GRB 180930A

E. Mazaeva (IKI), A. Kusakin (FAPHI), A. Pozanenko (IKI), I. Reva 
(FAPHI),  A. Volnova (IKI), M. Krugov (FAPHI) report on behalf of larger 
GRB follow-up collaboration:

We observed the field of GRB 180930A (Tohuvavohu et al., GCN  23279
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 ) 
with Zeiss-1000 1-m telescope of Tien Shan Astronomical Observatory 
starting on September 30 (UT) 21:55:14, obtaining a total of 31*120 s 
exposure in the Rc-band. Within enhanced XRT position (Osborne et al., 
GCN 23282
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 )  we do not detect any object. Preliminary photometry of the 
field is following.

Date       UT start t-T0    Filter Exp.   OT    Err. UL
                     (mid, days) (s)

2018-09-30 21:55:14 0.41030 R      31*120 n/d   n/d 20.1

The photometry is based on several nearby USNO-B1.0 stars.

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

Using the data set from T-240 to T+962 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 180930A (trigger #864584)
(Tohuvavohu, et al., GCN Circ. 23279
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 ).  The BAT ground-calculated position is
RA, Dec = 76.894, -25.124 deg which is 
  RA(J2000)  =  05h 07m 34.6s 
  Dec(J2000) = -25d 07' 25.6" 
with an uncertainty of 2.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 87%.

The mask-weighted light curve shows a single episode of weak emission from 
T-4 sec to T+4 sec with several peaks. T90 (15-350 keV) is 6.80 +- 0.95 sec 
(estimated error including systematics).

The time-averaged spectrum from T-3.24 to T+4.20 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.86 +- 0.28.  The fluence in the 15-150 keV band is 2.1 +- 0.4 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+0.14 sec in the 15-150 keV band
is 0.9 +- 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/864584/BA/

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

We have analysed 2.6 ks of XRT data for GRB 180930A (Tohuvavohu et al.
GCN Circ. 23279
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 ), from 212 s to 6.0 ks after the  BAT trigger. The data
comprise 47 s in Windowed Timing (WT) mode with the remainder in Photon
Counting (PC) mode. The enhanced XRT position for this burst was given
by Osborne et al. (GCN Circ. 23280
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 ).

The light curve can be modelled with a power-law decay with a decay
index of alpha=2.04 (+/-0.09).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.01 (+/-0.15). The
best-fitting absorption column is  7.2 (+3.7, -3.3) x 10^20 cm^-2, in
excess of the Galactic value of 2.1 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 3.3 x 10^-11 (3.9 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     7.2 (+3.7, -3.3) x 10^20 cm^-2
Galactic foreground: 2.1 x 10^20 cm^-2
Excess significance: 2.6 sigma
Photon index:	     2.01 (+/-0.15)

If the light curve continues to decay with a power-law decay index of
2.04, the count rate at T+24 hours will be 3.5 x 10^-5 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.2 x
10^-15 (1.4 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/00864584.

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

Daniele B. Malesani (DAWN/NBI and DARK/NBI) and Ana Sagues (NOT) report 
on behalf of a larger collaboration:

We observed the field of GRB 180930A (Tohuvavohu et al., GCN 23279
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 ) with 
the Nordic Optical Telescope (NOT) equipped with the AlFOSC camera. 
Observations were carried out as soon as the field became visible from 
La Palma, starting on 2018 Oct 1.153 UT (14.95 hr after the GRB). A 
total exposure of 1500 s in each of the SDSS r and z filters was secured.

Inside the UVOT-enhanced GRB position (Osborne et al., GCN 23282
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 ), we 
detect no sources down to r = 23.5, z = 22.8 (both AB, calibrated 
against nearby stars from the Pan-STARRS survey).

N. P. M. Kuin (UCL-MSSL) and A. Tohuvavohu (PSU)

report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 180930A
212 s after the BAT trigger (Tohuvavohu et al., GCN Circ. 23279
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 ).
No optical afterglow consistent with the XRT position
(Evans GCN Circ. 23280
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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           212          362          147         >21.2
white              212         2818          602         >21.1
v                  517         2620          226         >20.1
b                  443         2718          240         >20.7
u                  418         2693          245         >19.7
w1                 394         2669          253         >20.8
m2                 369         2644          233         >19.3
w2                 659         2595          194         >19.9

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).

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

Using 2552 s of XRT Photon Counting mode data and 3 UVOT
images for GRB 180930A, 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 = 76.86315, -25.11694 which is equivalent
to:

RA (J2000): 05h 07m 27.16s
Dec (J2000): -25d 07' 01.0"

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.

WeiKang Zheng and Alexei V. Filippenko (UC Berkeley) report on
behalf of the KAIT GRB team:

The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at
Lick Observatory, responded to Swift GRB 180930A (Tohuvavohu et al.,
GCN 23279
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 ) starting at 12:45:41 UT, 112 seconds after the burst
under dawn twilight condition. Observations were performed with an
automatic sequence in the clear (roughly R), V, and I filters,
and the exposure time was 20 s per image. We do not detect any
optical afterglow candidate within the enhanced XRT position error
circle (Evans et al., GCN 23280
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 ) neither in single image, nor in
the co-add images. The typical limiting magnitude of our single
clear image is about 18.5 mag calibrated to the Pan-STARRS1 catalog.

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

Using  promptly downlinked XRT event data for GRB 180930A, we find an
enhanced XRT position of the afterglow: RA, Dec: 76.8633, -25.1169
which is equivalent to:
   RA (J2000)  = 05 07 27.19
   Dec (J2000) = -25 07 00.8
with an uncertainty of 2.0 arcseconds (radius, 90% confidence).
Analysis of the promptly available data is online at
http://www.swift.ac.uk/sper/864584.

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.

A. Tohuvavohu (PSU), S. D. Barthelmy (GSFC), D. N. Burrows (PSU),
J.D. Gropp (PSU), J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL),
D. M. Palmer (LANL) and B. Sbarufatti (PSU) report on behalf of the
Neil Gehrels Swift Observatory Team:

At 12:43:49 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 180930A (trigger=864584).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 76.870, -25.138 which is 
   RA(J2000) = 05h 07m 29s
   Dec(J2000) = -25d 08' 17"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex
structure with a duration of about 20 sec.  The peak count rate
was ~1000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 12:47:17.6 UT, 208.3 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 76.86228, -25.11720 which is equivalent
to:
   RA(J2000)  = 05h 07m 26.95s
   Dec(J2000) = -25d 07' 01.9"
with an uncertainty of 3.6 arcseconds (radius, 90% containment). This
location is 78 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 (2.09 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 2.9
(+1.93/-1.74) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 211 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 none 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 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 0.02. 

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/too.html.)