GRB 180404A

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

The Swift/UVOT began settled observations of the field of GRB 180404A
90 s after the BAT trigger (Gropp et al., GCN Circ. 22589
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 ).
A source consistent with the XRT position
(Osborne et al. GCN Circ. 22592
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 )
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
   RA  (J2000) =  05:34:11.64 =  83.54850 (deg.)
   Dec (J2000) = -37:10:03.9  = -37.16774 (deg.)
with an estimated uncertainty of 0.50 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)          90          240          147         19.47 +/- 0.09
white               90          770          180         19.34 +/ -0.10
white             45830       52026         1028        >21.66
v                  632         5179           99        >18.9
b                  558          750           39        >19.4
u (fc)              302         552          246         18.95 +/- 0.12
u                  303          726          265         18.95 +/ -0.14
w1                 682          701           19        >17.8
m2                 656          676           19        >17.4
w2                 607         5094          216         19.45 +/- 0.28

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.04 in the direction of the burst
(Schlegel et al. 1998).

C. Guidorzi, R. Martone (U. Ferrara), S. Kobayashi (LJMU), C.G. Mundell 
(U. Bath), A. Gomboc (U. Nova Gorica), I.A. Steele (LJMU) on behalf of a 
large collaboration report:

We began observing Swift GRB180404A (Gropp et al. GCN 22589
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 ) on April 4, 
09:30 UT (0.36 days post burst) with the LCO 2-m Faulkes Telescope South 
unit in Siding Springs in the SDSS-R filter. We marginally detect the 
optical afterglow (Gropp et al.; Selsing et al. GCN 22591
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 ) with the 
following magnitude:

Mid time since GRB���� Exp������� Filter�������� Magnitude
(days)���������������� (s)
-------------------------------------------------------------
0.37������������������ 5x120����� SDSS-R�������� 21.3 +- 0.3
-------------------------------------------------------------

as calibrated against nearby USNO UCAC4 objects.

A. Tohuvavohu (PSU), S. J. LaPorte (PSU), K.L. Page (U. Leicester),
A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), A. Melandri
(INAF-OAB), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), J.A. Kennea (PSU)
and J.D. Gropp report on behalf of the Swift-XRT team:

We have analysed 3.9 ks of XRT data for GRB 180404A (Gropp et al. GCN
Circ. 22589
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 ), from 90 s to 52.0 ks after the  BAT trigger. The data
comprise 26 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. 22592
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 ).

The light curve can be modelled with a power-law decay with a decay
index of alpha=0.5 (+nan, -nan).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.62 (+0.27, -0.22). The
best-fitting absorption column is  consistent with the Galactic value
of 3.1 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 4.1 x 10^-11 (4.2 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3.1 (+/-5.1) x 10^20 cm^-2
Galactic foreground: 3.1 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.62 (+0.27, -0.22)

If the light curve continues to decay with a power-law decay index of
0.5, the count rate at T+24 hours will be 0.011 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.3 x
10^-13 (4.5 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/00821881.

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

S. D. Barthelmy (GSFC), J. R. Cummings (CPI), J. D. Gropp (PSU),
H. A. Krimm (NSF/USRA), 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-239 to T+654 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 180404A (trigger #821881)
(Gropp, et al., GCN Circ. 22589
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 ).  The BAT ground-calculated position is
RA, Dec = 83.540, -37.168 deg which is
    RA(J2000)  =  05h 34m 09.5s
    Dec(J2000) = -37d 10' 05.0"
with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 82%.
  
The mask-weighted light curve shows a weak emission that starts at T-25 sec,
followed by a bright peak which peaks at T+3 sec and ends at T+30 sec.
T90 (15-350 keV) is 35.2 +- 5.3 sec (estimated error including systematics).
  
The time-averaged spectrum from T-20.7 to T+24.2 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.95 +- 0.12.  The fluence in the 15-150 keV band is 1.3 +- 0.1 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+1.99 sec in the 15-150 keV band
is 1.3 +- 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/821881/BA/

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

R. Podesta, Carlos Lopez and F. Podesta
Observatorio Astronomico Felix Aguilar (OAFA)

Hugo Levato and Carlos Saffe
Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE)

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

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

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

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

D. Buckley, S. Potter
South African Astronomical Observatory


MASTER-OAFA  robotic telescope (MASTER-Net: http://observ.pereplet.ru) 
located in Argentina was pointed to the  GRB180404A (Gropp et al. GCN 
22589
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 ) 21 sec after notice time and 43 sec after trigger time at 
2018-04-04 00:46:18 UT.
On our first 10s exposure  set we haven`t found optical transient with 
17.4 5-sigma upper limit in
SWIFT XRT error-box (ra=83.549 dec=-37.17 r=4.2").

MASTER auto-detection system detected OT with RA,Dec=5h 34m 11s.66, -37d 
10m 03s.5 with unfiltered m_OT=19.8
on the summary image with 660s exposition started 2018-04-04 00:46:18.938UT,
that was discovered by Swift (Gropp et al. GCN 22589
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 ) and confirmed by 
VLT (Selsing et al. GCN 22591
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 )

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

The observations made on zenit distance = 42 degrees, galaxy latitude b = 
-30 degree.
The moon (87 % bright part) below the horizon (The altitude of the Moon is 
-1 degree ).
The sun  altitude  is -29.7 degree.

The message may be cited.



1

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

Using 646 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 180404A, 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 = 83.54906, -37.16807 which is equivalent
to:

RA (J2000): 05h 34m 11.77s
Dec (J2000): -37d 10' 05.1"

with an uncertainty of 2.0 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.

J. Selsing (DARK/NBI), D. Malesani (DAWN/NBI and DARK/NBI), D.A. Kann 
(HETH/IAA-CSIC), N.R. Tanvir (Univ. Leicester) report on behalf of the 
Stargate consortium:

We observed the optical counterpart of GRB 180404A (Gropp et al., GCN  
22589
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 ) using the ESO Very Large Telescope (VLT) UT2 equipped with the 
X-shooter spectrograph. Observations were carried out in robotic "rapid 
response mode" (RRM), initiated automatically following the X-ray 
localization notice.

In the 15-s r-band acquisition image, taken on 2018 Apr 4.0423 UT (15.3  
min after the trigger), the afterglow is clearly detected, at 
coordinates (J2000):

RA = 05:34:11.67
Dec = -37:10:04.1

We measure a magnitude R = 18.64 +- 0.1 (Vega), calibrated against 
nearby USNO stars, where the error is dominated by the calibration scatter.

Several spectra were acquired. We report here on the exposure with mid 
epoch Apr 4.0495 UT (that is, 25.6 min after the GRB), with 600 s 
exposure time, and covering the wavelength range 3000-25000 AA. The 
afterglow continuum trace is clearly detected. Superposed on it, several 
absorption features are visible, which we identify as Al III, Fe II, Mg 
II, and Mg I, all at a common redshift redshift of z = 1.000.

We acknowledge excellent support from the observing staff at Paranal, in 
particular Stephane Brillant, Luca Sbordone, Andrea Mehner, and Jose 
Velasquez.

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

At 00:45:35 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 180404A (trigger=821881).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 83.564, -37.170 which is 
   RA(J2000) = 05h 34m 15s
   Dec(J2000) = -37d 10' 10"
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 50 sec.  The peak count rate
was ~1900 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 00:47:02.1 UT, 86.5 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 83.54900, -37.16824 which is equivalent
to:
   RA(J2000)  = 05h 34m 11.76s
   Dec(J2000) = -37d 10' 05.7"
with an uncertainty of 4.2 arcseconds (radius, 90% containment). This
location is 43 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 89 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	05:34:11.63 =  83.54846
  DEC(J2000) = -37:10:03.9  = -37.16774
with a 90%-confidence error radius of about 0.65 arc sec. This position is 2.3
arc sec. from the center of the XRT error circle. The estimated magnitude is
19.40 with a 1-sigma error of about  0.16. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.04. 

Burst Advocate for this burst is J.D. Gropp (jdg44 AT psu.edu). 
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.)