- GCN NOTICE
TITLE: GCN/FERMI NOTICE
NOTICE_DATE: Sat 26 Sep 09 04:20:41 UT
NOTICE_TYPE: Fermi-GBM Flight Position
RECORD_NUM: 38
TRIGGER_NUM: 275631628
GRB_RA: 1.283d {+00h 05m 08s} (J2000),
1.405d {+00h 05m 37s} (current),
0.653d {+00h 02m 37s} (1950)
GRB_DEC: -66.117d {-66d 06' 59"} (J2000),
-66.062d {-66d 03' 44"} (current),
-66.395d {-66d 23' 41"} (1950)
GRB_ERROR: 6.17 [deg radius, statistical plus systematic]
GRB_INTEN: 291 [cnts/sec]
DATA_SIGNIF: 17.40 [sigma]
INTEG_TIME: 2.048 [sec]
GRB_DATE: 15100 TJD; 269 DOY; 09/09/26
GRB_TIME: 15626.99 SOD {04:20:26.99} UT
GRB_PHI: 259.00 [deg]
GRB_THETA: 45.00 [deg]
DATA_TIME_SCALE: 2.0480 [sec]
HARD_RATIO: 0.56
LOC_ALGORITHM: 3 (version number of)
MOST_LIKELY: 95% GRB
2nd_MOST_LIKELY: 4% Generic Transient
DETECTORS: 0,0,0, 1,0,0, 0,1,0, 0,0,0, 0,0,
SUN_POSTN: 182.95d {+12h 11m 49s} -1.28d {-01d 16' 43"}
SUN_DIST: 112.65 [deg] Sun_angle= -11.9 [hr] (East of Sun)
MOON_POSTN: 273.52d {+18h 14m 05s} -25.56d {-25d 33' 20"}
MOON_DIST: 65.93 [deg]
MOON_ILLUM: 50 [%]
GAL_COORDS: 310.25,-50.35 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS: 318.72,-57.41 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS: Fermi-GBM Flight-calculated Coordinates.
COMMENTS: This trigger occurred at longitude,latitude = 329.87,6.75 [deg].
- GCN NOTICE
TITLE: GCN/FERMI NOTICE
NOTICE_DATE: Sat 26 Sep 09 04:21:03 UT
NOTICE_TYPE: Fermi-GBM Ground Position
RECORD_NUM: 48
TRIGGER_NUM: 275631628
GRB_RA: 336.550d {+22h 26m 12s} (J2000),
336.716d {+22h 26m 52s} (current),
335.690d {+22h 22m 46s} (1950)
GRB_DEC: -62.730d {-62d 43' 47"} (J2000),
-62.680d {-62d 40' 48"} (current),
-62.985d {-62d 59' 03"} (1950)
GRB_ERROR: 1.00 [deg radius, statistical only]
DATA_SIGNIF: 340.20 [sigma]
DATA_INTERVAL: 2.048 [sec]
GRB_DATE: 15100 TJD; 269 DOY; 09/09/26
GRB_TIME: 15626.99 SOD {04:20:26.99} UT
GRB_PHI: 256.00 [deg]
GRB_THETA: 56.00 [deg]
E_RANGE: 44.032 - 279.965 [keV]
LOC_ALGORITHM: 413 (Gnd S/W Version number)
SUN_POSTN: 182.95d {+12h 11m 49s} -1.28d {-01d 16' 43"}
SUN_DIST: 113.06 [deg] Sun_angle= -10.3 [hr] (East of Sun)
MOON_POSTN: 273.52d {+18h 14m 05s} -25.56d {-25d 33' 19"}
MOON_DIST: 55.25 [deg]
MOON_ILLUM: 50 [%]
GAL_COORDS: 326.47,-47.21 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS: 308.90,-47.99 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS: Fermi-GBM Ground-calculated Coordinates.
COMMENTS: This Notice was ground-generated -- not flight-generated.
- GCN NOTICE
TITLE: GCN/FERMI NOTICE
NOTICE_DATE: Sat 26 Sep 09 04:20:57 UT
NOTICE_TYPE: Fermi-GBM Flight Position
RECORD_NUM: 49
TRIGGER_NUM: 275631628
GRB_RA: 350.000d {+23h 20m 00s} (J2000),
350.143d {+23h 20m 34s} (current),
349.259d {+23h 17m 02s} (1950)
GRB_DEC: -63.267d {-63d 15' 59"} (J2000),
-63.213d {-63d 12' 47"} (current),
-63.540d {-63d 32' 25"} (1950)
GRB_ERROR: 3.47 [deg radius, statistical plus systematic]
GRB_INTEN: 4438 [cnts/sec]
DATA_SIGNIF: 410.40 [sigma]
INTEG_TIME: 4.096 [sec]
GRB_DATE: 15100 TJD; 269 DOY; 09/09/26
GRB_TIME: 15626.99 SOD {04:20:26.99} UT
GRB_PHI: 255.00 [deg]
GRB_THETA: 50.00 [deg]
DATA_TIME_SCALE: 4.0960 [sec]
HARD_RATIO: 0.53
LOC_ALGORITHM: 3 (version number of)
MOST_LIKELY: 95% GRB
2nd_MOST_LIKELY: 4% Generic Transient
DETECTORS: 0,0,0, 1,0,0, 0,1,0, 0,0,0, 0,0,
SUN_POSTN: 182.95d {+12h 11m 49s} -1.28d {-01d 16' 43"}
SUN_DIST: 114.80 [deg] Sun_angle= -11.1 [hr] (East of Sun)
MOON_POSTN: 273.52d {+18h 14m 05s} -25.56d {-25d 33' 19"}
MOON_DIST: 61.37 [deg]
MOON_ILLUM: 50 [%]
GAL_COORDS: 319.02,-50.91 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS: 316.06,-52.03 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS: Fermi-GBM Flight-calculated Coordinates.
COMMENTS: This trigger occurred at longitude,latitude = 329.87,6.75 [deg].
- GCN NOTICE
TITLE: GCN/FERMI NOTICE
NOTICE_DATE: Sat 26 Sep 09 04:21:06 UT
NOTICE_TYPE: Fermi-GBM Ground Position
RECORD_NUM: 51
TRIGGER_NUM: 275631628
GRB_RA: 345.020d {+23h 00m 05s} (J2000),
345.174d {+23h 00m 42s} (current),
344.223d {+22h 56m 54s} (1950)
GRB_DEC: -64.540d {-64d 32' 23"} (J2000),
-64.488d {-64d 29' 14"} (current),
-64.808d {-64d 48' 29"} (1950)
GRB_ERROR: 1.00 [deg radius, statistical only]
DATA_SIGNIF: 426.80 [sigma]
DATA_INTERVAL: 4.096 [sec]
GRB_DATE: 15100 TJD; 269 DOY; 09/09/26
GRB_TIME: 15626.99 SOD {04:20:26.99} UT
GRB_PHI: 257.00 [deg]
GRB_THETA: 52.00 [deg]
E_RANGE: 44.032 - 279.965 [keV]
LOC_ALGORITHM: 413 (Gnd S/W Version number)
SUN_POSTN: 182.95d {+12h 11m 49s} -1.28d {-01d 16' 44"}
SUN_DIST: 112.95 [deg] Sun_angle= -10.8 [hr] (East of Sun)
MOON_POSTN: 273.52d {+18h 14m 05s} -25.56d {-25d 33' 19"}
MOON_DIST: 59.23 [deg]
MOON_ILLUM: 50 [%]
GAL_COORDS: 320.60,-48.59 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS: 312.01,-51.65 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS: Fermi-GBM Ground-calculated Coordinates.
COMMENTS: This Notice was ground-generated -- not flight-generated.
- GCN Circular #9933
Elisabetta Bissaldi (MPE) reports on behalf of the Fermi GBM Team:
"At 04:20:26.99 UT on 26 September 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090926 (trigger 275631628 / 090926181).
The on-ground calculated location, using the GBM trigger
data, is RA = 354.5, DEC = -64.2 (J2000 degrees,
equivalent to 23h 38m, -64d 12'), with an uncertainty
of 1.0 degree (radius, 1-sigma containment,
statistical only; there is additionally a systematic
error which is currently estimated to be 2 to 3 degrees).
The angle from the Fermi LAT boresight is 48 degrees.
Moreover, this burst was bright enough to result in
a Fermi spacecraft repointing maneuver.
The burst was also independently detected by INTEGRAL SPI-ACS.
The GBM light curve consists of single pulse
with a duration (T90) of 20 +/- 2 s (8-1000 keV).
The time-averaged spectrum from T0 to T0+21 s is
best fit by a Band function with Epeak = 314 (+/- 4) keV,
alpha = -0.75 (+/-0.01) and beta = -2.59 (+0.04/-0.05)
(C-stat 1136 for 478 d.o.f.).
The event fluence (8-1000 keV) in this time interval is
(1.45 +/- 0.04)E-04 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+3 s in the 8-1000 keV band
is 80.8 +/- 0.4 ph/s/cm^2.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."
- GCN Circular #9934
Takeshi Uehara, Hiromitsu Takahashi (Hiroshima University) and
Julie McEnery (NASA/GSFC) report on behalf of the Fermi LAT team:
At 04:20:26.99 (UT) on 26 Sep 2009, the Fermi Large Area Telescope
(LAT) detected gamma rays from the long GRB 090926, which was
triggered and located by the Fermi Gamma-ray Burst Monitor (GBM)
(trigger 275631628 / 090926181, GCN9933). The angle of the GBM best
position (RA, Dec= 354.5, -64.2) with respect to the LAT boresight was
~52 degrees at the time of the trigger, which is close the edge of our
field of view.
The data from the Fermi LAT shows a significant increase in the event
rate within 2.5 degrees of the GBM location 7 s after the GBM trigger
that is spatially and temporally correlated with the GBM emission with
high significance. More than 150 photons above 100 MeV and more
than 20 photons above 1 GeV are observed up to more than 200 s after
the GBM trigger. The highest energy photon is a 19.6 GeV event which is
observed 26 seconds after the GBM trigger.
The best LAT on-ground localization is found to be (RA, Dec = 353.56,
-66.34) with a 90% containment radius of 0.07 deg (statistical; 68%
containment radius: 0.04 deg, preliminary systematic
error is less than 0.1 deg) which is consistent with the GBM localization.
A Swift TOO request has been issued.
Further analysis is ongoing.
The points of contact for this burst is
Takeshi Uehara : uehara@hep01.hepl.hiroshima-u.ac.jp
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 #9936
L. Vetere (PSU), P.A. Evans and M.R. Goad (U. Leicester) report
on behalf of the Swift-XRT team:
Using 3190 s of XRT Photon Counting mode data and 4 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 =353.40070, -66.32390 which is equivalent to:
RA (J2000): 23 33 36.18
Dec (J2000): -66 19 25.9
with an uncertainty of 1.5 arcsec (radius, 90% confidence).
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) and Evans
et al. (2009, MNRAS, 397, 1177).
This circular is an official product of the Swift-XRT team.
- GCN Circular #9937
J. Haislip, D. Reichart, K. Ivarsen, A. LaCluyze, A. Foster, J. Moore, A.
Oza, M. Schubel, J. Styblova, A. Trotter, J. A. Crain, and M. Nysewander
report:
Skynet observed the Fermi/LAT localization of GRB 090926A (Uehara et al.,
GCN 9934) with four of the 16" PROMPT telescopes at CTIO beginning 19.0
hours after the trigger in UBVRI.
We detect an optical source within the Swift/XRT localization (Vetre et
al., GCN 9936) that is not in the DSS (POSS-II Red), at
RA = 23:33:36.02
DEC = -66:19:26.5
Stacking only images that increase the limiting magnitude yields:
mean
time
since cal.
trig. tel. exp. fil. magnitude stars
(h) (# x s)
19.9 PROMPT-2 22 x 80 V 18.81 +0.10 -0.09 52 NOMAD
20.0 PROMPT-5 22 x 80 I 18.24 +0.04 -0.04 165 USNO B1
20.0 PROMPT-4 24 x 80 R 18.06 +0.03 -0.03 230 USNO B1
- GCN Circular #9938
C. Gronwall (PSU) and L. Vetere (PSU) report on behalf of the
Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 090926A
approximately 13 hours after the Fermi/GBM trigger (Bissaldi,
GCN Circ. 9933). In a 357 sec observation in the white filter, we
find a candidate optical afterglow within the XRT error circle (Vetere
et al., GCN Circ. 9936) at
RA(J2000) = 23:33:36.037 = 353.400154
Dec(J2000) = -66:19:26.64 = 66.324067
with a 90%-confidence error radius of about 0.11 arc sec. This position
is 0.99 arc sec. from the center of the XRT error circle and is
consistent
with the optical afterglow position found by Skynet/PROMPT (Haislip et
al., GCN Circ. 9937). The estimated magnitude is 18.78 +/- 0.04.
This value is not corrected for the Galactic extinction due to the
reddening of E(B-V) = 0.03 in the direction of the burst
(Schlegel et al. 1998).
- GCN Circular #9942
D. Malesani (DARK/NBI), P. Goldoni (APC/Univ. Paris 7 and SAp/CEA), J.
P. U. Fynbo (DARK/NBI), V. D'Elia (ASDC and INAF/OAR), S. Covino
(INAF/OABr), H. Flores (Paris Obs.), A.J. Levan (Univ. Warwick), S. D.
Vergani (APC/Univ. Paris 7), K. Wiersema (Univ. Leicester), report on
behalf of the X-shooter GRB collaboration:
We observed the afterglow of GRB 090926A (Bissaldi, GCN 9933; Uehara et
al., GCN 9934; Vetere et al., GCN 9936; Haislip et al., GCN 9937) with
the X-shooter spectrograph mounted on the ESO-VLT UT2. Observations were
taken as part of the instrument Science Verification phase. X-shooter is
a broad-band single-object spectrograph covering the wavelength range
from the UV to the infrared (3300-22000 AA).
At the beginning of the observation (22.0 hr after the GRB), the
afterglow had R = 17.9 as measured from the acquisition image. Four
spectra lasting 1800 s each were secured.
The spectrum has high signal to noise and shows a wealth of absorption
features, together with a broad depression around 3780 AA, which we
interpret as a DLA. We identify CIV 1548 and 1550, Si II 1304 and 1526,
SiII* 1533, FeII 1608, MgII 2798 and 2803, and several others, from
which we measure a redshift z=2.1062. We caution that the wavelength
solution is based on archival calibration data.
We thank the ESO observing staff, in particular Joel Vernet, Thomas
Bensby, and Stephane Brillant.
- GCN Circular #9948
S. R. Oates (MSSL-UCL) and L. Vetere (PSU) report on behalf
of the Swift/UVOT team:
The Swift/UVOT began observerving the field of Fermi GRB 090926A
47ks after the Fermi GBM and LAT trigger (Bissaldi., GCN Circ. 9933;
Uehara ., GCN Circ. 9934). We detect a fading optical afterglow in
white,
v and u filters at the position reported by UVOT (Gronwall et al.,
GCN Circ. 9938) and Skynet/PROMPT (Haislip et al., GCN Circ 9937).
The lightcurve appears to rebrighten from 70ks to the end of
current observations.
Preliminary magnitudes are reported below.
Filter T_start(s) T_stop(s) Exposure Mag Err
-------------------------------------------------------
white 46977 47341 358 18.71 +/- 0.04
white 69902 70369 459 19.32 +/- 0.05
v 47348 47712 358 18.45 +/- 0.16
u 46608 46972 358 18.21 +/- 0.07
u 69429 69896 459 18.85 +/- 0.09
u 86050 86613 554 18.52 +/- 0.07
-------------------------------------------------------
The above magnitudes are not corrected for the Galactic extinction
corresponding to a reddening of E_{B-V} = 0.02 mag (Schlegel et al.,
1998, ApJS, 500, 525). The photometry is on the UVOT flight system
described in Poole et al. (2008, MNRAS, 383,627).
- GCN Circular #9951
K. Noda, E. Sonoda, N. Ohmori, K. Kono, H. Hayashi,
A. Daikyuji, Y. Nishioka, M. Yamauchi (Univ. of Miyazaki),
Y. Hanabata, T. Uehara, T. Takahashi, Y. Fukazawa (Hiroshima U.),
M. Ohno, M. Suzuki, M. Kokubun, T. Takahashi (ISAS/JAXA),
W. Iwakiri, M. Tashiro, Y. Terada, A. Endo, K. Onda,
T. Sugasahara (Saitama U.), Y. Urata (NCU),
T. Enoto, K. Nakazawa, K. Makishima (Univ. of Tokyo),
K. Yamaoka, S. Sugita (Aoyama Gakuin U.), Y. E. Nakagawa,
T. Tamagawa (RIKEN), S. Hong (Nihon U.), N. Vasquez (Tokyo Tech.),
on behalf of the Suzaku WAM team, report:
The very bright, Fermi-LAT detected GRB 090926A (Fermi-GBM trigger
#275631628/ 090926181; Bissaldi, GCN 9933; Uehara et al., GCN 9934)
triggered the Suzaku Wide-band All-sky Monitor (WAM)
which covers an energy range of 50 keV - 5 MeV at 04:20:27.168 UT (=T0).
The observed light curve shows a multi-peaked structure, lasting from
T0-0.5 s to T0+16.5 s, followed by a weak tail seen up to ~T0+34.5s.
The total duration (T90) was about 13 s and the fluence in
100 - 1000 keV was 9.71(-0.40, +0.22)x 10-5 erg/cm2.
The 1-s peak flux measured from T0+3.5 s was 30.6(-2.3, +1.6) photons/cm2/s
in the same energy range.
Preliminary result shows that the time-averaged spectrum from
T0-0.5 s to T0+34.5 s is well fitted by a GRB Band model as follows.
the low-energy photon index alpha: -1.09 (-0.27, +0.37),
the high-energy photon index beta: -2.63 (-0.17, +0.11),
and the peak energy Epeak: 434 (-30, +32) keV (chi2/d.o.f = 29.7/23).
All the quoted errors are at statistical 90% confidence level,
in which the systematic uncertainties are not included.
The light curves for this burst is now available at:
http://www.astro.isas.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/trig/grb_table.html
- GCN Circular #9953
J. Haislip, D. Reichart, K. Ivarsen, A. LaCluyze, A. Foster, J. Moore, A.
Oza, M. Schubel, J. Styblova, A. Trotter, J. A. Crain, and M. Nysewander
report:
Skynet continued to observe the afterglow (Haislip et al., GCN 9937) of GRB
090926A (Bissaldi, GCN 9933) with four of the 16" PROMPT telescopes at CTIO
throughout the night in BVRI.
We find that the light curve brightens from the beginning of our
observations (about 19 hours after the trigger) to about 1 day after the
trigger in all bands, which is consistent with the findings of Oates &
Vetere (GCN 9948) in UVOT's u band.
Around 1 day, the light curve peaks at R = 17.8 mag (calibrated to 82 USNO
B1 stars) and begins to fade. A second, smaller rebrightening begins
around 26 hours and peaks at R = 18.0 mag around 27 hours.
- GCN Circular #9959
S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks,
P. Oleynik, M. Ulanov, and D. Svinkin on behalf of
the Konus-Wind and Konus-RF teams, and
T. Cline on behalf of the Konus-Wind team, report:
The long bright GRB 090926A (Fermi-GBM trigger 275631628 / 090926181:
Bissaldi, GCN 9933) localized by Fermi-LAT (Uehara et al., GCN 9934)
triggered Konus-Wind at T0=15628.683 s UT (04:20:28.683).
It was also detected by Konus-RF instrument onboard CORONAS-PHOTON s/c
in the waiting mode while being at high latitudes.
The burst light curve shows a multipeaked structure with a total
duration of ~16 s, followed by a weak tail seen up to ~T0+50 s.
As observed by Konus-Wind the burst
had a fluence of 1.80(-0.07, +0.08)x10^-4 erg/cm2,
and a 16-ms peak flux measured from T0+8.944 s
of 2.91(-0.54, +0.56)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).
The time-integrated spectrum of the burst
(from T0 to T0+26.880 s) can be fitted (in the 20 keV - 10 MeV
range) by GRB (Band) model for which:
the low-energy photon index alpha = -0.76 +/- 0.03,
the high energy photon index beta = -2.59(-0.13, +0.10),
the peak energy Ep = 321 +/- 12 keV (chi2 = 106.0/84 dof).
The emission is clearly seen up to ~10 MeV.
All the quoted errors are at the 90% confidence level.
Assuming z = 2.1062 (Malesani et al., GCN 9942)
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 ~2.0x10^54 erg,
the peak luminosity (L_iso)_max ~ 1.0x10^54 erg/s, and Ep_rest ~1000 keV.
The Konus-Wind light curve of this GRB is available
at http://www.ioffe.ru/LEA/GRBs/GRB090926_T15628/
- GCN Circular #9961
L. Vetere (PSU) reports on behalf of the Swift-XRT team:
We have analyzed the first 21.8 ks of Swift-XRT data of FERMI
GRB090926A (Bissaldi et al., GCN Circ. 9933). The UVOT-enhanced XRT
position for this burst was given in GCN Circ.9936 (Vetere et al.).
The data are entirely in Photon Counting (PC) mode from T+46.7 ks
to T+203 ks. The light curve shows a decaying behaviour with some
flaring activity. It is best fitted by a power-law with decay index
1.29+/-0.2. Assuming the X-ray emission from the burst continues
to decline at the present rate, the predicted count rate at T+3d
is 0.009 cts/s.
The average spectrum is best fit by an absorbed power-law model
with a photon spectral index of 2.6 (+0.3,-0.2) and an absorption
column density of 1.0 (+0.5,-0.3)e21 cm-2 in excess of the Galactic
value of 2.7e20 cm-2 (Kalberla et al. 2005). The counts-to-observed
0.3-10 keV flux conversion factor deduced from this spectrum is
3.5e-11 erg cm-2 count-1. The average observed (unabsorbed) fluxes
are 1.3 (1.9)E-12 ergs cm-2 s-1. Errors are given at the 90%
confidence level.
This circular is an official product of the Swift-XRT team.
- GCN Circular #9972
Elisabetta Bissaldi (MPE), Michael S. Briggs (UA Huntsville),
Frederic Piron (IN2P3/LPTA), Hiromitsu Takahashi and
Takeshi Uehara (Hiroshima University)
report on behalf of the Fermi LAT and GBM teams:
Further analysis of GRB 090926A (Bissaldi GCN 9933, Uehara et al. GCN 99934,
Vetere et al. GCN 9336) reveals it is detected in the Fermi Large Area
Telescope (LAT) at least until 300 s after the Fermi Gamma-Ray Burst Monitor
(GBM) trigger time, T0=04:20:26.99 UT, with some indication for very
extended emission up to a few kilo-seconds.
Spectral analysis of the main emission episode, from T0 to T0+20.7 s, is
well-fit by a Band function with Epeak = 268 +/- 4 keV,
alpha = -0.693 +/ 0.009 and beta = -2.342 +/- 0.011
(C-STAT 1277 for 699 d.o.f.). Additionally, an effective area correction
of 0.8 and 0.85 is applied to both BGO detectors with respect to the NaI
detectors and LAT.
The brightest interval, i.e. from T0+8.5 s to T0+10.5 s, includes a bright,
narrow spike that is present from ~10 keV to >100 MeV. It shows a deviation
from the Band function. The parameters for this multi-component fit
(C-STAT = 781 for 697 d.o.f.) are Band_Epeak = 233 +/- 8,
Band_alpha = -0.43 +/- 0.06, Band_beta = -3.00 +/- 0.13,
and a power-law index of -1.845 +/- 0.019 for the additional component.
In this case, the effective area correction applied to both BGOs is 0.76.
The fluence between 10 keV and 10 GeV is (2.47 +/- 0.03)E-04 erg/cm^2
within the 21 seconds (the GBM T90) following the GBM trigger.
The points of contact for this burst are:
Takeshi Uehara (uehara@hep01.hepl.hiroshima-u.ac.jp) and
Elisabetta Bissaldi (ebs@mpe.mpg.de).
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 #9982
J. Haislip, D. Reichart, K. Ivarsen, A. LaCluyze, A. Foster, J. Moore, A.
Oza, M. Schubel, J. Styblova, A. Trotter, J. A. Crain, and M. Nysewander
report:
Skynet has continued to observe the afterglow (Haislip et al., GCN 9937) of
GRB 090926A (Bissaldi, GCN 9933) with four of the 16" PROMPT telescopes at
CTIO in BVRI.
Since peaking in brightness approximately 1 day after the trigger (Haislip
et al., GCN 9953), the afterglow has been fading with a power-law index of
approximately -1.4.
At 4.1 days after the trigger, it's magnitude is R = 20.09 +0.10 -0.09
(statistical) 0.57 (systematic; calibrated to 172 USNO B1 stars).
Skynet's most recent BVRI light curve, calibrated to USNO B1 and NOMAD
stars, can be found here:
http://skynet.unc.edu/grb/grb090926a.jpg
- GCN Circular #9984
J. Haislip, D. Reichart, K. Ivarsen, A. LaCluyze, A. Foster, J. Moore, A.
Oza, M. Schubel, J. Styblova, A. Trotter, J. A. Crain, and M. Nysewander
report:
Skynet has continued to observe the afterglow (Haislip et al., GCN 9937) of
GRB 090926A (Bissaldi, GCN 9933) with four of the 16" PROMPT telescopes at
CTIO in BVRI.
After peaking in brightness approximately 1 day after the trigger (Haislip
et al., GCN 9953), the afterglow had been fading with a power-law index of
approximately -1.4 until approximately 4 days after the trigger (Haislip,
et al., GCN 9982).
Between 4 and 6 days after the trigger, the afterglow has been fading with
a shallower power-law index of approximately -0.8.
At 6.1 days after the trigger, its magnitude is R = 20.40 +0.11 -0.10
(statistical) +/- 0.57 (systematic; calibrated to 172 USNO B1 stars).
Skynet's most recent BVRI light curve, calibrated to USNO B1 and NOMAD
stars, can be found here:
http://skynet.unc.edu/grb/grb090926a.jpg
- GCN Circular #10003
J. Haislip, D. Reichart, K. Ivarsen, A. LaCluyze, A. Foster, J. Moore, A.
Oza, M. Schubel, J. Styblova, A. Trotter, J. A. Crain, and M. Nysewander
report:
Skynet has continued to observe the afterglow (Haislip et al., GCN 9937) of
GRB 090926A (Bissaldi, GCN 9933) with two of the 16" PROMPT telescopes at
CTIO in RI.
After peaking in brightness approximately 1 day after the trigger (Haislip
et al., GCN 9953) and fading with a power-law index of around -1.4 until
approximately 4 days after the trigger (Haislip, et al., GCN 9982), the
afterglow faded with a shallower power-law index of around -0.8 until
approximately 6 days after the trigger (Haislip et al., GCN 9984).
Between 6 and 11 days after the trigger, the afterglow has been fading with
a steeper power-law index of around -1.7.
At 11.1 days after the trigger, its magnitude is R = 21.45 +0.22 -0.18
(statistical) +/- 0.57 (systematic; calibrated to 172 USNO B1 stars).
Skynet's most recent BVRI light curve, calibrated to USNO B1 and NOMAD
stars, can be found here:
http://skynet.unc.edu/grb/grb090926a.jpg
Continued observations with larger telescopes are encouraged.
- GCN Circular #10009
S. K. Chakrabarti, A. Nandi, D. Debnath, T. C. Kotoch (ICSP, Kolkata, Ind=
ia),
A. R. Rao, J. P. Malkar, M. K. Hingar, V. K. Agrawal (TIFR, Mumbai, India=
),=20
T. R. Chidambaram, P. Vinod, S. Sreekumar (VSSC, Thiruvananthapuram, Indi=
a),
Y. D. Kotov, A. S. Buslov, V. N. Yurov, V. G. Tyshkevich, A. I. Arkhangel=
skij,
R. A.Zyatkov (MephI, Moscow, Russia) report:
The very bright GRB 090926A (FERMI-GBM trigger 275631628 / 090926181;
Bissaldi, GCN 9933) is detected by RT-2 Experiment onboard CORONAS-PHOTON
satellite at T0 =3D 04h 20m 27s (UT). The satellite was in LIGHT mode (po=
inting
towards the SUN) for a short duration at a high latitude in its orbit. Du=
ring
this time, the GOOD time (away from the polar and SAA regions) observatio=
n was
for 348 sec starting at 04h 16m 55sec (UT) and ending at 04h 22m 43sec (U=
T).
The burst light curve consists of multiple peaks of total duration of ~ 1=
7
sec, followed by a weak tail ending at ~ T0+30 sec. The strongest peak co=
unt
rate is ~ 1200 cts/sec.
This burst is also independently detected by KONUS-RF, another instrument
onboard CORONAS-PHOTON satellite (Golenetskii et al., 2009, GCN 9959).
Both RT-2/S and RT-2/G detectors have registered the burst profile of thi=
s
bright GRB in the energy band of 15 =96 ~1000 keV with strongest emission=
in the
energy band of 60 =96 215 keV.
=20
The light curve is available at the web-site:
http://csp.res.in/rt2_files/grb090926-lc.html
- GCN Circular #10020
Aquib Moin (Curtin Institute of Radio Astronomy / Australia Telescope
National Facility), Dale A. Frail (National Radio Astronomy
Observatory), Steven Tingay (Curtin Institute of Radio Astronomy),
Jean-Pierre Macquart (Curtin Institute of Radio Astronomy) report:
We observed the UVOT-enhanced XRT position (GCN 9936) of the Fermi
LAT/GBM burst GRB090926a (GCN 9933, 9972) at 5.5 GHz with the Australia
Telescope Compact Array (ATCA) between 05:00:00 UT and 10:00:00 UT on
October 01, 2009. The ATCA was in its most compact configuration giving
a synthesized beam of 138 x 78 arcsec.
We did not detect a radio source at the XRT position of the GRB090926a
(GCN 9936). The radio flux density at the GRB position found out to be
-0.271 =B1 0.727 mJy/beam.
No further observations are planned.
The Australia Telescope Compact Array (/ Parkes telescope / Mopra
telescope / Long Baseline Array) is part of the Australia Telescope
which is funded by the Commonwealth of Australia for operation as a
National Facility managed by CSIRO.
See the GRB field image at:=20
http://cira.ivec.org/dokuwiki/doku.php/grb/grb090926a_field_image
- GCN Circular #10049
S. B. Cenko, D. A. Perley, B. E. Cobb, J. S. Bloom, and N. R. Butler (UC
Berkeley) report on behalf of a larger collaboration:
We have imaged the field of the Fermi GRB090926A (Bissaldi et al., GCN
9933; Uehara et al., GCN 9934) with the Gemini Multi-Object Spectrograph
mounted on the 8-m Gemini South telescope. Observations were taken in
the Sloan g', r', and i' filters beginning at 2:28 UT on 19 October 2009
(~ 22.9 d after the GBM trigger).
We detect a faint source in all filters at the location of the optical
afterglow (Haislip et al., GCN 9937, Gronwall et al., GCN 9938). Using
several unsaturated USNO-B objects in the field of view, along with the
filter transformations of Jordi, Grebel, and Ammon (2006 A&A 460, 339), we
measure a magnitude of r' ~ 23.7 for this source. Along with its
relatively blue color (g' - i' ~ 0), the object appears marginally
extended, suggesting it is likely dominated by emission from the host
galaxy of GRB090926A. We caution, however, that the host candidate is
partially blended with a nearby object (~ 1.5" in the SW direction, just
outside the optical and X-ray afterglow error circle) of comparable
magnitude, which likely affects the photometry.
Comparing with the last reported R-band detection (R ~ 21.5 at t ~ 11.1 d;
Haislip et al., GCN 10003), the optical decay must have significantly
steepened from previous measurements (power-law index alpha >~ 2.5). A
similar steepening is hinted at in the latest XRT observations of this
source (see http://astro.berkeley.edu/~nat/swift/00020113/bat_xrt.jpg),
suggesting a possible jet break. Using the measured redshift of z = 2.1
(Malesani et al., GCN 9942), the isotropic gamma-ray energy derived from
the Konus-Wind instrument (E_iso ~ 2e54 erg; Golenetskii et al., GCN
9959), and assuming expansion into a constant density medium (n ~ 1
cm^-3) with a gamma-ray efficiency ~ 20%, we infer an opening angle ~ 0.1
rad. The collimation-corrected prompt energy release would therefore be
large, E ~ 1e52 erg.
,)
- GCN Circular #10113
B. E. Cobb (UC Berkeley) reports:
Using the ANDICAM instrument on the 1.3m telescope at CTIO, we
obtained optical/IR imaging of the error region of GRB 090926a
(GCN 9933, Bissaldi et al.) over several epochs. For each epoch,
total summed exposure times amounted to 36 minutes in I and
30 minutes in J.
The afterglow of GRB 090926a (e.g. GCN 9937, Haislip et al.;
GCN 9938, Gronwall et al.) is detected in our images with
the following magnitudes (calibrated using Landolt standard stars
in the optical and 2MASS stars in the IR):
time
post-burst I mag J mag
20.60 hrs 18.17+/-0.06 17.28+/-0.07
71.74 hrs 19.53+/-0.07 18.35+/-0.09
119.18 hrs 20.33+/-0.10 19.16+/-0.13
Between ~21 and 119 hours post-burst, the afterglow fades
with a rate of alpha ~ -1.1+/-0.1 (where afterglow flux is
proportional to t^alpha).
- GCN Report 254.1
GCN_Report 254.1 has been posted:
http://gcn.gsfc.nasa.gov/reports/report_254_1.pdf
by L. Vetere
at PSU
titled: "Swift Observations on Fermi GRB 090926A"
- 1004.2900 from 19 Apr 10
S. B. Cenko et al.: Afterglow Observations of Fermi-LAT Gamma-Ray Bursts and the Emerging Class of Hyper-Energetic Events
Bloom, P. Chandra, D. B. Fox, D. A. Perley, J. X. Prochaska, A. V. Filippenko, K. Glazebrook, K. M. Ivarsen, M. M. Kasliwal, S. R. Kulkarni, A.
P. LaCluyze, S. Lopez, A. N. Morgan, M. Pettini, V. R. Rana
We present broadband (radio, optical, and X-ray) light curves and spectra of the afterglows of four long-duration gamma-ray bursts (GRBs
090323, 090328, 090902B, and 090926A) detected by the Gamma-Ray Burst Monitor (GBM) and Large Area Telescope (LAT) instruments on the Fermi
satellite. With its wide spectral bandpass, extending to GeV energies, Fermi is sensitive to GRBs with very large isotropic energy releases
(10e54 erg). Although rare, these events are particularly important for testing GRB central-engine models. When combined with spectroscopic
redshifts, our afterglow data for these four events are able to constrain jet collimation angles, the density structure of the circumburst
medium, and both the true radiated energy release and the kinetic energy of the outflows. In agreement with our earlier work, we find that the
relativistic energy budget of at least one of these events (GRB 090926A) exceeds the canonical value of 10e51 erg by an order of magnitude.
Such energies pose a severe challenge for models in which the GRB is powered by a magnetar or neutrino-driven collapsar, but remain compatible
with theoretical expectations for magneto-hydrodynamical (MHD) collapsar models. Our jet opening angles (theta) are similar to those found for
pre-Fermi GRBs, but the large initial Lorentz factors (Gamma_0) inferred from the detection of GeV photons imply theta Gamma_0 ~ 70-90, values
which are above those predicted in MHD models of jet acceleration. Finally, we find that these Fermi-LAT events preferentially occur in a
low-density circumburst environment, and we speculate that this might result from the lower mass-loss rates of their lower-metallicity
progenitor stars. Future studies of Fermi-LAT afterglows in the radio with the order-of-magnitude improvement in sensitivity offered by the
EVLA should definitively establish the relativistic energy budgets of these events.
- 1105.2485 from 13 May 11
Hendrik J. van Eerten et al.: Observational implications of gamma-ray burst afterglow jet simulations and numerical light curve calculations
We discuss jet dynamics for narrow and wide gamma-ray burst (GRB) afterglow jets and the observational implications of numerical simulations of
relativistic jets in two dimensions. We confirm earlier numerical results that sideways expansion of relativistic jets is logarithmic and find
that this also applies to narrow jets with half opening angle of 0.05 radians. As a result, afterglow jets remain highly nonspherical until
after they have become nonrelativistic. Although sideways expansion steepens the afterglow light curve after the jet break, the jet edges
becoming visible dominates the jet break, which means that the jet break is sensitive to the observer angle even for narrow jets. Failure to
take the observer angle into account can lead to an overestimation of the jet energy by a factor 2-4. This weakens the challenge posed to the
magneter energy limit by extreme events such as GRB090926A. Late time radio calorimetry based on a spherical nonrelativistic outflow model
remains relevant in case the observer is approximately on-axis and where differences of a few in flux level between model and simulation are
acceptable. However, this does not imply sphericity of the outflow and therefore does not translate to high observer angles relevant to orphan
afterglows. For more accurate calorimetry and in order to model significant late time features such as the rise of the counterjet, detailed jet
imulations remain indispensable.
- 1109.5191 from 27 Sep 11
Robert J. Nemiroff et al.: Limiting properties of light and the universe with high energy photons from Fermi-detected Gamma Ray Bursts
Quantum Cosmology (gr-qc)
An analysis of four Fermi-detected gamma-ray bursts (GRBs) is given that sets upper limits on the energy dependence of the speed and dispersion
of light across the universe. The analysis focuses on photons recorded above 1 GeV for Fermi detected GRB 080916C, GRB 090510A, GRB 090902B,
and GRB 090926A. Upper limits on time scales for statistically significant bunching of photon arrival times were found and cataloged. In
particular, the most stringent limit was found for GRB 090510A at redshift $z \gtrsim 0.897$ for which $\Delta t < 0.00136$ sec, a limit driven
by three separate photon bunchings. These photons occurred among the first seven super-GeV photons recorded for GRB 090510A and contain one
pair with an energy difference of $\Delta E \gtrsim 23.5$ GeV. The next most limiting burst was GRB 090902B at a redshift of $z \gtrsim 1.822$
for which $\Delta t < 0.161$, a limit driven by several groups of photons, one pair of which had an energy difference $\Delta E \gtrsim$ 1.56
GeV. Resulting limits on the differential speed of light and Lorentz invariance were found for all of these GRBs independently. The strongest
limit was for GRB 090510A with $\Delta c / c < 6.09$ x $10^{-21}$. Given generic dispersion relations across the universe where the time delay
is proportional to the photon energy to the first or second power, the most stringent limits on the dispersion strengths were $k_1 <$ 1.38 x
$10^{-5}$ sec Gpc$^{-1}$ GeV$^{-1}$ and $k_2 <$ 3.04 x $10^{-7}$ sec Gpc$^{-1}$ GeV$^{-2}$ respectively. Such upper limits result in upper
bounds on dispersive effects created, for example, by dark energy, dark matter or the spacetime foam of quantum gravity. Relating these
dispersion constraints to loop quantum gravity energy scales specifically results in limits of $M_1 c^2 >$ 7.43 x $10^{21}$ GeV and $M_2 c^2 >$
7.13 x $10^{11}$ GeV respectively.
- 1203.1577 from 8 Mar 12
J. R. Sacahui et al.: The long and the short of the high energy emission in GRB090926A: an external shock
SSC emission from a reverse shock has been suggested as the origin for the high energy component lasting 2 s in the prompt phase of GRB98080923
(Fraija et al. 2012). The model describes spectral indices, fluxes and the duration of the high-energy component as well as a long keV tail
present in the prompt phase of GRB980923. Here, we present an extension of this model to describe the high-energy emission of GRB090926A. We
argue that the emission consist of two components, one with a duration less than 1s during the prompt phase, and a second, longer-lasting GeV
phase lasting hundred of seconds after the prompt phase. The short high-energy phase can be described as SSC emission from a reverse shock
similar to that observed in GRB980923, while the longer component arises from the forward shock. The main assumption is that the jet is
magnetized and evolves in the thick-shell case, and the calculated fluxes and break energies are all consistent with the observed values. A
comparison between the resulting parameters obtained for GRB980923 and GRB090926A suggests differences in burst tails that could be
attributable to the circumburst medium, and this could account for previous analyses reported in the literature for other bursts. We find that
the density of the surrounding medium inferred from the observed values associated to the forward shock agrees with standard values for host
galaxies such as the one associated to GRB090926A.
- 1212.4418 from 19 Dec 12
N. Fraija et al.: Long and short high energy components presented in GRBs
We present a leptonic model on the external shock framework to describe the long- and short- lasting GeV component of some GRBs. This model was
already applied successfully to GRB 090926A, and we extend it to describe the high-energy emission of GRB 090902B and GRB 090510. We argue that
the high-energy emission consists of two components, one at MeV energies with a duration of a few seconds during the prompt phase, and a second
GeV component lasting hundred of seconds after the prompt phase. The short high-energy component can be described as SSC emission from a
reverse shock and the longer component arises from SSC emission of the forward shock. The main assumption of our model is that the jet is
magnetized and evolves in the thick-shell case. The calculated fluxes and break energies are all consistent with the observed values.
- 1308.2506 from 13 Aug 13
A.R. Rao et al.: Time resolved spectral analysis of the prompt emission of long gamma ray bursts with GeV Emission
We make a detailed time resolved spectroscopy of bright long gamma ray bursts (GRBs) which show significant GeV emissions (GRB 080916C, GRB
090902B, and GRB 090926A). In addition to the standard Band model, we also use a model consisting of a blackbody and a power-law to fit the
spectra. We find that for the latter model there are indications for an additional soft component in the spectra. While previous studies have
shown that such models are required for GRB 090902B, here we find that a composite spectral model consisting of two black bodies and a power
law adequately fit the data of all the three bright GRBs. We investigate the evolution of the spectral parameters and find several generic
interesting features for all three GRBs, like a) temperatures of the black bodies are strongly correlated to each other, b) flux in the black
body components are strongly correlated to each other, c) the temperatures of the black body trace the profile of the individual pulses of the
GRBs, and d) the characteristics of the power law component like the spectral index and the delayed onset bear a close similarity to the
emission characteristics in the GeV regions. We discuss the implications of these results to the possibility of identifying the radiation
mechanisms during the prompt emission of GRBs.
- 1308.2819 from 14 Aug 13
Rupal Basak et al.: A lingering non-thermal component in the GRB prompt emission: predicting GeV emission from the MeV spectrum
The high energy GeV emission of gamma-ray bursts (GRBs), detected by \emph{Fermi}/LAT, has a significantly different morphology compared to the
lower energy MeV emission, detected by \emph{Fermi}/GBM. Though the late time GeV emission is believed to be synchrotron radiation produced via
an external shock, this emission as early as the prompt phase is puzzling. Meaningful connection between these two emissions can be drawn only
by an accurate description of the prompt MeV spectrum. We perform a time-resolved spectroscopy of the GBM data of long GRBs having significant
GeV emission, using a model consisting of 2 blackbodies and a power-law. We examine in detail the evolution of the spectral components and
found that GRBs having high GeV emission (GRB 090902B and GRB 090926A) have a delayed onset of the power-law component, in the GBM spectrum,
which lingers at the later part of the prompt emission. This behaviour mimics the flux evolution in LAT. In contrast, bright GBM GRBs with an
order of magnitude lower GeV emission (GRB 100724B and GRB 091003) show a coupled variability of the total and the power-law flux. Further, by
analyzing the data for a set of 17 GRBs, we find a strong correlation between the power-law fluence in the MeV and the LAT fluence (Pearson
correlation: r=0.88 and Spearman correlation: $\rho=0.81$). We demonstrate that this correlation is not influenced by the correlation between
the total and the power-law fluences at a confidence level of 2.3$\sigma$. We speculate the possible radiation mechanisms responsible for the
correlation.
- 1412.3342 from 11 Dec 14
Qing-Wen Tang et al.: Measuring the bulk Lorentz factors of gamma-ray bursts with Fermi
Gamma-ray bursts (GRBs) are powered by ultra-relativistic jets. Usually a minimum value of the Lorentz factor of the relativistic bulk motion
is obtained based on the argument that the observed high energy photons ($\gg {\rm MeV}$) can escape without suffering from absorption due to
pair production. The exact value, rather than a lower limit, of the Lorentz factor can be obtained if the spectral cutoff due to such
absorption is detected. With the good spectral coverage of the Large Area Telescope (LAT) on {\em Fermi}, measurements of such cutoff become
possible, and two cases (GRB 090926A and GRB 100724B) have been reported to have high-energy cutoffs or breaks. We systematically search for
such high energy spectral cutoffs/breaks from LAT and GBM observations of the prompt emission of GRBs detected since August 2011. Seven more
GRBs are found to have cutoff-like spectral feature at energies of $\sim20-300$ MeV. Assuming that these cutoffs are caused by pair-production
absorption within the source, the bulk Lorentz factors of these GRBs are obtained. We further find that the Lorentz factors are correlated with
the isotropic gamma-ray luminosity of the bursts, indicating that more powerful GRB jets move faster.
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