Gamma-ray Burst 161104A

(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 04 Nov 16 09:42:41 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     720568,   Seg_Num: 0
GRB_RA:           77.881d {+05h 11m 31s} (J2000),
                  77.981d {+05h 11m 56s} (current),
                  77.582d {+05h 10m 20s} (1950)
GRB_DEC:         -51.452d {-51d 27' 07"} (J2000),
                 -51.433d {-51d 25' 57"} (current),
                 -51.511d {-51d 30' 40"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       564 [cnts]    Image_Peak=80 [image_cnts]
TRIGGER_DUR:     0.064 [sec] 
TRIGGER_INDEX:   10418     E_range: 25-100 keV
BKG_INTEN:       21553 [cnts]
BKG_TIME:        34934.89 SOD {09:42:14.89} UT
BKG_DUR:         8 [sec]
GRB_DATE:        17696 TJD;   309 DOY;   16/11/04
GRB_TIME:        34946.73 SOD {09:42:26.73} UT
GRB_PHI:         -142.09 [deg]
GRB_THETA:        13.00 [deg]
SOLN_STATUS:     0x3
RATE_SIGNIF:     27.25 [sigma]
IMAGE_SIGNIF:    9.20 [sigma]
MERIT_PARAMS:     +1  +0  +0  -4  +2  +0  +0  +0 +26  +0 
SUN_POSTN:       219.96d {+14h 39m 51s}  -15.56d {-15d 33' 31"}
SUN_DIST:        105.27 [deg]   Sun_angle= 9.5 [hr] (West of Sun)
MOON_POSTN:      273.66d {+18h 14m 38s}  -18.73d {-18d 44' 05"}
MOON_DIST:       108.50 [deg]
MOON_ILLUM:      19 [%]
GAL_COORDS:      258.49,-36.22 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       62.18,-73.72 [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 = 270.71,-5.43 [deg].

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 04 Nov 16 09:44:10 UT
NOTICE_TYPE:     Swift-XRT Position
TRIGGER_NUM:     720568,   Seg_Num: 0
GRB_RA:           77.6232d {+05h 10m 29.56s} (J2000),
                  77.7242d {+05h 10m 53.81s} (current),
                  77.3237d {+05h 09m 17.69s} (1950)
GRB_DEC:         -51.4183d {-51d 25' 05.8"} (J2000),
                 -51.3983d {-51d 23' 53.8"} (current),
                 -51.4787d {-51d 28' 43.2"} (1950)
GRB_ERROR:       5.0 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       2.95e-09 [erg/cm2/sec]
GRB_SIGNIF:      9.16 [sigma]
IMG_START_DATE:  17696 TJD;   309 DOY;   16/11/04
IMG_START_TIME:  35004.98 SOD {09:43:24.98} UT,   58.2 [sec] since BAT Trigger Time
TAM[0-3]:        327.65 237.19 261.63 243.52
AMPLIFIER:       2
WAVEFORM:        134
SUN_POSTN:       219.96d {+14h 39m 51s}  -15.56d {-15d 33' 32"}
SUN_DIST:        105.40 [deg]   Sun_angle= 9.5 [hr] (West of Sun)
MOON_POSTN:      273.67d {+18h 14m 41s}  -18.74d {-18d 44' 05"}
MOON_DIST:       108.49 [deg]
MOON_ILLUM:      19 [%]
GAL_COORDS:      258.45,-36.38 [deg] galactic lon,lat of the burst
ECL_COORDS:       61.67,-73.64 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        The XRT position is 9.84 arcmin from the BAT position.  
COMMENTS:        WARNING: The centroided position is more than 100 rows or columns from the center of the FOV.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 04 Nov 16 09:44:18 UT
NOTICE_TYPE:     Swift-XRT Image
TRIGGER_NUM:     720568,   Seg_Num: 0
GRB_RA:           77.6232d {+05h 10m 29.5s} (J2000),
                  77.7242d {+05h 10m 53.8s} (current),
                  77.3237d {+05h 09m 17.6s} (1950)
GRB_DEC:         -51.4183d {-51d 25' 05.8"} (J2000),
                 -51.3983d {-51d 23' 53.8"} (current),
                 -51.4787d {-51d 28' 43.2"} (1950)
GRB_ERROR:       4.7 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       84 [cnts]
IMG_START_DATE:  17696 TJD;   309 DOY;   16/11/04
IMG_START_TIME:  35004.98 SOD {09:43:24.98} UT,   58.2 [sec] since BAT Trigger Time
CENTROID_X:      482.68,  raw= 483  [pixels]
CENTROID_Y:      132.31,  raw= 132  [pixels]
ROLL:            142.13 [deg]
GAIN:            1
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   -390.10
GRB_POS_XRT_Z:   418.14
IMAGE_URL:       sw00720568000msxps_rw.img
SUN_POSTN:       219.96d {+14h 39m 51s}  -15.56d {-15d 33' 32"}
SUN_DIST:        105.40 [deg]   Sun_angle= 9.5 [hr] (West of Sun)
MOON_POSTN:      273.67d {+18h 14m 41s}  -18.74d {-18d 44' 05"}
MOON_DIST:       108.49 [deg]
MOON_ILLUM:      19 [%]
GAL_COORDS:      258.45,-36.38 [deg] galactic lon,lat of the burst
ECL_COORDS:       61.67,-73.64 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Image.  
COMMENTS:        WARNING: The centroided position is more than 100 rows or columns from the center of the FOV.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 04 Nov 16 09:44:28 UT
NOTICE_TYPE:     Swift-XRT Processed Image
TRIGGER_NUM:     720568,   Seg_Num: 0
GRB_RA:           77.6232d {+05h 10m 29.5s} (J2000),
                  77.7242d {+05h 10m 53.8s} (current),
                  77.3237d {+05h 09m 17.6s} (1950)
GRB_DEC:         -51.4183d {-51d 25' 05.8"} (J2000),
                 -51.3983d {-51d 23' 53.8"} (current),
                 -51.4787d {-51d 28' 43.2"} (1950)
GRB_ERROR:       4.7 [arcsec, radius, statistical plus systematic]
GRB_INTEN:       84 [cnts]
IMG_START_DATE:  17696 TJD;   309 DOY;   16/11/04
IMG_START_TIME:  35004.98 SOD {09:43:24.98} UT,   58.2 [sec] since BAT Trigger Time
CENTROID_X:      482.68,  raw= 483  [pixels]
CENTROID_Y:      132.31,  raw= 132  [pixels]
ROLL:            142.13 [deg]
GAIN:            1
MODE:            3, Long Image mode
WAVEFORM:        134
EXPO_TIME:       2.50 [sec]
GRB_POS_XRT_Y:   -390.10
GRB_POS_XRT_Z:   418.14
IMAGE_URL:       sw00720568000msxps_rw.img
SUN_POSTN:       219.96d {+14h 39m 51s}  -15.56d {-15d 33' 33"}
SUN_DIST:        105.40 [deg]   Sun_angle= 9.5 [hr] (West of Sun)
MOON_POSTN:      273.67d {+18h 14m 42s}  -18.74d {-18d 44' 05"}
MOON_DIST:       108.49 [deg]
MOON_ILLUM:      19 [%]
GAL_COORDS:      258.45,-36.38 [deg] galactic lon,lat of the burst
ECL_COORDS:       61.67,-73.64 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Processed Image.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 04 Nov 16 09:45:59 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     720568,   Seg_Num: 0
POINT_RA:         77.877d {+05h 11m 30s} (J2000)
POINT_DEC:       -51.444d {-51d 26' 36"} (J2000)
POINT_ROLL:      142.131d
IMG_START_DATE:  17696 TJD;   309 DOY;   16/11/04
IMG_START_TIME:  35014.55 SOD {09:43:34.55} UT,   67.8 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        0.966
N_STARS:         41
X_OFFSET:        544 [pixels]
Y_OFFSET:        528 [pixels]
X_MAX:           1503 [pixels]
Y_MAX:           1487 [pixels]
DET_THRESH:      8
PHOTO_THRESH:    4
SL_URL:          sw00720568000msufc0067.fits
SUN_POSTN:       219.96d {+14h 39m 51s}  -15.56d {-15d 33' 34"}
SUN_DIST:        105.28 [deg]   Sun_angle= 9.5 [hr] (West of Sun)
MOON_POSTN:      273.69d {+18h 14m 45s}  -18.74d {-18d 44' 06"}
MOON_DIST:       108.50 [deg]
MOON_ILLUM:      19 [%]
GAL_COORDS:      258.48,-36.22 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       62.18,-73.71 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 04 Nov 16 09:46:30 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     720568,   Seg_Num: 0
POINT_RA:         77.877d {+05h 11m 30s} (J2000)
POINT_DEC:       -51.444d {-51d 26' 36"} (J2000)
POINT_ROLL:      142.131d
IMG_START_DATE:  17696 TJD;   309 DOY;   16/11/04
IMG_START_TIME:  35014.55 SOD {09:43:34.55} UT,   67.8 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        0.966
N_STARS:         41
X_OFFSET:        544 [pixels]
Y_OFFSET:        528 [pixels]
X_MAX:           1503 [pixels]
Y_MAX:           1487 [pixels]
DET_THRESH:      8
PHOTO_THRESH:    4
SL_URL:          sw00720568000msufc0067.fits
SUN_POSTN:       219.96d {+14h 39m 51s}  -15.56d {-15d 33' 34"}
SUN_DIST:        105.28 [deg]   Sun_angle= 9.5 [hr] (West of Sun)
MOON_POSTN:      273.69d {+18h 14m 46s}  -18.74d {-18d 44' 06"}
MOON_DIST:       108.50 [deg]
MOON_ILLUM:      19 [%]
GAL_COORDS:      258.48,-36.22 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       62.18,-73.71 [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:     Fri 04 Nov 16 09:47:18 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     720568,   Seg_Num: 0
POINT_RA:         77.877d {+05h 11m 30s} (J2000)
POINT_DEC:       -51.444d {-51d 26' 36"} (J2000)
ROLL:            142.131d
IMG_START_DATE:  17696 TJD;   309 DOY;   16/11/04
IMG_START_TIME:  35014.55 SOD {09:43:34.55} UT,   67.8 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     499945431
X_OFFSET:        440 [pixels]
Y_OFFSET:        1728 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       600
Y_GRB_POS:       2047
BINNING_INDEX:   1
IM_URL:          sw00720568000msuni0085.fits
SUN_POSTN:       219.96d {+14h 39m 52s}  -15.56d {-15d 33' 35"}
SUN_DIST:        105.28 [deg]   Sun_angle= 9.5 [hr] (West of Sun)
MOON_POSTN:      273.70d {+18h 14m 48s}  -18.74d {-18d 44' 06"}
MOON_DIST:       108.50 [deg]
MOON_ILLUM:      19 [%]
GAL_COORDS:      258.48,-36.22 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       62.18,-73.71 [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:     Fri 04 Nov 16 09:47:40 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     720568,   Seg_Num: 0
POINT_RA:         77.877d {+05h 11m 30s} (J2000)
POINT_DEC:       -51.444d {-51d 26' 36"} (J2000)
ROLL:            142.131d
IMG_START_DATE:  17696 TJD;   309 DOY;   16/11/04
IMG_START_TIME:  35014.55 SOD {09:43:34.55} UT,   67.8 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     499945431
X_OFFSET:        440 [pixels]
Y_OFFSET:        1728 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       600
Y_GRB_POS:       2047
BINNING_INDEX:   1
IM_URL:          sw00720568000msuni0085.fits
SUN_POSTN:       219.97d {+14h 39m 52s}  -15.56d {-15d 33' 35"}
SUN_DIST:        105.28 [deg]   Sun_angle= 9.5 [hr] (West of Sun)
MOON_POSTN:      273.70d {+18h 14m 49s}  -18.74d {-18d 44' 06"}
MOON_DIST:       108.50 [deg]
MOON_ILLUM:      19 [%]
GAL_COORDS:      258.48,-36.22 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:       62.18,-73.71 [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_catalog_image.fits.gz file does not exist; skipping the attachment.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 04 Nov 16 09:47:54 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     720568,   Seg_Num: 0
GRB_RA:           77.881d {+05h 11m 31s} (J2000),
                  77.981d {+05h 11m 56s} (current),
                  77.582d {+05h 10m 20s} (1950)
GRB_DEC:         -51.452d {-51d 27' 07"} (J2000),
                 -51.433d {-51d 25' 57"} (current),
                 -51.511d {-51d 30' 40"} (1950)
GRB_DATE:        17696 TJD;   309 DOY;   16/11/04
GRB_TIME:        34946.87 SOD {09:42:26.87} UT
TRIGGER_INDEX:   10418
GRB_PHI:         -142.09 [deg]
GRB_THETA:        13.00 [deg]
DELTA_TIME:      -77.00 [sec]
TRIGGER_DUR:     0.064 [sec] 
SOLN_STATUS:     0x3
RATE_SIGNIF:     27.25 [sigma]
IMAGE_SIGNIF:    9.20 [sigma]
LC_URL:          sw00720568000msb.lc
SUN_POSTN:       219.97d {+14h 39m 52s}  -15.56d {-15d 33' 35"}
SUN_DIST:        105.27 [deg]   Sun_angle= 9.5 [hr] (West of Sun)
MOON_POSTN:      273.70d {+18h 14m 49s}  -18.74d {-18d 44' 06"}
MOON_DIST:       108.49 [deg]
MOON_ILLUM:      19 [%]
GAL_COORDS:      258.49,-36.22 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       62.18,-73.72 [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 = 270.71,-5.43 [deg].

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 04 Nov 16 09:58:34 UT
NOTICE_TYPE:     Swift-XRT Position UPDATE
TRIGGER_NUM:     720568,   Seg_Num: 0
GRB_RA:           77.8923d {+05h 11m 34.15s} (J2000),
                  77.9930d {+05h 11m 58.32s} (current),
                  77.5937d {+05h 10m 22.47s} (1950)
GRB_DEC:         -51.4589d {-51d 27' 32.0"} (J2000),
                 -51.4393d {-51d 26' 21.5"} (current),
                 -51.5180d {-51d 31' 04.8"} (1950)
GRB_ERROR:       4.5 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN:       1.00e-10 [erg/cm2/sec]
GRB_SIGNIF:      10.00 [sigma]
IMG_START_DATE:  17696 TJD;   309 DOY;   16/11/04
IMG_START_TIME:  35015.00 SOD {09:43:35.00} UT,   68.3 [sec] since BAT Trigger Time
TAM[0-3]:        100.00 100.00 100.00 100.00
AMPLIFIER:       1
WAVEFORM:        31
SUN_POSTN:       219.97d {+14h 39m 53s}  -15.56d {-15d 33' 43"}
SUN_DIST:        105.26 [deg]   Sun_angle= 9.5 [hr] (West of Sun)
MOON_POSTN:      273.80d {+18h 15m 12s}  -18.74d {-18d 44' 09"}
MOON_DIST:       108.47 [deg]
MOON_ILLUM:      19 [%]
GAL_COORDS:      258.50,-36.21 [deg] galactic lon,lat of the burst
ECL_COORDS:       62.19,-73.73 [deg] ecliptic lon,lat of the burst
COMMENTS:        SWIFT-XRT Coordinates.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        This is an Update Notice -- the RA,Dec values herein supersede the previous XRT_POS Notice.  
COMMENTS:        TAM values, flux and significance fields are not valid.  
COMMENTS:        This position was automatically generated on the ground using  
COMMENTS:        Photon Counting data telemetered via TDRSS (SPER data).  
COMMENTS:        See http://www.swift.ac.uk/sper/docs.php for details.  
COMMENTS:        The probability that this is a serendipitous source in the  
COMMENTS:        SPER window is 0.11% < P(seren) < 0.58%.

GCN Circular #20123
B. Mingo (U Leicester), A. P. Beardmore (U Leicester), D. N. Burrows (PSU), P.A. Evans (U Leicester), K. L. Page (U Leicester) and T. N. Ukwatta (LANL) report on behalf of the Swift Team:
At 09:42:26 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 161104A (trigger=720568). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 77.881, -51.452 which is
```
   RA(J2000) = 05h 11m 31s
   Dec(J2000) = -51d 27' 07"
```
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single peak structure with a duration of about 0.3 sec. The peak count rate was ~6000 counts/sec (15-350 keV), at ~0.1 sec after the trigger.
The XRT began observing the field at 09:43:24.9 UT, 58.3 seconds after the BAT trigger. The position determined from promptly downlinked data is incorrect because the XRT centroided on a cosmic ray. Using promptly downlinked data we find an uncatalogued X-ray source located at RA, Dec 77.89236, -51.45898 which is equivalent to:
```
   RA(J2000)  = 05h 11m 34.17s
   Dec(J2000) = -51d 27' 32.3"
```
with an uncertainty of 4.5 arcseconds (radius, 90% containment). This location is 35 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. We cannot determine whether the source is fading at the present time. No spectrum from the promptly downlinked event data is yet available to determine the column density.
UVOT took a finding chart exposure of 101 seconds with the White filter starting 67 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 none of the XRT error circle. 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 0.02.
Burst Advocate for this burst is B. Mingo (bm188 AT le.ac.uk). 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 #20124
M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team.
Using 95 s of XRT Photon Counting mode data and 1 UVOT images for GRB 161104A, 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 = 77.89359, -51.46011 which is equivalent to:
```
RA (J2000): 05h 11m 34.46s
Dec (J2000): -51d 27' 36.4"
```
with an uncertainty of 3.2 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) and Evans et al. (2009, MNRAS, 397, 1177).
This circular was automatically generated, and is an official product of the Swift-XRT team.
GCN Circular #20128
D.N. Burrows (PSU), T.G.R. Roegiers (PSU), L.M. McCauley (PSU), B. Mingo (U. Leicester), A.P. Beardmore (U. Leicester), A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC) and B. Mingo (U Leicester) report on behalf of the Swift-XRT team:
We have analysed 6.3 ks of XRT data for GRB 161104A (Mingo et al. GCN Circ. 20123), from 68 s to 23.6 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Goad et al. (GCN Circ. 20124).
The light curve can be modelled with a power-law decay with a decay index of alpha=0.37 (+0.17, -0.16).
If the light curve continues to decay with a power-law decay index of 0.37, the count rate at T+24 hours will be 1.6 x 10^-3 count s^-1
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00720568.
This circular is an official product of the Swift-XRT team.
GCN Circular #20129
A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC), B. Mingo (U Leicester), D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU), T. N. Ukwatta (LANL) (i.e. the Swift-BAT team):
Using the data set from T-240 to T+150 sec from the recent telemetry downlink, we report further analysis of BAT GRB 161104A (trigger #720568) (Mingo, et al., GCN Circ. 20123). The BAT ground-calculated position is RA, Dec = 77.906, -51.447 deg which is
```
   RA(J2000)  =  05h 11m 37.3s
   Dec(J2000) = -51d 26' 49.7"
```
with an uncertainty of 1.8 arcmin, (radius, sys+stat, 90% containment). The partial coding was 99%.
The mask-weighted light curve shows a single spike that starts at at ~T-0.02, peaks at ~T+0.02, and ends at~T+0.1. T90 (15-350 keV) is 0.1 +- 0.02 sec (estimated error including systematics).
The time-averaged spectrum from T-0.0 to T+0.1 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.57 +- 0.20. The fluence in the 15-150 keV band is 3.1 +- 0.5 x 10^-8 erg/cm2. The 1-sec peak photon flux measured from T-0.46 sec in the 15-150 keV band is 0.6 +- 0.1 ph/cm2/sec. All the quoted errors are at the 90% confidence level.
Using a 4-ms binned light curve, the lag analysis finds a lag of 2.0 +/- 8.0 ms for the 100-350 keV to 25-50 keV band, and -3.5 +/- 8.0 ms for the 50-100 keV to 15-25 keV band. These values are consistent with those of a short GRB.
The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/720568/BA/
GCN Circular #20130
M. H. Siegel (PSU) and B. Mingo (U. Leicester) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 161104A 69 s after the BAT trigger (Mingo et al., GCN Circ. 20123). No optical afterglow consistent with the XRT position (Goad et al. GCN Circ. 20124) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial exposures are:
```
Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white               69          170           99         >20.8
w1                4984         5184          197         >19.9
m2                4779         4979          197         >21.7
w2                5805         6005          197         >19.9
```
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.02 in the direction of the burst (Schlegel et al. 1998).
GCN Circular #20132
A. Nicuesa Guelbenzu, S. Schmidl (both TLS Tautenburg) and J. Greiner (MPE Garching) report on behalf of the GROND team:
We observed the field of GRB 161104A (Swift trigger 720568; Mingo et al., GCN 20123) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2m MPG telescope at the ESO La Silla Observatory (Chile).
Observations started at 04:00 UT on 2016-11-05, 18 hours after the GRB trigger. They were performed at an average seeing of 1" and at an average airmass of 1.2. Inside the enhanced 3.2" XRT position (GCN 20124, Goad et al.) we find a single source at coordinates:
Source A
```
RA (J2000.0) = 05:11:34.46
DEC (J2000.0) = -51:27:36.3
```
with an uncertainty of 0.5" in each coordinate.
At the border of the XRT error circle lie two more sources at coordinates:
Source B
```
RA (J2000.0) = 05:11:34.31
DEC (J2000.0) = -51:27:33.6
```
Source C
```
RA (J2000.0) = 05:11:34.73
DEC (J2000.0) = -51:27:34.2
```
Their r'-band AB magnitudes are:
```
Source A
r' = 24.1 +- 0.1 mag,
Source B
r' = 24.3 +- 0.1 mag,
Source C
r' = 25.1 +- 0.3 mag,
```
For the moment no evidence for a fading of any of these objects can be stated.
Given magnitudes are calibrated against GROND zeropoints and are not corrected for the Galactic foreground extinction corresponding to a reddening of E_(B-V) = 0.01 mag in the direction of the burst (Schlafly & Finkbeiner 2011).
We thank Angela Hempel, La Silla, for performing the observations.
GCN Circular #20137
E. Troja (UMD/GSFC), A. Watson (UNAM), S. Covino (INAF), W. H. Lee (UNAM), N. Butler (ASU), J. Becerra-Gonzalez (UMD/GSFC), A. Lien (UMBC), T. Sakamoto (AGU) and N. Gehrels (NASA/GSFC) report:
We observed the field of the short GRB 161104A (Mingo et al., GCN 20123) with the Gemini Multi-Object Spectrograph (GMOS) on the 8m Gemini South telescope. We acquired 6x120s exposures in the r-band beginning at 02:53 UT on 05 November 2016 (~17 hours after the Swift trigger) and under good observing conditions.
The three sources reported by Nicuesa Guelbenzu et al. (GCN 20132) are detected with similar magnitudes, showing no significant variability between our observations and the GROND exposures taken 1 hour later. Within the enhanced XRT position (Goad et al., GCN 20124) we detect an additional faint, point-like source not reported by Nicuesa Guelbenzu et al. (GCN 20132). The position of this source is RA, Dec = 05:11:34.5, -51:27:33.90 (J2000), accurate to about 0.5" in each coordinate. We measure a preliminary magnitude of r~24.6 (AB).
The lack of detection in the subsequent GROND observations suggests that the source significantly faded, however such rapid decay rate is unusual for a GRB optical afterglow.
We thank the Gemini staff and observers for rapidly scheduling and executing these observations.
GCN Circular #20166
R. Margutti (Northwestern U.), E. Berger (Harvard U.), and W. Fong (U. Arizona) report:
"We observed the location of the short GRB161104A with the Chandra X-ray Observatory (CXO) on 2016 Nov 8th, 14:41:45 UT, 364 ks after trigger (Mingo et al., GCN 20123) under a pre-approved guest observer program (PI Berger). No X-ray source is detected within the enhanced XRT position (Goad et al., GCN 20124). In particular, we do not find evidence for statistically significant X-ray emission at the location of the optical source reported by Troja et al., GCN 20137 at RA, Dec = 05:11:34.5, -51:27:33.90. Using 19.8 ks of CXO observations we infer a 3 sigma count-rate limit of 3.0E-4 c/s in the 0.5-8 keV energy range. The neutral hydrogen absorption in the direction of the transient is 1.4E+20 cm-2 (Kalberla et al., 2005). Assuming the spectral parameters that best fit the Swift-XRT observations (power-law photon index Gamma=1.36 and no evidence for intrinsic neutral hydrogen absorption, Burrows et al., GCN 20128) the inferred absorbed (unabsorbed) flux limit is Fx< 4.4E-15 erg/s/cm2 (Fx<4.5E-15 erg/s/cm2) in the 0.3-10 keV energy range. Our observations indicate a steepening of the X-ray afterglow temporal decay. Starting from 20 ks after trigger, the X-ray afterglow decays as t^-alpha with alpha>1.3.
We thank the CXO team for rapid scheduling of our observations."
GCN Circular #20168
W. Fong (University of Arizona) and R. Chornock (Ohio University) report:
We imaged the location of the short-duration GRB 161104A (Mingo et al., GCN 20213) with the Inamori-Magellan Areal Camera and Spectrograph (IMACS) mounted on the Magellan/Baade 6.5-m telescope at a mid-time of 2016 Nov 7.170 UT (2.77 days post-burst). We obtained 6x360-sec of r-band exposures in 1.0" seeing at an airmass of 1.3. We clearly detect the four optical sources reported from GROND (Nicuesa Guelbenzu et al.; GCN 20132) and Gemini (Troja et al.; GCN 20137) imaging. Given the relatively poor seeing, accurate photometry of the individual sources is challenging. However, the sources appear to have similar relative flux levels as previously reported, suggesting a lack of significant variability in any of these sources. We note that Source A (Nicuesa Guelbenzu et al.; GCN 20132) is fully coincident with the latest XRT position*, while the three remaining sources are on the outskirts of the position.
In addition, we obtained 3x1800-sec of spectroscopy with Magellan/IMACS on 2016 Nov 8 UT in 0.6" seeing at an airmass of 1.1. We used the 200 line grism and the f/2 camera to cover 4000-10000 Angstroms. The slit was aligned through Sources A and B (Nicuesa Guelbenzu et al.; GCN 20132) and also serendipitously passed through a nearby extended source 6.1" from the center of the XRT position (Source X; RA=5:11:34.77, Dec=-51:27:41.8). The spectrum of Source A exhibits a red continuum indicative of an early-type galaxy with prominent Ca II H+K stellar absorption lines at z=0.793. Source B has a faint trace with a single possible emission line of unknown identification near 9780 Angs. The spectrum of Source X is also that of an early-type galaxy at z=0.788. We note that both Sources A and X lack prominent emission lines of either [O II] 3727 or H-beta. The similarity in the redshifts of Sources A and X, their early-type galaxy spectra, and the abundance of extended sources in the vicinity of the XRT position may signify an origin from a cluster or group.
We thank Magellan telescope operators Hernan, Jorge and Mauricio for their assistance with these observations.
*http://www.swift.ac.uk/xrt_positions/
Redshift z= 0.793 +- 0.003 from host galaxy emission (CaII H&K)
W.-F. Fong et al. 2022, ApJ 940, 56

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