Gamma-ray Burst 050916

(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:     Fri 16 Sep 05 16:38:08 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     155408,   Seg_Num: 0
GRB_RA:          135.992d {+09h 03m 58s} (J2000),
                 136.038d {+09h 04m 09s} (current),
                 135.594d {+09h 02m 23s} (1950)
GRB_DEC:         -51.425d {-51d 25' 31"} (J2000),
                 -51.448d {-51d 26' 53"} (current),
                 -51.226d {-51d 13' 32"} (1950)
GRB_ERROR:       4.00 [arcmin radius, statistical only]
GRB_INTEN:       0 [cnts]    Image_Peak=2191 [image_cnts]
TRIGGER_DUR:     120.000 [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:        13629 TJD;   259 DOY;   05/09/16
GRB_TIME:        59752.26 SOD {16:35:52.26} UT
GRB_PHI:         -145.36 [deg]
GRB_THETA:        41.39 [deg]
SOLN_STATUS:     0x13
RATE_SIGNIF:     0.00 [sigma]
IMAGE_SIGNIF:    8.77 [sigma]
MERIT_PARAMS:     +1  +0  +0  +7  +1  -1  +0  +1 -45  +1 
SUN_POSTN:       174.41d {+11h 37m 37s}   +2.42d {+02d 25' 11"}
SUN_DIST:         62.92 [deg]
MOON_POSTN:      337.48d {+22h 29m 55s}  -12.92d {-12d 54' 59"}
MOON_DIST:       112.99 [deg]
MOON_ILLUM:      97 [%]
GAL_COORDS:      271.41, -3.05 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      169.09,-62.82 [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:     Fri 16 Sep 05 16:39:29 UT
NOTICE_TYPE:     Swift-XRT Nack-Position
TRIGGER_NUM:     155408,   Seg_Num: 0
POINT_RA:        136.019d {+09h 04m 05s} (J2000)
POINT_DEC:       -51.421d {-51d 25' 16"} (J2000)
GRB_DATE:        13629 TJD;   259 DOY;   05/09/16
GRB_TIME:        59962.14 SOD {16:39:22.14} UT
COUNTS:          9    Min_needed= 20
STD_DEV:         0.00   Max_StdDev_for_Good=28.44 [arcsec]
PH2_ITER:        4    Max_iter_allowed= 4
ERROR_CODE:      1
COMMENTS:        SWIFT-XRT Nack Position.  
COMMENTS:        No source found in the image.

GCN/SWIFT NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 16 Sep 05 16:41:05 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     155408,   Seg_Num: 0
GRB_RA:          135.992d {+09h 03m 58s} (J2000),
                 136.038d {+09h 04m 09s} (current),
                 135.594d {+09h 02m 23s} (1950)
GRB_DEC:         -51.425d {-51d 25' 31"} (J2000),
                 -51.448d {-51d 26' 53"} (current),
                 -51.226d {-51d 13' 32"} (1950)
GRB_DATE:        13629 TJD;   259 DOY;   05/09/16
GRB_TIME:        59752.26 SOD {16:35:52.26} UT
TRIGGER_INDEX:   20000
GRB_PHI:         -145.36 [deg]
GRB_THETA:        41.39 [deg]
DELTA_TIME:      0.00 [sec]
TRIGGER_DUR:     120.000 [sec] 
LC_URL:          sw00155408000msb.lc
SUN_POSTN:       174.41d {+11h 37m 37s}   +2.42d {+02d 25' 11"}
SUN_DIST:         62.92 [deg]
MOON_POSTN:      337.48d {+22h 29m 55s}  -12.92d {-12d 54' 59"}
MOON_DIST:       112.99 [deg]
MOON_ILLUM:      97 [%]
GAL_COORDS:      271.41, -3.05 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      169.09,-62.82 [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/SWIFT NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 16 Sep 05 16:41:59 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     155408,   Seg_Num: 0
POINT_RA:        136.020d {+09h 04m 05s} (J2000)
POINT_DEC:       -51.422d {-51d 25' 17"} (J2000)
POINT_ROLL:      44.181d
GRB_DATE:        13629 TJD;   259 DOY;   05/09/16
GRB_TIME:        59959.74 SOD {16:39:19.74} UT
FILTER:          3, V
BKG_MEAN:        0.000000
N_STARS:         190
X_OFFSET:        476 [pixels]
Y_OFFSET:        555 [pixels]
X_MAX:           1435 [pixels]
Y_MAX:           1514 [pixels]
DET_THRESH:      8
PHOTO_THRESH:    3
SL_URL:          sw00155408000msufc.fits
SUN_POSTN:       174.41d {+11h 37m 38s}   +2.42d {+02d 25' 08"}
SUN_DIST:         62.91 [deg]
MOON_POSTN:      337.51d {+22h 30m 03s}  -12.90d {-12d 54' 03"}
MOON_DIST:       113.01 [deg]
MOON_ILLUM:      97 [%]
GAL_COORDS:      271.41, -3.03 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      169.11,-62.81 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN/SWIFT NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 16 Sep 05 16:42:40 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     155408,   Seg_Num: 0
POINT_RA:        136.020d {+09h 04m 05s} (J2000)
POINT_DEC:       -51.422d {-51d 25' 17"} (J2000)
POINT_ROLL:      44.181d
GRB_DATE:        13629 TJD;   259 DOY;   05/09/16
GRB_TIME:        59959.74 SOD {16:39:19.74} UT
FILTER:          3, V
BKG_MEAN:        0.000000
N_STARS:         190
X_OFFSET:        476 [pixels]
Y_OFFSET:        555 [pixels]
X_MAX:           1435 [pixels]
Y_MAX:           1514 [pixels]
DET_THRESH:      8
PHOTO_THRESH:    3
SL_URL:          sw00155408000msufc.fits
SUN_POSTN:       174.41d {+11h 37m 38s}   +2.42d {+02d 25' 08"}
SUN_DIST:         62.91 [deg]
MOON_POSTN:      337.51d {+22h 30m 03s}  -12.90d {-12d 54' 03"}
MOON_DIST:       113.01 [deg]
MOON_ILLUM:      97 [%]
GAL_COORDS:      271.41, -3.03 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      169.11,-62.81 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Source List.  
COMMENTS:        If you have elected to receive attachments:  
COMMENTS:        The uvot_catalog_srclist.fits file does not exist; skipping the attachment.

GCN notice #3991
D. Morris (PSU), D. Burrows (PSU), J. Cummings (GSFC/NRC), N. Gehrels (GSFC), C. Gronwall (PSU), S. T. Holland (GSFC/UMBC), J. Kennea (PSU), K. Page (U. Leicester), D. Palmer (LANL) on behalf of the Swift team:
At 16:35:52 UT, Swift-BAT triggered and located GRB050916 (trigger=155408). The spacecraft slewed immediately after processing the 120-second long image. The BAT on-board calculated location is RA,Dec 135.992d, -51.425d {09h 03m 58s, -51d 25' 31"} (J2000), with an uncertainty of 3 arcmin (radius, 90% containment, stat+sys). The BAT raw light curve showed one very broad peak from T+0 to T+180 sec, with a spike at about T+40 to T+45 sec. The peak count rate was ~500 counts/sec (15-350 keV), at T+40 sec. However, Swift was in the sunlit part of its orbit so the current heightened solar activity can produce variation in the BAT raw detector count rates, and a trustworthy light curve will require analysis of the full data set after the next ground contact.
XRT began observing at 16:39:22 UT, 210 seconds after the BAT trigger. The count rate was too low for an on-board centroid. The spectrum is consistent with a weak source. The XRT position will be available following the next ground station contact.
The UVOT began observing at 16:39:20 UT, 208 seconds after the BAT trigger. No UVOT image was sent through TDRSS, however, the processed source list shows no new source. The BAT source is at low galactic latitude and has high extinction.
We are currently in the portion of the orbits where the spacecraft does not pass over the Malindi downlink station. Therefore, it will be ~6 hours before we have access to the full data set for the refined analyses.
GCN notice #3995
D. Morris (PSU), D.N. Burrows (PSU) report on behalf of the Swift/XRT team:
The Swift XRT began observing the long weak burst GRB 050916 (trigger #155408, Morris et al., GCN 3991) at 16:35:52 UT, but was unable to obtain an on-board centroid. Analysis of the initial ground-processed data finds a faint, fading, and uncataloged source at coordinates:
```
RA(J2000) = 09 03 56.8
Dec(J2000) = -51 25 46.8
```
We estimate an uncertainty of 8 arcseconds (90% containment). This position lies 20 arcseconds from the BAT position reported in GCN 3991.
GCN notice #3996
D. C. Morris (PSU), D. N. Burrows (PSU), and N. Gehrels (GSFC) report on behalf of the Swift XRT team:
We have analysed the first six orbits of data for GRB050916 (GCN 3991, Morris et al., 2005). Using xrtcentoid, the refined position is:
```
RA(J2000) = 09h 03m 56.8s
Dec(J2000) = -51d 25' 50.3"
```
with an uncertainty of 8 arcsec. This is 3.5 arcsec from the original XRT position (GCN 3995, Morris et al., 2005) and 23 arcsecs from the initial BAT position..
The XRT began taking data at 16:39:22, 210 seconds after the BAT trigger. The early data (
The overall spectrum of all the data is well fit (reduced chi-sq of 1.04) by a power law with neutral hydrogen equal to the galactic column density of 1.1e22 :
NH=1.1e22(frozen) gamma=1.77 + / - 0.09
Due to the low overall number of events, separate fits to the flaring and non-flaring portions of the lightcurve are poorly contrained and do not show any significant evidence of spectral evolution:
```
flaring:
NH=0.89e22 + / - 0.16e22
gamma= 1.54 + / - 0.19

non-flaring:
NH=1.12e22 + / - 0.34e22
gamma=1.85 + / - 0.37
```
Assuming that the decay slope has returned to ~-1.5 after the flare, the expected count rate at T+1e5s is ~2e-3 cts/s which converts to an unabsorbed flux of 2.4e-13 ergs cm^-2s^-1. The peak flux (seen at the start of the XRT observation and at the peak of the flare) is 0.5 cts/s, for a peak unabsorbed flux of 6e-11 ergs cm^-2s^-1.
GCN notice #4003
E. Fenimore (LANL), L. Barbier (GSFC), S. Barthelmy (GSFC), J. Cummings (GSFC/NRC), N. Gehrels (GSFC), D. Hullinger (UMD), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), J. Nousek (PSU), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/NRC), G. Sato (ISAS), M. Tripicco (GSFC-SSAI), J. Tueller (GSFC), on behalf of the Swift-BAT team:
Using the complete data set from T-300 to T+300 sec, we report further analysis of Swift-BAT GRB 050916 (trigger #155408) (Morris, et al., GCN 3991). The refined BAT ground position is (RA,Dec) = 136.005, -51.411 {09h 04m 01.1s,-51d 24' 39"} [deg; J2000] +- 1.8 arcmin, (radius, sys+stat, 90% containment). This is 1.4 arcmin from the XRT refined position reported by Morris et al. (GCN 3996), The partial coding was 41%.
The light curve shows a broad peak from T+0 to T+66 and a second weaker peak from T+80 to T+100. T90 (15-150 keV) is (90 +- 10) sec (estimated error including systematics).
The power law index of the time-averaged spectrum is 1.83 +- 0.32. The fluence in the 15-150 keV band is (1.1 +- 0.4) x 10^-6 erg/cm^2. The 1-sec peak photon flux measured from T+44 sec in the 15-150 keV band is (0.66 +- 0.23) ph/cm2/sec. All the quoted errors are at the 90% confidence level.
GCN notice #4004
GRB050916: Swift/UVOT Upper Limits
P. J. Brown (PSU), D. Morris (PSU), H. Huckle (UCL-MSSL), B. Hancock (UCL-MSSL), and N. Gehrels (GSFC) report on behalf of the Swift/UVOT team:
The Swift/UVOT began observing the field of GRB 050916 (Swift Trigger #155408) on 2005/09/16 at 16:39:20 UT, 207 seconds after the BAT trigger (Morris et al. GCN 3991). No source is detected within the XRT error circle (Morris et al. GCN 3996) in the initial 100 second V-band image down to a 5-sigma upper limit of 17.9, or in summed exposures in any of the UVOT filters down to the following 5-sigma upper limits:
```
Filter  T_range (s)     Exp (s)  5sigma UL

V       207 - 74,597     4455     19.9
B       353 - 65,371     4374     20.7
U       339 - 63,016     4207     20.4
UVW1    325 - 58,536     4152     20.1
UVM2    311 - 53,803     4223     20.0
UVW2    368 - 69,038     3706     20.2
```
The magnitudes are uncorrected for extinction, which is extremely high as this direction lies in the galactic plane.

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Jochen Greiner, last update: 19-Sep-2005 [Disclaimer]