Gamma-ray Burst 090531B

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Sun 31 May 09 18:36:15 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      48
TRIGGER_NUM:     265487758
GRB_RA:          249.950d {+16h 39m 48s} (J2000),
                 250.118d {+16h 40m 28s} (current),
                 249.060d {+16h 36m 14s} (1950)
GRB_DEC:         -43.783d {-43d 46' 59"} (J2000),
                 -43.801d {-43d 48' 03"} (current),
                 -43.686d {-43d 41' 08"} (1950)
GRB_ERROR:       7.28 [deg radius, statistical plus systematic]
GRB_INTEN:       266 [cnts/sec]
DATA_SIGNIF:     10.90 [sigma]
INTEG_TIME:      1.024 [sec]
GRB_DATE:        14982 TJD;   151 DOY;   09/05/31
GRB_TIME:        66956.49 SOD {18:35:56.49} UT
GRB_PHI:         120.00 [deg]
GRB_THETA:        25.00 [deg]
DATA_TIME_SCALE: 1.0240 [sec]
HARD_RATIO:      0.42
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      95%  GRB
2nd_MOST_LIKELY:   4%  Generic Transient
DETECTORS:       0,0,0, 0,0,0, 0,0,0, 1,1,0, 0,0,
SUN_POSTN:        68.82d {+04h 35m 18s}  +22.01d {+22d 00' 38"}
SUN_DIST:        158.18 [deg]   Sun_angle= 11.9 [hr] (West of Sun)
MOON_POSTN:      167.97d {+11h 11m 52s}   +1.13d {+01d 08' 04"}
MOON_DIST:        85.13 [deg]
MOON_ILLUM:      57 [%]
GAL_COORDS:      340.27,  1.92 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      254.58,-21.41 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 80.12,13.00 [deg].

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 31 May 09 18:36:16 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     353728,   Seg_Num: 0
GRB_RA:          252.064d {+16h 48m 15s} (J2000),
                 252.221d {+16h 48m 53s} (current),
                 251.232d {+16h 44m 56s} (1950)
GRB_DEC:         -36.025d {-36d 01' 27"} (J2000),
                 -36.041d {-36d 02' 25"} (current),
                 -35.937d {-35d 56' 12"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       5954 [cnts]    Image_Peak=323 [image_cnts]
TRIGGER_DUR:     1.024 [sec] 
TRIGGER_INDEX:   155     E_range: 50-350 keV
BKG_INTEN:       24141 [cnts]
BKG_TIME:        66939.21 SOD {18:35:39.21} UT
BKG_DUR:         8 [sec]
GRB_DATE:        14982 TJD;   151 DOY;   09/05/31
GRB_TIME:        66956.17 SOD {18:35:56.17} UT
GRB_PHI:          11.97 [deg]
GRB_THETA:        12.55 [deg]
SOLN_STATUS:     0x20000003
RATE_SIGNIF:     48.41 [sigma]
IMAGE_SIGNIF:    11.06 [sigma]
MERIT_PARAMS:     +1  +0  +0  +0  +3  +1  +0  +1 +96  +0 
SUN_POSTN:        68.82d {+04h 35m 18s}  +22.01d {+22d 00' 38"}
SUN_DIST:        165.66 [deg]   Sun_angle= 11.8 [hr] (West of Sun)
MOON_POSTN:      167.97d {+11h 11m 52s}   +1.13d {+01d 08' 03"}
MOON_DIST:        86.03 [deg]
MOON_ILLUM:      57 [%]
GAL_COORDS:      347.22,  5.76 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      255.16,-13.50 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT-BAT GRB Coordinates.  
COMMENTS:        This is a rate 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 = 164.90,7.24 [deg].  
COMMENTS:           
COMMENTS:        NOTE: This BAT event is temporally(0.0<100sec) coincident with the FERMI_GBM event (trignum=265487758).

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Sun 31 May 09 18:36:56 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      58
TRIGGER_NUM:     265487758
GRB_RA:          249.080d {+16h 36m 19s} (J2000),
                 249.242d {+16h 36m 58s} (current),
                 248.222d {+16h 32m 53s} (1950)
GRB_DEC:         -40.010d {-40d 00' 35"} (J2000),
                 -40.029d {-40d 01' 42"} (current),
                 -39.909d {-39d 54' 30"} (1950)
GRB_ERROR:       2.63 [deg radius, statistical only]
DATA_SIGNIF:     14.80 [sigma]
DATA_INTERVAL:   1.024 [sec]
GRB_DATE:        14982 TJD;   151 DOY;   09/05/31
GRB_TIME:        66956.49 SOD {18:35:56.49} UT
GRB_PHI:         126.00 [deg]
GRB_THETA:        22.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   413 (Gnd S/W Version number)
SUN_POSTN:        68.82d {+04h 35m 18s}  +22.01d {+22d 00' 38"}
SUN_DIST:        161.98 [deg]   Sun_angle= 12.0 [hr] (West of Sun)
MOON_POSTN:      167.97d {+11h 11m 54s}   +1.13d {+01d 07' 53"}
MOON_DIST:        84.06 [deg]
MOON_ILLUM:      57 [%]
GAL_COORDS:      342.65,  4.92 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      253.31,-17.78 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 31 May 09 18:39:25 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     353728,   Seg_Num: 0
GRB_RA:          252.064d {+16h 48m 15s} (J2000),
                 252.221d {+16h 48m 53s} (current),
                 251.232d {+16h 44m 56s} (1950)
GRB_DEC:         -36.025d {-36d 01' 27"} (J2000),
                 -36.041d {-36d 02' 25"} (current),
                 -35.937d {-35d 56' 12"} (1950)
GRB_DATE:        14982 TJD;   151 DOY;   09/05/31
GRB_TIME:        66956.17 SOD {18:35:56.17} UT
TRIGGER_INDEX:   155
GRB_PHI:          11.97 [deg]
GRB_THETA:        12.55 [deg]
DELTA_TIME:      64.00 [sec]
TRIGGER_DUR:     1.024 [sec] 
SOLN_STATUS:     0x3
RATE_SIGNIF:     48.41 [sigma]
IMAGE_SIGNIF:    11.06 [sigma]
LC_URL:          sw00353728000msb.lc
SUN_POSTN:        68.83d {+04h 35m 18s}  +22.01d {+22d 00' 39"}
SUN_DIST:        165.66 [deg]   Sun_angle= 11.8 [hr] (West of Sun)
MOON_POSTN:      167.99d {+11h 11m 59s}   +1.12d {+01d 07' 16"}
MOON_DIST:        86.00 [deg]
MOON_ILLUM:      57 [%]
GAL_COORDS:      347.22,  5.76 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      255.16,-13.50 [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 a rate 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 = 164.90,7.24 [deg].

GCN Circular #9461
J. R. Cummings (NASA/UMBC), S. D. Barthelmy (GSFC), N. Gehrels (NASA/GSFC), C. Gronwall (PSU), S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU), V. Mangano (INAF-IASFPA), C. B. Markwardt (CRESST/GSFC/UMD), P. T. O'Brien (U Leicester), K. L. Page (U Leicester), D. M. Palmer (LANL), T. Sakamoto (NASA/UMBC) and B. Sbarufatti (INAF-IASFPA) report on behalf of the Swift Team:
At 18:35:56 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 090531B (trigger=353728). Swift will execute a delayed slew to the burst. The BAT on-board calculated location is RA, Dec 252.064, -36.025 which is
```
   RA(J2000)  =  16h 48m 15s
   Dec(J2000) = -36d 01' 27"
```
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows an initial bright spike at T_zero, then two much smaller spikes at T+21 sec and T+35 sec. The peak count rate was ~7000 counts/sec (15-350 keV), at ~0 sec after the trigger.
Due to an observing constraint, Swift will not slew until T0+50.1 minutes. There will be no XRT or UVOT data until this time.
Burst Advocate for this burst is J. R. Cummings (jayc AT milkyway.gsfc.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/too.html.)
GCN Circular #9462
B. E. Schaefer (Louisiana State), T. Guver (U Arizona), S. B. Pandey (U Mich), report on behalf of the ROTSE collaboration:
ROTSE-IIIc, located at the H.E.S.S. site at Mt. Gamsberg, Namibia, responded to GRB 090531 (Swift trigger 353728; J. R. Cummings et al., GCN 9461), producing images beginning 7.3 s after the GCN notice time. An automated response took the first image at 18:36:22.3 UT, 26.1 s after the burst, and during the gamma-ray emission, under excellent conditions. We took 10 5-sec, 10 20-sec and 50 60-sec exposures. These unfiltered images are calibrated relative to USNO A2.0 (R). Imaging is on going.
Comparison to the DSS (second epoch) reveals no new sources within the 3-sigma Swift/BAT error circle, for both single images and coadding into sets of 10; however, we are limited as the field is somewhat crowded. Individual images have limiting magnitudes ranging from 15.3-16.0; we set the following specific limits.
```
start UT       end UT      t_exp(s)   mlim   t_start-tGRB(s)  Coadd?
--------------------------------------------------------------------
18:36:22.3   18:36:27.3         5     15.3           26.1       N
18:47:31.3   18:52:11.6       280     16.3          695.1       Y
```

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 31 May 09 19:29:09 UT
NOTICE_TYPE:     Swift-XRT Nack-Position
TRIGGER_NUM:     353728,   Seg_Num: 0
POINT_RA:        252.006d {+16h 48m 01s} (J2000)
POINT_DEC:       -36.026d {-36d 01' 34"} (J2000)
IMG_START_DATE:  14982 TJD;   151 DOY;   09/05/31
IMG_START_TIME:  70111.12 SOD {19:28:31.12} UT,   3154.9 [sec] since BAT Trigger Time
COUNTS:          1    Min_needed= 20
STD_DEV:         0.00   Max_StdDev_for_Good=28.44 [arcsec]
PH2_ITER:        0    Max_iter_allowed= 4
ERROR_CODE:      1
COMMENTS:        SWIFT-XRT Nack Position.  
COMMENTS:        No source found in the image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 31 May 09 19:43:11 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     353728,   Seg_Num: 0
POINT_RA:        252.003d {+16h 48m 01s} (J2000)
POINT_DEC:       -36.027d {-36d 01' 35"} (J2000)
POINT_ROLL:      167.864d
IMG_START_DATE:  14982 TJD;   151 DOY;   09/05/31
IMG_START_TIME:  70805.05 SOD {19:40:05.05} UT,   3848.9 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        4.196
N_STARS:         190
X_OFFSET:        357 [pixels]
Y_OFFSET:        215 [pixels]
X_MAX:           1316 [pixels]
Y_MAX:           1174 [pixels]
DET_THRESH:      17
PHOTO_THRESH:    10
SL_URL:          sw00353728000msufc3848.fits
SUN_POSTN:        68.87d {+04h 35m 29s}  +22.02d {+22d 01' 01"}
SUN_DIST:        165.68 [deg]   Sun_angle= 11.8 [hr] (West of Sun)
MOON_POSTN:      168.53d {+11h 14m 07s}   +0.85d {+00d 51' 11"}
MOON_DIST:        85.36 [deg]
MOON_ILLUM:      58 [%]
GAL_COORDS:      347.19,  5.79 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      255.11,-13.51 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 31 May 09 19:43:11 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     353728,   Seg_Num: 0
POINT_RA:        252.003d {+16h 48m 01s} (J2000)
POINT_DEC:       -36.027d {-36d 01' 35"} (J2000)
POINT_ROLL:      167.864d
IMG_START_DATE:  14982 TJD;   151 DOY;   09/05/31
IMG_START_TIME:  70805.05 SOD {19:40:05.05} UT,   3848.9 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        4.196
N_STARS:         190
X_OFFSET:        357 [pixels]
Y_OFFSET:        215 [pixels]
X_MAX:           1316 [pixels]
Y_MAX:           1174 [pixels]
DET_THRESH:      17
PHOTO_THRESH:    10
SL_URL:          sw00353728000msufc3848.fits
SUN_POSTN:        68.87d {+04h 35m 29s}  +22.02d {+22d 01' 01"}
SUN_DIST:        165.68 [deg]   Sun_angle= 11.8 [hr] (West of Sun)
MOON_POSTN:      168.53d {+11h 14m 07s}   +0.85d {+00d 51' 11"}
MOON_DIST:        85.36 [deg]
MOON_ILLUM:      58 [%]
GAL_COORDS:      347.19,  5.79 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      255.11,-13.51 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 31 May 09 19:43:49 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     353728,   Seg_Num: 0
POINT_RA:        252.003d {+16h 48m 01s} (J2000)
POINT_DEC:       -36.027d {-36d 01' 35"} (J2000)
POINT_ROLL:      167.864d
IMG_START_DATE:  14982 TJD;   151 DOY;   09/05/31
IMG_START_TIME:  70805.05 SOD {19:40:05.05} UT,   3848.9 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        4.196
N_STARS:         190
X_OFFSET:        357 [pixels]
Y_OFFSET:        215 [pixels]
X_MAX:           1316 [pixels]
Y_MAX:           1174 [pixels]
DET_THRESH:      17
PHOTO_THRESH:    10
SL_URL:          sw00353728000msufc3848.fits
SUN_POSTN:        68.87d {+04h 35m 29s}  +22.02d {+22d 01' 01"}
SUN_DIST:        165.69 [deg]   Sun_angle= 11.8 [hr] (West of Sun)
MOON_POSTN:      168.53d {+11h 14m 08s}   +0.85d {+00d 51' 01"}
MOON_DIST:        85.35 [deg]
MOON_ILLUM:      58 [%]
GAL_COORDS:      347.19,  5.79 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      255.11,-13.51 [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:     Sun 31 May 09 19:45:02 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     353728,   Seg_Num: 0
POINT_RA:        252.003d {+16h 48m 01s} (J2000)
POINT_DEC:       -36.027d {-36d 01' 35"} (J2000)
ROLL:            167.864d
IMG_START_DATE:  14982 TJD;   151 DOY;   09/05/31
IMG_START_TIME:  70805.05 SOD {19:40:05.05} UT,   3848.9 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     265491609
X_OFFSET:        676 [pixels]
Y_OFFSET:        534 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       836
Y_GRB_POS:       694
BINNING_INDEX:   1
IM_URL:          sw00353728000msuni3853.fits
SUN_POSTN:        68.87d {+04h 35m 29s}  +22.02d {+22d 01' 01"}
SUN_DIST:        165.69 [deg]   Sun_angle= 11.8 [hr] (West of Sun)
MOON_POSTN:      168.54d {+11h 14m 11s}   +0.85d {+00d 50' 43"}
MOON_DIST:        85.34 [deg]
MOON_ILLUM:      58 [%]
GAL_COORDS:      347.19,  5.79 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      255.11,-13.51 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Image.  
COMMENTS:        The GRB Position came from the Window Position in the Mode Command.  
COMMENTS:        The image has 2x2 binning (compression).

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 31 May 09 19:45:20 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     353728,   Seg_Num: 0
POINT_RA:        252.003d {+16h 48m 01s} (J2000)
POINT_DEC:       -36.027d {-36d 01' 35"} (J2000)
ROLL:            167.864d
IMG_START_DATE:  14982 TJD;   151 DOY;   09/05/31
IMG_START_TIME:  70805.05 SOD {19:40:05.05} UT,   3848.9 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     265491609
X_OFFSET:        676 [pixels]
Y_OFFSET:        534 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       836
Y_GRB_POS:       694
BINNING_INDEX:   1
IM_URL:          sw00353728000msuni3853.fits
SUN_POSTN:        68.87d {+04h 35m 29s}  +22.02d {+22d 01' 01"}
SUN_DIST:        165.69 [deg]   Sun_angle= 11.8 [hr] (West of Sun)
MOON_POSTN:      168.55d {+11h 14m 11s}   +0.84d {+00d 50' 38"}
MOON_DIST:        85.34 [deg]
MOON_ILLUM:      58 [%]
GAL_COORDS:      347.19,  5.79 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      255.11,-13.51 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Image.  
COMMENTS:        The GRB Position came from the Window Position in the Mode Command.  
COMMENTS:        The image has 2x2 binning (compression).  
COMMENTS:        All 4 attachments are included.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 31 May 09 20:32:50 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     353728,   Seg_Num: 0
GRB_RA:          252.0748d {+16h 48m 17.95s} (J2000),
                 252.2317d {+16h 48m 55.61s} (current),
                 251.2423d {+16h 44m 58.16s} (1950)
GRB_DEC:         -36.0349d {-36d 02' 05.6"} (J2000),
                 -36.0510d {-36d 03' 03.4"} (current),
                 -35.9473d {-35d 56' 50.2"} (1950)
GRB_ERROR:       3.4 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.11e-12 [erg/cm2/sec]
GRB_SIGNIF:      3.00 [sigma]
IMG_START_DATE:  14982 TJD;   151 DOY;   09/05/31
IMG_START_TIME:  70111.11 SOD {19:28:31.11} UT,   3154.9 [sec] since BAT Trigger Time
TAM[0-3]:        327.61 237.19 261.35 242.66
AMPLIFIER:       2
WAVEFORM:        134
SUN_POSTN:        68.91d {+04h 35m 37s}  +22.02d {+22d 01' 18"}
SUN_DIST:        165.68 [deg]   Sun_angle= 11.8 [hr] (West of Sun)
MOON_POSTN:      168.94d {+11h 15m 47s}   +0.64d {+00d 38' 40"}
MOON_DIST:        84.96 [deg]
MOON_ILLUM:      58 [%]
GAL_COORDS:      347.22,  5.75 [deg] galactic lon,lat of the burst
ECL_COORDS:      255.17,-13.51 [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 #9464
C. Gronwall (PSU) and J. R. Cummings (NASA/UMBC) report on behalf of the UVOT Team:
In response to GRB090531B (Swift/BAT trigger 353728; Cummings et al., GCN Circ. 9461) at 18:35:56 UT, UVOT took a finding chart exposure of 150 seconds with the White filter starting 3848 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 (Sbarufatti et al., GCN Circ. 9463) The typical 3-sigma upper limit has been about 19.6 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 1.12.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 31 May 09 20:50:26 UT
NOTICE_TYPE:     Swift-UVOT Position
TRIGGER_NUM:     353728,   Seg_Num: 0
GRB_RA:          252.0748d {+16h 48m 17.95s} (J2000),
                 252.2317d {+16h 48m 55.61s} (current),
                 251.2423d {+16h 44m 58.16s} (1950)
GRB_DEC:         -36.0349d {-36d 02' 05.6"} (J2000),
                 -36.0510d {-36d 03' 03.4"} (current),
                 -35.9473d {-35d 56' 50.2"} (1950)
GRB_ERROR:       10.0 [arcsec radius, statistical only]
GRB_MAG:         19.50 +/- 3.00 [mag]
FILTER:          10, White
IMG_START_DATE:  14982 TJD;   151 DOY;   09/05/31
IMG_START_TIME:  70807.00 SOD {19:40:07.00} UT,   3850.8 [sec] since BAT Trigger Time
SUN_POSTN:        68.92d {+04h 35m 40s}  +22.02d {+22d 01' 24"}
SUN_DIST:        165.68 [deg]   Sun_angle= 11.8 [hr] (West of Sun)
MOON_POSTN:      169.09d {+11h 16m 22s}   +0.57d {+00d 34' 14"}
MOON_DIST:        84.80 [deg]
MOON_ILLUM:      58 [%]
GAL_COORDS:      347.22,  5.75 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      255.17,-13.51 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT UVOT Position Notice.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.

GCN Circular #9465
T. N. Ukwatta (GWU), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL), T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC) (i.e. the Swift-BAT team):
Using the data set from T-61 to T+242 sec from the recent telemetry downlink, we report further analysis of BAT GRB 090531B (trigger #353728) (Cummings, et al., GCN Circ. 9461). The BAT ground-calculated position is RA, Dec = 252.070, -36.015 deg, which is
```
   RA(J2000)  =  16h 48m 16.8s 
   Dec(J2000) = -36d 00' 53.4" 
```
with an uncertainty of 2.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 100%.
The mask-weighted light curve shows an initial bright spike with a total width of 1.3 sec. It returns to baseline and then starts (!T+15 sec) a long smooth rise to a peak around T+40 sec and a smooth decline ending at ~T+110 sec. The spike is spectrally harder than the long smooth peak. This lightcurve is consistance with a short hard burst with an extended emission. T90 (15-350 keV) is 80 +- 23 sec (estimated error including systematics).
The time-averaged spectrum from T-13.0 to T+67.0 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.51 +- 0.22. The fluence in the 15-150 keV band is 7.1 +- 0.9 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T+0.2 sec in the 15-150 keV band is 1.25 +- 0.1 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/353728/BA/
GCN Circular #9469
P. Schady (MSSL-UCL) and J. R. Cummings (NASA/UMBC) report on behalf of the Swift/UVOT team:
The Swift/UVOT observed the field of GRB 090531B starting 3924 s after the BAT trigger (Cummings et al., GCN Circ. 9461), once the GRB came out of Earth limb observing constraint. No optical afterglow is detected in any of the UVOT exposures at the position of the X-ray afterglow (Sbarufatti et al., GCN Circ. 9463), with the following three-sigma upper limits:
```
Filter  T_mid(s)  Exp(s)   3-sig Mag UL

white    3934      74      > 20.52
v        4105      98      > 19.08
b        4926      98      > 20.06
u        4721      98      > 19.74
uvw1     4515      98      > 19.65
uvm2     4310      98      > 19.32
uvw2     5336      98      > 19.61
```
The values quoted above are not corrected for the large Galactic extinction due to the reddening of E(B-V)=1.12 in the direction of the burst (Schlegel et al. 1998). The photometry is on the UVOT photometric system described in Poole et al. (2008, MNRAS, 383, 627).
GCN Circular #9470
E. Sonoda, K. Noda, N. Ohmori, K. Kono, H. Hayasi, A. Daikyuji, Y. Nisioka, M. Yamauchi (University of Miyazaki)
We have observed the field covering the error circle of GRB090531B (Swift trigger 353728, GCN 9461(J. R. Cummings et al.)) with the unfiltered CCD camera on the 30-cm telescope at University of Miyazaki. The observation was started 18:37:28 UT (92 s after the Swift trigger), under cloudy condition. First image was obtained at 18:41:05 UT (309 s after the Swift trigger). We have compared our data of 30 sec exposures with the USNO-A2.0 catalog. There is no new source at the reported position. (GCN 9462(B. E. Schaefer et al.), GCN 9464(C. Gronwall et al.) GCN 9465(T. N. Ukwatta et al.), GCN 9469(P. Schady et al.))
Preliminary analysis shows there is no new source brighter than 14.6 mag.
GCN Circular #9471
P. Schady (MSSL-UCL) and J. R. Cummings (NASA/UMBC) report on behalf of the Swift/UVOT team:
We report a mistake in a few of the times provided in GCN 9469, including the start time of the observations, which was in fact 3849 s after the BAT trigger (Cummings et al., GCN Circ. 9461). Also, the exposure times of the UVOT observations should have been two times the values given.
The corrected 3-sigma upper limits for the UVOT observations of the field of GRB 090531B are provided below.
```
Filter T_mid(s)  Exp(s)  3-sig Mag UL

white    3924      147      > 20.52
v        4105      197      > 19.08
b        4926      197      > 20.06
u        4721      197      > 19.74
uvw1     4515      197      > 19.65
uvm2     4310      197      > 19.32
uvw2     5336      197      > 19.61
```
The values quoted above are not corrected for the large Galactic extinction due to the reddening of E(B-V)=1.12 in the direction of the burst (Schlegel et al. 1998). The photometry is on the UVOT photometric system described in Poole et al. (2008, MNRAS, 383, 627).
GCN Circular #9475
T. N. Ukwatta (GWU/GSFC), S. D. Barthelmy (GSFC), J. R. Cummings (NASA/UMBC), T. Sakamoto (GSFC/UMBC), M. Stamatikos (GSFC/ORAU), N. Gehrels (GSFC) (for the Swift-BAT team):
For GRB 090531B (Cummings et al. GCN 9461), the BAT team has analyzed spectral lags for the data from T-1.0 sec to T+2.0 sec using non-mask weighted light curves with 16 msec time binning. The spectral lags were measured between standard canonical BAT energy bands: channel 1 (15-25 keV), 2 (25-50 keV), 3 (50-100 keV) and 4 (100-350 keV) are given below.
```
Lag Ch3-Ch2 : -2 +/- 9 msec
Lag Ch4-Ch2 : 11 +/- 5 msec
Lag Ch4-Ch3 :  8 +/- 3 msec
```
The signal-to-noise ratio in channel 1 is too weak to make a lag measurement.
These lag values are consistent with lags observed for short hard burst with extended emission.
GCN Circular #9480
A. Rossi (Tautenburg), F. Olivares, T. Kruehler and J. Greiner (all MPE Garching) report on behalf of the GROND team:
We observed the field of GRB 090531B (Swift trigger 353728, Cummings et al. 2009, GCN #9461) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2m MPI/ESO telescope at La Silla Observatory (Chile).
Observations started on 1 June 2009 at 00:03 UT, 5.5 hours after the burst and continued until 00:50 UT under mediocre seeing (~1.5), cirrus and Moon light. A second epoch started at 04:33 UT under better conditions, consisting of 72 min exposure in g'r'i'z' and 60 min in JHK.
We find three objects within the XRT error circle (Sbaruffatti et al. 2009, GCN #9463), and another three at the outer circumference of the error circle (see finding chart on http://www.mpe.mpg.de/~jcg/grb090531B.html). Within +-0.2 mag, none of these objects shows any variability between 5.5 and 10 hrs post-burst, and thus are most likely foreground objects.
In empty regions of the error circle, the first epoch yields the following upper limits (all AB):
```
g' > 22.9
r' > 22.6
i' > 22.1
z' > 22.8
J  > 20.1
H  > 19.8
K  > 19.2
```
which were obtained using the USNO and 2MASS field stars as reference. However, given the poor conditions and preliminary photometric calibration, a variable object might be hidden behind one of the foreground objects, and masked in the difference image due to the distorted PSF from the first epoch. In that case, the upper limits would be about 2 mag brighter. No correction has been applied for the strong foreground reddening of E(B-V)=1.11 mag (Schlegel et al. 1998).
GCN Circular #9481
B. E. Cobb (UC Berkeley) reports:
Using the ANDICAM instrument on the 1.3m telescope at CTIO, we obtained optical/IR imaging of the error region of GRB 090531b (GCN 9461, Cummings et al.) over two epochs with mid-exposure times of 2009-06-01 02:56 UT and 2009-06-02 05:26 UT (8.3 and 34.8 hours post-burst). Total summed exposure times for each observation amounted to 36 minutes in R and 30 minutes in J.
While there are a number of sources in and around the position of the GRB X-ray afterglow (GCN 9463, Sbarufatti et al.; GCN 9480, Rossi et al.), image differencing of the two epochs using the ISIS image subtraction program does not reveal any significant variable source. The sky limiting magnitude of the images is I>21.1 and J>18.5 (where optical photometry is calibrated using USNO-B1 stars and IR photometry with 2MASS; these limits have not been corrected for Galactic reddening).
GCN Circular #9501
S. Guiriec (UAH) reports on behalf of the Fermi GBM Team:
"At 18:35:56.49 UT on 31 May 2009, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 090531B (trigger 265487758 / 090531775) which was also detected by the SWIFT-BAT (Cummings et al. 2008, GCN 9461). The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight is 25 degrees.
The GBM light curve consists of a single peak with a duration (T90) of about 2 s (8-1000 keV). The time-averaged spectrum from T0-0.23 s to T0+0.77 s is adequately fit by a Band function with Epeak = 2166(+675-408) keV, alpha = -0.71(+0.10-0.10), and beta = -2.47(+0.25-0.46) (Castor C-Stat 780 for 602 d.o.f.).
The event fluence (8-1000 keV) in this time interval is (6.20 +/- 0.18)E-07 erg/cm^2. The 1-sec peak photon flux measured starting from T0-0.23 s in the 8-1000 keV band is 1.49 +/- 0.04 ph/s/cm^2.
The spectral and temporal analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."

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Jochen Greiner, last update: 10-Jun-2009 [Disclaimer]