GRB 191123A

A. Tohuvavohu (U Toronto), J.D. Gropp (PSU), A. Y. Lien (GSFC/UMBC),
K. L. Page (U Leicester) and B. Sbarufatti (PSU) report on behalf of
the Neil Gehrels Swift Observatory Team:

At 10:38:44 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 191123A (trigger=939079).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 215.261, +22.842 which is 
   RA(J2000) = 14h 21m 03s
   Dec(J2000) = +22d 50' 30"
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 150 sec.  The peak count rate
was ~1500 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 10:39:54.1 UT, 69.8 seconds after
the BAT trigger. The position determined from promptly downlinked data
differs significantly from the on-board position, suggesting that the
XRT may have centroided on a cosmic ray; the initial XRT position
notice should be treated with caution. Using promptly downlinked data
we find an uncatalogued X-ray source with an enhanced position: RA, Dec
215.2619, 22.8600 which is equivalent to:
   RA(J2000)  = 14h 21m 02.87s
   Dec(J2000) = +22d 51' 36.0"
with an uncertainty of 2.1 arcseconds (radius, 90% containment). This
location is 64 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 (3.01 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 2.9
(+2.28/-2.01) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 78 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	14:21:02.87 = 215.26196
  DEC(J2000) = +22:51:36.3  =  22.86008
with a 90%-confidence error radius of about 0.75 arc sec. This position is 9.7
arc sec. from the center of the XRT error circle. The estimated magnitude is
18.13 with a 1-sigma error of about  0.15. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.04. 

Burst Advocate for this burst is A. Tohuvavohu (aaronb AT swift.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/)

N. P. M. Kuin (UCL-MSSL) and A. Tohuvavohu (U Toronto)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of
GRB 191123A  78 s after the BAT trigger (Tohuvavohu et al.,
GCN Circ. 26279
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 ). A candidate optical afterglow was
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         78          228          147     18.26+-0.07
u_FC            290          540          246    >19.89
white           869         1019          147     19.28+-0.13

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).

I observed the field of GRB 191123A (Tohuvavohu et al., GCN Circular 26279
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 )
with remote telescope T21 (0.43-m f/6.8 reflector + CCD + f/4.5 focal
reducer) of iTelescope.Net in New Mexico Observatory. Two images with a
luminance filter and with 120 seconds exposure time were obtained on
2019-11-23. Average time of images: 12:13:54 UT (5710 seconds after
trigger; Binx1) and 12:16:38 UT (5874 seconds after trigger; Binx2). I did
not detect any optical transients (magnitude limit of about 19.0 G from
Gaia DR2 catalogue).

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

Using 1802 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 191123A, 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 = 215.26186, +22.85991 which is equivalent
to:

RA (J2000): 14h 21m 2.85s
Dec (J2000): +22d 51' 35.7"

with an uncertainty of 1.7 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.

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

We have analysed 6.2 ks of XRT data for GRB 191123A (Tohuvavohu et al.
GCN Circ. 26279
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 ), from 76 s to 18.5 ks after the  BAT trigger. The data
comprise 540 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. 26284
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 ).

The late-time light curve (from T0+5.6 ks) can be modelled with a
power-law decay with a decay index of alpha=1.00 (+/-0.15).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.52 (+/-0.05). The
best-fitting absorption column is  6.7 (+1.6, -1.5) x 10^20 cm^-2, in
excess of the Galactic value of 3.0 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.98 (+0.12, -0.11)
and a best-fitting absorption column of 4.8 (+2.6, -1.8) x 10^20 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.3 x 10^-11 (3.7 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     4.8 (+2.6, -1.8) x 10^20 cm^-2
Galactic foreground: 3.0 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.98 (+0.12, -0.11)

If the light curve continues to decay with a power-law decay index of
1.00, the count rate at T+24 hours will be 0.022 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 7.2 x
10^-13 (8.1 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/00939079.

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

S. Laha (GSFC/UMBC), S. D. Barthelmy (GSFC), J. R. Cummings (CPI),
H. A. Krimm (NSF), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU),  
A. Tohuvavohu (U Toronto), 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 191123A (trigger #939079)
(Tohuvavohu, et al., GCN Circ. 26279
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 ).  The BAT ground-calculated position is
RA, Dec = 215.289, 22.823 deg which is 
  RA(J2000)  =  14h 21m 09.3s 
  Dec(J2000) = +22d 49' 23.5" 
with an uncertainty of 2.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 85%.

The mask-weighted light curve shows a pair of pulses, each with some sub-
structure.  The first starts at ~T-10 sec, peaks at T+0 and decays by T+40 sec.
The second pulse starts at T+110 sec, peaks soon afterward and decays by 
T+180 sec.  T90 (15-350 keV) is 275.1 +- 102.4 sec (estimated error including 
systematics).

The time-averaged spectrum from -2.1 to 288.1 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.67 +- 0.25.  The fluence in the 15-150 keV band is 1.2 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+111.77 sec in the 15-150 keV band
is 1.2 +- 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/939079/BA/

N. P. M. Kuin (UCL-MSSL) and A. Tohuvavohu (U. Toronto)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 191123A
78 s after the BAT trigger (Tohuvavohu et al., GCN Circ. 26279
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 ).
A source consistent with the XRT position (Goad et al. GCN Circ. 26284
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 )
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  14:21:02.88 = 215.26200 (deg.)
    Dec (J2000) = +22:51:36.1  =  22.86002 (deg.)
with an estimated uncertainty of 0.44 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               78          228          147         18.25 +/- 0.05
v                  620         2111          175         18.28 +/- 0.19
b                  546         1168           58         19.18 +/- 0.25
u                  290         6376          501        >20.4
w1                 669         6171          372        >19.9
m2                1074         5966          216        >19.8
w2                 595        12186          944        >20.9

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).