GRB 050906
GCN Circular 3926
Subject
GRB 050906: Swift/BAT Detection of a possible burst
Date
2005-09-06T11:10:45Z (20 years ago)
From
Hans Krimm at NASA-GSFC <krimm@milkyway.gsfc.nasa.gov>
H. Krimm (GSFC/USRA), V. La Parola (IASF-CNR), M. de Pasquale (MSSL),
S. Barthelmy (GSFC), A. Blustin (MSSL) , D. Burrows (PSU),
N. Gehrels (GSFC), C. Gronwall (PSU), C. Pagani (PSU), K. Page (U. Leicester)
on behalf of the Swift team:
At 10:32:05 UT, Swift-BAT triggered and located GRB050906 (trigger=153866).
The spacecraft slewed immediately. The BAT on-board calculated location
is RA,Dec 52.803d, -14.625d {+03h 31m 13s, -14d 37' 30"} (J2000), with an
uncertainty of 3 arcmin (radius, 90% containment, stat+sys). This was a
64-msec trigger. The BAT TDRSS light curve shows hints of emission, but it is
not possible to separate source variations from background variations
at this early stage in the analysis. Given that this is at high galactic
latitude, we believe this is a burst rather than a hard x-ray transient.
XRT slewed promptly to the target and observation started at UT 10:33:24
with XRT in auto state, 79 seconds after the GRB trigger. XRT did not reveal
any source with the on board algorithm. The TDRSS light curve suggests the
presence of a weak source. We are waiting for downlinked data to
determine a position.
The Ultraviolet and Optical telescope (UVOT) could not perform any prompt
observation of this event because it was in safe mode.
[GCN OPS NOTE(06sep05): Per author's request: "XRT slewed promptly at the target"
was changed to "XRT slewed promptly to the target", and "prompt obervation" to
"prompt observation".]
GCN Circular 3927
Subject
GRB 050906: Bright galaxy in BAT error box
Date
2005-09-06T11:42:14Z (20 years ago)
From
Andrew Levan at U.of Leicester <anl@star.le.ac.uk>
Andrew Levan, Nial Tanvir (University of Hertfordshire)
The BAT error box for the possible GRB 050906 (Swift trigger #=153866,
Krimm et al. GCN 3926) contains the bright (K~11), low redshift galaxy IC
328 (part of a small group) at z=0.03 (130 Mpc). Such galaxies are rare in
GRB error boxes. If GRB 050906 is a long duration GRB the presence of the
galaxy could be indicative of a GRB 980425/SN1998bw -like event. If the
burst is short then the distance to IC 328 is somewhat larger than the
distance at which the giant flare from SGR 1806-20 could have been
observed. Either possibility would be of considerable interest, so
although the reality of the burst has yet to be confirmed, afterglow
searches are to be encouraged.
GCN Circular 3931
Subject
GRB050906: P60 Observations
Date
2005-09-06T18:43:23Z (20 years ago)
From
Derek Fox at PSU <dfox@astro.psu.edu>
Derek B. Fox (Penn State), S. Bradley Cenko (Caltech) and Brian
P. Schmidt (RSAA, ANU) report on behalf of a larger collaboration:
"The Robotic Palomar 60-Inch Telescope (P60) responded automatically
to the Swift localization of the possible GRB050906 (Trigger #153866;
Krimm et al., GCN 3926) and began imaging 114s after the burst. No
new sources are apparent in the individual images by comparison to the
second-generation DSS. At the mean epochs of our coadded R-band and
i-band images, we can set the following limits on the magnitude of any
new point source within the Swift/BAT localization region:
Time (UT) Delta Limit (mag)
===================================
10:39:55 +7m50s R > 19.7
10:41:41 +9m36s I > 19.8
11:04:32 +32m27s R > 20.4
11:07:49 +35m44s I > 20.5
===================================
Photometric zero-points are derived from the USNO-B1.0 catalog R-band
and I-band magnitudes for this field for our R- and i-filter images,
respectively.
Moreover, we note that there is no new point source apparent near
or superposed on the bright galaxy inside the BAT error circle
(Levan & Tanvir, GCN 3927) by comparison to the DSS."
GCN Circular 3933
Subject
GRB 050906: Radio Observations
Date
2005-09-06T19:12:44Z (20 years ago)
From
Dale A. Frail at NRAO <dfrail@nrao.edu>
P. B. Cameron (Caltech) and D. A. Frail (NRAO) report on behalf of a
larger collaboration:
"We have undertaken two short (~20 min) VLA observations at a
frequency of 8.46 GHz toward the BAT error circle of GRB 050906 (GCN
3926) on Sept. 6.52 UT and Sept. 6.58. There is a single radio source
displaced about 1 arcmin north of IC328 at a position (J2000):
RA = 03:31:11.75
DEC=-14:37:18.1
The astrometry error at this point is +/-0.5 arcsec. The source did
not vary significantly between the two epochs separated by ~1.4hrs.
Further observations are planned to determine.
Further observations are planned.
The National Radio Astronomy Observatory is a facility of the National
Science Foundation operated under cooperative agreement by Associated
Universities, Inc."
GCN Circular 3934
Subject
GRB 050906: Swift XRT upper limit
Date
2005-09-06T19:59:02Z (20 years ago)
From
David Burrows at PSU/Swift <dxb15@psu.edu>
C. Pagani (PSU/INAF-OAB), V. La Parola(INAF-IASF), D. N. Burrows (PSU)
report on behalf of the Swift XRT team:
The Swift XRT has observed the field of GRB050906 for 6.0 ks. There are 2
faint serendipitous sources in 5.2 ks of data taken in photon-counting
mode. Source #1 is marginally detected (at a flux of roughly 8e-14 erg
cm-2 s-1), while Source #2 is brighter.
The nearest X-ray source to the BAT position is source #1, which is 3.9
arcmin from the on-board BAT position (Krimm et al. 2005, GCN 3926) and 6.3
arcmin from the refined BAT position (Krimm et al., private
communication). No X-ray sources are found in the BAT error circle down to
a 90% confidence upper limit of ~8e-14 erg cm-2 s-1.
No X-ray emission is detected from the position of the galaxy IC328
reported by Levan et al. 2005 (GCN 3927). The nearest X-ray source to the
galaxy position is also Source #1, which is 4.6 arcmin away.
No X-ray emission is detected from the position of the radio source
reported by Cameron and Frail 2005 (GCN 3933). Source #1 is also closest
to the reported radio source, at a distance of 3.7 arcmin.
No further observations are planned with the XRT.
This message can be cited.
GCN Circular 3935
Subject
GRB 050906: Swift-BAT refined analysis
Date
2005-09-06T21:44:01Z (20 years ago)
From
Hans Krimm at NASA-GSFC <krimm@milkyway.gsfc.nasa.gov>
A. Parsons (GSFC), C. Sarazin (U. Virginia), L. Barbier (GSFC),
S. Barthelmy (GSFC), J. Cummings (GSFC/NRC), D. Hullinger (GSFC/UMD),
E. Fenimore (LANL), N. Gehrels (GSFC), H. Krimm (GSFC/USRA),
C. Markwardt (GSFC/UMD), F. Marshall (GSFC), D. Palmer (LANL),
T. Sakamoto (GSFC/NRC), G. Sato (ISAS), T. Takahashi (ISAS),
J. Tueller (GSFC) on behalf of the Swift-BAT team:
Using the data set from T-60 to T+120 sec from the recent telemetry
downlink, we report further analysis of Swift-BAT GRB 050906
(trigger #153866) (Krimm, et al., GCN 3926). The refined BAT ground position
is (RA,Dec) = 52.841,-14.652 {+03h 31m 22s, -14d 39' 00"} [deg; J2000]
+- 2.6 arcmin, (90% containment). This is 2.7 arcmin from the position
reported in Krimm et al. 2005, GCN 3926. The partial coding was 77%.
The mask weighted light curve shows a small excess mostly in the
25-100 keV energy range. This a short burst of duration T90 (15-350 keV)
128 +- 16 milliseconds. (estimated error including systematics).
The power law index of the time-averaged spectrum fit over T+0 to T+0.128 sec
is 1.91 +- 0.42. The fluence in the 15-150 keV band is (5.9 +/-
3.2) x 10^-8 erg/cm2.
The 1-s peak photon flux measured from T0 in the 15-150 keV
band is (0.22 +/- 0.11) ph/cm2/s. All the quoted errors are at the 90%
confidence level.
The BAT error circle includes the relatively bright, nearby galaxy
IC 328 (Levan & Tanvir GCN 3927). The 2MASS K magnitude of this galaxy
is K20 = 11.51. The density of galaxies this bright on the sky is
about 1 per square deg (Kochanek, C. S., et al. 2001, ApJ, 560, 566).
Thus, the probability of finding a galaxy this bright in the BAT 3 arcmin
error circle is about 0.008. The redshift of IC 328 is 0.0308
(da Costa, L. N., et al. 1998, AJ, 116, 1), giving a luminosity distance
of dL = 133 Mpc for the WMAP cosmology. At this distance, the galaxy
luminosity is ~10^11 Lsun(K), which is slightly greater than L*.
The number density of galaxies at least this luminous is ~0.0006/Mpc^3.
Thus, the probability of finding a galaxy at least this luminous at a
redshift as small as that of IC 328 within 3 arcmin of the BAT position
is about 0.001.
IC 328 appears to be a spiral galaxy, and is quite blue (U-B = -0.6;
Coziol, R. et al., 1994, AJ, 108, 405). With these colors, it is
likely to have active star formation. Thus, this host is quite different
than the hosts of the two short-hard bursts GRB 050509b and GRB 050724,
which appear to have occurred in or near red elliptical galaxies.
It is possible that this GRB was caused by an SGR superflare in IC 328
(Levan & Tanvir GCN 3927, Palmer, D.M., et al. 2005, Nature, 434, 1107;
Hurley, K. et al. 2005, Nature, 434, 1098), although an underluminous
collapsar or NS-NS merger can not be ruled out.
GCN Circular 3936
Subject
GRB 050906: MARGE Optical Limits
Date
2005-09-06T23:42:46Z (20 years ago)
From
Heather Swan at U.of Michigan/ROTSE <hflewell@umich.edu>
Heather F. Swan (U Mich), and Ian Smith (Rice), report on behalf of
the MARGE collaboration:
The AEOS Burst Camera (ABC), attached to the AEOS telescope, located at
the Maui Space Surveillance System on Haleakala, responded to GRB 050906
(Swift trigger 153866), producing images between 10:47 and 10:59 UT,
starting 15 minutes after Swift-BAT triggered and located this burst.
These are 1s and 10s optical images were taken with a low resolution
grating. With the revised BAT coordinates (GCN 3935), the ABC FoV
covers roughly 1/2 of the BAT error box, including IC 328. Comparison of the 10
second images (which start at 10:55 UT) to the DSS (second epoch) reveals
no new sources to a limiting magnitude of 19. Further analysis of these
images is in progress.
[GCN OPS NOTE(06sep05): Per author's request, the author-line was added; and
the FROM_line was changed from Flewelling to Swan.]
GCN Circular 3940
Subject
GRB 050906: Optical observations at the Very Large Telescope
Date
2005-09-08T00:06:42Z (20 years ago)
From
Pall Jakobsson at Niels Bohr Inst <pallja@astro.ku.dk>
Pall Jakobsson, Jens Hjorth, Johan P. U. Fynbo, Brian L. Jensen,
Darach Watson, Jose Maria Castro Ceron, Kristian Pedersen,
Jesper Sollerman (DARK, NBI), Nial Tanvir, Andrew Levan
(University of Hertfordshire) and Javier Gorosabel (IAA-CSIC)
report:
Using FORS2 on the 8.2-m Antu Telescope at ESO/Paranal we have
obtained deep VRI-band imaging of the BAT error circle of
GRB 050906 (GCN 3935) on Sep 7.4. No new sources are apparent in
the combined images by comparison to the DSS. At the position of
the radio source (GCN 3933) we detect a faint red object. Using
photometric zeropoints from the ESO webpages we estimate the
following magnitude for this source: V = 26.2, R = 24.5, I = 23.0.
An R-band image of the field around the radio source (located
outside the BAT error circle) is shown at:
http://www.astro.ku.dk/~pallja/grb050906.jpg
GCN Circular 3955
Subject
GRB 050906: RTT150 optical observations
Date
2005-09-09T10:14:37Z (20 years ago)
From
Rodion Burenin at IKI, Moscow <rodion@hea.iki.rssi.ru>
R. Zhuchkov, I. Bikmaev, N. Sakhibullin (KSU/AST),
I. Khamitov, Z. Aslan (TUG), U. Kiziloglu (METU), E. Gogus (Sabanci U.),
R. Burenin, M. Pavlinsky, R. Sunyaev (IKI)
report:
We observed the error box of GRB 050906 (Parsons et al., GCN 3935) with
Russian-Turkish 1.5-m telescope (RTT150, Bakirlitepe, TUBITAK National
Observatory, Turkey). We made 6x300s exposures in R and similar set of
exposures in I between 00:07--01:16 UT on Sep. 07, and also a set of 300s
exposures in R band between 00:46-01:35 UT on Sep 08.
Comparing our two epochs we found no new or fading source brighter than
R~22.9. The limiting magnitude in I is 20.5.
We specially checked that between our two epochs there were no new or
variable sources superimposed on the bright nearby galaxy IC 328 (Levan
& Tanvir GCN 3927).
This message may be cited.
GCN Circular 3956
Subject
GRB 050906: Possible X-ray Counterpart
Date
2005-09-09T18:16:53Z (20 years ago)
From
Derek Fox at PSU <dfox@astro.psu.edu>
D. B. Fox (PSU), C. Pagani (PSU/INAF-OAB), L. Angelini (GSFC),
D. N. Burrows (PSU), J. P. Osborne (U. Leicester), and V. La Parola
(INAF-IASF) report:
"We have analyzed the Swift/XRT observations of the BAT localization
region for the short-hard burst GRB 050906 (Parsons et al., GCN 3935).
During the first orbit only, there is evidence for an excess of counts
near the position:
RA 03:31:15.6, Dec -14:36:37 (J2000)
where we have corrected the XRT coordinates by roughly 6-arcsec from
the native astrometry using a bright star / X-ray source in the field.
Within a 20-pixel (47-arcsec) radius of this position, 6 photons are
detected where 0.9 photons are expected from the background,
representing a detection at 99.7%-confidence when considered over the
full XRT field of view. If due to an astrophysical source, the
source's estimated count rate is 7.5 +/- 5.2 cts/ksec (90%-confidence)
over the 798 seconds of observation, and the source positional
uncertainty is 18 arcsec (90%-confidence radius). Subsequent XRT
observations reveal no further excess count detections within this
region. The source location is not coincident with either the VLA
source (Cameron & Frail, GCN 3933) or the bright galaxy (Levan &
Tanvir, GCN 3927; Parsons et al., GCN 3935) that have been identified
in observations of this burst.
We note that: (1) The location of the excess is 13 arcsec outside the
2.6-arcmin radius (90%-confidence) BAT localization region (Parsons et
al., GCN 3935); (2) The temporal distribution of the counts during the
first orbit is consistent with the temporal distribution of the
detector background counts (88%-confidence via two-sided K-S test);
(3) The spatial distribution of the counts appears flat rather than
PSF-like (unquantified); and (4) The source region lies within a
region of increased local background, towards the end of the first
orbit, due to emission from the bright Earth limb (two counts arrive
during the last 100 seconds; however, the event grades are distinct
from those associated with the bright Earth limb). Given these
caveats, we are not confident that the counts excess represents the
detection of an astrophysical source. However, if it is due to a real
source, it is the most likely X-ray counterpart to GRB 050906."
GCN Circular 4060
Subject
GRB 050906, summary of radio observations
Date
2005-10-05T19:17:44Z (20 years ago)
From
Dale A. Frail at NRAO <dfrail@nrao.edu>
P. B. Cameron (Caltech) and D. A. Frail (NRAO) report on behalf of a
larger collaboration:
"Following our preliminary radio observations (GCN#3933), we have
undertaken four further observations of the field of GRB050906 with
the VLA at frequency of 8.46 GHz. In time order, they were centered on
the possible X-ray counterpart position (GCN#3956), the previously
reported radio source (GCN#3933), and two epochs of the refined BAT
error circle (GCN#3935). The observations were taken on September
10.35, 11.50, 11.52 and October 3.41 (all dates UT).
We find no radio sources within the XRT error circle with a limiting 2
sigma flux density of 61 uJy. The previously identified radio source,
(GCN#3933), which now lies outside of the refined BAT error circle,
has shown no significant variability and is likely a background
extragalactic source.
Within the refined BAT error circle (GCN#3935) there are no
significantly variable radio sources. The typical rms noise of each
observation is 40-50 uJy.
The National Radio Astronomy Observatory is a facility of the National
Science Foundation operated under cooperative agreement by Associated
Universities, Inc."