| Summary table |
|---|
| Variable |
Value |
Source |
| T0 |
6:46:21 UTC |
GCN_circulars,Swift Det |
| ra |
64.4516° |
Swift |
| decl |
-32.9522° |
Swift |
| pos_error |
1.81e-04° |
Swift |
| T90 |
11.2 s |
Swift |
| T90_start |
6:46:21 UTC |
Swift |
| fluence |
1.10e-06 erg/cm² |
Swift |
| T100 |
11.2 s |
|
| GBM_located |
False |
|
| mjd |
58233.2821875 |
GCN_circulars,Swift Det |
| IPN table |
|---|
| GRB_name |
GRB180425A |
| ra |
64.4708° |
| decl |
-32.9500° |
| pos_error |
5.00e-02° |
| Swift table |
|---|
| GRB_name |
GRB180425A |
| t_trigger |
6:46:21 UTC |
| ra |
64.4516° |
| decl |
-32.9522° |
| pos_error |
1.81e-04° |
| T90 |
11.2 s |
| fluence |
1.10e-06 erg/cm² |
| GCN 22672 table |
|---|
| GRB_name |
GRB180425A |
| GCN_number |
22672 |
| Detection_method |
Swift Det |
| t_trigger |
6:46:21 UTC |
| ra |
64.4690° |
| decl |
-32.9560° |
| Circular_text |
TITLE: GCN CIRCULAR
NUMBER: 22672
SUBJECT: GRB 180425A: Swift detection of a burst
DATE: 18/04/25 07:01:11 GMT
FROM: David Palmer at LANL
F. E. Marshall (NASA/GSFC), P. D'Avanzo (INAF-OAB),
P. A. Evans (U Leicester), H. A. Krimm (NSF/USRA),
A. Melandri (INAF-OAB), K. L. Page (U Leicester) and
D. M. Palmer (LANL) report on behalf of the Neil Gehrels Swift
Observatory Team:
At 06:46:21 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 180425A (trigger=828672). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 64.469, -32.956 which is
RA(J2000) = 04h 17m 53s
Dec(J2000) = -32d 57' 20"
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 15 sec. The peak count rate
was ~1800 counts/sec (15-350 keV), at ~2 sec after the trigger.
The XRT began observing the field at 06:47:40.0 UT, 78.2 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source with an enhanced position: RA, Dec 64.4517,
-32.9519 which is equivalent to:
RA(J2000) = 04h 17m 48.41s
Dec(J2000) = -32d 57' 06.9"
with an uncertainty of 2.2 arcseconds (radius, 90% containment). This
location is 54 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 (2.90 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 2
(+2.26/-2.02) x 10^21 cm^-2 (90% confidence).
The initial flux in the 2.5 s image was 5.37e-10 erg cm^-2 s^-1 (0.2-10
keV).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 87 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
0.03.
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 22673 table |
|---|
| GRB_name |
GRB180425A |
| GCN_number |
22673 |
| Detection_method |
Swift-XRT Det |
| ra |
64.4516° |
| decl |
-32.9522° |
| Circular_text |
TITLE: GCN CIRCULAR
NUMBER: 22673
SUBJECT: GRB 180425A: Enhanced Swift-XRT position
DATE: 18/04/25 09:07:46 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 1083 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 180425A, 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 = 64.45159, -32.95216 which is equivalent
to:
RA (J2000): 04h 17m 48.38s
Dec (J2000): -32d 57' 07.8"
with an uncertainty of 1.8 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 22674 table |
|---|
| GRB_name |
GRB180425A |
| GCN_number |
22674 |
| Detection_method |
Swift-UVOT Other |
| Circular_text |
TITLE: GCN CIRCULAR
NUMBER: 22674
SUBJECT: GRB 180425A: Swift/UVOT Upper Limits
DATE: 18/04/25 14:10:33 GMT
FROM: Sam Emery at MSSL-UCL
S.W.K. Emery (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 180425A
88 s after the BAT trigger (Marshall et al., GCN Circ. 22672).
No optical afterglow consistent with the XRT position
(Osborne et al., GCN Circ. 22673)
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 early exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
white 88 1201 353 >21.0
u 302 1152 285 >20.5
v 631 1250 78 >18.5
b 557 1176 58 >19.4
uvw1 680 1299 78 >19.0
uvm2 827 1275 58 >18.5
uvw2 606 1226 58 >19.0
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 22675 table |
|---|
| GRB_name |
GRB180425A |
| GCN_number |
22675 |
| Detection_method |
Swift-BAT Det |
| ra |
64.4500° |
| decl |
-32.9490° |
| Circular_text |
TITLE: GCN CIRCULAR
NUMBER: 22675
SUBJECT: GRB 180425A: Swift-BAT refined analysis
DATE: 18/04/25 14:53:09 GMT
FROM: Hans Krimm at NSF/NASA-GSFC
T. Sakamoto (AGU), 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), M. Stamatikos (OSU),
T. N. Ukwatta (LANL) (i.e. the Swift-BAT team):
Using the data set from T-240 to T+962 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 180425A (trigger #828672)
(Marshall, et al., GCN Circ. 22672). The BAT ground-calculated position is
RA, Dec = 64.450, -32.949 deg which is
RA(J2000) = 04h 17m 48.1s
Dec(J2000) = -32d 56' 58.1"
with an uncertainty of 1.5 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 27%.
The mask-weighted light curve shows a single triangular shaped peak beginning
at T-2 sec, peaking at T+3 sec and declining to background by T+14 sec.
T90 (15-350 keV) is 11.2 +- 2.6 sec (estimated error including systematics).
The time-averaged spectrum from T+0.06 to T+12.73 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.35 +- 0.13. The fluence in the 15-150 keV band is 1.1 +- 0.1 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+2.33 sec in the 15-150 keV band
is 2.2 +- 0.3 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/828672/BA/
|
| GCN 22676 table |
|---|
| GRB_name |
GRB180425A |
| GCN_number |
22676 |
| Detection_method |
Swift-XRT Other |
| Circular_text |
TITLE: GCN CIRCULAR
NUMBER: 22676
SUBJECT: GRB 180425A: Swift-XRT refined Analysis
DATE: 18/04/25 15:32:33 GMT
FROM: Phil Evans at U of Leicester
P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), A.
Tohuvavohu (PSU), S. J. LaPorte (PSU), J.A. Kennea (PSU), J.P. Osborne
(U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester)
and F.E. Marshall report on behalf of the Swift-XRT team:
We have analysed 6.7 ks of XRT data for GRB 180425A (Marshall et al.
GCN Circ. 22672), from 84 s to 23.0 ks after the BAT trigger. The data
comprise 132 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. 22673).
The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=1.20 (+0.11, -0.12). At T+446 s the decay
steepens to an alpha of 2.09 (+0.33, -0.28) before breaking again at
T+2630 s to a final decay with index alpha=0.34 (+/-0.30).
A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.02 (+0.15, -0.14). The
best-fitting absorption column is 8.0 (+3.8, -3.4) x 10^20 cm^-2, in
excess of the Galactic value of 2.9 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.98 (+0.19, -0.18)
and a best-fitting absorption column of 1.2 (+/-0.5) x 10^21 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum is 3.4 x 10^-11 (4.2 x 10^-11) erg cm^-2
count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 1.2 (+/-0.5) x 10^21 cm^-2
Galactic foreground: 2.9 x 10^20 cm^-2
Excess significance: 3.0 sigma
Photon index: 1.98 (+0.19, -0.18)
If the light curve continues to decay with a power-law decay index of
0.34, the count rate at T+24 hours will be 0.016 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.3 x
10^-13 (6.6 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/00828672.
This circular is an official product of the Swift-XRT team.
|