GRB 180728A

J. Selsing (DAWN/NBI), L. Izzo (HETH/IAA-CSIC), A. Rossi (INAF/OAS),
D. B. Malesani (DAWN/NBI and DARK/NBI), K. E. Heintz (Univ. Iceland and 
DAWN/NBI), A. de Ugarte Postigo (HETH/IAA-CSIC), P. Schady (Univ. Bath),
R. L. C. Starling (Univ. Leicester), J. Sollerman (OKC Stockholm),
G. Leloudas (DTU space), Z. Cano (BCA), J.  P. U. Fynbo (DAWN/NBI),
M. Della Valle (INAF-Naples), E. Pian (INAF/OAS), D. A. Kann (HETH/IAA-CSIC),
D. A. Perley (LJMU), E. Palazzi (INAF/OAS), S. Klose (TLS Tautenburg),
J. Hjorth (DARK/NBI), S. Covino (INAF-OAB), V. D'Elia (SSDC),
N. R. Tanvir (Univ. Leicester), A. J.  Levan (Univ. Warwick),
D. Hartmann (Clemson U.), and C. Kouveliotou (GWU)
report on behalf of a larger collaboration:

We observed again the SN associated with GRB 180728A (Starling et al., 
GCN 23046
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 ; Izzo et al., GCN 23142
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 ) with the ESO VLT UT2 equipped with 
X-shooter. Observations had a mean epoch of 2018 August 21.078 UT (23.3 
days after the GRB) and spanned the wavelength range 3200-20,900 AA.

The features previously observed in our spectroscopic sequence (Izzo et 
al., GCN 23142
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 ) have evolved and become more prominent. Using the 
Superfit tool (Howell et al. 2005, ApJ, 634, 1190; 
http://www.dahowell.com/superfit.html) we find a convincing match with 
the type-Ic SN 2002ap at a phase of 8 days after maximum. The timing is 
consistent with the epoch of our observation (21 days after the GRB 
after correcting for cosmic time dilation). We thus conclusively 
classify the SN as a broad-lined type-Ic SN. We note however that the 
velocity measured at this epoch (~10,000 km/s) is at the low end of what 
measured for GRB-associated SNe (e.g. Modjaz et al. 2016, 832, 108).

The SN associated to GRB 180728A has been dubbed SN 2018fip via the 
Transient Name Server: https://wis-tns.weizmann.ac.il/object/2018fip

[GCN OPS NOTE(28aug18): Per author's request, AdUP was added to the
author list.]

V. Lipunov, E. Gorbovskoy, N.Tiurina, D.Vlasenko, V.Kornilov, A.Kuznetsov,
V.Chazov, I.  Gorbunov, D.Zimnukhov, D.Kuvshinov, 
P.Balanutsa,V.Vladimirov,
Lomonosov Moscow State University,SAI

D. Buckley,
South African Astronomical Observatory (SAAO)

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

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

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

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

O. Gres, N.M.Budnev , Yu.Ishmuhametova
Irkutsk State University (ISU)

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

MASTER Global Robotic Net ( Lipunov et al., 2010, Advances in Astronomy, 
vol. 2010, 30L) inspected GRB 180728A
(SwiftBAT GRB discovery : Starling et al. GCN 23046
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 ;
MASTER optical counterpart discovery: Lipunov et al. GCN 23048
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 ;GCN23050;
SwiftXRT: Perri et al. GCN 23049
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 ; Redshift, VLT: Rossi et al. GCN 23055
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 ;
SN discovery,VLT: Izzo et al. GCN 23142
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 ).
every night since the discovery.

There are unfiltered limits at MASTER images and absolute magnitude of 
SN ( Izzo et al. GCN 23142
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 ) for
Omega_Vac = 0.7 and H_0 = 70 km/s/Mpc and Galactic extinction 0.1 for our 
red ccd:

Date_Time,UT            |   Exp,s | MASTER-Site |  m_lim| M

2018-07-29 21:18:37.092 |    2340 | MASTER-SAAO |  21.8 | -16.3
2018-07-30 21:07:24.839 |    1440 | MASTER-SAAO |  20.8 | -17.3
2018-07-30 21:07:24.912 |    1440 | MASTER-SAAO |  21.4 | -16.7
2018-08-01 19:11:32.906 |    1620 | MASTER-SAAO |  20.9 | -17.2
2018-08-01 19:15:07.977 |    1620 | MASTER-SAAO |  20.9 | -17.2
2018-08-02 17:03:40.025 |    3780 | MASTER-SAAO |  20.8 | -17.2
2018-08-02 18:12:49.446 |    3960 | MASTER-SAAO |  20.9 | -17.2
2018-08-03 17:53:21.097 |    4140 | MASTER-SAAO |  20.8 | -17.3
2018-08-03 17:53:21.347 |    4140 | MASTER-SAAO |  21.1 | -17.0
2018-08-03 23:21:10.842 |    3420 | MASTER-OAFA |  20.6 | -17.5
2018-08-04 17:05:35.120 |    2700 | MASTER-SAAO |  20.9 | -17.2
2018-08-04 17:12:46.879 |    2880 | MASTER-SAAO |  20.8 | -17.3
2018-08-04 23:07:09.154 |     720 | MASTER-OAFA |  20.5 | -17.6
2018-08-05 22:18:29.225 |    3240 | MASTER-SAAO |  20.8 | -17.3
2018-08-05 22:22:04.704 |    3240 | MASTER-SAAO |  21.1 | -17.0
2018-08-05 23:08:46.934 |    1260 | MASTER-OAFA |  21.5 | -16.5
2018-08-06 18:46:19.565 |    3600 | MASTER-SAAO |  20.8 | -17.3
2018-08-06 18:46:19.605 |    3600 | MASTER-SAAO |  20.8 | -17.3
2018-08-07 00:26:41.653 |     900 | MASTER-OAFA |  20.4 | -17.7
2018-08-07 03:30:36.096 |    2520 | MASTER-OAFA |  20.6 | -17.5
2018-08-07 17:15:34.447 |    3780 | MASTER-SAAO |  20.9 | -17.2
2018-08-07 18:23:07.857 |    3780 | MASTER-SAAO |  21.7 | -16.4
2018-08-08 17:59:05.042 |    4140 | MASTER-SAAO |  20.8 | -17.3
2018-08-08 18:02:42.597 |    4140 | MASTER-SAAO |  20.9 | -17.2
2018-08-08 23:11:34.904 |    3240 | MASTER-OAFA |  21.9 | -16.2
2018-08-09 18:55:17.807 |     540 | MASTER-SAAO |  20.8 | -17.2
2018-08-09 18:58:54.517 |     540 | MASTER-SAAO |  20.8 | -17.2
2018-08-09 23:04:26.723 |    3240 | MASTER-OAFA |  20.5 | -17.5
2018-08-10 17:00:41.943 |    2520 | MASTER-SAAO |  20.9 | -17.1
2018-08-11 00:08:05.570 |    4500 | MASTER-OAFA |  20.7 | -17.3
2018-08-11 18:43:29.720 |    7020 | MASTER-SAAO |  20.9 | -17.1
2018-08-11 23:12:32.140 |    3240 | MASTER-OAFA |  20.6 | -17.4
2018-08-12 19:46:57.192 |    7560 | MASTER-SAAO |  22.1 | -15.9
2018-08-12 19:46:57.246 |    7560 | MASTER-SAAO |  20.9 | -17.1
2018-08-12 23:18:02.053 |    3240 | MASTER-OAFA |  19.8 | -18.2
2018-08-13 07:43:55.504 |    3420 | MASTER-OAFA |  21.2 | -16.8

We have carried out preliminary photometry of MASTER early observations
  (Lipunov et al. GCN 23048
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 ; GCN23050
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 ;) also we report about 
considerable polarization of optical radiation of gamma burst the first 
minute after its beginning.

This message can be cited.

L. Izzo (HETH/IAA-CSIC), A. Rossi (INAF/OAS), D. B. Malesani (DAWN/NBI and DARK/NBI), K. E. Heintz (Univ. Iceland and DAWN/NBI), J. Selsing (DAWN/NBI), P. Schady (Univ. Bath), R. L. C. Starling (Univ. Leicester), J. Sollerman (OKC Stockholm), G. Leloudas (DTU space), Z. Cano (BCA), J. P. U. Fynbo (DAWN/NBI), M. Della Valle (INAF-Naples), E. Pian (INAF/OAS), D. A. Kann (HETH/IAA-CSIC), D. A. Perley (LJMU), E. Palazzi (INAF/OAS), S. Klose (TLS Tautenburg), J. Hjorth (DARK/NBI), S. Covino (INAF-OAB), V. D���Elia (SSDC), N. R. Tanvir (Univ. Leicester), A. J. Levan (Univ. Warwick), D. Hartmann (Clemson U.), C. Kouveliotou (GWU) report:

We report the results of continued photometric and spectroscopic follow-up of GRB 180728A at z = 0.117 (Starling et al., GCN 23046
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 ; Lipunov et al., GCN 23048
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 ; Rossi et al., GCN 23055
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 ; Heintz et al., GCN 23067
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 ) obtained with the X-shooter instrument on the ESO/VLT UT2, Chile.

Up to now, we have observed at three epochs, specifically at 6.27, 9.32 and 12.28 days after the GRB trigger. The optical counterpart is visible in all epochs using the X-shooter acquisition camera in the g, r and z filters. We report a rebrightening of 0.5 +- 0.1 mag in the r band between 6.27 and 12.28 days. This is consistent with what is observed in many other low-redshift GRBs, which in those cases is indicative of an emerging type Ic SN.

The spectra cover the wavelength range 3,000 - 21,000 AA. All the spectra have been corrected for the Galactic extinction (A_V = 0.92), while the host extinction is likely to be small, as indicated by our early-time spectra of the afterglow (Rossi et al., GCN 23055
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 ; Heintz et al., GCN 23067
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 ). The continuum shows a strong peak around 4500 AA (rest frame; 12.28 days after the GRB), but a black body is not a good fit, as the observed peak is too narrow. The peak shifts to longer wavelengths with time. Over the three epochs, significant features develop, including a broad absorption at ~7600 AA and a deep trough around 4900 AA (all rest frame), visible in our latest spectrum. However, over the covered epochs there is not much resemblance with other broad-lined SNe seen in previous low-redshift GRBs.

For the last spectrum, we attempted the identification of a few features. In particular, we identify the broad dip at 7600 AA as due to the blend O I 8446 AA and Ca II 8492 AA, at the expansion velocity of ~30,000 km s^-1. At this velocity, we also identify the Si II 6355 doublet, as well as C II 6580. The width of the lines spans several thousands km s^-1. Independent of the interpretation of the lines, the overall shape of the continuum, together with the presence of several absorption features a few thousands km s^-1 wide, strongly indicate that this is a SN. The lack of identified H and He in the spectra suggests a classification of type Ic.

A plot of the spectrum obtained at Day 12.28 compared with GRB 980425/SN 1998bw and XRF 100316D/SN 2010bh can be found at the following link : 

http://www.astro.ku.dk/~malesani/GRB/180728A/Day12_vs_98bw_2010bh_flux.png

Further observations are planned for this event, which are possible thanks to ESO director's discretionary time allocated to our project (program 2101.D-5044, PI Rossi). Further observations of this GRB/SN, particularly at different wavelengths, are strongly encouraged.

We thank the ESO staff for their kind availability in executing our series of observations, in particular we want to thank Boris Haeussler, Emanuela Pompei, John Pritchard, Luca Sbordone, Marcela Espinoza, Nestor Jimenez, Rodrigo Palomino, Steffen Mieske, Stephane Brillant. We also thank Dilyar Barat (ANU) and Francesco D���Eugenio (Univ. Ghent) for kindly providing their telescope time to observe the GRB/SN during their visitor run at ESO/VLT.

V. Sharma and D. Bhattacharya (IUCAA), V. Bhalerao (IIT-B), A. R. Rao (TIFR) and S. Vadawale (PRL) report on behalf of the Astrosat CZTI collaboration:

Analysis of Astrosat CZTI data showed the detection of a long GRB 180728A, which was also detected by Swift (Starling R. L. C. et al., GCN 23046
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 ), Fermi-GBM (Veres P. et al., GCN 23053
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 ) and Konus-Wind (Frederiks D. et al., GCN 23061
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 ).

The source was clearly detected in the 40-200 keV energy range. The light curve shows a single peak of emission with peak at 17:29:13.50 UT. The measured peak count rate is 1849.2 cts/s above the background in combined data of four quadrants, with a total of 6236 cts. The local mean background count rate was 650.8 cts/s. Using cumulative rates, we measure a T90 of 13.4 s.

It was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range.

CZTI GRB detections are reported regularly on the payload site at http://astrosat.iucaa.in/czti/?q=grb. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, ISAC, IUCAA, SAC and PRL. The Indian Space Research Organisation funded, managed and facilitated the project.

K. E. Heintz (Univ. Iceland and DAWN/NBI), L. Izzo (HETH/IAA-CSIC), A. Rossi (INAF-OAS), A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), D. B. Malesani (DAWN/NBI, DARK/NBI), D. A. Perley (LJMU), C. C. Thoene (HETH/IAA-CSIC), J. P. U. Fynbo (DAWN/NBI), B. Milvang-Jensen (DAWN/NBI), D. A. Kann (HETH/IAA-CSIC), N. R. Tanvir (U. Leicester), A. J. Levan (U. Warwick), S. Schulze (Weizmann), and G. Pugliese (API/U. Amsterdam) report on behalf of the Stargate collaboration;

We observed again the optical afterglow of the bright, low-redshift GRB 180728A (Starling et al., GCN 23046
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 ; Lipunov et al., GCB 23048; Rossi et al., GCB 23055) with the ESO VLT UT2 equipped with the X-shooter spectrograph. Observations were carried out around July 30.21 UT (35.5 hr after the GRB).

In our observations, the afterglow has faded significantly compared to our previous observation (Rossi et al., GCN 23055
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 ), reaching a magnitude of R ~ 20 (Vega). Continuum is detected across the whole observed range 3000-25000 AA, despite at lower S/N. Weak emission lines from a faint host are now visible, corresponding to Halpha, Hbeta, [N II], [O III] 5008 at the GRB redshift. The small Balmer decrement is consistent with negligible dust extinction in the host galaxy.

After excluding the host emission lines and correcting for Galactic extinction, the observed continuum can be fit with a single power-law with spectral index ~ 0.6 (F_nu~nu^-beta). In particular, we do not see evidence in any of our spectra for broad undulations or deviations from a power-law behavior as reported by Buckley et al. (ATel 11897).
A figure showing our spectrum can be seen at:
https://www.astro.ku.dk/~malesani/GRB/180728A/GRB180728A_spec.png

We acknowledge expert support from the ESO observing staff in Paranal,
in particular Pascale Hibon, Bin Yang, and Romain Thomas.

R. Ruffini, Y. Aimuratov, C. L. Bianco, Y. C. Chen, D. M. Fuksman, M. Karlica, R. Moradi, D. Primorac, J.A. Rueda, N. Sahakyan, Y. Wang, on behalf of the ICRANet team, report:

GRB 180728A has T90=6.4s (P. Veres et al., GCN 23053
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 ), peak energy 142 (-15.+20) keV, and isotropic energy (2.33 +/- 0.10)x10^51 erg (D. Frederiks, et al., GCN 23061
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 ). It presents the typical characteristic of a subclass of long GRBs called X-ray flashes (XRFs, see Ruffini et al., ApJ 832 (2016) 136), originating from a tight binary of a FeCO Core undergoing a supernova explosion in presence of a companion neutron star (NS) which undergoes hypercritical accretion. The outcome (see Fig. [1]) is a new binary composed by a more massive NS (MNS) and a newly born NS (vNS). Using the averaged observed value (Cano et al., 2016), and considering the redshift z=0.117 (A. Rossi et al., GCN 23055
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 ), a bright optical signal will peak at 14.7 +/- 2.9 days after the trigger (12 August 2018, uncertainty from August 9th to August 15th) at the location of RA 253.56472 and DEC -54.04451, with an uncertainty 0.43 arc sec (S. J. LaPorte et al., GCN 23064
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 ). The follow-up observations, especially the optical bands for the SN, as well as attention to binary NS pulsar behaviors in the X-ray afterglow emission, are recommended.


[1] Link: http://www.icranet.org/documents/180728A_f1.png

Figure Caption: Snapshot of the binary system formed by the MNS and by the vNS together with the SN ejecta density. See for details Fig. 7 of Ruffini et al., ApJ 832 (2016) 136.

GRB 180728A: Swift/UVOT Detection

S. J. LaPorte (PSU) and R. L. C. Starling (U. Leicester)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 180728A
1740 s after the BAT trigger (Starling et al., GCN Circ. 23046
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 ).
A source consistent with the enhanced XRT position
(Osborne et al. GCN Circ. 23051
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 )
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  16:54:15.53 =  253.56472 (deg.)
    Dec (J2000) = -54:02:40.2 =  -54.04451 (deg.)
with an estimated uncertainty of 0.43 arc sec. (radius, 90% confidence),
consistent with MASTER OT J165415.75-540239.27 (Lipunov et al., GCN #23050
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 ).

Preliminary detections 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             1740         1890          147         16.25 +/- 0.03
white             7713         15148         465         17.28 +/- 0.03 
v                 1897         1917           20         16.07 +/- 0.14
b                 1995         2013           18         16.58 +/- 0.10
u                 1970         1990           20         15.93 +/- 0.10
w1                1946         1966           20         16.20 +/- 0.17
m2                1921         2114           39         16.60 +/- 0.18
w2                2045         2065           19         16.37 +/- 0.19

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.29 in the direction of the burst
(Schlegel et al. 1998).

D. Frederiks, S. Golenetskii, R.Aptekar, A. Kozlova,
A.Lysenko,  D. Svinkin, A. Tsvetkova,  M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:

The long, very bright GRB 180728A
(Swift-BAT detection: Starling et al., GCN 23046
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 ;
Fermi-GBM detection: Veres et al., GCN 23053
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 )
triggered Konus-Wind (KW) at T0=62954.093 s UT (17:29:14.093).

The burst light curve shows a smooth pulse with a total duration
(T100) of ~17 s. The emission is seen up to ~10 MeV.

As observed by Konus-Wind, the burst had a fluence of
(5.14 �� 0.29)x10^-5 erg/cm2 and a 64-ms peak energy flux,
measured from T0+15.168, of (1.94 �� 0.15)x10^-5 erg/cm2
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+19.2 s)
is best fit in the 30 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -1.48 (-0.10,+0.12),
the high energy photon index beta = -2.57 (-0.18,+0.12),
the peak energy Ep = 97 (-6,+7) keV,
chi2 = 94/96 dof.

The spectrum near the peak count rate (measured from T0+1.280 s
to T0+1.792 s) is best fit in the 20 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -1.44 (-0.15,+0.15),
the high energy photon index beta = -2.81 (-1.44,+0.24),
the peak energy Ep = 127 (-13,+18) keV,
chi2 = 54/56 dof.

Assuming the redshift z=0.117 (Rossi et al., GCN 23055
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 )
and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315,
and Omega_Lambda = 0.685 (Planck Collaboration, 2014),
we estimate the following rest-frame parameters:
the isotropic energy release E_iso is (2.33 �� 0.10)x10^51 erg,
the peak luminosity L_iso is (9.51 �� 0.58)x10^50 erg/s
(both in the 1-10000 keV rest-frame band).
The rest-frame peak energy of the time-integrated spectrum,
Epi,z, is 108(-7, 8) keV, and the rest-frame peak energy of
the 'peak' spectrum, Epp,z, is 142(-15, 20) keV.
With these energetics, the burst lies on the upper
edges of 68% prediction bands for both 'Amati' and 'Yonetoku'
relations built for the sample of 138 long KW GRBs with known
redshifts (Tsvetkova et al., ApJ 850 161, 2017).

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB180728_T62954/

All the quoted errors are estimated at the 90% confidence level.
All the presented results are preliminary.

A. Rossi (INAF-OAS), L. Izzo (HETH/IAA-CSIC), B. Milvang-Jensen
(DAWN/NBI), D. A. Perley (LJMU), A. de Ugarte Postigo (HETH/IAA-CSIC and
DARK/NBI), D. A. Kann (HETH/IAA-CSIC), A. J. Levan (U. Warwick), N. R.
Tanvir (U. Leicester), S. Covino (INAF/Brera), and D. B. Malesani
(DAWN/NBI and DARK/NBI) report on behalf of the Stargate collaboration:

We observed the optical counterpart of GRB 180728A (Starling et al., GCN
23046
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 ; Lipunov et al., GCN 23048
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 ) with the ESO VLT UT2 equipped with the
X-shooter spectrograph.  One 600 s spectrum was taken during evening
twilight on 2018 July 28 beginning at 23:13 UT, plus two additional 600
s spectra on 2018 July 29 beginning at 05:10 UT.  The spectra cover a
wavelength range from 3000-25000 AA.

A red continuum is detected across the spectral range. We detect
absorption features due to Mg II (3124,3132), Mg I (3187), and Ca II
(4395,4434) at a consistent redshift of z=0.117, which we propose as the
redshift of the GRB.  Galactic ISM absorption features of Ca II and Na I
are also detected.

This GRB resembles the famous GRB 030329, but slightly less energetic
(E_iso = 2e+51 erg given the fluence value provided by Veres et al., GCN
23053
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 ).  It is the closest energetic (E_iso > 1e+51 erg) GRB with a
measured redshift to date.

We note that although Galactic extinction in this direction is
significant (A_V = 0.763; Schlafly et al. 2011, ApJ 737:103) a campaign
to study the anticipated associated supernova should still be practical
with moderate-aperture telescopes at this redshift.

We acknowledge the ESO observing staff at Paranal, in particular Pascale
Hibon and R. Thomas.

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

Using the data set from T-239 to T+667 sec from the recent telemetry 
downlink,
we report further analysis of BAT GRB 180728A (trigger #850471)
(Starling, et al., GCN Circ. 23046
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 ).  The BAT ground-calculated position is
RA, Dec = 253.574, -54.037 deg which is
    RA(J2000)  =  16h 54m 17.7s
    Dec(J2000) = -54d 02' 13.7"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 57%.

The mask-weighted light curve shows a relatively faint, soft precursor 
near the
trigger time, lasting about 3 seconds.  This was followed by a single, much
brighter pulse, which consisted of two overlapping peaks.   This pulse 
began at
T+11 sec, peaked at T+13 sec, and faded to background by T+40 sec.
T90 (15-350 keV) is 8.68 +- 0.30 sec (estimated error including 
systematics).

The time-averaged spectrum from T-0.24 to T+36.51 sec is best fit by a 
simple
power-law model.  The power law index of the time-averaged spectrum is
1.97 +- 0.03.  The fluence in the 15-150 keV band is 2.96 +- 0.06 x 
10^-5 erg/cm2.
The 1-sec peak photon flux measured from T+12.61 sec in the 15-150 keV band
is 132.0 +- 2.9 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/850471/BA/

P. Veres, C. Meegan, and B. Mailyan (all UAH)
report on behalf of the Fermi GBM Team:

"At 17:29:02.28 UT on 28 July 2018, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 180728A (trigger 554491747 / 180728728)
which was also detected by the Swift/BAT (Starling et al., GCN 23046
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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 35 degrees.

The GBM light curve consists of a precursor and a very bright peak
with a duration (T90) of about 6.4 s (50-300 keV).
The time-averaged spectrum from T0+9.2s to T0+23.6 s is
best fit by a Band function with Epeak = 79.2 +/- 1.4 keV,
alpha = -1.54 +/- 0.01, and beta = -2.46 +/- 0.02.

The event fluence (10-1000 keV) in this time interval is
(5.65 +/- 0.02)E-5 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+11.1 s in the 10-1000 keV band
is 231.0 +/- 1.2 ph/s/cm^2.

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

[GCN OPS NOTE(29jul18):  As pointed out by A.Kann, the "170728A"
in the Subject-line was corrected to "180728A".]

A. Tohuvavohu (PSU), S. J. LaPorte (PSU), J.A. Kennea (PSU), J.P.
Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U.
Leicester), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAB), P. D'Avanzo
(INAF-OAB) and R.L.C. Starling report on behalf of the Swift-XRT team:

We have analysed 7.2 ks of XRT data for GRB 180728A (Starling et al.
GCN Circ. 23046
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 ), from 1.7 ks to 26.6 ks after the  BAT trigger. The
data comprise 1.9 ks 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. 23051
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 ).

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=0.56 (+/-0.05). At T+5559 s  the decay
steepens to an alpha of 1.49 (+0.29, -0.14) before breaking again at
T+14.6 ks to a final decay with index alpha=0.58 (+0.23, -2.08).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.886 (+0.020, -0.017). The
best-fitting absorption column is  consistent with the Galactic value
of 3.2 x 10^21 cm^-2 (Willingale et al. 2013). The PC mode spectrum has
a photon index of 1.75 (+/-0.09) and a best-fitting absorption column
of 3.8 (+/-0.5) x 10^21 cm^-2. The counts to observed (unabsorbed)
0.3-10 keV flux conversion factor deduced from this spectrum  is 4.5 x
10^-11 (6.2 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3.8 (+/-0.5) x 10^21 cm^-2
Galactic foreground: 3.2 x 10^21 cm^-2
Excess significance: 2.2 sigma
Photon index:	     1.75 (+/-0.09)

If the light curve continues to decay with a power-law decay index of
0.58, the count rate at T+24 hours will be 0.65 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.0 x
10^-11 (4.0 x 10^-11) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00850471.

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 1791 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 180728A, 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 = 253.56514, -54.04454 which is equivalent
to:

RA (J2000): 16h 54m 15.63s
Dec (J2000): -54d 02' 40.3"

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.

V. Lipunov, E. Gorbovskoy, N.Tiurina, D.Vlasenko, V.Kornilov, A.Kuznetsov, 
V.Chazov, I.  Gorbunov, D.Zimnukhov, D.Kuvshinov, P.Balanutsa,
V.Vladimirov,
Lomonosov Moscow State University,SAI

D. Buckley,
South African Astronomical Observatory (SAAO)

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

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

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

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

O. Gres, N.M.Budnev , Yu.Ishmuhametova
Irkutsk State University (ISU)

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

MASTER-SAAO robotic telescope (MASTER-Net: http://observ.pereplet.ru, Lipunov 
et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa 
(South African Astronomical Observatory) was detected new optical 
object (Lipunov et al., GCN Circ #23048
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 ) MASTER OT J165415.75-540239.27
at Swift XRT position (Starling et al., GCN
#23046
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 ; Perri et al., GCN #23049
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 ;):

RA, DEC = 16h 54m 15.75s , -54d 02m 39.27s
Error ~1 arcsec

We see a gradual attenuation of the OT on an automatic light 
curve. Thus, the transient is an optical counterpart of the gamma-ray 
burst GRB 180728A.

The automatic light curve is available at 
http://observ.pereplet.ru/images/MASTER_OT_J165415.75-540239.27.jpg


The message may be cited.

M. Perri (ASDC), P.A. Evans (U. Leicester), J.P. Osborne (U.
Leicester), D.N. Burrows (PSU), J.A. Kennea (PSU) and G. Cusumano
(INAF-IASF PA) report on behalf of the Swift-XRT team:

The XRT began observing the field of GRB 180728A at 17:57:51.5 UT,
1730.8 seconds after the BAT trigger. XRT found a bright, uncatalogued
X-ray source located at RA, Dec 253.5648, -54.0437 which is equivalent
to:
   RA(J2000)  = +16h 54m 15.55s
   Dec(J2000) = -54d 02' 37.3"
with an uncertainty of 5.8 arcseconds (radius, 90% containment). This
location is 46 arcseconds from the BAT onboard position, within the BAT
error circle. No event data are yet available to determine the column
density using X-ray spectroscopy.

The initial flux in the 2.5 s image was 7.92e-10 erg cm^-2 s^-1 (0.2-10
keV).

V. Lipunov, E. Gorbovskoy, N.Tiurina, D.Vlasenko, V.Kornilov, A.Kuznetsov, 
V.Chazov, I.  Gorbunov, D.Zimnukhov, D.Kuvshinov, P.Balanutsa,
V.Vladimirov,
Lomonosov Moscow State University,SAI

D. Buckley,
South African Astronomical Observatory (SAAO)

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

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

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

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

O. Gres, N.M.Budnev , Yu.Ishmuhametova
Irkutsk State University (ISU)

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

MASTER-SAAO robotic telescope (MASTER-Net: http://observ.pereplet.ru, 
Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in 
South Africa (South African Astronomical Observatory) was pointed to the 
GRB180728A 22 sec after notice time and 38 sec after trigger time at 
2018-07-28 17:29:38 UT in two polarizations. On our first (10s exposure) 
set we  found  new optical object (transient) within SWIFT error-box 
(ra=253.567 dec=-54.0308  r=0.05) :

MASTER OT J165415.75 -540239.27
RA, DEC = 16h 54m 15.75s , -54d 02m 39.27s
m ~ 14.5

We  see a surprising automatic light curve  when the source has 
risen to constant magnitude during first ~30 minutes!

The observations made on zenit distance = 28 degrees, galaxy latitude b = 
-7 degree.
The moon (99 % bright part) is 11 degrees above the horizon. The distance 
between  moon and  object is 61
The sun  altitude  is -19.8 degree.
The object can be observed till 2018-07-29 05:17:09

The message may be cited.

R. L. C. Starling (U Leicester), S. D. Barthelmy (GSFC),
A. Y. Lien (GSFC/UMBC), M. J. Moss (George Washington University),
K. L. Page (U Leicester) and D. M. Palmer (LANL) report on behalf of
the Neil Gehrels Swift Observatory Team:

At 17:29:00 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 180728A (trigger=850471).  Swift did not slew immediately
due to the Earth limb constraint.  The BAT on-board calculated location is 
RA, Dec 253.569, -54.031 which is 
   RA(J2000) = 16h 54m 17s
   Dec(J2000) = -54d 01' 50"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a small precursor
followed 10 seconds later by a bright FRED pulse of ~20 s duration. 
The peak count rate was ~100,000 counts/sec (15-350 keV), at ~13 sec 
after the trigger. 

Due to an observing constraint, Swift will not slew until T0+23.6
minutes. There will be no XRT or UVOT data until this time. 

Burst Advocate for this burst is R. L. C. Starling (rlcs1 AT star.le.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.)