Gamma-ray Burst 150428A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Tue 28 Apr 15 01:31:42 UT
NOTICE_TYPE:     Swift-BAT GRB Position 
TRIGGER_NUM:     639275,   Seg_Num: 0   
GRB_RA:          188.543d {+12h 34m 10s} (J2000),
                 188.738d {+12h 34m 57s} (current),
                 187.907d {+12h 31m 38s} (1950)
GRB_DEC:          +6.981d {+06d 58' 51"} (J2000),
                  +6.896d {+06d 53' 47"} (current),
                  +7.256d {+07d 15' 23"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       32842 [cnts]    Image_Peak=657 [image_cnts]
TRIGGER_DUR:     12.160 [sec]    
TRIGGER_INDEX:   491     E_range: 50-350 keV
BKG_INTEN:       137147 [cnts]
BKG_TIME:        5346.49 SOD {01:29:06.49} UT
BKG_DUR:         64 [sec]
GRB_DATE:        17140 TJD;   118 DOY;   15/04/28
GRB_TIME:        5440.83 SOD {01:30:40.83} UT
GRB_PHI:          36.79 [deg]
GRB_THETA:        43.71 [deg]
SOLN_STATUS:     0x10103
RATE_SIGNIF:     29.83 [sigma]
IMAGE_SIGNIF:    12.63 [sigma]
MERIT_PARAMS:     +1  +0  +0  +4  +3  +2  +0  +0 +83  +0
SUN_POSTN:        35.11d {+02h 20m 27s}  +14.00d {+14d 00' 06"}
SUN_DIST:        146.51 [deg]   Sun_angle= -10.2 [hr] (East of Sun)
MOON_POSTN:      151.09d {+10h 04m 22s}   +8.21d {+08d 12' 40"}
MOON_DIST:        37.33 [deg] 
MOON_ILLUM:      69 [%] 
GAL_COORDS:      290.65, 69.44 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      185.06,  9.80 [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 position matches one of the nearby galaxy sources in the
+on-board catalog!
COMMENTS:        This does not match any source in the on-board catalog.
COMMENTS:        This matches a source in the ground catalog: I3521,   delta=0.211 [deg].
COMMENTS:        This is a GRB in nearby galaxy or it is noise.
COMMENTS:        This trigger occurred at longitude,latitude = 16.92,19.05 [deg].

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Tue 28 Apr 15 01:31:56 UT
NOTICE_TYPE:     Swift-BAT Transient Position
TRIGGER_NUM:     639275,   Seg_Num: 0
GRB_RA:          188.543d {+12h 34m 10s} (J2000),
                 188.738d {+12h 34m 57s} (current),
                 187.907d {+12h 31m 38s} (1950)
GRB_DEC:          +6.981d {+06d 58' 51"} (J2000),
                  +6.896d {+06d 53' 47"} (current),
                  +7.256d {+07d 15' 23"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       32842 [cnts]    Image_Peak=657 [image_cnts]
TRIGGER_DUR:     12.160 [sec]    
TRIGGER_INDEX:   491     E_range: 50-350 keV
BKG_INTEN:       137147 [cnts]
BKG_TIME:        5346.49 SOD {01:29:06.49} UT
BKG_DUR:         64 [sec]
GRB_DATE:        17140 TJD;   118 DOY;   15/04/28
GRB_TIME:        5440.83 SOD {01:30:40.83} UT
GRB_PHI:          36.79 [deg]
GRB_THETA:        43.71 [deg]
SOLN_STATUS:     0x10103
RATE_SIGNIF:     29.83 [sigma]
IMAGE_SIGNIF:    12.63 [sigma]
MERIT_PARAMS:     +1  +0  +0  +4  +3  +2  +0  +0 +83  +0
SUN_POSTN:        35.11d {+02h 20m 27s}  +14.00d {+14d 00' 06"}
SUN_DIST:        146.51 [deg]   Sun_angle= -10.2 [hr] (East of Sun)
MOON_POSTN:      151.09d {+10h 04m 23s}   +8.21d {+08d 12' 38"}
MOON_DIST:        37.33 [deg] 
MOON_ILLUM:      69 [%] 
GAL_COORDS:      290.65, 69.44 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      185.06,  9.80 [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 does not match any source in the on-board catalog.
COMMENTS:        This matches a source in the ground catalog: I3521,   delta=0.211
+[deg].
COMMENTS:        This is not a GRB -- it is a hard x-ray transient.
COMMENTS:        This trigger occurred at longitude,latitude = 16.92,19.05 [deg].

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Tue 28 Apr 15 01:33:47 UT
NOTICE_TYPE:     Swift-XRT Nack-Position
TRIGGER_NUM:     639275,   Seg_Num: 0
POINT_RA:        188.570d {+12h 34m 17s} (J2000)
POINT_DEC:        +6.953d {+06d 57' 12"} (J2000)
IMG_START_DATE:  17140 TJD;   118 DOY;   15/04/28
IMG_START_TIME:  5616.73 SOD {01:33:36.73} UT,   175.9 [sec] since BAT Trigger Time
COUNTS:          14    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:     Tue 28 Apr 15 01:36:48 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     639275,   Seg_Num: 0
POINT_RA:        188.570d {+12h 34m 17s} (J2000)
POINT_DEC:        +6.953d {+06d 57' 12"} (J2000)
POINT_ROLL:      308.500d
IMG_START_DATE:  17140 TJD;   118 DOY;   15/04/28
IMG_START_TIME:  5619.93 SOD {01:33:39.93} UT,   179.1 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        2.254
N_STARS:         21
X_OFFSET:        743 [pixels]
Y_OFFSET:        459 [pixels]
X_MAX:           1702 [pixels]
Y_MAX:           1418 [pixels]
DET_THRESH:      12
PHOTO_THRESH:    6
SL_URL:          sw00639275000msufc0179.fits
SUN_POSTN:        35.12d {+02h 20m 28s}  +14.00d {+14d 00' 10"}
SUN_DIST:        146.54 [deg]   Sun_angle= -10.2 [hr] (East of Sun)
MOON_POSTN:      151.13d {+10h 04m 32s}   +8.20d {+08d 11' 57"}
MOON_DIST:        37.32 [deg]
MOON_ILLUM:      69 [%]
GAL_COORDS:      290.74, 69.42 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      185.10,  9.78 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Tue 28 Apr 15 01:37:18 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     639275,   Seg_Num: 0
POINT_RA:        188.570d {+12h 34m 17s} (J2000)
POINT_DEC:        +6.953d {+06d 57' 12"} (J2000)
POINT_ROLL:      308.500d
IMG_START_DATE:  17140 TJD;   118 DOY;   15/04/28
IMG_START_TIME:  5619.93 SOD {01:33:39.93} UT,   179.1 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        2.254
N_STARS:         21
X_OFFSET:        743 [pixels]
Y_OFFSET:        459 [pixels]
X_MAX:           1702 [pixels]
Y_MAX:           1418 [pixels]
DET_THRESH:      12
PHOTO_THRESH:    6
SL_URL:          sw00639275000msufc0179.fits
SUN_POSTN:        35.12d {+02h 20m 28s}  +14.00d {+14d 00' 10"}
SUN_DIST:        146.54 [deg]   Sun_angle= -10.2 [hr] (East of Sun)
MOON_POSTN:      151.14d {+10h 04m 33s}   +8.20d {+08d 11' 53"}
MOON_DIST:        37.31 [deg]
MOON_ILLUM:      69 [%]
GAL_COORDS:      290.74, 69.42 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      185.10,  9.78 [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:     Tue 28 Apr 15 01:38:22 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     639275,   Seg_Num: 0
POINT_RA:        188.570d {+12h 34m 17s} (J2000)
POINT_DEC:        +6.953d {+06d 57' 12"} (J2000)
ROLL:            308.500d
IMG_START_DATE:  17140 TJD;   118 DOY;   15/04/28
IMG_START_TIME:  5619.93 SOD {01:33:39.93} UT,   179.1 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     451877633
X_OFFSET:        1062 [pixels]
Y_OFFSET:        778 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1222
Y_GRB_POS:       938
BINNING_INDEX:   1
IM_URL:          sw00639275000msuni0193.fits
SUN_POSTN:        35.12d {+02h 20m 28s}  +14.00d {+14d 00' 11"}
SUN_DIST:        146.54 [deg]   Sun_angle= -10.2 [hr] (East of Sun)
MOON_POSTN:      151.15d {+10h 04m 35s}   +8.20d {+08d 11' 44"}
MOON_DIST:        37.31 [deg]
MOON_ILLUM:      69 [%]
GAL_COORDS:      290.74, 69.42 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      185.10,  9.78 [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:     Tue 28 Apr 15 01:38:31 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     639275,   Seg_Num: 0
POINT_RA:        188.570d {+12h 34m 17s} (J2000)
POINT_DEC:        +6.953d {+06d 57' 12"} (J2000)
ROLL:            308.500d
IMG_START_DATE:  17140 TJD;   118 DOY;   15/04/28
IMG_START_TIME:  5619.93 SOD {01:33:39.93} UT,   179.1 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     451877633
X_OFFSET:        1062 [pixels]
Y_OFFSET:        778 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       1222
Y_GRB_POS:       938
BINNING_INDEX:   1
IM_URL:          sw00639275000msuni0193.fits
SUN_POSTN:        35.12d {+02h 20m 28s}  +14.00d {+14d 00' 11"}
SUN_DIST:        146.54 [deg]   Sun_angle= -10.2 [hr] (East of Sun)
MOON_POSTN:      151.15d {+10h 04m 35s}   +8.20d {+08d 11' 43"}
MOON_DIST:        37.30 [deg]
MOON_ILLUM:      69 [%]
GAL_COORDS:      290.74, 69.42 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      185.10,  9.78 [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 #17765
K. L. Page (U Leicester), M. M. Chester (PSU), N. Gehrels (NASA/GSFC), J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL), F. E. Marshall (NASA/GSFC), T. Sakamoto (AGU), B. Sbarufatti (INAF-OAB/PSU) and M. H. Siegel (PSU) report on behalf of the Swift Team:
At 01:30:40 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 150428A (trigger=639275). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 188.543, +6.981 which is
```
   RA(J2000) = 12h 34m 10s
   Dec(J2000) = +06d 58' 51"
```
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 50 sec. The peak count rate was ~1700 counts/sec (15-350 keV), at ~17 sec after the trigger.
The XRT began observing the field at 01:33:36.7 UT, 175.9 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source located at RA, Dec 188.53889, 6.95211 which is equivalent to:
```
   RA(J2000)  = 12h 34m 09.33s
   Dec(J2000) = +06d 57' 07.6"
```
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This location is 105 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.
A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (1.63 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 9.3 (+6.64/-5.03) x 10^21 cm^-2 (90% confidence).
UVOT took a finding chart exposure of 150 seconds with the White filter starting 179 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers none of the XRT error circle. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.02.
Burst Advocate for this burst is K. L. Page (klp5 AT leicester.ac.uk). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/too.html.)
GCN Circular #17767
F. Knust (MPE Garching), D. A. Kann (TLS Tautenburg), T. Kruehler (ESO), and J. Greiner (MPE Garching) report on behalf of the GROND team:
We observed the field of GRB 150428A (Swift trigger 639275; Page et al., GCN #17765) 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 02:24 UT on 2015-04-28, 53 minutes after the GRB trigger, following a delay due to the labeling of the event as "not a GRB" in the BACODINEs. They were performed at an average seeing of 0".9 and at an average airmass of 1.2.
We detect a source at (J2000):
```
RA =    12:34:09.26
Dec. = +06:57:08.7
```
with an error of 0".5 in each coordinate.
Based on 25 min of total exposure time in g'r'i'z' centered 1.41 hrs after the GRB, we estimate the following preliminary magnitudes (all in AB system):
```
g' = 24.1 +/- 0.4 mag,
r' = 23.0 +/- 0.1 mag,
i' = 22.7 +/- 0.1 mag, and
z' = 23.2 +/- 0.2 mag.
```
At this time, we cannot establish fading. At this position, we also detect a source in the SDSS, which implies that this would be the host galaxy of this GRB. We note the hydrogen column density as derived from X-rays (Page et al., GCN #17765) is much higher than the (very low) Galactic NH, implying this may be an optically dust-suppressed event.
Given magnitudes are calibrated against SDSS field stars and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V)=0.02 mag in the direction of the burst (Schlegel et al. 1998).
GCN Circular #17768
J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the Swift-XRT team.
Using 147 s of XRT Photon Counting mode data and 1 UVOT images for GRB 150428A, 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 = 188.53878, +6.95390 which is equivalent to:
```
RA (J2000): 12h 34m 9.31s
Dec (J2000): +06d 57' 14.0"
```
with an uncertainty of 1.9 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 #17769
D. A. Perley (Caltech) reports on behalf of a larger collaboration:
We observed the field of GRB 150428A (Page et al., GCN 17765) using the Palomar 60-inch robotic telescope starting at UT 03:40:50 on the night of 2015-04-28, acquiring a sequence of r, i, and z-band exposures under excellent seeing conditions.
Stacking a series of 9x180s i-band images between 03:44 and 04:25 UT, we detect no sources within the enhanced XRT error circle (Osborne et al., GCN 17768) down to a limiting magnitude of i > 22.7 mag at a median time of 2.65 hours after the trigger. We note that the source reported by GROND (Knust et al., GCN 17767) is not within the enhanced error circle, but we marginally detect this source at a similar magnitude (i = 22.8 +/- 0.3 mag).
GCN Circular #17770
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 150428A (Page, et al., GCN 17765) 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 28.14 to 2015/04 28.27 UTC (1.80 to 4.88 hours after the BAT trigger), obtaining a total of 2.49 hours exposure in the r, i and z bands.
We find no uncatalogued source within the Swift-XRT error circle (Osborne, et al., GCN 17768). In comparison with the SDSS DR9, we obtain the following upper limits (3-sigma):
```
  r     > 23.94
  i     > 23.90
  z     > 19.56
```
These magnitudes are in the AB system and are not corrected for Galactic extinction in the direction of the GRB. We note that the source detected by GROND (Knust, et al., GCN 17767) and P60 (Perley, GCN 17769) is not consistent with the enhanced X-ray position. For the GROND source, in comparison with the SDSS DR9, we obtain the following detections and upper limit (3-sigma):
```
  r     = 23.41 +/- 0.22
  i     = 22.75 +/- 0.14
  z     > 19.56
```
The RATIR observations of the GROND source, therefore, do not show evidence of fading between the GROND and RATIR epochs of observations. Further RATIR observations are ongoing.
We thank the staff of the Observatorio Astron=F3mico Nacional in San Pedro M=E1rtir.
GCN Circular #17771
M. I. Andersen (NBI/StarPlan), D. Xu (NAOC/CAS), M. Kuffmeier (StarPlan), and D. Evans (Keele U.) report on behalf of a larger collaboration:
We observed the field of GRB 150428A (Page et al., GCN 17765) using the Danish 1.56m telescope located at La Silla, Chile. Observations started at 01:56:33 UT on 2015-04-28 (i.e., 0.43 hr post-burst) and 12x180s R-band images were obtained.
We marginally detect a source in the stacked image at coordinates
```
R.A. = 12:34:09.227
Dec. = +6:57:14.07
```
Error Radius: ~ 1 arcsec,
consistent with the enhanced XRT position (Osborne et al., GCN 17768). Preliminary reduction shows that the source has m(R) = 22.50 +/- 0.43 mag at a median time of 0.887 hr post-burst, calibrated with two nearby SDSS stars. It could be the afterglow of the GRB.
We also detect the source reported by GROND (Knust et al., GCN 17767). It is extended in the northwest-southeast direction. Its position is not consistent with the present enhanced XRT position, as noted by P60 (Perley, GCN 17769).
GCN Circular #17774
W. H. Baumgartner (GSFC/UMBC), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC),=20 N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL),0 T. Sakamoto (AGU), M. Stamatikos (OSU), T. N. Ukwatta (LANL) (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 150428A (trigger #639275) (Page, et al., GCN Circ. 17765). The BAT ground-calculated position is RA, Dec =3D 188.539, 6.967 deg which is
```
  RA(J2000) =   12h 34m 09.3s=20
  Dec(J2000) = +06d 58' 00.8=E2=80=9D=20
```
with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment). The partial coding was 16%.
The mask-weighted light curve shows a multi-peaked structure that starts = at=20 ~ T-40 sec and ends at ~ T+60 sec. T90 (15-350 keV) is 53.2 +- 15.1 sec=20 (estimated error including systematics).=20
The time-averaged spectrum from T-39.0 to T+38.6 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.28 +- 0.09.=20 The fluence in the 15-150 keV band is 6.3 +- 0.3 x 10^-6 erg/cm2. The 1-sec peak=20 photon flux measured from T+17.4 sec in the 15-150 keV band is 3.0 +- 0.5 ph/cm2/sec. =20 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/639275/BA/
GCN Circular #17777
K. L. Page (U Leicester) reports on behalf of the Swift-XRT team:
We have analysed 1.3 ks of XRT data for GRB 150428A (Page et al. GCN Circ. 17765), from 160 s to 32.5 ks after the BAT trigger. The data comprise 8 s in Windowed Timing (WT) mode (taken while Swift was slewing), with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Osborne et al. (GCN Circ. 17768).
The light curve can be modelled with a power-law decay with a decay index of alpha=0.75 (+/-0.05).
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.0 (+0.4, -0.3). The best-fitting absorption column is 5.3 (+2.4, -1.9) x 10^21 cm^-2, in excess of the Galactic value of 1.6 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 4.1 x 10^-11 (6.8 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Total column:	     5.3 (+2.4, -1.9) x 10^21 cm^-2
Galactic foreground: 1.6 x 10^20 cm^-2
Excess significance: 4.4 sigma
Photon index:	     2.0 (+0.4, -0.3)
```
If the light curve continues to decay with a power-law decay index of 0.75, the count rate at T+24 hours will be 0.028 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.2 x 10^-12 (1.9 x 10^-12) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00639275.
This circular is an official product of the Swift-XRT team.
GCN Circular #17778
D.Buckley, S. Potter, A.Kniazev, M.Kotze South African Astronomical Observatory
E. Gorbovskoy, V. Lipunov, N.Tyurina, V.Kornilov, P.Balanutsa, A.Kuznetsov, D.Kuvshinov, Lomonosov Moscow State University, Sternberg Astronomical Institute
K.Ivanov, S.Yazev, N.M.Budnev, O.Gres, O.Chuvalaev, V.A.Poleshchuk Irkutsk State University
A. Tlatov, A.V. Parhomenko, D. Dormidontov, V.Sennik Kislovodsk Solar Station of the Pulkovo Observatory
V.Yurkov, Yu.Sergienko, D.Varda, E.Sinyakov Blagoveschensk Educational State University, Blagoveschensk
V.Krushinski, I.Zalozhnih, A. Popov Ural Federal University, Kourovka
Hugo Levato and Carlos Saffe Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE)
Claudio Mallamaci, Carlos Lopez and Federico Podest Observatorio Astronomico Felix Aguilar (OAFA)
MASTER II robotic telescope (MASTER-Net: http://observ.pereplet.ru) located in SAAO was pointed to the GRB150428A (Page et al, GCN 17765) 28 sec after notice time and 90 sec after trigger time at 2015-04-28 01:32:10 UT in two polarizations. On our first single and coadd images we haven`t found optical transient within SWIFT error-box . The observations made on a high zenith distance ~ 80 d. We obtain a followin upper limits:
```
Date start  T_s-T_tr   T_m-T_trig     Expt.  Limit Coadd
                       (mean_time)
01:32:10.9    90          100          20      16.0   no
01:32:43.2   122          132          20      16.0   no
01:33:14.7   153          168          30      16.4   no
01:33:14.7   153          224         120      17.0    3
01:33:14.7   153          583         770      18.5    9
```
Also, we can not confirm Danish 1.56m OT (Andersen et. al GCN 17771), because they do not see it on our images with upper limits specified above.
The message may be cited.
GCN Circular #17785
M. M. Chester (PSU) and K. L. Page (U Leicester) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 150428A 179 s after the BAT trigger (Page et al., GCN Circ. 17765). No optical afterglow consistent with the enhanced XRT position (Osborne et al. GCN Circ. 17768) 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) exposure and one subsequent exposure are:
```
Filter         T_start(s)   T_stop(s)      Exp(s)     UL (3-sigma)

white_FC           179         329          147        >20.9
u                 3572        3726          152        >19.9
```
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.02 in the direction of the burst (Schlegel et al. 1998).
GCN Circular #17802
S. Golenetskii, R.Aptekar, D. Frederiks, V. Pal'shin, P. Oleynik, M. Ulanov, D. Svinkin, A. Tsvetkova, A.Lysenko, and T. Cline on behalf of the Konus-Wind team, report:
The long-duration GRB 150428A (Swift-BAT trigger #639275: Page, et al., GCN Circ. 17765; Baumgartner, et al., GCN Circ. 17774) was detected by Konus-Wind in the waiting mode.
The burst light curve shows a single pulse which started approximately at BAT trigger time T0(BAT) and has a duration of ~45 s.
As observed by Konus-Wind, the burst had a fluence of 1.61(-0.09,+0.10)x10^-5 erg/cm2 and a 2.944-s peak flux, measured from ~T0(BAT)+21 s, of 5.5(-0.7,+0.9)x10^-7 erg/cm2 (both in the 20 - 1200 keV energy range).
Modelling the K-W 3-channel time-integrated spectrum (from T0(BAT)-3 s to T0(BAT)+41 s) by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) yields alpha = -1.04(-0.12,+0.14), and Ep = 275(-29,+37) keV.
All the quoted errors are estimated at the 1 sigma confidence level. All the presented results are preliminary.
The K-W light curve of this burst is available at http://www.ioffe.rssi.ru/LEA/GRBs/GRB150428A/
GCN Circular #30324
James Leung (University of Sydney/CSIRO), Poonam Chandra (NCRA-TIFR), Emil Lenc (CSIRO), Tara Murphy (University of Sydney), Ziteng Wang (University of Sydney/CSIRO)
ASKAP J123409+065712 is a radio source found in a search of Australian Square Kilometre Array Pathfinder (ASKAP) data (SB10736). The radio source position is consistent with the enhanced Swift-XRT position (Osborne et al., GCN Circ. 17768) and inconsistent with the GROND source position (Knust et al., GCN Circ. 17767).
We conducted further observations of the radio source with the Australia Telescope Compact Array (ATCA) and the upgraded Giant Metrewave Radio Telescope (uGMRT). We summarise these observations in the table below.
```
Date (UTC) | Telescope | Freq (GHz) | Peak Flux Density (uJy/beam)
------------------------------------------------------------------
2019/12/05 | ASKAP     | 1.4        | 363 +/- 56
2021/05/21 | ATCA      | 5.5        |  94 +/- 26
2021/06/13 | uGMRT     | 1.3        | 386 +/- 17
```
The fitted position of the radio source from the uGMRT observation is
```
RA: 12:34:09.296
Dec: +06:57:13.83
```
Observations of the radio source do not show any evidence for fading in epochs separated by 555 days and we therefore conclude the source is likely the host galaxy of GRB 150428A.
We thank CSIRO and GMRT staff for supporting these observations during these especially difficult times.

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Jochen Greiner, last update: 26-Jun-2021 [Disclaimer]