- GCN Circular #5491
S. Mereghetti, A. Paizis (IASF, Milano), D.Gotz (CEA, Saclay), S.Shaw,
M.Beck (ISDC, Versoix), and J. Borkowski (CAMK, Torun) on
behalf of the IBAS Localization Team report:
A GRB lasting about 20 s has been detected by IBAS in IBIS/ISGRI data at
18:44:00 UT on September 1 2006.
The refined coordinates (J2000) derived from the off-line analysis are:
RA: 287.15758 [degrees],
DEC: -6.63957 [degrees]
with an uncertainty of 2.5 arcmin.
This message can be cited.
- GCN Circular #5492
J. French (UCD Dublin) and P.Kubanek (AsU AV CR Ondrejov & ISDC Versoix)
on behalf of the Watcher collaboration reports:
We observed GRB 060901, detected by INTEGRAL, with 40cm Watcher
telescope, located at Boyden Observatory, South Africa, starting at
20:06:00 UT, 82 min after ISGRI/IBAS detection. At location mention in
GCN Circ. 5491 we do see few sources not present in USNO, which are all
visible on ESO archive plates.
We place conservative limit R 18 mag for any OT from this GRB. Futher
observations and analysis are in progress.
- GCN Circular #4493
S. Mereghetti (IASF, Milano), D.Gotz (CEA, Saclay) on behalf of the IBAS
Localization Team report:
GRB 060901 was relatively bright and saturated the ISGRI telemetry.
Preliminary estimates of the peak flux and fluence in the 20-200 keV
energy range are 6.6 ph (7x10e-7 erg)/cmq/s and 3.5x10e-6 erg/cmq.
Due to the telemetry gaps these should be considered as lower limits
- GCN Circular #5494
J. Racusin (PSU), D. Grupe (PSU), S. Hunsberger (PSU), and N. Gehrels
(NASA/GSFC) report on behalf of the Swift XRT team:
Swift/XRT began a target of opportunity observation of the INTEGRAL
detected GRB 060901 (Mereghetti et al., GCN Circ. 5491) at 22:30 UT
September 1 2006 (~3.8 hours after the burst). We have analyzed the first
3 orbits of XRT data and we find a previously uncatalogued source at the
following coordinates:
RA(J2000): 19:08:37.98
Dec(J2000): -6:38:07.84
with an estimated uncertainty of 4.9 arcseconds radius (90% containment).
This position is 14.8 arcseconds from the INTEGRAL position given in GCN
Circ. 5491. Further observations and analysis are in progress.
This is an official product of the Swift XRT team.
- GCN Circular #5495
B. E. Cobb (Yale), part of the larger SMARTS consortium, reports:
Using the ANDICAM instrument on the 1.3m telescope at CTIO, we
obtained optical/IR imaging of the error region of GRB 060901
(GCN 5491, Mereghetti et al.) with a mid-exposure time of
2006-09-02 00:24:54 UT, which is ~5.7 hours post-burst.
Total summed exposure times amounted to 15 minutes in I and V and
12 minutes in J and K.
Within the error region of the X-ray afterglow detection
(GCN 5494, Racusin et al.), we detect a stellar object in
all wavebands that is apparent in both USNO and 2MASS.
Additionally, in the J-band observation there is a very
marginal detection of a source inside the X-ray error region at:
RA = 19:08:38.2
Dec = -06:38:06.14
The nature of this source is unclear, however, because
of the low significance of the detection and the fact
that the object is too dim to have previously been
detected in 2MASS. We also do not know if the object is fading.
The approximate limiting magnitudes of our images are:
J > 18.5
K > 17.4
I > 21.2
These values are calibrated against several USNO-B1.0
stars in the I-band, and 2MASS stars in J and K.
- GCN Circular #5496
GRB 060901: Swift/XRT Refined Analysis
J. Racusin (PSU) reports on behalf of the Swift XRT team:
We have analyzed the first 4 orbits of Swift XRT observations of GRB
060901 (Mereghetti et al., GCN Circ. 5491), with a total exposure of 3 ks.
The refined position is:
RA(J2000): 19:08:37.93
Dec(J2000): -6:38:08.1
with an estimated uncertainty of 4.3 arcseconds (90% containment). This
position is 0.7 arcseconds from the preliminary XRT position given in GCN
Circ. 5494 (Racusin et al.) and 14.5 arcseconds from the INTEGRAL position
given in GCN Circ. 5491 (Mereghetti et al.).
The 0.2-10 keV light curve in Photon Counting (PC) mode starts ~14 ks
after the burst. The X-ray afterglow is faint, initially 0.05 counts/s,
decaying with a slope of -1.7 +/- 0.7.
The preliminary spectral fit to the PC data gives a spectral power law
photon index of 2.1 +/- 0.6 in the [0.3-10] keV band, assuming Galactic
absorption (2.34e21cm^-2). The average (in the time range 14 - 30 ks from
trigger) estimated unabsorbed 0.3-10 keV flux was ~2.6e-12 erg cm^-2 s^-1.
The XRT count rate extrapolated to T+24 hr is estimated to be ~0.003
counts/s, corresponding to an unabsorbed 0.3-10 keV flux of about 4.4e-13
erg cm^-2 s^-1.
This circular is an official product of the Swift XRT Team.
- GCN Circular #5497
B. E. Cobb (Yale), part of the larger SMARTS consortium, reports:
Additional analysis of the data described in GCN 5495 indicates
that the possible J-band source was a spurious detection and, therefore,
not associated with GRB 060901.
- GCN Circular #5498
S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks, and
T. Cline on behalf of the Konus-Wind team report:
The long GRB 060901 (Mereghetti et al., GCN 5491, 5493)
triggered Konus-Wind at T0=67439.385 s UT (18:43:59.385).
The Konus-Wind light curve shows a single pulse
with a duration of ~8 sec,
followed by a weak tail seen up to T-T0 ~15 sec.
The spectrum of the pulse
(accumulated from T-T0=0 to T-T0=7.936 sec)
is well fitted (in the 20 keV - 2 MeV range)
by GRBM (Band) model for which:
the low-energy photon index is alpha = -0.77(-0.23, +0.26),
the high energy photon index beta = -2.31(-0.36, +0.18),
the break energy E0 = 156(-46, +71) keV (chi2 = 48/61 dof).
The peak energy Ep = 191(-30, +40) keV.
The burst total fluence is 1.51(-0.19,+0.14)x10^-5 erg/cm2
and peak flux on 256-ms time scale measured from T-T0=2.496 sec
3.06(-0.61, +0.54)x10^-6 erg/cm2/sec
(both in the 20 keV - 2 MeV energy range).
All the quoted errors are at the 90% confidence level.
- GCN Circular #5499
A. Pelangeon & J-L. Atteia (LATT-OMP) report:
We have used the spectral parameters of GRB 060901
provided by Golenetskii et al. (GCNC 5498) to
compute the spectral pseudo-redshift** of this burst
detected by INTEGRAL (Mereghetti et al., GCNC 5491).
We find a pseudo-redshift pz= 2.0 +/- 0.5
** cf. http://www.ast.obs-mip.fr/grb/pz
- GCN Circular #5500
A. Breeveld (MSSL/UCL) and J. Racusin (PSU) report on behalf of the
Swift/UVOT team:
The Swift/UVOT began taking data on 2006-09-01 at 22:33:37 on the field
of the INTEGRAL burst 060901 about 4 hours after the burst (Mereghetti
et al., GCN 5491) . At the position of the XRT error circle (Racusin
et al., GCN 5494) there are no new sources, although there is a
catalogued source. There is no source seen either at the position of
the new source in J band reported by Cobb et al. (GCN 5495). In the
summed UVOT images we obtain the following 3 sigma upper limits:
Filter T_range(s) Exp(s) 3sig_UL(mag)
V 19306-19729 413.2 19.4
B 22900-23805 885.1 20.6
U 29566-29619 51.4 19.2
UVW1 28660-29560 885.6 20.6
UVW2 13777-17580 657.5 20.9
White (160-650nm) 23812-23821 8.7 18.7
- GCN Circular #5501
K. Wiersema (University of Amsterdam) and C.C. Thoene (DARK Cosmology
Centre) report:
Using DFOSC on the Danish 1.5m telescope at La Silla we obtained R band
imaging of the error circle of Integral burst GRB060901.
Observations consisted of a series of 5 min exposures, starting at 1 Sep
23:46 UT and lasted until 2 Sep 02:19 UT. A second epoch was taken
from 03:59 UT to 04:25 UT.
We performed PSF matched image subtraction (Alard 2000) on the dataset as
the field is very crowded. We find no significantly varying source in or
near the XRT error circle (Racusin, GCN5496). Our full stacked dataset
reaches a limiting magnitude of R~23.9.
- GCN Circular #6188
K. Wiersema (University of Amsterdam), E. Rol (University of Leicester)
and C. C. Thoene (DARK Cosmology Centre) report:
We re-analysed the data we took of INTEGRAL GRB 060901, as reported
earlier in GCN 5501, supplemented with late time observations.
We obtained three epochs of imaging in R band using DFOSC on the Danish
1.5m telescope at La Silla. The first two epochs were reported in GCN5501,
and we re-observed the GRB position on September 8, midpoint 6.3 days
after the burst. The first two epochs are close together in time, and
suffered from bad seeing (~1.6 arcsec) and proximity to the bright Moon.
The third epoch, while much shorter in exposure time and at full Moon,
reaches a deeper magnitude limit than epoch 2 due to good
seeing (~1 arcsec).
The field is very crowded and the XRT error circle (Racusin, GCN 5496)
partly overlaps with a bright star (present in the USNO-B catalogue with
number 0833-0546379, possibly a blend of multiple stars), so we performed
PSF matched image subtraction (Alard 2000) on the three epochs. A
subtraction of the first two epochs does not yield a candidate afterglow
(Wiersema & Thoene, GCN5501), but a subtraction of the first and third
epoch reveals a clear, fading, residual located in the XRT error circle,
at position:
RA: 19:08:37.9
DEC: -06:38:07.4
With conservative astrometric errors of 0.4 arcsec.
There are no other variable sources in the XRT error circle, but the
source is located in the wing of the much brighter USNO star. We
tentatively identify the variable object as the optical afterglow of GRB
060901. Using artificial stars with the subtractions, we find the OT
candidate to be already below the (3-sigma) limiting magnitude of the
second epoch image, and are able to derive a magnitude for the first epoch
(midpoint 0.26 days after burst). of R ~ 22.6 +/- 0.5. We note that the
Galactic extinction in this direction is considerable, at A_R ~1.8 mag.
An image of the three epochs, the subtraction and the XRT error circle can
be found on:
http://staff.science.uva.nl/~kwrsema/grb060901/
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