Gamma-ray Burst 140928A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

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Results of Observations

GCN Circular #16847
R. Desiante (Udine University & INFN Trieste), E. Bissaldi (University & INFN Trieste), D. Kocevski (NASA/GSFC), J. L. Racusin (NASA/GSFC), F. Longo (University & INFN Trieste) and M. Arimoto (Tokyo Tech) report on behalf of the Fermi-LAT team:
At 10:29:53.55 on September 28, 2014, Fermi-GBM (trigger 433592996/140928437) triggered on GRB 140928A, which entered the Fermi-LAT field of view at T0+1550 s, and was observed until T0+3200 s, during which the LAT detected high-energy emission.
The best LAT on-ground location is found to be:
RA, Dec = 43.81 , -56.08 (J2000)
with an error radius of 0.16 deg (90% containment, statistical error only). This was 110 deg from the LAT boresight at the time of the trigger.
The data from the Fermi-LAT show a significant increase in the event rate at a position consistent with the GBM localization.
More than 20 photons above 100 MeV are observed from 1550 s (when the GRB entered the LAT FOV) to 3200s (when the spacecraft entered the SAA) after the GBM trigger.
The highest-energy photon is a 35 GeV event which is observed 3100 seconds after the GBM trigger.
A Swift ToO has been approved for this burst.
The Fermi-LAT point of contact for this burst is Makoto Arimoto (arimoto@hp.phys.titech.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.
GCN Circular #16848
C. Pagani, K. L. Page and P. A. Evans (U. Leicester) report on behalf of the Swift-XRT team:
We have analysed 2.5 ks of XRT data for the Fermi/LAT-detected burst: GRB 140928A (Desiante et al., GCN Circ. 16847) from 40.7 ks to 52.7 ks after the Fermi/LAT trigger. The data are entirely in Photon Counting (PC) mode. An X-ray source is detected within the Fermi/LAT error circle. Using 2472 s of PC mode data and 2 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 43.69878, -55.92883 which is equivalent to:
```
RA (J2000): 02h 54m 47.71s
Dec(J2000): -55d 55' 43.8"
```
with an uncertainty of 1.5 arcsec (radius, 90% confidence). This position is 588 arcsec from the Fermi/LAT position. The light curve is consistent with a constant source of mean count rate 1.9e-01 ct/sec.
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.83 (+0.26, -0.24). The best-fitting absorption column is 2.4 (+1.0, -0.9) x 10^21 cm^-2, in excess of the Galactic value of 1.6 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.3 x 10^-11 (4.4 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Total column:	     2.4 (+1.0, -0.9) x 10^21 cm^-2
Galactic foreground: 1.6 x 10^20 cm^-2
Excess significance: 4.2 sigma
Photon index:	     1.83 (+0.26, -0.24)
```
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00020418.
This circular is an official product of the Swift-XRT team.
GCN Circular #16849
K. Varela (MPE Garching), D. A. Kann, S. Klose (both TLS Tautenburg), and J. Greiner (MPE Garching) report on behalf of the GROND team:
We observed the field of the Fermi LAT-detected GRB 140928A (Fermi GBM trigger 433592996; Desiante et al., GCN #16847) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2m MPG telescope at ESO La Silla Observatory (Chile).
Observations started at 08:43.51 UT on 2014-09-29, 22.23 hrs after the GRB trigger. They were performed at an average seeing of 1".5 and at an average airmass of 1.2.
We detect a source inside the enhanced 1".5 Swift-XRT error circle (Pagani et al., GCN #16848), at
```
RA  (J2000.0) =  02:54:47.72
DEC (J2000.0) = -55:55:44.0
```
with an uncertainty of 0".5 in each coordinate.
Based on total exposures of 460 s in g'r'i'z' and 480 s in JHK, we measure the following preliminary magnitudes and upper limits (AB magnitude system):
```
g' = 21.3 +/- 0.1,
r' = 20.8 +/- 0.1,
i' = 20.7 +/- 0.1,
z' = 20.4 +/- 0.1,
J  = 20.2 +/- 0.2,
H  = 20.1 +/- 0.2, and
K  > 18.8.
```
We propose this source to be the optical/NIR afterglow of GRB 140928A. At present we cannot decide if the source is fading.
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) = 0.01 mag in the direction of the burst (Schlegel et al. 1998).
GCN Circular #16850
A. von Kienlin (MPE) and C. Meegan (UAH) report on behalf of the Fermi GBM Team:
"At 10:29:53.55 UT on 28 September 2014, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 140928A (trigger 433592996 / 140928437) which was also detected by Fermi/LAT (Desiante et al. 2014, GCN 16847) and Swift (Pagani et al. 2014, GCN 16848). The GBM on-ground location is consistent with the LAT/Swift position.
The angle from the Fermi LAT boresight is 110 degrees.
This burst was also independently detected by INTEGRAL SPI-ACS.
The GBM light curve shows a structured pulse with a duration (T90) of about 14 s (50-300 keV). The time-averaged spectrum from T0-3.072 s to T0+8.192 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.12 +/- 0.13 and the cutoff energy, parameterized as Epeak, is 732 +/- 72 keV.
The event fluence (10-1000 keV) in this time interval is 1.02 +/- 0.04)E-05 erg/cm^2. The 1.024-sec peak photon flux measured starting from T0+5.12 s in the 10-1000 keV band is 4.8 +/- 0.3 ph/s/cm^2.
A Band function fits the spectrum equally well with Epeak= 671 +/- 82 keV, alpha = -0.05 (+0.16/-0.13) and beta = -2.6 (+0.3/-0.4).
The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."
GCN Circular #16851
D. Kopac (LJMU), C. Guidorzi (U. Ferrara), C. Mundell (LJMU), on behalf of a large collaboration report:
Using the Las Cumbres Observatory Global Telescope Network (LCOGTN) 1-m telescope in Cerro Tololo (Chile), we began observing Fermi GRB 140928A, which was detected also by the Fermi/LAT (Desiante et al., GCN 16847). Optical observations in r' and i' filters (5 x 120s sequences) started on September 29 at 05:16:17 UT, i.e. ~18.8 hours after the Fermi/GBM trigger.
At the position consistent with the XRT position (Pagani et al., GCN 16848) and with the GROND position (Varela et al., GCN 16849) we detect an un-catalogued source with a preliminary magnitude of R = 20.1 +/- 0.2 at t_mid = 18.9 hours since the Fermi/GBM trigger time. The magnitude is calibrated against nearby USNO-B1 stars.
GCN Circular #16852
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. S. Briggs, C. Meegan, and V. Pelassa, on behalf of the Fermi GBM team,
S. Barthelmy, J. Cummings, N. Gehrels, H. Krimm, and D. Palmer, on behalf of the Swift-BAT team, and
A. von Kienlin, X. Zhang, A. Rau, V. Savchenko, E. Bozzo, and C. Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team, report:
The long-duration GRB 140928A (Desiante et al., GCN Circ. 16847) has been observed by Fermi (GRB trigger 433592996; von Kienlin et al., GCN Circ. 16850), Konus-Wind, INTEGRAL (SPI-ACS), MESSENGER (GRNS), and Swift (BAT), so far, at about 37794 s UT (10:29:54). The burst was outside the coded field of view of the BAT.
We have triangulated it to a Konus-GBM annulus centered at RA(2000)=14.055 deg (00h 56m 13s) Dec(2000)=+2.376 deg (+2d 22' 33"), whose radius is 63.085 +/- 0.902 deg (3 sigma) and to a Konus-MESSENGER annulus centered at RA(2000)=26.945 deg (01h 47m 47s) Dec(2000)=+14.819 deg (+14d 49' 08"), whose radius is 72.142 +/- 0.121 deg (3 sigma).
The Swift (XRT) source (Pagani et al., GCN Circ. 16848) is inside the annuli, at the distance between the source and the central line of the Konus-MESSENGER annulus of 17 arcsec.
A triangulation map is posted at http://www.ioffe.ru/LEA/GRBs/GRB140928_T37793/IPN/
The Konus-Wind time history and spectrum will be given in a forthcoming GCN Circular.
GCN Circular #16853
C. Guidorzi (U. Ferrara), D. Kopac, C. Mundell (LJMU), S. Dichiara (U. Ferrara) on behalf of a large collaboration report:
Using the Las Cumbres Observatory Global Telescope Network (LCOGTN) 1-m telescope in Cerro Tololo (Chile), we re-observed Fermi GRB 140928A (Desiante et al., GCN 16847; von Kienlin and Meegan GCN 16850) in the r' filter starting on September 30, 07:14:36 UT, i.e. ~1.86 days after the Fermi trigger time.
The optical afterglow (Varela et al., GCN 16849; Kopac et al. GCN 16851) is still clearly detected with R = 21.2 +/- 0.1 mag at a mid time of 1.88 days post burst (total exposure of 1680 s). The magnitude is calibrated against nearby USNO-B1 stars.
A comparison with our previous report (Kopac et al.) suggests an average power-law decay index alpha = 1.2 +- 0.2.
GCN Circular #16854
S. Golenetskii, R.Aptekar, D. Frederiks, V. Pal'shin, P. Oleynik, M. Ulanov, D. Svinkin, A. Tsvetkova, A. Lysenko, and T. Cline on behalf of the Konus-Wind team, report:
The long-duration, intense GRB 140928A (Fermi-LAT detection: Desiante et al., GCN 16847; Fermi-GBM detection: von Kienlin and Meegan, GCN 16850; IPN triangulation: Hurley et al., GCN 16852) triggered Konus-Wind at T0=37793.602 s UT (10:29:53.602).
The burst light curve shows two emission episodes with a total duration of ~69 s. The first emission episode lasts from ~T0-6 s to ~T0+15 s and the second episode lasts from ~T0+42 s to ~T0+63 s (Fermi-GBM missed the second episode probably due to the Earth occultation). The IPN data confirm the second episode belongs to the same GRB. The emission is seen up to ~15 MeV.
As observed by Konus-Wind, the burst had a fluence of 8.6(-1.4,+1.3)x10^-5 erg/cm2, and a 64-ms peak energy flux, measured from T0+9.248 s, of 1.7(-0.3,+0.3)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+57.856 s) is best fit in the 20 keV - 10 MeV range by a GRB (Band) model with the following parameters: the low-energy photon index alpha = -1.17(-0.09,+0.12), the high energy photon index beta = -2.09(-0.32,+0.16), the peak energy Ep = 304(-66,+80) keV, chi2 = 73/84 dof.
The spectrum near the peak count rate (measured from T0+6.912 to T0+16.896 s) is best fit in the 20 keV - 15 MeV range by a GRB (Band) model with the following parameters: the low-energy photon index alpha = -1.11(-0.08,+0.09), the high energy photon index beta = -2.27(-0.34,+0.17), the peak energy Ep = 318(-46,+59) keV, chi2 = 84/93 dof.
The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB140928_T37793/
All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.
GCN Circular #16856
A. Cucchiara, S. B. Cenko (NASA-GSFC), D.A.Perley (Caltech), report on behalf of a larger collaboration:
"On September 30.18 UT (1.75 days after the burst) we observed the field of the Fermi/LAT GRB 140928A (Desiante et al. GCN 16847, Varela et al. GCN 16849) with the Gemini-South telescope equipped with the GMOS spectrograph. We obtain 2x1200s exposure under non optimal conditions (1.5-2 arcseconds seeing) with the R400 grating, covering the 6000-10000 Angstrom wavelength range.
We detect a featureless continuum down to 6000A, no features are detected neither in emission nor in absorption.
We thank Cristiano Guidorzi for providing a finding chart and the Gemini staff for carry out this observations."
GCN Circular #16864
M. Morii, M. Serino (RIKEN), M. Nakajima, H. Negoro (Nihon U.), S. Nakahira, S. Ueno, H. Tomida, M. Kimura, M. Ishikawa, Y. E. Nakagawa (JAXA), T. Mihara, M. Sugizaki, J. Sugimoto, T. Takagi, A. Yoshikawa, M. Matsuoka (RIKEN), N. Kawai, T. Yoshii, Y. Tachibana (Tokyo Tech), A. Yoshida, T. Sakamoto, Y. Kawakubo, H. Ohtsuki (AGU), H. Tsunemi, D. Uchida (Osaka U.), K. Fukushima, T. Onodera, K. Suzuki, T. Namba, M. Fujita, F. Honda (Nihon U.), Y. Ueda, M. Shidatsu, T. Kawamuro, T. Hori (Kyoto U.), Y. Tsuboi, A. Kawagoe (Chuo U.), M. Yamauchi, Y. Morooka (Miyazaki U.), K. Yamaoka (Nagoya U.) report on behalf of the MAXI team:
MAXI/GSC observed the field of GRB 140928A at a scan transit centered at 2014-09-28 10:41:09 UT with a triangular response of 123-s duration. This center time is 675 sec after the Fermi/GBM trigger time (2014-09-28 10:29:53.55 UT, GCN #16850). The source was located on the edge of the FoV where the source PSF was only partially covered in the sensitive region of the GSC. We therefore estimated the flux using PSF fitting of the photon image. We marginally detected the afterglow of this GRB with 29 +17/-14 mCrab (4-10 keV) and 13 +11/-8 mCrab (2-4 keV) (1 sigma errors). Here, we assumed the source constancy during the scan transit. We did not detect this source at the previous scan (centered at 09:08:25 UT) and the following scan (centered at 12:13:46 UT), with upper limits of 14 mCrab and 35 mCrab (90% C.L., 4-10 keV), respectively.
GCN Circular #16876
C. Pagani (U. Leicester) reports on behalf of the Swift team:
A second epoch of XRT data was collected on the field of the Fermi/LAT-detected burst: GRB 140928A (Desiante et al., GCN Circ. 16847) from 271 ks to 296 ks after the Swift/BAT trigger.
The X-ray source reported in GCN Circ. 16848, Pagani et al., coincident with the optical source reported in GCN Circ. 16849, Varela et al., GCN Circ. 16851, Kopac et al., and GCN Circ. 16856, Cucchiara et al., measured during the first epoch of XRT observations at a mean count rate of 1.9 x 10^-1 count s^-1 has now faded to a mean count rate of 9.5 x 10^-3 count s^-1 (0.3-10 keV). We therefore confirm that this is the X-ray afterglow of GRB 140928A.
This circular is an official product of the Swift-XRT team.

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Jochen Greiner, last update: 18-Oct-2014 [Disclaimer]