GRB 111020A
GCN Circular 12460
Subject
GRB 111020A: Swift detection of a short burst
Date
2011-10-20T06:46:03Z (14 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
T. Sakamoto (NASA/UMBC), M. M. Chester (PSU),
J. R. Cummings (NASA/UMBC), P. A. Evans (U Leicester),
C. Guidorzi (U Ferrara), V. Mangano (INAF-IASFPA),
K. L. Page (U Leicester), D. M. Palmer (LANL) and
P. Romano (INAF-IASFPA) report on behalf of the Swift Team:
At 06:33:49 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 111020A (trigger=505926). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 287.027, -37.985 which is
RA(J2000) = 19h 08m 06s
Dec(J2000) = -37d 59' 05"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a short single peak
structure with a duration of about 0.5 sec. The peak count rate
was ~3000 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 06:35:01.8 UT, 72.8 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 287.05305, -38.01178 which is
equivalent to:
RA(J2000) = 19h 08m 12.73s
Dec(J2000) = -38d 00' 42.4"
with an uncertainty of 4.1 arcseconds (radius, 90% containment). This
location is 121 arcseconds from the BAT onboard position, within the
BAT error circle. This position may be improved as more data are
received; the latest position is available at
http://www.swift.ac.uk/sper. We cannot determine whether the source is
fading at the present time.
A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 6.89
x 10^20 cm^-2 (Kalberla et al. 2005).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 79 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers none of
the XRT error circle. The 8'x8' region for the list of sources generated
on-board covers 100% of the XRT error circle. The list of sources is typically
complete to about 18 mag. No correction has been made for the expected
extinction corresponding to E(B-V) of 0.43.
Burst Advocate for this burst is T. Sakamoto (Taka.Sakamoto AT nasa.gov).
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 12461
Subject
GRB 111020A: Planned XMM-Newton observation
Date
2011-10-20T08:10:40Z (14 years ago)
From
Norbert Schartel at XMM-Newton/ESA <too@xmm.esac.esa.int>
XMM-Newton will observe GRB 111020A at location
(RA=19h 08m 12.73s, DEC=-38d 00' 42.4", J2000),
starting at 19:41:49 UT, on October 20, 2011,
for an exposure of 30,000 seconds.
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GCN Circular 12462
Subject
GRB 111020A: BOOTES-3 Optical Upper Limit.
Date
2011-10-20T15:07:24Z (14 years ago)
From
Juan Carlos Tello at IAA-CSIC <jtello@iaa.es>
J. C. Tello (IAA-CSIC), A. de Ugarte Postigo (IAA-CSIC, DARK/NBI), A. J.
Castro-Tirado, J. Gorosabel (IAA-CSIC), on behalf of a larger collaboration,
report:
We have observed the field of the short GRB 111020A, detected by Swift/BAT
(Palmer et al., GCNC 12460) with the 0.6m Yock-Allen telescope at the
BOOTES-3 station in Blenheim (New Zealand). Unfiltered images were obtained
starting 69.72 minutes after the burst (07:43:32 UT), no new source is
visible in the co-added image with total exposure 6900 sec (115 images
ending in 09:40:53 UT), the limiting magnitude for the combined image is R =
19.5 (calibrated against USNO B1.0).
USNO B1-0519-0893471, a catalogued R=18.7 magnitude source is at the edge of
the XRT circle but shows no evident variability.
GCN Circular 12463
Subject
GRB 111020A: Enhanced Swift-XRT position
Date
2011-10-20T15:32:42Z (14 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester)
report on behalf of the Swift-XRT team.
Using 2124 s of XRT Photon Counting mode data and 3 UVOT
images for GRB 111020A, 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 = 287.05219, -38.01216 which is equivalent
to:
RA (J2000): 19h 08m 12.53s
Dec (J2000): -38d 00' 43.8"
with an uncertainty of 1.6 arcsec (radius, 90% confidence).
This position may be improved as more data are received. The latest
position can be viewed at http://www.swift.ac.uk/xrt_positions. Position
enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans
et al. (2009, MNRAS, 397, 1177).
This circular was automatically generated, and is an official product of the
Swift-XRT team.
GCN Circular 12464
Subject
GRB 111020A: Swift-BAT refined analysis
Date
2011-10-20T15:49:32Z (14 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
T. Sakamoto (GSFC/UMBC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC),
H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC), D. M. Palmer (LANL),
G. Sato (ISAS), M. Stamatikos (OSU), J. Tueller (GSFC), T. N. Ukwatta (MSU)
(i.e. the Swift-BAT team):
Using the data set from T-240 to T+963 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 111020A (trigger #505926)
(Sakamoto, et al., GCN Circ. 12460). The BAT ground-calculated position is
RA, Dec = 287.029, -38.031 deg, which is
RA(J2000) = 19h 08m 06.9s
Dec(J2000) = -38d 01' 50.3"
with an uncertainty of 2.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 74%.
The mask-weighted light curve shows a single spike starting at ~T+0.0, peaking
at ~T+0.1 sec, and ending at ~T+1.0 sec. There is a hint (at the 2.5-sigma level)
of a soft tail out to ~T+10 sec. T90 (15-350 keV) is 0.40 +- 0.09 sec
(estimated error including systematics).
The time-averaged spectrum from T-0.04 to T+0.39 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.37 +- 0.26. The fluence in the 15-150 keV band is 6.5 +- 1.0 x 10^-8 erg/cm2.
The 1-sec peak photon flux measured from T-0.32 sec in the 15-150 keV band
is 0.9 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence
level.
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/505926/BA/
GCN Circular 12465
Subject
GRB 111020A: Faulkes Telescope South observations
Date
2011-10-20T16:07:13Z (14 years ago)
From
Nial Tanvir at U.Leicester <nrt3@star.le.ac.uk>
C. Guidorzi (U. Ferrera), N. R. Tanvir (U. Leicester), C. Mottram,
D. Bersier (Liverpool JMU), report:
On 2011 October 20 at 11:02:37 UT the 2-m Faulkes Telescope
South began observing short GRB 111020A (Sakamoto et al., GCN Circ.
12460) using the Ri filters, corresponding to approximately 4.5 hours
after the burst trigger time.
We detect no uncatalogued sources, either inside or near the
enhanced XRT error circle (Osborne et al. GCN Circ. 12463),
to the following limiting magnitudes:
Mid time from Total Exp Filter Magnitude
trigger (hours) (s)
------------------------------------------------
4.75 6x300 R> 21.0
5.32 6x300 i> 21.7
------------------------------------------------
Magnitudes have been calibrated from nearby USNOB-1
stars using their R2 and I nominal values.
GCN Circular 12466
Subject
GRB 111020A: Swift/UVOT Upper Limits
Date
2011-10-20T19:47:57Z (14 years ago)
From
Samantha Oates at MSSL <sro@mssl.ucl.ac.uk>
S. R. Oates (MSSL-UCL) and T. Sakamoto (NASA/UMBC)
report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 111020A
80 s after the BAT trigger (Sakamoto et al., GCN Circ. 12460).
No optical afterglow consistent with the XRT position (Osborne et al., GCN Circ. 12463)
is detected in the initial UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system
(Poole et al. 2008, MNRAS, 383, 627) for the first finding chart (FC)
exposure and subsequent exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
white_FC 80 230 147 >20.0
u_FC 292 542 246 >19.6
white 80 7160 766 >20.3
v 622 6135 275 >18.8
b 547 6956 471 >19.9
u 292 18728 1973 >20.3
w1 670 18066 2242 >21.0
m2 6140 22385 2310 >21.1
w2 1027 5930 216 >20.5
This photometry may be complicated by the presence of a catalogued source
approximately 3'' away from the centre of the enhanced XRT error circle.
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.43 in the direction of the burst
(Schlegel et al. 1998).
GCN Circular 12467
Subject
GRB 111020A: Gemini-South i-band observations
Date
2011-10-21T01:58:38Z (14 years ago)
From
Wen-fai Fong at CFA <wfong@cfa.harvard.edu>
W. Fong (Harvard), E. Berger (Harvard) and D. Fox (PSU) report:
We imaged the location of the short GRB 111020A (GCN 12460) with GMOS on the
Gemini-South 8-m telescope on 2011 October 21.01 UT (mid-time of 17.7 hours
post-burst). We obtained 9x180s exposures in i-band with 0.8" seeing.
We find no sources within the enhanced XRT error circle (GCN 12463) to a
3-sigma limiting magnitude of i~25 mag.
However, we find two faint objects just outside of the XRT error circle with
coordinates (J2000):
S1:
RA = 19:08:12.501
Dec = -38:00:41.80
S2:
RA = 19:08:12.698
Dec = -38:00:44.46
S1 has a brightness of i~23.7 mag and appears to be point-like. S2 is
fainter, at the threshold of detectability with a brightness of i~25 mag.
The nearest galaxy is located at:
G1:
RA = 19:08:12.231
Dec = -38:00:48.80
with a magnitude of i~23.3 mag, and 6.2" from the center of the XRT error
circle.
GCN Circular 12468
Subject
GRB 111020A: Swift-XRT refined Analysis
Date
2011-10-21T07:36:44Z (14 years ago)
From
Vanessa Mangano at INAF-IASFPA <vanessa@ifc.inaf.it>
V. Mangano (INAF IASFPA) and T. Sakamoto (NASA/UMBC) reports on behalf
of the Swift-XRT team:
We have analysed 20 ks of XRT data for GRB 111020A (Sakamoto et al.
GCN Circ. 12460), from 59 s to 69.8 ks after the BAT trigger. The data
comprise 7 s in Windowed Timing (WT) mode (taken while Swift was
slewing), with the remainder in Photon Counting (PC) mode. The enhanced
XRT position for this burst was given by Osborne et al. (GCN. Circ
12463).
The light curve can be modelled with a power-law decay with a decay
index of alpha=0.72 (+/-0.06).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.14 (+0.19, -0.41). The
best-fitting absorption column is 10.0 (+5.4, -1.8) x 10^21 cm^-2, in
excess of the Galactic value of 6.9 x 10^20 cm^-2 (Kalberla et al.
2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum is 5.3 x 10^-11 (1.2 x 10^-10) erg
cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 10.0 (+5.4, -1.8) x 10^21 cm^-2
Galactic foreground: 6.9 x 10^20 cm^-2
Excess significance: 8.9 sigma
Photon index: 2.14 (+0.19, -0.41)
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00505926.
This circular is an official product of the Swift-XRT team.
GCN Circular 12469
Subject
GRB 111020A: EVLA observations
Date
2011-10-21T14:26:47Z (14 years ago)
From
Wen-fai Fong at CFA <wfong@cfa.harvard.edu>
W. Fong, A. Zauderer and E. Berger (Harvard) report:
"We observed the position of GRB 111020A (GCN 12460) with the EVLA beginning
on 2011 October 20.98 UT (16.9 hours post-burst) at a mean frequency of 5.8
GHz. In 1 hour of observations we do not detect any radio source within the
enhanced XRT error circle (GCN 12463) to a 3-sigma limit of ~50 microJy.
Further observations are in progress."
GCN Circular 12470
Subject
GRB 111020A: Gemini-South additional observations and limit on an optical afterglow
Date
2011-10-22T02:47:44Z (14 years ago)
From
Wen-fai Fong at CFA <wfong@cfa.harvard.edu>
W. Fong and E. Berger (Harvard) report:
"We re-imaged the field of GRB 111020A (GCN 12640) with GMOS on the
Gemini-South telescope on 2011 October 22.01 UT (mid-time of 1.7 days
post-burst, and 23.1 hours after our initial observations; GCN 12467). We
obtained 11x180s exposures in i-band in 0.73" seeing.
We still detect the two faint sources S1 and S2 from our previous GMOS
observation (GCN 12467), and neither source shows evidence for fading.
Digital image subtraction of the two epochs using the ISIS package reveals
no residuals inside or near the XRT error circle. We therefore place a
limit on the optical afterglow of i~25 mag at 17.7 hours after the burst."
GCN Circular 12477
Subject
GRB 111020A Spectral lag analysis
Date
2011-10-22T20:25:56Z (14 years ago)
From
Takanori Sakamoto at NASA/GSFC <takanori@milkyway.gsfc.nasa.gov>
T. Sakamoto (GSFC/UMBC), S. D. Barthelmy (GSFC),
J. Norris (BSU), T. N. Ukwatta (MSU)
We report the spectral lag analysis for GRB 111020A (GCN Circ. 12460)
based on the BAT data. Using 64 ms binned light curves, the spectral
lag for 15-25 keV to 50-100 keV is 124 +36/-38 msec. This significant
lag is due to a broader pulse in the 15-25 keV band comparing to that
in the 50-100 keV band which indicates the strong pulse evolution from
hard to soft. Although the burst duration itself is short (T90 = 400 ms;
GCN Circ. 12464), this positive lag argues against a "short" classification.
However, there is a possibility that the broader pulse seen in the
15-25 keV band is composed from two pulses instead of a single pulse.
If this is the case, the lag result above could be confused by
cross-correlating the 2nd pulse in the 15-25 keV and the 1st pulse
in the 50-100 keV band. Due to the limiting signal-to-noise in the
light curve data, it is not possible to claim whether the broad pulse
in the 15-25 keV has two pulses or just a single pulse.
Give the large non-zero lag and the possible double peak interpretation
that could cause a false lag, we think it equally like that this burst
is short or long.
[GCN OPS NOTE(24oct11): Per author's request, the T90 value typo
was corrected to 400 ms.]
GCN Circular 12492
Subject
GRB 111020A: Chandra Observation
Date
2011-10-24T20:28:14Z (14 years ago)
From
Edo Berger at Harvard <eberger@cfa.harvard.edu>
E. Berger, R. Margutti, and W. Fong (Harvard) report:
"We observed the field of the short GRB 111020A (GCN 12640) with the Chandra
X-ray Observatory + ACIS-S starting on 2011 October 23.14 UT (2.86 days
after the burst) for a total of 19.8 ksec. We clearly detect a source in
coincidence with the enhanced XRT error circle (GCN 12463) at the following
coordinates (J2000):
RA = 19:08:12.502
DEC = -38:00:42.58
with an uncertainty of about 0.5". The position includes a minor correction
to the Chandra astrometry using two X-ray sources with stellar counterparts
in our Gemini i-band images (which were astrometrically matched to the 2MASS
catalog; GCNs 12467, 12470). The Chandra position is offset by 1.2" from
the centroid of the most recent XRT position (which has a 90% containment
uncertainty of 1.6"). Further analysis of the Chandra data is on-going.
We thank Harvey Tananbaum and the CXO scheduling staff for rapidly approving
and executing this observation."
GCN Circular 12739
Subject
XMM-Newton observation of the short GRB 111020A
Date
2011-12-28T16:55:48Z (13 years ago)
From
Sergio Campana at INAF-OAB <sergio.campana@brera.inaf.it>
S. Campana (INAF-Osservatorio astronomico di Brera) reports:
XMM-Newton observed the short GRB 111020A (Sakamoto et al.
2011, GCN 12460) on Oct 20, 2011 21:50:05 UT (15.3 hr after
the burst onset).
The ~20 ks observation was affected in the first part by a mild enhanced
background event which we filtered out. The resulting pn/MOS1/MOS2
exposure times were 15, 17 and 17 ks, respectively.
A source is well detected at a position consistent with the Swift's
(Osborne et al. 2011, GCN 12463) and Chandra's (Berger et al. 2011,
GCN 12492) ones.
The pn count rate is (2.2+/-0.2)x10^{-2} cts/s.
We extracted 422, 166, and 142 source photons from the pn, MOS1,
and MOS2, respectively.
The spectrum can be fitted with a power law model including a
non-negligible
absorption component in addition to the Galactic one (6.9x10^{20} cm^{-2}).
The best fit power law implies a photon index of Gamma=1.9+/-0.3
(90% c.l. for one parameter of interest) and an additional column
density of
NH=(6+/-2)x10^{21} cm^{-2} (90% c.l.). This provides a lower limit to the
intrinsic column density. The reduced chi^2 of the fit is 0.83 (31 d.o.f.).
The unabsorbed 0.5-10 keV is ~2x10^{-13} erg/cm^2/s.