GRB 180623A

K. L. Page (U Leicester), S. D. Barthelmy (GSFC), D. N. Burrows (PSU),
A. Deich (PSU), S. W. K Emery (UCL-MSSL), J.D. Gropp (PSU),
F. E. Marshall (NASA/GSFC) and D. M. Palmer (LANL) report on behalf of
the Neil Gehrels Swift Observatory Team:

At 16:41:56 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 180623A (trigger=844015).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 214.511, -60.294, which is 
   RA(J2000)  =  14h 18m 03s
   Dec(J2000) = -60d 17' 38"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows 4 large peaks and many
little peaks with a total duration of about 90 sec.  The peak count rate
was ~6500 counts/sec (15-350 keV), at ~61 sec after the trigger. 

The XRT began observing the field at 16:43:13.3 UT, 76.9 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source with an enhanced position: RA, Dec 214.5295,
-60.2539 which is equivalent to:
   RA(J2000)  = 14h 18m 07.08s
   Dec(J2000) = -60d 15' 13.9"
with an uncertainty of 2.1 arcseconds (radius, 90% containment). This
location is 148 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 does not constrain the column density. 

The initial flux in the 2.5 s image was 1.31e-08 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of nominal 150.000 seconds with the
White  filter starting 85 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 8'x8'
region for the list of  sources generated on-board covers 100% of the
XRT error circle. The typical 3-sigma upper limit has been about 19.6
mag. The list of  sources is typically complete to about 18 mag. No
correction has been made for  the large, but uncertain, extinction
expected. 

Although this source is close to the Galactic plane (lat = 0.83 degrees), 
its distance from the Galactic center (46 degrees), the presence 
of significant flux above 100 keV, and the complexity and overall
shape of the lightcurve are consistent with a GRB that is aligned
with the plane due to random coincidence. 

Burst Advocate for this burst is K. L. Page (klp5 AT leicester.ac.uk). 
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, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) 
report on behalf of the Swift-XRT team.

Using 3088 s of XRT Photon Counting mode data and 6 UVOT
images for GRB 180623A, 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 = 214.52879, -60.25352 which is equivalent
to:

RA (J2000): 14h 18m 6.91s
Dec (J2000): -60d 15' 12.7"

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.

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

We have analysed 7.7 ks of XRT data for GRB 180623A (Page et al. GCN
Circ. 22828
Loading...
 
 ), from 83 s to 18.2 ks after the  BAT trigger. The data
comprise 90 s in Windowed Timing (WT) mode with the remainder in Photon
Counting (PC) mode. The enhanced XRT position for this burst was given
by Evans et al. (GCN Circ. 22829
Loading...
 
 ).

The late-time light curve (from T0+4.5 ks) can be modelled with a
power-law decay with a decay index of alpha=1.72 (+/-0.14).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.73 (+0.20, -0.19). The
best-fitting absorption column is  6.4 (+/-0.7) x 10^22 cm^-2, in
excess of the Galactic value of 1.5 x 10^22 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 2.04 (+0.27, -0.25)
and a best-fitting absorption column of 6.6 (+/-0.9) x 10^22 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 9.0 x 10^-11 (2.9 x 10^-10) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     6.6 (+/-0.9) x 10^22 cm^-2
Galactic foreground: 1.5 x 10^22 cm^-2
Excess significance: 9.9 sigma
Photon index:	     2.04 (+0.27, -0.25)

If the light curve continues to decay with a power-law decay index of
1.72, the count rate at T+24 hours will be 2.3 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.0 x
10^-13 (6.5 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/00844015.

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

N. P. M. Kuin (UCL-MSSL) and K. L. Page (U. Leicester)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 180623A
86 s after the BAT trigger (Page et al., GCN Circ. 22828
Loading...
 
 ).
A source consistent with the XRT position (Evans et al. GCN Circ. 22829
Loading...
 
 )
is detected in the initial UVOT exposures.

The UVOT refined position is ra, deg = 214.5288,-60.2541 deg which is
RA = 14:18:06.9
Dec = -60:15:14.8
with an estimated uncertainty of 1".

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               86          236          150        >20.68
white              878          997          119         20.04 +/- 0.24
v                  629         6296          432        >19.2
b                18042        18207          162         19.86 +/- 0.28
u                  299        17732         2252        >21.6
w1                 678        16819         1318        >20.8
m2                 653         6501          432        >20.0
w2                 604         6092          432        >20.0

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 7.04 in the direction of the burst
(Schlegel et al. 1998).

S. D. Barthelmy (GSFC), J. R. Cummings (CPI),
H. A. Krimm (NSF/USRA), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), K. L. Page (U Leicester),
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-240 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 180623A (trigger #844015)
(Page et al., GCN Circ. 22828
Loading...
 
 ).  The BAT ground-calculated position is
RA, Dec = 214.528, -60.268 deg which is
  RA(J2000)  =  14h 18m 06.8s
  Dec(J2000) = -60d 16' 05.6"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 63%.

The mask-weighted light curve shows a multi-peaked structure that starts
at ~T-60 s and ends at ~T+115 s. The three main peaks occur at ~T0, ~T+25 s,
and ~T+60 s, respectively. T90 (15-350 keV) is 114.9 +- 6.8 sec (estimated
error including systematics). Note that the burst entered the BAT FOV around
~ T-90 s. Therefore, there might be additional burst emission beforehand.

The time-averaged spectrum from T-61.8 to T+114.1 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.45 +- 0.04.  The fluence in the 15-150 keV band is 1.2 +- 0.02 x 10^-5 erg/cm2.
The 1-sec peak photon flux measured from T+59.11 sec in the 15-150 keV band
is 5.6 +- 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/844015/BA/

N. P. M. Kuin (UCL-MSSL) and K. L. Page (U. Leicester)
report on behalf of the Swift/UVOT team:

The Source reported in our previous GCN Circ. No 22831 is
in fact a source present in the DSS survey. The extinction
of this bursts is very high, so there is no afterglow seen.
Our apologies for this error.

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 180623A
(Swift detection: Page et al., GCN Circ. 22828
Loading...
 
 ;
Swift-BAT refined analysis: Barthelmy et al., GCN Circ. 22833
Loading...
 
 )
triggered Konus-Wind at T0=60141.775 s UT (16:42:21.775).

The burst light curve shows a multipeaked structure
started at ~T0-69 s with a total duration of ~114 s.
The emission is seen up to ~2 MeV.

As observed by Konus-Wind, the burst
had a fluence of 3.15(-0.24,+0.28)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+2.208 s,
of 2.94(-0.98,+1.01)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+49.408 s)
is best fit in the 20 keV - 4 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -1.03(-0.16,+0.17)
and Ep = 233(-33,+48) keV (chi2 = 63/70 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.1
(chi2 = 61/69 dof).

The spectrum near the maximum count rate
(measured from T0+0.256 to T0+8.448 s)
is best fit in the 20 keV - 4 MeV range
by a power law with exponential cutoff model
with  alpha = -0.78(-0.17,+0.19)
and Ep = 390(-63,+91) keV (chi2 = 59/70 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.3
(chi2 = 59/69 dof).

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB180623_T60141/

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