GRB 180331B
GCN Circular 22573
Subject
GRB 180331B: Swift detection of a burst
Date
2018-03-31T15:58:51Z (7 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@milkyway.gsfc.nasa.gov>
A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (GSFC), A. Deich (PSU),
J.D. Gropp (PSU), J. A. Kennea (PSU), K. L. Page (U Leicester) and
A. Tohuvavohu (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:
At 15:38:39 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 180331B (trigger=820513). Swift executed a delayed slewed
due to an observing constraint. The BAT on-board calculated location is
RA, Dec 196.820, +61.725, which is
RA(J2000) = 13h 07m 17s
Dec(J2000) = +61d 43' 30"
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 ~1500 counts/sec (15-350 keV), at ~2 sec after the trigger.
The XRT began observing the field at 15:49:43.0 UT, 663.7 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 196.7829, 61.7271 which
is equivalent to:
RA(J2000) = 13h 07m 07.91s
Dec(J2000) = +61d 43' 37.5"
with an uncertainty of 2.4 arcseconds (radius, 90% containment). This
location is 63 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. No
spectrum from the promptly downlinked event data is yet available to
determine the column density.
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 667 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
0.01.
Burst Advocate for this burst is A. Y. Lien (amy.y.lien AT 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 Circular 22575
Subject
GRB 180331B: Enhanced Swift-XRT position
Date
2018-03-31T19:14:44Z (7 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 1501 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 180331B, 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 = 196.78337, +61.72625 which is equivalent
to:
RA (J2000): 13h 07m 8.01s
Dec (J2000): +61d 43' 34.5"
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 Circular 22576
Subject
GRB 180331B: Swift-BAT refined analysis
Date
2018-03-31T23:43:44Z (7 years ago)
From
Amy Lien at GSFC <amy.y.lien@nasa.gov>
M. Stamatikos (OSU), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), H. A. Krimm (NSF/USRA),
A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), T. Sakamoto (AGU),
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 180331B (trigger #820513)
(Lien et al., GCN Circ. 22573). The BAT ground-calculated position is
RA, Dec = 196.781, 61.735 deg which is
RA(J2000) = 13h 07m 07.6s
Dec(J2000) = +61d 44' 05.9"
with an uncertainty of 2.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 30%.
The mask-weighted light curve shows a double-peaked structure that starts
at ~T-20 s and ends at ~T+140 s. The two peaks occur at ~T-20 s and ~T+1 s,
respectively. T90 (15-350 keV) is 147.0 +- 33.1 sec (estimated error including systematics).
The time-averaged spectrum from T-22.03 to T+142.97 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
2.48 +- 0.22. The fluence in the 15-150 keV band is 1.9 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+0.97 sec in the 15-150 keV band
is 2.8 +- 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/820513/BA/
GCN Circular 22577
Subject
GRB 180331B: AbAO optical observations
Date
2018-04-01T03:30:42Z (7 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
A. Volnova (IKI), A. Pozanenko (IKI), E. Mazaeva (IKI), R. Inasaridze
(AbAO), V. Ayvazian (AbAO), O. Kvaratskhelia (AbAO), G. Kapanadze
(AbAO), I. Molotov (KIAM), report on behalf of larger GRB follow-up
collaboration:
We observed the field of GRB 180331B (Lien et al., GCN 22573) with
AS-32 (0.7m) telescope of Abastumani Observatory starting on Mar. 31
(UT) 17:49:41. We do not detect any object within enhanced XRT
position (Goad et al., GCN 22575). Preliminary photometry of the field
is following.
Date UT start t-T0 Filter Exp. OT Err. UL
(mid, days) (s)
2018-03-31 17:49:41 0.11370 CR 38*60 n/d n/d 22.3
The photometry is based on nearby USNO-B1.0 stars (R2 magnitude).
GCN Circular 22578
Subject
GRB 180331B: Swift-XRT refined Analysis
Date
2018-04-01T04:53:44Z (7 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), J.A. Kennea (PSU), B.
Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), P.A. Evans (U.
Leicester), S.L. Gibson (U. Leicester), J.P. Osborne (U. Leicester), A.
D'Ai (INAF-IASFPA) and report on behalf of the Swift-XRT team: report
on behalf of the Swift-XRT team:
We have analysed 6.6 ks of XRT data for GRB 180331B, from 671 s to 25.2
ks after the BAT trigger. The data are entirely in Photon Counting
(PC) mode.
The light curve can be modelled with a power-law decay with a decay
index of alpha=0.30 (+/-0.04).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.80 (+0.13, -0.12). The
best-fitting absorption column is 8.7 (+3.5, -3.2) x 10^20 cm^-2, in
excess of the Galactic value of 1.6 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 3.7 x 10^-11 (4.2 x 10^-11) erg
cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 8.7 (+3.5, -3.2) x 10^20 cm^-2
Galactic foreground: 1.6 x 10^20 cm^-2
Excess significance: 3.7 sigma
Photon index: 1.80 (+0.13, -0.12)
If the light curve continues to decay with a power-law decay index of
0.30, the count rate at T+24 hours will be 0.082 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.0 x
10^-12 (3.5 x 10^-12) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00820513.
This circular is an official product of the Swift-XRT team.
GCN Circular 22579
Subject
GRB 180331B: Swift/UVOT Upper Limits
Date
2018-04-01T09:38:55Z (7 years ago)
From
Paul Kuin at MSSL <npkuin@gmail.com>
N. P. M. Kuin (UCL-MSSL) and A. Y. Lien (GSFC/UMBC)
report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB
180331B 668 s after the BAT trigger (Lien et al., GCN Circ. 22573).
No optical afterglow consistent with the XRT position Goad er al.,
(GCN Circ. 22575) is detected in the initial UVOT exposures,
consistent with the report of Volnova et al. (GCN Circ. 22577).
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 668 818 147 >21.2
white 668 2066 412 >21.8
v 1056 2115 136 >19.2
b 1156 2041 117 >20.3
u 1130 2016 117 >20.3
w1 849 1992 78 >20.2
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.01 in the direction of the burst
(Schlegel et al. 1998).