GRB 180411A

Z. Liu (NAOC/U. Leicester), A. P. Beardmore (U Leicester),
A. A. Breeveld (UCL-MSSL), A. Deich (PSU), J.D. Gropp (PSU),
J. A. Kennea (PSU), A. Y. Lien (GSFC/UMBC),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester) and
A. Tohuvavohu (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 12:27:43 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 180411A (trigger=824451).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 356.829, +66.791 which is 
   RA(J2000) = 23h 47m 19s
   Dec(J2000) = +66d 47' 26"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multi-peaked
structure with a duration of about 100 sec.  The peak count rate
was ~8000 counts/sec (15-350 keV), at ~53 sec after the trigger. 

The XRT began observing the field at 12:28:50.4 UT, 66.7 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source located at RA, Dec 356.85453,
66.77831 which is equivalent to:
   RA(J2000)  = 23h 47m 25.09s
   Dec(J2000) = +66d 46' 41.9"
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This
location is 58 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 (8.31 x
10^21 cm^-2, Willingale et al. 2013), with an excess column of 1.2
(+0.97/-0.75) x 10^22 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 1.35e-08 erg cm^-2 s^-1 (0.2-10
keV). 

There are no UVOT data available at the present time. 

Burst Advocate for this burst is Z. Liu (zl182 AT leicester.ac.uk). 
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.)

S.L. Gibson (U. Leicester), A. D'Ai (INAF-IASFPA), A. Melandri
(INAF-OAB), P. D'Avanzo (INAF-OAB), B. Sbarufatti (INAF-OAB/PSU), D.N.
Burrows (PSU), A. Tohuvavohu (PSU), J.P. Osborne (U. Leicester) and Z.
Liu report on behalf of the Swift-XRT team:

We have analysed 9.3 ks of XRT data for GRB 180411A (Liu et al. GCN
Circ. 22630
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 ), from 72 s to 29.8 ks after the  BAT trigger. The data
comprise 200 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The refined XRT position is RA, Dec =
356.8540, +66.7785 which is equivalent to:

RA (J2000): 23 47 24.97
Dec(J2000): +66 46 42.5

with an uncertainty of 3.5 arcsec (radius, 90% confidence).

The late-time light curve (from T0+4.4 ks) can be modelled with a
power-law decay with a decay index of alpha=1.09 (+/-0.07).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.68 (+/-0.10). The
best-fitting absorption column is  1.54 (+0.16, -0.15) x 10^22 cm^-2,
in excess of the Galactic value of 8.3 x 10^21 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 2.01 (+/-0.16) and a
best-fitting absorption column of 1.91 (+0.25, -0.23) x 10^22 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 5.9 x 10^-11 (1.3 x 10^-10) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.91 (+0.25, -0.23) x 10^22 cm^-2
Galactic foreground: 8.3 x 10^21 cm^-2
Excess significance: 7.7 sigma
Photon index:	     2.01 (+/-0.16)

If the light curve continues to decay with a power-law decay index of
1.09, the count rate at T+24 hours will be 0.032 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.9 x
10^-12 (4.1 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/00824451.

This circular is an official product of the Swift-XRT team.

C. B. Markwardt (GSFC), S. D. Barthelmy (GSFC), J. R. Cummings (CPI),
H. A. Krimm (NSF/USRA), A. Y. Lien (GSFC/UMBC), Z. Liu (NAOC/U. Leicester),
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-60 to T+243 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 180411A (trigger #824451)
(Z. Liu, et al., GCN Circ. 22630
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 ).  The BAT ground-calculated position is
RA, Dec = 356.840, 66.790 deg, which is 
   RA(J2000)  =  23h 47m 21.6s 
   Dec(J2000) = +66d 47' 25.2" 
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 97%.
 
The mask-weighted light curve show two major episodes of overlapping peaks
with the first starting at ~T-15 sec, peaking at ~T+5 sec, and second episode
starting at ~T+42 sec, peaking at ~T+52 sec, and returning to zero ~T+180 sec.
T90 (15-350 keV) is 77.5 +- 0.9 sec (estimated error including systematics).
 
The time-averaged spectrum from T-7.02 to T+92.38 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.46 +- 0.03.  The fluence in the 15-150 keV band is 1.2 +- 0.0 x 10^-05 erg/cm2.
The 1-sec peak photon flux measured from T+51.74 sec in the 15-150 keV band
is 6.1 +- 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/824451/BA/

S. Poolakkil (UAH), A. von Kienlin (MPE) and C. Meegan (UAH) report on
behalf of the Fermi GBM Team:

"At 12:27:40.97 UT on 11 April 2018, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 180411A (trigger 545142465 / 180411519),
which was also detected by the Swift/BAT (Liu et al. 2018, GCN 22630
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 ).
The GBM on-ground location is consistent with the Swift position.

The angle from the Fermi LAT boresight
at the GBM trigger time is 150 degrees.

The GBM light curve shows two peaks
with a duration (T90) of about 77.6 s (50-300 keV).
The time-averaged spectrum from T0-3.1 s to T0+79.8 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -1.18 +/- 0.05 and
the cutoff energy, parameterized as Epeak, is 358 +/- 30 keV.

The event fluence (10-1000 keV) in this time interval is
(3.276 +/- 0.085)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+54.27 s in the 10-1000 keV band
is 10.5 +/- 0.79 ph/s/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."

B. Stecklum, S. Klose, and C. Hoegner (Thueringer Landessternwarte 
Tautenburg) report:

We imaged the field of GRB 180411A (Liu et al., GCN 22630
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 ) in the Rc band 
using the Tautenburg Schmidt telescope equipped with the prime focus CCD 
camera. Observations started at 19:49 UT, about 7.5 hr after the burst.

Inside the XRT error circle (radius 3.5 arcsec; Gibson et al., GCN 22632
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 ) 
we do not find any source. At a mean time of 19:53 UT we constrain the 
magnitude of any optical transient to R>22 mag.

A. A. Breeveld (UCL-MSSL) and Z. Liu (NAOC/U. Leicester)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began observations of the field of GRB 180411A 64 s after 
the BAT trigger (Liu et al., GCN Circ. 22630
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 ) with a settling exposure 
in the V filter. The UVOT safety circuit tripped 3.4s into the following 
UV grism exposure, most likely due to the bright star HD223128, 5.08 
arcmin from the burst position.

No optical afterglow consistent with the enhanced XRT position (Gibson 
et al. GCN Circ. 22632
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 ) is seen in the 9.3s V settling exposure to a 
preliminary 3-sigma upper limit of 16.8 mag using the UVOT photometric 
system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373).

The magnitude is not corrected for the Galactic extinction
due to the reddening of E(B-V) = 1.104 in the direction of the burst
(Schlegel et al. 1998).

D. Frederiks, S. Golenetskii, R.Aptekar, M. Ulanov, D. Svinkin,
A. Tsvetkova, A.Lysenko, A. Kozlova, and T. Cline,
on behalf of the Konus-Wind team, report:

The long GRB 180411A (Swift/BAT detection: Liu et al., GCN 22630
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 ;
Markwardt et al., GCN 22633
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 ; Fermi-GBM detection: Poolakkil, GCN 22634
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 )
triggered Konus-Wind at T0=44862.530 s UT (12:27:42.530).

The KW light curve shows two multipeaked pulses with
a total duration of ~90 s.
The emission is seen up to ~10 MeV.

As observed by Konus-Wind, the burst had a fluence of
(4.01 �� 0.91)x10^-5 erg/cm2 and a 64-ms peak energy flux,
measured from T0+50.496, of (3.3 �� 0.7)x10^-6 erg/cm2
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+82.368 s)
is best fit in the 20 keV - 15 MeV range by by the GRB (Band)
function with the following model parameters:
the low-energy photon index alpha = -1.17 (-0.12,+0.15),
the high energy photon index beta = -2.39 (-0.90,+0.31),
the peak energy Ep = 239 (-49,+55) keV,
chi2 = 90/97 dof.

The spectrum near the peak count rate (measured from T0+41.408
to T0+57.792 s) is best fit in the 20 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.89 (-0.13,+0.16),
the high energy photon index beta = -2.49 (-0.77,+0.31),
the peak energy Ep = 255 (-40,+44) keV,
chi2 = 96/97 dof.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB180411_T44862/

All the quoted errors are estimated at the 90% confidence level.
All the presented results are preliminary.

V. Pal'shin, A. Yoshida, T. Sakamoto, Y. Kawakubo, A. Tezuka, S. Matsukawa,
H. Onozawa (AGU), K. Yamaoka (Nagoya U), S. Nakahira (RIKEN), I. Takahashi (IPMU),
Y. Asaoka, S. Ozawa, S. Torii (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U),
W. Ishizaki (ICRR), M. L. Cherry (LSU), S. Ricciarini (U of Florence),
A. V. Penacchioni, P. S. Marrocchesi (U of Siena)
and the CALET collaboration:

The long-duration GRB 180411A (Swift-BAT trigger #824451: Liu, et al., GCN Circ. 22630
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 ,
Markwardt et al., GCN Circ. 22633
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 ; Fermi-GBM detection: Poolakkil, von Kienlin and
Meegan, GCN Circ. 22634
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 ) triggered the CALET Gamma-ray Burst Monitor (CGBM) at
12:28:26.665 UTC on 11 April 2018.  The trigger occurred at the exit from the SAA,
44 sec after the BAT trigger.  The burst signal was seen by all CGBM detectors.

The burst light curve shows a multi-peaked structure which starts at T-35 sec, peaks at
T+9 sec and ends at T+36 sec. The T90 and the T50 durations measured by the SGM data are
60.0 +- 6.7 sec and 20.4 +- 9.0 sec (40-1000 keV), respectively.  Since CGBM missed the
initial part of the burst, these values underestimate the real burst durations.

The ground processed light curve is available at

http://cgbm.calet.jp/cgbm_trigger/ground/1207484873/

The CALET data used in this analysis are provided by the Waseda CALET Operation Center
located at the Waseda University.