GRB 070721B
GCN Circular 6713
Subject
GRB 070721B: correct afterglow position
Date
2007-08-06T14:34:46Z (19 years ago)
From
Daniele Malesani at Niels Bohr Inst,Dark Cosmology Center <malesani@astro.ku.dk>
D. Malesani (DARK) reports:
I have looked again at the NOT and VLT images of GRB 070721B (Ziaeepour
et al., GCN 6640), and realized there has been some confusion in what
reported in our GCNs 6651 and 6655.
The correct afterglow position is (J2000):
RA = 02:12:32.97
Dec = -02:11:40.4
with an estimated error of 0.5". This position is within 0.4" of and
consistent with the UVOT afterglow position as reported by Schady (GCN
6641). In the finding chart (Malesani et al., GCN 6651) posted at
http://www.astro.ku.dk/~malesani/GRB/070721B/
the afterglow corresponds to object #1, and not #2 as written in GCN
6655 (Fynbo et al.). Object #2 (RA = 02:12:33.03, Dec = -02:11:40.6) is
a closeby, real object, likely unrelated to the GRB. The redshift
z=3.626 reported in GCN 6651 correctly refers to the afterglow.
I apologize for any confusion this may have created.
GCN Circular 6705
Subject
VLA non-detection of GRB 070721B
Date
2007-08-04T02:25:07Z (19 years ago)
From
Poonam Chandra at U Virginia/NRAO <pc8s@virginia.edu>
Poonam Chandra (NRAO/UVA) and Dale A. Frail (NRAO) report on
behalf of the Caltech-NRAO-Carnegie GRB Collaboration:
"We used the Very Large Array to observe the field of view toward
GRB 070721B (GCN 6640) at a frequency of 8.46 GHz on 2007 Aug 3rd
at 10.42 UT. The radio afterglow of the GRB is undetected either at
Swift-XRT position (GCN 6646) or at ESO-VLT position (GCN 6651).
The map rms is 29 uJy.
The National Radio Astronomy Observatory is a facility of the National
Science Foundation operated under cooperative agreement by Associated
Universities, Inc."
GCN Circular 6655
Subject
GRB 070721B: further observations and analysis
Date
2007-07-24T15:00:42Z (19 years ago)
From
Daniele Malesani at Niels Bohr Inst,Dark Cosmology Center <malesani@astro.ku.dk>
J.P.U. Fynbo (DARK), P. Jakobsson (Univ. Hertfordshire), D. Malesani, J.
Hjorth (DARK), I. Ilyn (AIP), report:
We have obtained further observations of GRB 070721B (Ziaeepour et al.,
GCN Report 73). We also performed further analysis on our images of the
optical afterglow of GRB 070721B (Malesani et al., GCN 6651).
Our first observation was carried out with the Nordic Optical Telescope
(mean time July 22.173 UT, i.e. 17.6 hr after the trigger). Close to the
UVOT position, we detect a single source at the following coordinates
(J2000, against USNO-B1):
RA = 02:12:33.00
Dec = -02:11:41.4
This position is consistent with source #2 reported by Malesani et al.
(GCN 6651).
We have also obtained further imaging with the ESO-VLT on July 23.409 UT
(47.3 hr after the trigger). We find that source #2 has faded compared
to the two previous epochs. We hence confirm that object #2 is the
optical afterglow of GRB 070721B. Object #1, reported by Malesani et al.
(GCN 6651), is most likely a spurious source caused by a reflection from
the bright star 0877-0042643 in the field (R~6.5).
In our 2-dimensional spectrum we also note the presence of bright
high-redshift galaxy with a redshift z=3.62, very close to the redshift
of GRB 070721B (Malesani et al., GCN 6651). This object is 21" away of
the afterglow, which corresponds to ~150 kpc at z=3.62.
We acknowledge the ESO staff for excellent support.
GCN Circular 6651
Subject
GRB 070721B: optical observations and proposed redshift
Date
2007-07-22T19:37:46Z (19 years ago)
From
Daniele Malesani at Niels Bohr Inst,Dark Cosmology Center <malesani@astro.ku.dk>
D. Malesani (DARK), P. Jakobsson (Univ. Hertfordshire), J.P.U. Fynbo, J.
Hjorth and P.M. Vreeswijk (DARK) report:
We observed the optical counterpart of GRB 070721B (Ziaeepour et al.,
GCN 6640; Schady, GCN 6641) with the ESO-VLT equipped with FORS2.
Close to the UVOT position (Schady, GCN 6641), we detect two objects:
1: RA = 02:12:32.97, Dec = -02:11:41.0
2: RA = 02:12:33.03, Dec = -02:11:41.6
We note that object #1 is consistent with the UVOT position, while #2 is
1.6" away. We estimate R~23.8 and R~24.3 on Jul 22.319 UT (21.6 hr after
the GRB) for objects #1 and #2, respectively.
We acquired spectra for both objects. Thanks to the detection of a DLA
and several metallic lines, we infer for object #2 a redshift z=3.626.
The spectrum is typical of a GRB afterglow, and we thus suggest that
object #2 is the optical counterpart of GRB 070721B. This redshift is
also consistent with the nondetection of the object in filters bluer
than V (De Pasquale & Ziaeepour, GCN 6650). Further observations are
planned to test the variability of both objects.
A finding chart and a plot of the 2D spectrum is available at:
http://www.astro.ku.dk/~malesani/GRB/070721B
We acknowledge excellent support from the ESO staff, in particular
Angela Cortes, Dominique Naef and Yuri Beletsky. We thank Massimiliano
De Pasquale for useful discussion.
GCN Circular 6650
Subject
Swift/UVOT observations of GRB070721B optical afterglow.
Date
2007-07-21T21:37:28Z (19 years ago)
From
Massimiliano de Pasquale at MSSL-UCL <mdp@mssl.ucl.ac.uk>
M. De Pasquale and H. Ziaeepour (MSSL/UCL) report on the
behalf of the Swift/UVOT:
The optical afterglow of GRB070721B (Ziaeepour et al. GCN 6640, Schady
et al. 6641) is detected by Swift/UVOT in White filter and V filter
finding chart exposures, taken 100s-200s and 207-607s after the BAT
trigger. It is not detected at 3sigma level in other exposures, either
single or summed ones in all filters, till ~7000s after the trigger.
In the following table, we report the magnitudes of the afterglow for
the exposures where the source is detected with at least 3sigma level,
and 3sigma upper limits otherwise.
Filter Time(s) Exp(s) Magnitude
White 100-200 99 16.82 +/- 0.1
White 701-711 10 >18.8
White 855-955 99 >19.9
White 5089-6716 393 >20.9
V 207-453 399 16.7 +/- 0.1
V 621-641 19 >17.5
V 961-1116 154 >18.3
V 5500-5699 199 >18.7
B 687-850 19 >18.4
B 4884-6519 393 >20.4
U 662-835 39 >18.5
U 4679-6314 393 >20.1
UW1 638-658 39 >18.8
UW1 638-6109 432 >20.2
UM2 613-786 39 >18.9
UM2 613-5904 432 >20.6
UW2 780-800 19 >18.8
UW2 780-6902 385 >20.3
These values are not corrected for the Galactic
reddening towards the bursts E(B-V)=0.02 mag (Schlegel,
Finkbeiner & Davic, 1998)
GCN Circular 6649
Subject
GRB 070721B, Further Swift-BAT refined analysis
Date
2007-07-21T20:44:28Z (19 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
S. D. Barthelmy (GSFC), J. Cummings (GSFC/UMBC), C. Markwardt (GSFC/UMD),
D. Palmer (LANL), T. Sakamoto (GSFC/ORAU), H. Ziaeepour (UCL-MSSL)
(on behalf of the Swift-BAT team):
Using the data set from T-239 to T+903 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 070721B (trigger #285654)
(Ziaeepour, et al., GCN Circ. 6640; and Palmer, et al., GCN Circ. 6643).
Beyond the previously reported description of the mask-weighted lightcurve
(Palmer, 6643), the burst had a second episode of emission with multiple peaks
from T+230 sec to T+380. We note that there are still gaps in the downlinked
lightcurve data (1: T+530 to T+670, and 2: T+720 to T+830 sec) and as such,
we can not say anything about burst emission in these two intervals.
T90 (15-350 keV) is 340 +- 10 sec (estimated error including systematics).
The time-averaged spectrum from T-6.7 to T+359.9 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.34 +- 0.11. The fluence in the 15-150 keV band is 3.6 +- 0.2 x 10^-06 erg/cm2.
The 1-sec peak photon flux measured from T-0.19 sec in the 15-150 keV band
is 1.5 +- 0.3 ph/cm2/sec. All the quoted errors are at the 90% confidence
level.
GCN Circular 6647
Subject
GRB 070721B : Faulkes Telescope South observations
Date
2007-07-21T18:43:02Z (19 years ago)
From
Andrea Melandri at Liverpool John Moores U <axm@astro.livjm.ac.uk>
A. Melandri, (Liverpool JMU), C. Guidorzi (Uni-Bicocca/INAF-OAB),
I.A. Steele, C.G. Mundell, D. Carter, R.J. Smith, C.J. Mottram,
D.F. Bersier, S. Kobayashi, M.J. Burgdorf, M.F. Bode (Liverpool JMU),
A. Gomboc (Ljubljana), P. O'Brien, E. Rol, N. Bannister (Leicester)
report
We observed the field of GRB 070721B (trigger=285654, Ziaeepour
et al., GCN 6640) with the Faulkes Telescope South on 2007 Jul 21
starting at 16:01:21 UT (~5.45 hours after the trigger).
We do not detect any new source inside the refined XRT error circle
(Beardmore et al., GCN 6646) and we do not detect the UVOT candidate
reported by Schady et al. (GCN 6641) in our optical images.
We can set an upper limit for this burst of R>19.3 and I>17.8
@ 6.4 and 6.2 hours after the trigger, respectively.
GCN Circular 6646
Subject
GRB 070721B: Swift-XRT refined analysis
Date
2007-07-21T18:32:41Z (19 years ago)
From
Andy Beardmore at U Leicester <apb@star.le.ac.uk>
A.P. Beardmore, K.L. Page, P.A. Evans (U. Leicester) and H. Ziaeepour
(MSSL-UCL) report on behalf of the Swift-XRT team :
We have analysed the first three orbits of Swift-XRT data on GRB 070721B
(Ziaeepour et al., GCN 6640). Using 5.78ks of Photon Counting mode data,
we find a refined XRT position of RA, Dec = 33.13710, -2.19462 which is
RA(J2000): 02:12:32.90
Dec(J2000): -02:11:40.6
with an uncertainty of 3.5 arcseconds (90% containment radius). This
is 35 arcseconds from the refined BAT position reported by Palmer et
al. (GCN 6643), 8.9 arcsec from the original XRT position reported in
Ziaeepour et al. (GCN 6640), and 0.7 arcseconds from the UVOT position
reported by Schady (GCN 6641).
The X-ray light curve shows an initial steep decay from T+100s to
T+144s, followed by a number of flares from T+255s to T+800s
which reached a maximum count rate of 50 count/s at T+315s. The
underlying decay is a powerlaw with a slope of approximately -0.9,
though it is difficult to be precise with the data available so far.
The X-ray spectrum from the Windowed Timing mode data obtained during
the non-flare intervals from the 1st orbit (T+144s to T+220s and
T+400s to T+475s) can be fit with an absorbed powerlaw to give a photon
index of 1.48 +0.18-0.16 and a column density of 1.9 (+1.8-1.9) e20 cm^-2,
consistent with the Galactic value of 2.3e20 cm^-2 in this direction
(Kalberla et al. 2005). The observed 0.3-10 keV flux is 2.37+/-0.25 e-10
ergs cm^-2 s^-1, which corresponds to an unabsorbed flux of
2.45+/-0.25 e-10 ergs cm^-2 s^-1.
If the underlying decay continues at the same rate, we predict an XRT
count rate of 0.025 count/s at T+24hr, which corresponds to an observed
0.3-10keV flux of 1.4e-12 ergs cm^-2 s^-1.
This circular is an official product of the Swift-XRT team.
GCN Circular 6643
Subject
GRB 070721B, Swift-BAT refined analysis
Date
2007-07-21T14:22:17Z (19 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
D. Palmer (LANL), L. Barbier (GSFC), S. D. Barthelmy (GSFC),
J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC),
H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), A. Parsons (GSFC),
T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU),
J. Tueller (GSFC), T. Ukwatta (GWU), H. Ziaeepour (UCL-MSSL)
(i.e. the Swift-BAT team):
Using the data set from T-119 to T+183 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 070721B (trigger #285654)
(Ziaeepout, et al., GCN Circ. 6640). The BAT ground-calculated position is
RA, Dec = 33.128, -2.198 deg which is
RA(J2000) = 2h 12m 30.8s
Dec(J2000) = -2d 11' 54"
with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 23%.
The mask-weighted light curve shows a large main peak starting at ~T-20 sec,
peaking at ~T+0 sec, and ending at ~T+70 sec. We caution that currently
we only have downlinked data out to T+183 sec, and that there is a hint
of activity past T+70 sec. But we wanted to get this circular out without
waiting for further downlinks due to the uncertainites given the GCN Notices
problems earlier. T90 (15-350 keV) is 31.5 +- TTT sec (estimated error
including systematics).
The time-averaged spectrum from T-6.7 to T+33.7 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.31 +- 0.11. The fluence in the 15-150 keV band is 2.1 +- 0.1 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T-0.14 sec in the 15-150 keV band
is 1.5 +- 0.3 ph/cm2/sec. All the quoted errors are at the 90% confidence
level.
GCN Circular 6641
Subject
GRB070721B: A bright UVOT candidate
Date
2007-07-21T12:05:59Z (19 years ago)
From
Patricia Schady at MSSL/Swift <ps@mssl.ucl.ac.uk>
P. Schady (MSSL-UCL) reports on behalf of the Swift team
The Swift/UVOT observed the field of GRB 070721B and took a finding chart
exposure of 100 seconds with the White (160-650 nm) filter starting ~50
seconds after the BAT trigger. A candidate afterglow was found on-board in
the rapidly available 2.7'x2.7' sub-image, consistent with the XRT
position (Ziaeepour et al., GCN 6640) at
RA(J2000) = 02:12:32.95 = 33.1373 degrees
DEC(J2000) = -02:11:40.6 = -2.1946 degrees
with a 1-sigma error radius of about 0.9 arc sec. This position is 9.7
arcsec. from the center of the BAT error circle. The estimated magnitude
is 15.9 with a 1-sigma error of about 0.5 mag. No correction has been made
for the estimated Galactic reddenning of E(B-V)=0.02 mag (Schlegel,
Finkbeiner & Davic, 1998)
GCN Circular 6640
Subject
GRB 070721B: Swift detection of a burst
Date
2007-07-21T11:16:00Z (19 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
H. Ziaeepour (UCL-MSSL), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), D. N. Burrows (PSU),
P. A. Evans (U Leicester), K. L. Page (U Leicester) and
P. Schady (MSSL-UCL) report on behalf of the Swift Team:
At 10:33:48 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 070721B (trigger=285654). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 33.131, -2.184 (J2000) with an uncertainty of 3 arcmin
(radius, 90% containment, including systematic uncertainty).
Like the previous trigger, there continues be a problem with the messages,
so we are not able to say anything about the lightcurve at this time.
The XRT found a bright, uncatalogued source at
RA(J2000) = 33.13506
DEC(J2000) = -2.19602
which is 45.7 arcseconds from the BAT position. We do not have
an error estimate, but the typical uncertainty for on-board centroids
is 6 arcseconds. The source flux was about 1.296e-09 cgs. While we don't
have the usual GCN notices for this trigger, the realtime
telemetry from the spacecraft indicates that the source is fading.
At the moment no UVOT data are available. We are waiting for the next
Malindi pass to download more data.
Burst Advocate for this burst is H. Ziaeepour (hz AT mssl.ucl.ac.uk).
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.)