GRB 070616

R. L. C. Starling (U Leicester), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), D. N. Burrows (PSU),
P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC),
C. Guidorzi (Univ Bicocca&INAF-OAB), J. A. Kennea (PSU),
C. B. Markwardt (CRESST/GSFC/UMD), F. E. Marshall (NASA/GSFC),
P. T. O'Brien (U Leicester), J. P. Osborne (U Leicester),
K. L. Page (U Leicester), D. M. Palmer (LANL), A. M. Parsons (GSFC),
G. Sato (GSFC/ISAS), M. Stamatikos (NASA/ORAU),
D. E. Vanden Berk (PSU) and L. Vetere (PSU) report on behalf of the
Swift Team:

At 16:29:33 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 070616 (trigger=282445).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 32.155, +56.948 which is 
   RA(J2000)  =  02h 08m 37s
   Dec(J2000) = +56d 56' 53"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows nothing much 
around T_zero (as is typical for image triggers).  We note that there
is bright and variable activity in the TDRSS lightcurve starting at T+100 sec
and lasting to 600 sec.  This may be long-term burst activity, although we can
not rule out a contribution from a bright galactic source such as Cyg X-1
coming into the FOV (due to the slew).  We will be able to separate this 
ambiguity when we get the full Malindi data to construct a mask-weighted 
lightcurve. 

The XRT began observing the field at 16:31:44 UT, 131 seconds after the
BAT trigger. XRT found a bright, variable and fading, uncatalogued X-ray source. 
Using prompt downlinked data we find a position of 
located at RA, Dec 32.1513, +56.9451 which is
   RA(J2000)  =  02h 08m 36.3s
   Dec(J2000) =  56d 56' 42.5"
with an uncertainty of 4.9 arcseconds (radius, 90% containment). 
This location is 12.7 arcseconds from the BAT on-board position,
within the BAT error circle. The initial flux in the 2.5s image
was 7.6e-09 erg/cm2/s (0.2-10 keV). 
We note that this is 3.1 arcseconds from source USNO-B1.0 1469-0076513. 


UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm)
filter starting 142 seconds after the BAT trigger. No 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 18.5 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 large, but uncertain extinction expected.

M. Stamatikos (GSFC/ORAU), L. Barbier (GSFC), S.D. Barthelmy (GSFC),
J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC),
H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL),
A. Parsons (GSFC), T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS),
R.L.C. Starling (U Leicester), J. Tueller (GSFC), T. Ukwatta (GWU)
(i.e. the Swift-BAT team):
 
Using the data set from T-239 to T+497 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 070616 (trigger #282445)
(Starling, et al., GCN Circ. 6542
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 ).  The BAT ground-calculated position is
RA, Dec = 32.096, 56.946 deg  which is 
   RA(J2000)  = 02h 08m 23.0s 
   Dec(J2000) = 56d 56' 45" 
with an uncertainty of 2.6 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 60%.
 
The mask-weighted light curve shows many peaks.  The burst started with 
a low-level smooth emission at ~T-55 sec continuing smoothly and increasing
slowly until ~T+100 sec when the main emission started. The main peak is
at T+120 sec.  Smaller overlapping peaks continue out past T+500 sec
(the limit of the downloaded data so far).  We are currently in the gap
of Malindi downlink passes, and will not receive more data until
03:30 UT 17 Jul 07.  We will issue another Circular then describing
the activity beyond T+500 sec and giving the T90 value.  T90 is at least 175 sec.

Since we do not have the full data set downlinked yet, we will not
quote any spectral parameters at this time.

D. A. Kann, U. Laux, B. Stecklum and S. Klose (TLS Tautenburg) report:

We observed the field of Swift GRB 070616 (Starling et al., GCN 6542
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 ) with 
the Tautenburg 1.34m Schmidt telescope. A single 600 second image in Ic 
was obtained before clouds forced us to shut down. The airmass was 1.95.

At the XRT position (Starling et al., GCN 6542
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 ), we do not detect any 
afterglow. Assuming the USNO B1.0 star at RA = 02:08:34.67,
Dec. = +56:56:22.3 to have I = 15.44, we derive the following upper limit 
for the image:

date		time (days)	exp. time	Ic limit
070617.00838	0.32119		600		20.3

We caution that, as Starling et al. (GCN 6542
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 ) noted, this is very close 
to a star in the USNO B1.0 catalog. Thus, the true limiting magnitude at 
the XRT position is much shallower than what is stated above.

Judging from the early BAT/XRT light curve, this is a real GRB that 
happens to lie close to a bright star by chance. As the field is crowded, 
the probability of such a chance alignement is non-negligible.

This message may be cited.

M. De Pasquale (MSSL/UCL), R. Starling (Univ. Leicester)
and P. Schady (MSSL/UCL) report, on the behalf ot the Swift
UVOT team:

  The Swift UVOT telescope began its White filter finding
chart exposure of GRB070616 (Starling et al., GCN circ 6542
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 )
144 seconds after the trigger. The XRT position lies on
a bright object, listed in the USNO-B1.0 catalogue, therefore
we caution that this source strongly affects the photometry.
In the XRT error circle we do not detect any optical
afterglow. We derive the following 3 sigma upper limits:


Filter  Time after trigger (s)  Exposure (s)   3s U.L.

  White       144-243              98            18.3

  V           250-649             390            18.1


  White       144-979             209            18.6

  V           250-1122            547            18.3

  B           729-738             10             17.1

  U           707-874             39             17.2

  UW1         680-850             39             17.1

  UM2         655-825             39             17.3

  UW2         758-777             20             17.0


  No correction has been made for the high Galactic
reddening of E(B-V)=0.4. We note that this value should
be taken with caution, having the burst occurred at low
Galactic latitude.

T. Fatkhullin, V. Sokolov (SAO-RAS, Russia), E. Sonbas
(Cukurova Univ., Turkey), A. de Ugarte Postigo, M. Jelínek,
J. Gorosabel (IAA-CSIC, Spain), D. Pérez-Ramírez (Univ.
de Jaén, Spain), S. Guziy (Nikolaev St. Univ., Ukraine) and
A. J. Castro-Tirado (IAA-CSIC, Spain),

report:

"Following the detection by SWIFT of GRB 070616 (Starling
et al. GCNC 6542), we have obtained single VRI frames at the
6m BTA SAO-RAS telescope at Nizhnij Arkhyz (Russia), starting
at 23:57 UT (i.e. 7.5 hr after the event). Within the SWIFT/XRT
error box , we detect in all filters a faint (R ~ 22), reddened
point-like source. Preliminary astrometry yielded RA (J2000)
= 02 08 36.00; Dec (J2000) = +56 56 41.0  (+/- 1"), a position
very close to the USNO B-1 star reported by Kann et al. (GCNC
6545). Further observations are needed to confirm if this is the
optical afterglow to GRB 070616. "

This message can be quoted.

A. de Ugarte Postigo (IAA-CSIC) T. Fatkhullin
(SAO-RAS, Russia), A. J. Castro-Tirado (IAA-CSIC,
Spain) on behalf of a larger collaboration report:

"We have redone astrometry of the optical afterglow
candidate reported by Fatkhullin et al. (GCNC 6547)
for GRB 070616 (Starling et al. GCNC 6542). The
updated position for the object is (J2000, +/- 0.5"):

R.A.: 02:08:36.12
Dec. +56:56:39.7

A finding chart can be found at:

http://www.iaa.es/~deugarte/GRBs/070616/GRB070616.gif "

This message can be quoted.

R.L.C. Starling (U. Leicester) reports, on behalf of the Swift XRT team:

We have analysed the first eight orbits of Swift XRT data (18.6 ks of data 
out to T0+5.8E4s) for GRB 070616 (Starling et al., GCN Circ. 6542
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 ).

Using 1.1 ks of overlapping XRT PC mode data and UVOT V-band data, we
obtain an astrometrically corrected X-ray position (using the USNO-B1 
catalogue) of 

RA(J2000) = 02 08 36.70
Dec(J2000)= +56 56 43.9

with an error of 2.3 arcseconds (radius, 90% containment).
This is 3.7 arcsec from the initially reported XRT position
and 6.4 arcsec from the BAT position (GCN Circ. 6542
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 ), and 6.3 arcsec from 
the possible optical transient reported in De Ugarte Postigo et al. (GCN
Circ. 6548
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 ). The error circle overlaps with the USNO-B1.0 source noted in 
GCN Circ. 6542
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 .

The lightcurve began with a constant flux up to T0+536s, and then decayed 
with alpha=-4.6 until about T0+1000s. A steep decay follows this, though
there are not enough data to accurately measure its slope. 
After T0+1400s the decay continues with a shallower slope of alpha=-1.2.
Several small flares appear on top of the continuum emission up to 
T0+1000s, some of which may be simultaneous with BAT peaks.

The PC mode spectrum including 14.6 ks of data from the second orbit 
onwards is well fit with a power law of photon index
Gamma=2.4+0.2,-0.1 (90%) absorbed only by the large Galactic column of 
3.4E21 cm^-2.
The 0.3-10 keV observed (unabsorbed) flux is 2.2E-12 (4.0E-12) erg/cm^2/s,
corresponding to a count rate of 4.9E-02 count/s.

The predicted fluxes at T0+24h and T0+48h are 2.3E-13 and 9.9E-14 
erg/cm^2/s respectively, assuming the decay continues with alpha=-1.2.

This is an official product of the Swift XRT team.

G. Sato (GSFC/ISAS) and S. Barthelmy (GSFC)
on behalf of the Swift-BAT team:

The time-averaged spectrum from T-2.6 to T+602.2 sec is best fit
by a simple power-law model.  The power law index of the time-averaged
spectrum is 1.61 +- 0.04.  The fluence in the 15-150 keV band is
1.92 +- 0.03 x 10^-5 erg/cm2.  The 1-sec peak photon flux measured
from T+139.74 sec in the 15-150 keV band is 1.9 +- 0.1 ph/cm2/sec.
All the quoted errors are at the 90% confidence level.
 
The mask-weighted light curve shows many peaks.  The burst started with 
a low-level smooth emission at ~T-55 sec continuing smoothly and increasing
slowly until ~T+100 sec when the main emission started.  The main peak is
at T+120 sec.  Smaller overlapping peaks continue out past T+550 sec.
In particular, there is a small peak from T+730 to T+850 sec which is coincident
with a peak (flare) in the XRT lightcurve (Fig 2, GCN Report 66.1,
Starling et al.).  T90 (15-350 keV) is 402 +- 10 sec (estimated error
including systematics).

M. Yoshida, K. Yanagisawa, Y. Shimizu, S. Nagayama (OAO, NAOJ)
and N. Kawai (Tokyo Tech) report on behalf of the MITSuME
collaboration:

We performed optical imaging observation (g', Rc, and Ic) of the
field of GRB 070616 (Starling et al. GCN 6542
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 ) with 50cm MITSuME
telescope at Okayama Astrophysical Observatory from UT 18:04:40
(1h 35m after burst) to UT 18:10:30 on June 16 2007.

We coadded 5 CCD frames for each band. Exposure time of each
frame is 1 minute. We made flux calibration using USNO B1.0
catalg. We could not identify new source at the position of the
afterglow candidate reported by Fatkhullin et al. (GCN 6547
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 ) and
Ugarte Postigo (GCN 6548
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 ). Three sigma limiting magnitudes of
our observation are listed below.

----------------------------------------------------
band  mid-UT (2007)      exp.time     upper limit
g'    June 16 18:07:35   5 x 1 min.   19.5 mag
Rc    June 16 18:07:35   5 x 1 min.   18.9 mag
Ic    June 16 18:07:35   5 x 1 min.   18.4 mag
----------------------------------------------------

T. Ishimura, Y. Yatsu, T. Shimokawabe, N. Vasquez, Y.kudo, and 
N. Kawai (TokyoTech) report on behalf of the MITSuME collaboration:

We observed the error box of GRB070616 (Starling et al. GCN 6542
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 )
with the 3-color 50cm MITSuME Telescope at Akeno, Japan starting
at 16:52:26 June 16 UT, 22m53s after the trigger under a poor sky
condition with clouds and a high airmass.
In the co-added images of Ic, Rc, and g' bands, we did not detect
any afterglow candidate in the XRT error circle.  The 3-sigma limiting
magnitudes based on USNO-B1.0 (I-band) and NOMAD (R-band,g'-band)
stars are following.

Filter   start time   end time    Exposure   Mag (3-sigma upper limit)
-----------------------------------------------------------------
g'       16:52:26     18:03:39    58 x 60 s    17.8
Rc       16:52:26     18:03:39    58 x 60 s    19.1
Ic       16:52:26     18:03:39    58 x 60 s    18.6
-----------------------------------------------------------------

M. De Pasquale (MSSL/UCL), R. Starling (Univ. Leicester),
F. E. Marshall (NASA/GSFC), S. Holland (CREEST/USRA/GSFC),
P. Schady (MSSL/UCL), M.J. Page (MSSL/UCL) report, on the
behalf of the UVOT team:

  After a careful investigation of the refined XRT error circle of
GRB070616 (Starling et al, GCN circ 6550
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 ), which contains the
bright (V=14.4) star USNO-B1.0 1469-0076513, we find good evidence
to suggest that the optical afterglow is detected in the early
Swift/UVOT observations.

  The count rates in V and U band exposures between 250 and 1050
seconds after the trigger show a significant excess (at the 10
sigma level in the V band combined image and at the 5 sigma level
in the U band combined image) with respect to late observations
(T>1 day). This excess corresponds to an optical source of V=16.5
and U=16.9. The source appears to have disappeared in exposures
taken later than 1100s, thus suggesting a drop in the optical flux
suggestive of a GRB afterglow behaviour. We obtain a 3 sigma upper
limit of V>17.9 at T= 6ks after the trigger.

  The blended image of the star plus the afterglow is extended
compared to other stars in the image. Fitting it with two point
sources indicates that the afterglow is about 1.8" west and 0.9"
north of USNO-B1.0 star with a statistical uncertainty of ~0.3"
in each axis (90% confidence). A detection of the afterglow in
the U band indicates a redshift less than ~3.

  Analysis of another star in the same field of view reveals no
change of flux throughout the observations, thus ruling out
instrumental effects. While we cannot completely exclude that
the star in the XRT error circle might have varied mimicking a
GRB afterglow, observations carried out for the further 2 days
suggest a constant source. Furthermore, the UV magnitudes of the
star in the XRT error circle do not show any significant variation
corresponding to those seen in the optical filters, thus
supporting the afterglow hypothesis.

K. Morigami, N. Kodaka, K. Onda, M. Tashiro, M. Suzuki, Y. Urata,
A. Endo (Saitama U.), T. Uehara, M. Ohno, T. Takahashi, Y. Fukazawa,
C. Kira (Hiroshima U.), T. Enoto, R. Miyawaki, K. Nakazawa,
K. Makishima (Univ. of Tokyo), K. Yamaoka, Y. E. Nakagawa,
S. Sugita (Aoyama Gakuin U.), T. Tamagawa, Y. Terada (RIKEN),
S. Hong (Nihon U.), M. Kokubun, M. Suzuki, T. Takahashi (ISAS/JAXA),
E. Sonoda, M.Yamauchi, S. Maeno, H. Tanaka, R. Hara (Univ. of Miyazaki),
and Suzaku WAM team report:

The long burst, GRB 070616 (Swift/BAT trigger #282445; Starling et al.,
GCN circ 6542
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 ; Sakamoto et al., GCN circ 6543
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 ; Starling et al., GCN
Report 66.2) triggered the Suzaku Wide-band All-sky Monitor (WAM)
covering 50 keV to 5 MeV at 16:31:50 UT (T0), which was 137 second
after the Swift/BAT trigger time. Since The WAM BST mode data did not
cover the Swift/BAT trigger time, we employed continuous monitoring
(TRN) data to evaluate the whole light curve and the averaged spectrum
of the burst. The observed light curve exhibits multiple peaked
structures preceded by a precursor-like emission (from T0-163 to T0-158 
seconds). Although Starling et al. reported a very long duration, over 
600 seconds (GCN Report 66.1), the Suzaku/WAM covered only 140 seconds 
from the start of the main peaks before the entry of the SAA region in 
the orbit.

The derived fluence in 100-1000 keV was more than
6.6 (-0.6, +0.7) x 10^-6 erg/cm^2. The 1-s peak flux was
1.40 (-0.17,+0.16) photons/cm^2/s in the same energy range.

Preliminary result shows that the time-averaged spectrum from T0-10 to
T0+30 seconds is well fitted with a single power-law of a photon
index Gamma = 2.36 (-0.12, +0.12) in the 100-1000 keV energy range.

All the quoted errors are at statistical 90% confidence level, while
the systematic errors are not considered.

The light curve data for this burst is available at the following web site.

http://www.astro.isas.ac.jp/suzaku/HXD-WAM/WAM-GRB/grb/trig/grb_table.html

N. Kodaka,  K. Onda, Y. Urata, W. Iwakiri, T. Sugasahara, M. Tashiro
(Saitama-U),  M. Kuwahara (TUS/RIKEN), T. Tamagawa (RIKEN) F. Usui
(ISAS/JAXA) report:

"We observed the error region of GRB 070616 (Swift/BAT trigger #282445;
Starling et al., GCN 6542
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 ; Sakamoto et al., GCN circ 6543
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 ; Starling et
al., GCN Report 66.2) with the very wide-field camera WIDGET located at
Kiso, Japan. The WIDGET monitored the region with repeat of unfiltered
5-second exposures between 27 seconds before and 136 seconds after the
burst.

We did not find any  optical emission from the afterglow position
(Fatkhullin et al. GCN  6547
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 ). The 1-sigma limiting magnitude of
each frame derived by the Tycho-2 catalog was around V=11.8 magnitudes."

This message may be cited.

D. A. Kann & A. C. Wilson (TLS Tautenburg) report:

We reobserved the field of GRB 070616 (Starling et al., GCN 6542
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 ) with the 
Tautenburg 1.34m Schmidt telescope. We obtained 6 x 300 second images in 
the I band in good observing conditions but with a few passing clouds. 
Using the same USNOB1.0 star as used by Kann et al. (GCN 6545
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 ), we 
determine the following limiting magnitude:

date            time (days)     exp. time       Ic limit
070715.00750    28.32031        6 x 300         21.6

Using this star and three other unsaturated, isolated stars, we determine 
differential magnitudes between the star that is blended with the 
afterglow (de Pasquale et al., GCN 6557
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 ) and these stars at both epochs.

We find that between the two epochs the star has become fainter by 0.064, 
0.023, 0.041 and 0.001 magnitudes in comparison to the other four stars. 
The typical errors are 0.02 magnitudes.

We therefore conclude that we detect no significant fading between epoch 
one (star + possibly blended afterglow) and epoch two (star only), placing 
a limit of Ic > 20 on the afterglow at the first epoch (Kann et al., GCN 
6545
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 ).

This message may be cited.