GRB 180823A

B. Sbarufatti (PSU), H. A. Krimm (NSF/USRA),
F. E. Marshall (NASA/GSFC) and A. Tohuvavohu (PSU) report on behalf of
the Neil Gehrels Swift Observatory Team:

At 19:04:32 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 180823A (trigger=855434).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 210.349, +14.884 which is 
   RA(J2000) = 14h 01m 24s
   Dec(J2000) = +14d 53' 03"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve, which is superimposed 
on a declining background, shows a double-peaked structure with a 
duration of about 40 sec.  The peak count rate was ~2000 counts/sec 
(15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 19:06:02.2 UT, 89.2 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 210.35630, 14.89029 which
is equivalent to:
   RA(J2000)  = 14h 01m 25.51s
   Dec(J2000) = +14d 53' 25.0"
with an uncertainty of 5.4 arcseconds (radius, 90% containment). This
location is 34 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. 

The initial flux in the 2.5 s image was 3.10e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of  37 seconds with the White
filter  starting 379 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 is expected to be  about 18.5 mag. No correction
has been made  for the expected extinction corresponding to E(B-V) of
0.02. 

Burst Advocate for this burst is B. Sbarufatti (bxs60 AT 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/too.html.)

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

Using 2364 s of XRT Photon Counting mode data and 7 UVOT
images for GRB 180823A, 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 = 210.35583, +14.89245 which is equivalent
to:

RA (J2000): 14h 01m 25.40s
Dec (J2000): +14d 53' 32.8"

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.

A. Tohuvavohu (PSU), S. J. LaPorte (PSU), S.L. Gibson (U. Leicester),
Z. Liu (NAOC / U. Leicester), J.P. Osborne (U. Leicester), P. D'Avanzo
(INAF-OAB), V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), J.A. Kennea (PSU)
and B. Sbarufatti report on behalf of the Swift-XRT team:

We have analysed 7.7 ks of XRT data for GRB 180823A (Sbarufatti et al.
GCN Circ. 23169
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 ), from 331 s to 39.4 ks after the  BAT trigger. The
data comprise 46 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. 23170
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 ).

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.00 (+/-0.04).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.99 (+0.19, -0.18). The
best-fitting absorption column is  1.2 (+/-0.5) x 10^21 cm^-2, in
excess of the Galactic value of 1.2 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 3.3 x 10^-11 (4.2 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.2 (+/-0.5) x 10^21 cm^-2
Galactic foreground: 1.2 x 10^20 cm^-2
Excess significance: 3.7 sigma
Photon index:	     1.99 (+0.19, -0.18)

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 0.013 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.3 x
10^-13 (5.3 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/00855434.

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

Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William
H. Lee (UNAM), Michael G. Richer (UNAM), Ori Fox (STScI), J. Xavier
Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (UVI), Eleonora
Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC), Jes��s
Gonz��lez (UNAM), Carlos Rom��n-Z����iga (UNAM), Harvey Moseley (GSFC), John
Capone (UMD), V. Zach Golkhou (U. Wash.), and Vicki Toy (UMD) report:

We observed the field of GRB 180823A (Sbarufatti, et al., GCN 23169
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 ) with
the Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on
the 1.5m Harold Johnson Telescope at the Observatorio Astron��mico Nacional
on Sierra San Pedro M��rtir from 2018/08 24.14 to 2018/08 24.19 UTC (8.40 to
9.45 hours after the BAT trigger), obtaining a total of 0.40 hours exposure
in the r and i bands and 0.29 hours exposure in the Z, Y, J, and H bands.

For a source within the Swift-XRT error circle (Evans, et al., GCN 23170
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 ),
in comparison with the SDSS DR9 and 2MASS catalogs, we obtain the following
upper limits (3-sigma):

 r > 22.20
 i > 22.05
 Z > 20.84
 Y > 19.72
 J > 20.45
 H > 19.12

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.

We thank the staff of the Observatorio Astron��mico Nacional in San Pedro
M��rtir.

GRB 180823A: Swift/UVOT Upper Limits

S. Sebzda (PSU) and B. Sbarufatti (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 180823A
381 s after the BAT trigger (Sbarufatti et al., GCN Circ. 23169
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 ).
No optical afterglow consistent with the XRT position
(Goad et al. GCN Circ. 23170
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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 initial exposures are:

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

white              381          417           36         >19.1
white              381         4476          380         >20.9
v                 4686        10356          927         >19.2
b                 4071         4271          197         >19.7
u                 3866         4066          197         >19.8
m2               10361        10803          435         >19.8
w2                4482         4681          197         >20.0

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.02 in the direction of the burst
(Schlegel et al. 1998).

A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (GSFC),  J. R. Cummings (CPI),
H. A. Krimm (NSF/USRA), C. B. Markwardt (GSFC), D. M. Palmer (LANL),
T. Sakamoto (AGU), B. Sbarufatti (PSU), M. Stamatikos (OSU),
T. N. Ukwatta (LANL) (i.e. the Swift-BAT team):

Using the data set from T-43 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 180823A (trigger #855434)
(Sbarufatti, et al., GCN Circ. 23169
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 ).  The BAT ground-calculated position is
RA, Dec = 210.358, 14.901 deg which is 
  RA(J2000)  =  14h 01m 25.9s 
  Dec(J2000) = +14d 54' 03.2" 
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 92%.

The available data starts as the burst is rising, but it appears that it includes the
entire burst.   The mask-weighted light curve shows a double-peaked structure, 
starting at ~T-43 seconds, with comparably sized peaks at ~T+5 and ~T+20 sec,
and returning to near background by T+70 seconds, with a fainter tail out past
T+100 seconds.  A spacecraft slew took the burst location out of the BAT field
of view around T+450 seconds. T90 (15-350 keV) is 80.3 +- 6.9 sec (estimated 
error including systematics).

The time-averaged spectrum from T-37.5 to T+72.0 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.58 +- 0.05.  The fluence in the 15-150 keV band is 7.8 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+18.33 sec in the 15-150 keV band
is 2.3 +- 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/855434/BA/