GRB 150608A

M.G. Bernardini (INAF-OAB), P. D'Avanzo (INAF-OAB) and A. Melandri 
(INAF-OAB)
report on behalf of the Swift-XRT team:

A second epoch of XRT data was collected on the field of the MAXI-detected
burst: GRB 150608A (Arimoto, et al., GCN Circ. 17912
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 ) on 2015 June 13.
The observations consist of 2 ks of PC mode data, from T0+389 ks to 
T0+395 ks.

The X-ray source reported in GCN Circ. 17917
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 , Bernardini et al., 
measured at
a mean count rate of 8.3e-01 count/sec (0.3-10 keV) in the first epoch 
of XRT
observations has faded to a mean count rate of (7.1e-03+/-2.2e-03) 
count/sec
(0.3-10 keV) in the second epoch. Assuming a power-law decay, the 
corresponding
decay index is alpha=1.28 (-0.11, +0.17).  We therefore confirm that 
this is
the X-ray afterglow of GRB 150608A.

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

Y.Saito, T.Fujiwara, T. Yoshii, Y. Tachibana, H. Ohuchi, Y. Yano,
S. Kurita, Y.Ono, S.Harita, Y.Muraki, Y. Yatsu, and N. Kawai (Tokyo Tech)
report on behalf of the MITSuME collaboration:

We observed the field of GRB 150608A (M.Arimoto et al., GCN Circular #17912
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 ) with the optical three color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50 cm telescope of Akeno Observatory, Yamanashi, Japan.

The observation started on 2015-06-09 18:17:37 UT (~30.5 h after the burst). We cound not detect any optical point source in the error circle of the previously reported afterglow detected by Swift-XRT (M.G.Bernardini et al., GCN Circular #17917
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 ) in all three bands.

Three sigma upper limits are listed below.

T0+[hour]      MID-UT      T-EXP[sec]         g'           Rc           Ic
---------------------------------------------------------------------------------------
  30.5131     18:23:03          600            > 17.9     > 18.0     > 17.4
---------------------------------------------------------------------------------------
T0+ : Elapsed time after the burst
T-EXP: Total Exposure time
We used GSC2.3 catalog for flux calibration

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:

A long-duration GRB triggered Konus-Wind on June 8, 2015
at T0=42325.791 s UT (11:45:25.791), ~80 s before
the MAXI trigger (GRB 150608A; Arimoto, et al., GCN Circ. 17912
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 ).

The KW light curve shows a multi-peaked complex which
started at ~T0-75 s and lasted until ~T0+5 s.
This phase of the emission was followed, in ~75 s,
by a weaker pulse, which triggered MAXI.
Taking into account the proximity of this burst
to the MAXI/GSC trigger and consistency of the
KW ecliptic latitude response with the position
of GRB 150608A we suggest that KW observed
the main part of GRB 150608A.

The K-W light curve of this burst is available at
http://www.ioffe.rssi.ru/LEA/GRBs/GRB150608_T42325/

As observed by Konus-Wind, the burst had a fluence of 
2.4(-0.3,+0.3)x10^-5 erg/cm2, and a 2.944-s peak flux,
measured from T0-0.302 s, of 8.8(-1.2,+1.2)x10^-7 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

Since the bulk of the burst emission lies before the triggered
mode record, the spectral analysis was performed using
KW 3-channel waiting mode data.

Modeling the 3-channel time-integrated spectrum
(from T0-73.209 s to T0+5.586 s) by a power law
with exponential cutoff (CPL) model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
yields alpha = -1.56 �� 0.14, and Ep = 209 �� 46 keV.

Modelling the 3-channel spectrum near the peak count rate
(from T0-3.246 s to T0+2.642 s) by the CPL model
yields alpha = -0.94 �� 0.26, and Ep = 199 �� 37 keV.

All the quoted errors are estimated at the 1 sigma confidence level.
All the presented results are preliminary.

M.G. Bernardini (INAF-OAB), P. D'Avanzo (INAF-OAB), A. Melandri
(INAF-OAB), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU), A.
Amaral-Rogers (U. Leicester), J.P. Osborne (U. Leicester), A. D'ai
(INAF-IASFPA), A. Maselli  (INAF-IASFPA), D.N. Burrows (PSU) and P.A.
Evans (U. Leicester) report on behalf of the Swift-XRT team:

Swift-XRT has performed follow-up observations of the MAXI-detected
burst GRB 150608A (Arimoto et al. GCN Circ. 17912
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 ) in a series of
observations tiled on the sky. The total exposure time is 3.1 ks,
distributed over 7 tiles; the maximum exposure at a single sky location
was 955 s. The observations started at T0+8.0 ks, and are entirely in
Photon Counting (PC) mode. 

An uncatalogued X-ray source is detected in the data collected between
T0+9.1 ks and T0+14.7 ks. This source is above the RASS limit and is
therefore likely the GRB afterglow. The position of this source is RA,
Dec=13.1663, -0.6442 which is equivalent to:

RA (J2000): 00:52:39.90
Dec(J2000): -00:38:39.0

with an uncertainty of 3.6 arcsec (radius, 90% confidence).  This
position is 29.1 arcmin from the MAXI position.  The light curve is
consistent with a constant source of mean count rate 8.3e-01 ct/sec. 

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.78 (+0.28, -0.26). The
best-fitting absorption column is  9.8 (+8.3, -6.0) x 10^20 cm^-2,
consistent with the Galactic value of 3.8 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 3.5 x 10^-11 (4.0 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     9.8 (+8.3, -6.0) x 10^20 cm^-2
Galactic foreground: 3.8 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.78 (+0.28, -0.26)

The results of the XRT-team automatic analysis of the likely afterglow
are at http://www.swift.ac.uk/xrt_products/TILED_GRB00045/index_2.php.
The results of the full analysis of the tiled XRT observations are
available at http://www.swift.ac.uk/xrt_products/TILED_GRB00045.

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

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

Swift has initiated a series of observations, tiled on the sky, of the
MAXI GRB 150608A. Automated analysis of the XRT data will
be presented online at http://www.swift.ac.uk/xrt_products/TILED_GRB00045

Any uncatalogued X-ray sources detected in this analysis will be
reported on this website and via GCN COUNTERPART notices. The probability of finding
serendipitous sources, unrelated to the MAXI event is high: 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.

M. Arimoto (Tokyo Tech), H. Negoro (Nihon U.),
S. Ueno, H. Tomida, S. Nakahira, M. Kimura, M. Ishikawa, Y. E. Nakagawa (JAXA),
T. Mihara, M. Sugizaki, M. Serino, M. Shidatsu, J. Sugimoto, T.
Takagi, M. Matsuoka (RIKEN),
N. Kawai, T. Yoshii, Y. Tachibana, Y. Ono, T. Fujiwara (Tokyo Tech),
A. Yoshida, T. Sakamoto, Y. Kawakubo, H. Ohtsuki (AGU),
H. Tsunemi, R.Imatani (Osaka U.),
M. Nakajima, K. Tanaka, T. Masumitsu (Nihon U.),
Y. Ueda, T. Kawamuro, T. Hori (Kyoto U.),
Y. Tsuboi, S. Kanetou (Chuo U.),
M. Yamauchi, D. Itoh (Miyazaki U.),
K. Yamaoka (Nagoya U.), M. Morii (ISM)
report on behalf of the MAXI team:

The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray
transient source at 11:46:50 UT.
Assuming that the source flux was constant over the transit,
we obtain the source position at

(R.A., Dec) = (13.389 deg, -0.213 deg) = (00 53 33, -00 12 46) (J2000)

with a statistical 90% C.L. elliptical error region
with long and short radii of 0.50 deg and 0.22 deg, respectively.
The roll angle of long axis from the north direction is 30.0 deg
counterclockwise.
There is an additional systematic uncertainty of 0.1 deg (90%
containment radius).

The X-ray flux averaged over the scan was 294 +- 58 mCrab
(4-10keV, 1 sigma error).

Without assumptions on the source constancy,we obtain a rectangular error
box for the transient source with the following corners:
(R.A., Dec) = (12.424 deg, -0.277 deg) = (00 49 41, -00 16 37) (J2000)
(R.A., Dec) = (12.873 deg, 0.622 deg) = (00 51 29, +00 37 19) (J2000)
(R.A., Dec) = (14.875 deg, -0.382 deg) = (00 59 29, -00 22 56) (J2000)
(R.A., Dec) = (14.462 deg, -1.299 deg) = (00 57 50, -01 17 56) (J2000)
There was no significant excess flux in the previous transit at 6/8 10:14 UT.