Gamma-ray Burst 130807A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Wed 07 Aug 13 10:27:24 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     565651,   Seg_Num: 0
GRB_RA:          269.801d {+17h 59m 12s} (J2000),
                 270.015d {+18h 00m 04s} (current),
                 269.015d {+17h 56m 04s} (1950)
GRB_DEC:         -27.613d {-27d 36' 44"} (J2000),
                 -27.613d {-27d 36' 44"} (current),
                 -27.610d {-27d 36' 34"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       4963 [cnts]    Image_Peak=260 [image_cnts]
TRIGGER_DUR:     1.024 [sec] 
TRIGGER_INDEX:   146     E_range: 25-100 keV
BKG_INTEN:       31864 [cnts]
BKG_TIME:        37525.11 SOD {10:25:25.11} UT
BKG_DUR:         8 [sec]
GRB_DATE:        16511 TJD;   219 DOY;   13/08/07
GRB_TIME:        37543.29 SOD {10:25:43.29} UT
GRB_PHI:         -167.84 [deg]
GRB_THETA:        24.78 [deg]
SOLN_STATUS:     0x3
RATE_SIGNIF:     12.96 [sigma]
IMAGE_SIGNIF:    9.29 [sigma]
MERIT_PARAMS:     +1  +0  +0  +0  +2  +0  +0  +1 +69  +0 
SUN_POSTN:       137.55d {+09h 10m 12s}  +16.31d {+16d 18' 36"}
SUN_DIST:        134.78 [deg]   Sun_angle= -8.8 [hr] (East of Sun)
MOON_POSTN:      141.96d {+09h 27m 50s}   +9.77d {+09d 46' 12"}
MOON_DIST:       128.09 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:        2.66, -1.90 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      269.82, -4.17 [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 = 209.27,20.46 [deg].

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Wed 07 Aug 13 10:27:39 UT
NOTICE_TYPE:     Swift-XRT Nack-Position
TRIGGER_NUM:     565651,   Seg_Num: 0
POINT_RA:        269.805d {+17h 59m 13s} (J2000)
POINT_DEC:       -27.614d {-27d 36' 51"} (J2000)
IMG_START_DATE:  16511 TJD;   219 DOY;   13/08/07
IMG_START_TIME:  37628.24 SOD {10:27:08.24} UT,   84.9 [sec] since BAT Trigger Time
COUNTS:          11    Min_needed= 20
STD_DEV:         0.00   Max_StdDev_for_Good=28.44 [arcsec]
PH2_ITER:        1    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:     Wed 07 Aug 13 10:29:45 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     565651,   Seg_Num: 0
GRB_RA:          269.801d {+17h 59m 12s} (J2000),
                 270.015d {+18h 00m 04s} (current),
                 269.015d {+17h 56m 04s} (1950)
GRB_DEC:         -27.613d {-27d 36' 44"} (J2000),
                 -27.613d {-27d 36' 44"} (current),
                 -27.610d {-27d 36' 34"} (1950)
GRB_DATE:        16511 TJD;   219 DOY;   13/08/07
GRB_TIME:        37543.29 SOD {10:25:43.29} UT
TRIGGER_INDEX:   146
GRB_PHI:         -167.84 [deg]
GRB_THETA:        24.78 [deg]
DELTA_TIME:      -57.00 [sec]
TRIGGER_DUR:     1.024 [sec] 
SOLN_STATUS:     0x3
RATE_SIGNIF:     12.96 [sigma]
IMAGE_SIGNIF:    9.29 [sigma]
LC_URL:          sw00565651000msb.lc
SUN_POSTN:       137.55d {+09h 10m 12s}  +16.31d {+16d 18' 34"}
SUN_DIST:        134.77 [deg]   Sun_angle= -8.8 [hr] (East of Sun)
MOON_POSTN:      141.98d {+09h 27m 55s}   +9.76d {+09d 45' 50"}
MOON_DIST:       128.07 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:        2.66, -1.90 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      269.82, -4.17 [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 = 209.27,20.46 [deg].

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Wed 07 Aug 13 10:35:23 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     565651,   Seg_Num: 0
POINT_RA:        269.806d {+17h 59m 13s} (J2000)
POINT_DEC:       -27.612d {-27d 36' 43"} (J2000)
POINT_ROLL:      265.917d
IMG_START_DATE:  16511 TJD;   219 DOY;   13/08/07
IMG_START_TIME:  37688.33 SOD {10:28:08.33} UT,   145.0 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        1.128
N_STARS:         190
X_OFFSET:        266 [pixels]
Y_OFFSET:        298 [pixels]
X_MAX:           1705 [pixels]
Y_MAX:           1737 [pixels]
DET_THRESH:      9
PHOTO_THRESH:    4
SL_URL:          sw00565651000msufc0145.fits
SUN_POSTN:       137.55d {+09h 10m 13s}  +16.31d {+16d 18' 30"}
SUN_DIST:        134.78 [deg]   Sun_angle= -8.8 [hr] (East of Sun)
MOON_POSTN:      142.02d {+09h 28m 06s}   +9.75d {+09d 44' 58"}
MOON_DIST:       128.03 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:        2.66, -1.90 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      269.83, -4.17 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Wed 07 Aug 13 10:35:52 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     565651,   Seg_Num: 0
POINT_RA:        269.806d {+17h 59m 13s} (J2000)
POINT_DEC:       -27.612d {-27d 36' 43"} (J2000)
POINT_ROLL:      265.917d
IMG_START_DATE:  16511 TJD;   219 DOY;   13/08/07
IMG_START_TIME:  37688.33 SOD {10:28:08.33} UT,   145.0 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        1.128
N_STARS:         190
X_OFFSET:        266 [pixels]
Y_OFFSET:        298 [pixels]
X_MAX:           1705 [pixels]
Y_MAX:           1737 [pixels]
DET_THRESH:      9
PHOTO_THRESH:    4
SL_URL:          sw00565651000msufc0145.fits
SUN_POSTN:       137.55d {+09h 10m 13s}  +16.31d {+16d 18' 30"}
SUN_DIST:        134.78 [deg]   Sun_angle= -8.8 [hr] (East of Sun)
MOON_POSTN:      142.03d {+09h 28m 07s}   +9.75d {+09d 44' 53"}
MOON_DIST:       128.03 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:        2.66, -1.90 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      269.83, -4.17 [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:     Wed 07 Aug 13 10:36:38 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     565651,   Seg_Num: 0
POINT_RA:        269.806d {+17h 59m 13s} (J2000)
POINT_DEC:       -27.612d {-27d 36' 43"} (J2000)
ROLL:            265.917d
IMG_START_DATE:  16511 TJD;   219 DOY;   13/08/07
IMG_START_TIME:  37688.33 SOD {10:28:08.33} UT,   145.0 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     397564099
X_OFFSET:        825 [pixels]
Y_OFFSET:        857 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       985
Y_GRB_POS:       1017
BINNING_INDEX:   1
IM_URL:          sw00565651000msuni0156.fits
SUN_POSTN:       137.55d {+09h 10m 13s}  +16.31d {+16d 18' 29"}
SUN_DIST:        134.77 [deg]   Sun_angle= -8.8 [hr] (East of Sun)
MOON_POSTN:      142.04d {+09h 28m 08s}   +9.75d {+09d 44' 46"}
MOON_DIST:       128.02 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:        2.66, -1.90 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      269.83, -4.17 [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:     Wed 07 Aug 13 10:36:49 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     565651,   Seg_Num: 0
POINT_RA:        269.806d {+17h 59m 13s} (J2000)
POINT_DEC:       -27.612d {-27d 36' 43"} (J2000)
ROLL:            265.917d
IMG_START_DATE:  16511 TJD;   219 DOY;   13/08/07
IMG_START_TIME:  37688.33 SOD {10:28:08.33} UT,   145.0 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     397564099
X_OFFSET:        825 [pixels]
Y_OFFSET:        857 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       985
Y_GRB_POS:       1017
BINNING_INDEX:   1
IM_URL:          sw00565651000msuni0156.fits
SUN_POSTN:       137.56d {+09h 10m 13s}  +16.31d {+16d 18' 29"}
SUN_DIST:        134.77 [deg]   Sun_angle= -8.8 [hr] (East of Sun)
MOON_POSTN:      142.04d {+09h 28m 09s}   +9.75d {+09d 44' 44"}
MOON_DIST:       128.02 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:        2.66, -1.90 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      269.83, -4.17 [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 Circular #15082
SUBJECT: GRB 130807A: Swift detection of a GRB or Galactic transient
A. Melandri (INAF-OAB), D. N. Burrows (PSU), P. A. Evans (U Leicester), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA), F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL), M. H. Siegel (PSU), M. Stamatikos (OSU/NASA/GSFC) and R. L. C. Starling (U Leicester) report on behalf of the Swift Team:
At 10:25:43 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 130807A (trigger=565651). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 269.801, -27.613 which is
```
   RA(J2000) = 17h 59m 12s
   Dec(J2000) = -27d 36' 44"
```
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single-peaked structure with a duration of at least 30 sec. The peak count rate was ~2000 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 10:27:08.2 UT, 85.0 seconds after the BAT trigger. Although a bright and variable source is apparent in the promptly downloaded light curve, the instrument did not centroid on the source in the initial 2.5-s promptly downloaded image, and the XRT stayed in WT mode for the remainder of the short first snapshot until Swift slewed away from the target. We therefore will have to wait until the second orbit to localize the XRT counterpart.
UVOT took a finding chart exposure of 166 seconds with the U filter starting 145 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 25% of the BAT error circle. Because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the sub-image. The 8'x8' region for the list of sources generated on-board covers 100% of the BAT error circle. Because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the region. No correction has been made for the large, but uncertain extinction expected.
Due to the proximity of this source to the Galactic center (3.3 degrees from the center) it is more likely that this is a Galactic source rather than a cosmological GRB. Determination of the nature of this source will require the full downlinked data.
Burst Advocate for this burst is A. Melandri (andrea.melandri 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 NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Wed 07 Aug 13 11:47:59 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     565651,   Seg_Num: 0
POINT_RA:        269.776d {+17h 59m 06s} (J2000)
POINT_DEC:       -27.611d {-27d 36' 40"} (J2000)
POINT_ROLL:      265.971d
IMG_START_DATE:  16511 TJD;   219 DOY;   13/08/07
IMG_START_TIME:  41115.64 SOD {11:25:15.64} UT,   3572.3 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        1.656
N_STARS:         190
X_OFFSET:        311 [pixels]
Y_OFFSET:        611 [pixels]
X_MAX:           1270 [pixels]
Y_MAX:           1570 [pixels]
DET_THRESH:      11
PHOTO_THRESH:    5
SL_URL:          sw00565651000msufc3572.fits
SUN_POSTN:       137.60d {+09h 10m 25s}  +16.29d {+16d 17' 39"}
SUN_DIST:        134.70 [deg]   Sun_angle= -8.8 [hr] (East of Sun)
MOON_POSTN:      142.62d {+09h 30m 29s}   +9.56d {+09d 33' 40"}
MOON_DIST:       127.40 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:        2.65, -1.88 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      269.80, -4.17 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Wed 07 Aug 13 11:48:26 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     565651,   Seg_Num: 0
POINT_RA:        269.776d {+17h 59m 06s} (J2000)
POINT_DEC:       -27.611d {-27d 36' 40"} (J2000)
POINT_ROLL:      265.971d
IMG_START_DATE:  16511 TJD;   219 DOY;   13/08/07
IMG_START_TIME:  41115.64 SOD {11:25:15.64} UT,   3572.3 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        1.656
N_STARS:         190
X_OFFSET:        311 [pixels]
Y_OFFSET:        611 [pixels]
X_MAX:           1270 [pixels]
Y_MAX:           1570 [pixels]
DET_THRESH:      11
PHOTO_THRESH:    5
SL_URL:          sw00565651000msufc3572.fits
SUN_POSTN:       137.60d {+09h 10m 25s}  +16.29d {+16d 17' 39"}
SUN_DIST:        134.70 [deg]   Sun_angle= -8.8 [hr] (East of Sun)
MOON_POSTN:      142.63d {+09h 30m 30s}   +9.56d {+09d 33' 36"}
MOON_DIST:       127.39 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:        2.65, -1.88 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      269.80, -4.17 [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.gz file does not exist; skipping the attachment.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Wed 07 Aug 13 11:50:22 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     565651,   Seg_Num: 0
POINT_RA:        269.776d {+17h 59m 06s} (J2000)
POINT_DEC:       -27.611d {-27d 36' 40"} (J2000)
ROLL:            265.971d
IMG_START_DATE:  16511 TJD;   219 DOY;   13/08/07
IMG_START_TIME:  41115.64 SOD {11:25:15.64} UT,   3572.3 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     397567526
X_OFFSET:        630 [pixels]
Y_OFFSET:        930 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       790
Y_GRB_POS:       1090
BINNING_INDEX:   1
IM_URL:          sw00565651000msuni3583.fits
SUN_POSTN:       137.60d {+09h 10m 25s}  +16.29d {+16d 17' 37"}
SUN_DIST:        134.70 [deg]   Sun_angle= -8.8 [hr] (East of Sun)
MOON_POSTN:      142.64d {+09h 30m 34s}   +9.55d {+09d 33' 18"}
MOON_DIST:       127.38 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:        2.65, -1.88 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      269.80, -4.17 [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:     Wed 07 Aug 13 11:50:37 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     565651,   Seg_Num: 0
POINT_RA:        269.776d {+17h 59m 06s} (J2000)
POINT_DEC:       -27.611d {-27d 36' 40"} (J2000)
ROLL:            265.971d
IMG_START_DATE:  16511 TJD;   219 DOY;   13/08/07
IMG_START_TIME:  41115.64 SOD {11:25:15.64} UT,   3572.3 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     397567526
X_OFFSET:        630 [pixels]
Y_OFFSET:        930 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       790
Y_GRB_POS:       1090
BINNING_INDEX:   1
IM_URL:          sw00565651000msuni3583.fits
SUN_POSTN:       137.60d {+09h 10m 25s}  +16.29d {+16d 17' 37"}
SUN_DIST:        134.70 [deg]   Sun_angle= -8.8 [hr] (East of Sun)
MOON_POSTN:      142.64d {+09h 30m 35s}   +9.55d {+09d 33' 15"}
MOON_DIST:       127.37 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:        2.65, -1.88 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      269.80, -4.17 [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 Circular #15083
C. B. Markwardt (GSFC), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), A. Y. Lien (NASA/GSFC/ORAU), A. Melandri (INAF-OAB), D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU), T. N. Ukwatta (MSU) (i.e. the Swift-BAT team):
Using the data set from T-60 to T+243 sec from the recent telemetry downlink, we report further analysis of BAT GRB 130807A (trigger #565651) (Melandri, et al., GCN Circ. 15082). The BAT ground-calculated position is RA, Dec = 269.801, -27.616 deg, which is
```
    RA(J2000)  =  17h 59m 12.4s
    Dec(J2000) = -27d 36' 56.7"
```
with an uncertainty of 1.7 arcmin, (radius, sys+stat, 90% containment). The partial coding was 92%.
Based on the currently available event data, the mask-weighted light curve shows an initial FRED-like peak starting at T-10 sec, peaking at T=0 sec and decaying to background by T+50 sec. This is followed by at least two more weaker peaks, one from roughly T+90 sec to T+130 sec and the second beginning at T+160 sec and continuing until the data cuts off at T+243 seconds. The two later peaks are coincident with flares seen in the Swift/XRT data. We note also that the Swift satellite slewed away from the source location at ~T+300 seconds, while an XRT flare was still ongoing. Since we do not have all of the data, we cannot determine T90 at this time.
The time-averaged spectrum from T-12.18 to T+163.82 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 0.31 +- 0.89, and Epeak of 75.9 +- 35.2 keV (chi squared 56.96 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 1.2 +- 0.2 x 10^-06 erg/cm2 and the 1-sec peak flux measured from T-4.68 sec in the 15-150 keV band is 0.4 +- 0.1 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.46 +- 0.17 (chi squared 63.40 for 57 d.o.f.). All the quoted errors are at the 90% confidence level.
The current analysis of the BAT data does not allow us to distinguish between the interpretations of this event as either a GRB or galactic transient. These results will be updated as more event data becomes available.
Examination of archival images from the Swift/BAT transient monitor through 3:03 UT, August 6, 2013 (~31.5 hours before the trigger) shows no sign of earlier emission from the location of trigger 565651.
The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/565651/BA/
GCN Circular #15085
A. Melandri (INAF/OAB), D.N. Burrows (PSU), P. Romano (INAF-IASFPA), H.A. Krimm (GSFC/USRA), J.P. Osborne, P.A. Evans (U. Leicester), N. Gehrels (GSFC) report on behalf of the Swift team.
We have analysed 14.4 ks of XRT data for GRB 130807A (Melandri et al. GCN Circ. 15082), from 88 s to 80 ks after the BAT trigger. The XRT position for this burst is RA, Dec = 269.8007, -27.6159 which is equivalent to:
```
RA (J2000): 17h 59m 12.16s
Dec (J2000): -27d 36' 57.5"
```
with an uncertainty of 3.6 arcsec (radius, 90% confidence).
In the first orbit (WT mode) the source is initially detected at a rate of ~10 XRT count/s, rising to ~100 c/s at the end of the first orbit. During this period the spectrum can be fit by an absorbed power- law model with a photon index of 1.56 +/- 0.08. The source showed an absorption column of (8.6 +/- 1.0) x 10^21 cm^-2, slightly in excess with respect to the Galactic value of 6 x 10^21 cm^-2 (Kalberla et al. 2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 8.0 x 10^-11 (1.2 x 10^-10) erg cm^-2 count^-1.
In the second orbit (PC mode) the source had become much fainter (~0.03 c/s), and much softer, with a photon index of 2.3 (+0.5, -0.4).The source still showed an absorption column (9.0 +/- 5.0 x 10^21 cm^-2) consistent with the Galactic value. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 5.0 x 10^-11 (1.7 x 10^-10) erg cm^-2 count^-1. Starting with the second orbit, the light curve rose from a count rate of ~0.015 c/s after ~4 ks to a maximum of ~0.06 c/s at ~10 ks (with slope of -1.5 +/- 0.1). After that it decayed with a slope of 0.9 +/- 0.1, reaching the count rate of ~0.012 c/s at ~75 ks.
The light curve behaviour (at late times) is unusual, but not unprecedented, for a GRB. The BAT and XRT spectral indices are similar to those observed for GRB 060124 (BAT spectrum gamma = 1.89 +/- 0.19, XRT-WT spectrum gamma = 1.40+/-0.01, XRT-PC spectrum gamma = 2.1+/-0.1; Romano et al., 2006, A&A, 456, 917) and for the transient supermassive black hole Swift J1644+57 (Burrows et al., 2011, Nature, 476, 421), but inconsistent with what generally observed for a Supergiant Fast X-ray Transient. The dynamical range of GRB 130807A (~3300) is similar to what observed for GRB 060124 or for a typical SFXT, but very different from what was observed for Swift J1644+57.
The source was not detected in the BAT transient monitor (15-50 keV) before 3:03 UT, August 6, 2013, the most recent monitor epoch currently available. Events like Swift J1644+57 or SFXTs are usually detected in X-rays for several days before the trigger, Swift J1644+57 behaved similarly. It is therefore likely that BAT trigger 565651 was a somewhat unusual GRB rather than a Galactic or extragalactic transient, in spite of its proximity to the Galactic center.
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/possible_GRBs/00565651/source1
GCN Circular #15086
M. De Pasquale (UCL-MSSL) and A. Melandri (INAF-OAB) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 130807A 145 s after the BAT trigger (Melandri et al., GCN Circ. 15082). No optical source consistent with the XRT position (Melandri et al., GCN Circ. 15085) is detected in the UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent summed exposures are:
```
Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white_FC          3572         3722          147         >20.3
white             3572         5573          541         >21.1
v                 4348         5984          393         >19.3
b                 3732         5369          393         >20.3
u_FC               145          311          163         >19.7
u                  145         5164          360         >19.9
w1                4759         4959          197         >19.6
m2                4552         6078          284         >19.7
w2                4143         5780          393         >20.2
```
The magnitudes in the table are not corrected for the strong Galactic extinction corresponing to the reddening of E(B-V) = 2.03 in the direction of the burst (Schlegel et al. 1998).
GCN Circular #15087
M. De Pasquale (UCL-MSSL) reports on behalf of the Swift/UVOT team:
In the previous GCN Circ. 15086 "GRB130807A: Swift/UVOT observations", the sentence "No optical source" should be changed into "No uncatalogued optical source".
I apologize for the mistake.
ATEL #5268
Title: Swift observations of GRB 130807A/SWIFT J1759.2-2736
A. Melandri (INAF/OAB), D. N. Burrows (PSU), K. Page (U Leicester), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/NASA), P. Romano (INAF/IASFPA), S. D. Barthelmy (NASA/GSFC), D. Malesani (DARK/NBI), V. D;Elia (ASI-ASDC), G. Tagliaferri (INAF-OAB), N. Gehrels (NASA/GSFC)
At 10:25:43 UT on 2013 August 7th Swift/BAT triggered on and located a transient source, initially named GRB 130807A (trigger=565651; Melandri et al., GCN #15082). The best available position for this source is
```
RA (J2000): 17h 59m 12.16s

Dec (J2000): -27d 36' 57.5"
```
with an uncertainty of 3.6 arcsec (radius, 90% confidence). This location does not correspond with any known cataloged object and is close to the Galactic center (3.3 degrees from the center).
The mask-weighted BAT light curve shows an initial FRED-like peak starting at T-10 sec, peaking at T=0 sec and decaying to background by T+50 sec. This was followed by at least two more weaker peaks, one from roughly T+90 sec to T+130 sec and the second beginning at T+160 sec and continuing until the data cut off at T+243 seconds (Markwardt et al., GCN #15083). The two later peaks are coincident with flares seen in the Swift/XRT data. From the BAT point of view, the detection is consistent either with a long, moderately soft burst, or with a Galactic source.
The XRT light curve showed initially some flare activity between ~10 and ~100 cts/s during the first 300 s. At late times (t>3000s) the source became much fainter, rising from a count rate of ~0.015 c/s after ~3 ks to a maximum of ~0.06 c/s at ~10 ks (with slope alpha of -1.23 (+ 0.44, -0.27), F ∝ t^-α). After that it decayed with a slope of 1.21 (+ 0.30, -0.24) reaching the count rate of ~0.012 c/s at ~80 ks. Then between ~1 and ~5 days the X-ray count rate became roughly constant, decaying with an index of 0.3 (+0.3, -0.6) and consistent with the value of ~0.003 cts/s. This is rather unusual behavior for a GRB lightcurve, raising again the issue of the nature of this source.
The BAT and XRT spectral indices are similar to those observed for GRB 060124 (BAT spectrum gamma = 1.89 +/- 0.19, XRT-WT spectrum gamma = 1.40+/-0.01, XRT-PC spectrum gamma = 2.1+/-0.1; Romano et al., 2006, A&A, 456, 917) and for the transient Tidal Disruption Event Swift J1644+57 (Burrows et al., 2011, Nature, 476, 421), but inconsistent with what generally observed for a Supergiant Fast X-ray Transient. The dynamical range of GRB 130807A (~3300) is similar to that observed for GRB 060124 or for a typical SFXT, but very different from what was observed for Swift J1644+57.
The source was not detected in the BAT hard X-ray transient monitor (15-50 keV) in one-day averages over the period from 2013 August 1-11. This tells us that there is no significant emission in this energy range either before or after the trigger interval. Events like Swift J1644+57 or SFXTs are usually detected in X-rays for several days before the trigger, and events like Swift J1644+57 are detected for multiple days after the trigger. We note that due to its proximity to the Galactic center the extinction towards this object is quite high (E(B-V) = 2.03, Schlegel et al., 1998), there is no detection of an optical counterpart by UVOT with an 3 sigma upper limit of v>19 (De Pasquale & Melandri, GCN #15086).
The nature of this event is still ambiguous: trigger 565651 might be a somewhat unusual GRB, a Galactic transient or even an extragalactic transient, in spite of its proximity to the Galactic center.
Further observations at all wavelengths are strongly encouraged.
GCN Report 449.1
GCN_Report 449.1 has been posted: http://gcn.gsfc.nasa.gov/reports/report_449_1.pdf by A. Melandri at INAF-OAB titled: "Swift Observations of GRB 130807A"

Back to JG's homepage

Jochen Greiner, last update: 26-Apr-2014 [Disclaimer]