GRB 050421
GCN Circular 3296
Subject
Swift Detection of GRB050421
Date
2005-04-21T05:52:28Z (20 years ago)
From
Louis M Barbier at NASA/GSFC/Swift <lmb@cosmicra.gsfc.nasa.gov>
L. Barbier (GSFC), D. Palmer (LANL), D. Burrows (PSU), A. Blustin (MSSL),
C. Markwardt (GSFC/UMd), N. Gehrels (GSFC), P. Roming (PSU)
At 04:11:52 UT, the Swift Burst Alert Telescope (BAT) triggered and
located on-board GRB050421 (trigger # 115135). The BAT on-board
calculated location is RA, Dec 307.241, +73.665 (20:28:58, 73:39:54)
(J2000) with an uncertainty of 4 arcmin (radius, 3-sigma, including estimated
systematic uncertainty). The BAT light curve showed a weak,
multipeak structure with a duration of about 10 seconds. The peak
count rate was measured by BAT to be 1000 counts/sec
in the 15 - 350 keV band.
The Swift spacecraft slewed promptly onto the BAT position and
observations by the Swift X-Ray Telescope (XRT) began at 04:13:42 UT
with the XRT in the auto state. An uncatalogued X-ray source was
detected at the following position: RA, Dec 307.2542, +73.6528
(20:29:01, 73:39:10) (J2000) with an uncertainty of 5
arcsec (radius). This is 46 arcsec from the BAT position
reported above.
The Swift Ultra-Violet/Optical Telescope (UVOT) began observations 112
seconds after the burst at 04:13:44 UT. Information on UVOT
observations will be published in the next GCN.
GCN Circular 3297
Subject
GRB 050421: Optical observations at the INT
Date
2005-04-21T07:43:55Z (20 years ago)
From
Alberto Castro-Tirado at Inst.de Astro. de Andalucia <ajct@iaa.es>
A. de Ugarte Postigo (IAA-CSIC), J. Furnes, R. Corradi (ING, La Palma),
M. Jelinek, J. Gorosabel and A. J. Castro-Tirado (IAA-CSIC Granada),
report:
"Following the detection by SWIFT/BAT of GRB 050421 (Barbier et al. GCN
Circ. 3296), we started observations at the 2.5m Isaac Newton Telescope at
Observatorio del Roque de los Muchachos in La Palma. The first 120-s image
(in the Sloan i-band filter), started on Apr 21.1858 UT (i.e. 15.7 min
after the
event). We do not see any object within the reported SWIFT/XRT position.
Further analysis of additional i-band images is in progress."
This message can be quoted.
GCN Circular 3298
Subject
GRB 050421: BOOTES-2 simultaneous optical observations
Date
2005-04-21T07:57:42Z (20 years ago)
From
Alberto Castro-Tirado at Inst.de Astro. de Andalucia <ajct@iaa.es>
M. Jelinek, A. J. Castro-Tirado, J. Gorosabel, A. de Ugarte Postigo
(IAA-CSIC Granada),
P. Kubanek, R. Hudec (Astronomical Institute of the Academy of Sciences,
Ondrejov),
T. J. Mateo Sanguino (Universidad de Huelva), T. Soria, R. Fern�ndez
(EELM-CSIC,
M�laga) and J. Fabregat (Universidad de Valencia)
report:
"The BOOTES-2 very wide field camera, located at the Estaci�n
Experimental de La Mayora (EELM-CSIC) in M�laga, observed the region of
the sky containing the SWIFT/BAT error box
for GRB 050421 (Barbier et al. GCN 3296) as part of its routine
observing schedule. A 30 s
exposure started at 04:12:00 UT (8 s after the onset of the 10 s long
burst), with the previous
frame starting at 04:11:00 UT. A limiting (unfiltered) magnitude of 9.0
is derived for any prompt
optical flash arising from this event."
This message can be quoted.
GCN Circular 3299
Subject
GRB050421: P60 Observations
Date
2005-04-21T09:54:40Z (20 years ago)
From
S. Bradley Cenko at Caltech <cenko@srl.caltech.edu>
S. Bradley Cenko and Derek B. Fox (Caltech) report on behalf of the
Caltech-NRAO-GRB collaboration:
We have imaged the field of GRB050421 (GCN #3296) with the automated
Palomar 60-inch telescope. Observations consisted of 17 x 120 s images
in the Kron R band, taken at a mean epoch of 08:50 UT (~ 4.6 hours after
the burst). We find no sources in the XRT error circle reported in GCN
#3296. Our 3.0-sigma limiting magnitude, estimated by comparison with
several stars from the Guide Star Catalog, is approximately R < 22.0.
GCN Circular 3300
Subject
GRB 050421: NIR observations
Date
2005-04-21T10:08:29Z (20 years ago)
From
Daniele Malesani at SISSA-ISAS,Trieste,Italy <malesani@sissa.it>
D. Fugazza (INAF-OABr), L.A. Antonelli, V. Testa (INAF-OAR), L. Di
Fabrizio, G. Tessicini (INAF-TNG), and D. Malesani (SISSA), report on
behalf of a larger collaboration:
We imaged the field of GRB 050421 (Barbier et al., GCN 3296) with the
Italian 3.6m TNG. Observations were carried out under moderate observing
conditions (seeing ~0.8"), just before the dawn. Exposures were acquired
in the K filter, for a total integration time of 20 min, starting on Apr
21.2313 UT (mean time Apr 21.2453 UT, 1.7 h after the GRB).
We find no sources within the XRT error circle, down to a limiting
magnitude K = 18.6 (3 sigma).
This message can be cited.
GCN Circular 3301
Subject
GRB 050421: early Swift XRT analysis results
Date
2005-04-21T10:59:17Z (20 years ago)
From
David Burrows at PSU/Swift <dxb15@psu.edu>
O. Godet, M. Goad, K. Page, J. Osborne (U. Leicester), D. N. Burrows (PSU),
N. Gehrels (NASA/GSFC) report on behalf of the Swift XRT team:
We have analyzed the Swift XRT data from the first orbit observation of GRB
050421. The refined coordinates are:
RA(J2000) = 20h 29m 01.75s
Dec(J2000) = +73d 39' 17.4"
This position is 40 arcseconds from the BAT position given in GCN 3296
(Barbier et al 2005). We estimate a total uncertainty of 5 arcseconds radius
(90% containment). We note that this refined position is 8.1 arcseconds
from the XRT position reported in GCN 3296. Optical observers should
re-check their images for sources in the new error circle.
Our 0.2-10 keV light curve covers the interval 116-591 sec after the BAT
trigger. It is well-fit with a broken powerlaw with initial slope of 0.9
+1.1/-1.6 breaking to a steeper slope of 3.3 +0.6/-0.3 after 147 +/-10 sec.
All errors are 90% confidence. A single power law decline is not a good
fit to the data.
A preliminary spectral fit to the WT mode data gives a power law photon index
of 1.23 +0.37/-0.34 (error at 90% confidence level) in the 0.3-10 keV band,
assuming Galactic absorption (1.44 E21 cm^-2) and a possible excess in the
absorption of 6 +4/-3 E21 cm^-2. The unabsorbed 0.3-10 keV flux is 8.5E-10
erg cm^-2 s^-1 in the interval 116-171 sec after the BAT trigger.
GCN Circular 3302
Subject
GRB050421
Date
2005-04-21T12:48:00Z (20 years ago)
From
Guy Pooley at MRAO, Cambridge, UK <ggp1@cam.ac.uk>
The field of GRB050421 (GCN 3296, using the updated position
in GCN 3301) was observed with the Ryle Telescope in Cambridge
at 15 GHz from 08:37 to 12:12 UT on 2005 Apr 21 (4h25m to 8h
after the trigger). The angular resolution is 25".
A formal measure of the flux density at the position in GCN 3301
is 0.59 mJy with an rms noise 0.27 mJy, and is therefore not
a convincing detection.
This message is quotable.
Guy Pooley, Astrophysics, Cavendish Laboratory
GCN Circular 3303
Subject
GRB 050421: NIR observations re-examination
Date
2005-04-21T13:01:48Z (20 years ago)
From
Daniele Malesani at SISSA-ISAS,Trieste,Italy <malesani@sissa.it>
V. Testa, L.A. Antonelli (INAF-OAR), D. Fugazza (INAF-OABr), L. Di
Fabrizio, G. Tessicini (INAF-TNG), and D. Malesani (SISSA), report on
behalf of a larger collaboration:
After the revision of the XRT position (Godet et al., GCN 3301) of the
X-ray afterglow of GRB 050421 (Barbier et al., GCN 3296), we re-examined
our TNG K-band images (Fugazza et al., GCN 3300).
We find no sources within the revised XRT error box down to the 3-sigma
limit K > 18.6.
This message can be cited.
GCN Circular 3304
Subject
GRB 050421: ROTSE-III Optical Limits
Date
2005-04-21T15:24:42Z (20 years ago)
From
Eli Rykoff at U of Michigan/ROTSE <erykoff@umich.edu>
E.S. Rykoff (U Mich), S.A. Yost (U Mich), H. Swan (U Mich) report on
behalf of the ROTSE collaboration:
ROTSE-IIIb, located at McDonald Observatory, Texas, responded to GRB
050421 (Swift trigger 115135), producing images beginning 9.7 s after
the GCN notice time. An automated response took the first image at
04:12:58.8 UT, 67.2 s after the burst, under good conditions. These
observations were affected by the bright moon. We took 10 5-sec, and 350
20-sec eposures. These unfiltered images are calibrated relative to USNO
A2.0 (R).
Comparison to the DSS (second epoch) reveals no new sources within the
3-sigma BAT error circle including the 3-sigma XRT error circle (GCN
3301). Individual images have limiting magnitudes ranging from
16.49-17.34. In particular, we set a limit of magnitude 16.49 in a
single 5 s exposure, starting 67.1 s after the burst. Coadding images
into sets of 10 reveals no new sources down to limits of 17.8 (t0+61.7s
- t0+130.7s) and 18.4 (t0+144s - t0+431s)
GCN Circular 3305
Subject
GRB 050421: Swift-BAT refined analysis
Date
2005-04-21T15:44:53Z (20 years ago)
From
Louis M Barbier at NASA/GSFC/Swift <lmb@cosmicra.gsfc.nasa.gov>
T. Sakamoto (GSFC/NRC), L. Barbier (GSFC), S. Barthelmy (GSFC),
J. Cummings (GSFC/NRC), E. Fenimore (LANL), N. Gehrels (GSFC),
D. Hullinger (UMD), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD),
T. Mitani (ISAS), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/NRC),
G. Sato (ISAS), M. Suzuki (Saitama), J. Tueller (GSFC),
on behalf of the Swift/BAT team:
At 04:11:52 UT Swift-BAT detected GRB 050421 (trigger=115135)
(GCN Circ 3296, Barbier et al.). The refined BAT ground position
is (RA,Dec) = 307.306, +73.665, [deg; J2000] +- 3.4 arcmin, (95%
containment). The partial coding was 91%.
The light curve has a FRED structure with a rise in < 1 second and a decay
in ~10 seconds. T90 (15-350 keV) is (10.3 +- 2) seconds
(estimated error including systematics).
The photon index of the time-averaged spectrum is 1.7 +-0.4.
The fluence in the 15-350 keV band is (1.8 +- 0.7 ) x 10^-7 erg/cm2.
The 1-s peak photon flux measured from T0+1.4 seconds in the 15-350
keV band and is (0.5 +- 0.1) ph/cm2/s. All the quoted errors are at the 90%
confidence level.
GCN Circular 3306
Subject
GRB 050421: IR Observations
Date
2005-04-21T15:58:46Z (20 years ago)
From
Josh Bloom at Harvard/CFA <jbloom@cfa.harvard.edu>
J. S. Bloom (UCB) reports on behalf of a larger collaboration:
"We observed the field of GRB 050421 (GCN 3296, GCN 3301) with the
PAIRITEL 1.3m on Mt. Hopkins over several epochs. In a 502 sec exposure
beginning on 2005-04-21 11:23:45 UT, we find a faint source in J,H,Ks,
consistent with XRT position, located at:
RA 20:29:00.94
DEC +73:39.19.2 (J2000; uncertainty ~ 0.5 arcsec)
We have not checked the variability of this source so its identification
as the afterglow cannot be confirmed at this time. We note that there is
also a JHKs source just outside the XRT 5 arcsec error radius at (end
figures): 02.01, 22.3."
This message may be cited.
GCN Circular 3307
Subject
GRB 050421: Swift-UVOT observation
Date
2005-04-21T17:36:02Z (20 years ago)
From
Alexander Blustin at MSSL-UCL <ajb@mssl.ucl.ac.uk>
A. Blustin (MSSL), L. Barbier (GSFC), K. McGowan (MSSL),
P. Roming (PSU), M. De Pasquale (MSSL), S. T. Holland (GSFC),
N. Gehrels (GSFC), K. Mason (MSSL), J. Nousek (PSU), on behalf
of the Swift UVOT team
Starting with the data taken ~245s after the BAT trigger (Barbier
et al., GCN 3296) we have co-added the early time data of GRB 050421
in each of the Ultra-Violet/Optical Telescope (UVOT) V, B and U
bands. The co-added images are made up of 9 x 10s exposures. No
source is detected within the revised XRT error circle (Godet et al.,
GCN 3301) in any of the bands; we estimate the five sigma magnitude
upper limits from the co-added images to be:
Filter Upper limit
V 17.5
B 19.1
U 18.8
The magnitudes are based on preliminary zero-points, measured in
orbit, and will require refinement with further calibration.
This message may be cited.
GCN Circular 3308
Subject
GRB050421: Radio Observations
Date
2005-04-21T17:49:52Z (20 years ago)
From
Alicia Soderberg at Caltech <ams@astro.caltech.edu>
A. M. Soderberg (Caltech) and D. A. Frail (NRAO) report on behalf of
the Caltech-NRAO-Carnegie GRB Collaboration:
"We observed the field centered on the BAT position of the Swift burst
GRB 050421 (GCN#3296) using the VLA at a frequency of 8.46 GHz
on Apr 21.62 UT (t ~ 0.4 days after the burst).
We do not detect any radio sources within the XRT error circle (GCN#3301).
We place a 2-sigma detection limit of 34 uJy on the field."
GCN Circular 3309
Subject
GRB050421: Radio Observations
Date
2005-04-21T18:43:58Z (20 years ago)
From
Alicia Soderberg at Caltech <ams@astro.caltech.edu>
A. M. Soderberg (Caltech) and D. A. Frail (NRAO) report on behalf of
the Caltech-NRAO-Carnegie GRB Collaboration:
"We observed the field centered on the BAT position of the Swift burst
GRB 050421 (GCN#3296) using the VLA at a frequency of 8.46 GHz
on Apr 21.62 UT (t ~ 0.4 days after the burst).
We do not detect any radio sources within the XRT error circle (GCN#3301).
We place a 2-sigma detection limit of 34 uJy on the field."
GCN Circular 3310
Subject
GRB 050421: Further Analysis of IR imaging
Date
2005-04-21T19:00:29Z (20 years ago)
From
Josh Bloom at Harvard/CFA <jbloom@cfa.harvard.edu>
C. Blake and J. S. Bloom report on behalf of a larger collaboration:
"Following further analysis of ~2000 seconds of J,H,Ks observations of
the field of GRB 050421 (GCN 3296, GCN 3301) with the PAIRITEL 1.3m on
Mt. Hopkins we cannot confirm variability in the source reported in GCN
3306. Furthermore, analysis of our full J,H,Ks data set from UT April 21
does not reveal any sources detected at >3 sigma within the XRT
error-circle."
This message may be cited.
GCN Circular 3311
Subject
GRB 050421: SLOTIS observations
Date
2005-04-21T21:25:54Z (20 years ago)
From
Peter A. Milne at super-LOTIS <pmilne@as.arizona.edu>
SUBJECT: GRB 050421: SLOTIS observations
FROM: P.A.Milne at Steward Observatory
P.A.Milne, G.G.Williams (Steward Obs), H.-S.Park (LLNL),
on behalf of the Super-LOTIS GRB team report:
On Apr 20/21, we observed the field of GRB 050421
(SWIFT trigger 115135) starting at UT=08:01:56 (230m after the burst),
and again at UT=10:31:56 (480m after the burst) with the 0.6m SLOTIS
telescope at Kitt Peak, AZ. We obtained 30 x 30-sec images during
each observation.
Comparison of the two resulting co-added images to the relevant
DSS2 image reveals no new sources within the BAT error circle
(GCN 3301). No new source was detected at the location of
the potential counterpart reported by Bloom (GCN 3306),
Blake and Bloom (GCN 3310).
The first epoch was affected by the bright moon and high airmass.
The upper limit of a source in that field is about 17.5 magnitude.
The second epoch images were obtained under more favorable
conditions, and the upper limit of a source in that field is
about 20.0 magnitude.
This message may be cited.
GCN Circular 3313
Subject
GRB 050421: NIR observations
Date
2005-04-22T02:30:07Z (20 years ago)
From
Paul Price at IfA,UH <price@ifa.hawaii.edu>
P.A. Price (IfA), T. Minezaki (U. Tokyo), L. Cowie (IfA) and Y. Yoshii
(U. Tokyo) report on behalf of the UH-MAGNUM GRB collaboration:
We observed the XRT position of GRB 050421 (Godet et al., GCN #3301)
with the automated MAGNUM telescope + MIP dual-beam optical-NIR imager,
commencing at April 21.57 UTC (9.4 hours after the GRB). We obtained
9x60 sec images in JHK, reaching limiting magnitudes of J ~ 20.3 mag, H
~ 19 mag, K ~ 18.6 mag (from comparison with a single 2MASS star). We
do not detect any afterglow candidate in the XRT error circle.
This message may be cited.