GRB 050709

M. Bayliss, J. Haislip, A. Foster, D. Reichart report on behalf of the UNC
team of the FUN GRB Collaboration:

The PROMPT-5 telescope automatically responded to HETE2-SXC alert
3862 for GRB 050709 and imaged the field for 3600s in Rc beginning
approximately 27 hours after the time of the GRB.  Preliminary analysis
reveals no new source down to the limit of the DSS.

PROMPT is still being built and commissioned.

N. Butler, G. Ricker, J-L. Atteia, N. Kawai, D. Lamb, and S. Woosley,
on behalf of the HETE Science Team;
 
M. Arimoto, T. Donaghy, E. Fenimore, M. Galassi, C. Graziani,
J. Kotoku, M. Maetou, M. Matsuoka, Y. Nakagawa, T. Sakamoto, R. Sato,
Y. Shirasaki, M. Suzuki, T. Tamagawa, K. Tanaka, Y. Yamamoto,
and A. Yoshida, on behalf of the HETE WXM Team;
 
G. Crew, J. Doty, G. Prigozhin, R. Vanderspek, J. Villasenor,
J. G. Jernigan, A. Levine, G. Azzibrouck, J. Braga, R. Manchanda,
and G. Pizzichini, on behalf of the HETE Operations and HETE
Optical-SXC Teams;
 
M. Boer, J-F Olive, J-P Dezalay, and K. Hurley, on behalf of the HETE
FREGATE Team;
 
report:

The HETE FREGATE, WXM, and SXC instruments detected GRB 050709 at 22:36:37
UT (81396.7 SOD) on 9 July 2005.  This was a single hard pulse 100ms long,
followed about 30s later by a soft, faint, approximately 150s long pulse
from the same location.  The later pulse was only detected by WXM and SXC,
since the spectrum of its emission was confined to below 10 keV.

The WXM obtained a localization in flight.  However, the spacecraft
attitude-control system had experienced an upset approximately 19 minutes
earlier, so HETE was drifting at the time of the trigger, and real-time
aspect information was not available.  Consequently, the location was not
distributed in real time.

Ground analysis of the data from the optical cameras has provided reliable
aspect despite the issues associated with the high spacecraft drift rate. 
A GCN Notice was sent out at 22:00:29 UT on 10 July 2005, upon the
resolution of spacecraft aspect issues.  The 90% confidence region of the
WXM location may be expressed as a circle centered at

  R.A. = +23h 01m 44s ; Dec. = -38d 59' 52" (J2000)

with a radius of 14.5'.

Ground analysis of the SXC data yields a refined location with a 90%
confidence region that may be expressed as a circle centered at

  R.A. = +23h 01m 30s ; Dec. = -38d 58' 33" (J2000)

with a radius of 1.34'.

A preliminary spectral analysis based on a fit of a cutoff power-law model
to  the initial spike indicates that Epk ~ 90 keV.  The 30-400 keV fluence
is 1.0E-06 erg cm^-2, while the  2-30 keV fluence is 4.0E-07 keV.  The
enormously softer character of the tail emission suggests that it may be
possible to interpret it as the onset of the afterglow of this burst.  If
this interpretation is correct, then GRB050709 is a localized short hard
burst.

A light curve, skymap, and spectral information for GRB 050709 are
provided at the following URL:

http://space.mit.edu/HETE/Bursts/GRB050709/

B. Monard (Bronberg Obs.) reports on behalf
of the AAVSO International High Energy Network:

We observed the localization of the HETE burst GRB050709
(Graziana et al. GCN 3570
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 ) with the 30cm telescope of Bronberg
Observatory.  532 seconds of stacked unfiltered observations
with mipoint at 050711.127 (28.4hrs after the burst) reached
a limiting magnitude of CR=20.0.  No new object is present
in the HETE SXC error box to a limiting magnitude of 19.5R,
compared to the DSS-2 red image.  The images also covered
about 1/2 of the WXM error box.

The AAVSO thanks the Curry Foundation for their continued support of the
AAVSO International High Energy Network.

S. Bradley Cenko, Derek B. Fox (Caltech), Edo Berger (Carnegie), and
Brian Lee (Toronto) report on behalf of the Caltech-NRAO-Carnegie
collaboration:

We have have obtained two epochs of imaging of the field of GRB 050709
(GCN 3570
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 ) with the 40-inch Swope telescope at Las Campanas Observatory.
Both epochs consisted of 3 x 600 sec images in the Sloan i' filter.  The
time of the first epoch was approximately 11 July 2005 4:15 UT (~ 29.6
hours after the burst), while the second epoch was taken 6.3 hours
later.  

Image subtraction of the two epochs reveals no variables sources to a
limiting magnitude of i' < 20.3 (estimated by comparison with several
USNO-B stars in the field).

A. Morgan, D. Grupe, C. Gronwall, J. Racusin, A. Falcone (PSU), F. 
Marshall (GSFC), M. Chester (PSU), and N. Gehrels (GSFC) report on 
behalf of the Swift UVOT and XRT teams:

HETE detected GRB 050709 at 22:36:37 UT on 9 July 2005. (Butler et al., 
GCN 3570
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 ).  Swift executed a Target of Opportunity observation of the 
HETE position.  The Swift Ultra-Violet/Optical Telescope (UVOT) and 
X-Ray Telescope (XRT) began observations of GRB 050709 at UT 13:06:53 on 
11 July 2005, approximately 38.5 hrs after the HETE detection.

We detect no new source with either telescope within the 1.34' HETE 
error circle.  In the V filter of the UVOT, we find the following 5 
sigma and 3 sigma limiting magnitudes (in 6" radius apertures measured 
at the HETE position):

Filter    Lim_Mag      Lim_mag   Exposure time (s)   T_range (hr)
          5sigma       3sigma

V         21.08        21.64        17752            38.50 - 50.27

For XRT data, we assumed a typical spectrum.  We find the following 1 
sigma and 3 sigma upper limits (in 50" radius apertures measured at the 
HETE position):

Lim_Flux     Lim_Flux   Exposure time (s)   T_range (hr)
1sigma       3sigma

2e-14        6e-14         15243            38.50 - 50.27

The limiting flux is given in units of erg/s/cm^2.  T_range is the range 
from the HETE detection from the beginning of the first observation to 
the end of the last.

The UVOT magnitudes are based on preliminary zero-points, measured in 
orbit, and will require refinement with further calibration.

This message may be cited.

P. B. Cameron (Caltech) and D. A. Frail (NRAO) report on behalf of the
Caltech-NRAO-Carnegie collaboration:

"We observed the field of GRB050709 (GCN 3570
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 ) with the Very Large Array
at 8.5 GHz on July 11.51 UT. We detect one known source with
Ra=23h01m32.1s Dec=-38d59m27s from the 20-cm NVSS (Condon et al. 1998).
There are no new radio sources above 5-sigma in the SXC error region,
where sigma=21.5 uJy. Further observations are planned."

D.B. Fox (Caltech), D.A. Frail (NRAO), P.B. Cameron (Caltech), and
S.B. Cenko (Caltech) report on behalf of the Caltech-NRAO-Carnegie GRB
Collaboration:

"We have observed the HETE localization region for GRB050709, a likely
short-hard gamma-ray burst (Butler et al., GCN 3570
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 ) with the Chandra
X-ray Observatory + ACIS, in a single 44 ksec observation beginning at
2005 July 12.2 UT (mean epoch 2.52 days after the burst).  Excluding
intervals of significant background flares, we retain 38.4 ksec good
time.  Performing a standard "wavdetect" analysis, we identify three
sources within the SXC error circle.  The fainter two of these sources
are very close to each other and are coincident with the bright radio
(NVSS/20-cm and 8.5 GHz) source identified by Cameron & Frail (GCN
3578
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 ).  The brightest source within the error circle has a total of
49.5 +/- 8.8 counts (0.3-8.0 keV) and is located at:

    RA 23:01:26.96, Dec -38:58:39.5 (J2000),

where we have made a slight (0.4") adjustment to the native astrometry
based on the optical/X-ray coincidence of three other sources in the
field, and estimate our positional uncertainty as less than 0.5".  

This position is ~1" distant from an R~20.5 mag point-like object
visible in images from the Digitized Sky Survey.  Given that our
position is marginally consistent with this object, and that we cannot
at this time demonstrate significant fading behavior, we caution
observers that the source could be revealed to be a coronally-active
star or AGN.  Nonetheless, we consider it a reasonable afterglow
candidate; in particular, the X-ray flux (~8.4E-15 erg/cm2/s, 2-10
keV) is consistent with a ~t**(-1.4) power-law decay from the
afterglow peak observed by the SXC (assuming this peak reached ~3E-10
erg/cm2/s, 2-10 keV, at 100 sec after the burst); this flux and decay
rate would also be consistent with the Swift XRT non-detection (Morgan
et al., GCN 3577
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 ).

A particularly intriguing prospect given observations of the
short-hard burst GRB050509B (Barthelmy et al., GCN 3385
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 ; Prochaska et
al., GCN 3390
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 ) is that the DSS object 1" distant from this candidate
afterglow may be the burst host galaxy."

GRB050709.94 : Chandra source optical counterpart

B. L. Jensen, U. G. J��rgensen, J. Hjorth, J. P. U. Fynbo, D. Watson,
J. M. Castro Cer��n, K. Pedersen, H. Pedersen, J. Sollerman (DARK
Cosmology Centre, Niels Bohr Institute)

"Using the Danish 1.54m+DFOSC (La Silla), we have obtained R-band images
of the field of the SXC-source associated with GRB 050709.94 (Butler et
al., GCN#3570
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 ) for two nights (July 11.3 and 12.3 UT) under good
conditions (0.7" and 1.0" seeing, respectively). At the location of the
Chandra source (Fox et al., GCN#3585
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 ), we clearly detect the object
present on the DSS.

In the image with the best seeing (the first night), this object
resolves into two sources separated by about 1". The 0.5" Chandra
error-circle covers the fainter, eastern-most, of these two sources.

In the image from the second night, the objects are not clearly
resolved. Aperture photometry of both objects together in the two epochs
(at t+33h and t+56h) do not indicate significant R-band variability.

Images of the objects are shown at:
http://www.astro.ku.dk/~brian_j/grb/grb050709.94/ "

P.A. Price (IfA, Hawaii), K. Roth (Gemini), and D.W. Fox (Caltech)
report on behalf of a larger collaboration:

We have observed a candidate host galaxy of GRB 050709 with the Gemini
North telescope and GMOS spectrograph at 2005 July 13.58 UT.  The
observations were made under clouds, at high airmass, and with morning
twilight interfering with the some of the observations.

The source acquired is the brighter of the two sources reported by
Jensen et al. (GCN #3589
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 ; "Source B").  The long slit likely does not
cover the position of the fainter of the two sources which is coincident
with the Chandra source ("Source A").

We have reduced 2x900 sec integrations and identify emission lines at
approximate observed wavelengths of 7617A and 5810A which we associate
with Halpha and [O III]5007 at an approximate redshift of z = 0.16.
Fainter emission lines are observed at 5754A and 5641A, corresponding to
[O III]4959 and Hbeta, and thus we believe the redshift is secure.

If source A is the afterglow of GRB 050709, then it is seen in
projection about 3 kpc from Source B, suggesting that Source B may be
the host galaxy.  The similarity of this case with the previous
potential association of the short/hard GRB 050509B with a low-redshift
galaxy (Bloom et al., GCN #3386
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 ) is suggestive.  If GRB 050709 is at z =
0.16, then the isotropic-equivalent energy release is about 6 x 10^49
erg (based on Butler et al., GCN #3570
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 ).

A definitive measurement of the distance scale to short/hard GRBs awaits
the demonstration of variability of the X-ray or optical emission.  We
encourage deep observations to ascertain the nature of Source A and, in
particular, to search for variability.



We thank the staff of the Gemini North telescope for outstanding support
for these observations.

P. A. Price (IfA, Hawaii), B. L. Jensen, U. G. Jargensen, J. Hjorth, J.
P. U. Fynbo, D. Watson, J. M. Castro Ceron, K. Pedersen, H. Pedersen,
and J. Sollerman (DARK Cosmology Centre, Niels Bohr Institute) report:

We have performed PSF-matched image subtraction on the images acquired
by Jensen et al. (GCN #3589
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 ).  The images were obtained from the Danish
1.54m+DFOSC at La Silla on 2005 July 11.3 and 12.3 UT.

PSF-matched image subtraction using the Pan-STARRS Optimal Image
Subtraction (POI Sub) code reveals a residual, in the sense that the
source fades between the first and the second epochs.  The position of
the variable source corresponds to the source identified by Jensen et
al. (GCN #3589
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 ) on the edge of a nearby galaxy (z=0.16; Price, Roth &
Fox, GCN #3605
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 ) as consistent with the Chandra source (Fox et al., GCN
#3585
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 ).  This detection of optical variability increases the likelihood
that this source is the afterglow of the short/hard GRB 050709.

A figure showing the subtraction is available at
http://www.ifa.hawaii.edu/~price/grb050709candidate.jpg

This message may be cited.

M. Boer, G. Ricker, J-L. Atteia, N. Kawai, D. Lamb, and S. Woosley, on
behalf of the HETE Science Team;

M. Arimoto, T. Donaghy, E. Fenimore, M. Galassi, C. Graziani,
J. Kotoku, M. Maetou, M. Matsuoka, Y. Nakagawa, T. Sakamoto, R. Sato,
Y. Shirasaki, M. Suzuki, T. Tamagawa, K. Tanaka, Y. Yamamoto,
and A. Yoshida, on behalf of the HETE WXM Team;

N. Butler, G. Crew, J. Doty, G. Prigozhin, R. Vanderspek,
J. Villasenor, J. G. Jernigan, A. Levine, G. Azzibrouck, J. Braga,
R. Manchanda, and G. Pizzichini, on behalf of the HETE Operations and
HETE Optical-SXC Teams;

J-F Olive, J-P Dezalay, and K. Hurley, on behalf of the HETE FREGATE
Team;

report:

We have performed a joint fit to the WXM and FREGATE spectral data
for GRB 050709, in order to refine the numbers initially reported in
GCN 3570
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  (Butler et al. 2005) for the short and long pulse components.

The short pulse is well-fit (chi2/DOF= 35.37/48) by a power-law times
exponential model with photon index alpha = -0.7 +/- 0.2 and nu-F_nu peak
energy Epeak = 83 +18/-12 keV.  The energy fluences of the short pulse
are

S_E(2-30 keV)   = (9.3 +/- 0.9) x 10^(-8) erg cm^-2 and
S_E(30-400 keV) = (2.9 +/- 0.4) x 10^(-7) erg cm^-2.

The X-ray to gamma-ray fluence ratio is thus 0.32.  The t90 duration of
the short pulse is 220 +/- 50 ms in the 2-25 keV energy band and 70 +/- 10
ms in the 30-400 keV band.  The t90 duration and Epeak of the short
pulse are consistent with those found for short/hard GRBs (see, e.g.,
Ghirlanda, Ghisellini, & Celotti 2004, A&A, 422, L55 for plots of the
short/hard GRB Epeak distribution).

The long pulse is well fit (chi2/DOF = 108.86/138) by a power-law model
with photon index beta = -2.2 +0.2/-0.4.  The energy fluences of the
long pulse are

S_E(2-30 keV)   = (7.1 +/- 1.5) x 10^(-7) erg cm^-2 and
S_E(30-400 keV) = (3.9 +4.1/-2.7) x 10^(-7) erg cm^-2.

These spectral results are preliminary because there is a linear trend
in the background that affects the spectral analysis of the long pulse
and has not yet been taken into account.  The t90 of the long pulse is
130 +/- 7 s in the 2-25 keV energy band.

Using the redshift of z = 0.16 measured by Price et al. (2005; GCN 3605
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 ),
the isotropic-equivalent energy of the short pulse in the 1-10,000 keV
energy band in the rest frame of the source is

Eiso (short pulse) = (2.7 +1.1/-0.3) x 10^(49) erg,

using Omega_M=0.3, Omega_Lambda=0.7, and h=0.65.  The Eiso and Epeak
values for the short pulse place it well off of the Amati et al. (2002;
A&A, 390, 81) relation for long duration GRBs.

Taking a time interval 0.060 s in the rest frame of the source
(corresponding to t90 = 0.07 s in the 30-400 keV energy band in the
observer frame) and assuming the same cosmology and energy band as
used above for the Eiso determination, the luminosity of the short
pulse in the 1-10,000 keV energy band in the rest frame of the source
is

Liso (short pulse) = (5.2 +/- 1.4) x 10^(50) erg s^-1.

Taking even this short time interval, the Liso and Epeak values for the
short pulse place it off the Yonetoku et al. (2004; ApJ, 609, 935)
correlation for long duration GRBs.

A composite lightcurve showing the short and long pulses in both the
2-25 keV and 30-400 keV bands can be found at

http://space.mit.edu/HETE/Bursts/GRB050709 .

L.A. Antonelli, M.L. Conciatore (INAF/OAR), D. Malesani (SISSA), S. 
Covino, P. D'Avanzo, S. Campana, G. Tagliaferri (INAF/OABr), M. Della 
Valle (INAF/OAA), F. Fiore, G.L. Israel, L. Stella (INAF/OAR), G. 
Chincarini (Univ. Milano-Bicocca), report on behalf of the MISTICI 
collaboration:

The Chandra X-ray observatory observed a second time the field of the 
GRB 050709 (Butler et al., GCN 3570
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 ; Boer et al., GCN 3653
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 ). The 
observation, performed with ACIS, started on 2005 Jul 25.86234 UT and 
ended on 2005 Jul 26.09042, for a total exposure time of 18284 s. The 
X-ray source reported by Fox et al. (GCN 3585
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 ) and coincident with the 
proposed optical counterpart (Jensen et al., GCN 3589
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 ; Price et al., 
GCN 3612
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 ) is still marginally detected in the second epoch.

We obtained for this source a count rate of (8.4+/-3.5)E-4 cts/s in the 
(0.3-8.0 keV) band.
This count rate compared to the one obtained in the previous 
observation in the same band (1.2+/-0.2)E-3 cts/s (Fox et al., GCN 
3585
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 ) does not allow us to firmly establish any variability for the 
proposed X-ray afterglow.

This message can be cited.

P. B. Cameron (Caltech), F. A. Harrison (Caltech) and D. A. Frail (NRAO)
report on behalf of the Caltech-NRAO-Carnegie GRB Collaboration:

"We have observed the HETE localization region for GRB050709 (GCN 3570
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 )
with the Chandra X-ray Observatory + ACIS, in a second 18.2 ksec
observation beginning at 2005 July 25.86 UT (mean epoch 16.04 days after
the burst).

In contrast to earlier reports by Antonelli et al. (GCN 3686
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 ), we find
that the X-ray source reported earlier by Fox et al. (GCN 3585
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 ) has faded.
In reanalyzing both epochs, we measure 10 +/- 3 counts (0.3 - 8.0 keV) for
the second epoch, corresponding to a count rate of 5.5 +/- 1.6 e-4 cts/s.
This compares to 1.3 +/- 0.2 e-3 cts/s measured for the first epoch,
confirming that the source has faded with a decay of t**-0.46 +/- 0.18
since the first Chandra epoch. Although this decay is shallower than
typical for an afterglow, the variability implies it is the likely
counterpart to the GRB.

We thank the staff at the Chandra X-ray Center for their execution of this
Target of Opportunity observation and rapid processing of the data."

J. Haislip, J. Kirschbrown, D. Reichart report on behalf of the UNC team of
the FUN GRB Collaboration:

Under the control of Skynet, PROMPT automatically observed the localization
of the probable short-hard GRB 050709 (Butler et al., GCN 3570
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 ; Boer et
al., GCN 3653
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 ) beginning 1.1 days after the burst (Bayliss et al., GCN
3569
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 ) and again beginning 8.3 days after the burst.

3-sigma limiting magnitudes are based on 5 USNO-B1.0 stars:

Mean Time 	Integration 	Filter 	Limiting 	Telescope
Since GRB 	Time 			Magnitude

1d 5h 36m 	82 x 80s 	Rc 	21.6 		PROMPT-5
8d 9h 3m 	136 x 80s 	Rc 	21.6 		PROMPT-5

We detect the host galaxy (Fox et al., GCN 3585
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 ; Price et al., GCN 3612
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 )
in both epochs and measure its brightness to be Rc = 21.16 +/- 0.26 and Rc
= 21.06 +/- 0.21, respectively.  PSF-matched image subtraction using ISIS2
(Alard 2000) does not reveal the afterglow (Price et al., GCN 3612
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 ).

PROMPT is still being built and commissioned.

Alard, C. 2000, A&AS, 114, 363