| Summary table |
|---|
| Variable |
Value |
Source |
| T0 |
3:12:04 UTC |
GCN_circulars,Swift Det |
| ra |
169.6365° |
Swift |
| decl |
-48.3445° |
Swift |
| pos_error |
1.94e-04° |
Swift |
| T90 |
13.7 s |
Swift |
| T90_start |
3:12:04 UTC |
Swift |
| fluence |
2.60e-07 erg/cm² |
Swift |
| T100 |
13.7 s |
|
| GBM_located |
False |
|
| mjd |
58348.13337962963 |
GCN_circulars,Swift Det |
| IPN table |
|---|
| GRB_name |
GRB180818A |
| ra |
169.6125° |
| decl |
-48.3500° |
| pos_error |
5.00e-02° |
| Swift table |
|---|
| GRB_name |
GRB180818A |
| t_trigger |
3:12:04 UTC |
| ra |
169.6365° |
| decl |
-48.3445° |
| pos_error |
1.94e-04° |
| T90 |
13.7 s |
| fluence |
2.60e-07 erg/cm² |
| GCN 23146 table |
|---|
| GRB_name |
GRB180818A |
| GCN_number |
23146 |
| Detection_method |
Swift Det |
| t_trigger |
3:12:04 UTC |
| ra |
169.6110° |
| decl |
-48.3440° |
| Circular_text |
TITLE: GCN CIRCULAR
NUMBER: 23146
SUBJECT: GRB 180818A: Swift detection of a burst
DATE: 18/08/18 03:25:43 GMT
FROM: David Palmer at LANL
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),
D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the
Neil Gehrels Swift Observatory Team:
At 03:12:04 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 180818A (trigger=853824). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 169.611, -48.344 which is
RA(J2000) = 11h 18m 27s
Dec(J2000) = -48d 20' 39"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a single-peaked
structure with a duration of about 10 sec. The peak count rate
was ~800 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 03:13:18.0 UT, 74.0 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source with an enhanced position: RA, Dec
169.6364, -48.3444 which is equivalent to:
RA(J2000) = 11h 18m 32.73s
Dec(J2000) = -48d 20' 39.7"
with an uncertainty of 2.4 arcseconds (radius, 90% containment). This
location is 60 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 (1.14 x
10^21 cm^-2, Willingale et al. 2013), with an excess column of 8.5
(+7.18/-5.58) x 10^21 cm^-2 (90% confidence).
The initial flux in the 2.5 s image was 1.28e-09 erg cm^-2 s^-1 (0.2-10
keV).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 82 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 100% 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
0.11.
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.)
|
| GCN 23147 table |
|---|
| GRB_name |
GRB180818A |
| GCN_number |
23147 |
| Detection_method |
Swift-XRT Det |
| ra |
169.6368° |
| decl |
-48.3444° |
| Circular_text |
TITLE: GCN CIRCULAR
NUMBER: 23147
SUBJECT: GRB 180818A: Enhanced Swift-XRT position
DATE: 18/08/18 05:32:00 GMT
FROM: Phil Evans at U of Leicester
J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester)
report on behalf of the Swift-XRT team.
Using 1503 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 180818A, 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 = 169.63679, -48.34440 which is equivalent
to:
RA (J2000): 11h 18m 32.83s
Dec (J2000): -48d 20' 39.9"
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 23148 table |
|---|
| GRB_name |
GRB180818A |
| GCN_number |
23148 |
| Detection_method |
Swift-XRT Other |
| Circular_text |
TITLE: GCN CIRCULAR
NUMBER: 23148
SUBJECT: GRB 180818A: Swift-XRT refined Analysis
DATE: 18/08/18 09:38:04 GMT
FROM: Phil Evans at U of Leicester
V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), J.A. Kennea (PSU), B.
Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), K.L. Page (U.
Leicester), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester),
A. Melandri (INAF-OAB) and F.E. Marshall report on behalf of the
Swift-XRT team:
We have analysed 6.9 ks of XRT data for GRB 180818A (Marshall et al.
GCN Circ. 23146), from 80 s to 17.2 ks after the BAT trigger. The data
comprise 587 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Osborne et al. (GCN Circ. 23147).
The light curve can be modelled with an initial power-law decay with an
index of alpha=6.0 (+0.8, -0.6), followed by a break at T+172 s to an
alpha of 0.63 (+/-0.10).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.8 (+0.5, -0.4). The
best-fitting absorption column is 8.9 (+3.1, -2.6) x 10^21 cm^-2, in
excess of the Galactic value of 1.1 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 3.2 x 10^-11 (1.2 x 10^-10) erg
cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 8.9 (+3.1, -2.6) x 10^21 cm^-2
Galactic foreground: 1.1 x 10^21 cm^-2
Excess significance: 4.9 sigma
Photon index: 2.8 (+0.5, -0.4)
If the light curve continues to decay with a power-law decay index of
0.63, the count rate at T+24 hours will be 4.5 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.4 x
10^-13 (5.5 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/00853824.
This circular is an official product of the Swift-XRT team.
|
| GCN 23150 table |
|---|
| GRB_name |
GRB180818A |
| GCN_number |
23150 |
| Detection_method |
Swift-UVOT Other |
| Circular_text |
TITLE: GCN CIRCULAR
NUMBER: 23150
SUBJECT: GRB 180818A: Swift/UVOT Upper Limits
DATE: 18/08/18 14:15:56 GMT
FROM: Paul Kuin at MSSL
N. P. M. Kuin (UCL-MSSL) and F. E. Marshall (NASA/GSFC)
report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 180818A
83 s after the BAT trigger (Marshall et al., GCN Circ. 23146). No
optical afterglow consistent with the XRT position (Osborne et al. GCN
Circ. 23147) 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 83 232 147 >20.7
u_FC 241 490 246 >20.1
white 83 7151 785 >21.9
v 570 11683 1198 >19.8
b 496 6946 510 >20.8
u 241 17153 1326 >20.9
w1 621 13097 985 >20.1
m2 596 12588 1199 >20.5
w2 546 7357 510 >20.7
The magnitudes in the table are not corrected for the Galactic extinction
due to the
reddening of E(B-V) = 0.11 in the direction of the burst (Schlegel et al.
1998).
|
| GCN 23154 table |
|---|
| GRB_name |
GRB180818A |
| GCN_number |
23154 |
| Detection_method |
Swift-BAT Det |
| ra |
169.6980° |
| decl |
-48.3440° |
| Circular_text |
TITLE: GCN CIRCULAR
NUMBER: 23154
SUBJECT: GRB 180818A: Swift-BAT refined analysis
DATE: 18/08/19 01:00:13 GMT
FROM: Amy Lien at GSFC
S. D. Barthelmy (GSFC), J. R. Cummings (CPI),
H. A. Krimm (NSF/USRA), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), F. E. Marshall (NASA/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 180818A (trigger #853824)
(Marshall et al., GCN Circ. 23146). The BAT ground-calculated position is
RA, Dec = 169.698, -48.344 deg which is
RA(J2000) = 11h 18m 47.5s
Dec(J2000) = -48d 20' 37.9"
with an uncertainty of 2.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 78%.
The mask-weighted light curve shows a single-pulsed structure that starts
at ~T-2 s, peaks at ~T+2 s, and ends at ~T+14 s. T90 (15-350 keV) is
13.7 +- 4.1 sec (estimated error including systematics).
The time-averaged spectrum from T-2.14 to T+14.10 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
2.15 +- 0.36. The fluence in the 15-150 keV band is 2.6 +- 0.6 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+1.64 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/853824/BA/
|