- GCN NOTICE
TITLE: GCN/FERMI NOTICE
NOTICE_DATE: Thu 21 Jul 11 04:48:10 UT
NOTICE_TYPE: Fermi-GBM Flight Position
RECORD_NUM: 59
TRIGGER_NUM: 332916465
GRB_RA: 327.550d {+21h 50m 12s} (J2000),
327.725d {+21h 50m 54s} (current),
326.791d {+21h 47m 10s} (1950)
GRB_DEC: -37.900d {-37d 53' 59"} (J2000),
-37.846d {-37d 50' 43"} (current),
-38.134d {-38d 08' 01"} (1950)
GRB_ERROR: 3.93 [deg radius, statistical plus systematic]
GRB_INTEN: 1527 [cnts/sec]
DATA_SIGNIF: 153.80 [sigma]
INTEG_TIME: 4.096 [sec]
GRB_DATE: 15763 TJD; 202 DOY; 11/07/21
GRB_TIME: 17263.75 SOD {04:47:43.75} UT
GRB_PHI: 180.00 [deg]
GRB_THETA: 45.00 [deg]
DATA_TIME_SCALE: 4.0960 [sec]
HARD_RATIO: 0.66
LOC_ALGORITHM: 3 (version number of)
MOST_LIKELY: 96% GRB
2nd_MOST_LIKELY: 3% Generic Transient
SUN_POSTN: 120.21d {+08h 00m 50s} +20.54d {+20d 32' 17"}
SUN_DIST: 150.58 [deg] Sun_angle= 10.2 [hr] (West of Sun)
MOON_POSTN: 3.66d {+00h 14m 38s} +7.08d {+07d 05' 00"}
MOON_DIST: 56.02 [deg]
MOON_ILLUM: 69 [%]
GAL_COORDS: 5.30,-50.71 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS: 316.46,-23.28 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS: Fermi-GBM Flight-calculated Coordinates.
- GCN NOTICE
TITLE: GCN/FERMI NOTICE
NOTICE_DATE: Thu 21 Jul 11 13:37:53 UT
NOTICE_TYPE: Fermi-GBM Flight Position
RECORD_NUM: 46
TRIGGER_NUM: 332916465
GRB_RA: 323.617d {+21h 34m 28s} (J2000),
323.790d {+21h 35m 10s} (current),
322.866d {+21h 31m 28s} (1950)
GRB_DEC: -33.367d {-33d 21' 59"} (J2000),
-33.315d {-33d 18' 52"} (current),
-33.590d {-33d 35' 22"} (1950)
GRB_ERROR: 3.83 [deg radius, statistical plus systematic]
GRB_INTEN: 1820 [cnts/sec]
DATA_SIGNIF: 86.80 [sigma]
INTEG_TIME: 1.024 [sec]
GRB_DATE: 15763 TJD; 202 DOY; 11/07/21
GRB_TIME: 17263.75 SOD {04:47:43.75} UT
GRB_PHI: 177.00 [deg]
GRB_THETA: 50.00 [deg]
DATA_TIME_SCALE: 1.0240 [sec]
HARD_RATIO: 0.43
LOC_ALGORITHM: 3 (version number of)
MOST_LIKELY: 95% GRB
2nd_MOST_LIKELY: 4% Generic Transient
DETECTORS: 0,0,0, 0,0,0, 1,1,0, 0,0,0, 0,0,
SUN_POSTN: 120.57d {+08h 02m 18s} +20.47d {+20d 28' 03"}
SUN_DIST: 155.72 [deg] Sun_angle= 10.5 [hr] (West of Sun)
MOON_POSTN: 7.74d {+00h 30m 56s} +8.72d {+08d 43' 04"}
MOON_DIST: 59.24 [deg]
MOON_ILLUM: 66 [%]
GAL_COORDS: 12.09,-47.40 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS: 314.96,-17.91 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS: Fermi-GBM Flight-calculated Coordinates.
COMMENTS: This trigger occurred at longitude,latitude = 44.73,-0.77 [deg].
- GCN NOTICE
TITLE: GCN/FERMI NOTICE
NOTICE_DATE: Thu 21 Jul 11 13:38:05 UT
NOTICE_TYPE: Fermi-GBM Flight Position
RECORD_NUM: 59
TRIGGER_NUM: 332916465
GRB_RA: 327.550d {+21h 50m 12s} (J2000),
327.725d {+21h 50m 54s} (current),
326.791d {+21h 47m 10s} (1950)
GRB_DEC: -37.900d {-37d 53' 59"} (J2000),
-37.846d {-37d 50' 43"} (current),
-38.134d {-38d 08' 01"} (1950)
GRB_ERROR: 3.93 [deg radius, statistical plus systematic]
GRB_INTEN: 1527 [cnts/sec]
DATA_SIGNIF: 153.80 [sigma]
INTEG_TIME: 4.096 [sec]
GRB_DATE: 15763 TJD; 202 DOY; 11/07/21
GRB_TIME: 17263.75 SOD {04:47:43.75} UT
GRB_PHI: 180.00 [deg]
GRB_THETA: 45.00 [deg]
DATA_TIME_SCALE: 4.0960 [sec]
HARD_RATIO: 0.66
LOC_ALGORITHM: 3 (version number of)
MOST_LIKELY: 96% GRB
2nd_MOST_LIKELY: 3% Generic Transient
DETECTORS: 0,0,0, 0,0,0, 1,1,0, 0,0,0, 0,0,
SUN_POSTN: 120.58d {+08h 02m 18s} +20.47d {+20d 28' 03"}
SUN_DIST: 150.79 [deg] Sun_angle= 10.2 [hr] (West of Sun)
MOON_POSTN: 7.74d {+00h 30m 57s} +8.72d {+08d 43' 07"}
MOON_DIST: 59.68 [deg]
MOON_ILLUM: 66 [%]
GAL_COORDS: 5.30,-50.71 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS: 316.46,-23.28 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS: Fermi-GBM Flight-calculated Coordinates.
COMMENTS: This trigger occurred at longitude,latitude = 44.73,-0.77 [deg].
- GCN NOTICE
TITLE: GCN/FERMI NOTICE
NOTICE_DATE: Thu 21 Jul 11 13:41:12 UT
NOTICE_TYPE: Fermi-GBM Ground Position
RECORD_NUM: 58
TRIGGER_NUM: 332916465
GRB_RA: 331.440d {+22h 05m 46s} (J2000),
331.611d {+22h 06m 27s} (current),
330.700d {+22h 02m 48s} (1950)
GRB_DEC: -36.450d {-36d 27' 00"} (J2000),
-36.393d {-36d 23' 36"} (current),
-36.694d {-36d 41' 36"} (1950)
GRB_ERROR: 1.00 [deg radius, statistical only]
DATA_SIGNIF: 163.80 [sigma]
DATA_INTERVAL: 4.096 [sec]
GRB_DATE: 15763 TJD; 202 DOY; 11/07/21
GRB_TIME: 17263.75 SOD {04:47:43.75} UT
GRB_PHI: 176.00 [deg]
GRB_THETA: 43.00 [deg]
E_RANGE: 44.032 - 279.965 [keV]
LOC_ALGORITHM: 4143 (Gnd S/W Version number)
SUN_POSTN: 120.58d {+08h 02m 19s} +20.47d {+20d 28' 01"}
SUN_DIST: 148.61 [deg] Sun_angle= 9.9 [hr] (West of Sun)
MOON_POSTN: 7.76d {+00h 31m 03s} +8.73d {+08d 43' 41"}
MOON_DIST: 56.47 [deg]
MOON_ILLUM: 66 [%]
GAL_COORDS: 7.44,-53.88 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS: 320.18,-23.09 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS: Fermi-GBM Ground-calculated Coordinates.
COMMENTS: In the LAT Field-of-view.
COMMENTS: Bright hard burst in the GBM.
COMMENTS: This Notice was ground-generated -- not flight-generated.
- GCN Circular #12187
D. Tierney (UCD) and A. von Kienlin (MPE)
report on behalf of the Fermi GBM Team:
"At 04:47:43.75 UT on 21 July 2011, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 110721A (trigger 332916465 / 110721200).
The on-ground calculated location, using the GBM trigger
data, is RA = 331.42, DEC = -36.42 (J2000 degrees,
equivalent to 22h 05m, -36d 25'), with an uncertainty
of 1.00 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 43.00 degrees.
The GBM light curve consists of a fast rise, exponential decay (FRED)
with a duration (T90) of 24.45 s (50-300 keV).
The time-averaged spectrum from T0-0.32 s to T0+11.97 s is
best fit by a Band function with Epeak = 372.50 (+26.50/-23.60) keV,
alpha = -0.94 (+/-0.02), and beta = -1.77 (+/-0.02)
(C-Stat 945.78 for 591 d.o.f.).
The event fluence (10-1000 keV) in this time interval is
(3.52 +/- 0.03)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+1.98 s in the 10-1000 keV band
is 31.35 +/- 0.38 ph/s/cm^2.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."
- GCN Circular #12188
V. Vasileiou (CNRS/IN2P3/LUPM), F. Piron (CNRS/IN2P3/LUPM), D. Tierney (UCD), A.
von Kienlin (MPE), S. Guiriec (UAH), and J. L. Racusin (NASA/GSFC) report on
behalf of the Fermi-LAT team:
At 04:47:45 on July 21, 2011, Fermi-LAT detected high energy
emission from GRB 110721A, which was also detected by Fermi-GBM (trigger
332916465, Tierney et al. (GCN 12187)), and Integral (SPI ACS
trigger 6326).
The best preliminary LAT on-ground location is found to be (RA, DEC)=
(333.4,-39.0) (J2000; deg) with an error radius of 0.75 (0.51) deg
at 90% (68%) containment (statistical error only), which was 40 deg from the LAT
boresight at the time of the trigger. We further report that
the Fermi Observatory executed an autonomous repoint maneuver
to follow this trigger for the next 2.5 hours, subject to
Earth-angle constraints.
The data from the Fermi-LAT show a significant increase in the
event rate that is spatially and temporally correlated with the
GBM emission with high significance. This detection was independently
confirmed by the blind on-ground GRB search of the LAT data. More
than 20 (1) photons above 100 MeV (1 GeV) using a standard event
selection and about 1000 photons using a non-standard event
selection sensitive mostly to tens-of-MeV energies are observed
within 20 sec. The lightcurve at tens-of-MeV energies has a Fast Rise
Exponential Decay (FRED) profile with an ~16 sec duration
similar to the GBM results. The highest energy event has an 1.7 GeV
energy, was observed about 0.7 sec after the trigger, and was
associated to the GRB with a high (>0.9) probability.
Preliminary spectral analyses on the LAT data taken during the
first 20 sec after the trigger resulted in a -2.9+-0.4 spectral index
and a 3.3+-0.8 x 10^-4 ph/cm^2/sec average flux integrated over E>100 MeV. This
spectral index is considerably softer than the extrapolation of the GBM spectral
index at E>100 MeV energies (Tierney et al. (GCN 12187)), which suggests a
spectral cutoff or softening of the spectrum.
A Swift Target of Opportunity observation has been requested and tiling
observations are ongoing.
The Fermi LAT point of contact for this burst is Vlasios Vasileiou
(vlasios.vasileiou@lupm.in2p3.fr).
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.
- GCN Circular #12191
S. Golenetskii, R.Aptekar, D. Frederiks, E. Mazets, V. Pal'shin,
P. Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf
of the Konus-Wind team, report:
The bright hard long GRB 110721A
(Fermi-GBM detection: Tierney and von Kienlin, GCN 12187;
Fermi-LAT detection: Vasileiou et al., GCN 12188)
triggered Konus-Wind at T0=3D17266.887s UT (04:47:46.887)
The burst light curve shows a single FRED-like pulse
with a total duration of ~25 s.
The emission is seen up to ~10 MeV, a hard-to-soft
spectral evolution is noticeable in the course of the event.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB110721_T17266/
As observed by Konus-Wind the burst
had a fluence of (8.8 =B1 0.9)x10-5 erg/cm2,
and a 64-ms peak flux, measured from T0+1.984 s,
of (2.3 =B1 0.2)x10-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).
The time-integrated spectrum of the burst
(measured from T0 to T0+26.624 s) can be fitted
in the 20 keV - 10 MeV range by the GRB (Band)
model, for which:
the low-energy photon index alpha =3D -1.02 (-0.14, +0.16),
the high energy photon index beta =3D -1.77 (-0.13, +0.07),
the peak energy Ep =3D 393(-104, +199) keV,
chi2 =3D 109.8/84 dof.
The spectrum at the maximum count rate
(measured from T0+0.256 to T0+2.304 s) is best fitted
in the 20 keV - 10 MeV range by the GRB (Band)
model, for which:
the low-energy photon index alpha =3D -1.0 (-0.2, +0.2),
the high energy photon index beta =3D -2.0 (-0.5, +0.2),
the peak energy Ep =3D 1130(-490, +550) keV,
chi2 =3D 74.1/74 dof.
All the quoted results are preliminary.
All the quoted errors are at the 90% confidence level.
- GCN Circular #12192
J. Greiner (MPE), A.C. Updike (NASA/GSFC), T. Kruehler (DARK/NBI),
V. Sudilovsky (MPE) report:
We have analyzed the first 4 tiles of the Swift/XRT observations on the
0.75 deg Fermi/LAT radius error box (Vasileiou et al., GCN 12188) of
the bright Fermi/GBM GRB 110721A (Tierney and von Kienlin, GCN 12187).
In the pointing with OBS-ID 00020169 we find a single X-ray source
at RA(2000.0)=22h14m38.27s, Decl(2000.0)= -38:35:36.3 (+-6.8 arcsec).
We observed this position simultaneously in g'r'i'z'JHK with GROND
(Greiner et al. 2008, PASP 120, 405) mounted at the 2.2 m MPI/ESO
telescope at La Silla Observatory (Chile). Observations started at
06:33 UT on July 22, about 26 hrs after the GRB trigger. They were
performed at an average seeing of 1.0" and at an average airmass of 1.
We found a single point source within the 6.8" Swift-XRT error circle,
at coordinates
RA(2000.0) = 22h 14m 38.19s,
Decl(2000.0) = -38d 35' 35.7"
with an uncertainty of +-0.3".
Based on 1840 s of total exposures in g'r'i'z' and 1920 s in JHK, we
estimate preliminary magnitudes (all AB system) of
g = 24.3 +/- 0.2
r = 22.9 +/- 0.1
i = 22.3 +/- 0.1
z = 21.8 +/- 0.1
J = 21.0 +/- 0.2
H = 20.5 +/- 0.2
K > 18.8
These optical and NIR magnitudes are calibrated against GROND zeropoints
and 2MASS field stars, respectively, and are not corrected for the
expected Galactic foreground extinction corresponding to a reddening of
E(B-V)=0.016 mag in the direction of the burst (Schlegel et al. 1998).
The spectral energy distribution (SED) is well fit by a powerlaw, typical
for GRB afterglows. The low-level g'-band flux can either be fit with
Ly-alpha at a redshift of z~3.2, or host-intrinsic extinction.
We obtained another epoch of observations starting at 6:21 UT on Jul 23,
at an average seeing of 1.4". Within the errors (+-0.2 mag), the object
exhibits the same brightness in both observations.
We note that the chance coincidence to find 1 X-ray source in 4 Swift/XRT
pointings of the given exposure is nearly 100%. Also, the 4 tiles only
cover 30% of the area of the Fermi/LAT error circle. However, the powerlaw
shape of the SED of the optical/NIR source make this a good candidate
for the counterpart of GRB 110721A. Our second observation is inconclusive,
unfortunately - the non-fading behaviour could either be due to a plateau
of the emission from the afterglow, or indicate a non-GRB nature.
We suggest spectroscopic observations of this object to reveal its nature.
- GCN Circular #12193
E. Berger (Harvard) reports on behalf of a larger collaboration:
"We obtained spectroscopic observations of the candidate optical counterpart
(GCN 12192) of the LAT burst GRB110721A (GCN 12188) with GMOS on the
Gemini-South 8-m telescope starting on 2011 July 24.20 UT. A total of 3600
sec was obtained on source with a wavelength coverage of about 4000-8100
ang. We find two clear absorption features at 5487 and 5436 ang, with a
significant decline in flux at shorter wavelengths, but to a non-zero
level. The two features match CaII H&K at a redshift of z=0.382, or could
alternatively represent Ly-alpha absorption with the highest redshift being
z=3.512. No other features are detected at wavelengths corresponding to
other typical lines at either redshift. Given the detectable flux blueward
of 5430 ang (down to at least 4600 ang), and the fact that the source
appears to be extended in our i-band acquisition image (with seeing of about
0.7"), we consider the possibility that the object is an early-type galaxy
at z=0.382 to be more likely.
We thank Jochen Greiner for sharing a finding chart of GRB110721A from GROND
data."
- GCN Circular #12194
S. T. Holland (CRESST/USRA/GSFC), and
C. A. Swenson (PSU)
report on behalf of the Swift/UVOT team:
Swift/UVOT began observations of the field of the weak X-ray source
that may be associated with GRB 110721A (Greiner et al., 2011, GCNC
12192) 54,869 s after the Fermi/GBM trigger (Tierney & von Kienlin,
2011, GCNC 12187). We do not detect the GROND optical source in the
UVOT images. Our preliminary upper limits are consistent with the
faint nature of the GROND source. The 3-sigma UVOT upper limits are
Filter T_start(s) T_stop(s) Exp(s) Upper Limit
----------------------------------------------------------
v 56,146 56,853 672 >20.8
u 54,867 55,509 632 >21.4
white 55,516 56,158 632 >22.4
----------------------------------------------------------
These upper limits are on the UVOT photometric system of Poole et al.,
2008, MNRAS, 383, 627). The upper limits are not corrected for the
Galactic extinction due to the reddening of E_{B-V} = 0.02 mag in the
direction of the burst (Schlegel et al., 1998, ApJS, 500, 525).
- GCN Circular #12195
K. Hurley and J. Goldsten, on behalf of the MESSENGER NS GRB team,
S. Golenetskii, R. Aptekar, E. Mazets, V. Pal'shin, D. Frederiks,
D. Svinkin, and T. Cline on behalf of the Konus-Wind team,
V. Connaughton, M. Briggs, and C. Meegan, on behalf of the Fermi
GBM team,
A. von Kienlin, X. Zhang, and A. Rau, on behalf of the
INTEGRAL SPI-ACS GRB team, and
E. Costa, E. Del Monte, I. Donnarumma, Y. Evangelista, M. Feroci,
I. Lapshov, F. Lazzarotto, L. Pacciani, M. Rapisarda, P. Soffitta,
for the SuperAGILE team, report:
The Fermi GRB 110721A (GCN 12187, 12188) was also observed by
AGILE MCAL and SuperAGILE (but outside the coded field of view
of SuperAGILE), INTEGRAL SPI-ACS, Konus-Wind, and MESSENGER GRNS.
We have triangulated it to a preliminary 3 sigma error box whose
area is 2250 square arcminutes, and whose coordinates are:
Center: RA=332.456 o = 22 h 09 m 49 s DEC=-38.628 o = -38 o 37 ' 40 "
Corners: 333.674=22 h 14 m 42 s -38.570=-38 o 34 ' 13 "
331.191=22 h 04 m 46 s -38.964=-38 o 57 ' 49 "
333.709=22 h 14 m 50 s -38.241=-38 o 14 ' 26 "
331.240=22 h 04 m 58 s -38.641=-38 o 38 ' 28 "
This error box intersects the LAT error circle to form a joint
error box whose area is approximately 1200 square arcminutes.
A map is posted at ssl.berkeley.edu/ipn3/110721.
The counterpart candidate reported by Greiner et al. (GCN 12192)
lies just outside the IPN error box, making it unlikely that it is
related to the GRB.
- GCN Circular #12212
D. Grupe (PSU), C.A. Swenson (PSU), J.L. Racusin (NASA/GSFC),
& C. Wolf (PSU) report on behalf of the Swift team.
We report on the Swift follow-up observations of the field of the
afterglow candidate reported by Greiner et al. (GCN Circ. 12192) of
the FERMI GBM/LAT detected burst GRB 110721A (Tierney & v. Kienlin,
GCN Circ. 12187; Vasileiou et al., GCN Circ. 12188). Greiner et al.
found a faint X-ray source in one of the tiling Swift observations
(Obs ID 20169, 1.8 ks) which was also detected by GROND. This
field was observed by Swift again approximately 150 hours after
the FERMI trigger for 4.9 ks with the XRT in photon counting mode
(Obs ID 20174). We did not detect any source in the 0.3-10 keV
band at the position reported by Greiner et al. (GCN Circ. 12192).
We determined a 3 sigma upper limit of 2.5 e-3 counts/s. The
comparison of this new observation to the X-ray afterglow
candidate with a count rate of (3.8+6.14-3.16)e-3 counts/s (in the
1.8 ks observation 20169) is inconclusive as it could be
consistent with either a constant source or fading.
Based on the source detection in Obs ID 20169, if we assume a
standard X-ray spectrum with Galactic foreground absorption and
the standard cosmology for a source at a redshift of z=0.382 as
reported by Berger (GCN Circ. 12193) the luminosity in the
0.3-10 keV band is 2e43 ergs/s. This luminosity is consistent
with that of a low luminosity AGN.
Note that some of the Swift observations of the fields around
GRB 110721A were unusable because this region was difficult for
the star trackers to achieve lock. Therefore, no further
observations are planned.
- GCN Circular #12245
Poonam Chandra (RMC), S. Bradley Cenko (UC Berkeley),
and Dale A. Frail (NRAO)report on behalf of a larger collaboration:
We observed the field of the potential X-ray afterglow (GCN 12192,
12212) of the Fermi GBM (GCN 12187) and LAT (12188) GRB 110721A
with the EVLA on 2011 July 26.29 UT at 4.5 and 7.9 GHz. The field of view
is dominated by the radio bright AGN PKS 2211-388, located 9" from the
XRT localization. PKS 2211-388 has 7.9 GHz flux of 0.35 Jy and
4.5 GHz flux of 0.75 Jy in our EVLA observations. We suggest that
the proposed X-ray counterpart is instead associated with PKS 2211-388.
The potential optical counterpart (GCN 12192), likely to be an
early-type galaxy at z=0.382 (GCN 12193), is located ~ 10" from
PKS 2211-388. Given the large offset and the spectral type,
we consider it unlikely to be related to either PKS 2211-388 or GRB 110721A.
- 1207.6109 from 27 Jul 12
The Fermi LAT Collaboration et al.: GRB110721A: An extreme peak energy and signatures of the photosphere
GRB110721A was observed by the Fermi Gamma-ray Space Telescope using its two instruments the Large Area Telescope (LAT) and the Gamma-ray Burst
Monitor (GBM). The burst consisted of one major emission episode which lasted for ~24.5 seconds (in the GBM) and had a peak flux of 5.7\pm0.2 x
10^{-5} erg/s/cm^2. The time-resolved emission spectrum is best modeled with a combination of a Band function and a blackbody spectrum. The
peak energy of the Band component was initially 15\pm2 MeV, which is the highest value ever detected in a GRB. This measurement was made
possible by combining GBM/BGO data with LAT Low Energy Events to achieve continuous 10--100 MeV coverage. The peak energy later decreased as a
power law in time with an index of -1.89\pm0.10. The temperature of the blackbody component also decreased, starting from ~80 keV, and the
decay showed a significant break after ~2 seconds. The spectrum provides strong constraints on the standard synchrotron model, indicating that
alternative mechanisms may give rise to the emission at these energies.
- 1208.1790 from 10 Aug 12
P. Veres et al.: The extremely high peak energy of GRB 110721A in the context of a dissipative photosphere synchrotron emission model
The Fermi observations of GRB 110721A (The Fermi LAT Collaboration et al. 2012) have revealed an unusually high peak energy $\sim 15$ MeV in
the first time bin of the prompt emission. We find that an interpretation is unlikely in terms of internal shock models, and confirm that a
standard black-body photospheric model also falls short. We show that dissipative photospheric synchrotron models, on the other hand, are able
to accommodate such high peak values.
- 1208.1812 from 10 Aug 12
Bing Zhang et al.: GRB 110721A: photosphere "death line" and the physical origin of the GRB "Band" function
The prompt emission spectra of gamma-ray bursts (GRBs) usually have a dominant component that is well described by a phenomenological "Band"
function. The physical origin of this spectral component is debated. Although the traditional interpretation is synchrotron radiation of
non-thermal electrons accelerated in internal shocks or magnetic dissipation regions, a growing trend in the community is to interpret this
component as emission from the dissipative photosphere of a GRB fireball. We analyze the time dependent spectrum of GRB 110721A detected by
Fermi GBM and LAT, and pay special attention to the rapid evolution of the peak energy $E_p$. We define a "death line" of baryonic photospheric
emission in the $E_p - L$ plane, and show that $E_p$ of GRB 110721A at the earliest epoch has a very high $E_p \sim 15$ MeV that is beyond the
"death line". This rules out the baryonic photosphere model for the "Band" component for this burst. Together with the finding that an
additional "shoulder" component exists in this burst that is consistent with a photospheric origin, we suggest that at least for some bursts,
the "Band" component must invoke a non-thermal origin (e.g. synchrotron or inverse Compton) in the optically thin region of a GRB outflow. We
also suggest that the rapid "hard-to-soft" spectral evolution is consistent with quick discharge of magnetic energy in a magnetically-dominated
outflow.
- 1208.5287 from 28 Aug 12
Daisuke Yonetoku et al.: Magnetic Structures in Gamma-Ray Burst Jets Probed by Gamma-Ray Polarization
We report polarization measurements in two prompt emissions of gamma-ray bursts, GRB 110301A and GRB 110721A, observed with the Gamma-ray burst
polarimeter (GAP) aboard IKAROS solar sail mission. We detected linear polarization signals from each burst with polarization degree of $\Pi =
70 \pm 22$% with statistical significance of $3.7 \sigma$ for GRB 110301A, and $\Pi = 84^{+16}_{-28}$% with $3.3 \sigma$ confidence level for
GRB 110721A. We did not detect any significant change of polarization angle. These two events had shorter durations and dimmer brightness
compared with GRB 100826A, which showed a significant change of polarization angle, as reported in Yonetoku et al. (2011). Synchrotron emission
model can be consistent with all the data of the three GRBs, while photospheric quasi-thermal emission model is not favorable. We suggest that
magnetic field structures in the emission region are globally-ordered fields advected from the central engine.
- 1305.3611 from 17 May 13
Shabnam Iyyani et al.: Variable jet properties in GRB110721A: Time resolved observations of the jet photosphere
{\it Fermi Gamma-ray Space Telescope} observations of GRB110721A have revealed two emission components from the relativistic jet: emission from
the photosphere, peaking at $\sim 100$ keV and a non-thermal component, which peaks at $\sim 1000$ keV. We use the photospheric component to
calculate the properties of the relativistic outflow. We find a strong evolution in the flow properties: the Lorentz factor decreases with time
during the bursts from $\Gamma \sim 1000$ to $\sim 150$ (assuming a redshift $z=2$; the values are only weakly dependent on unknown efficiency
parameters). Such a decrease is contrary to the expectations from the internal shocks and the isolated magnetar birth models. Moreover, the
position of the flow nozzle measured from the central engine, $r_0$, increases by more than two orders of magnitude. Assuming a moderately
magnetised outflow we estimate that $r_0$ varies from $10^6$ cm to $\sim 10^9$ cm during the burst. We suggest that the maximal value reflects
the size of the progenitor core. Finally, we show that these jet properties naturally explain the observed broken power-law decay of the
temperature which has been reported as a characteristic for GRB pulses.
- 1409.3584 from 15 Sep 14
He Gao et al.: Photosphere emission from a hybrid relativistic outflow with arbitrary dimensionless entropy and magnetization in GRBs
Recent broad-band observations of GRBs with the Fermi satellite call for a "hybrid" central engine, with both a hot "fireball" component and a
cold "Poynting flux" component. We develop a theory of photosphere emission from such a hybrid relativistic outflow with an arbitrary
dimensionless entropy $\eta$ and magnetization $\sigma_0$ at the central engine. We develop two approaches: a "bottom-up" approach to predict
the temperature and luminosity of the photosphere emission and its relative brightness with respect to the non-thermal emission component from
an optically thin region; and a "top-down" approach to diagnose central engine parameters based on the observed photosphere emission
properties. For both approaches, we consider two possibilities: one is that the Poynting flux does not suffer significant dissipation beneath
the photosphere, while the other is that there is such dissipation. From our bottom-up approach, we show that a variety of observed GRB prompt
emission spectra with different degrees of photosphere emission can be reproduced. In order to reproduce the observed spectra, the outflows of
most GRBs need to have a significant $\sigma$, both at the central engine, and at the photosphere. The $\sigma$ value at $10^{15}$ cm from the
central engine is usually also greater than unity, so that internal-collision-induced magnetic reconnection and turbulence (ICMART) may be the
mechanism to power the non-thermal emission. We apply our top-down approach to the time-resolved spectral data of GRB 110721A, and find that
the temporal behavior of the blackbody component in its time-resolved spectrum can be well interpreted with a time-varying $(\eta,\sigma_0)$ at
the central engine, instead of invoking a varying engine base size $r_0$. (abridged)
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