GRB 120805A
GCN Circular 13588
Subject
GRB 120805A: Swift detection of a burst
Date
2012-08-05T21:57:05Z (13 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
E. Troja (NASA/GSFC/ORAU), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), D. N. Burrows (PSU),
N. Gehrels (NASA/GSFC), C. Gronwall (PSU), S. T. Holland (STScI),
J. A. Kennea (PSU), O. M. Littlejohns (U Leicester),
K. L. Page (U Leicester) and D. M. Palmer (LANL) report on behalf of
the Swift Team:
At 21:28:09 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 120805A (trigger=530031). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 216.533, +5.802 which is
RA(J2000) = 14h 26m 08s
Dec(J2000) = +05d 48' 08"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a complex
structure with a duration of about 50 sec. The peak count rate
was ~500 counts/sec (15-350 keV), at ~2 sec after the trigger.
The XRT began observing the field at 21:30:13.0 UT, 123.1 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 216.54056, 5.82571 which is equivalent
to:
RA(J2000) = 14h 26m 09.73s
Dec(J2000) = +05d 49' 32.6"
with an uncertainty of 4.3 arcseconds (radius, 90% containment). This
location is 89 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 2.22
x 10^20 cm^-2 (Kalberla et al. 2005).
UVOT took a finding chart exposure of 90 seconds with the White filter
starting 126 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 0.03.
Burst Advocate for this burst is E. Troja (eleonora.troja 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 13589
Subject
GRB 120805A: TAROT Calern observatory optical observations
Date
2012-08-05T22:01:24Z (13 years ago)
From
Alain Klotz at CESR-CNRS <Alain.Klotz@free.fr>
Klotz A. (IRAP-CNRS-OMP), Gendre B. (ASDC/INAF-OAR),
Boer M. (UNS-CNRS-OCA), Atteia J.L. (IRAP-CNRS-OMP) report:
We imaged the field of GRB 120805A detected by SWIFT
(trigger 530031) with the TAROT robotic telescope (D=25cm)
located at the Calern observatory, France.
The observations started 77.2s after the GRB trigger
(19.3s after the notice). The elevation of the field decreased from
20 degrees above horizon and weather conditions
were moonlight.
The first image is trailed with a duration of 60.0s
(see the description in Klotz et al., 2006, A&A 451, L39).
We do not detect any OT in the BAT error box
with a limiting magnitude of:
t0+77.2s to t0+137.2s : R > 15.9
The second image is 30.0s exposure in tracking mode:
t0+152.6s to t0+182.6s : R > 16.2
We co-added a series of exposures:
t0+152.6s to t0+851s : R > 17.4
Magnitudes were estimated with the nearby USNO-B1 stars
and are not corrected for galactic dust extinction.
N.B. Galactic coordinates are lon=353.7578 lat=+58.9832
and the galactic extinction in R band is about 0.1 magnitude
estimated from D. Schlegel et al. 1998ApJ...500..525S.
This message may be cited.
GCN Circular 13590
Subject
GRB120805A: Liverpool Telescope observations
Date
2012-08-05T23:35:45Z (13 years ago)
From
David Bersier at Liverpool John Moores U <dfb@astro.livjm.ac.uk>
David Bersier (LJMU), Drejc Kopac (Ljubljana) report
The Liverpool Telescope (La Palma) started robotic observations of GRB
120805A 3 minutes after detection by Swift (Troja et al, GCN 13588). We
find no credible afterglow candidate in the XRT error circle. We find
upper limits of 18.9 in the r band 30 minutes after burst and 18.7 in the
i band 47 minutes after burst.
[GCN OPS NOTE(06aug12): Per author's request, in the Subject-line the "120521C"
has been changed to "120805A".]
GCN Circular 13591
Subject
GRB 120805A: 1.23m CAHA observations
Date
2012-08-05T23:49:45Z (13 years ago)
From
Javier Gorosabel at IAA-CSIC <jgu@iaa.es>
J. Gorosabel (IAA-CSIC), N. Huelamo (CAB-CSIC), R. Sanchez-Ramirez
(IAA-CSIC), A. de Ugarte Postigo (IAA-CSIC, DARK), T. Kruehler (DARK),
A.J. Castro-Tirado (IAA-CSIC), J.C. Tello (IAA-CSIC), M. Jelinek
(IAA-CSIC), report on behalf of a larger collaboration:
"I-band observations conducted with the Calar Alto 1.23m telescope at
21:41:19.1--22:04:02.4 UT (obs started ~13 minutes post GRB) for GRB
120805A reveal no object inside the XRT position (GCN Circ. 13588) down to
I~18 (Vega). However, we note the presence an object located at
RA(J2000)=14:26:09.12, DEC(J2000)=05:49:31.7 (error of ~0.5" in both
coordinates) with a magnitude of I~17.5 which seems not to be at the SDSS.
Given the lack of a refined XRT position yet, we are cautious about the
possible relation of this object with the GRB 120805A optical afterglow."
GCN Circular 13592
Subject
GRB 120805A: Swift-XRT refined Analysis
Date
2012-08-06T09:57:04Z (13 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
D.N. Burrows (PSU), C. Pagani (U. Leicester), A.P. Beardmore (U.
Leicester), P.A. Evans (U. Leicester), B. Sbarufatti (INAF-OAB/PSU), G.
Stratta (ASDC), P. D'Avanzo (INAF-OAB), J.A. Kennea (PSU), M.C. Stroh
(PSU) and E. Troja report on behalf of the Swift-XRT team:
We have analysed 6.1 ks of XRT data for GRB 120805A (Troja et al. GCN
Circ. 13588), from 126 s to 13.6 ks after the BAT trigger. The data
comprise 115 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The refined XRT position is RA, Dec =
216.5411, +5.82554 which is equivalent to:
RA (J2000): 14 26 09.86
Dec(J2000): +05 49 31.9
with an uncertainty of 3.6 arcsec (radius, 90% confidence).
The light curve can be modelled with a series of power-law decays. The
light curve initially rises, with an index alpha=-1.497 (+0.951,
-0.003). At T+191 s it breaks to an alpha of 2.33 (+0.14, -0.12) before
breaking again at T+2805 s to a final decay with index alpha=0.3
(+/-0.7).
A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.43 (+0.22, -0.20). The
best-fitting absorption column is 2.1 (+0.9, -0.8) x 10^21 cm^-2, in
excess of the Galactic value of 2.2 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 5.1 x 10^-11 (6.0 x 10^-11) erg
cm^-2 count^-1.
A summary of the WT-mode spectrum is thus:
Total column: 2.1 (+0.9, -0.8) x 10^21 cm^-2
Galactic foreground: 2.2 x 10^20 cm^-2
Excess significance: 3.7 sigma
Photon index: 1.43 (+0.22, -0.20)
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00530031.
This circular is an official product of the Swift-XRT team.
GCN Circular 13594
Subject
GRB 120805A: Swift-BAT refined analysis
Date
2012-08-06T13:44:59Z (13 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
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), T. Sakamoto (GSFC/UMBC),
G. Sato (ISAS), M. Stamatikos (OSU), E. Troja (NASA/GSFC/ORAU),
J. Tueller (GSFC), T. N. Ukwatta (MSU)
(i.e. the Swift-BAT team):
Using the data set from T-239 to T+330 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 120805A (trigger #530031)
(Troja, et al., GCN Circ. 13588). The BAT ground-calculated position is
RA, Dec = 216.536, 5.853 deg, which is
RA(J2000) = 14h 26m 08.5s
Dec(J2000) = +05d 51' 09.7"
with an uncertainty of 2.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 37%.
The mask-weighted light curve shows several overlapping peaks starting at
~T-8 sec, peaking at ~T+8 sec, and returning to baseline around T+110 sec.
T90 (15-350 keV) is 48.00 +- 22.63 sec (estimated error including systematics).
The time-averaged spectrum from T-15.39 to T+32.61 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.20 +- 0.28. The fluence in the 15-150 keV band is 8.2 +- 1.4 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+8.11 sec in the 15-150 keV band
is 0.37 +- 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/530031/BA/
GCN Circular 13598
Subject
GRB 120805A: Swift/UVOT Upper Limits
Date
2012-08-06T19:09:10Z (13 years ago)
From
Craig Swenson at PSU/Swift <cswenson@astro.psu.edu>
C. A. Swenson (PSU) and E. Troja (NASA/GSFC/ORAU)
report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 120805A
127 s after the BAT trigger (Troja et al., GCN Circ. 13588).
No optical afterglow consistent with the refined XRT position (Burrows
et al., GCN Circ. 13592) is detected in the initial UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial
exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
white 127 7557 579 >22.0
v 1339 11924 1248 >20.8
b 1265 7352 490 >21.5
u 1240 7146 490 >20.5
w1 1216 13611 1253 >21.3
m2 1364 12829 1141 >21.6
w2 1487 7763 432 >21.6
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.03 in the direction of the burst
(Schlegel et al. 1998).
GCN Circular 13638
Subject
GRB 120805A: Enhanced Swift-XRT position
Date
2012-08-14T08:26:46Z (13 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:
We have reinvestigated the XRT position of GRB 120805A. Using 2.6 ks of
XRT Photon Counting mode data and 2 UVOT images, 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 =
216.53836, 5.82525 which is equivalent to:
RA (J2000): 14 26 09.21
Dec (J2000): +05 49 30.9
with an uncertainty of 2.7 arcsec (radius, 90% confidence). This
position is 10" from the unenhanced XRT position reported in GCN Circ.
13592. The size of the astrometric correction, which is responsible for
this shift, was such that the enhanced position was initially rejected
and not circulated automatically. Position enhancement is described by
Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397,
1177).
This corrected position is our best XRT position, and is 1.5 arcsec from
the optical counterpart proposed in GCN Circ. 13591, supporting the
identification of that source as the afterglow. We thank Daniele
Malesani for drawing this to our attention.
This circular is an official product of the Swift-XRT team.
GCN Circular 13639
Subject
GRB 120805A: optical afterglow confirmation from the NOT
Date
2012-08-14T12:10:51Z (13 years ago)
From
Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst <malesani@dark-cosmology.dk>
D. Malesani, T. Kruehler (DARK/NBI), A. de Ugarte Postigo (IAA/CSIC and
DARK/NBI), D. Xu (WIS), N. R. Tanvir (Univ. Leicester), J. Gorosabel
(IAA/CSIC), P. Jakobsson (Univ. Iceland), S. Geier (NOT and DARK/NBI),
T. Pursimo (NOT), report on behalf of a larger collaboration.
We observed the field of GRB 120805A (Troja et al., GCN 13588) on two
epochs with the NOT optical telescope, located in La Palma (Canary
Islands). The two observations were carried out on mean dates Aug 5.936
and 13.896 UT, that is 1.0 hr and 8.0 days after the GRB, respectively.
The source first noticed by Gorosabel et al. (GCN 13591) is detected in
both our images, and it varied significantly between the two epochs, as
well as compared to the CAHA report (Gorosabel et al., GCN 13591). We
note that the object position is now fully consistent with the revised
XRT error circle (Evans, GCN 13638). We thus conclude that this source
is the optical afterglow of GRB 120805A.
The source varied by only about 2 mag between the two NOT epochs
(corresponding to a power-law decay slope of ~0.3), suggesting that in
the later image the host galaxy could be contributing to the total light.
A picture showing the two NOT epochs is posted at this URL:
http://www.astro.ku.dk/~malesani/GRB/120805A/GRB120805A_comparison.jpg
We thank Phil Evans for discussion about the XRT localization of this
afterglow.
GCN Circular 13651
Subject
GRB 120805A: Liverpool Telescope optical candidate detection
Date
2012-08-15T07:30:58Z (13 years ago)
From
Cristiano Guidorzi at Ferrara U,Italy <guidorzi@fe.infn.it>
C. Guidorzi (U. Ferrara) and C.G. Mundell (LJMU) report
on behalf of a large collaboration:
The Liverpool Telescope automatically observed GRB 120805A
(Troja et al. GCN Circ. 13588) as previously reported (Bersier
et al GCN Circ. 13590). We also detected the optical candidate
identified by Gorosabel et al. (GCN Circ. 13591) at the
following position, within the UVOT-enhanced XRT error circle
(Evans et al. GCN Circ. 13638):
RA(J2000) = 14:26:09.11
Dec(J2000)= +05:49:32.1
with an uncertainty of 1". The optical afterglow candidate
is detected in both r' and i' filters with the following
magnitudes:
Mid time from Total Exp Filter Magnitude
trigger (min) (s)
------------------------------------------------
16.0 6x10 r' 20.9 +- 0.3
50.0 3x120 i' 20.9 +- 0.2
------------------------------------------------
Magnitudes are calibrated against nearby USNOB-1 stars.