Gamma-ray Burst 120811A

(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:     Sat 11 Aug 12 02:35:42 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     530581,   Seg_Num: 0
GRB_RA:          257.183d {+17h 08m 44s} (J2000),
                 257.373d {+17h 09m 29s} (current),
                 256.429d {+17h 05m 43s} (1950)
GRB_DEC:         -22.736d {-22d 44' 08"} (J2000),
                 -22.751d {-22d 45' 04"} (current),
                 -22.672d {-22d 40' 19"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       6189 [cnts]    Image_Peak=212 [image_cnts]
TRIGGER_DUR:     1.024 [sec] 
TRIGGER_INDEX:   137     E_range: 15-50 keV
BKG_INTEN:       42099 [cnts]
BKG_TIME:        9302.47 SOD {02:35:02.47} UT
BKG_DUR:         8 [sec]
GRB_DATE:        16150 TJD;   224 DOY;   12/08/11
GRB_TIME:        9318.92 SOD {02:35:18.92} UT
GRB_PHI:           9.01 [deg]
GRB_THETA:        15.72 [deg]
SOLN_STATUS:     0x10D
RATE_SIGNIF:     10.24 [sigma]
IMAGE_SIGNIF:    7.05 [sigma]
MERIT_PARAMS:     +0  +0 +95  +0  +1  -3  +0  +1 +48  +0 
SUN_POSTN:       141.27d {+09h 25m 04s}  +15.18d {+15d 10' 36"}
SUN_DIST:        119.53 [deg]   Sun_angle= -7.7 [hr] (East of Sun)
MOON_POSTN:       61.13d {+04h 04m 31s}  +20.71d {+20d 42' 24"}
MOON_DIST:       164.78 [deg]
MOON_ILLUM:      38 [%]
GAL_COORDS:        0.60, 10.34 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      258.19,  0.18 [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 matches a source in the on-board catalog: Num=10363=4U_1708-23,   delta=0.100 [deg].  
COMMENTS:        This matches a source in the ground catalog: 4U_1708-23,   delta=0.100 [deg].  
COMMENTS:        This is not a GRB.  
COMMENTS:        This trigger occurred at longitude,latitude = 185.48,-7.36 [deg].

GCN NOTICE

  
TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 11 Aug 12 02:35:57 UT
NOTICE_TYPE:     Swift-BAT Transient Position
TRIGGER_NUM:     530581,   Seg_Num: 0
GRB_RA:          257.183d {+17h 08m 44s} (J2000),
                 257.373d {+17h 09m 29s} (current),
                 256.429d {+17h 05m 43s} (1950)
GRB_DEC:         -22.736d {-22d 44' 08"} (J2000),
                 -22.751d {-22d 45' 04"} (current),
                 -22.672d {-22d 40' 19"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       6189 [cnts]    Image_Peak=212 [image_cnts]
TRIGGER_DUR:     1.024 [sec] 
TRIGGER_INDEX:   137     E_range: 15-50 keV
BKG_INTEN:       42099 [cnts]
BKG_TIME:        9302.47 SOD {02:35:02.47} UT
BKG_DUR:         8 [sec]
GRB_DATE:        16150 TJD;   224 DOY;   12/08/11
GRB_TIME:        9318.92 SOD {02:35:18.92} UT
GRB_PHI:           9.01 [deg]
GRB_THETA:        15.72 [deg]
SOLN_STATUS:     0x10D
RATE_SIGNIF:     10.24 [sigma]
IMAGE_SIGNIF:    7.05 [sigma]
MERIT_PARAMS:     +0  +0 +95  +0  +1  -3  +0  +1 +48  +0 
SUN_POSTN:       141.27d {+09h 25m 04s}  +15.18d {+15d 10' 36"}
SUN_DIST:        119.53 [deg]   Sun_angle= -7.7 [hr] (East of Sun)
MOON_POSTN:       61.13d {+04h 04m 31s}  +20.71d {+20d 42' 25"}
MOON_DIST:       164.78 [deg]
MOON_ILLUM:      38 [%]
GAL_COORDS:        0.60, 10.34 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      258.19,  0.18 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT-BAT Transient Coordinates.  
COMMENTS:        This is a rate trigger.  
COMMENTS:        A point_source was found.  
COMMENTS:        This matches a source in the on-board catalog: Num=10363=4U_1708-23,   delta=0.100 [deg].  
COMMENTS:        This matches a source in the ground catalog: 4U_1708-23,   delta=0.100 [deg].  
COMMENTS:        This is not a GRB -- it is a hard x-ray transient.  
COMMENTS:        This trigger occurred at longitude,latitude = 185.48,-7.36 [deg].

GCN NOTICE

  
TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 11 Aug 12 02:39:20 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     530581,   Seg_Num: 0
GRB_RA:          257.183d {+17h 08m 44s} (J2000),
                 257.373d {+17h 09m 29s} (current),
                 256.429d {+17h 05m 43s} (1950)
GRB_DEC:         -22.736d {-22d 44' 08"} (J2000),
                 -22.751d {-22d 45' 04"} (current),
                 -22.672d {-22d 40' 19"} (1950)
GRB_DATE:        16150 TJD;   224 DOY;   12/08/11
GRB_TIME:        9318.92 SOD {02:35:18.92} UT
TRIGGER_INDEX:   137
GRB_PHI:           9.01 [deg]
GRB_THETA:        15.72 [deg]
DELTA_TIME:      -43.00 [sec]
TRIGGER_DUR:     1.024 [sec] 
SOLN_STATUS:     0x10D
RATE_SIGNIF:     10.24 [sigma]
IMAGE_SIGNIF:    7.05 [sigma]
LC_URL:          sw00530581000msb.lc
SUN_POSTN:       141.27d {+09h 25m 04s}  +15.18d {+15d 10' 33"}
SUN_DIST:        119.53 [deg]   Sun_angle= -7.7 [hr] (East of Sun)
MOON_POSTN:       61.16d {+04h 04m 38s}  +20.71d {+20d 42' 36"}
MOON_DIST:       164.81 [deg]
MOON_ILLUM:      38 [%]
GAL_COORDS:        0.60, 10.34 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      258.19,  0.18 [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 matches a source in the on-board catalog.  
COMMENTS:        This matches a source in the ground catalog: 4U_1708-23,   delta=0.100 [deg].  
COMMENTS:        This is not a GRB.  
COMMENTS:        This trigger occurred at longitude,latitude = 185.48,-7.36 [deg].

GCN NOTICE

  
TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 11 Aug 12 02:45:25 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     530581,   Seg_Num: 0
GRB_RA:          257.183d {+17h 08m 44s} (J2000),
                 257.373d {+17h 09m 29s} (current),
                 256.429d {+17h 05m 43s} (1950)
GRB_DEC:         -22.736d {-22d 44' 08"} (J2000),
                 -22.751d {-22d 45' 04"} (current),
                 -22.672d {-22d 40' 19"} (1950)
GRB_DATE:        16150 TJD;   224 DOY;   12/08/11
GRB_TIME:        9318.92 SOD {02:35:18.92} UT
TRIGGER_INDEX:   137
GRB_PHI:           9.01 [deg]
GRB_THETA:        15.72 [deg]
DELTA_TIME:      -43.00 [sec]
TRIGGER_DUR:     1.024 [sec] 
SOLN_STATUS:     0x10D
RATE_SIGNIF:     10.24 [sigma]
IMAGE_SIGNIF:    7.05 [sigma]
LC_URL:          sw00530581000msb.lc
SUN_POSTN:       141.27d {+09h 25m 05s}  +15.17d {+15d 10' 29"}
SUN_DIST:        119.52 [deg]   Sun_angle= -7.7 [hr] (East of Sun)
MOON_POSTN:       61.21d {+04h 04m 51s}  +20.72d {+20d 42' 55"}
MOON_DIST:       164.86 [deg]
MOON_ILLUM:      38 [%]
GAL_COORDS:        0.60, 10.34 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      258.19,  0.18 [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 matches a source in the on-board catalog.  
COMMENTS:        This matches a source in the ground catalog: 4U_1708-23,   delta=0.100 [deg].  
COMMENTS:        This is not a GRB.  
COMMENTS:        This trigger occurred at longitude,latitude = 185.48,-7.36 [deg].

GCN NOTICE

  
TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 11 Aug 12 02:48:45 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     530581,   Seg_Num: 0
GRB_RA:          257.183d {+17h 08m 44s} (J2000),
                 257.373d {+17h 09m 29s} (current),
                 256.429d {+17h 05m 43s} (1950)
GRB_DEC:         -22.736d {-22d 44' 08"} (J2000),
                 -22.751d {-22d 45' 04"} (current),
                 -22.672d {-22d 40' 19"} (1950)
GRB_DATE:        16150 TJD;   224 DOY;   12/08/11
GRB_TIME:        9318.92 SOD {02:35:18.92} UT
TRIGGER_INDEX:   137
GRB_PHI:           9.01 [deg]
GRB_THETA:        15.72 [deg]
DELTA_TIME:      -43.00 [sec]
TRIGGER_DUR:     1.024 [sec] 
SOLN_STATUS:     0x10D
RATE_SIGNIF:     10.24 [sigma]
IMAGE_SIGNIF:    7.05 [sigma]
LC_URL:          sw00530581000msb.lc
SUN_POSTN:       141.27d {+09h 25m 06s}  +15.17d {+15d 10' 26"}
SUN_DIST:        119.52 [deg]   Sun_angle= -7.7 [hr] (East of Sun)
MOON_POSTN:       61.24d {+04h 04m 58s}  +20.72d {+20d 43' 05"}
MOON_DIST:       164.89 [deg]
MOON_ILLUM:      38 [%]
GAL_COORDS:        0.60, 10.34 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      258.19,  0.18 [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 matches a source in the on-board catalog.  
COMMENTS:        This matches a source in the ground catalog: 4U_1708-23,   delta=0.100 [deg].  
COMMENTS:        This is not a GRB.  
COMMENTS:        This trigger occurred at longitude,latitude = 185.48,-7.36 [deg].

GCN NOTICE

  
TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sat 11 Aug 12 02:52:30 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     530581,   Seg_Num: 0
GRB_RA:          257.183d {+17h 08m 44s} (J2000),
                 257.373d {+17h 09m 29s} (current),
                 256.429d {+17h 05m 43s} (1950)
GRB_DEC:         -22.736d {-22d 44' 08"} (J2000),
                 -22.751d {-22d 45' 04"} (current),
                 -22.672d {-22d 40' 19"} (1950)
GRB_DATE:        16150 TJD;   224 DOY;   12/08/11
GRB_TIME:        9318.92 SOD {02:35:18.92} UT
TRIGGER_INDEX:   137
GRB_PHI:           9.01 [deg]
GRB_THETA:        15.72 [deg]
DELTA_TIME:      -43.00 [sec]
TRIGGER_DUR:     1.024 [sec] 
SOLN_STATUS:     0x10D
RATE_SIGNIF:     10.24 [sigma]
IMAGE_SIGNIF:    7.05 [sigma]
LC_URL:          sw00530581000msb.lc
SUN_POSTN:       141.28d {+09h 25m 07s}  +15.17d {+15d 10' 23"}
SUN_DIST:        119.52 [deg]   Sun_angle= -7.7 [hr] (East of Sun)
MOON_POSTN:       61.28d {+04h 05m 06s}  +20.72d {+20d 43' 17"}
MOON_DIST:       164.92 [deg]
MOON_ILLUM:      38 [%]
GAL_COORDS:        0.60, 10.34 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      258.19,  0.18 [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 matches a source in the on-board catalog.  
COMMENTS:        This matches a source in the ground catalog: 4U_1708-23,   delta=0.100 [deg].  
COMMENTS:        This is not a GRB.  
COMMENTS:        This trigger occurred at longitude,latitude = 185.48,-7.36 [deg].

GCN Circular #13618
B.-B. Zhang (PSU), S. D. Barthelmy (GSFC), N. Gehrels (NASA/GSFC), C. Gronwall (PSU), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA) and D. M. Palmer (LANL) report on behalf of the Swift Team:
At 02:35:18 UT, the Swift Burst Alert Telescope (BAT) triggered and located a possible GRB (120811A, trigger=530581). Swift did not slew to the location. The BAT on-board calculated location is RA, Dec 257.183, -22.736 which is
```
   RA(J2000)  =  17h 08m 44s
   Dec(J2000) = -22d 44' 08"   
```
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows a single peak with a duration of about 30 sec. The peak count rate was ~2500 counts/sec (15-350 keV), at ~0 sec after the trigger.
This source was matched to a source 4U 1708-23 (== X Oph X-2) in the on-board catalog, with an offset from the catalog position of 6 arcminutes. However, the latest position available is from the 1972 UHURU catalog, which has a large position uncertainty consistent with this offset.
At this time we cannot determine whether this is a GRB, the catalogued 4U 1708-23, or some previously-unknown Galactic transient.
Burst Advocate for this burst is B.-B. Zhang (bbzhang AT psu.edu). 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 #13633
S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (GSFC/UMBC), M. Stamatikos (OSU), J. Tueller (GSFC), T. N. Ukwatta (MSU), B.-B. Zhang (PSU) (i.e. the Swift-BAT team):
Using the data set from T-239 to T+963 sec from recent telemetry downlinks, we report further analysis of BAT GRB 120811A (trigger #530581) (Zhang, et al., GCN Circ. 13618). The BAT ground-calculated position is RA, Dec = 257.184, -22.735 deg, which is
```
   RA(J2000)  =  17h 08m 44.1s 
   Dec(J2000) = -22d 44' 06.7" 
```
with an uncertainty of 2.6 arcmin, (radius, sys+stat, 90% containment). The partial coding was 98%.
The mask-weighted light curve shows two overlapping peaks starting at ~T-20 sec, peaking at ~T+2 sec, ending at ~T+25 sec with a flat section out to ~T+160 sec. T90 (15-350 keV) is 166 +- 52 sec (estimated error including systematics).
The time-averaged spectrum from T-14.16 to T+169.06 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.95 +- 0.20. The fluence in the 15-150 keV band is 1.1 +- 0.1 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+0.43 sec in the 15-150 keV band is 1.0 +- 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/530581/BA/
While the BAT lightcurve and spectral results are consistant with a GRB origin for this trigger, given that the galactic coordinates are (lon,lat)=(0.6,10.3) deg, we cannot rule out a galactic source origin.
GCN Circular #13641
B.-B. Zhang (PSU), S. R. Oates (UCL-MSSL), K. L. Page (U Leicester), P.A. Evans (U. Leicester), D. N. Burrows (PSU), J. R. Cummings (GSFC/UMBC), J. A. Kennea (PSU),H. A. Krimm (GSFC/USRA), E. Helder (PSU) and S. D. Barthelmy (GSFC) report on behalf of the Swift-XRT and Swift-UVOT team:
We report further Swift XRT-UVOT observations of GRB 120811A (Zhang et al, GCN 13618).
We performed 9.1 ks follow-up XRT observations of the field at T0+1.6 hr, T0+0.27 day, T0+0.94 days and T0+3.1 days (where T0 = 2012 Aug 11 at 02:35:18 UT ), in order to determine whether or not the X-ray source had faded. We find a fading source with count rates in the 0.3-10 keV band as follows :
```
T-T0                     Count Rate
(5.8+/-0.2) x10^3 s     0.05+/-0.01 count/s
(2.2+/-0.01)x10^4 s     0.02+/-0.01 count/s
(8.1+/-0.03)x10^4 s     0.02+/-0.001 count/s
(2.7+/-0.2) x10^5 s   < 0.005 count/s
```
The data are entirely in Photon Counting (PC) mode. Using 1227 s of PC mode data and 2 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 257.16542, -22.71054 , which is equivalent to:
```
RA (J2000): 17h 08m 39.70s
Dec(J2000): -22d 42' 38.0"
```
with an uncertainty of 2.8 arcsec (radius, 90% confidence).
The light curve can be modelled with a power-law decay with a decay index of alpha=0.31 (+0.13, -0.12).
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.9 (+/-0.5). The best-fitting absorption column is 7.4 (+4.2, -3.0) x 10^21 cm^-2, in excess of the Galactic value of 1.5 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 5.5 x 10^-11 (9.7 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Total column:	     7.4 (+4.2, -3.0) x 10^21 cm^-2
Galactic foreground: 1.5 x 10^21 cm^-2
Excess significance: 3.2 sigma
Photon index:	     1.9 (+/-0.5)
```
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00530581.
The fact that the XRT source is fading suggests that Swift trigger 530581 (Zhang et al., GCN Circ. 13618) is most likely a GRB.
The Swift/UVOT began settled observations of the field of GRB 120811A 5627 s after the BAT trigger (Zhang et al., GCN Circ. 13618). No optical afterglow consistent with the XRT position 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           6243        6443         197        > 20.7    
v               6654        6853         197        > 19.1    
b               6038        7593         313        > 20.2    
u               5832        7468         393        > 20.0     
uvw1            5627        7263         393        > 19.9
uvw2            6449        6649         197        > 19.8    
```
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.77 in the direction of the burst (Schlegel et al. 1998).
This circular is an official product of the Swift-XRT and Swift-UVOT team.
GCN Report 413.1
GCN_Report 413.1 has been posted: http://gcn.gsfc.nasa.gov/reports/report_413_1.pdf by B.-B. Zhang at PSU titled: "Swift Observations of GRB 120811A"

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Jochen Greiner, last update: 10-Jan-2013 [Disclaimer]