GRB 181123B

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

At 05:33:03 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 181123B (trigger=873186).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 184.348, +14.589 which is 
   RA(J2000) = 12h 17m 23s
   Dec(J2000) = +14d 35' 22"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single peak
structure with a duration of about 0.4 sec.  The peak count rate
was ~5000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 05:34:23.3 UT, 80.2 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 184.36663, 14.59889 which is equivalent
to:
   RA(J2000)  = 12h 17m 27.99s
   Dec(J2000) = +14d 35' 56.0"
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This
location is 74 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 83 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
0.03. 

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: http://www.swift.psu.edu/too.html.)

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

Using  promptly downlinked XRT event data for GRB 181123B, we find an
enhanced XRT position of the afterglow: RA, Dec: 184.3670, 14.5979
which is equivalent to:
   RA (J2000)  = 12 17 28.08
   Dec (J2000) = +14 35 52.5
with an uncertainty of 2.1 arcseconds (radius, 90% confidence).
Analysis of the promptly available data is online at
http://www.swift.ac.uk/sper/873186.

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.

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

Using 987 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 181123B, 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 = 184.36687, +14.59789 which is equivalent
to:

RA (J2000): 12h 17m 28.05s
Dec (J2000): +14d 35' 52.4"

with an uncertainty of 1.8 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.

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

We have analysed 6.3 ks of XRT data for GRB 181123B (Lien et al. GCN
Circ. 23432
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 ), from 95 s to 16.0 ks after the  BAT trigger. The data are
entirely in Photon Counting (PC) mode. The enhanced XRT position for
this burst was given by Osborne et al. (GCN Circ. 23433
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 ).

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.31 (+0.15, -0.14).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.99 (+0.30, -0.20). The
best-fitting absorption column is  3.9 (+6.4, -0.8) x 10^20 cm^-2,
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 3.2 x 10^-11 (3.6 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3.9 (+6.4, -0.8) x 10^20 cm^-2
Galactic foreground: 3.1 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.99 (+0.30, -0.20)

If the light curve continues to decay with a power-law decay index of
1.31, the count rate at T+24 hours will be 1.9 x 10^-4 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.1 x
10^-15 (6.7 x 10^-15) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00873186.

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

GRB 181123B: Swift/UVOT Upper Limits

S. R. Oates (U.Warwick) 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 181123B
84 s after the BAT trigger (Lien et al., GCN Circ. 23432
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 ).
No optical afterglow consistent with the XRT position
(Osborne et al. GCN Circ. 23434
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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            84          233          147         >20.3
u_FC               296          546          246         >19.5
white               84         6529          727         >21.0
v                  626        10922         1228         >19.8
b                  551         6324          432         >20.1
u                  296         6119          659         >20.1
w1                4278        12566         1113         >20.2
m2                5509        11827         1082         >20.5
w2                5100         6734          393         >19.8

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.03 in the direction of the burst
(Schlegel et al. 1998).

W. Fong (Northwestern Univ.), N. R. Tanvir (U. Leicester) and A. J. Levan (U. Warwick) report on behalf of a larger collaboration:

"We observed the location of the short-duration GRB 181123B (Lien et al., GCN 23432
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 ) with the Gemini Multi-Object Spectrograph (GMOS) mounted on the Gemini-North 8-meter telescope. We obtained 18x90-sec each in the i-band at a mid-time of 2018 November 23.618 UT (9.2 hr post-burst). The observations have an airmass range of 1.4-1.9, 0.9��� seeing, and were taken in thick, variable clouds. We detect a faint source consistent with the UVOT-enhanced XRT position (Evans et al., GCN 23433
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 ; Osborne et al., GCN 23434
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 ) at the position:

RA(J2000) = 12:17:27.95
Dec(J2000) = +14:35:52.5
+/- 0.05" in each coordinate

The source has a preliminary magnitude of i~23.32 +/- 0.25 AB mag, not corrected for Galactic extinction. Both astrometry and photometry are calibrated to SDSS. The source appears to be marginally extended; however, at present it is too weak of a detection to make a strong conclusion.

Further observations are planned. We thank the Gemini staff, and in particular observers Julia Scharwaechter and Michael Hoenig, for their assistance with these observations."

K. Paterson and W. Fong (Northwestern) report:

"We observed the field of the short-duration GRB 181123B (Lien et al., GCN 23432
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 ) with the Multi-Object Spectrometer For Infra-Red Exploration (MOSFIRE) mounted on the 10-m Keck I telescope, starting on 2018 November 23 at 14:43:18 UT, 9.2 hours post-burst. We obtained 2100-sec of observations in the J-band in 1.0" seeing.

In our combined stack, we identify a near-IR source consistent with the X-ray position of the afterglow (Evans et al., GCN 23433
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 ; Osborne et al., GCN 23434
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 ) and the Gemini optical source (Fong et al., GCN 23439
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 ). Calibrated to 2MASS, we estimate a preliminary brightness of J(AB) = 22.94 +/- 0.19 mag. At this point it is not possible to tell whether this source is point-like or extended.

We thank the Keck Observatory staff, in particular Arina, Joel, Alessandro, Josh and Randy, for their assistance with planning and executing these observations."

J. P. Norris (BSU), S. D. Barthelmy (GSFC), A. Y. Lien (GSFC/UMBC)
report:

We report the spectral lag analysis and the search for extended emission
for GRB 181123B (Lien et al., GCN Circ. 23432
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 ).

Using the 8-ms binned light curve, the spectral lag of the short pulse 
is 6 (+11, -11) ms for the 100-350 keV to 25-50 keV bands, and 10 (+14, -11) ms
for the 50-100 keV to 15-25 keV bands.  These lag values are consistent with 
a short GRB.

The Bayesian block analysis using the mask-tagged light curves suggests that 
there may be a marginal (~ 3 sigma) extended emission that lasts until ~T+60 s.

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

R. Podesta, F. Podesta, C. Lopez, C.Francile
Observatorio Astronomico Felix Aguilar (OAFA)

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

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

D. Buckley,
South African Astronomical Observatory

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

O. Gres, N.M. Budnev, Yu.Ishmuhametova
Applied Physics Institute of Irkutsk State University

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


MASTER-OAFA robotic telescope (MASTER-Net: http://observ.pereplet.ru,
Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in
Argentina (OAFA observatory of San Juan National University) was pointed 
to the  GRB181123B (Lien et al.,GCN 23432)  at 2018-11-23 
08:15:00 UT. On our 4-th (180s exposure)  set we  not found  optical 
transient within Swift error-box (ra=184.367 dec=14.5975 r=0.05) brighter 
than 17.0.


The galactic latitude b = -60 deg., longitude l = 98 deg.
The observations made on zenit distance = 32 deg.The moon ( 1 % bright
part) below the horizon (The altitude of the Moon is -44 deg. ).
The sun  altitude  is -50.0 deg.
The object can be observed till 2018-10-10 09:24:14


MASTER-Kislovodsk robotic telescope (MASTER-Net: 
http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, 
vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station 
of Pulkovo observatory) was pointed to the  GRB181123B (Lien et al., 
GCN 23432
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 ) 63194 sec after 
notice time and 63194 sec after trigger time at 2018-11-23 23:06:17 UT. On 
our 10-th (180s exposure)  set , obtained 72767 sec after tigger time at 
2018-11-24 01:45:51 UT, we  not found  optical transient within Swift 
error-box (ra=184.367 dec=14.5975 r=0.05) brighter than 18.1.

The galactic latitude b = 75 deg., longitude l = 272 deg.
The observations made on zenit distance = 53 deg.The moon (99 % bright 
part) is 34 deg. above the horizon. The distance between  moon and  object 
is 106
The sun  altitude  is -26.2 deg.
The object can be observed till sunrise at 2018-11-24 04:14:26

Q. B. Yi, C. K. Li, X. B. Li, G. Li, J. Y. Liao, S. L. Xiong, 
C. Z. Liu, X. F. Li, Z. W. Li, Z. Chang, X. F. Lu, J. L. Zhao,
A. M. Zhang, Y. F. Zhang, C. L. Zou (IHEP), Y. J. Jin, 
Z. Zhang (THU), T. P. Li (IHEP/THU), F. J. Lu, L. M. Song, 
H. Y. Wang, M. Wu, Y. P. Xu, S. N. Zhang (IHEP), 
report on behalf of the Insight-HXMT team: 

At 2018-11-23T05:33:03.09 (T0), the Insight-HXMT/HE detected 
GRB 181123B (trigger ID: HEB181123231) in a routine search of the data,
which was also detected by the SWIFT/BAT (J. P. Norris et al. 2018, GCN 23443
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 )

The Insight-HXMT/HE light curve mainly consists of a 
pulse with a duration (T90) of 0.23 s measured from T0+0.16 s. 
The 50-ms peak rate, measured from T0+0.28 s, is 5091.4 cnts/s. 
The total counts from this burst is 2060.5 counts. 
URL_LC:  http://www.hxmt.org/images/GRB/HEB181123231_lc.jpg 

All measurements above are made with the CsI detectors operating in the 
regular mode with the energy range of about 80-800 keV (record energy). 
Only gamma-rays with energy greater than about 200 keV can penetrate 
the spacecraft and leave signals in the CsI detectors installed inside 
of the telescope. 

Insight-HXMT is the first Chinese space X-ray telescope, which was 
fundedjointly by the China National Space Administration (CNSA) and 
the Chinese Academy of Sciences (CAS). 
More information could be found at: http://www.hxmt.org.

K. Paterson, W. Fong (Northwestern), K. De (Caltech), K. Alexander, D. Coppejans, A. Hajela, R. Margutti, and G. Terreran (Northwestern) report:

"We observed the field of the short-duration GRB 181123B (Lien et al., GCN 23432
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 ) with the Multi-Object Spectrometer For Infra-Red Exploration (MOSFIRE) mounted on the 10-m Keck I telescope, starting on 2018 November 26 at 14:57:43 UT, 1.94 days after our previous MOSFIRE observations (Paterson et al. GCN 23440
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 ) and 3.38 days after the burst. We obtained 2142-sec of observations in the J-band in 0.7" seeing and clear conditions.

We detect a NIR source that is clearly extended, with a brightness and position consistent with our previous observations (Paterson et al. GCN 23440
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 ) and with the Gemini optical source position (Fong et al. GCN 23439
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 ). Image subtraction between our MOSFIRE observations also yields no residuals in or around the XRT position (Evans et al. GCN 23433
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 ; Osborne et al. GCN 23434
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 ) or the position of the optical source. Given the lack of residuals and the extended nature of the NIR source, we propose this as the host galaxy of GRB 181123B. We also place a 3-sigma upper limit of J>23.3 mag (AB, for epoch 1 at 9.2 hr post-burst) on afterglow emission from GRB 181123B.

We thank the Keck staff for their assistance with these ToO observations."

G. E. Anderson (Curtin), M. E. Bell (UTS), J. Stevens (CASS), P. J. Hancock (Curtin),
J. C. A. Miller-Jones (Curtin), A. Bahramian (Curtin), K. W. Bannister (CASS),
A. J, van der Horst (GWU), S. D. Ryder (Macquarie), J-P. Macquart (Curtin),
R. M. Plotkin (Curtin), A. Rowlinson (UvA)

We used the Australia Telescope Compact Array (ATCA) rapid-response mode
to perform a triggered radio observation of the short GRB 181123B. The ATCA
responded to the Swift-BAT detection (Lien et al., GCN 23432
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 ), automatically
scheduling observations to begin on 2018 Nov 23.753 UT for 8.5 hours
(12.5 hours post-burst), when the GRB had risen above the horizon. No radio
source was detected at the XRT/optical position (Evans et al., GCN 23433
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 ,
Fong et al., GCN 23439
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 ), with 3 sigma upper-limits of 66 microJy and 69 microJy
at 5 and 9 GHz, respectively.

We thank the ATCA and CSIRO Astronomy and Space Science (CASS) staff for
supporting this new mode of operation.