GRB 190821A

A. D'Ai (INAF-IASFPA), E. Ambrosi (INAF-IASFPA), V. D'Elia (SSDC),
J.D. Gropp (PSU), J. A. Kennea (PSU), N. J. Klingler (PSU),
H. A. Krimm (NSF), S. J. LaPorte (PSU), A. Y. Lien (GSFC/UMBC),
F. E. Marshall (NASA/GSFC), M. J. Moss (GWU),
K. L. Page (U Leicester), D. M. Palmer (LANL), B. Sbarufatti (PSU),
K. K. Simpson (PSU) and A. Tohuvavohu (PSU) report on behalf of the
Neil Gehrels Swift Observatory Team:

At 17:10:03 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 190821A (trigger=921722).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 250.077, -34.022 which is 
   RA(J2000) = 16h 40m 18s
   Dec(J2000) = -34d 01' 16"
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 ~2200 counts/sec (15-350 keV), at ~30 sec after the trigger. 

The XRT began observing the field at 17:11:21.8 UT, 78.0 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 250.05464, -34.00719 which
is equivalent to:
   RA(J2000)  = 16h 40m 13.11s
   Dec(J2000) = -34d 00' 25.9"
with an uncertainty of 3.6 arcseconds (radius, 90% containment). This
location is 85 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 (3.35 x
10^21 cm^-2, Willingale et al. 2013), with an excess column of 3.2
(+2.68/-2.37) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 2.95e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 88 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. Because of the density of catalogued stars, further
analysis is required to report an upper limit for any afterglow in the
sub-image. The 8'x8' region for the list of sources generated on-board covers
100% of the XRT error circle. Because of the density of catalogued stars,
further analysis is required to report an upper limit for any afterglow in the
region. No correction has been made for the expected extinction corresponding
to E(B-V) of 0.54. 

Burst Advocate for this burst is A. D'Ai (antonino.dai AT inaf.it). 
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/)

Klotz A., Noysena.K., Atteia J.L. (CNRS-OMP-IRAP),
Boer, M., Eymar, L. (CNRS-ARTEMIS),
Gendre B. (UWA - Univ. Western Australia)
Peyrot, A., Teng J.P., Thierry P. (Les Makes observatory)
report:

We imaged the field of GRB 190821A detected by SWIFT
(trigger 921722) with the T60 tele-operated telescope (D=60cm)
located at Les Makes Observatory, Reunion Island, France.

The observations started 790s after the GRB trigger.
On the first image of 120s (Clear filter) we detect the
optical afterglow compatible with the position of XRT
(Lien et al. GCNC 25427).

start�� end������ R
(sec) (sec)
790���� 910���� 18.4 +/- 0.2

Further images are comming.

Magnitudes were estimated with the nearby NOMAD1 stars
and are not corrected for galactic dust extinction.

V. Lipunov, F.Balakin, E. Gorbovskoy, V. Kornilov, N.Tyurina, 
P.Balanutsa,A.Kuznetsov, F.Balakin, V. Vladimirov, D. Vlasenko,
I. Gorbunov,D.Zimnukhov, V.Senik, A.Chasovnikov, A.Pozdnyakov, 
A.Chasovnikov, 
V.Topolev, D.Kuvshinov(Lomonosov Moscow State University, SAI, Physics 
Department),
R. Rebolo, M. Serra (The Instituto de Astrofisica de Canarias IAC),
R. Podesta, C.Lopez, F. Podesta, C.Francile (Observatorio Astronomico Felix 
Aguilar OAFA),
H. Levato (Instituto de Ciencias Astronomicas, de la Tierra y del Espacio 
ICATE),
D. Buckley (South African Astronomical Observatory SAAO),
O. Gress, N.M. Budnev, O.Ershova (Irkutsk State University, API),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo 
Observatory),
V. Yurkov, A. Gabovich, Yu. Sergienko (Blagoveschensk Educational State 
University)

There is known star at Swift XRT position (GCN 25427
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 , GCN 25431
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 ).
Its brightnes not changes during 1 hour, after 41 sec after trigger in 
MASTER images (GCN  25429
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 ).
This message may be cited.

B. Mailyan, S. Lesage  and C. Meegan (all UAH)
report on behalf of the Fermi GBM Team:

"At 17:10:34.08 UT on 21 August 2019, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 190821A (trigger 588100239/ 190821716),
which was also detected by the Swift/BAT (D'Ai et al. 2019, GCN 25427
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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 85 degrees.

The GBM lightcurve shows an initial bright pulse followed
by longer duration emission containing multiple peaks.
with a duration (T90) of about 60 s (50-300 keV).
The time-averaged spectrum from T0-4 s to T0+34 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -1.7 +/- 0.15 and
the cutoff energy, parameterized as Epeak, is 29 +/- 6 keV.

The event fluence (10-1000 keV) in this time interval is
(2.54 +/- 0.17)E-06 erg/cm^2. The 1-sec peak photon flux
measured starting from T-0.128 s in the 10-1000 keV band
is 4.9 +/- 0.25 ph/s/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog:
https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html

For Fermi GBM data and info, please visit the official Fermi GBM Support
Page:
https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"

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

Using 1074 s of XRT Photon Counting mode data and 3 UVOT
images for GRB 190821A, 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 = 250.05481, -34.00711 which is equivalent
to:

RA (J2000): 16h 40m 13.15s
Dec (J2000): -34d 00' 25.6"

with an uncertainty of 1.6 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. D. Gropp (PSU), A. Tohuvavohu (PSU), J.A. Kennea (PSU), J.P. Osborne
(U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U.
Leicester), A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB), M.G.
Bernardini (INAF-OAB) and A. D'Ai report on behalf of the Swift-XRT
team:

We have analysed 6.7 ks of XRT data for GRB 190821A (D'Ai et al. GCN
Circ. 25427
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 ), from 84 s to 33.9 ks after the  BAT trigger. The data
comprise 290 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Goad et al. (GCN Circ. 25436
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 ).

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=7.82 (+0.18, -0.87). At T+140 s  the decay
flattens to an alpha of -0.4 (+/-0.5) before breaking again at T+1047 s
to a final decay with index alpha=1.06 (+0.17, -0.16).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.75 (+0.18, -0.11). The
best-fitting absorption column is  consistent with the Galactic value
of 3.3 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed
(unabsorbed) 0.3-10 keV flux conversion factor deduced from this
spectrum  is 4.4 x 10^-11 (5.9 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3.3 (+/-1.0) x 10^21 cm^-2
Galactic foreground: 3.3 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.75 (+0.18, -0.11)

If the light curve continues to decay with a power-law decay index of
1.06, the count rate at T+24 hours will be 0.015 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.8 x
10^-13 (9.0 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/00921722.

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

F.Balakin, V. Lipunov, E. Gorbovskoy, V. Kornilov, N.Tyurina,
P.Balanutsa,A.Kuznetsov, F.Balakin, V. Vladimirov, D. Vlasenko,
I. Gorbunov,D.Zimnukhov, V.Senik, A.Chasovnikov, A.Pozdnyakov, A.Chasovnikov,
V.Topolev, D.Kuvshinov(Lomonosov Moscow State University, SAI, Physics
Department),
R. Rebolo, M. Serra (The Instituto de Astrofisica de Canarias IAC),
R. Podesta, C.Lopez, F. Podesta, C.Francile (Observatorio Astronomico Felix
Aguilar OAFA),
H. Levato (Instituto de Ciencias Astronomicas, de la Tierra y del Espacio
ICATE),
D. Buckley (South African Astronomical Observatory SAAO),
O. Gress, N.M. Budnev, O.Ershova (Irkutsk State University, API),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
V. Yurkov, A. Gabovich, Yu. Sergienko (Blagoveschensk Educational State
University)


MASTER-SAAO very wide field cameras (d=82 mm, FOV = 2x384 sq. degree) 
syncronously observed GRB190821A (D'Ai et al. GCN 25427
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 )  position before, 
during and after trigger time. We do not see OT at Swift XRT (Gropp et al. 
GCN 25444
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 ) position up to 12 mag.   The syncronous observation movie is 
avalable here:

http://master.sai.msu.ru/static/MASTER_SAAO_GRB190822A.gif

MASTER-SAAO robotic telescope  (Global MASTER-Net: 
http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, 
vol. 2010, 30L)  located in South Africa (South African Astronomical 
Observatory) was pointed to the Swift GRB190821A  errorbox  8 sec after 
notice time and 41 sec after trigger time at 2019-08-21 17:10:44 UT, with 
upper limit up to  18.4 mag (Lipunov et al. GCN 25429
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 ; GCN 25433
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 ). 
Observations 
started at twilight.  We alse do not see OT at Swift XRT.  The 
observations began at zenit distance =  3 deg. The sun  altitude  is -12.4 
deg.

Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=1111516



This message may be cited.

GRB 190821A: Swift/UVOT Upper Limits

K. K. Simpson (PSU) and A. D'Ai (INAF-IASFPA)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 190821A
89 s after the BAT trigger (D'Ai et al., GCN Circ. 25427
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 ).
No optical afterglow consistent with the XRT position
(Goad et al. GCN Circ. 25436
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 )
is detected in the initial UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first
finding chart (FC) exposure and subsequent exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white_FC            89          239          147         >19.1
white               89         5595          344         >19.5
v                 5806         6006          197         >18.3
b                 5191         5390          197         >19.9
u                  303        11409          336         >19.6
w1                9373         9551          175         >18.9
m2                6011         6164          151         >19.7
w2                5602         5801          197         >20.2

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.53 in the direction of the burst
(Schlegel et al. 1998).

S. D. Barthelmy (GSFC), J. R. Cummings (CPI),
A. D'Ai (INAF-IASFPA), H. A. Krimm (NSF),
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+963 sec from the recent telemetry
downlink,
we report further analysis of BAT GRB 190821A (trigger #921722)
(D'Ai et al., GCN Circ. 25427
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 ).  The BAT ground-calculated position is
RA, Dec = 250.070, -34.027 deg which is
   RA(J2000)  =  16h 40m 16.9s
   Dec(J2000) = -34d 01' 35.5"
with an uncertainty of 1.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 83%.

The mask-weighted light curve shows a multi-peaked structure that starts
at ~T-3 s and ends at ~T+60 s. The highest peak occurs at ~T+30 s.
T90 (15-350 keV) is 57.1 +- 2.6 sec (estimated error including systematics).

The time-averaged spectrum from T-3.3 to T+59.5 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.03 +- 0.10.  The fluence in the 15-150 keV band is 2.4 +- 0.1 x 10^-6
erg/cm2.
The 1-sec peak photon flux measured from T+29.98 sec in the 15-150 keV band
is 2.8 +- 0.3 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/921722/BA/