- GCN Circular #9021
Masanori Ohno (ISAS/JAXA), Sara Cutini (ASDC), Julie McEnery (NASA/GSFC),
Jim Chiang (SLAC/KIPAC), Elmar Koerding (AIM/Saclay) report on behalf of
the Fermi LAT team, and Alexander van der Horst (NASA/MSFC/ORAU) reports
on behalf of the Fermi GBM team.
"At 00:02:42.63 UT on 23 March 2009, the Fermi Gamma-Ray Burst Monitor
(GBM) triggered and located GRB 090323 (trigger 259459364 / 090323002).
The GBM light curve consists of multiple peaks and has a duration of
~150 seconds.
The Fermi Large Area Telescope (LAT) has significantly, with more than
5 sigma, detected this GRB. Emission was observed in the LAT up to a few
GeV. The high-energy emission commences several seconds after the GBM
trigger time, and we see marginal evidence in the LAT that it continues
for up to a couple of kilo-seconds.
The best LAT on-ground localization is found to be (RA,Dec=190.69, 17.08)
with a 68% (resp. 90%) containment radius of 0.09 deg (resp. 0.14,
statistical), and a systematic error less than 0.1 deg. The GBM on-ground
localization is consistent with this LAT localization within statistical
and systematic uncertainties.
We further report that the Fermi Observatory executed a maneuver following
this trigger and tracked the burst location for the next 5 hours, subject
to Earth-angle constraints.
Further analysis is ongoing.
The points of contact for this burst are Masanori Ohno (LAT,
ohno@astro.isas.jaxa.jp) and Alexander van der Horst (GBM,
Alexander.J.VanDerHorst@nasa.gov).
The Fermi LAT is a pair conversion telescope designed to cover the
energy band from 20 MeV to greater than 300 GeV. It is the product
of an international collaboration between NASA and DOE in the U.S.
and many scientific institutions across France, Italy, Japan and Sweden.
This message can be cited."
- GCN Circular #9023
K. Hurley and J. Goldsten, on behalf of the MESSENGER NS GRB
team,
A. von Kienlin, G. Lichti, and A. Rau, on behalf of the
INTEGRAL SPI-ACS GRB team, and
V. Connaughton, M. Briggs, and C. Meegan, on behalf of the Fermi GBM
team, report:
MESSENGER (GRNS) and INTEGRAL (SPI-ACS) have so far observed
GRB090323 (Ohno et al. GCN 9021). We have triangulated this
burst to a preliminary annulus centered at RA, Dec = 149.980, +11.232,
whose radius is 39.826 +/- 0.286 degrees (3 sigma). This
annulus intersects the GBM localization, and the LAT localization
lies 0.007 degrees from the center line of this annulus. A
map has been posted at ssl.berkeley.edu/ipn3/090323 showing the
GBM contours and best-fit position, the IPN annulus, and the LAT
best-fit position and error circle.
The IPN localization may be improved.
- GCN Circular #9024
J. Kennea (PSU), P. Evans and M. Goad (U Leicester) report on behalf of
the Swift/XRT Team:
At 19:27UT on March 23rd, 2009, Swift began a TOO observation of the
Fermi/LAT error circle of GRB 090323 (GCN #9021). Ground analysis of the
initial data finds an uncatalogued point source inside the LAT error
circle. Currently only one orbit of data has been downlinked so it is not
possible to determine if the source is fading.
Using 1137 s of XRT Photon Counting mode data and 2 UVOT images, 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 =
190.70940, 17.05390 which is equivalent to:
RA (J2000): 12 42 50.26
Dec (J2000): +17 03 14.2
with an uncertainty of 2.7 arcsec (radius, 90% confidence). This position
is 1.9 arcminutes from the LAT on-ground localization given in GCN #9021.
This position may be improved as more data are received. The latest
position can be viewed at http://www.swift.ac.uk/xrt_positions. Position
enhancement is described by Goad et al. (2007, A&A, 476, 1401
http://www.swift.ac.uk/xrt_positions/Goad.pdf), the current algorithm is
an extension of this method.
- GCN Circular #9026
Adria C. Updike (Clemson University), Robert Filgas (Tautenburg Obs.),
Thomas Kruehler, Jochen Greiner (MPE Garching), and Sheila McBreen
(University College Dublin) report on behalf of the GROND team:
We observed the field of GRB 090323 (Fermi trigger 259459364 / 090323002;
Ohno et al., GCN #9021) simultaneously in g'r'i'z'JHK with GROND (Greiner
et al. 2008, PASP 120, 405) mounted at the 2.2 m ESO/MPI telescope at La
Silla Observatory (Chile).
Observations started at 02:50 UT on March 24, 26 hours and 48 minutes time
after the GRB trigger, and are continuing. They were performed at an
average seeing of 1.3" and at an average airmass of 1.8.
We found a single point source within the 2.7" Swift-XRT error circle
reported by Kennea et al. (GCN #9024) at
RA (J2000.0) = 12h 42m 50.29s
DEC (J2000.0) = +17d 03' 11.6"
with an uncertainty of 0.5".
Based on the first 8 min of total exposures in g'r'i'z' J H Ks, we
estimate preliminary magnitudes (all in AB system) of
g' = 21.64 +/- 0.07 mag,
r' = 20.03 +/- 0.03 mag,
i' = 19.64 +/- 0.02 mag,
z' = 19.39 +/- 0.02 mag,
J = 19.24 +/- 0.02 mag,
H = 18.86 +/- 0.02 mag, and
K = 18.58 +/- 0.03 mag
Given magnitudes are calibrated against GROND zeropoints as well
as 2MASS field stars and are not corrected for the expected Galactic
foreground extinction corresponding to a reddening of E_(B-V)= 0.02 mag in
the direction of the burst (Schlegel et al. 1998).
Based on the given magnitudes, we find a photometric redshift of z = 4.0
+/- 0.3.
- GCN Circular #9027
S. B. Cenko and D. A. Perley (UC Berkeley) report on behalf of a larger
collaboration:
We have imaged the field of GRB090323 (Ohno et al., GCN 9021) with the
automated Palomar 60-inch telescope. Observations were taken in the Sloan
r' and i' filters beginning at 2009 Mar 24 04:20 UT (~ 28.30 hr after the
burst). Inside the XRT error circle (Kennea et al., GCN 9024) we find a
single source consistent with the position repored by Updike et al (GCN
9026). At this epoch we measure magnitudes of r' = 20.5, i' = 20.0,
suggesting the source has faded since the observations reported therein
(referenced with respected to several nearby SDSS sources). We therefore
confirm this object is the afterglow of GRB090323.
- GCN Circular #9028
R. Chornock, D. A. Perley, S. B. Cenko, and J. S. Bloom (UC Berkeley) report on
behalf of a larger collaboration:
We performed spectroscopy on the afterglow of GRB 090323 (Ohno et al., GCN 9021;
Updike et al., GCN 9026; Cenko and Perley, GCN 9027) using Gemini-South (GMOS)
starting at 05:58 UT on 2009-03-24, approximately 30 hours after the trigger.
We conducted a series of four exposures of 600 seconds, two using the B600
grating centered at 6000 Angstroms and two with the R400 grating centered at
8000 Angstroms.
The first spectrum shows strong absorption blueward of 5580 Angs, which we
identify as the onset of the Lyman-alpha forest at z=3.6. There are also narrow
absorptions with multiple components from C IV, O I, C II, and Si IV at a
consistent redshift of z=3.57. Further analysis is ongoing.
We would like to thank the Gemini-S staff, in particular Etienne Artigau, Lucas
Fuhrman, and Benoit Neichel, for their support with these observations.
- GCN Circular #9030
S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks, P.
Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf of the Konus-Wind
team, report:
The long GRB 090323 (Fermi-GBM trigger 259459364 / 090323002) localized
by Fermi-LAT (Ohno et al., GCN 9021; the LAT localization was confirmed
by the IPN triangulation: Hurley et al., GCN 9023) triggered Konus-Wind
at T0=174.632 s UT (00:02:54.632).
The burst light curve shows several pulses with a total duration of
~160 s, followed by a weak tail marginally seen up to ~T0+300 s in all
energy bands.
As observed by Konus-Wind the burst
had a fluence of 2.02(-0.25, +0.28)x10^-4 erg/cm2,
and a 256-ms peak flux measured from T0+58.240 s
of 5.96(-1.06, +1.09)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).
The time-integrated spectrum of the burst
(from T0 to T0+145.664 s) can be fitted (in the 20 keV - 10 MeV
range) by GRB (Band) model for which:
the low-energy photon index alpha = -0.96(-0.09, +0.12),
the high energy photon index beta = -2.09(-0.22, +0.16),
the peak energy Ep = 416(-73, +76) keV (chi2 = 104.0/89 dof).
All the quoted errors are at the 90% confidence level.
Assuming z = 3.6 (Chornock et al., GCN 9028)
and a standard cosmology model with H_0 = 70 km/s/Mpc, Omega_M = 0.27,
Omega_\Lambda = 0.73, the isotropic energy release E_iso ~5.6x10^54 erg,
the peak luminosity (L_iso)_max ~ 7.6x10^53 erg/s, and Ep_rest ~1900keV.
The Konus-Wind light curve of this GRB is available
at http://www.ioffe.ru/LEA/GRBs/GRB090323_T00174/
- GCN Circular #9031
M. Perri and G. Stratta (ASDC) report on behalf of the Swift-XRT team:
We have analysed the first 6 ks of Swift-XRT data of the Fermi GRB
090323 (Ohno et al., GCN Circ. 9021). The data, starting at 2009-03-23
19:27:51 UT and ending at 2009-03-24 09:47:02 UT, is all taken in
Photon Counting (PC) mode.
The X-ray source reported by Kennea et al. (GCN Circ. 9024) is found to
be fading and we thus confirm that it was the afterglow of GRB 090323.
In the time interval T+70 ks-T+121 ks the X-ray light-curve can be
modelled by a simple power law with a decay index alpha=2.1 (+0.9)(-0.7).
The X-ray spectrum is well fit by an absorbed power-law model with a
photon index of 2.2 (+/-0.4) and a column density consistent with the
Galactic one in the direction of the source (1.7e20 cm**-2, Kalberla
et al. 2005). The estimated 3-sigma (2-sigma) upper limit on the
intrinsic column density at z=3.6 (Chornock et al., GCN Circ. 9028) is
5.1e22cm**-2 (2.7e22cm**-2). All the quoted errors are at the 90%
confidence level.
Assuming the X-ray emission continues to decline at the same rate, we
predict a 0.3-10 keV XRT count rate of 5e-3 count/s at T+48hr, which
corresponds to an observed 0.3-10 keV flux of ~2e-13 erg/cm**2/s.
This circular is an official product of the Swift-XRT Team.
- GCN Circular #9032
E. A. Hoversten (PSU) reports on behalf of the Swift UVOT team:
The Swift/UVOT began settled observations of the field of
GRB 090323 70 ks after the Fermi LAT trigger (Ohno et al., GCN 9021).
The afterglow is detected in the UVOT white filter at:
RA (J2000) 12:42:50.29
Dec (J2000) 17:03:11.8
with an estimated uncertainty of 0.8 arcsec (radius, 90% confidence).
This position is consistent with the UVOT enhanced XRT position (Kennea
et al., GCN 9024) as well as the optical position determined by
GROND (Updike et al., GCN 9026) The afterglow candidate does not
appear in the DSS images. Photometry from the second set of Swift
observations may be indicative of fading, but is not deep enough to be
conclusive.
UVOT magnitudes and 3-sigma upper limits are reported in the following
table:
Filter T_start T_stop Exp(s) Mag (3-sigma upper limit)
-----------------------------------------------------
WHITE 70287 75931 1196 21.66 +/- 0.28
WHITE 115572 121460 601 > 21.60
V 70667 76062 517 > 19.88
U 69906 75078 1200 > 21.02
The quoted upper limits have not been corrected for the expected
Galactic extinction along the line of sight of E(B-V) = 0.03 mag.
All photometry is on the UVOT photometric system described in Poole et al.
(2008, MNRAS, 383, 627).
- GCN Circular #9033
D. A. Kann, U. Laux and S. Stecklum (TLS Tautenburg) report:
We observed the afterglow (Updike et al., GCN 9026, Cenko et al. GCN 9027)
of the intense Fermi GBM/LAT GRB 090323 (Ohno et al., GCN 9021) with the
1.34m Schmidt telescope of the TLS Tautenburg observatory under inclement
conditions (low transparency, passing clouds). We obtained 8 Rc frames of
600 seconds exposure time each before clouds shut us down. The afterglow
is faintly detected in each single image and clearly detected in the
complete stack.
Assuming the star at RA = 12 42 39.3, Dec. = +17 05 05.7 to have Rc =
17.15 (USNOR1=17.17, USNOR2=17.12), we measure the following afterglow
magnitude:
days after trigger Rc dRc (statistical)
1.87751 20.88 0.04
This value is only slightly fainter than those reported ~18 hours earlier
(Updike et al., GCN 9026, Cenko et al. GCN 9027), which may indicate the
following:
- The afterglow is undergoing a plateau phase or possibly even a
rebrightening (if it faded more inbetween).
- The magnitude of the comparison star is highly incorrect (e.g., variable
star). But we also used several other comparison stars and find agreement
within +/- 0.2 mags.
If the afterglow truly is this bright, this makes it one of the most
luminous afterglows every detected, comparable or even exceeding the
recent GRB 090313 (Perley et al., GCN 8985, de Ugarte Postigo et al.,
8992). The very low foreground extinction, excellent observability, low
influence of moonlight combined with the extreme high energy properties
(possible several ksec long tail emission in LAT, Ohno et al., GCN 9021,
extremely high isotropic energy release, Golenetskii et al., GCN 9030) and
the spectroscopic redshift (Chornock et al., GCN 9028) make this a GRB of
special interest, and more observations, especially with medium-size
telescopes, are encouraged. If weather permits, Tautenburg will continue
observations.
This message may be cited.
- GCN Circular #9034
X.F. Wang, L.P. Xin, W.K. Zheng, Y.L. Qiu, J.Y. Wei,
j. Wang, J.S. Deng and J.Y. Hu on behalf of EAFON report:
We have observed GRB090323 (Ohno et al.GCN 9021;
Updike et al.GCN 9026; Cenko et al. GCN 9027)
with Xinglong TNT telescope from Mar.24,14:51:14(UT),
38.8 hr after the burst. After combined 10*600s R
band images, the optical afterglow was detected about
R=20.55 mag at the mean time of 1.651 days after the
trigger, with the same calibration star
(RA = 12 42 39.3, Dec. = +17 05 05.7, Rc=17.15)
of kann et al., (GCN 9033).
Further observation is suggested,
for the late slowly decay of the optical afterglow.
This message may be cited.
For more information about Xinglong GRBs Follow-up
observations, please visit the website:
http://www.xinglong-naoc.org/grb/
- GCN Circular #9035
A.J. van der Horst (NASA/MSFC/ORAU) reports on behalf of the
Fermi GBM team:
"We have performed spectral analysis of the GBM data for GRB 090323
(GCN 9021). The analysis was restricted to the first ~70 seconds of
GRB emission, because after that time the Fermi Observatory executed
a maneuver following this bright GRB, which caused rapid, significant
changes in the source angles of the various detectors and in the
background behaviour.
The spectrum from T0-2.0 s to T0+71.7 s is best fit by a power-law
function with a high-energy exponential cutoff. The power-law index
is -0.89 +/- 0.03, and the cutoff energy, parameterized as Epeak, is
697 +/- 51 keV (chi squared 379.4 for 359 d.o.f.). At a redshift of
3.57 (GCN 9028), the Epeak in the GRB rest frame, Epeak_rest, is
3.19 +/- 0.23 MeV.
The event fluence (8-1000 keV) in this time interval is
(1.00 +/- 0.01)E-4 erg/cm^2. The 1-sec peak photon flux
measured starting from T0+65.5 s in the 8-1000 keV band
is 12.3 +/- 0.4 ph/s/cm^2.
This time interval consists of two main emission peaks, from T0-2.0 s
to T0+33.8 s and from T0+33.8 s to T0+71.7 s. Both of these shorter
intervals are also best fit by a power-law function with a high-energy
exponential cutoff. For the first interval the power-law index is
-1.00 +/- 0.03, Epeak is 1173 +/- 175 keV, Epeak_rest is 5.36 +/- 0.80
MeV, and the fluence (8-1000 keV) is (3.68 +/- 0.06)E-5. For the second
interval the power-law index is -0.83 +/- 0.03, Epeak is 574 +/- 34 keV,
Epeak_rest is 2.62 +/- 0.16 MeV, and the fluence (8-1000 keV) is
(6.35 +/- 0.09)E-5.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."
- GCN Circular #9036
D. A. Perley, C. R. Klein, A. N. Morgan, and E. Petigura (UC Berkeley)
report:
We observed the afterglow of GRB 090323 (Ohno et al., GCN 9021; Updike
et al., GCN 9026; Cenko et al., GCN 9027) with the Nickel 40in telescope
at Lick Observatory starting at UT 06:45 on 2009-03-25 for a series of
5- and 10- minute exposures totaling 55 minutes of integration time
under photometric conditions. The afterglow is detected in the stacked
frame. Using the same calibration star mentioned in Kann et al. (GCN
9033), we calculate a magnitude of R = 21.3 +/- 0.2 at a mid-time of
t=2.30 days after the trigger. This suggests (within the uncertainty)
that the afterglow has faded significantly since the observations of
Kann et al. and Wang et al. (GCN 9034) ~12 hours prior and that the
optical flattening phase may have ended. Additional observations are
planned.
- GCN Circular #9037
R. Burenin, A. Tkachenko, M. Pavlinsky, R. Sunyaev (IKI),
I. Khamitov, Z. Eker (TUG), U. Kiziloglu (METU), E. Gogus (Sabanci Uni.),
I. Bikmaev, N. Sakhibullin (KSU/AST)
report:
The optical afterglow of GRB 090323 (Updike et al., GCN 9026, Cenko et
al., GCN 9027) was observed with Russian-Turkish 1.5-m telescope
(RTT150, Bakirlitepe, TUBITAK National Observatory, Turkey). We obtained
6x600s exposures in sdss-r filter, centered at March 25, 01:30 UT,
i.e. 2.059 days after the burst.
The afterglow is detected in all frames. Using the same calibration star
as it was used by Kann et al. (GCN 9033), we esimate the magnitude of
the OT as R=20.85+-0.04. During our observations we also marginally
detected gradual decline of the afterglow brightness at a rate of
approximately 0.3 mag/hour, which is steeper than that assumed by the
comparison with the data obtained by Perley et al. (GCN 9036).
Our light curve and finding chart can be found at:
http://hea.iki.rssi.ru/grb/090323/indexeng.html
- GCN Circular #9039
C. Guidorzi (U. Ferrara), I. A. Steele, A. Melandri, D. Bersier
(Liverpool JMU),
A. Gomboc (U. Ljubljana), S. Kobayashi, C.J. Mottram, C.G. Mundell,
R.J. Smith (Liverpool JMU), P. O'Brien, N. Bannister, N. Tanvir (U.
Leicester)
on behalf of a large collaboration report:
The 2-m Faulkes Telescope South (Siding Spring, Australia) began observing
the afterglow (Updike et al., GCN Circ. 9026; Cenko et al., GCN Circ. 9027)
of the Fermi GBM/LAT GRB 090323 (Ohno et al., GCN Circ. 9021; van der Horst
et al., GCN Circ. 9035) on March 25, 11:50:55 UT, i.e. at 2.49 days post
burst.
Observations were carried out in filters R and i. The afterglow is
clearly detected in both filters with the following magnitudes:
Filter Tmid(days) Exposure(s) Mag
-------------------------------------------------
i 2.50 6x300 21.3 +/- 0.2
R 2.53 6x300 21.7 +/- 0.1
-------------------------------------------------
Magnitudes are calibrated with respect to nearby SDSS stars.
Comparing with previous reports (Kann et al., GCN Circ. 9033; Wang et al.,
GCN Circ. 9034; Perley et al., GCN Circ. 9036; Burenin et al., GCN Circ.
9037)
we confirm the steepening of the decay.
- GCN Circular #9041
D. A. Kann, U. Laux and S. Stecklum (TLS Tautenburg) report:
We observed the afterglow (Updike et al., GCN 9026, Cenko et al. GCN 9027)
of the intense Fermi GBM/LAT GRB 090323 (Ohno et al., GCN 9021) with the
1.34m Schmidt telescope of the TLS Tautenburg observatory under decent
conditions (low transparency). We obtained 11 Rc frames of 600 seconds
exposure time each before dawn shut us down. The afterglow is faintly
detected in some single images and well-detected in the
complete stack.
Using the same comparison star as Kann et al. (GCN 9033), we measure the
following afterglow magnitude:
days after trigger Rc dRc (statistical)
5.10418 22.67 0.20
Using other published data (Updike et al., GCN 9026, Wang et al., GCN
9034, Perley et al. GCN 9036, Guidorzi et al., GCN 9039) as well as
additional TLS data from the first observation run, we find that all data
agree decently well with a single power law decay with a slope alpha ~
1.8. Therefore, there does not seem to be a plateau phase, but there is
also no sign of a break yet. The relatively steep decay makes it unclear
if this is a steep pre-break decay slope or a shallow post-break decay
slope. In the latter case, it will be possible to track the afterglow for
a very long time. Further deep, high S/N observations with larger
telescopes are advised.
This message may be cited.
- GCN Circular #9042
D. A. Perley (UC Berkeley) reports:
On the night of 2009-03-27 (UT) I returned to the location of the
afterglow of GRB 090323 (Updike et al., GCN 9026; Cenko et al., GCN
9027) with the Nickel 40-inch telescope at Lick Observatory and acquired
an additional series of 900s R-band exposures between 05:12 and 12:26 UT
totaling 260 minutes of integration time.
While not clearly visible in individual exposures, the afterglow is
detected in stacked frames. Using the calibration star of Kann et al.
(GCN 9033), I measure a magnitude of R = 22.63 +/- 0.18 at an
observation mid-point of t = 4.36 days in a stack of all observations
throughout the night, consistent with the absence of a break in the
light curve reported by Kann et al. (GCN 9041).
I thank Mo Ganeshalingam for the exchange of observing time.
- GCN Circular #9043
F. Harrison (Caltech), B. Cenko (UC Berkeley), D. A. Frail (NRAO),
P. Chandra (RMC), and S. Kulkarni (Caltech) report:
"We observed the field centered at the optical afterglow (GCN
Circ. 9026) of the Fermi GBM/LAT GRB 090323 (GCN Circ. 9021, GCN
Circ. 9035) on March 27.38 UT using the Very Large Array (VLA) at a
frequency of 8.46 GHz. We detect an unresolved radio source at the
GRB afterglow position with the flux density of 225+/-35 uJy at
a (J2000) position of:
RA = 12h 42m 50.292s
DEC = +17d 03' 11.90"
with an uncertainty of 0.05" 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 #9047
A.J. van der Horst (NASA/MSFC/ORAU) reports on behalf of a large
collaboration:
"We observed the position of the GRB 090323 afterglow at 4.9 GHz with the
Westerbork Synthesis Radio Telescope at March 27 17.92 UT to March 28
5.91 UT, i.e. 4.74 - 5.24 days after the burst (GCN 8980).
We detect a radio source with a flux density of 105 +/- 24 microJy
at the position of the optical counterpart (GCN 9021).
We would like to thank the WSRT staff for scheduling and obtaining these
observations."
- GCN Circular #9051
A. de Ugarte Postigo (ESO), D. Xu, D. Malesani, J. Hjorth,
J.P.U. Fynbo (DARK/NBI), P. Jakobsson (Univ. of Iceland),
A. Adamo (Stockholm Univ.) on behalf of a larger collaboration
report:
We have observed the field of GRB 090323 (Ohno et al. GCN 9021)
with the 2.5m NOT telescope (+ALFOSC) at Roque de los Muchachos
Observatory (Spain). The mean epoch of our observations is March
29.323 UT (6.327 days after the burst). The afterglow (Kennea et
al. GCN 9024, Updike et al. GCN 9026) is clearly detected in the
6x300s combined exposure with R=22.80+/-0.06. As photometric
reference we used the object indicated by Kann et al. (GCN 9033).
Our measurement is consistent with the absence of a light curve
steepening, as noted one day earlier by Kann et al. (GCN 9041).
A lightcurve composed of GCN data together with our observation
shows a possible flattening during the last 3 days.
Further observations are foreseen.
- GCN Circular #9063
D. A. Kann, U. Laux, F. Ludwig and S. Stecklum (TLS Tautenburg) report:
We observed the afterglow (Updike et al., GCN 9026, Cenko et al. GCN 9027)
of the intense Fermi GBM/LAT GRB 090323 (Ohno et al., GCN 9021) with the
1.34m Schmidt telescope of the TLS Tautenburg observatory at several
epochs.
At ~6 days after the GRB, conditions were bad (low transparency and
passing clouds). We obtained 21 Rc frames of 600 seconds exposure time
each. Only four of these are usable. The afterglow is faintly detected in
the complete stack.
Using the same comparison star as Kann et al. (GCN 9033), we measure the
following afterglow magnitude:
days after trigger Exposure Rc dRc (statistical)
5.89127 4 x 600 23.13 0.50
At ~7 days after the GRB, conditions were very bad (almost complete
overcast). We obtained 1 Rc frames of 600 seconds exposure time which had
good quality. The afterglow is not detected.
days after trigger Exposure Rc
6.99881 1 x 600 > 22.50
This limit is not constraining.
At ~9 days after the GRB, conditions were very good (good transparency,
good seeing, but influence of moonlight). We obtained 12 Rc frames of 600
seconds exposure time each. The afterglow is faintly detected in the
complete stack.
days after trigger Exposure Rc dRc (statistical)
8.90324 12 x 600 23.64 0.36
Compared to the flattening of the decay noted by de Ugarte Postigo et al.
(GCN 9051) and already hinted at in earlier TLS and Lick data (Kann et
al., GCN 9041, Perley, GCN 9042), the decay has steepened again, an
indication of a (jet?) break. On the other hand, the last TLS detection
agrees well with the extrapolation of the earlier decay (Kann et al., GCN
9041), indicating that the plateau may be a rebrightening/optical flare
spanning a few days.
Due to increasing moonlight, no further TLS observations are planned.
This message may be cited.
- GCN Circular #9324
V. Rumyantsev (CrAO), A. Pozanenko (IKI) report on behalf of larger GRB
follow-up collaboration:
We observed the afterglow (Updike et al., GCN 9026; Cenko et al., GCN 9027)
of Fermi GRB 090323 (GBM trigger 259459364 / 090323002; Ohno et al., GCN
9021) on Apr. 28 and Apr. 29 with Shajn telescope of CrAO. We clearly
detect the afterglow in R and do not detect in I- filter. Astrometry of the
afterglow is RA(J2000): 12 42 50.29 Dec(J2000): +17 03 11.98 with
uncertainty of 0.2 arcsec is compatible with reported in GCN 9026.
A photometry of combined images based on USNO-B1.0 star RA=12:42:39.3
Dec=+17:05:05.7 (previously used by Kann et al. GCN 9033) is following:
T0+ Filter, Exposure, mag., err. Seeing
(d) (s)
5.9934 R 91x60 22.7 +/- 0.1 1.6"
6.8990 I 84x60 >22.4 (3sigma) 2.9"
The combined image of the observation on Apr. 28 can be found at
http://grb.rssi.ru/GRB090323/GRB090323_R_ZTSh_090328.gif
Our photometry in R is compatible with estimations obtained in nearby epochs
(Kann et al. GCN 9041, de Ugarte Postigo et al. GCN 9051) and confirms the
flattening of the light curve mentioned by de Ugarte Postigo et al. (GCN
9051). The non-detection of the afterglow in I-filter in second epoch of
our observation (T0+6.899 d) tentatively supports the steepening of light
curve discussed by Kann et al. (GCN 9063). Indeed the upper limit I > 22.4
is translating into R > 22.8 provided the color index R-I ~ 0.4 obtained
from observations of Updike et al. (GCN 9026) and Guidorzi et al. (GCN
9039) is not changing along late time light curve.
- 1003.3885 from 23 Mar 10
S. McBreen et al.: Optical and near-infrared follow-up observations of four Fermi/LAT GRBs : Redshifts, afterglows, energetics and host galaxies
Fermi can measure the spectral properties of gamma-ray bursts over a very large energy range and is opening a new window on the prompt emission
of these energetic events. Localizations by the instruments on Fermi in combination with follow-up by Swift provide accurate positions for
observations at longer wavelengths leading to the determination of redshifts, the true energy budget, host galaxy properties and facilitate
comparison with pre-Fermi bursts. Multi-wavelength follow-up observations were performed on the afterglows of four bursts with high energy
emission detected by Fermi/LAT : GRB090323, GRB090328, GRB090510 and GRB090902B. They were obtained in the optical/near-infrared bands with
GROND mounted at the MPG/ESO 2.2m telescope and additionally of GRB090323 in the optical with the 2 m telescope in Tautenburg, Germany. Three
of the events are classified as long bursts while GRB090510 is a well localized short GRB with GeV emission. In addition, host galaxies were
detected for three of the four bursts. Spectroscopic follow-up was initiated with the VLT for GRB090328 and GRB090510. The afterglow
observations in 7 bands are presented for all bursts and their host galaxies are investigated. Knowledge of the distance and the local dust
extinction enables comparison of the afterglows of LAT-detected GRBs with the general sample. The spectroscopic redshifts of GRB090328 and
GRB090510 were determined to be z=0.7354+/-0.0003 and z=0.903 +/- 0.001 and dust corrected star-formation rates of 4.8 Mdot yr^-1 and 0.60
M_dot yr^-1 were derived for their host galaxies, respectively. The afterglows of long bursts exhibit power-law decay indices alpha from less
than 1 to ~2.3 and spectral indices (beta) values from 0.65 to ~1.2 which are fairly standard for GRB afterglows. Constraints are placed on the
jet half opening angles of less than 2.1 deg to greater than 6.4 deg which allows limits to be placed on the beaming corrected energies. These
range from less than 5x10^50 erg to the one of the highest values ever recorded, greater than 2.2x10^52 erg for GRB090902B, and are not
consistent with a standard candle. The extremely energetic long Fermi bursts have optical afterglows which lie in the top half of the
brightness distribution of all optical afterglows detected in the Swift era or even in the top 5% if incompleteness is considered. The
properties of the host galaxies of these LAT detected bursts in terms of extinction, star formation rates and masses do not appear to differ
from previous samples.
- 1305.3689 from 17 May 13
Martin Lemoine et al.: On the magnetisation of gamma-ray burst blast waves
The origin of magnetic fields that permeate the blast waves of gamma-ray bursts is a long-standing problem. The present paper argues that in
four GRBs revealing extended emission at >100 MeV, with follow-up in the radio, optical and X-ray domains at later times, this magnetisation
can be described as the partial decay of the microturbulence that is generated in the shock precursor. Assuming that the extended high energy
emission can be interpreted as synchrotron emission of shock accelerated electrons, we model the multi-wavelength light curves of GRB 090902B,
GRB 090323, GRB 090328 and GRB 110731A, using a simplified then a full synchrotron calculation with power law decaying microturbulence
\epsilon_B \propto t^{\alpha_t} (t denotes the time since injection through the shock, in the comoving blast frame). We find that these models
point to a consistent value of the decay exponent -0.5 < \alpha_t < -0.4.
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