GRB 150831B
GCN Circular 18227
Subject
GRB 150831B: Swift/UVOT Upper Limits
Date
2015-09-01T20:59:18Z (11 years ago)
From
Frank Marshall at GSFC <femarsha@khamseen.gsfc.nasa.gov>
F. E. Marshall (NASA/GSFC) reports on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 150831B
3089 s after the BAT trigger (Marshall et al., GCN Circ. 18215).
No optical afterglow consistent with the refined XRT position
(D'Avanzo et al., GCN Circ. 18222) is detected in the initial UVOT
exposures. We note that this is a very crowded field.
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 3089 3239 147 >20.6
v 3246 3445 197 >18.2
b 8838 9745 885 >20.3
u 3861 5659 158 >19.4
w1 3656 3856 197 >19.2
m2 3451 3651 197 >20.2
The magnitudes in the table are not corrected for the large
Galactic extinction in the direction of the burst
(Schlegel et al. 1998).
GCN Circular 18223
Subject
GRB 150831B: Swift-BAT refined analysis
Date
2015-09-01T13:21:00Z (11 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC),
H. A. Krimm (GSFC/USRA), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC),
F. E. Marshall (GSFC), D. M. Palmer (LANL), 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 150831B (trigger #653978)
(Marshall et al., GCN Circ. 18215). The BAT ground-calculated position is
RA, Dec = 271.030, -27.243 deg, which is
RA(J2000) = 18h 04m 07.2s
Dec(J2000) = -27d 14' 34.4"
with an uncertainty of 2.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 7%.
The mask-weighted light curve shows two peaks starting at ~T-0.5 sec,
peaking at ~T+1 sec, and ending at ~T+8 sec. T90 (15-350 keV)
is 6.2 +- 1.0 sec (estimated error including systematics).
The time-averaged spectrum from T-0.58 to T+6.84 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.87 +- 0.19. The fluence in the 15-150 keV band is 1.4 +- 0.2 x 10^-06 erg/cm2.
The 1-sec peak photon flux measured from T-0.15 sec in the 15-150 keV band
is 6.1 +- 1.1 ph/cm2/sec. All the quoted errors are at the 90% confidence
level.
In the BAT energy band, the hardness ratio vs T90 is typical of a GRB origin,
but not inconsistant with a galactic origin. The T90 is too long for a
magnetar origin. We also note that the fading in the X-ray band is tyical
for a GRB (D'Avanzo, GCN 18222).
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/653978/BA/
GCN Circular 18222
Subject
GRB 150831B: Swift-XRT refined Analysis
Date
2015-09-01T10:58:46Z (11 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
P. D'Avanzo (INAF-OAB), T.G.R. Roegiers (PSU), L.M. McCauley (PSU),
J.A. Kennea (PSU), C. Pagani (U. Leicester), A.P. Beardmore (U.
Leicester), V. D'Elia (ASDC), A. D'ai (INAF-IASFPA) and F. E. Marshall
(NASA/GSFC) report on behalf of the Swift-XRT team:
We have analysed 3.8 ks of XRT data for GRB 150831B (Marshall et al.
GCN Circ. 18215), from 3.1 ks to 28.3 ks after the BAT trigger. The
data are entirely in Photon Counting (PC) mode. The refined XRT
position is RA, Dec = 271.0396, -27.2590 which is equivalent to:
RA (J2000): 18 04 09.49
Dec(J2000): -27 15 32.4
with an uncertainty of 3.7 arcsec (radius, 90% confidence).
The light curve can be modelled with a power-law decay with a decay
index of alpha=1.32 (+0.26, -0.21).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.5 (+0.7, -0.6). The
best-fitting absorption column is 1.7 (+1.0, -0.7) x 10^22 cm^-2, in
excess of the Galactic value of 5.1 x 10^21 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum is 4.4 x 10^-11 (1.6 x 10^-10) erg
cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 1.7 (+1.0, -0.7) x 10^22 cm^-2
Galactic foreground: 5.1 x 10^21 cm^-2
Excess significance: 2.9 sigma
Photon index: 2.5 (+0.7, -0.6)
If the light curve continues to decay with a power-law decay index of
1.32, the count rate at T+24 hours will be 1.7 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 7.6 x
10^-14 (2.7 x 10^-13) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00653978.
This circular is an official product of the Swift-XRT team.
GCN Circular 18221
Subject
GRB 150831B: MASTER-IAC early optical observations
Date
2015-09-01T07:28:29Z (11 years ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres
The Instituto de Astrofisica de Canarias
V. Lipunov, E. Gorbovskoy, N.Tyurina, V.Kornilov,
P.Balanutsa, A.Kuznetsov, D.Kuvshinov, E.Popova
Lomonosov Moscow State University, Sternberg Astronomical Institute
K.Ivanov, O.Gres, N.M.Budnev, S.Yazev,
Irkutsk State University
D.Buckley, S. Potter, A.Kniazev, M.Kotze
South African Astronomical Observatory
A. Tlatov, A.V. Parhomenko, D. Dormidontov, V.Sennik
Kislovodsk Solar Station of the Pulkovo Observatory
V.Yurkov, Yu.Sergienko, D.Varda, E.Sinyakov, A.Gabovich
Blagoveschensk Educational State University, Blagoveschensk
V.Krushinski, I.Zalozhnih
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;
http://161.72.133.2/)
located in IAC was pointed to the GRB150831B 24 sec after notice time
and 56 sec after trigger time at 2015-08-31 22:20:23 UT (Swift: Marshall
et al., GCN 18215; and Fermi: Veres and C. Meegan, GCN 18220) .
On our first (10s exposure) set (two polarisations) we did not found
optical transient
within SWIFT error-box (Marshall et al., GCN 18215; Evans et al., GCN
18217) brighter then 16.3. The observations were stoped by beautifull
Canarian sun rise ( see
http://observ.pereplet.ru/images/webcam01spt2015.jpg ) at 2015-09-01
06:37:36 UT.
Pro.type Date time + - Exp.time Limit Filt. Tube.
Start
Alert 2015-08-31 22:20:23 10 16.3 P WEST
Alert 2015-08-31 22:20:23 10 15.6 P EAST
Alert 2015-08-31 22:21:07 20 16.4 P WEST
Alert 2015-08-31 22:21:07 20 15.9 P EAST
Alert 2015-08-31 22:21:37 30 16.8 P WEST
Alert 2015-08-31 22:21:37 30 16.2 P EAST
Alert 2015-08-31 22:22:18 30 0.0* P WEST
Alert 2015-08-31 22:22:18 30 16.2 P EAST
Alert 2015-08-31 22:22:57 40 16.9 P WEST
Alert 2015-08-31 22:22:57 40 16.3 P EAST
Alert 2015-08-31 22:23:47 50 17.0 P WEST
Alert 2015-08-31 22:23:47 50 16.5 P EAST
Alert 2015-08-31 22:24:47 60 17.0 P WEST
Alert 2015-08-31 22:24:47 60 16.5 P EAST
Alert 2015-08-31 22:25:56 80 17.2 P WEST
Alert 2015-08-31 22:25:56 80 16.6 P EAST
Alert 2015-08-31 22:27:26 100 17.2 P WEST
Alert 2015-08-31 22:27:26 100 16.6 P EAST
Alert 2015-08-31 22:29:17 120 17.3 P WEST
Alert 2015-08-31 22:29:17 120 16.6 P EAST
Alert 2015-08-31 22:31:27 140 17.3 P WEST
Alert 2015-08-31 22:31:27 140 16.7 P EAST
Alert 2015-08-31 22:33:57 170 17.3 P WEST
Alert 2015-08-31 22:33:57 170 16.7 P EAST
* - no stars
Our server hase a lot of job in Milky Way star dust now.
This message may be cited.
GCN Circular 18220
Subject
GRB 150831B: Fermi GBM detection
Date
2015-09-01T04:53:10Z (11 years ago)
From
Peter Veres at ELTE,Budapest <veresp@gmail.com>
P. Veres (UAH) and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:
"At 22:19:27.158 UT on 31 August 2015, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 150831B (trigger 462752371 / 150831930)
which was also detected by the Swift/BAT and XRT
(Marshall et al. 2015, GCN 18215 and Evans et al. 2015, GCN 18217)
The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight at the GBM trigger time is 96
degrees.
The GBM light curve has a duration (T90) of about 13.8 s (50-300 keV).
The time-averaged spectrum from T0-4.0 s to T0+6.3 s is
adequately fit by a power law function with an exponential
high-energy cutoff. The power law index is -0.93 +/- 0.12 and
the cutoff energy, parameterized as Epeak, is 82.3 +/- 5.5 keV.
The event fluence (10-1000 keV) in this time interval is
(2.51 +/- 0.11)E-6 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+0.1 s in the 10-1000 keV band
is 9.1 +/- 0.4 ph/s/cm^2.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."
GCN Circular 18217
Subject
GRB 150831B: Swift-XRT observations
Date
2015-08-31T23:37:00Z (11 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
P.A. Evans (U. Leicester), J.P. Osborne (U. Leicester), D.N. Burrows
(PSU), J.A. Kennea (PSU), S. Campana (INAF-OAB) and G. Cusumano
(INAF-IASF PA) report on behalf of the Swift-XRT team:
The XRT began observing the field of GRB 150831B at 23:10:52.8 UT,
3085.5 seconds after the BAT trigger. Using promptly downlinked data we
find an uncatalogued X-ray source located at RA, Dec 271.03936,
-27.25933 which is equivalent to:
RA(J2000) = 18h 04m 09.45s
Dec(J2000) = -27d 15' 33.6"
with an uncertainty of 3.9 arcseconds (radius, 90% containment). This
location is 64 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 5.13
x 10^21 cm^-2 (Willingale et al. 2013).
GCN Circular 18215
Subject
GRB 150831B: Swift detection of a probable burst
Date
2015-08-31T22:34:04Z (11 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@milkyway.gsfc.nasa.gov>
F. E. Marshall (NASA/GSFC), S. D. Barthelmy (GSFC),
A. Y. Lien (GSFC/UMBC), D. M. Palmer (LANL) and T. Sakamoto (AGU)
report on behalf of the Swift Team:
At 22:19:27 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 150831B (trigger=653978). Swift did not slew due to observing
constraint. The BAT on-board calculated location is
RA, Dec 271.021, -27.252, which is
RA(J2000) = 18h 04m 05s
Dec(J2000) = -27d 15' 07"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve shows a couple of overlapping peaks
structure with a total duration of about 3 sec. The peak count rate
was ~2000 counts/sec (15-350 keV), at ~0 sec after the trigger.
Due to an observing constraint, Swift will not slew until T0+49.6
minutes. There will be no XRT or UVOT data until this time.
We note that this source is in the projected direction of the
Galactic bulge (lon,lat = 3.51,-2.66) and for that reason there
is a strong possibility that this is a Galactic source. However, its
light curve and the presence of flux above 100 keV are more consistent
with a cosmological GRB.
Determination of the nature of this event will require XRT observations
and the full downlinked dataset.
Burst Advocate for this burst is F. E. Marshall (marshall AT milkyway.gsfc.nasa.gov).
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.)