GRB 050406
GCN Circular 3185
Subject
GRB 050406: Magellan optical observations
Date
2005-04-07T00:36:33Z (22 years ago)
From
Edo Berger at Carnegie Obs <eberger@ociw.edu>
Edo Berger, Gus Oemler, and Mike Gladders (Carnegie Observatories) report:
"On 2005, April 6.99 UT we imaged the position of GRB 050406 (GCN 3180)
with LDSS-3 on the Magellan/Clay telescope in the r-band and i-band.
Within the 5" radius XRT error circle (GCN 3184) we find a single faint
source (r~22 mag) close to the detection threshold of both images. The
position of this object is (J2000):
RA = 02:17:52.3
DEC= -50:11:15
with an uncertainty of about 0.5" in each coordinate. At the present we
cannot confirm whether the object has faded."
GCN Circular 3184
Subject
GRB 050406: early Swift XRT analysis results
Date
2005-04-06T21:45:48Z (22 years ago)
From
David Burrows at PSU/Swift <dxb15@psu.edu>
M. Capalbi, M. Perri (ASDC), P. Romano, A. Moretti, C. Pagani, G.
Tagliaferri (INAF-OAB), D. Malesani (SISSA), D. N. Burrows, J. Kennea, D.
Grupe (PSU), K. Page, M. Goad, A. Beardmore (U. Leicester), V. La Parola,
T. Mineo (IASF/Palermo), N. Gehrels (NASA/GSFC), and S. Kobayashi (PSU)
report on behalf of the Swift XRT team:
We have analyzed the Swift XRT data from the first orbit observation
of GRB 050406 (Parsons et al., GCN3180; Cusumano et al., GCN 3186). The
new refined coordinates are:
RA(J2000) = 2h 17m 52.64s
Dec(J2000) = -50:11:18.80
This position is 28 arcseconds from the refined BAT position given in GCN
3183 (Krimm et al. 2005). We estimate an uncertainty of 5 arcseconds
radius (90% containment).
This is 30 arcsec from the refined BAT position (Krimm et al., GCN
3183) and 3.2 arcsec from the preliminary XRT position (GCN 3186).
The [0.2-10] keV light curve in Windowed Timing (WT) and Photon Counting
(PC) mode starts 106 seconds from the BAT trigger (T0). At the beginning,
the count rate is rapidly rising, peaking at about 218 seconds from T0.
Then it decays very fast, possibly flattening at T-T0=300 seconds.
A preliminary spectral fit to the WT data gives a spectral power law photon
index of 2.1 � 0.3 in the [0.5-10] keV band, assuming Galactic absorption
(3.3E20cm^-2). The average (in the time range 100-700 seconds from
trigger) estimated unabsorbed 0.5-10 keV flux is then about 2.8E-11 erg
cm^-2 s^-1.
GCN Circular 3183
Subject
GRB 050406 BAT refined analysis
Date
2005-04-06T19:57:04Z (22 years ago)
From
Hans Krimm at NASA-GSFC <krimm@milkyway.gsfc.nasa.gov>
H. Krimm (GSFC/USRA), L. Barbier, S. Barthelmy (GSFC),
J. Cummings (GSFC/NRC), E. Fenimore (LANL), N. Gehrels (GSFC),
D. Hullinger (UMD), D.Q. Lamb (U. Chicago), C. Markwardt (GSFC/UMD),
D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/NRC),
G. Sato (ISAS), M. Suzuki (Saitama), M. Tashiro (Saitama U.),
J. Tueller (GSFC), on behalf of the Swift/BAT team:
At 15:58:48.40 UT Swift-BAT detected GRB 050406 (trigger=113872)
(GCN Circ 3180, Parsons et al.). The refined BAT ground position is
(RA,Dec) = 34.471 -50.181, [deg; J2000] +- 3 arcmin, (95%
containment). This is 28 arc seconds from the position determined
on-board and originally reported.
Examination of the mask weighted light curve confirms that only the initial
peak is associated with the burst. The other possible emission reported
in GCN Circ 3180 is attributed to background fluctuations.
The shape of the peak is fast-rise, exponential decay in the 15-25 keV
band. In the 25-50 keV band, the peak starts ~2 secs earlier and the
shape is more symmetric. We derive T90 (15-25 keV) = 3 seconds
+/- 1 s, and T90 (15-350 keV) = 5 seconds +/- 1 s. Errors on T90
include systematics.
Analysis of the event data shows that this is a very soft burst with
no significant flux above 50 keV. Plotting GRB 050406 on a color-color
diagram indicates that this burst may have the characteristics of an
X-ray Flash. The fluence derived from the event data is
9.0 X 10^-8 erg/cm^2 in the 15-350 keV band, and
4.8 X 10^-8 erg/cm^2 in the 15-50 keV band. The 1-s peak flux
(T+0.6 s) is 3.2 ph/cm^2/s (15-25 keV). The photon index of the
1-s peak spectrum (T+0 s) is 2.32 +/- 0.53 (90% confidence).
The time-averaged spectrum yields a photon index of 2.38 +/- 0.34
(90% confidence). Both the 1-s and time-averaged spectra are well
fit by a simple power-law.
GCN Circular 3182
Subject
GRB 050406: Early observations with Swift-UVOT
Date
2005-04-06T19:07:04Z (22 years ago)
From
Martin Still at NASA/GSFC Swift SSC <Martin.Still@gsfc.nasa.gov>
W. Landsman (GSFC), S. Hunsberger (PSU), A. Breeveld (MSSL), P. Roming
(PSU), K. Mason, P. Schady (MSSL), M. Ivanushkina (PSU), T. Poole
(MSSL), C. Gronwall (PSU), A. Blustin (MSSL), P. Brown, S. Rosen, K.
McGowan, M. De Pasquale (MSSL), P. Boyd (GSFC/UMBC), S. T. Holland, M.
Still (GSFC/USRA), S. Koch (PSU), M. Carter, H. Huckle (MSSL), P. Broos
(PSU), T. Kennedy, P. Smith, B. Hancock (MSSL), J. Nousek (PSU), N.
Gehrels (GSFC), on behalf of the Swift UVOT team.
The Swift Ultra-Violet/Optical Telescope (UVOT) began settled
observations of the field of GRB 050406 (Parsons et al; GCN 3180) at
16:00:16 UT, 88s after the BAT trigger. The first data taken after
spacecraft settling was a 100s V image with pixel size 0.5x0.5 arcsec
and a field of view of 17x17 arcmin. Mid-exposure time was 138s after
the trigger. A comparison against the Digitized Sky Survey reveals no
new sources in the field down to a 3-sigma background limit of V =
18.8. This limit is based upon preliminary flight calibrations.
GCN Circular 3181
Subject
GRB 050406: Swift XRT Position
Date
2005-04-06T17:32:02Z (22 years ago)
From
Jamie A. Kennea at PSU/Swift-XRT <kennea@astro.psu.edu>
G. Cusumano (IASF/Palermo), J. Kennea, D. N. Burrows, J. E. Hill, D. Grupe, J. A. Nousek (PSU),
J. P. Osborne, K. Page, M. Goad, A. Beardmore, A. F. Abbey, A. A. Wells (U. Leicester), S. Campana, A. Moretti, C. Pagani, P. Romano, G. Tagliaferri, G. Chincarini (OAB), V. Mangano (IASF/Palermo), P. Giommi, M. Capalbi, M. Perri (ASDC), L. Angelini, F. Marshall, N. White, N. Gehrels (NASA/GSFC), P. Roming, P. Meszaros (PSU), P. Schady (MSSL), report on behalf of the Swift XRT team:
The Swift BAT instrument detected a GRB at 15:58:48 UT on 6th April 2005 (GCN Circ 3161). The observatory executed an automated slew to the BAT position and the XRT began taking data at 16:00:15 UT. The XRT was in Auto state but was not able to centroid on the afterglow due to low source brightness. From downlinked data we find a uncataloged, fading X-ray source located at:
RA(J2000) = 2:17:52.4,
Dec(J2000) = -50:11:18.9.
We estimate an uncertainty of about 5 arcseconds.
[GCN_OPS_NOTE(12apr05): Per author's request, "Cusomano" was changed to "Cusumano".]
GCN Circular 3180
Subject
Swift-BAT detection of GRB 050406
Date
2005-04-06T17:04:17Z (22 years ago)
From
Ann M. Parsons at NASA/GSFC/Swift <parsons@milkyway.gsfc.nasa.gov>
A. Parsons (GSFC), S. Barthelmy (GSFC), J. Cummings (GSFC/NRC),
E. Fenimore (LANL), N. Gehrels (GSFC), D. Hullinger (UMD), S.
Hunsberger (PSU),
H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL),
T. Sakamoto (GSFC/NRC), G. Sato (ISAS), M. Suzuki (Saitama),
J. Tueller (GSFC) D. Burrows, J. Kennea, J. Nousek (PSU), G.
Chincarini,
P. Romano (INAF-OAB)
on behalf of the Swift team:
At 15:58:48.40 UT Swift-BAT triggered on burst GRB 050406 (trigger
113872).
The BAT-derived position is RA,Dec= 34.428, -50.178 (J2000).
Significant emission
has been detected for at least 3 sec with possible low significance
peaks over
an additional 30 sec. The peak count rate was 800 cnts/sec. The source
was
detected at 15 degrees off the bore-site and thus is in the fully-coded
field-of-view.
Swift slewed promptly and the UVOT imaged the field at the end of the
slew and did
not find a bright optical source in the 8 arcmin square binned field of
view centered
on the BAT position.
The XRT also imaged the field promptly and did not find a bright X-ray
source within
the field of view. Based on previous experience, this lack of prompt
x-ray afterglow
suggests either that this trigger is not a GRB, or that it is a very
interesting and
unusual GRB. The BAT rate trigger and image are significant enough to
lean
toward an interpretation of an unusual GRB.