GRB 180630A

P. D'Avanzo (INAF-OAB), C. Gronwall (PSU), J.D. Gropp (PSU),
J. A. Kennea (PSU), H. A. Krimm (NSF/USRA), F. E. Marshall (NASA/GSFC)
and T. Sakamoto (AGU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 11:11:51 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 180630A (trigger=845443).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 48.810, -87.482 which is 
   RA(J2000) = 03h 15m 14s
   Dec(J2000) = -87d 28' 54"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single-peaked
structure with a duration of about 10 sec.  The peak count rate
was ~6500 counts/sec (15-350 keV), at ~4 sec after the trigger. 

The XRT began observing the field at 11:13:13.4 UT, 81.6 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 48.95887, -87.47850 which
is equivalent to:
   RA(J2000)  = 03h 15m 50.13s
   Dec(J2000) = -87d 28' 42.6"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 26 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. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 1.34
x 10^21 cm^-2 (Willingale et al. 2013). 

The initial flux in the 2.5 s image was 6.12e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 87 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	03:15:56.02 =  48.98342
  DEC(J2000) = -87:28:42.4  = -87.47844
with a 90%-confidence error radius of about 0.62 arc sec. This position is 5.7
arc sec. from the center of the XRT error circle. The estimated magnitude is
17.44 with a 1-sigma error of about  0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.13. 

Burst Advocate for this burst is P. D'Avanzo (paolo.davanzo AT brera.inaf.it). 
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.)

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

Using 1171 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 180630A, 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 = 48.98081, -87.47880 which is equivalent
to:

RA (J2000): 03h 15m 55.39s
Dec (J2000): -87d 28' 43.7"

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.

R. Hamburg (UAH), A. von Kienlin (MPE), and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:

"At 11:11:54.41 UT on 30 June 2018, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 180630A (trigger 552049919 / 180630467)
which was also detected by the Swift BAT and XRT instruments
(D'Avanzo et al. 2018, GCN 22872
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 ).
The GBM on-ground location is consistent with the Swift position.

The angle from the Fermi LAT boresight at the GBM trigger time is 20
degrees.

The GBM light curve consists of a single structured peak
with a duration (T90) of about 12 s (50-300 keV).
The time-averaged spectrum from T0-1.54s to T0+8.70 s is
best fit by a power law function with an exponential
high-energy cutoff. The power law index is -1.37 +/- 0.09 and
the cutoff energy, parameterized as Epeak, is 84 +/- 8 keV.
A Band function fits the spectrum equally well
with Epeak = 60 +/- 10 keV, alpha = -1.11 +/- 0.20,
and beta = -2.32 +/- 0.16.

The event fluence (10-1000 keV) in this time interval is
(2.5 +/- 0.1)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+1.15 s in the 10-1000 keV band
is 9.4 +/- 0.4 ph/s/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."

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

We have analysed 6.3 ks of XRT data for GRB 180630A (D'Avanzo et al.
GCN Circ. 22872
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 ), from 87 s to 29.0 ks after the  BAT trigger. The data
comprise 69 s in Windowed Timing (WT) mode with the remainder in Photon
Counting (PC) mode. The enhanced XRT position for this burst was given
by Beardmore et al. (GCN Circ. 22873
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 ).

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=3.04 (+0.61, -0.21). At T+155 s  the decay
flattens to an alpha of 0.25 (+0.26, -0.09). The light curve breaks
again at T+659 s to a decay with alpha=0.80 (+0.07, -0.05),  before a
final break at T+24.3 ks s after which the decay index is 4.4 (+3.6,
-2.2).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.91 (+0.21, -0.17). The
best-fitting absorption column is  consistent with the Galactic value
of 1.3 x 10^21 cm^-2 (Willingale et al. 2013). The PC mode spectrum has
a photon index of 1.64 (+/-0.12) and a best-fitting absorption column
of 1.7 (+0.5, -0.3) x 10^21 cm^-2. The counts to observed (unabsorbed)
0.3-10 keV flux conversion factor deduced from this spectrum  is 4.3 x
10^-11 (5.1 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.7 (+0.5, -0.3) x 10^21 cm^-2
Galactic foreground: 1.3 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.64 (+/-0.12)

If the light curve continues to decay with a power-law decay index of
4.4, the count rate at T+24 hours will be 4.3 x 10^-4 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.8 x
10^-14 (2.2 x 10^-14) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00845443.

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

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), M. Stamatikos (OSU), 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 180630A (trigger #845443)
(D'Avanzo, et al., GCN Circ. 22872
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 ).  The BAT ground-calculated position is
RA, Dec = 48.885, -87.476 deg which is
    RA(J2000)  =  03h 15m 32.5s
    Dec(J2000) = -87d 28' 33.4"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 59%.
  
The mask-weighted light curve shows a double-peaked structure.  The first pulse
starts at T0, peaks at T+4 sec and ends at T+15 sec.  The second weak pulse
starts at T+15 sec and ends at T+30 sec.  T90 (15-350 keV) is 18.85 +- 6.45 sec
(estimated error including systematics).
  
The time-averaged spectrum from T-0.36 to T+30.02 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.07 +- 0.10.  The fluence in the 15-150 keV band is 1.8 +- 0.1 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+3.65 sec in the 15-150 keV band
is 6.6 +- 0.4 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/845443/BA/

GRB 180630A: Swift/UVOT Detection

S. J. LaPorte (PSU) and P. D'Avanzo (INAF-OAB)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 180630A
88 s after the BAT trigger (D'Avanzo et al., GCN Circ. 22872
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 ).
A fading source consistent with the XRT position
(Beardmore et al. GCN Circ. 22873
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 )
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  03:15:55.74 =  48.98224 (deg.)
    Dec (J2000) = -87:28:42.3  = -87.47842 (deg.)
with an estimated uncertainty of 0.43 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               88          237          148         17.49 +/- 0.04
white             6384         6584          196         19.50 +/- 0.11
v                  629         1597          117         18.56 +/- 0.20
b                  555          748           39         18.76 +/- 0.19
u                  300          549          246         17.76 +/- 0.06
w1                 678         7392          510         19.42 +/- 0.17
m2                 654         7187          452         20.16 +/- 0.33
w2                 605         6777          255        >19.9

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.13 in the direction of the burst
(Schlegel et al. 1998).