GRB 180404B

V. Sharma (IUCAA), V. Bhalerao (IIT-B), D. Bhattacharya (IUCAA), A. R. Rao (TIFR) and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:

Analysis of AstroSat CZTI data showed the detection of a long GRB 180404B, which was also detected by Swift (Palmer D. et al., GCN 22590
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 ), Fermi-GBM (Kienlin A. V. et al., GCN 22597
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 ) and Konus-Wind (Svinkin D. et al., GCN 22609
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 ).

The source was clearly detected in the 40-200 keV energy range. The light curve shows multiple peaks of emission with strongest peak at 02:11:53.5 UT, ~9.5 s after the Swift trigger. The measured peak count rate is 281.6 cts/s above the background in combined data of four quadrants, with a total of 3662 cts. The local mean background count rate was 541 cts/s. Using cumulative rates, we measure a T90 of 44 s. 

It was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range.

CZTI GRB detections are reported regularly on the payload site at http://astrosat.iucaa.in/czti/?q=grb. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, ISAC, IUCAA, SAC and PRL. The Indian Space Research Organisation funded, managed and facilitated the project.

M. H. Siegel (PSU) and S. J. LaPorte (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 180404B
82 s after the BAT trigger (LaPorte et al., GCN Circ. 22590
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 ).
A fading source consistent with the XRT position
(Beardmore et al. GCN Circ. 22594
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 )
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
   RA  (J2000) =  03:33:34.23 =  53.39262 (deg.)
   Dec (J2000) = -50:12:54.2  = -50.21506 (deg.)
with an estimated uncertainty of 0.46 arc sec. (radius, 90% confidence).

Preliminary detections and 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 (fc)          82          231          147         18.66 +/- 0.09
white               82         1720          411         19.39 +/- 0.09
white             6421         6620          196        >20.7
v                  624         7031          510        >19.5
b                  550         7661          322        >20.3
u (fc)             295          545          245         19.49 +/- 0.31
u                  295         1670          343         19.70 +/- 0.29
u                 6011         7648          393        >20.1
w1                 674         7442          510        >20.6
m2                1600         7236          413        >20.5
w2                 600         6826          452        >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).

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

The long-duration GRB 180404B
(Swift-BAT detection: LaPorte et al., GCN Circ. 22590
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 ;
Fermi-GBM observation: von Kienlin, GCN Circ. 22597
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 )
triggered Konus-Wind at T0=7898.049 s UT (02:11:38.049).

The burst light curve shows the bright pulse
which starts at ~T0-3.4 s and has a total duration of ~29 s
followed by a weaker pulse seen up to ~T0+100 s.
The emission is seen up to ~2 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB180404_T07898/

As observed by Konus-Wind, the burst
had a fluence of 2.60(-0.16,+0.18)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+8.832 s,
of 2.07(-0.66,+0.66)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+73.984 s)
is best fit in the 20 keV - 5 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.65(-0.15,+0.16)
and Ep = 205(-17,+21) keV (chi2 = 82/73 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -3.0
(chi2 = 82/72 dof).

The spectrum near the maximum count rate
(measured from T0+8.448 to T0+16.640 s)
is best fit in the 20 keV - 5 MeV range
by a power law with exponential cutoff model:
with  alpha = -0.19(-0.16,+0.17)
and Ep = 186(-11,+12) keV (chi2 = 90/73 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -3.2
(chi2 = 90/72 dof).

All the quoted errors are at the 90% confidence level.
All the quoted values are preliminary.

J. R. Cummings (CPI), S. D. Barthelmy (GSFC),
H. A. Krimm (NSF/USRA), S. J. LaPorte (PSU),
A. Y. Lien (GSFC/UMBC), C. B. Markwardt (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-240 to T+962 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 180404B (trigger #821902)
(LaPorte et al., GCN Circ. 22590
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 ).  The BAT ground-calculated position is
RA, Dec = 53.390, -50.213 deg which is
  RA(J2000)  =  03h 33m 33.6s
  Dec(J2000) = -50d 12' 47.4"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 84%.

The mask-weighted light curve shows a major pulse that starts at ~ T-6 s and peaks
at ~ T+ 10 s. Another weaker pulse arises at the end of the major pulse at ~ T+40 s.
The second pulse peaks at ~ T+50 s and lasts until ~ T+200 s. T90 (15-350 keV)
is 111.5 +- 7.1 sec (estimated error including systematics).

The time-averaged spectrum from T-5.91 to T+195.64 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.35 +- 0.04.  The fluence in the 15-150 keV band is 1.20 +- 0.02 x 10^-5 erg/cm2.
The 1-sec peak photon flux measured from T+8.88 sec in the 15-150 keV band
is 5.2 +- 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/821902/BA/

D.N. Burrows (PSU), A. Tohuvavohu (PSU), S. J. LaPorte (PSU), J.P.
Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U.
Leicester), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAB), P. D'Avanzo
(INAF-OAB) and S.J. LaPorte report on behalf of the Swift-XRT team:

We have analysed 8.4 ks of XRT data for GRB 180404B (LaPorte et al. GCN
Circ. 22590
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 ), from 63 s to 30.6 ks after the  BAT trigger. The data
comprise 349 s in Windowed Timing (WT) mode (the first 5 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. The enhanced XRT position for this burst was given by Beardmore
et al. (GCN Circ. 22594
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 ).

The late-time light curve (from T0+5.2 ks) can be modelled with a
power-law decay with a decay index of alpha=1.52 (+0.14, -0.13).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.61 (+/-0.04). The
best-fitting absorption column is  3.00 (+0.25, -0.23) x 10^21 cm^-2,
in excess of the Galactic value of 1.1 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 2.06 (+/-0.14) and a
best-fitting absorption column of 4.2 (+/-0.7) x 10^21 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.8 x 10^-11 (6.2 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     4.2 (+/-0.7) x 10^21 cm^-2
Galactic foreground: 1.1 x 10^20 cm^-2
Excess significance: 10.0 sigma
Photon index:	     2.06 (+/-0.14)

If the light curve continues to decay with a power-law decay index of
1.52, 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 1.7 x
10^-13 (2.8 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/00821902.

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

A. von Kienlin (MPE) reports on behalf of the Fermi GBM Team:

"At 02:11:38.64 UT on 04 April 2018, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 180404B (trigger 544500703 / 180404091),
which was also detected by the Swift/BAT (LaPorte et al. 2018, GCN 22590
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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 61.3 degrees.

The GBM light curve shows a single bright peak followed by
a secondary emission episode with a duration (T90) of about 80 s (50-300 keV).
The time-averaged spectrum from T0+0.003 s to T0+33.281 s is well fit by
a power law function with an exponential
high-energy cutoff.  The power law index is -0.40 +/- 0.04 and
the cutoff energy, parameterized as Epeak, is 209 +/- 6 keV.

The event fluence (10-1000 keV) in this time interval is
(3.3 +/- 0.4)E-06 erg/cm^2. The 1.024-sec peak photon flux measured
starting from T0+12.86 s in the 10-1000 keV band
is 8.0 +/- 0.3 ph/s/cm^2.

A Band function fits the spectrum equally well
with Epeak= 204 +/- 8 keV, alpha = -0.38 +/- 0.04 and beta = -3.3 +/- 0.6.

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

V. Lipunov, E. Gorbovskoy, V.Kornilov, N.Tyurina, 
A.Kuznetsov, V.V.Chazov, A.V. Krylov, I. Gorbunov, D. Vlasenko, 
D.Zimnukhov, D.Kuvshinov, P.Balanutsa
Lomonosov Moscow State University,
Sternberg Astronomical Institute, Moscow State University

R. Podesta, F. Podesta, C. Lopez, C.Francile
Observatorio Astronomico Felix Aguilar (OAFA)

H.Levato, C. Saffe
Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE)

R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres
The Instituto de Astrofisica de Canarias

D. Buckley
South African Astronomical Observatory

O. Gres, N.M. Budnev, Yu.Ishmuhametova
Irkutsk State University

A. Tlatov, V.Senik, D. Dormidontov
Kislovodsk Solar Station of the Pulkovo Observatory

A. Gabovich, V. Yurkov, Yu. Sergienko
Blagoveschensk Educational State University, Blagoveschensk


MASTER-OAFA robotic telescope (MASTER-Net: http://observ.pereplet.ru) 
located in Argentina was pointed to the  GRB180404B (LaPorte et al. GCN 
22590
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 ; Beardmore et al. GCN 22594
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 ) 27 sec after notice time and 45 sec 
after trigger time at 2018-04-04 02:12:29 UT.
On our first 10s exposure  image with unfiltered mlim=16.5 (5-sigma) we 
don't found optical transient  within SWIFT error-box (ra=53.3792 
dec=-50.195 r=0.05 LaPorte et al. GCN 22590
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 )

MASTER auto-detection system detected OT with RA,Dec=53.392900; 
-50.214903
and unfiltered m_OT = 18.4 (automatic reduction)
on the summary image with 670s exposition started on 2018-04-04 02:12:29 
(mlim=19.7)

The message may be cited.


====================================================================


The observations started at zenit distance = 73 degrees, galaxy latitude b 
= -51 degree.
The moon (86 % bright part) is 16 degrees above the horizon. The distance 
between  moon and  object is 115
The sun  altitude was -46.8 degree.

A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester) 
report on behalf of the Swift-XRT team.

Using 305 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 180404B, 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 = 53.39268, -50.21550 which is equivalent
to:

RA (J2000): 03h 33m 34.24s
Dec (J2000): -50d 12' 55.8"

with an uncertainty of 2.9 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.

S. J. LaPorte (PSU), C. Gronwall (PSU), J.D. Gropp (PSU),
J. A. Kennea (PSU), A. Y. Lien (GSFC/UMBC),
F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU) and
A. Tohuvavohu (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 02:11:44 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 180404B (trigger=821902).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 53.384, -50.195 which is 
   RA(J2000) = 03h 33m 32s
   Dec(J2000) = -50d 11' 41"
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 50 sec.  The peak count rate
was ~9000 counts/sec (15-350 keV), at ~9 sec after the trigger. 

The XRT began observing the field at 02:12:53.9 UT, 69.9 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 53.3967, -50.2151 which is equivalent to:
   RA(J2000)  = +03h 33m 35.21s
   Dec(J2000) = -50d 12' 54.4"
with an uncertainty of 4.7 arcseconds (radius, 90% containment). This
location is 78 arcseconds from the BAT onboard position, within the BAT
error circle. No event data are yet available to determine the column
density using X-ray spectroscopy. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 81 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	03:33:34.24 =  53.39265
  DEC(J2000) = -50:12:54.1  = -50.21504
with a 90%-confidence error radius of about 0.76 arc sec. This position is 9.3
arc sec. from the center of the XRT error circle. The estimated magnitude is
18.61 with a 1-sigma error of about  0.15. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.01. 

Burst Advocate for this burst is S. J. LaPorte (extragsam AT gmail.com). 
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.)