GRB 050915B
GCN Circular 3987
Subject
GRB050915B: Swift-BAT detection of a long bright burst
Date
2005-09-15T22:06:17Z (20 years ago)
From
Jay R. Cummings at NASA/GSFC/Swift <jayc@milkyway.gsfc.nasa.gov>
A. Falcone (PSU), A. Beardmore (U. Leicester), D. Burrows (PSU),
J. Cummings (GSFC/NRC), D. Fox (PSU), N. Gehrels (GSFC),
S. T. Holland (GSFC/UMBC), J. Kennea (PSU), H. Krimm (GSFC/USRA),
C. Pagani (PSU), D. Palmer (LANL), A. Parsons (GSFC), E. Rol (U. Leicester),
P. Roming (PSU), P. Shady (MSSL),
on behalf of the Swift team:
At 21:23:04 UT, Swift-BAT triggered and located GRB050915B (trigger=155284).
The spacecraft slewed immediately. The BAT on-board calculated location
is RA,Dec 219.096d,-67.405d {14h 36m 23s, -67d 24' 16"} (J2000), with an
uncertainty of 3 arcmin (radius, 90% containment, stat+sys). The BAT light
curve showed two broad bright peaks from T-10 to T+40 sec. The peak count
rate was ~2800 counts/sec (15-350 keV), at T-2 sec.
XRT began observing at 21:25:20 UT, 136 seconds after the BAT trigger.
XRT was not able to centroid on any point source, but the downlinked
lightcurve shows that a bright, fading X-ray source was present in the
XRT field of view.
The UVOT began observing at 21:25:18 UT, 134 seconds after the BAT trigger.
No new source, with respect to the DSS, is detected in the initial 100 sec
V-band image. The 5-sigma limiting magnitude, in a circular aperture of
radius 6.0 arcseconds is V_lim = 17.7 mag. This magnitude is based on the
preliminary V-band zero-point, measured in orbit and will require refinement
with further calibration. It has not been corrected for extinction. The
estimated Galactic extinction in this direction is A_V = 1.29. The UVOT
image covers 25% of the 3 arcminute BAT error circle. The field is crowded.
We are currently in the portion of the orbits where the spacecraft does
not pass over the Malindi downlink station. Therefore, it will be ~3
hours before we have access to the full data set for the refined analyses.
GCN Circular 3988
Subject
GRB 050915b, SMARTS optical/IR observations
Date
2005-09-16T01:07:56Z (20 years ago)
From
Bethany Cobb at Yale U <cobb@astro.yale.edu>
B. E. Cobb and C. D. Bailyn (Yale), part of the larger SMARTS
consortium, report:
Using the ANDICAM instrument on the 1.3m telescope at CTIO, we
obtained optical/IR imaging of the error region of GRB 050915b
(GCN 3987, Falcone et al.), starting 2.0 hours after the burst at
2005-09-15 23:23 UT. Our optical images, in V and I, have a field of view
of 6'x6' and, therefore, cover the entire GRB error circle.
Our IR images, in J and K, have a smaller field of view, covering a region
totaling ~6 square arcminutes in the middle of the quoted error region.
Visual comparison of the optical images to the SDSS
and the IR images to 2MASS frames does not reveal any new sources.
Preliminary image differencing, using the ISIS image subtraction
program, also does not reveal any significant variable source within the
GRB error region.
Analysis of this data is ongoing.
GCN Circular 3989
Subject
GRB 050915B: XRT position
Date
2005-09-16T03:34:02Z (20 years ago)
From
Abe Falcone at PSU/Swift <afalcone@astro.psu.edu>
A. D. Falcone, D. N. Burrows, J. A. Kennea (PSU),
W. Voges (MPE), F. Marshall (GSFC)
report on behalf of the Swift XRT team:
The Swift XRT began observing the long bright burst GRB 050915B (Falcone
et al., GCN 3987) at 21:25:20 UT, but was unable to obtain an on-board
centroid. Analysis of the initial ground-processed data finds a bright,
fading, and uncataloged source at coordinates:
RA(J2000) = 14:36:26.5
Dec(J2000) = -67:24:36.5
We estimate an uncertainty of 8 arcseconds (90% containment). This
position lies 56 arcseconds from the BAT position reported in GCN 3987.
GCN Circular 3992
Subject
GRB 050915B: Swift/UVOT Upper Limits
Date
2005-09-16T20:19:47Z (20 years ago)
From
Stephen Holland at USRA/NASA/GSFC/SSC <sholland@milkyway.gsfc.nasa.gov>
GRB 050915B: Swift/UVOT Upper Limits
S. T. Holland (GSFC/USRA), A. Falcone (PSU), M. Carter (UCL/MSSL),
P. Smith (UCL/MSSL), and N. Gehrels (GSFC) report on behalf of the
Swift/UVOT team:
The Swift/UVOT began observing the field of GRB 050915B 121
seconds after the BAT trigger (Falcone et al. GCN 3987). No new source
is detected at the position of the XRT error circle (Falcone et
al. GCN 3989) in the initial 100 second V-band image down to a 5-sigma
upper limit of 17.5, or in summed exposures with any of the filters
down to the following 5-sigma magnitude upper limits:
Filter T_range (s) Exp (s) 5sig UL
V 133 - 25,406 1824 19.2
B 279 - 35,461 2983 20.4
U 265 - 31,288 2381 20.2
UVW1 251 - 30,503 2972 21.0
UVM2 237 - 29,595 3006 20.7
UVW2 294 - 35,995 2609 20.8
The magnitudes are uncorrected for extinction.
GCN Circular 3993
Subject
GRB 050915B: Swift-BAT refined analysis
Date
2005-09-16T21:14:11Z (20 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
J. Cummings (GSFC/NRC), M. Ajello (MPE), L. Barbier (GSFC),
S. Barthelmy (GSFC), E. Fenimore (LANL), R. Fink (GSFC),
N. Gehrels (GSFC), D. Hullinger (UMD), H. Krimm (GSFC/USRA),
C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC),
T. Sakamoto (GSFC/NRC), G. Sato (ISAS), J. Tueller (GSFC),
on behalf of the Swift-BAT team:
Using the full data set from T-90 to T+300 sec from the recent
telemetry downlinks, we report further analysis of Swift-BAT
GRB 050915B (trigger #155284) (Falcone, et al., GCN 3987). The
refined BAT ground position is (RA,Dec) = 219.112, -67.412 degrees
{14h 36m 26.8, -67d 24' 43"} (J2000) +-0.7 arcmin, (radius, sys+stat,
90% containment). This is within 8 arcseconds of the XRT counterpart
(Falcone et al. GCN 3989). The partial coding was 53% including
projection effects.
The mask-weighted light curve shows a rise from T-10 seconds to a
peak at T-4, dropping off to a lumpy plateau spanning T+0 to T+25,
then steadily declining to zero at T+50. No further instances of
emission are apparent on a 1 second timescale out to T+1200 sec.
T90 (15-350 keV) is (40 +- 1) sec (estimated error including systematics).
The time-averaged spectrum is well-fit by a power law with photon
index 1.89 +- 0.06. The fluence in the 15-150 keV band is
(3.4 +- 0.1) x 10^-6 erg/cm2. The 1-sec peak photon flux measured
from T-3.1 sec in the 15-150 keV band is (2.3 +- 0.2) ph/cm2/sec.
All quoted errors are at the 90% confidence level.
--
GCN Circular 3994
Subject
GRB 050915b, SMARTS optical/IR observations of the XRT position
Date
2005-09-16T23:09:33Z (20 years ago)
From
Bethany Cobb at Yale U <cobb@astro.yale.edu>
B. E. Cobb and C. D. Bailyn (Yale), part of the larger SMARTS
consortium, report:
Our ANDICAM observations reported in GCN 3988 were re-examined
following the detection of the X-ray afterglow of GRB 050915b (GCN 3989,
Falcone et al.). The position of the X-ray afterglow was captured in both
our optical and IR images.
Three sources are detected within the X-ray afterglow error region:
RA DEC
A) 14:36:26.04 -67:24:41.4
B) 14:36:26.35 -67:24:32.2
C) 14:36:27.30 -67:24:39.3
The first source (A) has a stellar profile and has previously been clearly
detected in both the SDSS and 2MASS surveys. The other two sources (B and C)
appear only slightly above the detection limits of our ANDICAM images.
Sources B and C are also weakly detected in the SDSS (and possibly in 2MASS).
These two sources, particularly source B, might be extended, though this is
uncertain due to the low significance of their detection.
The brightness of these sources does not vary significantly over our
period of observation.
Total summed exposure times amounted to 30 minutes in I and V and
24 minutes in J and K, with a mid-exposure time of 2005-09-15 00:01 UT
(~2.6 hours post-burst). The preliminary limiting magnitudes of our
images are as follows:
V < 21.4 +/- 0.1
I < 21.3 +/- 0.1
J < 18.3 +/- 0.2
K < 17.8 +/- 0.2
GCN Circular 5821
Subject
GRB 050915B: optical afterglow
Date
2006-11-13T22:50:34Z (19 years ago)
From
Daniele Malesani at Niels Bohr Inst,Dark Cosmology Center <malesani@astro.ku.dk>
D. Malesani (SISSA/ISAS & NBI-DARK), S. Covino (INAF/OABr), S.
Piranomonte (INAF/OAR), L.A. Antonelli (INAF/OAR), G. Chincarini (Univ.
Milano-Bicocca & INAF-OABr), P. D'Avanzo (INAF/OABr), L. Stella
(INAF/OAR), and G. Tagliaferri (INAF/OABr), report on behalf of the
MISTICI collaboration:
We observed the field of one-year-old GRB 050915B (Falcone et al., GCNs
3987, 389) with the ESO-VLT UT2 equipped with FORS1. Observations
started on 2005 Sep 16.01065 UT (2.87 hr after the GRB) and consisted in
a series of 24 R-band images lasting 1 minute each. The field was
observed again, in the R band, with the ESO-NTT equipped with the SuSI2
imager, with mean time 2005 Oct 1.0261 UT (15.13 days after the GRB).
The field is very crowded and reddened due to the low Galactic latitude
(b = -6.6 deg).
Inside the XRT error circle (Moretti et al. 2006, A&A, 448, L9) there
are three sources, but only two are consistent with the
boresight-corrected position (Butler 2006, astro-ph/0611031 + priv.
comm.), which has a 90% error radius of 1.4". One of them is clearly
fading between the VLT and NTT exposures, being undetectable in the NTT
images. Its coordinates (J2000) are:
alpha = 14:36:26.17
delta = -67:24:32.5
It is remarkable, however, that no fading is seen for this source over
the course of the VLT observation (2.87-3.66 hr after the GRB).
PSF-matched profile photometry revealed that the source was constant
(<R> = 21.68 +- 0.03) to within ~0.1 mag, with no trend for decline. In
the SuSI2 image (15 days after the burst), it has R > 23.4 (3-sigma
upper limit).
The other object consistent with the X-ray position has coordinates
alpha = 14:36:26.39
delta = -67:24:31.6
and is constant between the FORS1 and SuSI2 exposures at R = 21.2. This
source, which is just 1.5" away from the afterglow, might be consistent
with source "B" reported by Cobb & Bailyn. (GCN 3994).
This message can be cited.