCN 8425) with the 1.3-m Peters Automated Infrared Imaging Telescope (PAIRITEL). Observations with PAIRITEL began at 11:26:23 UT on Oct 28, 2008, 11 hours after the GRB trigger. We detect the afterglow in a 3727 sec mosaic of 7.8 sec simultaneous exposures in the J, H, and Ks filters. Preliminary photometry for the afterglow in these mosaics with midtime 12:13:59 Oct 28, 2008 UT yields J = 17.7 +- 0.1, H = 17.0 +- 0.1, and Ks = 16.1 +- 0.1 (all magnitudes given in the Vega system), calibrated to the 2MASS system. In intermediate mosiacs we find that the afterglow gets brighter during our ~1.5 hrs of observations. No correction for Galactic extinction (E(B-V) = 0.03; Schlegel et al. 1998) has been made to the above reported values.
These measurements indicate that the burst afterglow became brighter and redder following the measurements made by Clemens et al. (GCN 8424). Schady & Guidorzy (GCN 8431) report an optical brightening of the afterglow, consistent with the detected behavior in the NIR, around the time of our observations, and further measurements by Clemens et al. (GCN 8442) taken roughly 31 hours after the burst trigger show that the afterglow is redder than their initial observations.
GCN Report 176.1
GCN_Report 176.1 has been posted: http://gcn.gsfc.nasa.gov/reports/report_176_1.pdf by C. Guidorzi at INAF-OAB titled: "Final Swift report on GRB 081028"

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Jochen Greiner, last update: 15-Nov-2008 [Disclaimer]