Gamma-ray Burst 150423A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN/BACODINE POSITION NOTICE
  

  TITLE:           GCN/SWIFT NOTICE
  NOTICE_DATE:     Thu 23 Apr 15 06:28:24 UT
  NOTICE_TYPE:     Swift-BAT GRB Position
  TRIGGER_NUM:     638808,   Seg_Num: 0
  GRB_RA:          221.600d {+14h 46m 24s} (J2000),
                   221.784d {+14h 47m 08s} (current),
                   221.000d {+14h 44m 00s} (1950)
  GRB_DEC:         +12.288d {+12d 17' 18"} (J2000),
                   +12.225d {+12d 13' 29"} (current),
                   +12.497d {+12d 29' 51"} (1950)
  GRB_ERROR:       3.00 [arcmin radius, statistical only]
  GRB_INTEN:       1480 [cnts]    Image_Peak=148 [image_cnts]
  TRIGGER_DUR:     0.256 [sec] 
  TRIGGER_INDEX:   126     E_range: 50-350 keV
  BKG_INTEN:       16328 [cnts]
  BKG_TIME:        23274.51 SOD {06:27:54.51} UT
  BKG_DUR:         8 [sec]
  GRB_DATE:        17135 TJD;   113 DOY;   15/04/23
  GRB_TIME:        23284.69 SOD {06:28:04.69} UT
  GRB_PHI:          57.60 [deg]
  GRB_THETA:        12.32 [deg]
  SOLN_STATUS:     0x3
  RATE_SIGNIF:     41.24 [sigma]
  IMAGE_SIGNIF:    10.41 [sigma]
  MERIT_PARAMS:     +1  +0  +0  -2  +3  +0  +0  +0 +89  +0 
  SUN_POSTN:        30.59d {+02h 02m 23s}  +12.44d {+12d 26' 32"}
  SUN_DIST:        152.95 [deg]   Sun_angle= 11.3 [hr] (West of Sun)
  MOON_POSTN:       91.34d {+06h 05m 21s}  +18.24d {+18d 14' 22"}
  MOON_DIST:       122.41 [deg]
  MOON_ILLUM:      24 [%]
  GAL_COORDS:        9.75, 59.26 [deg] galactic lon,lat of the burst (or transient)
  ECL_COORDS:      214.94, 26.96 [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 = 287.46,5.11 [deg].  
  

• red DSS finding chart ps-file
  
  
• GCN NOTICE
  

  TITLE:           GCN/SWIFT NOTICE
  NOTICE_DATE:     Thu 23 Apr 15 06:29:48 UT
  NOTICE_TYPE:     Swift-XRT Nack-Position
  TRIGGER_NUM:     638808,   Seg_Num: 0
  POINT_RA:        221.605d {+14h 46m 25s} (J2000)
  POINT_DEC:       +12.292d {+12d 17' 31"} (J2000)
  IMG_START_DATE:  17135 TJD;   113 DOY;   15/04/23
  IMG_START_TIME:  23354.82 SOD {06:29:14.82} UT,   70.1 [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:     Thu 23 Apr 15 06:31:47 UT
  NOTICE_TYPE:     Swift-BAT GRB Lightcurve
  TRIGGER_NUM:     638808,   Seg_Num: 0
  GRB_RA:          221.600d {+14h 46m 24s} (J2000),
                   221.784d {+14h 47m 08s} (current),
                   221.000d {+14h 44m 00s} (1950)
  GRB_DEC:         +12.288d {+12d 17' 18"} (J2000),
                   +12.225d {+12d 13' 29"} (current),
                   +12.497d {+12d 29' 51"} (1950)
  GRB_DATE:        17135 TJD;   113 DOY;   15/04/23
  GRB_TIME:        23284.69 SOD {06:28:04.69} UT
  TRIGGER_INDEX:   126
  GRB_PHI:          57.60 [deg]
  GRB_THETA:        12.32 [deg]
  DELTA_TIME:      -57.00 [sec]
  TRIGGER_DUR:     0.256 [sec] 
  SOLN_STATUS:     0x3
  RATE_SIGNIF:     41.24 [sigma]
  IMAGE_SIGNIF:    10.41 [sigma]
  LC_URL:          sw00638808000msb.lc
  SUN_POSTN:        30.60d {+02h 02m 23s}  +12.44d {+12d 26' 34"}
  SUN_DIST:        152.95 [deg]   Sun_angle= 11.3 [hr] (West of Sun)
  MOON_POSTN:       91.37d {+06h 05m 28s}  +18.24d {+18d 14' 19"}
  MOON_DIST:       122.38 [deg]
  MOON_ILLUM:      24 [%]
  GAL_COORDS:        9.75, 59.26 [deg] galactic lon,lat of the burst (or transient)
  ECL_COORDS:      214.94, 26.96 [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 = 287.46,5.11 [deg].  
  

  
• GCN NOTICE
  

  TITLE:           GCN/SWIFT NOTICE
  NOTICE_DATE:     Thu 23 Apr 15 06:32:11 UT
  NOTICE_TYPE:     Swift-UVOT Source List
  TRIGGER_NUM:     638808,   Seg_Num: 0
  POINT_RA:        221.605d {+14h 46m 25s} (J2000)
  POINT_DEC:       +12.292d {+12d 17' 31"} (J2000)
  POINT_ROLL:      24.210d
  IMG_START_DATE:  17135 TJD;   113 DOY;   15/04/23
  IMG_START_TIME:  23358.35 SOD {06:29:18.35} UT,   73.7 [sec] since BAT Trigger Time
  FILTER:          10, White
  BKG_MEAN:        1.956
  N_STARS:         30
  X_OFFSET:        431 [pixels]
  Y_OFFSET:        572 [pixels]
  X_MAX:           1390 [pixels]
  Y_MAX:           1531 [pixels]
  DET_THRESH:      12
  PHOTO_THRESH:    6
  SL_URL:          sw00638808000msufc0073.fits
  SUN_POSTN:        30.60d {+02h 02m 23s}  +12.44d {+12d 26' 35"}
  SUN_DIST:        152.94 [deg]   Sun_angle= 11.3 [hr] (West of Sun)
  MOON_POSTN:       91.37d {+06h 05m 29s}  +18.24d {+18d 14' 19"}
  MOON_DIST:       122.38 [deg]
  MOON_ILLUM:      24 [%]
  GAL_COORDS:        9.76, 59.26 [deg] galactic lon,lat of the pointing direction
  ECL_COORDS:      214.95, 26.96 [deg] ecliptic lon,lat of the pointing direction
  COMMENTS:        SWIFT-UVOT Source List.  
  

• GCN NOTICE
  

  TITLE:           GCN/SWIFT NOTICE
  NOTICE_DATE:     Thu 23 Apr 15 06:32:48 UT
  NOTICE_TYPE:     Swift-UVOT Processed Source List
  TRIGGER_NUM:     638808,   Seg_Num: 0
  POINT_RA:        221.605d {+14h 46m 25s} (J2000)
  POINT_DEC:       +12.292d {+12d 17' 31"} (J2000)
  POINT_ROLL:      24.210d
  IMG_START_DATE:  17135 TJD;   113 DOY;   15/04/23
  IMG_START_TIME:  23358.35 SOD {06:29:18.35} UT,   73.7 [sec] since BAT Trigger Time
  FILTER:          10, White
  BKG_MEAN:        1.956
  N_STARS:         30
  X_OFFSET:        431 [pixels]
  Y_OFFSET:        572 [pixels]
  X_MAX:           1390 [pixels]
  Y_MAX:           1531 [pixels]
  DET_THRESH:      12
  PHOTO_THRESH:    6
  SL_URL:          sw00638808000msufc0073.fits
  SUN_POSTN:        30.60d {+02h 02m 23s}  +12.44d {+12d 26' 35"}
  SUN_DIST:        152.94 [deg]   Sun_angle= 11.3 [hr] (West of Sun)
  MOON_POSTN:       91.38d {+06h 05m 31s}  +18.24d {+18d 14' 18"}
  MOON_DIST:       122.37 [deg]
  MOON_ILLUM:      24 [%]
  GAL_COORDS:        9.76, 59.26 [deg] galactic lon,lat of the pointing direction
  ECL_COORDS:      214.95, 26.96 [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:     Thu 23 Apr 15 06:33:36 UT
  NOTICE_TYPE:     Swift-UVOT Image
  TRIGGER_NUM:     638808,   Seg_Num: 0
  POINT_RA:        221.605d {+14h 46m 25s} (J2000)
  POINT_DEC:       +12.292d {+12d 17' 31"} (J2000)
  ROLL:            24.210d
  IMG_START_DATE:  17135 TJD;   113 DOY;   15/04/23
  IMG_START_TIME:  23358.35 SOD {06:29:18.35} UT,   73.7 [sec] since BAT Trigger Time
  FILTER:          10, White
  EXPOSURE_ID:     451463371
  X_OFFSET:        750 [pixels]
  Y_OFFSET:        891 [pixels]
  WIDTH:           160 [pixels]
  HEIGHT:          160 [pixels]
  X_GRB_POS:       910
  Y_GRB_POS:       1051
  BINNING_INDEX:   1
  IM_URL:          sw00638808000msuni0087.fits
  SUN_POSTN:        30.60d {+02h 02m 23s}  +12.44d {+12d 26' 36"}
  SUN_DIST:        152.94 [deg]   Sun_angle= 11.3 [hr] (West of Sun)
  MOON_POSTN:       91.39d {+06h 05m 33s}  +18.24d {+18d 14' 18"}
  MOON_DIST:       122.37 [deg]
  MOON_ILLUM:      24 [%]
  GAL_COORDS:        9.76, 59.26 [deg] galactic lon,lat of the pointing direction
  ECL_COORDS:      214.95, 26.96 [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:     Thu 23 Apr 15 06:33:52 UT
  NOTICE_TYPE:     Swift-UVOT Processed Image
  TRIGGER_NUM:     638808,   Seg_Num: 0
  POINT_RA:        221.605d {+14h 46m 25s} (J2000)
  POINT_DEC:       +12.292d {+12d 17' 31"} (J2000)
  ROLL:            24.210d
  IMG_START_DATE:  17135 TJD;   113 DOY;   15/04/23
  IMG_START_TIME:  23358.35 SOD {06:29:18.35} UT,   73.7 [sec] since BAT Trigger Time
  FILTER:          10, White
  EXPOSURE_ID:     451463371
  X_OFFSET:        750 [pixels]
  Y_OFFSET:        891 [pixels]
  WIDTH:           160 [pixels]
  HEIGHT:          160 [pixels]
  X_GRB_POS:       910
  Y_GRB_POS:       1051
  BINNING_INDEX:   1
  IM_URL:          sw00638808000msuni0087.fits
  SUN_POSTN:        30.60d {+02h 02m 23s}  +12.44d {+12d 26' 36"}
  SUN_DIST:        152.94 [deg]   Sun_angle= 11.3 [hr] (West of Sun)
  MOON_POSTN:       91.39d {+06h 05m 33s}  +18.24d {+18d 14' 17"}
  MOON_DIST:       122.37 [deg]
  MOON_ILLUM:      24 [%]
  GAL_COORDS:        9.76, 59.26 [deg] galactic lon,lat of the pointing direction
  ECL_COORDS:      214.95, 26.96 [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 NOTICE
  

  TITLE:           GCN/SWIFT NOTICE
  NOTICE_DATE:     Thu 23 Apr 15 06:34:04 UT
  NOTICE_TYPE:     Swift-XRT Position
  TRIGGER_NUM:     638808,   Seg_Num: 0
  GRB_RA:          221.5787d {+14h 46m 18.88s} (J2000),
                   221.7625d {+14h 47m 03.00s} (current),
                   220.9785d {+14h 43m 54.84s} (1950)
  GRB_DEC:         +12.2825d {+12d 16' 57.0"} (J2000),
                   +12.2188d {+12d 13' 07.8"} (current),
                   +12.4917d {+12d 29' 30.2"} (1950)
  GRB_ERROR:       4.0 [arcsec radius, statistical plus systematic, 90% containment]
  GRB_INTEN:       1.00e-10 [erg/cm2/sec]
  GRB_SIGNIF:      10.00 [sigma]
  IMG_START_DATE:  17135 TJD;   113 DOY;   15/04/23
  IMG_START_TIME:  23366.00 SOD {06:29:26.00} UT,   81.3 [sec] since BAT Trigger Time
  TAM[0-3]:        100.00 100.00 100.00 100.00
  AMPLIFIER:       1
  WAVEFORM:        31
  SUN_POSTN:        30.60d {+02h 02m 24s}  +12.44d {+12d 26' 36"}
  SUN_DIST:        152.96 [deg]   Sun_angle= 11.3 [hr] (West of Sun)
  MOON_POSTN:       91.39d {+06h 05m 34s}  +18.24d {+18d 14' 17"}
  MOON_DIST:       122.35 [deg]
  MOON_ILLUM:      24 [%]
  GAL_COORDS:        9.71, 59.28 [deg] galactic lon,lat of the burst
  ECL_COORDS:      214.92, 26.94 [deg] ecliptic lon,lat of the burst
  COMMENTS:        SWIFT-XRT Coordinates.  
  COMMENTS:        This Notice was ground-generated -- not flight-generated.  
  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 0.58% < P(seren) < 1.1%.  
  

• GCN NOTICE
  

  TITLE:           GCN/SWIFT NOTICE
  NOTICE_DATE:     Thu 23 Apr 15 06:39:16 UT
  NOTICE_TYPE:     Swift-UVOT Source List
  TRIGGER_NUM:     638808,   Seg_Num: 0
  POINT_RA:        221.604d {+14h 46m 25s} (J2000)
  POINT_DEC:       +12.294d {+12d 17' 38"} (J2000)
  POINT_ROLL:      24.207d
  IMG_START_DATE:  17135 TJD;   113 DOY;   15/04/23
  IMG_START_TIME:  23570.34 SOD {06:32:50.34} UT,   285.7 [sec] since BAT Trigger Time
  FILTER:          7, U
  BKG_MEAN:        0.566
  N_STARS:         48
  X_OFFSET:        191 [pixels]
  Y_OFFSET:        332 [pixels]
  X_MAX:           1630 [pixels]
  Y_MAX:           1771 [pixels]
  DET_THRESH:      7
  PHOTO_THRESH:    3
  SL_URL:          sw00638808000msufc0285.fits
  SUN_POSTN:        30.60d {+02h 02m 24s}  +12.44d {+12d 26' 41"}
  SUN_DIST:        152.94 [deg]   Sun_angle= 11.3 [hr] (West of Sun)
  MOON_POSTN:       91.44d {+06h 05m 45s}  +18.24d {+18d 14' 13"}
  MOON_DIST:       122.32 [deg]
  MOON_ILLUM:      24 [%]
  GAL_COORDS:        9.76, 59.26 [deg] galactic lon,lat of the pointing direction
  ECL_COORDS:      214.94, 26.96 [deg] ecliptic lon,lat of the pointing direction
  COMMENTS:        SWIFT-UVOT Source List.  
  

• GCN NOTICE
  

  TITLE:           GCN/SWIFT NOTICE
  NOTICE_DATE:     Thu 23 Apr 15 06:39:37 UT
  NOTICE_TYPE:     Swift-UVOT Processed Source List
  TRIGGER_NUM:     638808,   Seg_Num: 0
  POINT_RA:        221.604d {+14h 46m 25s} (J2000)
  POINT_DEC:       +12.294d {+12d 17' 38"} (J2000)
  POINT_ROLL:      24.207d
  IMG_START_DATE:  17135 TJD;   113 DOY;   15/04/23
  IMG_START_TIME:  23570.34 SOD {06:32:50.34} UT,   285.7 [sec] since BAT Trigger Time
  FILTER:          7, U
  BKG_MEAN:        0.566
  N_STARS:         48
  X_OFFSET:        191 [pixels]
  Y_OFFSET:        332 [pixels]
  X_MAX:           1630 [pixels]
  Y_MAX:           1771 [pixels]
  DET_THRESH:      7
  PHOTO_THRESH:    3
  SL_URL:          sw00638808000msufc0285.fits
  SUN_POSTN:        30.60d {+02h 02m 24s}  +12.44d {+12d 26' 41"}
  SUN_DIST:        152.94 [deg]   Sun_angle= 11.3 [hr] (West of Sun)
  MOON_POSTN:       91.44d {+06h 05m 46s}  +18.24d {+18d 14' 13"}
  MOON_DIST:       122.32 [deg]
  MOON_ILLUM:      24 [%]
  GAL_COORDS:        9.76, 59.26 [deg] galactic lon,lat of the pointing direction
  ECL_COORDS:      214.94, 26.96 [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:     Thu 23 Apr 15 06:40:05 UT
  NOTICE_TYPE:     Swift-XRT Position UPDATE
  TRIGGER_NUM:     638808,   Seg_Num: 0
  GRB_RA:          221.5786d {+14h 46m 18.86s} (J2000),
                   221.7624d {+14h 47m 02.98s} (current),
                   220.9784d {+14h 43m 54.82s} (1950)
  GRB_DEC:         +12.2833d {+12d 16' 59.8"} (J2000),
                   +12.2196d {+12d 13' 10.7"} (current),
                   +12.4925d {+12d 29' 33.0"} (1950)
  GRB_ERROR:       2.4 [arcsec radius, statistical plus systematic, 90% containment]
  GRB_INTEN:       1.00e-10 [erg/cm2/sec]
  GRB_SIGNIF:      10.00 [sigma]
  IMG_START_DATE:  17135 TJD;   113 DOY;   15/04/23
  IMG_START_TIME:  23366.00 SOD {06:29:26.00} UT,   81.3 [sec] since BAT Trigger Time
  TAM[0-3]:        100.00 100.00 100.00 100.00
  AMPLIFIER:       1
  WAVEFORM:        31
  SUN_POSTN:        30.60d {+02h 02m 24s}  +12.44d {+12d 26' 41"}
  SUN_DIST:        152.96 [deg]   Sun_angle= 11.3 [hr] (West of Sun)
  MOON_POSTN:       91.45d {+06h 05m 47s}  +18.24d {+18d 14' 12"}
  MOON_DIST:       122.30 [deg]
  MOON_ILLUM:      24 [%]
  GAL_COORDS:        9.72, 59.28 [deg] galactic lon,lat of the burst
  ECL_COORDS:      214.92, 26.94 [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:        This position was enhanced using UVOT field astrometry.  
  COMMENTS:        The probability that this is a serendipitous source in the  
  COMMENTS:        SPER window is 0.58% < P(seren) < 1.1%.  
  

• GCN NOTICE
  

  TITLE:           GCN/SWIFT NOTICE
  NOTICE_DATE:     Thu 23 Apr 15 06:40:25 UT
  NOTICE_TYPE:     Swift-UVOT Image
  TRIGGER_NUM:     638808,   Seg_Num: 0
  POINT_RA:        221.604d {+14h 46m 25s} (J2000)
  POINT_DEC:       +12.294d {+12d 17' 38"} (J2000)
  ROLL:            24.207d
  IMG_START_DATE:  17135 TJD;   113 DOY;   15/04/23
  IMG_START_TIME:  23570.34 SOD {06:32:50.34} UT,   285.7 [sec] since BAT Trigger Time
  FILTER:          7, U
  EXPOSURE_ID:     451463583
  X_OFFSET:        750 [pixels]
  Y_OFFSET:        891 [pixels]
  WIDTH:           160 [pixels]
  HEIGHT:          160 [pixels]
  X_GRB_POS:       910
  Y_GRB_POS:       1051
  BINNING_INDEX:   1
  IM_URL:          sw00638808000msuni0299.fits
  SUN_POSTN:        30.60d {+02h 02m 25s}  +12.44d {+12d 26' 42"}
  SUN_DIST:        152.94 [deg]   Sun_angle= 11.3 [hr] (West of Sun)
  MOON_POSTN:       91.45d {+06h 05m 48s}  +18.24d {+18d 14' 12"}
  MOON_DIST:       122.31 [deg]
  MOON_ILLUM:      24 [%]
  GAL_COORDS:        9.76, 59.26 [deg] galactic lon,lat of the pointing direction
  ECL_COORDS:      214.94, 26.96 [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:     Thu 23 Apr 15 06:40:43 UT
  NOTICE_TYPE:     Swift-UVOT Processed Image
  TRIGGER_NUM:     638808,   Seg_Num: 0
  POINT_RA:        221.604d {+14h 46m 25s} (J2000)
  POINT_DEC:       +12.294d {+12d 17' 38"} (J2000)
  ROLL:            24.207d
  IMG_START_DATE:  17135 TJD;   113 DOY;   15/04/23
  IMG_START_TIME:  23570.34 SOD {06:32:50.34} UT,   285.7 [sec] since BAT Trigger Time
  FILTER:          7, U
  EXPOSURE_ID:     451463583
  X_OFFSET:        750 [pixels]
  Y_OFFSET:        891 [pixels]
  WIDTH:           160 [pixels]
  HEIGHT:          160 [pixels]
  X_GRB_POS:       910
  Y_GRB_POS:       1051
  BINNING_INDEX:   1
  IM_URL:          sw00638808000msuni0299.fits
  SUN_POSTN:        30.60d {+02h 02m 25s}  +12.44d {+12d 26' 42"}
  SUN_DIST:        152.94 [deg]   Sun_angle= 11.3 [hr] (West of Sun)
  MOON_POSTN:       91.45d {+06h 05m 49s}  +18.24d {+18d 14' 12"}
  MOON_DIST:       122.31 [deg]
  MOON_ILLUM:      24 [%]
  GAL_COORDS:        9.76, 59.26 [deg] galactic lon,lat of the pointing direction
  ECL_COORDS:      214.94, 26.96 [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 #17728
  C. Pagani (U Leicester), V. D'Elia (ASDC), K. L. Page (U Leicester), D. M. Palmer (LANL) and T. N. Ukwatta (LANL) report on behalf of the Swift Team:
  At 06:28:04 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 150423A (trigger=638808). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 221.600, +12.288 which is

     RA(J2000) = 14h 46m 24s
     Dec(J2000) = +12d 17' 18"
  

  with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single peak with a duration of about 0.5 sec. The peak count rate was ~6400 counts/sec (15-350 keV), at ~0 sec after the trigger.
  The XRT began observing the field at 06:29:14.8 UT, 70.1 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source with an enhanced position: RA, Dec 221.5787, 12.2833 which is equivalent to:

     RA(J2000)  = 14h 46m 18.90s
     Dec(J2000) = +12d 16' 60.0"
  

  with an uncertainty of 2.4 arcseconds (radius, 90% containment). This location is 76 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.
  A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 1.77 x 10^20 cm^-2 (Willingale et al. 2013).
  UVOT took a finding chart exposure of 150 seconds with the White filter starting 73 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 29% of the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. 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 0.03.
  Burst Advocate for this burst is C. Pagani (cp232 AT star.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 NOTICE
  

  TITLE:           GCN/SWIFT NOTICE
  NOTICE_DATE:     Thu 23 Apr 15 06:45:26 UT
  NOTICE_TYPE:     Swift-UVOT Source List
  TRIGGER_NUM:     638808,   Seg_Num: 0
  POINT_RA:        221.604d {+14h 46m 25s} (J2000)
  POINT_DEC:       +12.294d {+12d 17' 38"} (J2000)
  POINT_ROLL:      24.206d
  IMG_START_DATE:  17135 TJD;   113 DOY;   15/04/23
  IMG_START_TIME:  24148.70 SOD {06:42:28.70} UT,   864.0 [sec] since BAT Trigger Time
  FILTER:          10, White
  BKG_MEAN:        2.177
  N_STARS:         81
  X_OFFSET:        191 [pixels]
  Y_OFFSET:        332 [pixels]
  X_MAX:           1630 [pixels]
  Y_MAX:           1771 [pixels]
  DET_THRESH:      12
  PHOTO_THRESH:    6
  SL_URL:          sw00638808000msufc0864.fits
  SUN_POSTN:        30.61d {+02h 02m 25s}  +12.45d {+12d 26' 46"}
  SUN_DIST:        152.94 [deg]   Sun_angle= 11.3 [hr] (West of Sun)
  MOON_POSTN:       91.50d {+06h 06m 00s}  +18.24d {+18d 14' 08"}
  MOON_DIST:       122.27 [deg]
  MOON_ILLUM:      24 [%]
  GAL_COORDS:        9.76, 59.26 [deg] galactic lon,lat of the pointing direction
  ECL_COORDS:      214.94, 26.96 [deg] ecliptic lon,lat of the pointing direction
  COMMENTS:        SWIFT-UVOT Source List.  
  

• GCN NOTICE
  

  TITLE:           GCN/SWIFT NOTICE
  NOTICE_DATE:     Thu 23 Apr 15 06:45:42 UT
  NOTICE_TYPE:     Swift-UVOT Processed Source List
  TRIGGER_NUM:     638808,   Seg_Num: 0
  POINT_RA:        221.604d {+14h 46m 25s} (J2000)
  POINT_DEC:       +12.294d {+12d 17' 38"} (J2000)
  POINT_ROLL:      24.206d
  IMG_START_DATE:  17135 TJD;   113 DOY;   15/04/23
  IMG_START_TIME:  24148.70 SOD {06:42:28.70} UT,   864.0 [sec] since BAT Trigger Time
  FILTER:          10, White
  BKG_MEAN:        2.177
  N_STARS:         81
  X_OFFSET:        191 [pixels]
  Y_OFFSET:        332 [pixels]
  X_MAX:           1630 [pixels]
  Y_MAX:           1771 [pixels]
  DET_THRESH:      12
  PHOTO_THRESH:    6
  SL_URL:          sw00638808000msufc0864.fits
  SUN_POSTN:        30.61d {+02h 02m 25s}  +12.45d {+12d 26' 46"}
  SUN_DIST:        152.94 [deg]   Sun_angle= 11.3 [hr] (West of Sun)
  MOON_POSTN:       91.50d {+06h 06m 00s}  +18.24d {+18d 14' 08"}
  MOON_DIST:       122.27 [deg]
  MOON_ILLUM:      24 [%]
  GAL_COORDS:        9.76, 59.26 [deg] galactic lon,lat of the pointing direction
  ECL_COORDS:      214.94, 26.96 [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:     Thu 23 Apr 15 06:47:07 UT
  NOTICE_TYPE:     Swift-UVOT Image
  TRIGGER_NUM:     638808,   Seg_Num: 0
  POINT_RA:        221.604d {+14h 46m 25s} (J2000)
  POINT_DEC:       +12.294d {+12d 17' 38"} (J2000)
  ROLL:            24.206d
  IMG_START_DATE:  17135 TJD;   113 DOY;   15/04/23
  IMG_START_TIME:  24148.70 SOD {06:42:28.70} UT,   864.0 [sec] since BAT Trigger Time
  FILTER:          10, White
  EXPOSURE_ID:     451464162
  X_OFFSET:        750 [pixels]
  Y_OFFSET:        891 [pixels]
  WIDTH:           160 [pixels]
  HEIGHT:          160 [pixels]
  X_GRB_POS:       910
  Y_GRB_POS:       1051
  BINNING_INDEX:   1
  IM_URL:          sw00638808000msuni0878.fits
  SUN_POSTN:        30.61d {+02h 02m 26s}  +12.45d {+12d 26' 47"}
  SUN_DIST:        152.94 [deg]   Sun_angle= 11.3 [hr] (West of Sun)
  MOON_POSTN:       91.51d {+06h 06m 03s}  +18.24d {+18d 14' 07"}
  MOON_DIST:       122.26 [deg]
  MOON_ILLUM:      24 [%]
  GAL_COORDS:        9.76, 59.26 [deg] galactic lon,lat of the pointing direction
  ECL_COORDS:      214.94, 26.96 [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:     Thu 23 Apr 15 06:47:16 UT
  NOTICE_TYPE:     Swift-UVOT Processed Image
  TRIGGER_NUM:     638808,   Seg_Num: 0
  POINT_RA:        221.604d {+14h 46m 25s} (J2000)
  POINT_DEC:       +12.294d {+12d 17' 38"} (J2000)
  ROLL:            24.206d
  IMG_START_DATE:  17135 TJD;   113 DOY;   15/04/23
  IMG_START_TIME:  24148.70 SOD {06:42:28.70} UT,   864.0 [sec] since BAT Trigger Time
  FILTER:          10, White
  EXPOSURE_ID:     451464162
  X_OFFSET:        750 [pixels]
  Y_OFFSET:        891 [pixels]
  WIDTH:           160 [pixels]
  HEIGHT:          160 [pixels]
  X_GRB_POS:       910
  Y_GRB_POS:       1051
  BINNING_INDEX:   1
  IM_URL:          sw00638808000msuni0878.fits
  SUN_POSTN:        30.61d {+02h 02m 26s}  +12.45d {+12d 26' 47"}
  SUN_DIST:        152.94 [deg]   Sun_angle= 11.3 [hr] (West of Sun)
  MOON_POSTN:       91.52d {+06h 06m 04s}  +18.24d {+18d 14' 06"}
  MOON_DIST:       122.26 [deg]
  MOON_ILLUM:      24 [%]
  GAL_COORDS:        9.76, 59.26 [deg] galactic lon,lat of the pointing direction
  ECL_COORDS:      214.94, 26.96 [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 #17729
  K. Varela, F. Knust, J. Bodensteiner and J. Greiner (all MPE Garching) report on behalf of the GROND team:
  We observed the field of GRB 150423A (Swift trigger 638808; Pagani et al., GCN #17728) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2 m MPG telescope at ESO La Silla Observatory (Chile).
  Observations started at 06:32 UT on 2015-04-23, 4 min after the GRB trigger. They were performed at an average seeing of 0".8 and at an average airmass of 1.5.
  We detect a faint source within the 2.2" XRT error circle, at position

  RA (2000.0) = 14h 46m 18.9s
  Decl (2000.0) = +12d 17' 00"
  

  with an error of 0.5", about 1" away from the XRT centroid position.
  Based on 7.7 min of total exposure time in g'r'i'z' and 8.0 min in JHK, centered 24 min after the GRB, we estimate the following preliminary magnitudes (all in AB system):

  g' = 23.2 +/- 0.2 mag,
  r' = 23.1 +/- 0.2 mag,
  i' = 22.5 +/- 0.2 mag,
  z' = 22.0 +/- 0.2 mag,
  J  = 19.3 +/- 0.4 mag,
  H  > 18.4  mag, and
  K  > 17.5 mag.
  

  No statement can be made about fading at this stage. Since there is a faint source also in the SDSS, this might be the host galaxy rather than the afterglow.
  Given magnitudes are calibrated against SDSS (g'r'i'z') as well as 2MASS field stars and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V)=0.03 mag in the direction of the burst (Schlegel et al. 1998).
• GCN Circular #17730
  WeiKang Zheng and Alexei V. Filippenko (UC Berkeley) report on behalf of the KAIT GRB team:
  The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at Lick Observatory, responded to Swift GRB 150423A (Pagani et al., GCN 17728) starting at 06:30:00 UT, 116 s after the burst, under thin-cloudy condition. Observations were performed with an automatic sequence in the clear (roughly R), V, and I filters, and the exposure time was 20 s per image. We do not detect the optical source reported by Varela et al. (GCN 17729), in our images, nor any other new source within the XRT error circle. The typical limiting magnitude of our single clear image is about 17.0 calibrated to USNO B1.0.
• GCN Circular #17732
  K. Varela, F. Knust, and J. Greiner (all MPE Garching) report on behalf of the GROND team:
  Further to Varela et al. (GCN #17729), we report continued observations of the field of GRB 150423A (Swift trigger 638808; Pagani et al., GCN #17728) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2 m MPG telescope at ESO La Silla Observatory (Chile). The observations were performed at an average seeing of 1.0 and at an average airmass of 1.5.
  We detect 2 faint sources within or close to the 2.2" XRT error circle:
  Source #1, within the XRT error circle:

   RA (2000.0)   =  14h 46m 18.86s
   Decl (2000.0) = +12d 17' 00.7"
  

  with an error of 0.3".
  Source #2, just outside the XRT error circle:

   RA (2000.0)   =  14h 46m 19.04s
   Decl (2000.0) = +12d 17' 03.4
  

  with an error of 0.3". This source matches an object visible in the SDSS.
  Based on 25.1 min of total exposure time in g'r'i'z' and 20.0 min in JHK, centered 58 min after the GRB, we estimate the following preliminary magnitudes (all in AB system).
  Source #1:

  g' = 23.2 +/- 0.2 mag,
  r' = 23.1 +/- 0.2 mag,
  i' = 22.8 +/- 0.2 mag,
  z' = 22.6 +/- 0.2 mag,
  J  > 21.6 mag,
  H  > 21.0 mag, and
  Ks > 18.5 mag,
  

  Source #2:

  g' = 24.2 +/- 0.2 mag,
  r' = 23.3 +/- 0.2 mag,
  i' = 23.4 +/- 0.3 mag,
  z' = 22.9 +/- 0.2 mag,
  J  > 21.6 mag,
  H  > 21.0 mag, and
  Ks > 18.5 mag.
  

  The spectral energy distribution of source #1 is best fit with a power-law of slope beta = 0.8+-0.3 (without significant dust extinction), typical for GRB afterglows. Also, source #1 is brighter than source #2, but not visible in the SDSS. While we cannot establish clear fading, we suggest this object as the afterglow of GRB 150423A.
  Given magnitudes are calibrated against SDSS (g'r'i'z') as well as 2MASS field stars and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V)=0.03 mag in the direction of the burst (Schlegel et al. 1998).
• GCN Circular #17733
  D. A. Perley (Caltech) reports:
  I acquired observations of the optical afterglow candidate of GRB 150423A (Pagani et al., GCN 17726; Varela et al., GCN 17732) using the Low Resolution Imaging Spectrometer (LRIS) on the Keck I 10m telescope.
  Two epochs of V- and i-band imaging were acquired, the first beginning at UT 07:13 (approximately 0.75 hours after the trigger, as soon as the target cleared the telescope Nasmyth limit), the second beginning at UT 13:12 (approximately 6.75 hours after the trigger).
  The sources mentioned by Varela et al. are well-detected in both epochs. Source 2 remains constant between the frames, while Source 1 declines by approximately 0.9 magnitude in both V- and i-band, confirming that it is the optical afterglow.
  Shortly after the second imaging epoch, I also acquired 1600 seconds of low-resolution spectroscopy with the slit oriented to cover both S1 and S2. A faint trace is detected for both sources. Source 2 shows a clear emission line in the blue arm and at least one marginal emission line in the red arm, indicating a low to moderate redshift. Source 1 (the afterglow) shows no clear features in emission or absorption, but the signal is very weak. Further analysis will reported at a later time pending wavelength calibration of the spectra.
• GCN Circular #17735
  P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) report on behalf of the Swift-XRT team.
  Using 2017 s of XRT Photon Counting mode data and 4 UVOT images for GRB 150423A, 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 = 221.57899, +12.28349 which is equivalent to:

  RA (J2000): 14h 46m 18.96s
  Dec (J2000): +12d 17' 00.6"
  

  with an uncertainty of 1.8 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 #17736
  Owen Littlejohns (ASU), Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William H. Lee (UNAM), Michael G. Richer (UNAM), Chris Klein (UCB), Ori Fox (UCB), J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (ORAU/GSFC), Eleonora Troja (GSFC), Enrico Ramirez-Ruiz (UCSC), Jos=E9 A. de Diego (UNAM), Leonid Georgiev (UNAM), Jes=FAs Gonz=E1lez (UNAM), Carlos Rom=E1n-Z=FA=F1iga (UNAM), Neil Gehrels (GSFC), and Harvey Moseley (GSFC) report:
  We observed the field of GRB 150423A (Pagani, et al., GCN 17728) with the Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on the 1.5m Harold Johnson Telescope at the Observatorio Astron=F3mico
  Nacional on Sierra San Pedro M=E1rtir from 2015/04 23.41 to 2015/04 23.48 UTC (3.30 to 5.01 hours after the BAT trigger), obtaining a total of 1.42 hours exposure in the r, i and z bands.
  For a source within the Swift-XRT error circle (Evans, et al., GCN 17735), in comparison with the SDSS DR9, we obtain the following detections and upper limits (3-sigma):

    r     23.77 +/- 0.23
    i     23.62 +/- 0.26
    z     > 20.33
  

  These magnitudes are in the AB system and are not corrected for Galactic extinction in the direction of the GRB. Of the two sources reported by GROND (Varela, et al., GCN 17732), this source is at the position of source 1. Our observations show a fading of 0.8 magnitudes in the i band, implying a power-law decay with a temporal index, t^-0.5. Similarly to the Keck observations (Perley, GCN 17733), we also find source 2 reported by GROND to have remained at approximately constant brightness.
  Continued observations are planned.
  We thank the staff of the Observatorio Astron=F3mico Nacional in San Pedro M=E1rtir.
• GCN Circular #17737
  K.L. Page (U. Leicester), M. de Pasquale (INAF-IASFPA), A. Maselli (INAF-IASFPA), A. Melandri (INAF-OAB), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), A.P. Beardmore (U. Leicester) and C. Pagani report on behalf of the Swift-XRT team:
  We have analysed 8.1 ks of XRT data for GRB 150423A (Pagani et al. GCN Circ. 17728), from 78 s to 28.7 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Evans et al. (GCN Circ. 17735).
  The light curve can be modelled with a power-law decay with a decay index of alpha=0.86 (+/-0.09).
  A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.53 (+0.32, -0.21). The best-fitting absorption column is 2.9 (+10.0, -1.2) x 10^20 cm^-2, consistent with the Galactic value of 1.8 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.2 x 10^-11 (4.3 x 10^-11) erg cm^-2 count^-1.
  A summary of the PC-mode spectrum is thus:

  Total column:	     2.9 (+10.0, -1.2) x 10^20 cm^-2
  Galactic foreground: 1.8 x 10^20 cm^-2
  Excess significance: <1.6 sigma
  Photon index:	     1.53 (+0.32, -0.21)
  

  If the light curve continues to decay with a power-law decay index of 0.86, the count rate at T+24 hours will be 1.4 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.0 x 10^-14 (6.2 x 10^-14) erg cm^-2 s^-1.
  The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00638808.
  This circular is an official product of the Swift-XRT team.
• GCN Circular #17738
  D. A. Kann (TLS Tautenburg), T. Kruehler (ESO Chile), S. Klose (TLS Tautenburg) and J. Greiner (MPE Garching) report:
  We obtained a photometry sequence in BVRIz with VLT FORS2 of the optical afterglow (Varela et al., GCN # 17729, # 17732; Perley, GCN # 17733; Littlejohns et al., GCN # 17736) of the short GRB 150423A (Swift-638808, Pagani et al., GCN # 17728).
  Observations started on April 23, 2015, 08:02:19 UT, 94 minutes after the GRB. Seeing was 1".0 and airmass was 1.7.
  The afterglow is clearly detected in BVR. Analysis of Iz is pending.
  We find Rc = 22.8 +/- 0.1 in the first image (calibrated against SDSS standard stars transformed to Rc) and find it fades by approximately 0.4 magnitudes in the course of an hour (see also Perley, GCN # 17733; Littlejohns et al., GCN # 17736).
  We are indebted to Jonathan Smoker and Fernando Selman for VLT UT1 support.
• GCN Circular #17739
  F.E. Marshall (NASA/GSFC) and C. Pagani (U. Leicester) report on behalf of the Swift/UVOT team:
  The Swift/UVOT began settled observations of the field of GRB 150423A 74 s after the BAT trigger (Pagani et al., GCN Circ. 17728). No optical afterglow consistent with the optical position (Source 1 in Varela et al. GCN Circ. 17732; Perley GCN Circ. 17733) 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 first finding chart (FC) exposures and subsequent exposures are:

  Filter         T_start(s)   T_stop(s)      Exp(s)         Mag
  
  white_FC            74          223          147         >20.8
  u_FC               286          535          246         >20.2
  white               74         6067          733         >21.5
  v                  615         6477          452         >20.9
  b                  541         5862          255         >20.9
  u                  286         6924          513         >20.8
  w1                 665         6887          452         >20.9
  m2                5048         6682          393         >20.8
  w2                 591         6273          432         >21.6
  

  The magnitudes in the table 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).
• GCN Circular #17740
  T. N. Ukwatta (LANL), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), C. Pagani (U Leicester), D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU), (i.e. the Swift-BAT team):
  Using the data set from T-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 150423A (trigger #638808) (Pagani, et al., GCN Circ. 17728). The BAT ground-calculated position is RA, Dec = 221.601, 12.264 deg which is

     RA(J2000)  =  14h 46m 24.2s
     Dec(J2000) = +12d 15' 50.6"
  

  with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment). The partial coding was 92%.
  BAT light curve shows a single peak starting around T+0.0 sec and ending around T+0.25 sec. T90 (15-350 keV) is 0.22 +- 0.03 sec (estimated error including systematics).
  The time-averaged spectrum from T+0.01 to T+0.24 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 0.84 +- 0.24. The fluence in the 15-150 keV band is 6.3 +- 1.0 x 10^-08 erg/cm2. The 1-sec peak photon flux measured from T-0.37 sec in the 15-150 keV band is 0.9 +- 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/638808/BA/
• GCN Circular #17741
  W. Fong and P. Milne (University of Arizona) report on behalf of a larger collaboration:
  "We observed the field of the Swift short-duration GRB 150423A (Pagani et al., GCN 17728) with UFTI mounted on the 3.8-m United Kingdom Infrared Telescope (UKIRT) on Mauna Kea beginning on 2015 April 23.337 UT, at an average airmass of 1.1 in 0.55" seeing. We obtained 6600 sec of J-band imaging at a mid-time of 2.72 hr post-burst, and 6300 sec of K-band imaging at a mid-time of 4.93 hr post-burst. The afterglow (Source 1; Varela et al., GCN 17732; Perley, GCN 17733; Littlejohns et al., GCN 17736; Kann et al., GCN 17738) is weakly detected in both the J- and K-bands. We cannot establish fading over the course of our observations due to the weak detection of the source. We note that Source 2 (Varela et al., GCN 17732) is only detected in K-band.
  Further observations are planned."
• GCN Circular #17742
  D. Kuroda, K. Yanagisawa, Y. Shimizu, H. Toda (OAO, NAOJ), S. Nagayama (NAOJ), M. Yoshida (Hiroshima), K. Ohta (Kyoto) and N. Kawai(Tokyo Tech) report on behalf of MITSuME and OISTER collaboration:
  We observed the field of GRB 150423A (Pagani et al., GCNC 17728) with the optical three color (g', Rc and Ic) CCD camera attached to the MITSuME 50cm telescope of Okayama Astrophysical Observatory.
  The observation started on 2015-04-23 17:04:40 UT, (~10.6 h after the burst). We could not detect the previously reported afterglow (Varela et al., GCNC 17729,17732; Perley, GCNC 17233) in all the three bands.
  Three sigma upper limits of the OT are listed below. We used SDSS-DR8 catalog for flux calibration.

  #T0+[day]  MID-UT    T-EXP[sec]   g'     Rc     Ic
  -----------------------------------------------------
  0.49107    18:15:13    7200.0   >20.8  >20.8  >19.9
  -----------------------------------------------------
  T0+ : Elapsed time after the burst [day]
  T-EXP: Total Exposure time [sec]
  

• GCN Circular #17744
  D. A. Perley (Caltech) reports:
  Further to GCN 17733, I report analysis of the spectroscopy acquired of S2, the neighboring object located 4.0 arcseconds northeast of the optical afterglow of GRB 150423A, first announced by Varela et al. (GCN 17732).
  The spectrum of this object shows weak emission lines from OII (3727), OIII (5007), Halpha (6563), and marginally Hbeta (4861), all at a common redshift of z=0.456. No features are visible in the trace of S1 at any of the same wavelengths (or elsewhere in its spectrum).
  At this redshift, the offset between the sources corresponds to 23 kpc in projection.
  Further observations of S1 will be necessary to determine whether it is entirely afterglow or if it also contains flux from a (coincident) host galaxy, perhaps at a different redshift.
• GCN Circular #17747
  K. Wiersema (Leicester), A. Levan (Warwick), N. Tanvir (Leicester), C. MacLeod (IfA Edinburgh), F. Riddick (ING) report:
  We observed the position of GRB 150423A (Pagani et al. GCN 17728) using the ACAM instrument on the William Herschel Telescope, at La Palma. We obtained images with 5 x 300 sec exposure time in both sloan g and z bands, starting at 22:30 UT on 23 April 2015. The nearby galaxy (Varela et al. GCN 17732; Perley et al. GCN 17744) is clearly detected, but the afterglow (Varela et al. GCN 17732) is not significantly detected, with a 5 sigma limit of g~25.3 (calibrated using SDSS field objects). A low significance object may be present near the afterglow position in g band, as well as some faint galaxies, which may be candidate hosts. See here for an image of the field: http://www2.le.ac.uk/departments/physics/people/klaaswiersema/wht-observations-of-grb-150423a/view
• GCN Circular #17750
  E. Mazaeva (IKI), A. Volnova (IKI), A. Kusakin (Fesenkov Astrophysical Institute), A. Pozanenko (IKI) report on behalf of larger GRB follow-up collaboration:
  We observed the field of GRB 150423A (Pagani et al., GCNC 17728) with Zeiss-1000 (East) 1-m telescope of Tien Shan Astronomical Observatory starting on Apr. 23 (UT) 17:43:02. We obtained several images in R-filter. In a combined image we marginally detect the source S2 and do not detect the afterglow (Varela et al., GCN 17729). Coordinates of the S2 (J2000) 14 46 18.94 +12 17 04.4 with an uncertainty of 0.4" is marginally coincide with coordinates reported by Varela et al. (GCN 17729).
  A preliminary photometry is following

  date              UT start    t-T0         Filter  Exp.        S1       S2 
  S2_err
                                        (mid, days)        (s)
  
  2015-04-23 17:43:02  0.57561  R       25*600  >22.7   22.7   0.3
  

  and based on nearby SDSS DR9 stars:

   SDSS9_id R(Lupton)
   J144606.22+121513.3 15.42
   J144647.40+121502.9 17.54
   J144648.52+121523.3 15.15
  

• GCN Circular #17754
  Owen Littlejohns (ASU), Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William H. Lee (UNAM), Michael G. Richer (UNAM), Chris Klein (UCB), Ori Fox (UCB), J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (ORAU/GSFC), Eleonora Troja (GSFC), Enrico Ramirez-Ruiz (UCSC), Jos=E9 A. de Diego (UNAM), Leonid Georgiev (UNAM), Jes=FAs Gonz=E1lez (UNAM), Carlos Rom=E1n-Z=FA=F1iga (UN= AM), Neil Gehrels (GSFC), and Harvey Moseley (GSFC) report:
  We again observed the field of GRB 150423A (Pagani, et al., GCN 17728) with the Reionization and Transients Infrared Camera (RATIR; www.ratir.or= g) on the 1.5m Harold Johnson Telescope at the Observatorio Astron=F3mico Nacional on Sierra San Pedro M=E1rtir from 2015/04 24.18 to 2015/04 24.48 UTC (21.74 to 28.97 hours after the BAT trigger), obtaining a total of 5.69 hours exposure in the r, i and z bands.
  For a source within the Swift-XRT error circle (Evans, et al., GCN 17735), in comparison with the SDSS DR9, we obtain the following upper limits (3-sigma):

    r     > 24.82
    i     > 24.79
    z     > 22.07
  

  These magnitudes are in the AB system and are not corrected for Galactic extinction in the direction of the GRB. In comparison to the earlier epoch of RATIR observations (Littlejohns, et al., GCN 17736), these upper limits indicate fading of at least 1 magnitude in the r and i bands. This implies a continuing power-law decay temporal power-law index of t^-0.5 or steeper, which is consistent with the comparison between the first epoch of RATIR observations and the earlier GROND measurements (Varela, et al., GCN 17732). The magnitude of source 2, as reported in the GROND observations, is consistent with being constant in both epochs of RATIR data.
  We thank the staff of the Observatorio Astron=F3mico Nacional in San Pedro M=E1rtir.
• GCN Circular #17755
  D. Malesani (DARK/NBI), T. Kruehler (ESO), D. Xu (NAOC/CAS), G. Pugliese (API/Uva), D. Watson, J. P. U. Fynbo, B. Milvang-Jensen (DARK/NBI), A. de Ugarte Postigo (IAA/CSIC and DARK/NBI), N. R. Tanvir (U. Leicester), V. D'Elia (ASI/ASDC and INAF/Roma), K. Wiersema (U. Leicester), J. Greiner(MPE Garching), J. Japelj (U. Ljubljana) report on behalf of a larger collaboration:
  We observed the optical afterglow (Varela et al., GCNs 17729, 17732, Perley, GCN 17733, Littlejohns et al. GCN 17736, Kann et al. GCN 17738, Fong & Milne GCN 17741) of the Swift short-GRB 150423A (Pagani et al. GCN 17728) with the VLT equipped with the X-shooter spectrograph in the rapid response mode (RRM).
  A series of individual spectra with a total exposure time of around 5000 s were obtained starting on 2015-04-23 06:50 UT, which is 22 minutes after the BAT trigger.
  A preliminary analysis of the spectrum reveals a faint and blue continuum detected down to 3200 AA. This sets a robust upper limit of z < 2.5 to the redshift of the GRB. Similarly to Perley (GCNs 17733, 17744), we do not detect obvious absorption or emission features in our spectra. There is, however, a tentative detection of a doublet in absorption at around 6900 AA. If real, the lines match the Mg II doublet at a redshift of z = 1.394.
  We acknowledge the excellent support provided by Paranal staff, and in particular Fernando Selman and Emanuela Pompei.
• GCN Circular #17763
  S.Harita, T.Fujiwara, T. Yoshii, Y. Saito, Y. Tachibana, H. Ohuchi, Y. Yano, S. Kurita, Y.Ono, Y.Muraki, Y. Yatsu, and N. Kawai (Tokyo Tech)
  report on behalf of the MITSuME collaboration:
  We searched for the optical counterpart of GRB 150423A (C. Pagani et al. GCN Circular #17728) with the optical three color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50 cm telescope of Akeno Observatory, Yamanashi, Japan.
  The observation started on 2015-04-23 13:03:48 UT (~6.6 h after the burst). We did not find any new point source within XRT circle in all three bands.
  We obtained following limits for the magnitudes.

  T0+[sec]      MID-UT      T-EXP[sec]         g'           Rc           Ic
  ---------------------------------------------------------------------------------------
    23744     16:26:45          2940           >19.4      >19.3     > 18.4
  ---------------------------------------------------------------------------------------
  T0+ : Elapsed time after the burst
  T-EXP: Total Exposure time
  We used GSC2.3 catalog for flux calibration
  

• GCN Circular #17798
  I.A. Smith (Rice U.), N.R. Tanvir (U. of Leicester) report:
  We observed the location of the short GRB 150423A (Pagani et al., GCN Circ. 17728) using the SCUBA-2 sub-millimeter continuum camera on the James Clerk Maxwell Telescope. The observation started at 07:21 UT on 2015-04-23, corresponding to 53 minutes after the burst trigger. Exposures totaling 2.0 hours were made in good weather conditions. No source was detected, with the RMS background noise being 1.5 mJy/beam at 850 microns and 17.4 mJy/beam at 450 microns.
  We thank Callie Matulonis, Angus Mok, and Iain Coulson for the prompt support of these observations that were taken under project M15AI86.
• GCN Circular #17801
  E. Berger, R. Margutti (Harvard), and W. Fong (Univ. of Arizona) report:
  "We observed the location of the short GRB 150423A (GCN #17728) with the Chandra X-ray Observatory ACIS-S instrument starting on 2015 May 2.308 UT for a total of 23.3 ksec. At the location of the optical afterglow (GCNs #17732, 17733) we detect no significant X-ray emission, and place an upper limit on the count rate of 1.3e-4 cps (1" radius aperture). Using the spectral properties determined from the Swift/XRT data (GCN #17737) we place an upper limit on the flux of the X-ray afterglow at 9.17 days post-burst of 1.7e-15 erg/s/cm^2 (0.3-10 kev).
  We thank Belinda Wilkes, Harvey Tananbaum, and the Chandra X-ray Observatory staff for approving and carrying out this Director's Discretionary Time observation."
• GCN Circular #17803
  J. Mao, Y. Fan and J.-M. Bai (YNAO) report:
  We observed the field of GRB 150423A (Pagani et al., GCN 17728) with the 2.4-meter optical telescope at Gao-Mei-Gu (GMG) station of Yunnan Observatory. Observations began from 17:11:14 UT, May 2nd, 2015, about 9 days after the trigger. We did not detect any source / rebrightening feature at the afterglow position down to a limit of z~21.0 mag with poor observational condition.