GRB 061021
GCN Circular 5743
Subject
GRB 061021: Swift detection of a burst
Date
2006-10-21T15:58:47Z (19 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
A. Moretti (INAF-OAB), S. D. Barthelmy (GSFC), N. Gehrels (NASA/GSFC),
C. Guidorzi (Univ Bicocca&INAF-OAB), S. T. Holland (GSFC/USRA),
J. A. Kennea (PSU), C. B. Markwardt (GSFC/UMD),
F. E. Marshall (NASA/GSFC), S. B. Pandey (UCL-MSSL),
A. M. Parsons (GSFC), M. Stamatikos (NASA/ORAU),
R. L. C. Starling (U Leicester), G. Tagliaferri (INAF-OAB) and
H. Ziaeepour (UCL-MSSL) report on behalf of the Swift Team:
At 15:39:07 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 061021 (trigger=234905). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA,Dec 145.134, -21.928 {09h 40m 32s, -21d 55' 41"} (J2000)
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve shows a single peak
structure with a duration of about 12 sec. The peak count rate
was ~12000 counts/sec (15-350 keV), at ~2 sec after the trigger.
The XRT began observing the field at 15:40:20 UT, 73 seconds after the
BAT trigger. XRT found a variable, uncatalogued X-ray source
located at RA(J2000) = 09h 40m 35.6s, Dec(J2000) = -21d 57' 05.3", with an
estimated uncertainty of 7.0 arcseconds (90% confidence radius).
This location is 97 arcseconds from the BAT on-board position, within
the BAT error circle. The initial flux in the 2.5s image was
2.7e-09 erg/cm2/s (0.2-10 keV).
UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm)
filter starting 80 seconds after the BAT trigger. There is a candidate
afterglow in the rapidly available 2.7'x2.7' sub-image at
RA(J2000) = 09:40:36.12 = 145.1505
DEC(J2000) = -21:57:05.4 = -21.9515
with a 1-sigma error radius of about 0.5 arc sec. This position is 6.7 arc sec.
from the center of the XRT error circle. The estimated magnitude is 14.9 with a
1-sigma error of about 0.5 mag. No correction has been made for the expected
extinction corresponding to E(B-V) of 0.06.
GCN Circular 5744
Subject
GRB 061021, Swift-BAT refined analysis
Date
2006-10-21T18:42:58Z (19 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
D. Palmer (LANL), L. Barbier (GSFC), S. D. Barthelmy (GSFC),
J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC),
D. Hullinger (BYU-Idaho), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD),
A. Moretti (INAF-OAB), A. Parsons (GSFC), T. Sakamoto (GSFC/ORAU),
G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC)
on behalf of the Swift-BAT team:
Using the data set from T-240 to T+328 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 061021 (trigger #234905)
(Moretti, et al., GCN Circ. 5743). The BAT ground-calculated position
is RA,Dec = 145.146, -21.953 deg {9h 40m 35.0s, -21d 57' 10.4"} (J2000)
+- 0.6 arcmin, (radius, sys+stat, 90% containment). The partial coding was 64%.
The mask-weighted lightcurve shows a cusp-like peak starting at T+0 sec,
peaking at T+2.6 sec, and exponetially tailling off to background at T+90 sec.
T90 (15-350 keV) is 46 +- 1 sec (estimated error including systematics).
The time-averaged spectrum from T-0.0 to T+59.9 is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.31 +- 0.06. The fluence in the 15-150 keV band is 3.0 +- 0.1 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+2.44 sec in the 15-150 keV
band is 6.1 +- 0.3 ph/cm2/sec. All the quoted errors are at the 90%
confidence level.
GCN Circular 5745
Subject
GRB 061021: Swift/UVOT Observation
Date
2006-10-21T21:59:27Z (19 years ago)
From
Stephen Holland at USRA/NASA/GSFC/SSC <sholland@milkyway.gsfc.nasa.gov>
GRB 061021: Swift/UVOT Observations
S. T. Holland (NASA/GSFC & USRA) and A. Moretti (INAF-OAB) report on
behalf of the Swift/UVOT team:
The Swift/UVOT began observing the field of GRB 061021 at
15:40:27 on 2006-10-21, 80 s after the BAT trigger (Moretti et al.,
GCN Cir. 5743). An optical counterpart was detected in the White
filter (160-650 nm) at a position (RA,Dec) = (09:40:36.12,
-21:57:05.4) (J2000) with a 90% confidence interval of 0.6 arcsec.
The early photometry results are given for the UVOT filters
below where start is the time, in seconds, since the BAT trigger. The
quoted errors do not include the 0.1 mag systematic uncertainty in the
photometric zero points.
Filter Start Exposure Mag Err
V 187 275 16.76 0.06
5403 197 18.86 0.22
B 4789 197 19.15 0.13
6221 197 19.33 0.19
U 4584 197 18.18 0.12
6016 197 18.48 0.13
UVW1 4379 197 17.94 0.35
5812 197 18.41 0.17
UVM2 4175 197 17.63 0.17
5607 197 17.89 0.20
UVW2 5198 197 18.02 0.21
White 81 98 15.09 0.07
4993 197 18.05 0.08
6425 25 18.37 0.25
The values quoted above are not corrected for the expected Galactic
extinction of E_{B-V} = 0.06 mag (Schlegel et al. 1998).
GCN Circular 5746
Subject
GRB 061021: Swift-XRT refined analysis
Date
2006-10-21T22:38:01Z (19 years ago)
From
Alberto Moretti at Obs Brera Merate <alberto.moretti@brera.inaf.it>
A. Moretti (INAF-OAB), C. Guidorzi (Univ. Bicocca & INAF-OAB),
P. Romano (INAF-OAB) S. Campana (INAF-OAB) report on behalf of
the Swift-XRT team:
We have analysed the first 3 orbits of Swift-XRT data obtained for GRB
061021 (trigger=234905, GCN 5743). The data consist of 189 s in Windowed
Timing (WT) mode, starting 78 seconds after the BAT trigger and 5.5 ks
in Photon Counting (PC) mode. Using PC data we obtain a refined
position of:
RA(J2000) = 09h 40m 35.87s
Dec(J2000)= -21d 57' 07.2"
with an estimated uncertainty radius of 5 arcsec (90% containment).
This location is 3.8 arcseconds from the UVOT position (GCN 5745).
The light-curve, initially, shows a steep decay (alpha1=2.1+/-0.1) up
to a break at t_break=368+/-20.s. After the break, the afterglow
shows a shallow decay (alpha2=0.55+/-0.03) up to the end of the third
orbit (t=12.5 ks). At this point the observed count rate was 2.2
counts per second, corresponding to an unabsorbed flux of 1.4E-11
erg/cm2/sec.
The spectrum formed from all the WT data can be modelled with a
power-law of photon index Gamma = 1.88 +/- 0.07, with an absorbing
column of NH = (3.4 +/- 0.8)E20 cm^-2 consistent with the Galactic
value of 4.20E20 cm^-2. The spectrum formed from the PC data is
slightly softer than the WT spectrum: it can be modelled with a
power-law of photon index Gamma = 1.96 +/- 0.08.
All errors are quoted at 90% confidence level.
This circular is an official product of the Swift-XRT team.
GCN Circular 5747
Subject
GRB 061021 - VLT spectrum without lines
Date
2006-10-22T17:57:23Z (19 years ago)
From
Christina Thoene at Niels Bohr Institute,DARK Cosmo Ctr <cthoene@astro.ku.dk>
Christina C. Thoene, Johan P.U. Fynbo (DARK) and Pall Jakobsson (Univ. of
Hertfordshire) report on behalf of a larger collaboration:
We obtained a single 1800s spectrum of the OT of GRB 061021
(GCN 5743) on October 22, 08:07UT, 16.5h after the burst, using FORS1/VLT
and grism 300V. At the time of the observation, the OT had a magnitude of
about R=20.5, based on photometric zeropoints from the ESO webpages.
The spectrum displayed a smooth continuum with no emission or absorption
lines, although the S/N of the source was resonably high. From the lack of
the Ly-alpha forest, a firm upper limit of z<2.0 can be placed on the
redshift of the GRB. This is consistent with the UVOT observations (GCN
5745).
An image of the 2D spectrum can be found at
www.astro.ku.dk/~cthoene/GRBs/
We thank the staff at VLT for performing the observations, especially G.
James.
GCN Circular 5748
Subject
Konus-Wind observation of GRB 061021
Date
2006-10-23T14:22:58Z (19 years ago)
From
Valentin Pal'shin at Ioffe Inst <val@mail.ioffe.ru>
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 061021 (Swift-BAT trigger #234905:
Moretti et al., GCN 5743; Palmer et al., GCN 5744)
triggered Konus-Wind at T0=56348.304 s UT (15:39:08.304).
As observed by Konus-Wind the burst shows
a single pulse with a duration of ~10 s,
followed by a weak tail seen up to T-T0 ~60 s.
The spectrum of the pulse integrated from T0 to T0+8.448 s
is well fitted (in the 20 keV - 2 MeV range)
by a power law with exponential cutoff model:
dN/dE ~ E^(-alpha) * exp(-(2-alpha)*E/Ep)
with alpha = 1.22(-0.14, +0.12)
and Ep = 777 (-237, +549) keV (chi2 = 58/59 dof).
The fluence of this part is 9.93(-4.14, +0.69)x10^-6 erg/cm2
(in the 20 keV - 2 MeV range).
The spectrum of the tail integrated from T0+8.448 s to T0+57.600 s
can be fitted (in the 20 keV - 2 MeV range)
by a simple power law with the photon
index 1.93(-0.27, +0.32) (chi2 = 77/60 dof).
The fluence of this part is 3.43(-2.20, +0.83)x10^-6 erg/cm2
(in the 20 keV - 2 MeV range).
We note that because of the derived photon index is ~2,
this fluence value is very sensitive to the upper boundary
of the energy range.
The total burst fluence is 1.34(-0.47, +0.11)x10^-5 erg/cm2,
and the 256-ms peak flux measured from T0+0.608 s
3.72(-1.62, +0.53)x10^-6 erg/cm2/s
(both in the 20 keV - 2 MeV energy range).
All the quoted errors are at the 90% confidence level.
GCN Circular 5749
Subject
GRB 061021, Swift-BAT Lag analysis
Date
2006-10-23T20:10:07Z (19 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
GRB 061021, Swift-BAT Lag analysis
J. Norris (Stanford/SLAC) and S.D. Barthelmy (GSFC)
on behalf of the Swift-BAT team:
We have performed the lag analysis (Norris & Bonnell, ApJ, 2006)
on GRB 061021 (trigger 234905) (Moretti et al, GCN Circ 5743 &
Palmer et al, GCN Circ 5744) with the following results:
72 ms +28-48 ms between the 50-100 and 15-25 keV bands
98 ms +30-32 ms between the 100-350 and 25-50 keV bands
128 ms +49-35 ms between the 100-350 and 15-25 keV bands
(all with 16-ms binning).
We conclude that this is a Long Burst (and not a Short Burst
with Extended Emission).