GRB 071028
GCN Circular 7012
Subject
GRB 071028: Swift detection of a burst
Date
2007-10-28T18:00:32Z (18 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
J. L. Racusin (PSU), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), G. Cusumano (INAF-IASFPA),
N. Gehrels (NASA/GSFC), C. Gronwall (PSU), J. A. Kennea (PSU),
H. A. Krimm (GSFC/USRA), F. E. Marshall (NASA/GSFC),
P. T. O'Brien (U Leicester), C. Pagani (PSU), D. M. Palmer (LANL),
P. Romano (Univ. Bicocca & INAF-OAB), M. Stamatikos (NASA/ORAU),
M. C. Stroh (PSU), T. N. Ukwatta (GSFC/GWU) and L. Vetere (PSU)
report on behalf of the Swift Team:
At 17:41:01 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 071028 (trigger=295527). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 119.847, +21.498 which is
RA(J2000) = 07h 59m 23s
Dec(J2000) = +21d 29' 52"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). Even though this is an image trigger, there is
an indication of activity from about T+20 sec to T+50 sec.
The peak count rate was ~400 counts/sec (15-350 keV), at ~25 sec
after the trigger.
The XRT began observing the field at 17:42:59 UT, 118 seconds after the
BAT trigger. Using prompt downlinked data, we find a bright, variable,
uncatalogued X-ray source located at RA, Dec 119.8176, 21.4841 which is
RA(J2000) = 07 59 16.22
Dec(J2000) = +21 29 02.8
with an uncertainty of 4.1 arcsec (radius, 90% containment).
This location is 106 arcseconds from the BAT on-board position,
within the BAT error circle. The initial flux in the 2.5s image
was 7.2e-10 erg/cm2/s (0.2-10 keV).
UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm)
filter starting 128 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. There is a bright (12th mag) star in the XRT error circle
which severely limits our ability to detect a possible afterglow. No correction
has been made for extinction.
Burst Advocate for this burst is J. L. Racusin (racusin AT astro.psu.edu).
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 7013
Subject
GRB 071028, Swift-BAT refined analysis
Date
2007-10-28T21:31:20Z (18 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
J. Cummings (GSFC/UMBC), S. D. Barthelmy (GSFC), E. Fenimore (LANL),
N. Gehrels (GSFC), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD),
D. Palmer (LANL), J. L. Racusin (PSU), T. Sakamoto (GSFC/UMBC),
G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC),
T. Ukwatta (GWU)
(i.e. the Swift-BAT team):
Using the data set from T-239 to T+541 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 071028 (trigger #295527)
(Racusin, et al., GCN Circ. 7012). The BAT ground-calculated position is
RA, Dec = 119.828, 21.473 deg, which is
RA(J2000) = 07h 59m 18.6s
Dec(J2000) = 21d 28' 22"
with an uncertainty of 2.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.
The mask-weighted light curve shows a single FRED-like peak starting at
~T_zero, peaking at ~T+35 sec, and ending at ~T+110 sec.
T90 (15-350 keV) is 27.0 +- 1.0 sec (estimated error including systematics).
The time-averaged spectrum from T+19.2 to T+48.9 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.87 +- 0.26. The fluence in the 15-150 keV band is 3.0 +- 0.5 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+41.75 sec in the 15-150 keV band
is 0.3 +- 0.1 ph/cm2/sec. All the quoted errors are at the 90% confidence
level.
GCN Circular 7014
Subject
GRB 071028: Swift-XRT Team refined analysis
Date
2007-10-28T23:13:12Z (18 years ago)
From
Judith Racusin at PSU <racusin@astro.psu.edu>
J. Racusin (PSU) reports on behalf of the Swift-XRT Team:
We have analysed the first 2 orbits of Swift-XRT data obtained for GRB
071028 (Racusin et al. GCN Circ. 7012), totaling 61 s of Windowed Timing
(WT) data and 2.9 ks of Photon Counting (PC) data.
Using 399 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 = 119.81936, 21.48482 which is equivalent to:
RA (J2000): 07 59 16.65
Dec (J2000): +21 29 05.4
with an uncertainty of 1.9 arcsec (radius, 90% confidence). This is 6.5
arcsec from the previous XRT position (GCN Circ. 7012), and 51 arcsec from
the refined BAT position (Cummings et al., GCN Circ. 7013).
The bright X-ray light-curve can be fit by a broken power-law, with an
initial steep decay index of 3.3 +/- 0.4 followed by a flatter decay index
of 1.1 +/- 0.3 after a break at 475 +/- 150 seconds.
The WT data (124-182 seconds) can be modeled as an absorbed power-law,
with photon index of 1.9 +/- 0.2 and a total absorbing column of NH = (5.9
+/- 5.6)e20 cm^-2, consistent with the Galactic value of 5.1e20 cm^-2. The
0.3-10 keV observed (unabsorbed) flux during this time is 3.1e-10
(3.6e-10) erg cm^-2 s^-1.
Assuming the source continues to decay with the same decay index of 1.1,
we predict an XRT count rate of 5.5e-4 counts/s at T+24 hours, which
corresponds to an 0.3-10.0 keV observed flux of 2.3e-14 ergs cm^-2 s^-1.
This circular is an official product of the Swift-XRT team.
GCN Circular 7015
Subject
GRB071028: Xinglong EST V-band upper limit
Date
2007-10-29T03:32:13Z (18 years ago)
From
L.P. Xin at NAOC <xlp@bao.ac.cn>
L.P. Xin, M. Zhai, Y.L. Qiu, J.Y. Wei, J.Y. Hu, J.S. Deng,
J. Wang and W.K. Zheng on behalf of EAFON report:
We have imaged the field of GRB071028 (J. L. Racusin, GCN7012 ; J. Cummings,
GCN7013; J. Racusin, GCN7014) with EST 1m telescope at Xinglong Observatory.
The observations were started from 17:57:16 UT, 16.25min after the burst.
A series of V-band images were obtained . No new source was found in our
combined images within the error region of the XRT (J. L. Racusin, GCN7012)
but We found the location reported by J. Racusin(GCN7014) was consisting with
a very bright star in USNO-B1.0.
The 3 sigma limit of our V-band combined images derived from USNO-B1.0 R2mag
were :
------------------------------------
Band Mid time Exp time Limit Mag
V 30min 19*60 19.8
V 1.19hours 9*300s 19.98
V 2.98hours 14*600s 20.09
This message may be cited
GCN Circular 7016
Subject
Swift UVOT upper limits to GRB071028
Date
2007-10-29T17:12:39Z (18 years ago)
From
Patricia Schady at MSSL/Swift <ps@mssl.ucl.ac.uk>
P. Schady (MSSL/UCL) and J.L. Racusin (PSU) report on behalf of the Swift
UVOT team:
The Swift/UVOT observed the field of GRB 071028 (GCN 7012; Racusin et al.)
beginning 128 seconds after the BAT trigger. No afterglow is detected in
any of the UVOT filters within the XRT error circle (Racusin et al., GCN
7014). As already noted by Xin et al. (GCN 7015), the refined XRT position
(Racusin et al., GCN 7014) lies next to a very bright star (V<10 mag),
severely limiting the detection of an optical afterglow.
In the case of the white band and optical filters (v,b,u), contamination
from the nearby, bright star is causing the exposures to be affected by
coincidence loss to a degree that is outside the photometrically
calibrated range of UVOT. This limits the depth of our observations at the
XRT position in these filters to white > 13.86, v > 11.46, b > 12.68 and u
> 11.91.
The 3-sigma upper limits at the XRT position in co-added UV exposures are as
follows:
Filter Tmid Exp Magnitude
(s) (s) (3-sigma UL)
uvw1 5044 412 > 19.89
uvm2 4847 413 > 20.32
uvw2 5014 213 > 19.67
where Tmid is the mid time of the observations. The values quoted above are not
corrected for the expected Galactic extinction corresponding to a reddening of
E_{B-V} = 0.06 mag in the direction of the burst (Schlegel et al. 1998).
GCN Circular 7017
Subject
GRB 071028: SARA observations of variable source
Date
2007-10-29T21:58:11Z (18 years ago)
From
Adria C. Updike at Clemson U <aupdike@clemson.edu>
Adria C. Updike, Dieter H. Hartmann (Clemson University) and Gary D.
Henson (ETSU) report on behalf of the Clemson GRB Follow-Up Team:
We observed the field of GRB 071028 (GCN 7012, Racusin et al.) with the
0.9m SARA telescope on Kitt Peak beginning 15 hours and 25 minutes after
the trigger. Under variable cloud cover, we detect an apparently fading
source within the BAT circle, but outside the revised XRT position (GCN
7014, Racusin et al.), at RA=07:59:15.22, Dec=+21:28:32.052 (+/- 2
arcsec, J2000). This candidate source is approximately 0.5 arcmin to
the SW of the revised XRT position. In an hour of exposures, the source
faded from R ~ 17 to beyond our detection limit (R limit ~ 18.5 in a
single 120s exposure). The source was calibrated relative to 10 field
stars in the USNO B1.0 catalog. The separation between the candidate OT
and the revised XRT position makes this very unlikely to be the
afterglow of GRB 071028. Second epoch observations may be required to
establish the nature of this source.
The SARA website can be found at http://astro.fit.edu/sara/sara.html .
This message may be cited.