Gamma-ray Burst 140428A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 28 Apr 14 22:45:33 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     597519,   Seg_Num: 0
POINT_RA:        194.304d {+12h 57m 13s} (J2000)
POINT_DEC:       +28.341d {+28d 20' 28"} (J2000)
POINT_ROLL:      330.744d
IMG_START_DATE:  16775 TJD;   118 DOY;   14/04/28
IMG_START_TIME:  81754.52 SOD {22:42:34.52} UT,   51694.5 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        1.806
N_STARS:         17
X_OFFSET:        318 [pixels]
Y_OFFSET:        578 [pixels]
X_MAX:           1277 [pixels]
Y_MAX:           1537 [pixels]
DET_THRESH:      11
PHOTO_THRESH:    6
SL_URL:          sw00597519000msufc138094.fits
SUN_POSTN:        36.18d {+02h 24m 44s}  +14.36d {+14d 21' 20"}
SUN_DIST:        132.48 [deg]   Sun_angle= -10.6 [hr] (East of Sun)
MOON_POSTN:       32.62d {+02h 10m 29s}  +12.43d {+12d 25' 41"}
MOON_DIST:       135.68 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:       76.75, 88.24 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      180.72, 31.47 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 28 Apr 14 22:45:59 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     597519,   Seg_Num: 0
POINT_RA:        194.304d {+12h 57m 13s} (J2000)
POINT_DEC:       +28.341d {+28d 20' 28"} (J2000)
POINT_ROLL:      330.744d
IMG_START_DATE:  16775 TJD;   118 DOY;   14/04/28
IMG_START_TIME:  81754.52 SOD {22:42:34.52} UT,   51694.5 [sec] since BAT Trigger Time
FILTER:          10, White
BKG_MEAN:        1.806
N_STARS:         17
X_OFFSET:        318 [pixels]
Y_OFFSET:        578 [pixels]
X_MAX:           1277 [pixels]
Y_MAX:           1537 [pixels]
DET_THRESH:      11
PHOTO_THRESH:    6
SL_URL:          sw00597519000msufc138094.fits
SUN_POSTN:        36.18d {+02h 24m 44s}  +14.36d {+14d 21' 21"}
SUN_DIST:        132.48 [deg]   Sun_angle= -10.6 [hr] (East of Sun)
MOON_POSTN:       32.63d {+02h 10m 30s}  +12.43d {+12d 25' 44"}
MOON_DIST:       135.68 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:       76.75, 88.24 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      180.72, 31.47 [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:     Mon 28 Apr 14 22:46:47 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     597519,   Seg_Num: 0
POINT_RA:        194.304d {+12h 57m 13s} (J2000)
POINT_DEC:       +28.341d {+28d 20' 28"} (J2000)
ROLL:            330.744d
IMG_START_DATE:  16775 TJD;   118 DOY;   14/04/28
IMG_START_TIME:  81754.52 SOD {22:42:34.52} UT,   51694.5 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     420417766
X_OFFSET:        637 [pixels]
Y_OFFSET:        897 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       797
Y_GRB_POS:       1057
BINNING_INDEX:   1
IM_URL:          sw00597519000msuni138106.fits
SUN_POSTN:        36.18d {+02h 24m 44s}  +14.36d {+14d 21' 21"}
SUN_DIST:        132.48 [deg]   Sun_angle= -10.6 [hr] (East of Sun)
MOON_POSTN:       32.63d {+02h 10m 32s}  +12.43d {+12d 25' 51"}
MOON_DIST:       135.67 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:       76.75, 88.24 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      180.72, 31.47 [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:     Mon 28 Apr 14 22:47:03 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     597519,   Seg_Num: 0
POINT_RA:        194.304d {+12h 57m 13s} (J2000)
POINT_DEC:       +28.341d {+28d 20' 28"} (J2000)
ROLL:            330.744d
IMG_START_DATE:  16775 TJD;   118 DOY;   14/04/28
IMG_START_TIME:  81754.52 SOD {22:42:34.52} UT,   51694.5 [sec] since BAT Trigger Time
FILTER:          10, White
EXPOSURE_ID:     420417766
X_OFFSET:        637 [pixels]
Y_OFFSET:        897 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       797
Y_GRB_POS:       1057
BINNING_INDEX:   1
IM_URL:          sw00597519000msuni138106.fits
SUN_POSTN:        36.18d {+02h 24m 44s}  +14.36d {+14d 21' 21"}
SUN_DIST:        132.48 [deg]   Sun_angle= -10.6 [hr] (East of Sun)
MOON_POSTN:       32.64d {+02h 10m 33s}  +12.43d {+12d 25' 53"}
MOON_DIST:       135.67 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:       76.75, 88.24 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      180.72, 31.47 [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:     Mon 28 Apr 14 22:47:13 UT
NOTICE_TYPE:     Swift-UVOT Source List
TRIGGER_NUM:     597519,   Seg_Num: 0
POINT_RA:        194.304d {+12h 57m 13s} (J2000)
POINT_DEC:       +28.344d {+28d 20' 37"} (J2000)
POINT_ROLL:      330.744d
IMG_START_DATE:  16775 TJD;   118 DOY;   14/04/28
IMG_START_TIME:  81913.91 SOD {22:45:13.91} UT,   51853.9 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        0.016
N_STARS:         18
X_OFFSET:        78 [pixels]
Y_OFFSET:        338 [pixels]
X_MAX:           1517 [pixels]
Y_MAX:           1777 [pixels]
DET_THRESH:      2
PHOTO_THRESH:    2
SL_URL:          sw00597519000msufc138253.fits
SUN_POSTN:        36.18d {+02h 24m 44s}  +14.36d {+14d 21' 22"}
SUN_DIST:        132.48 [deg]   Sun_angle= -10.6 [hr] (East of Sun)
MOON_POSTN:       32.64d {+02h 10m 33s}  +12.43d {+12d 25' 54"}
MOON_DIST:       135.67 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:       76.82, 88.24 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      180.72, 31.47 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Source List.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 28 Apr 14 22:47:21 UT
NOTICE_TYPE:     Swift-UVOT Processed Source List
TRIGGER_NUM:     597519,   Seg_Num: 0
POINT_RA:        194.304d {+12h 57m 13s} (J2000)
POINT_DEC:       +28.344d {+28d 20' 37"} (J2000)
POINT_ROLL:      330.744d
IMG_START_DATE:  16775 TJD;   118 DOY;   14/04/28
IMG_START_TIME:  81913.91 SOD {22:45:13.91} UT,   51853.9 [sec] since BAT Trigger Time
FILTER:          7, U
BKG_MEAN:        0.016
N_STARS:         18
X_OFFSET:        78 [pixels]
Y_OFFSET:        338 [pixels]
X_MAX:           1517 [pixels]
Y_MAX:           1777 [pixels]
DET_THRESH:      2
PHOTO_THRESH:    2
SL_URL:          sw00597519000msufc138253.fits
SUN_POSTN:        36.18d {+02h 24m 44s}  +14.36d {+14d 21' 22"}
SUN_DIST:        132.48 [deg]   Sun_angle= -10.6 [hr] (East of Sun)
MOON_POSTN:       32.64d {+02h 10m 33s}  +12.43d {+12d 25' 56"}
MOON_DIST:       135.67 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:       76.82, 88.24 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      180.72, 31.47 [deg] ecliptic lon,lat of the pointing direction
COMMENTS:        SWIFT-UVOT Processed Source List.  
COMMENTS:        If you have elected to receive attachments:  
COMMENTS:        The uvot_catalog_srclist.fits.gz file does not exist; skipping the attachment.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 28 Apr 14 22:48:29 UT
NOTICE_TYPE:     Swift-UVOT Processed Image
TRIGGER_NUM:     597519,   Seg_Num: 0
POINT_RA:        194.304d {+12h 57m 13s} (J2000)
POINT_DEC:       +28.344d {+28d 20' 37"} (J2000)
ROLL:            330.744d
IMG_START_DATE:  16775 TJD;   118 DOY;   14/04/28
IMG_START_TIME:  81913.91 SOD {22:45:13.91} UT,   51853.9 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     420417925
X_OFFSET:        637 [pixels]
Y_OFFSET:        897 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       797
Y_GRB_POS:       1057
BINNING_INDEX:   1
IM_URL:          sw00597519000msuni138265.fits
SUN_POSTN:        36.18d {+02h 24m 44s}  +14.36d {+14d 21' 22"}
SUN_DIST:        132.48 [deg]   Sun_angle= -10.6 [hr] (East of Sun)
MOON_POSTN:       32.65d {+02h 10m 36s}  +12.43d {+12d 26' 05"}
MOON_DIST:       135.66 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:       76.82, 88.24 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      180.72, 31.47 [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:        If you have elected to receive attachments:  
COMMENTS:        The uvot_catalog_image.fits.gz file does not exist; skipping the attachment.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Mon 28 Apr 14 22:48:17 UT
NOTICE_TYPE:     Swift-UVOT Image
TRIGGER_NUM:     597519,   Seg_Num: 0
POINT_RA:        194.304d {+12h 57m 13s} (J2000)
POINT_DEC:       +28.344d {+28d 20' 37"} (J2000)
ROLL:            330.744d
IMG_START_DATE:  16775 TJD;   118 DOY;   14/04/28
IMG_START_TIME:  81913.91 SOD {22:45:13.91} UT,   51853.9 [sec] since BAT Trigger Time
FILTER:          7, U
EXPOSURE_ID:     420417925
X_OFFSET:        637 [pixels]
Y_OFFSET:        897 [pixels]
WIDTH:           160 [pixels]
HEIGHT:          160 [pixels]
X_GRB_POS:       797
Y_GRB_POS:       1057
BINNING_INDEX:   1
IM_URL:          sw00597519000msuni138265.fits
SUN_POSTN:        36.18d {+02h 24m 44s}  +14.36d {+14d 21' 22"}
SUN_DIST:        132.48 [deg]   Sun_angle= -10.6 [hr] (East of Sun)
MOON_POSTN:       32.65d {+02h 10m 36s}  +12.43d {+12d 26' 03"}
MOON_DIST:       135.66 [deg]
MOON_ILLUM:      0 [%]
GAL_COORDS:       76.82, 88.24 [deg] galactic lon,lat of the pointing direction
ECL_COORDS:      180.72, 31.47 [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 Circular #16177
D. Kocevski (NASA/GSFC/ORAU), S. D. Barthelmy (GSFC), A. Y. Lien (NASA/GSFC/ORAU), D. Malesani (DARK/NBI), C. B. Markwardt (NASA/GSFC) and D. M. Palmer (LANL) report on behalf of the Swift Team:
At 22:40:50 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 140428A (trigger=597519). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 194.342, +28.357, which is
```
   RA(J2000)  =  12h 57m 22s
   Dec(J2000) = +28d 21' 26"
```
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). Most of the expected realtime products were not available for this trigger so we have limited information. We know that the trigger duration is 4 seconds and the image significance is 9 sigma during that exposure. A light curve is not yet available.
We note that the position reported in TDRSS light curve notices are incorrect. The position reported above is correct.
Because of outage in the TDRSS telemetry downlink, all but one BAT light curve notice and all of the XRT notices are missing. Only a pair of UVOT SourceList and Image notices were received on the ground.
However, based on the strong detection in BAT, we believe that this is most likely a real GRB. We will issue a Circular when the full dataset is downlinked.
Burst Advocate for this burst is D. Kocevski (dankocevski AT gmail.com). 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 #16178
K.L. Page (U. Leicester), D. Malesani (DARK/NBI) and D. Kocevski (NASA/GSFC/ORAU) report on behalf of the Swift-XRT team:
We have analysed the initial downlinked Swift-XRT data for the possible GRB 140428A (GCN Circ. 16177) and find a fading X-ray source within the BAT field of view.
Using 1124 s of XRT Photon Counting mode data and 3 UVOT images, 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 =3D 194.36852, 28.38490 which is equivalent to:
```
RA (J2000):  12h 57m 28.45s
Dec (J2000): +28d 23=E2=80=B2 05.7=E2=80=B2=E2=80=B2
```
with an uncertainty of 1.7 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).
The light curve can be modelled with a power-law decay with a decay index of alpha=3D0.92 (+0.11,-0.10).
We therefore confirm that Swift trigger number 597519 is, indeed, a real GRB.
This circular is an official product of the Swift-XRT team.
GCN Circular #16179
D. Malesani (DARK/NBI), D. Xu (DARK/NBI), H. Dahle (Univ. Oslo), E. Soto (CUA), report on behalf of the Nordic GRB collaboration:
We observed the field of GRB 140428A (Kocevski et al., GCN 16177) with the NOT equipped with the ALFOSC imager. Observations started on 2014 Apr 29.223 UT (5.34 hr after the GRB) and consisted of 20 minutes in r and 12 in z.
Within the X-ray error circle (Page et al., GCN 16178), we do not find any object down to a depth r > 22.5 and z > 20.5 (all AB), calibrated to the SDSS.
DM thanks Thomas Kruehler (ESO) for insightful discussion.
GCN Circular #16180
D. A. Perley (Caltech) reports:
I observed the position of GRB 140428A (Kocevski et al., GCN 16177; Page et al., GCN 16178) using LRIS on the Keck I 10-meter telescope. A single 150-second imaging exposure was acquired simultaneously in both g and i filters. An faint source is well-detected inside the XRT error circle in the i-band image at the following location (J2000):
```
RA  =  12:57:28.392
dec = +28:23:06.28
```
However, the object is completely absent in g-band. Photometry relative to SDSS gives magnitudes of:
```
g > 26.42
i = 23.55 +/- 0.07
```
at a time of 06:09:30 UT (2014-04-29), 7.478 hours after the GRB trigger.
If this corresponds to the afterglow of the GRB, the red color suggests either a (moderately) high-redshift or dust-extinguished event. Further observations are planned.
GCN Circular #16181
D. A. Perley (Caltech) reports:
I re-observed the afterglow candidate of GRB 140428A in longslit mode using LRIS on the Keck I 10m telescope. One 940-second exposure was taken using the 400/8500 grating (red camera) and 600/4000 grism (blue camera).
In a provisional reduction, the spectrum of the object shows a weak, flat continuum between 7000 Angstroms and the red limit of the wavelength range at approximately 10100 Angstroms. The flux sharply drops to zero at 7000 angstroms, though there is faint flux detected in some places slightly further to the blue. No trace is detected on the blue camera.
If the drop at 7000 Angstroms is interpreted as a DLA and the onset of the Lyman-alpha forest, this would indicate a redshift for this object of approximately z=4.7.
GCN Circular #16182
F.J. Aceituno (OSN/IAA-CSIC), A.J. Castro-Tirado (IAA-CSIC/UMA), R. Sanchez-Ramirez (IAA-CSIC), J. Gorosabel (IAA-CSIC/UPV-EHU), report on behalf of a larger collaboration:
=93We observed the field of GRB 140428A (Kocevski et al., GCN 16177; Page= =20 et al., GCN 16178) with the 1.5m OSN telescope at Observatorio de Sierra Nevada. Three 300s images were acquired in the I-band starting on Apr 29, 00:09:39 UT (i.e. ~1.5 hours burst). A preliminary reduction clearly show= s the optical afterglow reported by Perley (GCNC 16180) with a Vega magnitude of I~20.8. This magnitude must be taken with caution given the likely presence of the Lyman-alpha break in the I-band filter pass-band.=94
GCN Circular #16186
H. A. Krimm (GSFC/USRA), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), D. Kocevski (NASA/GSFC/ORAU) A. Y. Lien (NASA/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU), J. Tueller (GSFC), T. N. Ukwatta (MSU) (i.e. the Swift-BAT team):
Using the data set from T-240 to T+602 sec from the recent telemetry downlink, we report further analysis of BAT GRB 140428A (trigger #597519) (Kocevski et al., GCN Circ. 16177). The BAT ground-calculated position is RA, Dec = 194.365, 28.331 deg which is
```
  RA(J2000)  =  12h 57m 27.5s
  Dec(J2000) = +28d 19' 53.4"
```
with an uncertainty of 2.2 arcmin, (radius, sys+stat, 90% containment). The partial coding was 70%.
The mask-weighted light curve shows a multi-peaked structure starts at ~T-14 s and ends at ~T+6 s. The structure contains two main peaks at ~T-4 s and ~T+2 s. T90 (15-350 keV) is 17.42 +- 5.90 sec (estimated error including systematics).
The time-averaged spectrum from T-14.19 to T+5.82 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.54 +- 0.26. The fluence in the 15-150 keV band is 3.4 +- 0.6 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T+1.30 sec in the 15-150 keV band is 0.6 +- 0.2 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/597519/BA/
GCN Circular #16187
F. E. Marshall (NASA/GSFC) and D. Kocevski (NASA/GSFC/ORAU) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 140428A 104 s after the BAT trigger (Kocevski et al., GCN Circ. 16177). No optical afterglow consistent with the optical position (Perley, GCN_Circ. 16180) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial exposures are:
```
Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white              104          254          147         >21.2
v                 5454         5653          197         >20.3
b                 4838         5039          197         >21.4
u                  264          271            7         >19.5
uw1               5864         6030          197         >20.5
```
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.009 in the direction of the burst (Schlegel et al. 1998).
GCN Circular #16191
F. Knust, K. Varela, J. Greiner (MPE Garching), and D. A. Kann (TLS Tautenburg) report on behalf of the GROND team:
We observed the field of GRB 140428A (Swift trigger 597519; Kocevski et al., GCN #16177) 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 La Silla Observatory (Chile).
Observations started at 00:43 UT on 2014-04-29, 2 hours after the GRB trigger. They were performed at an average seeing of 1.4" and at an average airmass of 1.9.
We found a single point source within the 1.7" Swift-XRT error circle reported by Page et al. (GCN #16178) at
```
RA (J2000.0) = 12h 57m 28.39s
DEC (J2000.0) = + 28d 23' 06.4"
```
with an uncertainty of 0.5" in each coordinate.
This source is consistent with the one reported by Perley (GCN #16180).
Based on the first 1133 s of total exposures in g'r'i'z' and 1920 s in JHK, we estimate preliminary magnitudes (all in AB system) of
```
g' > 24.4 mag,
r' = 23.6 +/- 0.2 mag,
i' = 21.7 +/- 0.1 mag,
z' = 21.5 +/- 0.1 mag,
J > 19.7 mag,
H > 20.6 mag, and
K > 19.1mag.
```
From our data, fading can not be established. We note that our r'-band magnitude is similar to that reported by Perley (GCN #16180) at a mid-time of 7.5 hrs after the GRB.
The spectral energy distribution is best-fit by a straight power-law and a sharp cut-off below the i'-band which cannot be modelled with extinction alone. If this is the GRB afterglow, the cut-off corresponds to a photometric redshift of z = 4.8 +-0.3, consistent with the Keck spectroscopy as reported by Perley (GCN #16181).
Given magnitudes are calibrated against SDSS (griz) as well as 2MASS (JHK) field stars and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V) = 0.01 mag in the direction of the burst (Schlegel et al. 1998).
GCN Circular #16252
K. Varela, C. Delvaux, and J. Greiner (all MPE Garching) report on behalf of the GROND team:
We re-observed the field of GRB 140428A (Swift trigger 597519; Kocevski et al., GCN #16177) 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 La Silla Observatory (Chile).
A second epoch obtained on May 6th at 02:01 UT, about 7 days after the trigger, shows that the source reported by Knust et al. (GCN # 16191) has clearly faded. We find z' > 23.3, suggesting that the source has faded by at least 1.9 mag, and confirming that this was the afterglow of GRB 140428A.

Back to JG's homepage

Jochen Greiner, last update: 12-May-2014 [Disclaimer]