Gamma-ray Burst 070721
(All information courtesy of the instrument teams.)
Previous IAU Circulars
Results of Observations
- GCN Circular #6639
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
E. Troja (INAF-IASFPA) report on behalf of the Swift Team:
At 10:01:08 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 070721 (trigger=285653). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 3.176, -28.546 (J2000) with an uncertainty of 3 arcmin
(radius, 90% containment, including systematic uncertainty).
We have very little further information at this time (lightcurve, etc)
because there appears to be a problem with the messages.
The spacecraft slewed promptly and the XRT found a source
RA(J2000) = 3.16355 degrees,
Dec(J2000) = -28.54928 degrees,
which is 40 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 3.25e-10 cgs. At this point
we do not have enough data to be able to tell whether this source is
fading. We note that there is a bright 2MASS object at this position:
2MASS 00123943-2832566 (2.5 arcseconds from the XRT position).
We are waiting for processing of the downlinked Malindi data
for more details.
At this moment no UVOT data are available. We are waiting for the
next Malindi pass to download more data.
We note that while writing this Circular, Swift slewed to the next
trigger following this one. This is unusual and raises the
possibility that this burst is not real. We will not be certain until
the Malindi data can b analyzed.
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.)
- GCN Circular (without number)
TO: GCN Customers
DT: 21 Jul 07
RE: Outage of Swift-to-GCN Operations
This morning (10:01:08 and 10:33:48 UT) there were two Swift-BAT
triggers (285653 and 285654) which at first glance appear
to be real GRBs. However, there was a problem in the connection
between the front-end part of GCN (swift_tdrss_receiver) and
the main GCN program (gcn_main) which prevented the Swift
GCN Notices from being distributed to the regular customer list.
This problem has been elimited. Normally, the parts of the GCN
system that monitor this (and other) connections was not able
to clear the problem and re-establish the connection. This loss
of connection occurs at the 2 or 3 times a year level, and the
automated reconnection monitor works within 4 minutes after
the start of the loss of connection. However, this time it did not
succeed. And to further compound the problem, the automated
notification (to me) of this connection problem did not work.
Hense the outage was allowed to continue without human intervention.
Peliminary investegations show that the connection was in a partial
state. The connection state was sufficient so as to not trip
the connection monitor, but was not fully connected to allow
the passage of data from the front-end program to the main program.
This new scenario will be futher investigated and a solution will
be found to prevent this new type of loss-of-service problem.
This problem affected only the Swift-related Notices. All the other
GCN Notice types were and continue to function normally. Nor did
it affect the Circulars.
I apologize for the loss of these two bursts.
The Swift team is waiting for the downlink of the full data sets
and will have the usual "refined analysis" circulars on these
Again, I apologize. GRBs are a rare commodity,oand to loose two
of them is serious and intolerable loss to the scientific community.
- GCN Circular #6642
T. Sakamoto (GSFC/ORAU), 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), D. Palmer (LANL),
A. Parsons (GSFC), 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-239 to T+352 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 070721A (trigger #285653)
(Ziaeepour, et al., GCN Circ. 6639). The BAT ground-calculated position is
RA, Dec = 3.144, -28.530 deg which is
RA(J2000) = 0h 12m 34.5s
Dec(J2000) = -28d 31' 47"
with an uncertainty of 2.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 72%.
The mask-weighted lightcurve has a single peak starting at ~T-4 sec,
peaking at ~T+1 sec, and ending at ~T+8 sec. T90 (15-350 keV) is
3.4 +- 0.2 sec (estimated error including systematics).
The time-averaged spectrum from T-0.1 to T+3.7 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
2.46 +- 0.41. The fluence in the 15-150 keV band is 7.1 +- 1.8 x 10^-8 erg/cm2.
The 1-sec peak photon flux measured from T+0.12 sec in the 15-150 keV band
is 0.7 +- 0.1 ph/cm2/sec. All the quoted errors are at the 90% confidence
We note that the fluence ratio in a simple power-law fit between the
25-50 keV band and the 50-100 keV band is 1.38. This fluence ratio is larger
than 1.32 which can be achieved in the Band function of alpha=-1.0, beta=-2.5,
and Epeak=30 keV. Thus, preliminary analysis shows that Epeak of the burst
is very likely around or below 30 keV. Therefore the burst can be classified
as an X-ray flash.
- GCN Circular #6644
P.A. Evans (U. Leicester) and H. Ziaeepour (UCL-MSSL) report on behalf of
the Swift/XRT team:
We have analyzed the first 1.3 ks of Swift XRT data for GRB 070721A
(Ziaeepour et al. GCN Circ. 6639), comprising 35 s in Windowed Timing (WT)
mode, and 1.3 ks in Photon Counting (PC) mode. The burst is clearly
detected. Using 799 s of overlapping XRT Photon Counting mode and UVOT
V-band data, we find an astrometrically corrected X-ray position (using
the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1
catalogue): RA, Dec = 3.16348, -28.55017 which is equivalent to:
RA (J2000): 00 12 39.24
Dec (J2000): -28 33 00.6
with an uncertainty of 2.3 arcsec (radius, 90% confidence). This position
is 3.2" from the initial XRT position reported in GCN Circ. 6639, and 95"
from the BAT-refined position reported by Sakamoto et al. (GCN Circ.
The XRT light curve shows a fading behaviour, which is well fitted by a
broken power-law. The initial decay followed a slope of alpha=2.97
(+0.57/-0.42). At T0+281 (+112/-71) s the decay shallows to an alpha of
The Photon Counting mode spectrum is well fitted by an absorbed power-law,
with a column density of 1.61e20 cm^-2 (the Galactic value) and a gamma of
2.24 (+0.33/-0.26). This is consistent with the value derived for the BAT
spectrum (GCN Circ 6642). The observed (unabsorbed) 0.3-10 keV flux is
6.53e-12 (8.23e-12) erg cm^-2 s^-1.
If the source continues to decay at the same rate, we predict a count rate
of 2.7e-3 counts/s at T0+24 hours, which corresponds to an observed
(unabsorbed) flux of 1.87e-13 (2.36e-13) erg cm^-2 s^-1.
This circular is an official product of the Swift/XRT team.
- GCN Circular #6645
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)
On 2007 Jul 21 at 13:47:14 UT the Faulkes Telescope South
observed the field of GRB070721A (trigger=285653, Ziaeepour
et al., GCN 6639).
No new source is detected inside the refined XRT error circle
(Evans et al., GCN 6644) and we can set an upper limit of
R > 20.0 between 3.9 and 4.8 hours after the trigger.
- GCN Circular #6648
P. Schady (MSSL-UCL) and H. Ziaeepour (MSSL-UCL) report on behalf of the
The Swift/UVOT observed the field of GRB 070721A starting 69 s after the
BAT trigger (Ziaeepour et al. GCN Circ.6639). We do not find any source,
in any of the UVOT observations inside the refined XRT error circle (Evans
et al., GCN Circ.6644). However, we note that there is an 18th mag star 4
arcseconds from the XRT refined position.
The 3-sigma upper limits for detecting a source inside the XRT error
Filter T_mid(s) Exp(s) Mag (3-sig upper limit)
White 1088 156 > 21.7
V 1194 453 > 20.9
B 1509 97 > 19.5
U 1359 117 > 20.0
UVW1 1334 117 > 19.6
UVM2 1309 117 > 19.2
UVW2 1530 97 > 19.4
where T_mid is the weighted mid time of the coadded exposure. The values
quoted above are not corrected for the expected Galactic extinction
corresponding to a reddening of E(B-V) = 0.01 mag in the direction of the
burst (Schlegel et al. 1998).
- GCN Report 72.1
GCN_Report 72.1 has been posted:
by H. Ziaeepour
titled: "Swift observations of GRB 070721A"
- GCN Circular #6674
D. Malesani, J.P.U. Fynbo, P.M. Vreeswijk (DARK), I. Ilyn (AIP), report
on behalf of a larger collaboration:
We observed the field of GRB 070721A (Ziaeepour et al., GCN 6639) in two
different epochs, using the NOT and VLT telescopes. Observations were
carried out 0.78 and 1.98 days after the GRB. A bright star (R~17.3) is
close to the XRT position (Evans & Ziaeepour, GCN 6640). Inside the XRT
error circle, we detect a single source at the coordinates (J2000,
RA = 00:12:39.13
Dec = -28:33:00.9
This source does not vary between the two epochs to within 0.2 mag, and
is pointlike under seeing conditions of 0.7". We measure R~22.9 using
VLT instrumental zeropoints (~0.1 mag error). No other sources are seen
inside the XRT error circle down to the limits reported below.
Mean UT T-T0 (d) t_exp (s) Instrument Rlim
Jul 22.20065 0.78320 4x600 NOT+StanCam 24.0
Jul 23.39637 1.97892 2x180 VLT+FORS2 25.5
T0 = trigger time = Jul 21.41745 UT.
This message can be cited.
- GCN Circular #6676
F. E. Marshall (NASA/GSFC), P. Schady (MSSL-UCL) and H. Ziaeepour (MSSL-UCL)
report on behalf of the Swift/UVOT team:
A comparison of the initial Swift/UVOT observations with those taken several days
after the BAT trigger (Ziaeepour et al. GCN Circ. 6639) reveals a weak, fading source
inside the refined XRT error circle (Evans et al. GCN Circ. 6644).
The source is only detected in the initial 100-s exposure with the white
filter starting 88 sec. after the trigger and the initial 400-s exposure with the V
filter starting 194 sec. after the trigger. The 2.4-sigma detection in
white corresponds to 21.4 mag., and the 3.4-sigma detection in V corresponds
to 20.2 mag. The best-fit position is RA, Dec = 3.16343,-28.55020, which is
RA (J2000): 00 12 39.22
Dec (J2000): -28 33 00.7
with an uncertainty of 2.0" (radius, 90% confidence).
The source is slightly blended with 18th mag star noted by
Schady and Ziaeepour (GCN Circ. 6648), which is 4.7" away.
- GCN Report 72.2
GCN_Report 72.2 has been posted:
by H. Ziaeepour
titled: "Final Swift observations of GRB 070721A"
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Jochen Greiner, last update: 04-Aug-2007