GRB 170526A
GCN Circular 21149
Subject
GRB 170526A: Swift detection of a burst
Date
2017-05-26T13:51:22Z (8 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@milkyway.gsfc.nasa.gov>
B. Sbarufatti (INAF-OAB/PSU), S. D. Barthelmy (GSFC),
S. B. Cenko (GSFC), C. Gronwall (PSU), J. A. Kennea (PSU),
N. P. M. Kuin (UCL-MSSL), A. Y. Lien (GSFC/UMBC), D. M. Palmer (LANL)
and M. H. Siegel (PSU) report on behalf of the Swift Team:
At 13:35:08 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 170526A (trigger=754549). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 4.708, +1.240 which is
RA(J2000) = 00h 18m 50s
Dec(J2000) = +01d 14' 22"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve shows a single peak
with a duration of about 8 sec. The peak count rate
was ~1200 counts/sec (15-350 keV), at ~5 sec after the trigger.
The XRT began observing the field at 13:37:13.2 UT, 124.3 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 4.7074, 1.2773 which is
equivalent to:
RA(J2000) = 00h 18m 49.79s
Dec(J2000) = +01d 16' 38.1"
with an uncertainty of 4.9 arcseconds (radius, 90% containment). This
location is 134 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 3.16
x 10^20 cm^-2 (Willingale et al. 2013).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 127 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 0.03.
Burst Advocate for this burst is B. Sbarufatti (boris.sbarufatti AT brera.inaf.it).
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/too.html.)
GCN Circular 21151
Subject
GRB 170526A: Enhanced Swift-XRT position
Date
2017-05-26T16:27:05Z (8 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester)
report on behalf of the Swift-XRT team.
Using 350 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 170526A, 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 = 4.70720, +1.27700 which is equivalent
to:
RA (J2000): 00h 18m 49.73s
Dec (J2000): +01d 16' 37.2"
with an uncertainty of 2.1 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 21154
Subject
GRB 170526A: Swift-XRT refined Analysis
Date
2017-05-27T04:29:59Z (8 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB),
A. Cholden-Brown (PSU), S. J. LaPorte (PSU), J.A. Kennea (PSU), S.L.
Gibson (U. Leicester), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester) and B. Sbarufatti report on behalf of the Swift-XRT team:
We have analysed 6.5 ks of XRT data for GRB 170526A (Sbarufatti et al.
GCN Circ. 21149), from 132 s to 46.4 ks after the BAT trigger. The
data are entirely in Photon Counting (PC) mode. The enhanced XRT
position for this burst was given by Goad et al. (GCN Circ. 21151).
The light curve can be modelled with a power-law decay with a decay
index of alpha=0.87 (+0.14, -0.12).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.8 (+/-0.5). The
best-fitting absorption column is 1.9 (+2.3, -1.6) x 10^21 cm^-2,
consistent with the Galactic value of 3.2 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 4.0 x 10^-11 (5.0 x
10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 1.9 (+2.3, -1.6) x 10^21 cm^-2
Galactic foreground: 3.2 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index: 1.8 (+/-0.5)
If the light curve continues to decay with a power-law decay index of
0.87, the count rate at T+24 hours will be 1.0 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.0 x
10^-14 (5.1 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/00754549.
This circular is an official product of the Swift-XRT team.
GCN Circular 21155
Subject
GRB 170526A: Swift/UVOT Upper Limits
Date
2017-05-27T13:28:48Z (8 years ago)
From
Samantha Oates at MSSL <sro@mssl.ucl.ac.uk>
S. R. Oates (Uni. of Warwick) and B. Sbarufatti (INAF-OAB/PSU)
report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 170526A
128 s after the BAT trigger (Sbarufatti et al., GCN Circ. 21149).
No optical afterglow consistent with the XRT position
(Goad et al. GCN Circ. 21151) 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 subsequent exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
white_FC 128 278 147 >19.9
white 128 4127 344 >20.4
v 4338 4537 197 >18.5
b 3722 5197 235 >19.7
u 286 5152 404 >19.4
w1 4748 4947 196 >19.1
m2 4542 4742 197 >19.3
w2 4133 4333 197 >19.5
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 21156
Subject
GRB 170526A, Swift-BAT refined analysis
Date
2017-05-27T18:52:59Z (8 years ago)
From
Amy Lien at GSFC <amy.y.lien@nasa.gov>
C. B. Markwardt (GSFC), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), H. A. Krimm (NSF/USRA),
A. Y. Lien (GSFC/UMBC), D. M. Palmer (LANL),
T. Sakamoto (AGU), B. Sbarufatti (INAF-OAB/PSU),
M. Stamatikos (OSU), T. N. Ukwatta (LANL)
(i.e. the Swift-BAT team):
Using the data set from T-327 to T+1275 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 170526A (trigger #754549)
(Sbarufatti et al., GCN Circ. 21149). The BAT ground-calculated position is
RA, Dec = 4.723, 1.277 deg which is
RA(J2000) = 00h 18m 53.6s
Dec(J2000) = +01d 16' 35.7"
with an uncertainty of 2.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 94%.
The mask-weighted light curve shows a weak pulse structure that starts
at ~T0, peaks at ~ T+1 s, and ends at ~ T+10 s. T90 (15-350 keV) is 7.9 +- 1.6 sec
(estimated error including systematics).
The time-averaged spectrum from T+1.1 to T+10.0 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.25 +- 0.42. The fluence in the 15-150 keV band is 1.6 +- 0.4 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+1.10 sec in the 15-150 keV band
is 0.3 +- 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/754549/BA/
GCN Circular 21213
Subject
GRB 170526A: 15 GHz upper limits from AMI
Date
2017-06-07T22:39:09Z (8 years ago)
From
Kunal Mooley at Oxford U <kunal.mooley@physics.ox.ac.uk>
K. P. Mooley (Hintze Fellow, Oxford), T. D. Staley, R. P. Fender
(Oxford), G. E. Anderson (Curtin), T. Cantwell (Manchester), D.
Titterington, S. H. Carey, J. Hickish, Y. C. Perrott, N. Razavi-Ghods,
P. Scott (Cambridge), K. Grainge, A. Scaife (Manchester)
The AMI Large Array robotically triggered on the Swift alert for GRB
170526A (Sbarufatti et al., GCN 21149) as part of the 4pisky program,
and subsequent follow up observations were obtained up to 10 days
post-burst. Our observations at 15 GHz on 2016 May 27.16, May 30.29, May
31.33 and Jun 03.28 (UT) do not reveal any radio source at the XRT
location (Goad et al., GCN 21151), with 3sigma upper limits of 312 uJy,
117 uJy, 96 uJy and 105 uJy respectively.
We thank the AMI staff for scheduling these observations. The AMI-GRB
database is a log of all GRB follow up observations with the AMI, and is
available at http://4pisky.org/ami-grb/.