GRB 190604B

K. L. Page (U Leicester), S. D. Barthelmy (GSFC), J.D. Gropp (PSU),
N. J. Klingler (PSU), S. J. LaPorte (PSU), A. Y. Lien (GSFC/UMBC),
F. E. Marshall (NASA/GSFC), M. J. Moss (GWU), D. M. Palmer (LANL),
B. Sbarufatti (PSU), M. H. Siegel (PSU), K. K. Simpson (PSU) and
A. Tohuvavohu (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 14:57:15 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 190604B (trigger=906654).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 297.587, -32.932 which is 
   RA(J2000) = 19h 50m 21s
   Dec(J2000) = -32d 55' 56"
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 250 sec, with two major peaks at 
~T0 and ~T+155 s. The peak count rate was ~4000 counts/sec (15-350 keV), 
at ~155 sec after the trigger. 

The XRT began observing the field at 14:59:12.5 UT, 116.8 seconds after
the BAT trigger. Using promptly downlinked data we find a bright, variable
uncatalogued X-ray source located at RA, Dec 297.53804, -32.97663 which
is equivalent to:
   RA(J2000)  = 19h 50m 09.13s
   Dec(J2000) = -32d 58' 35.9"
with an uncertainty of 3.6 arcseconds (radius, 90% containment). This
location is 218 arcseconds from the BAT onboard position. 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 consistent with the Galactic value of 1.36
x 10^21 cm^-2 (Willingale et al. 2013). 

The initial flux in the 0.1 s image was 1.11e-08 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 126 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
0.14. 

Burst Advocate for this burst is K. L. Page (klp5 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/)

P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:

Using  promptly downlinked XRT event data for GRB 190604B, we find an
enhanced XRT position of the afterglow: RA, Dec: 297.5413, -32.9782
which is equivalent to:
   RA (J2000)  = 19 50 09.92
   Dec (J2000) = -32 58 41.4
with an uncertainty of 2.0 arcseconds (radius, 90% confidence).
Analysis of the promptly available data is online at
http://www.swift.ac.uk/sper/906654.

Position enhancement is is described by Goad et al. (2007, A&A, 476,
1401) and Evans et al. (2009, MNRAS, 397, 1177).

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

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

Using 206 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 190604B, 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 = 297.54058, -32.97803 which is equivalent
to:

RA (J2000): 19h 50m 9.74s
Dec (J2000): -32d 58' 40.9"

with an uncertainty of 1.9 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.

A. A. Breeveld (UCL-MSSL) and K. L. Page (U Leicester) report on behalf 
of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 190604B 
128 s after the BAT trigger (Page et al., GCN Circ. 24742
Loading...
 
 ). A faint 
source is detected in the initial white UVOT exposure at a position 
consistent with the enhanced XRT source position (Evans et al., GCN 
Circ. 24746
Loading...
 
 ).

The preliminary detection 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     	128      276         146        19.90 �� 0.24
white     	618      812          39        >19.63
v         	669      861          39        >17.95
b         	594      787          39        >18.98
u         	338      588         246        >19.71
uvw1      	718      738          20        >17.44
uvw2      	645      837          39        >18.09

The magnitudes in the table are not corrected for the Galactic 
extinction due to the reddening of E(B-V) = 0.15 in the direction of the 
  burst (Schlegel et al. 1998).

M. Khandagale, H. Kumar, V. Karambelkar, V. Bhalerao(IITB), G. C. Anupama,
J. Stanzin (IIA) report on behalf of the GROWTH collaboration:

We observed the field of GRB190604B reported by K. L. Page et al., GCN
24742
Loading...
 
  at 2019-06-04 and 20:03:18.675 UT with the 0.7m GROWTH-India
telescope. We took 2 exposures of 600 seconds each in r filter. No source
was found within an uncertainty region of 3.6 arcseconds to RA(J2000) = 19h
50m 09.13s, Dec(J2000) = -32d 58' 35.9" (K. L. Page et al.,GCN 24742).

We obtained the following upper limits:

------------------------------------------------------------------

 JD(Start)| Exposure(sec) | Filter | lim_Mag |

------------------------------------------------------------------

2458639.335 | 600 | r | 20.33|

2458639.342 | 600 | r | 19.93|

------------------------------------------------------------------

The GROWTH India Telescope (GIT) is a 70-cm telescope with a 0.7 degree
field of view, set up by the Indian Institute of Astrophysics and the
Indian Institute of Technology Bombay with support from the Indo-US Science
and Technology Forum (IUSSTF) and the Science and Engineering Research
Board (SERB) of the Department of Science and Technology (DST), Government
of India (https://sites.google.com/view/growthindia/). It is located at the
Indian Astronomical Observatory (Hanle), operated by the Indian Institute
of Astrophysics (IIA).

J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU),
A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), J.P. Osborne
(U. Leicester), M.G. Bernadini (INAF-OAB), E. Ambrosi  (INAF-IASFPA) ,
V. D'Elia (ASDC) and K.L. Page report on behalf of the Swift-XRT team:

We have analysed 7.7 ks of XRT data for GRB 190604B (Page et al. GCN
Circ. 24742
Loading...
 
 ), from 120 s to 34.4 ks after the  BAT trigger. The data
comprise 285 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Evans et al. (GCN Circ. 24743
Loading...
 
 ).

The late-time light curve (from T0+4.9 ks) can be modelled with a
power-law decay with a decay index of alpha=0.94 (+/-0.12).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.40 (+/-0.03). The
best-fitting absorption column is  1.49 (+0.16, -0.13) x 10^21 cm^-2,
consistent with the Galactic value of 1.4 x 10^21 cm^-2 (Willingale et
al. 2013). The PC mode spectrum has a photon index of 2.02 (+/-0.12)
and a best-fitting absorption column of 3.0 (+/-0.5) x 10^21 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.6 x 10^-11 (5.4 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3.0 (+/-0.5) x 10^21 cm^-2
Galactic foreground: 1.4 x 10^21 cm^-2
Excess significance: 5.7 sigma
Photon index:	     2.02 (+/-0.12)

If the light curve continues to decay with a power-law decay index of
0.94, the count rate at T+24 hours will be 0.057 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.1 x
10^-12 (3.1 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/00906654.

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

Y.-D. Hu, X.-Y.Li, E. Fernandez-Garcia, A. Ayala and A. J. Castro-Tirado 
(IAA-CSIC),
I. Carrasco and C. Perez del Pulgar (Univ. de Malaga), M. D. 
Caballero-Garcia (ASU-CAS, CZ)
and R. Querel (NIWA), on behalf of a larger collaboration,

report:

The 60cm BOOTES-3/YA robotic telescope at NIWA Lauder in Otago (New 
Zealand) automatically
responded to the Swift GRB 190604B (Page et al. GCNC 24742) only 35 s 
after the burst). At
the position of the Swift/XRT enhanced X-ray position (Evans et al. GCNC 
24746), no optical
afterglow is detected down to R = 15.5 (for the 1-s image gathered at 
14:57:50 UT) or down to
19.8 mag (for the co-added 9x10s unfiltered images at mid-time 15:05:56 
UT, i.e. 8.7 min after
trigger).

We thank the staff at NIWA for its excellent support.

C. B. Markwardt (GSFC), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), H. A. Krimm (NSF),
A. Y. Lien (GSFC/UMBC), D. M. Palmer (LANL),
K. L. Page (U Leicester), 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 190604B (trigger #906654)
(Page et al., GCN Circ. 24742
Loading...
 
 ).  The BAT ground-calculated position is
RA, Dec = 297.546, -32.975 deg which is
   RA(J2000)  =  19h 50m 10.9s
   Dec(J2000) = -32d 58' 31.1"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 64%.

The mask-weighted light curve shows a multi-peaked structure that starts
from ~T-40 s and ends at ~T+240 s. There are two major peaks that occur
at ~T0 and ~T+158 s, respectively. T90 (15-350 keV) is 220.2 +- 4.7 sec
(estimated error including systematics).

The time-averaged spectrum from T-39.776 sec to T+239.504 sec is best fit
by a simple power-law model.  The power law index of the time-averaged
spectrum is 1.81 +- 0.04. The fluence in the 15-150 keV band
is 1.77 +- 0.04 x 10^-5 erg/cm2. The 1-sec peak photon flux measured from
T+157.54 sec in the 15-150 keV band is 7.3 +- 0.4 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/906654/BA/

S. Belkin (IKI), A. Novichonok (KIAM), A. Pozanenko (IKI), E. Mazaeva 
(IKI), A. Volnova (IKI), I. Molotov (KIAM), Sh. Ehgamberdiev (UBAI) 
report on behalf of larger IKI GRB FuN collaboration:

We observed the field of the Swift GRB 190604B (Page et al., GCN  24742
Loading...
 
 ) 
  with RC-36 0.36-m telescope of Kitab Observatory starting on June 04 
(UT) 22:26:32 in  Clear filter.    We do not find any optical source 
within  enhanced Swift-XRT position (Evans  et al., GCN  24746
Loading...
 
 ). The 
non-detection is consistent with BOOTES-3 results (Hu et al., GCN  24750
Loading...
 
 ).

Preliminary photometry of the field is following.

Date       UT start   t-T0       Filter Exp.   OT  Err.   UL(3sigma)
                       (mid, days)        (s)

2019-06-04 22:26:32   0.32068    CR     21*60  n/d  n/d   18.6

The photometry is based on the nearby USNO-B1 (R2) stars.

L. Izzo, D. A. Kann (both HETH/IAA-CSIC), D. B. Malesani (DTU Space), D. 
Hartmann (Clemson University), A. de Ugarte Postigo (HETH/IAA-CSIC, 
DARK/NBI), and N. R. Tanvir (Univ. Leicester) report on behalf of the 
Stargate Consortium:

We observed the field of GRB 190604B (Page et al., GCN 24742
Loading...
 
 ) with 
X-shooter mounted on the ESO VLT UT2 (Kueyen). Images were obtained in 
SDSS g'r'z', as well as a deeper 300 s r' exposure, centered at 05:24:16 
UT on June 05, 2019 (0.8483 days after the GRB trigger).

At the position of the UVOT afterglow (Breeveld et al., GCN 24747
Loading...
 
 ) and 
within the XRT error circle (Evans et al., GCN 24746
Loading...
 
 ), we detect a faint 
source only in the latter image.

Using a recent computation of the X-shooter acquisition camera 
zero-point value, the total number of counts, a seven arcsec radius 
aperture and the exposure time of 300 s, we derive a magnitude of r'(AB) 
= 23.27 +/- 0.09 mag.

Because of source faintness, no spectroscopy was attempted.