GRB 180805B

Daniele B. Malesani (DAWN/NBI and DARK/NBI) and Nicolas Crouzet (IAC) 
report:

We observed the field of the short GRB 180805B (D'Avanzo et al., GCN 
23076
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 ; Sakamoto et al., GCN 23082
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 ) using one of the 40-cm telescopes 
located in the Teide observatory (Canary Islands), part of the Las 
Cumbres Observatory network.

Observations consisted of 9x300 s exposures in the SDSS r filter, 
centered around the mean epoch Aug 6.19 UT (15.49 hr after the GRB). The 
PSF delivered to the image is around 3".

No object is detected within or close to the X-ray afterglow error 
circle (Evans et al., GCN 23077
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 ), down to a 3-sigma limiting magnitude 
of r = 20 AB, calibrated using nearby stars from the Pan-STARRS catalog.

A. Higgins (Univ. Leicester), K. Wiersema (Univ. Warwick)  and D. B. Malesani (DAWN/NBI and DARK/NBI) report:

We observed the field of GRB 180805B, classified as short with extended emission (D'Avanzo et al., GCN 23076
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 ; Sakamoto et al., GCN 23082
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 ), using the ESO New Technology Telescope (NTT) equipped with the EFOSC2 camera. Our observations consist of 9 images in i band, for a total of 1800 s exposure, with mid time 2018 August 6.28 UT (17.76 hr after the GRB trigger), and were
obtained as part of the SPLOT programme (Higgins et al. 2018, subm.).

No counterpart is detected inside the UVOT-enhanced XRT error circle (Evans et al., GCN 23077
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 ) in our coadded image, down to a 3-sigma upper limit i > 25 (AB), adopting i = 20.56 for the Pan-STARRS star at RA = 01:43:07.462, Dec = -17:28:30.90.

We thank D. Castex for support with these observations.

Alan M. Watson (UNAM), Nat Butler (ASU), Rosa L. Becerra (UNAM), William
H. Lee (UNAM), Carlos Rom��n-Z����iga (UNAM), Alexander Kutyrev (GSFC), and
Eleonora Troja (GSFC) report:

We observed the field of the short GRB 180805B (D'Avanzo et al., GCN
Circ. 23076
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 ) with the COATLI 50-cm telescope and interim imager at the
Observatorio Astron��mico Nacional on the Sierra de San Pedro M��rtir
(http://coatli.astroscu.unam.mx) from 2018-08-06 08:01 to 11:48 UTC
(18.98 to 22.77 hours after the trigger), obtaining a total of 2.98
hours of exposure in the w filter.

We do not detect any optical sources within the enhanced XRT error
region (Evans et al., GCN Circ. 23077
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 ) to a 5-sigma limiting magnitude
of

w > 22.5

This magnitude is calibrated against the USNO-B1 catalog (adjusted to an
approximate AB system) and is not corrected for Galactic extinction in
the direction of the GRB.

We thank the COATLI technical team (Fernando ��ngeles, Oscar Chapa,
Salvador Cuevas, Alejandro Farah, Jorge Fuentes, Rosal��a Langarica,
Fernando Quir��s, and Carlos Tejada) and the staff of the Observatorio
Astron��mico Nacional.

Y.-D. Hu, F.J. Aceituno, J. C. Tello and A.J. Castro-Tirado (IAA-CSIC 
Granada), on behalf of a larger collaboration, report:

Following the detection of GRB 180805B (short burst with extended 
emission) by Swift (D'Avanzo et al. GCNC 23076, Sakamoto et al. GCNC 
23082), optical images in the I-band were obtained at the 1.5m OSN 
telescope in Granada (Spain) starting at 03:08 (Aug 6), i.e. ~14 h 
postburst. No optical afterglow is detected in the co-added image (7 x 
300s, mid time at 03:26 UT, 14.4 h after the trigger) within the 
enhanced Swift/XRT error box (Evans et al. GCNC 23077) down to I=21.0, 
which is in agreement with the non-detections reported by Lipunov et al. 
(GCNC 23085), Malesani et al. (GCNC 23086) and Ramsay et al.(GCNC 
23087).

G.Ramsay (Armagh O.), K.Ulaczyk, D.Steeghs, J.Lyman (U. Warwick),
M.Dyer (U. Sheffield),  B.Gompertz, A.Levan, R.Cutter (U. Warwick)
K. Ackley, D.Galloway, E.Rol (Monash U.), V.Dhillon (U. Sheffield),
P.O'Brien, R.Starling (U. Leicester), S.Poshyachinda (NARIT),
D.Pollacco (U. Warwick), E.Thrane (Monash U.), E.Palle (IAC)

report on behalf of the GOTO collaboration:

In response to GRB 180805B (D'Avanzo et al. GCN 23076
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 ), the
Gravitational-wave Optical Transient Observer (GOTO) observed the
field near the Swift BAT/XRT detection.

Observations started at 2018-08-06T04:37:59 UT (15.5 hours after the
burst) consisting of a set of 6x120s exposures in our wide L filter
(400-700nm). We do not detect any optical source within the error
circle of the enhanced XRT location (Evans et al. GCN 23077
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 ) with a
5-sigma limit of V=20.4, using APASS calibrators on the stacked image.

We note that our observations were obtained between those of Lupinov
et al. GCN 23085
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  and Malesani et al. GCN 23086
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 .

GOTO is operated at the La Palma observing facilities of the University
of Warwick on behalf of a consortium including the University of
Warwick, Monash University, Armagh Observatory, the University of
Leicester, the University of Sheffield, the National Astronomical
Research Institute of Thailand (NARIT) and the Instituto de Astrofisica
de Canarias (IAC)

https://goto-observatory.org/

D. B. Malesani (DAWN/NBI and DARK/NBI), G. Pugliese (API/Univ. 
Amsterdam), P. D'Avanzo (INAF/Brera), N. R. Tanvir (Univ. Leicester), K. 
Wiersema (Univ. Warwick), report on behalf of the Stargate consortium:

We observed the field of GRB 180805B, classified as short with extended 
emission (D'Avanzo et al., GCN 23076
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 ; Sakamoto et al., GCN 23082
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 ), using 
the ESO Telescopes located in Cerro Paranal. Optical and near-infrared 
observations were obtained using the FORS2 and HAWK-I instruments, 
respectively. No counterpart is detected inside the UVOT-enhanced XRT 
error circle (Evans et al., GCN 23077
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 ) in either images, with the 
3-sigma upper limits summarized in the table below.

Filter  Mid time (UT)  Time since GRB (hr)  Limiting mag (Vega)
---------------------------------------------------------------
J       Aug 6.245      16.84                23.5
R       Aug 6.363      19.67                25.5

Calibration was carried out against a single 2MASS star for the J band, 
and using archival FORS2 zeropoints for the R band.

We note the presence of four extended objects within a few arcsec of the 
center of the XRT error circle, including a source 3.5" North of the GRB 
(R ~ 22.5) also visible in the Pan-STARRS r and i images. Their 
association with the GRB cannot be assessed at the present time.

We acknowledge excellent support from the ESO observing staff in 
Paranal, especially Stephane Brillant, Joe Anderson, and Bian Fuyan. DBM 
also acknowledges useful discussion with Amy Lien (GSFC/UMBC) about the 
classification of this GRB.

V. Lipunov, N.Tiurina, E. Gorbovskoy,
V.Kornilov, A.Kuznetsov, V.Chazov, I.  Gorbunov,
D.Zimnukhov, D.Kuvshinov, P.Balanutsa, V.Vladimirov, D. Vlasenko
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) 
located in SAAO was starting survey on the Swift short GRB with extended 
emission  GRB180805B (D'Avanzo et 
al., GCN #23076
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 ; Hamburg et al., GCN #23078
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 ;Sakamoto et al., GCN #23082
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 ) 
error-box 
(Evans et al., GCN #23077
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 ; )  37838 sec after notice time and 38322 
sec after trigger time at 2018-08-05 23:46:00 UT. The 5-sigma upper limit 
on our first (180s exposure)  set is about 20.5 mag

There is no OT detected.

The message may be cited.

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

We have analysed 6.6 ks of XRT data for GRB 180805B (D'Avanzo et al.
GCN Circ. 23076
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 ), from 82 s to 36.7 ks after the  BAT trigger. The data
comprise 197 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. 23077
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 ).

The light curve can be modelled with a series of power-law decays. The
light curve initially rises, with an index alpha=-1.5 (+0.0, -0.5). At
T+102 s it breaks to an alpha of 1.61 (+0.15, -0.65). The light curve
breaks again at T+241 s to a decay with alpha=3.1 (+/-0.4),  before a
final break at T+891 s s after which the decay index is 0.88 (+0.21,
-0.18).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 0.93 (+0.09, -0.06). The
best-fitting absorption column is  2.3 (+4.7, -0.7) x 10^20 cm^-2,
consistent with the Galactic value of 1.6 x 10^20 cm^-2 (Willingale et
al. 2013). The PC mode spectrum has a photon index of 1.90 (+0.25,
-0.23) and a best-fitting absorption column of 7.3 (+6.6, -5.4) x 10^20
cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 3.5 x 10^-11 (4.0 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     7.3 (+6.6, -5.4) x 10^20 cm^-2
Galactic foreground: 1.6 x 10^20 cm^-2
Excess significance: 1.7 sigma
Photon index:	     1.90 (+0.25, -0.23)

If the light curve continues to decay with a power-law decay index of
0.88, the count rate at T+24 hours will be 2.0 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.8 x
10^-14 (7.8 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/00851855.

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

T. Sakamoto (AGU), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), P. D'Avanzo (INAF-OAB),
H. A. Krimm (NSF/USRA), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), J. P. Norris (BSU),
D. M. Palmer (LANL), 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 180805B (trigger #851855)
(D'Avanzo et al., GCN Circ. 23076
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 ).  The BAT ground-calculated position is
RA, Dec = 25.877, -17.475 deg which is
  RA(J2000)  =  01h 43m 30.6s
  Dec(J2000) = -17d 28' 29.3"
with an uncertainty of 3.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 67%.

The mask-weighted light curve show a short pulse that starts from ~T-0.1 s,
peaks at ~T+0.1 s, and ends at ~T+0.7 s. The short pulse is followed by
some weak emission that lasts until ~ T+130 s. T90 (15-350 keV) is
122.5 +- 18.3 sec (estimated error including systematics).

The time-averaged spectrum from T-0.10 to T+127.46 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.13 +- 0.29.  The fluence in the 15-150 keV band is 9.6 +- 1.7 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T-0.11 sec in the 15-150 keV band
is 1.7 +- 0.2 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level.

The structure of the burst shows similarity to those of short GRBs with
extended emission. We thus perform further analysis on the short spike and the
tail emission.

The spectrum of the short pulse from T-0.001 to T+0.712 sec can be fitted by
a simple power-law model with power-law index of 0.66 +- 0.20 and
fluence (15-150 keV) of 1.7 +- 0.2 x 10^-7 erg/cm2. The spectrum of the
extended emission from T+0.712 to T+126.532 sec is best fit by a simple power-law
model, with power-law index of 1.16 +- 0.39 and fluence (15-150 keV) of
6.8 +- 1.6 x 10^-7 erg/cm2. These values are consistent with those of short GRBs
with extended emission (Lien & Sakamoto et al. 2016).

The lag analysis does not produce a well-constrained value due to the weakness
of the short pulse.

The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/851855/BA/

N. P. M. Kuin (UCL-MSSL) 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 180805B  85 s after the BAT trigger (D'Avanzo et al.,
GCN Circ. 23076
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 ).  No optical afterglow consistent with the
XRT position (Evans et al. GCN Circ. 23077
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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            85          235          147         >20.8
u_FC               297          546          246         >20.2
white               85         1544          392         >21.3
v                  626         1421           78         >18.6
b                  552         1519           97         >20.0
u                  297          546          246         >20.2
w1                 675         1470           97         >18.8
m2                1078         1097           19         >17.8
w2                 774         1569           78         >19.0

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).

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

"At 13:02:36.52 UT on 05 August 2018, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 180805B (trigger 555166961 / 180805543)
which was also detected by the Swift BAT and XRT instruments
(D'Avanzo et al. 2018, GCN 23076
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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 64
degrees.

The GBM light curve shows a single peak
with a duration (T90) of about 1 s (50-300 keV).
The time-averaged spectrum from T0-0.13 s to T0+0.58 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -0.5 +/- 0.2 and
the cutoff energy, parameterized as Epeak, is 346 +/- 75 keV.

The event fluence (10-1000 keV) in this time interval is
(5.9 +/- 0.7)E-07 erg/cm^2. The 64-ms peak photon flux measured
starting from T0+0.06 s in the 10-1000 keV band
is 8.3 +/- 1.1 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, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) 
report on behalf of the Swift-XRT team.

Using 1323 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 180805B, 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 = 25.78171, -17.49345 which is equivalent
to:

RA (J2000): 01h 43m 7.61s
Dec (J2000): -17d 29' 36.4"

with an uncertainty of 1.8 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.

P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), N. P. M. Kuin (UCL-MSSL),
A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC),
A. Melandri (INAF-OAB) and B. Sbarufatti (PSU) report on behalf of the
Neil Gehrels Swift Observatory Team:

At 13:02:36 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 180805B (trigger=851855).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 25.813, -17.503 which is 
   RA(J2000) = 01h 43m 15s
   Dec(J2000) = -17d 30' 11"
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 1.5 sec.  The peak count rate
was ~4000 counts/sec (15-350 keV), at ~0.1 sec after the trigger. 

The XRT began observing the field at 13:03:53.2 UT, 76.8 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source with an enhanced position: RA, Dec
25.7814, -17.4926 which is equivalent to:
   RA(J2000)  = 01h 43m 07.55s
   Dec(J2000) = -17d 29' 33.2"
with an uncertainty of 2.1 arcseconds (radius, 90% containment). This
location is 114 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 (1.63 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.1
(+2.89/-2.44) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 1.14e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 84 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 has been about 19.6 mag. 
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 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.)