GRB 071031
GCN Circular 7020
Subject
GRB 071031: Swift detection of a burst with an optical counterpart
Date
2007-10-31T01:24:38Z (18 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
M. C. Stroh (PSU), C. Gronwall (PSU), D. Grupe (PSU),
S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU),
H. A. Krimm (GSFC/USRA), C. Pagani (PSU), D. M. Palmer (LANL),
M. Stamatikos (NASA/ORAU), R. L. C. Starling (U Leicester),
T. N. Ukwatta (GSFC/GWU) and L. Vetere (PSU) report on behalf of the
Swift Team:
At 01:06:36 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 071031 (trigger=295670). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 6.458, -58.045 which is
RA(J2000) = 00h 25m 50s
Dec(J2000) = -58d 02' 42"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a single peaked
structure with a duration of about 30 sec. The peak count rate
was ~600 counts/sec (15-350 keV), at ~3 sec after the trigger.
The XRT began observing the field at 01:08:19 UT, 103 seconds after the
BAT trigger. XRT found a bright, fading, uncatalogued X-ray source
located at RA, Dec 6.4061, -58.0585 which is
RA(J2000) = 00h 25m 37.4s
Dec(J2000) = -58d 03' 30.6"
with an uncertainty of 4.7 arcseconds (radius, 90% containment).
This location is 110 arcseconds from the BAT on-board position,
within the BAT error circle. The initial flux in the 2.5s image
was 5.2e-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 112 seconds after the BAT trigger. There is a candidate afterglow
in the rapidly available 2.7'x2.7' sub-image at
RA(J2000) = 00:25:37.27 = 6.4053
DEC(J2000) = -58:03:34.2 = -58.0595
with a 1-sigma error radius of about 0.5 arc sec. This position is 3.9 arc sec.
from the center of the XRT error circle. The estimated magnitude is 19.8 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 0.01.
Burst Advocate for this burst is M. C. Stroh (stroh AT astroh.org).
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/too.html.)
GCN Circular 7021
Subject
GRB 071031: GROND detection in all bands
Date
2007-10-31T01:38:44Z (18 years ago)
From
Jochen Greiner at MPI <jcg@mpe.mpg.de>
T. Kruehler, J. Greiner, P. Afonso, A. Kuepcue-Yoldas,
A. Yoldas, G. Szokoly (all MPE Garching) report for the GROND team:
We started observing GRB 071031 (trigger 295670) simultaneously in grizJHK
with GROND, mounted at the 2.2m MPI/ESO telescope at La Silla (Chile),
about 60 sec after the alert. A bright object (r~15) is seen in all filters,
including the g-band, implying a redshift smaller than 3.5.
The coordinates are
RA (2000.0) = 00h 25m 37.2s
Decl (2000.0) = -58d 03' 30"
located within the XRT error circle, and consistent with the UVOT position.
GCN Circular 7022
Subject
GRB071031: Rapid PROMPT Detections
Date
2007-10-31T03:12:18Z (18 years ago)
From
Josh Haislip at U.North Carolina <haislip@physics.unc.edu>
J. Haislip, K. Ivarsen, D. Reichart, M. Nysewander, A. LaCluyze, J. A.
Crain, A. Foster, M. Schubel, J. Styblova, T. Brennan, and A. Trotter
report:
Skynet observed the localization of GRB 071031 (Stroh et al., GCN 7020)
with three of the 16" PROMPT telescopes at CTIO beginning 78 seconds after
the burst (24 seconds after notification) in UBVR.
We detect the afterglow (Stroh et al., GCN 7020). At 8.2 minutes after
the burst, we measure R ~ 18.2 mag calibrated to four USNO B1.0 stars.
GCN Circular 7023
Subject
GRB 071031: VLT high-resolution spectroscopy
Date
2007-10-31T03:19:47Z (18 years ago)
From
Daniele Malesani at Niels Bohr Inst,Dark Cosmology Center <malesani@astro.ku.dk>
C. Ledoux (ESO), P. Jakobsson (Univ. Herfordshire), A.O. Jaunsen (Univ.
Oslo), C.C. Thoene, P.M. Vreeswijk, D. Malesani, J.P.U. Fynbo, J. Hjorth
(DARK), report on behalf of a larger collaboration:
We observed the optical afterglow of GRB 071031 (Stroh et al., GCN 7020;
Kruehler et al., GCN 7021; Haislip et al., GCN 7022) with the ESO VLT.
Observations were triggered automatically in rapid response mode
starting on 2007 Oct 31 at 01:16 UT (9.3 min after the trigger). We
secured high- and low-resolution spectroscopy with UVES and FORS2,
respectively.
From the detection of a DLA and several metallic lines, including
fine-structure transitions, we determine the redshift to be z=2.692,
consistently in the UVES and FORS2 spectra. Further analysis is ongoing.
We acknowledge excellent support from the observing staff at Paranal, in
particular Stan Stefl and Rachel Gilmour.
GCN Circular 7024
Subject
GRB 071031, SMARTS afterglow observations
Date
2007-10-31T03:21:10Z (18 years ago)
From
Bethany Cobb at Yale U <cobb@astro.yale.edu>
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 071031
(GCN 7020, Stroh et al.), with a mid-exposure time of
2007-10-31 01:46 UT, which is ~40 minutes post-burst.
Several dithered images were obtained in each filter,
with total summed exposure times of 180s in each of BRIYJK and
120s in each of H and V.
The GRB afterglow (GCN 7020, Stroh et al. & GCN 7021, Kruehler et al.)
is detected at I=17.4+/-0.1 (Photometry is calibrated against USNO-B1.0
stars). Additional imaging at 1.5 hours post-burst indicates an
approximate decay rate of alpha~-0.6 (where afterglow flux is proportional
to t^alpha).
[GCN OPS NOTE(31oct07): Per author's request, the "071030" was changed
to "071031".]
GCN Circular 7025
Subject
GRB 071031: REM NIR and Optical observation
Date
2007-10-31T06:17:40Z (18 years ago)
From
Angelo Antonelli at Obs. Astro. di Roma <a.antonelli@oa-roma.inaf.it>
L.A. Antonelli, S. Covino, P. D'Avanzo, D. Fugazza, L. Calzoletti, S.
Campana, G. Chincarini, M.L. Conciatore, S. Cutini, V. D'Elia, F.
Dalessio, F. Fiore, P. Goldoni, D. Guetta, C. Guidorzi, G.L. Israel,
N. Masetti, A. Melandri, E. Meurs, L. Nicastro, E. Palazzi, E. Pian, S.
Piranomonte, L. Stella, G. Stratta, G. Tagliaferri, G. Tosti, V.
Testa, S.D. Vergani, F. Vitali report on behalf of the REM team:
The robotic 60-cm REM telescope located at La Silla (Chile) observed
the field of the GRB 071031 (Stroh et al., GCN 7020). Observations was
performed automatically in the both optical (R, I) and NIR (Z, J, H, K)
filters
under poor seeing condition starting at 01:08:19 UT (about 46 sec
after the
alert and 102 sec after the burst ) .
A preliminary analysis of the first set of R-band and H-band exposures
does
not reveal the optical afterglow candidate reported by Stroh et al.,
(GCN 7020),
Kruehler et al. (GCN 7021) and Haislip et al. (GCN. 7022). We derive
the
following upper limits of R > 16.4 (calibrated against USNO B1catalog)
and
H > 13.8 (calibrated against the 2MASS catalog).
Futher analysis are in progress.
GCN Circular 7027
Subject
GRB 071031: Swift-XRT Team refined analysis
Date
2007-10-31T15:34:32Z (18 years ago)
From
Michael Stroh at PSU/Swift <stroh@astroh.org>
M. C. Stroh, A. Falcone and J. L. Racusin (PSU) report on behalf of
the Swift-XRT Team:
We have analysed the first 4 orbits of Swift-XRT data obtained for GRB
071031 (Stroh et al. GCN Circ. 7020), totaling 658 s of Windowed
Timing (WT) data and 7.8ks of Photon Counting (PC) data.
Using 246 s of overlapping XRT Photon Counting mode and UVOT V-band
data, we find an astrometrically corrected X-ray position (using the
XRT-UVOT alignment and matching UVOT field sources to the USNO-B1
catalogue): RA, Dec = 6.40565, -58.05926 which is equivalent to:
RA (J2000): 00 25 37.36
Dec (J2000): -58 03 33.3
with an uncertainty of 2.0 arcsec (radius, 90% confidence). This is
2.9 and 1.1 arcsec from the previous XRT and UVOT positions
respectively (Stroh et al., GCN Circ 7020).
The light curve begins with a count rate ~150 cts/s and it is
dominated by flaring. Two of the flares reach ~200 cts/s while in WT
mode. By T+10 ks, the flux decreased down to a count rate ~0.01 cts/s.
Due to the amount of flaring in this X-ray light curve, we are unable
to determine the slope of the underlying power laws and thus are
presently unable to predict the count rate at T+24 hours.
The WT data (109-750 seconds) can be modeled as an absorbed power-law,
with photon index of 1.89 +/- 0.02 and a total absorbing column of NH
= (7.0 +/- 0.4)e20 cm^-2 which is greater than the Galactic value of
1.22e20 cm^-2. The 0.3-10 keV absorbed (unabsorbed) flux during this
time is 1.2e-9 (1.4e-9) erg cm^-2 s^-1.
This circular is an official product of the Swift-XRT team.
GCN Circular 7028
Subject
GRB 071031: Swift/UVOT detection of afterglow
Date
2007-10-31T18:10:56Z (18 years ago)
From
Alice Breeveld at MSSL-UCL <aad@mssl.ucl.ac.uk>
A. A. Breeveld (MSSL/UCL) and M. Stroh (PSU) report on behalf of the
Swift-UVOT team:
The Swift/UVOT observed the burst GRB 071031 (Stroh et al. GCN Circ.
7020) starting with the finding chart exposure in white, 114 seconds
after the BAT trigger. The afterglow is detected at the UVOT position
given in Stroh et al. (GCN Circ. 7020) in white, v and b until at least
7000s after the trigger. It is barely detected in u and not at all in
the UV filters; this is consistent with the redshift of z=2.692 found by
Ledoux et al. (GCN Circ. 7023). The brightness apparently increases for
the first few hundred seconds and then fades with an estimated temporal
slope in the v filter of alpha = 0.56.
The initial UVOT magnitudes and upper limits from single exposures or
co-added exposures are as follows:
Filter Tstart(s) Tstop(s) Exp(s) Mag
white 114 213 99.8 19.88 � 0.14
715 724 9.8 19.3 � 0.3
867 966 99.8 19.41 � 0.1
6778 6977 199.8 20.67 � 0.18
v 220 619 399.8 19.08 � 0.15
973 1219 246.2 18.5 � 0.13
11517 11816 299.8 19.93 � 0.32
b 700 709 9.8 >18.77 (3 sigma UL)
6573 6772 199.8 20.25 � 0.23
u 675 847 38.9 19.38 � 0.38
4933 6567 393.3 >20.82 (3 sigma UL)
uvw1 651 16990 1317.7 >21.41 (3 sigma UL)
uvm2 626 12782 1089.4 >21.23 (3 sigma UL)
uvw2 730 11206 1118.4 >21.46 (3 sigma UL)
The values quoted above are not corrected for the expected Galactic
extinction corresponding to a reddening of E_{B-V} = 0.012 mag in the
direction of the burst (Schlegel et al. 1998).
GCN Circular 7029
Subject
GRB 071031, Swift-BAT refined analysis
Date
2007-10-31T20:26:43Z (18 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
M. Stamatikos (GSFC/ORAU), 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), T. Sakamoto (GSFC/UMBC),
G. Sato (GSFC/ISAS), M. C. Stroh (PSU), J. Tueller (GSFC),
T. Ukwatta (GWU)
(i.e. the Swift-BAT team):
Using the data set from T-119 to T+297 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 071031 (trigger #295670)
(Stroh, et al., GCN Circ. 7020). The BAT ground-calculated position is
RA, Dec = 6.399, -58.048 deg, which is
RA(J2000) = 00h 25m 35.8s
Dec(J2000) = -58d 2' 51"
with an uncertainty of 2.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 75%.
The mask-weighted light curve shows multiple peaks. The first starts
at ~T-10 sec, peaks at ~T+5 sec, and is essentially back to baseline
by ~T+40 sec. The next largest peak starts at ~T+100 sec, peaks
at ~T+105 sec, and returns to baseline by ~T+180 sec.
T90 (15-350 keV) is 180 +- 10 sec (estimated error including systematics).
The time-averaged spectrum from T-4.5 to T+192.5 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
2.42 +- 0.29. The fluence in the 15-150 keV band is 9.0 +- 1.3 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+2.92 sec in the 15-150 keV band
is 0.5 +- 0.1 ph/cm2/sec. All the quoted errors are at the 90% confidence
level.
We note that the fluence ratio in a simple power-law fit between the
25-50 keV band and the 50-100 keV band is 1.34. This fluence ratio is larger
than 1.32 which can be achieved in the Band function of alpha=-1.0, beta=-2.5,
and Epeak=30 keV. Thus, preliminary analysis shows that Epeak of the burst
is very likely around or below 30 keV. Therefore the burst can be classified
as an X-ray flash.