Gamma-ray Burst 110420B

(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:     Wed 20 Apr 11 22:42:24 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     451794,   Seg_Num: 0
GRB_RA:          320.049d {+21h 20m 12s} (J2000),
                 320.229d {+21h 20m 55s} (current),
                 319.250d {+21h 17m 00s} (1950)
GRB_DEC:         -41.264d {-41d 15' 51"} (J2000),
                 -41.216d {-41d 12' 57"} (current),
                 -41.477d {-41d 28' 35"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       422 [cnts]    Image_Peak=56 [image_cnts]
TRIGGER_DUR:     0.032 [sec] 
TRIGGER_INDEX:   10319     E_range: 25-100 keV
BKG_INTEN:       25324 [cnts]
BKG_TIME:        81721.12 SOD {22:42:01.12} UT
BKG_DUR:         8 [sec]
GRB_DATE:        15671 TJD;   110 DOY;   11/04/20
GRB_TIME:        81731.68 SOD {22:42:11.68} UT
GRB_PHI:         129.28 [deg]
GRB_THETA:        32.37 [deg]
SOLN_STATUS:     0x3
RATE_SIGNIF:     34.19 [sigma]
IMAGE_SIGNIF:    8.11 [sigma]
MERIT_PARAMS:     +1  +0  +0  -5  +2  -2  +0  +0 -14  +0 
SUN_POSTN:        28.39d {+01h 53m 34s}  +11.65d {+11d 38' 48"}
SUN_DIST:         81.89 [deg]   Sun_angle= 4.5 [hr] (West of Sun)
MOON_POSTN:      247.63d {+16h 30m 30s}  -23.28d {-23d 16' 32"}
MOON_DIST:        62.16 [deg]
MOON_ILLUM:      89 [%]
GAL_COORDS:        0.55,-44.84 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      309.25,-24.40 [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 = 245.19,1.04 [deg].

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Wed 20 Apr 11 22:42:31 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      48
TRIGGER_NUM:     325032133
GRB_RA:          311.250d {+20h 45m 00s} (J2000),
                 311.442d {+20h 45m 46s} (current),
                 310.399d {+20h 41m 36s} (1950)
GRB_DEC:         -44.850d {-44d 51' 00"} (J2000),
                 -44.808d {-44d 48' 29"} (current),
                 -45.032d {-45d 01' 54"} (1950)
GRB_ERROR:       16.58 [deg radius, statistical plus systematic]
GRB_INTEN:       3242 [cnts/sec]
DATA_SIGNIF:     13.50 [sigma]
INTEG_TIME:      0.016 [sec]
GRB_DATE:        15671 TJD;   110 DOY;   11/04/20
GRB_TIME:        81731.73 SOD {22:42:11.73} UT
GRB_PHI:          20.00 [deg]
GRB_THETA:       130.00 [deg]
DATA_TIME_SCALE: 0.0160 [sec]
HARD_RATIO:      0.31
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      95%  GRB
2nd_MOST_LIKELY:   3%  Generic Transient
DETECTORS:       0,0,1, 0,0,1, 0,0,0, 0,0,0, 0,0,
SUN_POSTN:        28.39d {+01h 53m 34s}  +11.65d {+11d 38' 49"}
SUN_DIST:         89.16 [deg]   Sun_angle= 5.1 [hr] (West of Sun)
MOON_POSTN:      247.63d {+16h 30m 31s}  -23.28d {-23d 16' 32"}
MOON_DIST:        55.52 [deg]
MOON_ILLUM:      89 [%]
GAL_COORDS:      355.70,-38.43 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      301.28,-25.79 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 256.50,-18.32 [deg].

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Wed 20 Apr 11 22:42:46 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      58
TRIGGER_NUM:     325032133
GRB_RA:           70.010d {+04h 40m 02s} (J2000),
                  70.188d {+04h 40m 45s} (current),
                  69.223d {+04h 36m 54s} (1950)
GRB_DEC:         +29.330d {+29d 19' 48"} (J2000),
                 +29.351d {+29d 21' 05"} (current),
                 +29.233d {+29d 13' 59"} (1950)
GRB_ERROR:       90.00 [deg radius, statistical only]
DATA_SIGNIF:     18.50 [sigma]
DATA_INTERVAL:   0.016 [sec]
GRB_DATE:        15671 TJD;   110 DOY;   11/04/20
GRB_TIME:        81731.73 SOD {22:42:11.73} UT
GRB_PHI:           0.00 [deg]
GRB_THETA:         0.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   413 (Gnd S/W Version number)
SUN_POSTN:        28.39d {+01h 53m 34s}  +11.65d {+11d 38' 49"}
SUN_DIST:         42.66 [deg]   Sun_angle= -2.8 [hr] (East of Sun)
MOON_POSTN:      247.63d {+16h 30m 31s}  -23.28d {-23d 16' 33"}
MOON_DIST:       173.51 [deg]
MOON_ILLUM:      89 [%]
GAL_COORDS:      171.27,-11.39 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       72.52,  7.10 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        In the LAT Field-of-view.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.

GCN NOTICE

TITLE:          GCN/INTEGRAL NOTICE
NOTICE_DATE:    Wed 20 Apr 11 22:42:49 UT 
NOTICE_TYPE:    INTEGRAL SPI ACS Trigger
TRIGGER_NUM:    6164,   Sub_Num: 0
GRB_INTEN:      10.93 [sigma]  
GRB_TIME:       81731.94 SOD {22:42:11.94} UT
GRB_DATE:       15671 TJD;   110 DOY;   11/04/20
COMMENTS:       INTEGRAL SPI_ACS GRB Trigger.
COMMENTS:
COMMENTS:       NOTE: This SPIACS event is temporally(0.0<100sec) coincident with the SWIFT_BAT event (trignum=451794).
COMMENTS:
COMMENTS:       The SPIACS lightcurve can be found at:
COMMENTS:
+ftp://isdcarc.unige.ch/arc/FTP/ibas/spiacs/2011-04/2011-04-20T22-42-11.7729-14278-00007-0.lc

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Wed 20 Apr 11 22:45:45 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     451794,   Seg_Num: 0
GRB_RA:          320.049d {+21h 20m 12s} (J2000),
                 320.229d {+21h 20m 55s} (current),
                 319.250d {+21h 17m 00s} (1950)
GRB_DEC:         -41.264d {-41d 15' 51"} (J2000),
                 -41.216d {-41d 12' 57"} (current),
                 -41.477d {-41d 28' 35"} (1950)
GRB_DATE:        15671 TJD;   110 DOY;   11/04/20
GRB_TIME:        81731.71 SOD {22:42:11.71} UT
TRIGGER_INDEX:   10319
GRB_PHI:         129.28 [deg]
GRB_THETA:        32.37 [deg]
DELTA_TIME:      61.00 [sec]
TRIGGER_DUR:     0.032 [sec] 
SOLN_STATUS:     0x3
RATE_SIGNIF:     34.19 [sigma]
IMAGE_SIGNIF:    8.11 [sigma]
LC_URL:          sw00451794000msb.lc
SUN_POSTN:        28.39d {+01h 53m 34s}  +11.65d {+11d 38' 51"}
SUN_DIST:         81.89 [deg]   Sun_angle= 4.5 [hr] (West of Sun)
MOON_POSTN:      247.66d {+16h 30m 39s}  -23.28d {-23d 16' 40"}
MOON_DIST:        62.13 [deg]
MOON_ILLUM:      89 [%]
GAL_COORDS:        0.55,-44.84 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      309.25,-24.40 [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 = 245.19,1.04 [deg].

GCN Circular #11944
B. Sbarufatti (INAF-OAB/IASFPA), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester), D. N. Burrows (PSU), M. M. Chester (PSU), V. D'Elia (ASDC), S. T. Holland (CRESST/USRA/GSFC), E. A. Hoversten (PSU), J. A. Kennea (PSU), V. Mangano (INAF-IASFPA), A. Melandri (INAF-OAB), D. M. Palmer (LANL), M. Stamatikos (OSU/NASA/GSFC) and E. Troja (NASA/GSFC/ORAU) report on behalf of the Swift Team:
At 22:42:11 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 110420B (trigger=451794). Swift did not immediately slew because of an observing constraint. The BAT on-board calculated location is RA, Dec 320.049, -41.264, which is
```
   RA(J2000)  =  21h 20m 12s
   Dec(J2000) = -41d 15' 51"
```
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows a single spike with a duration of about 64 milli-sec. The peak count rate was ~6000 counts/sec (15-350 keV), at ~0 sec after the trigger.
Due to an observing constraint, Swift will not slew until T0+40.4 minutes. There will be no XRT or UVOT data until this time.
Burst Advocate for this burst is B. Sbarufatti (boris.sbarufatti 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 20 Apr 11 23:35:32 UT
NOTICE_TYPE:     Swift-XRT Nack-Position
TRIGGER_NUM:     451794,   Seg_Num: 0
POINT_RA:        320.080d {+21h 20m 19s} (J2000)
POINT_DEC:       -41.258d {-41d 15' 29"} (J2000)
IMG_START_DATE:  15671 TJD;   110 DOY;   11/04/20
IMG_START_TIME:  84289.20 SOD {23:24:49.20} UT,   2557.5 [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:     Wed 20 Apr 11 23:37:13 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     451794,   Seg_Num: 0
POINT_RA:        320.080d {+21h 20m 19s} (J2000)
POINT_DEC:       -41.258d {-41d 15' 28"} (J2000)
POINT_ROLL:      66.820d
IMG_START_DATE:  15671 TJD;   110 DOY;   11/04/20
IMG_START_TIME:  84293.71 SOD {23:24:53.71} UT,   2562.0 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        2.465
N_STARS:         41
X_OFFSET:        328 [pixels]
Y_OFFSET:        636 [pixels]
X_MAX:           1287 [pixels]
Y_MAX:           1595 [pixels]
DET_THRESH:      13
PHOTO_THRESH:    7
SL_URL:          sw00451794000msufc2562.fits
SUN_POSTN:        28.43d {+01h 53m 42s}  +11.66d {+11d 39' 35"}
SUN_DIST:         81.90 [deg]   Sun_angle= 4.5 [hr] (West of Sun)
MOON_POSTN:      248.21d {+16h 32m 51s}  -23.31d {-23d 18' 40"}
MOON_DIST:        61.73 [deg]
MOON_ILLUM:      89 [%]
GAL_COORDS:        0.56,-44.86 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      309.28,-24.40 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Wed 20 Apr 11 23:37:30 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     451794,   Seg_Num: 0
POINT_RA:        320.080d {+21h 20m 19s} (J2000)
POINT_DEC:       -41.258d {-41d 15' 28"} (J2000)
POINT_ROLL:      66.820d
IMG_START_DATE:  15671 TJD;   110 DOY;   11/04/20
IMG_START_TIME:  84293.71 SOD {23:24:53.71} UT,   2562.0 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        2.465
N_STARS:         41
X_OFFSET:        328 [pixels]
Y_OFFSET:        636 [pixels]
X_MAX:           1287 [pixels]
Y_MAX:           1595 [pixels]
DET_THRESH:      13
PHOTO_THRESH:    7
SL_URL:          sw00451794000msufc2562.fits
SUN_POSTN:        28.43d {+01h 53m 42s}  +11.66d {+11d 39' 36"}
SUN_DIST:         81.90 [deg]   Sun_angle= 4.5 [hr] (West of Sun)
MOON_POSTN:      248.22d {+16h 32m 52s}  -23.31d {-23d 18' 41"}
MOON_DIST:        61.72 [deg]
MOON_ILLUM:      89 [%]
GAL_COORDS:        0.56,-44.86 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      309.28,-24.40 [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 20 Apr 11 23:38:40 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     451794,   Seg_Num: 0
POINT_RA:        320.080d {+21h 20m 19s} (J2000)
POINT_DEC:       -41.258d {-41d 15' 28"} (J2000)
ROLL:            66.820d
IMG_START_DATE:  15671 TJD;   110 DOY;   11/04/20
IMG_START_TIME:  84293.71 SOD {23:24:53.71} UT,   2562.0 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     325034700
X_OFFSET:        647 [pixels]
Y_OFFSET:        955 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       807
Y_GRB_POS:       1115
BINNING_INDEX:   1
IM_URL:          sw00451794000msuni2569.fits
SUN_POSTN:        28.43d {+01h 53m 42s}  +11.66d {+11d 39' 37"}
SUN_DIST:         81.90 [deg]   Sun_angle= 4.5 [hr] (West of Sun)
MOON_POSTN:      248.23d {+16h 32m 55s}  -23.31d {-23d 18' 44"}
MOON_DIST:        61.71 [deg]
MOON_ILLUM:      89 [%]
GAL_COORDS:        0.56,-44.86 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      309.28,-24.40 [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 20 Apr 11 23:38:58 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     451794,   Seg_Num: 0
POINT_RA:        320.080d {+21h 20m 19s} (J2000)
POINT_DEC:       -41.258d {-41d 15' 28"} (J2000)
ROLL:            66.820d
IMG_START_DATE:  15671 TJD;   110 DOY;   11/04/20
IMG_START_TIME:  84293.71 SOD {23:24:53.71} UT,   2562.0 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     325034700
X_OFFSET:        647 [pixels]
Y_OFFSET:        955 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       807
Y_GRB_POS:       1115
BINNING_INDEX:   1
IM_URL:          sw00451794000msuni2569.fits
SUN_POSTN:        28.43d {+01h 53m 42s}  +11.66d {+11d 39' 37"}
SUN_DIST:         81.90 [deg]   Sun_angle= 4.5 [hr] (West of Sun)
MOON_POSTN:      248.23d {+16h 32m 56s}  -23.31d {-23d 18' 44"}
MOON_DIST:        61.71 [deg]
MOON_ILLUM:      89 [%]
GAL_COORDS:        0.56,-44.86 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      309.28,-24.40 [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 #11946
C. B. Markwardt (GSFC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), D. M. Palmer (LANL), T. Sakamoto (GSFC/UMBC), B. Sbarufatti (INAF-OAB/IASFPA), M. Stamatikos (OSU), J. Tueller (GSFC), T. N. Ukwatta (MSU) (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 SHB GRB 110420B (trigger #451794) (Sbarufatti, et al., GCN Circ. 11944). The BAT ground-calculated position is RA, Dec = 320.045, -41.277 deg, which is
```
   RA(J2000)  =  21h 20m 10.9s 
   Dec(J2000) = -41d 16' 38.0" 
```
with an uncertainty of 2.2 arcmin, (radius, sys+stat, 90% containment). The partial coding was 35%.
The mask-weighted light curve shows a FRED-like pulse starting at ~T+0.00 and ending at ~T+0.08 sec. T90 (15-350 keV) is 0.084 +- 0.021 sec (estimated error including systematics).
The time-averaged spectrum from T-0.004 to T+0.100 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index -1.52 +- 2.56, and Epeak of 79.5 +- 30.0 keV (chi squared 67.2 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 5.3 +- 1.1 x 10^-8 erg/cm2 and the 1-sec peak flux measured from T-0.45 sec in the 15-150 keV band is 0.7 +- 0.2 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.11 +- 0.27 (chi squared 73.8 for 57 d.o.f.). 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/451794/BA/
GCN Circular #11947
B. Sbarufatti (INAF-OAB/IASFPA), V. Mangano (INAF/IASFPA) report on behalf of the Swift-XRT team:
We have analyzed 4.5 ks of XRT data for GRB 110420B (Sbarufatti et al. GCN Circ. 11944), from 2.6 ks to 14.4 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. We find an afterglow candidate with XRT position RA, Dec = 320.10472, -41.29713 which is equivalent to:
```
RA (J2000): 21 20 25.13
Dec(J2000): -41 17 49.7
```
with an uncertainty of 4.0 arcsec (radius, 90% confidence). We cannot determine at the present time whether the source is fading. The source lies 3.2 arcmin from the BAT onboard position and 2.95 arcmin from the BAT refined position (Markwardt et al., GCN Circ. 11946). The observed rate is 4.5 x 10^-3 counts/s (1.4 x 10^-13 erg cm^-2 s^-1), corresponding to a 3.8 sigma level detection.
More data are needed in order to confirm the nature of the source.
GCN Circular #11949
P. Afonso (MPE Garching), A. Rossi, S. Klose (TLS Tautenburg), and J. Greiner (MPE Garching) report on behalf of the GROND team:
We observed the field of GRB 110420B (Swift trigger 451794; Sbarufatti et al. GCN 11944) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2 m MPI/ESO telescope on La Silla.
Observations started at 7:00 UT on April 21, 8.15 hours after the GRB trigger. They were obtained under challenging sky conditions, with a seeing > 1.5 arcsec, an average airmass of 1.7, bright moonlight, and passing cirrus.
In a first epoch, centered on the refined BAT error circle (Markwardt et al., GCN 11946), we do not detect any new object down to the DSS2 limit. The XRT error circle (Sbarufatti et al., GCN 11947) was not covered by these observations in g'r'i'z'.
A subsequent epoch started about 30 min later and was centered on the XRT afterglow candidate (Sbarufatti et al., GCN 11947). Here we note the presence of a relatively bright object at the border of the XRT error circle at coordinates RA, DEC (J2000) 21:20:25.389, -41:17:51.79 (+/- 0.5 arcsec), which could be a galaxy seen nearly face-on. This object is also visible in the DSS2-red image. Unfortunately, due to the bad seeing we cannot decide with certainty at the moment if this object is a galaxy or a star. Its r'-band magnitude is r'(AB) = 19.5 +/- 0.1. No other source is detected inside the XRT error circle down to r'(AB) = 23.2.
Magnitudes are derived by calibrating the images against GROND zeropoints and 2MASS field stars. We note that the Galactic reddening along the line of sight is E(B-V) = 0.03 mag (Schlegel et al. 1998).
GCN Circular #11950
S.D. Barthelmy (GSFC) and J. Norris (BSU) report:
For GRB 110420B (Trigger 451794, GCNs 11944 & 11946), the spectral lag analysis of the Swift-BAT data for 40 msec covering the spike, yields a lag of 0.6 +/-2.0 msec for the 25-50 to 100-300 keV bands and 2.4 +4/-2 msec for the 15-25 to 50-100 keV bands, both using a lightcurve binning of 2 msec.
GCN Circular #11952
Lin Lin (UAH) reports on behalf of the Fermi GBM Team:
"At 22:42:11.73 UT on 20 April 2011, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 110420B (trigger 325032133 / 110420946).
This burst was also detected by the Swift/BAT (Sbarufatti et al. 2011, GCN 11944). The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight is 123 degrees.
The GBM light curve shows a fast rise slow decay peak, with a duration (T90) of about 0.048 s (50-300 keV). The time-averaged spectrum from T0-0.024 s to T0+0.040 s is well fit by a power law function with an exponential high-energy cutoff. The power law index is -0.12 +/- 0.31 and the cutoff energy, parameterized as Epeak, is 296.8 +/- 58.7 keV.
The event fluence (10-1000 keV) in this time interval is (2.65 +/- 0.36)E-7 erg/cm^2. The 0.008-sec peak photon flux measured starting from T0-0.016 s in the 10-1000 keV band is 44.1 +/- 6.1 ph/s/cm^2.
The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."
GCN Circular #11953
B. Sbarufatti (INAF-OAB/IASFPA) and V. Mangano (INAF/IASFPA) report on behalf of the Swift XRT team:
Further observations of the field of GRB 110420B (Sbarufatti et al. GCN Circ. 11944) have shown that the X-ray source reported by Sbarufatti et al. (GCN Circ. 11947) has not faded. Moreover, the position is marginally consistent with the known X-ray source 1RXS J212024.5-411816. Therefore we conclude that the XRT source is not the burst afterglow.
This circular is an official product of the Swift-XRT team.

GCN Circular #11955
S. R. Oates (MSSL-UCL) & B. Sbarufatti (INAF-OAB/IASFPA) report on behalf of the Swift-UVOT team
The Swift/UVOT began settled observations of the field of GRB 110420B 2562 s after the BAT trigger (Sbarufatti et al., GCN Circ. 11944). No optical afterglow is found within the BAT error circle.
Preliminary 3-sigma upper limits using the UVOT photometric system (Poole et al. 2008, MNRAS, 383, 627) for the first finding chart (FC) exposure and subsequent exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag
###############################################################
white_FC          2562         2711          147         >20.6
white             2562         4765          540         >20.5
v                 3541        16124         1322         >19.9
b                 2926        22368          621         >20.4
u                 2720        28151         1730         >20.0
w1                3950        28007         2844         >19.6
m2                3745        27103         2416         >19.5
w2                3336        15211         1279         >19.7
###############################################################

The values quoted above are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.03 in the direction of the burst (Schlegel et al. 1998).

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Jochen Greiner, last update: 21-Apr-2011 [Disclaimer]