GRB 190204A

A. Y. Lien (GSFC/UMBC), M. G. Bernardini (INAF-OAB),
P. D'Avanzo (INAF-OAB), N. J. Klingler (PSU), A. Melandri (INAF-OAB),
D. M. Palmer (LANL) and A. Tohuvavohu (PSU) report on behalf of the
Neil Gehrels Swift Observatory Team:

At 05:46:01 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 190204A (trigger=887579 and 887580). 
Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 351.514, +54.878 which is 
   RA(J2000) = 23h 26m 03s
   Dec(J2000) = +54d 52' 42"
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 20 sec.  The peak count rate
was ~28000 counts/sec (15-350 keV), at ~5 sec after the trigger. 

The XRT began observing the field at 05:47:15.7 UT, 75.0 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 351.47755, 54.87623 which
is equivalent to:
   RA(J2000)  = 23h 25m 54.61s
   Dec(J2000) = +54d 52' 34.4"
with an uncertainty of 3.6 arcseconds (radius, 90% containment). This
location is 119 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 consistent with the Galactic value of 4.36
x 10^21 cm^-2 (Willingale et al. 2013). 

The initial flux in the 2.5 s image was 5.72e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 250 seconds with the U filter starting
295 seconds after the BAT trigger. There is a candidate afterglow in the
rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	23:25:54.58 = 351.47742
  DEC(J2000) = +54:52:34.9  =  54.87637
with a 90%-confidence error radius of about 0.63 arc sec. This position is 4.2
arc sec. from the center of the XRT error circle. The estimated magnitude is
17.76 with a 1-sigma error of about  0.15. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.38. 

This GRB resulted in two BAT triggers in the on-board processing (#887579 at 05:46:01 and #887580 at 05:46:06).  
We adopt the first trigger number and time as T0. 

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: /too.html.)

T. Oeda (Tokyo Tech), M. Nakajima (Nihon U.), S. Nakahira (RIKEN),
H. Negoro, A. Sakamaki, W. Maruyama, M. Aoki, K. Kobayashi (Nihon U.), 
T. Mihara, F. Yatabe, Y. Takao, M. Matsuoka (RIKEN),
T. Sakamoto, M. Serino, S. Sugita, T. Hashimoto, A. Yoshida (AGU), 
N. Kawai, M. Sugizaki, Y. Tachibana, K. Morita (Tokyo Tech), 
S. Ueno, H. Tomida, M. Ishikawa, Y. Sugawara, N. Isobe, R. Shimomukai, T. Midooka (JAXA), 
Y. Ueda, A. Tanimoto, T. Morita, S. Yamada, S. Ogawa (Kyoto U.), 
Y. Tsuboi, W. Iwakiri, R. Sasaki, H. Kawai, T. Sato (Chuo U.), 
H. Tsunemi, T. Yoneyama, K. Asakura, S. Ide (Osaka U.), 
M. Yamauchi, K. Hidaka, S. Iwahori (Miyazaki U.), 
T. Kawamuro (NAOJ), 
K. Yamaoka (Nagoya U.),
M. Shidatsu (Ehime U.),
Y. Kawakubo (LSU) 
report on behalf of the MAXI team:
The MAXI/GSC nova alert system triggered a bright X-ray transient at 05:45:55 UT on February 4, 2019.
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (351.341 deg, 54.761 deg) = (23 25 21, +54 45 38) (J2000)
with a 90% C.L. statistical error of 0.10 deg and an additional systematic uncertainty of 0.1 deg (90% containment radius).
The X-ray flux averaged over the scan was 2286 +- 126 mCrab
(4.0-10.0keV, 1 sigma error).
Without assumptions on the source constancy,we obtain a rectangular error
box for the transient source with the following corners:
(R.A., Dec) = (350.693, 54.635) deg = (23 22 46, +54 38 05) (J2000)
(R.A., Dec) = (350.828, 54.512) deg = (23 23 18, +54 30 43) (J2000)
(R.A., Dec) = (352.146, 54.985) deg = (23 28 35, +54 59 05) (J2000)
(R.A., Dec) = (352.013, 55.110) deg = (23 28 03, +55 06 35) (J2000).

The trigger time and position was consistent with that of GRB 190204A detected 
by Swift (Lien et al. 2019, GCN 23852
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 ).

T. Khanam, V. Sharma, D. Bhattacharya and  A. Vibhute (IUCAA),  V. Bhalerao (IIT-B), 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 190204A, which was also detected by Swift (Lien A. Y. et al., GCN Circ 23852
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 ) and MAXI/GSC (Oeda T. et al., GCN Circ 23854
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 ).

The source was clearly detected in the 20-200 keV energy range. The light curve shows multiple peaks of emission with the strongest peak at 05:46:06.5 UT. The measured peak count rate is 1455 cts/s above the background in the combined data of four quadrants, with a total of 5579 cts. The local mean background count rate was 569 cts/s. Using cumulative rates, we measure a T90 of 11.9 s. In preliminary analysis, we find that 578 Compton events are associated with this event.

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.

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

We have analysed 6.4 ks of XRT data for GRB 190204A (Lien et al. GCN
Circ. 23852
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 ), from 81 s to 13.0 ks after the  BAT trigger. The data
comprise 926 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The refined XRT position is RA, Dec =
351.4775, +54.8766 which is equivalent to:

RA (J2000): 23 25 54.59
Dec(J2000): +54 52 35.7

with an uncertainty of 3.6 arcsec (radius, 90% confidence).

The late-time light curve (from T0+4.8 ks) can be modelled with a
power-law decay with a decay index of alpha=1.36 (+/-0.16).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.740 (+0.022, -0.018). The
best-fitting absorption column is  consistent with the Galactic value
of 4.4 x 10^21 cm^-2 (Willingale et al. 2013). The PC mode spectrum has
a photon index of 1.83 (+0.12, -0.11) and a best-fitting absorption
column of 5.4 (+0.8, -0.7) x 10^21 cm^-2. The counts to observed
(unabsorbed) 0.3-10 keV flux conversion factor deduced from this
spectrum  is 4.6 x 10^-11 (6.8 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     5.4 (+0.8, -0.7) x 10^21 cm^-2
Galactic foreground: 4.4 x 10^21 cm^-2
Excess significance: 2.4 sigma
Photon index:	     1.83 (+0.12, -0.11)

If the light curve continues to decay with a power-law decay index of
1.36, the count rate at T+24 hours will be 9.9 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.5 x
10^-13 (6.8 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/00887579.

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

Alan M. Watson (UNAM), Nat Butler (ASU), Rosa L. Becerra (UNAM), Diego
Gonz��lez (UNAM), William H. Lee (UNAM), Margarita Pereyra (UNAM), Carlos
Rom��n-Z����iga (UNAM), Alexander Kutyrev (GSFC), and Eleonora Troja (GSFC)
report:

We observed the field of GRB 190204A (Lien et al., GCN Circ. 23852
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 ) with
the COATLI 50-cm telescope and interim imager at the Observatorio
Astron��mico Nacional on the Sierra de San Pedro M��rtir
(http://coatli.astroscu.unam.mx) from 2019-02-04 05:46:35 to 2019-02-04
05:57:30 (from 34 to 689 seconds after the trigger), obtaining a total
of 345 seconds of exposure in the w filter.

At the position of the UVOT afterglow candidate (Lien et al., GCN Circ.
23852
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 ), we detect a source that fades from w = 13.5 to w = 17.5 over the
course of our observations. A power-law fit suggest a temporal index of
-1.44 +/- 0.03.

Our w magnitudes are calibrated against the USNO-B1 catalog (adjusted to
an approximate AB system) and are not corrected for Galactic extinction
in the direction of the GRB.

We thank the COATLI technical team and the staff of the Observatorio
Astron��mico Nacional.

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

Using 2532 s of XRT Photon Counting mode data and 6 UVOT
images for GRB 190204A, 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 = 351.47820, +54.87637 which is equivalent
to:

RA (J2000): 23h 25m 54.77s
Dec (J2000): +54d 52' 34.9"

with an uncertainty of 1.5 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.

Paul 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 190204A
84 s after the BAT trigger (Lien et al., GCN Circ. 23852
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 ).
The updated UVOT position is:

The preliminary UVOT position is:
    RA  (J2000) =  23:25:54.58 = 351.47744 (deg.)
    Dec (J2000) = +54:52:35.1  =  54.87642 (deg.)
with an estimated uncertainty of 0.4 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               84          233          147         16.84 +/- 0.07
white              576          596           20         18.66 +/- 0.20
v                  626         1247           78         18.30 +/- 0.23
b                  551         1507           85         19.29 +/- 0.21
u                  296          546          246         17.85 +/- 0.10
w1                 676         1470           97        >18.3
m2                 651         1444           97        >19.5
w2                 602         1395           97        >18.7

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.38 in the direction of the burst
(Schlegel et al. 1998).

A. Volnova (IKI),  A. Pozanenko (IKI),  E. Klunko (ISTP), R. Inasaridze
(AbAO), E. Mazaeva (IKI), S. Belkin (IKI)  report   on behalf of
IKI-GRB-FuN:

We observed the field of localization of  GRB 190204A   (Lien et al. GCN
23852
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 )    with AZT-33IK telescope of Sayan observatory (Mondy).   We
started observations on Feb. 04 (UT) 13:10:12 in R-filter. We do not
detect  the optical afterglow (Lien et al.  GCN 23852
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 ; Watson et al.,
GCN  23861
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 ;  Kuin et al., GCN  23863
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 ). Preliminary photometry of the
field is following.

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

2019-02-04  13:10:12  0.32583     R      25*120      n/d     n/d   20.3

The photometry is based on nearby SDSS stars:
SDSS_id                         R_Lupton
J232549.70+545348.8 16.978 0.014
J232550.46+545253.5 17.052 0.014
J232544.33+545253.6 16.085 0.013


Our observation confirm rapid initial decay of the afterglow detected by
UVOT (Kuin et al., GCN  23863
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 ).

A. S. Moskvitin (SAO RAS)
report on behalf of larger GRB follow-up team.

We observed the field of the GRB 190204A (Lien et al., GCNC #23852)
with the Zeiss-1000 telescope of SAO RAS (+ CCD photometer)
on February, 4, 15:36:17--16:44:07 UT (mid. time 16:10:12).
The observations were carried out in Rc band.

We detected the OT (Lien et al., GCNC #23852; Watson et al.,
GCNC #23861; Kuin & Lien, GCNC #23863)
in the stacked 12 x 300 sec. image.

Preliminary brightness of OT is R = 21.9 +/- 0.1 (T-T0 = 0.4335 d).
The calibrations is based on nearby SDSS stars (Volnova et al.,
GCNC #23867), magnitudes converted with the Lupton 2005 equations.

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

The long-duration GRB 190204A
(Swift detection: Lien et al., GCN Circ. 23852
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 ;
MAXI/GSC detection: Oeda et al., GCN Circ. 23854
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 ;
AstroSat CZTI detection: Khanam et al., GCN Circ. 23856
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 )
triggered Konus-Wind at T0=20755.832 s UT (05:45:55.832).

The burst light curve shows a multipeaked structure
started at ~T0-1 s with a total duration of ~49 s.
The emission is seen up to ~10 MeV.

As observed by Konus-Wind, the burst
had a fluence of 5.31(-0.51,+0.53)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+8.288 s,
of 2.17(-0.28,+0.29)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+17.408 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.88(-0.07,+0.08),
the high energy photon index beta = -2.43(-0.30,+0.18),
the peak energy Ep = 308(-30,+33) keV
(chi2 = 76/98 dof).

The spectrum near the maximum count rate
(measured from T0+7.680 to T0+9.472 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.85(-0.07,+0.08),
the high energy photon index beta = -2.70(-0.58,+0.25),
the peak energy Ep = 387(-39,+46) keV
(chi2 = 69/66 dof).

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB190204_T20755/

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

T. Sakamoto (AGU), 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), M. Stamatikos (OSU),
T. N. Ukwatta (LANL) (i.e. the Swift-BAT team):

Using the data set from T-234 to T+968 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 190204A (trigger #887579 and #887580)
(Lien et al., GCN Circ. 23852
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 ). In this circular, we adopted the trigger time
from the first trigger (#887579), 2019-02-04 05:46:01 UT, to be consistent
with the T0 quoted in other circulars.
The BAT ground-calculated position is
RA, Dec = 351.491, 54.884 deg which is
   RA(J2000)  =  23h 25m 57.8s
   Dec(J2000) = +54d 53' 02.4"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 48%.

The mask-weighted light curve shows several overlapping pulses that starts
at ~T-7 s and ends at ~T+55 s. The main peak occurs at ~T+5 s.
T90 (15-350 keV) is 26.4 +- 7.5 sec (estimated error including systematics).

The time-averaged spectrum from T-6.93 to T+53.82 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.30 +- 0.04.  The fluence in the 15-150 keV band is 1.3 +- 0.03 x 10^-5 erg/cm2.
The 1-sec peak photon flux measured from T+4.55 sec in the 15-150 keV band
is 30.5 +- 0.9 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/887580/BA/
(Please note that this page shows the automatic analysis from the 2nd trigger #887580,
because BAT associated most of the data with this trigger ID. Thus, the T0 displayed in
the webpage is 4.995 sec later than the trigger time referenced in this circular.)

T. Ito, A. Yoshida, T. Sakamoto, V. Pal'shin, S. Sugita (AGU),
Y. Kawakubo (LSU), A. Tezuka, S. Matsukawa, H. Onozawa, H. Morita,
Y. Sone (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 GRB 190204A (Swift-BAT triggers #887579 and #887580:
Lien et al., GCN Circ. 23852
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 , Sakamoto et al., GCN Circ.23872
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 ;
MAXI/GSC detection: Oeda et al., GCN Circ. 23854
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 ;
AstroSat CZTI detection: Khanam et al., GCN Circ. 23856
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 ;
Konus-Wind observation: Kozlova et al., GCN Circ. 23869
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 )
triggered the CALET Gamma-ray Burst Monitor (CGBM)
at 05:46:05.075 UTC on 4 February 2019.
No real-time CGBM GCN notice was distributed about this trigger
because the real-time communication from the ISS was off (loss of signal).
The burst signal was seen by all CGBM detectors.

The burst light curve shows a single pulse which starts at T-7.7 sec,
peaks at 1.1 sec and ends at T+5.8 sec.
The T90 and T50 durations measured by the SGM data are
11.0 +- 2.0 sec and 2.2 +- 0.5 sec (40-1000 keV), respectively.
The ground processed light curve is available at

http://cgbm.calet.jp/cgbm_trigger/ground/1233294225/

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