GRB 150627A

M. Arimoto (Tokyo Tech), J.E. McEnery (NASA/GSFC), F. Longo (Trieste)
and M. Axelsson (KTH Stockholm) report on behalf of the Fermi-LAT team:


At 04:23:23.68 UT on June 27, 2015, Fermi-LAT detected high-energy emission
from GRB 150627A, which was also detected by Fermi-GBM (trigger
457071806/ 150627183).
The best LAT on-ground location is found to be

 RA, Dec = 117.49, -51.56 (J2000)

 with an error radius of 0.05 deg (90 per cent containment,
statistical error only).
This was 75 deg from the LAT boresight at the time of the trigger and triggered
an autonomous repoint of the spacecraft.

 The data from the Fermi-LAT show a significant increase in the event rate
that is spatially and temporally correlated with the trigger with high
significance.
The highest-energy photon is a 8.1 GeV event which is observed 259 s
after the GBM trigger.

 A Swift ToO has been requested for this burst.

 The Fermi-LAT point of contact for this burst is
Makoto Arimoto (arimoto@hp.phys.titech.ac.jp)


The Fermi-LAT is a pair conversion telescope designed to cover the energy band
from 20 MeV to greater than 300 GeV. It is the product of an international
collaboration between NASA and DOE in the U.S. and many scientific institutions
across France, Italy, Japan and Sweden.

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

Swift has initiated a ToO observation of the Fermi/LAT GRB 150627A. 
Automated analysis of the XRT data will be presented online at
http://www.swift.ac.uk/ToO_GRBs/00020539

Any uncatalogued X-ray sources detected in this analysis will be
reported on this website and via GCN COUNTERPART notices. These are
not necessarily related to the Fermi/LAT event. Any X-ray source
considered to be a probable afterglow candidate will be reported via a 
GCN Circular after manual consideration.

Details of the XRT automated analysis methods are detailed in Evans et
al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8).

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

H.-F. Yu (MPE), E. Burns, V. Connaughton, A. Goldstein (UAH), and M. Gibby (Jacobs)
report on behalf of the Fermi GBM Team:

"At 04:23:23.68 UT on 27 June 2015, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 150627A (trigger 457071806 / 150627183),
which was also detected by the Fermi LAT (Arimoto et al., GCN 17971
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 ).
The GBM on-ground location is consistent with the LAT position.

The GBM trigger resulted in an Autonomous Repoint Request (ARR) 
that was accepted and the spacecraft slewed to the GBM in-flight 
location. At the GBM trigger time, the angle of the LAT localization 
to the LAT boresight is 75 deg.

The GBM light curve consists of multiple pulses
with a duration (T90) of about 65 s (50-300 keV).
The time-averaged spectrum from T0-3.072 s to T0+92.161 s is
best fit by a Band function with Epeak = 233 +/- 5 keV,
alpha = -1.04 +/- 0.01, and beta = -2.18 +/- 0.02.

The event fluence (10-1000 keV) in this time interval is
(1.90 +/- 0.01)E-4 erg/cm^2. The 1.024-sec peak photon flux measured
starting from T0+59.521 s in the 10-1000 keV band
is 65.2 +/- 0.6 ph/s/cm^2.

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

B.P. Gompertz (U. Leicester), A. Melandri (INAF-OAB), P. D'Avanzo
(INAF-OAB), V. D'Elia (ASDC), D.N. Burrows (PSU), T.G.R. Roegiers
(PSU), L.M. McCauley (PSU), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester) and P.A. Evans (U. Leicester) report on behalf of the
Swift-XRT team:

Swift-XRT has performed follow-up observations of the
Fermi/LAT-detected burst GRB 150627A (Arimoto et al. GCN Circ. 17971
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 ),
collecting 4.9 ks of Photon Counting (PC) mode data between T0+33.6 ks
and T0+51.0 ks. 

An uncatalogued X-ray source is detected inside or close to the
Fermi/LAT error region and is above the RASS limit, and is therefore
likely the GRB afterglow.  The position of this source is RA,
Dec=117.4706, -51.4900 which is equivalent to:

RA (J2000): 07:49:52.94
Dec(J2000): -51:29:23.9

with an uncertainty of 3.5 arcsec (radius, 90% confidence).  This
position is 4.3 arcmin from the Fermi/LAT position. 

The light curve can be modelled with a power-law decay with a decay
index of alpha=2.2 (+/-0.3).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.99 (+/-0.13). The
best-fitting absorption column is  3.5 (+/-0.6) x 10^21 cm^-2, in
excess of the Galactic value of 2.6 x 10^21 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 3.8 x 10^-11 (5.8 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3.5 (+/-0.6) x 10^21 cm^-2
Galactic foreground: 2.6 x 10^21 cm^-2
Excess significance: 2.8 sigma
Photon index:	     1.99 (+/-0.13)

If the light curve continues to decay with a power-law decay index of
2.2, the count rate at T+24 hours will be 0.066 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.5 x
10^-12 (3.8 x 10^-12) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis of the likely afterglow
are at http://www.swift.ac.uk/ToO_GRBs/00020539/index_1.php.
The results of the full analysis of the XRT observations are available
at http://www.swift.ac.uk/ToO_GRBs/00020539.

[GCN OPS NOTE(28jun15):  Per author's request, the copy of the 
Swift-UVOT circular on this burst was deleted.  See GCN 17977
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  for the 
formal UVOT report on this burst.]

Paul Kuin (MSSL-UCL), Marissa McCauley (PSU) and Daniele Malesani 
(DARK/NBI) report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of the Fermi GRB 
150627A 33622 s after the LAT trigger (Arimoto et al., GCN Circ. 17971
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 ; 
Yu et al., GCN Circ. 17975
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 ).

An optical object consistent with the XRT position (Gompertz et al., GCN 
Circ. 17976
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 ) is detected at RA, Dec = 117.47108, -51.489417 deg (J2000), 
which is equivalent to:

RA (J2000):  07:49:53.06
Dec(J2000): -51:29:21.9

with an uncertainty of 1".

Preliminary detections using the UVOT photometric system (Breeveld et 
al. 2011, AIP Conf. Proc. 1358, 373) for the initial exposures are:

Filter           T_start(s)   T_stop(s)       Exp(s)      Mag

white         33963          34289         335     19.11+/-0.10
white         39860          40112         248     19.55+/-0.17
white         45659          45863         204     19.28+/-0.14
v         34304          34601         298     19.02+/-0.32
v         40117          40346         225     18.98+/-0.36
u         33622          38243         577     18.90+/-0.10
u         43668          45654         966     19.00+/-0.11

The magnitudes in the table are not corrected for the Galactic 
extinction due to the reddening of E(B-V) = 0.32 in the direction of the 
burst (Schlegel et al. 1998).

While no optical variability can be securely inferred from the UVOT 
photometry, the source is not visible in the DSS survey, and brighter 
than its limit, which suggests it to be the optical afterglow of GRB 
150627A.

V. Lipunov, E. Gorbovskoy,  N.Tyurina, V.Kornilov, 
P.Balanutsa,A.Kuznetsov,D.Kuvshinov,
Lomonosov Moscow State University, Sternberg Astronomical Institute


D.Buckley, S. Potter, A.Kniazev, M.Kotze
South African Astronomical Observatory


Rafael Rebolo, Miquel Serra, N. Lodieu, G. Israelian, L. Suarez-Andres
The Instituto de Astrofisica de Canarias


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

K.Ivanov, O.Gres, N.M.Budnev, S.Yazev, O.Chuvalaev, V.A.Poleshchuk
Irkutsk State University

V.Yurkov, Yu.Sergienko, D.Varda, E.Sinyakov, A.Gabovich
Blagoveschensk Educational State University, Blagoveschensk

V.Krushinski, I.Zalozhnih
Ural Federal University, Kourovka

Hugo Levato and Carlos Saffe
Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE)

Claudio Mallamaci, Carlos Lopez and Federico Podest
Observatorio Astronomico Felix Aguilar (OAFA)

MASTER II  robotic telescope (MASTER-Net: http://observ.pereplet.ru) 
located in SAAO was pointed to the  GRB150627.18 10133 sec after notice 
time and 55479 sec after trigger time at 2015-06-27 19:48:02 
16:32:07 UT. On our 
first (180s exposure)  set we  found optical transient within LAT 
error-box (ra=07 49 57 dec=-51 33 34 r=0.500000, Arimoto et al., GCN 
17791
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 ) brighter then 16.87.

07h 49m 53.05s , -51d 29m 21s.4  error =+-1.0
m ~ 19.0

This postion 2 arcsec close X-ray position (Gompertz et al., 17976)
The 5-sigma upper limit has been about 16.87mag
The message may be cited.

V. Lipunov (Lomonosov MSU)

I am sorry for mistake.
The correct time of the first exposition is 2015-06-27 16:32:07 (43664 s 
after trigger).
I am out from good internet now. So, I did no see UVOT OT detection
Paul Kuin et al.,GCN 17977 .

The message may be cited.

S. Golenetskii, R. Aptekar, D. Frederiks, V. Pal'shin, P. Oleynik,
M. Ulanov, D. Svinkin, A. Tsvetkova, A. Lysenko, and T. Cline
on behalf of the Konus-Wind team, report:

The long-duration, bright GRB 150627A
(Fermi-LAT detection: Arimoto, et al., GCN Circ. 17971
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 ;
Fermi-GBM detection: Yu, GCN Circ. 17975
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 )
triggered Konus-Wind at T0=15806.292 s UT (04:23:26.292).

The burst light curve shows a bright multi-peaked structure
from ~T0-6 s to ~T0+80 s followed by a weak tail,
which is traceable out to ~T0 + 150 s.
The emission is seen up to ~15 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB150627_T15806/

As observed by Konus-Wind, the burst
had a fluence of 2.34(-0.11,+0.12)x10^-4 erg/cm2,
and a 64-ms peak flux, measured from T0+12.240 s,
of 2.02(-0.27,+0.27)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+81.408 s)
is best fit in the 20 keV - 15 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.98(-0.04,+0.05),
the high energy photon index beta = -2.25(-0.08,+0.07),
the peak energy 217(-13,+14) keV
(chi2 = 125/96 dof)

The spectrum near the maximum count rate
(measured from T0+9.728 to T0+12.800 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.55(-0.07,+0.08),
the high energy photon index beta = -2.52(-0.29,+0.18),
the peak energy 412(-38,+40) keV
(chi2 = 114/94 dof)

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