Gamma-ray Burst 130504

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN Circular #14574
D. Kocevski (NASA/GSFC), M. Ohno (Hiroshima U.), J. Racusin (NASA/GSFC), G. Vianello (Stanford), V. Vasileiou (LUPM), and E. Troja (CRESST) report on behalf of the Fermi-LAT team:
At 23:30:15 UT on 04 May 2013, Fermi LAT detected high energy emission from GRB 130504C, which was also detected by Fermi-GBM (trigger 389402940 / 130504979). The GBM detection triggered an autonomous repoint of the spacecraft.
The best LAT on-ground location is found to be RA=91.715, DEC=3.846 (J2000) with an error radius of 0.155 deg (68% containment, statistical error only).
The burst was about 40 deg from the LAT boresight at the time of the trigger and the spacecraft slew brought the source within the LAT field of view for the next 2200 seconds. The data from the Fermi LAT show long lasting emission with >70 photons above 100 MeV observed out to 1000s seconds with a TS of >70. Multi-peaked emission lasting roughly 40 seconds can be seen using the non-standard LAT Low Energy (LLE) with a significance of ~26 sigma. The highest energy LAT photon has an energy of ~5 GeV arriving 251 seconds after the trigger.
A Swift TOO request has been submitted.
A GBM circular is forthcoming.
The Fermi LAT point of contact for this burst is Daniel Kocevski (daniel.kocevski@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.
GCN Circular #14583
J. Michael Burgess (UAH), Valerie Connaughton (UAH) and Shaolin Xiong (UAH) report on behalf of the Fermi GBM Team:
"At 23:28:57.518 UT on 04 May 2013, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 130504C (trigger 389402940 / 130504978).
High peak flux from the GRB caused GBM to issue a repoint request that reoriented the satellite to place the GRB near the LAT boresight for 2.5 hours, subject to Earth limb contraints.
The on-ground calculated location, using the GBM trigger data, is RA = 90.71, DEC = 4.45 (J2000 degrees, equivalent to 06 h 02 m, 4 d 27 '), with an uncertainty of 1.0 degrees (radius, 1-sigma containment, statistical only; there is additionally a systematic error which is currently estimated to be 2 to 3 degrees). This location is consistent with the LAT location. The angle from the Fermi LAT boresight is 47 degrees.
This burst was also independently detected by INTEGRAL SPI-ACS.
The GBM light curve consists of about 5 peaks associated with the GRB and 1 peak associated with a solar flare about 100 seconds prior to T0. The duration (T90) of the GRB is about 74 s (50-300 keV). The time-averaged spectrum from T0-2.0 s to T0+120.0 s is adequately fit by a Band function with Epeak = 637 +/- 34 keV, alpha = -1.23 +/- 0.01, and beta = -2.28 +/- 0.08
The event fluence (10-1000 keV) in this time interval is (1.34 +/- 0.01)E-04 erg/cm^2. The 1-sec peak photon flux measured starting from T0+30.8 s in the 10-1000 keV band is 43 +/- 0.5 ph/s/cm^2.
The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."
GCN Circular #14584
P. D'Avanzo, A. Melandri (INAF-OAB) report on behalf of the Swift team:
We have analysed 1.3 ks of Swift-XRT data for the Fermi 130504C (Kocevski GCN Circ. 14574; Burgess et al. GCN Circ. 14583), from 65.6 ks to 70.1 ks after the LAT trigger. The data are all in Photon Counting (PC) mode.
We detect an uncatalogued X-ray source inside the LAT error circle (Kocevski GCN Circ. 14574), at the following position: RA, Dec=91.63047, 3.83388 which is equivalent to:
```
RA (J2000): 06 06 31.3
Dec (J2000): +03 50 01.96
```
with an uncertainty of 4.8 arcsec (radius, 90% confidence). The count rate at this position is (4.4 +/- 0.7) x 10^-2 cts/s. At the present stage, it is not possible to determine whether the source is fading.
GCN Circular #14587
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 long-duration intense GRB 130504C (Fermi-LAT detection: Kocevski et al., GCN 14574; Fermi-GBM detection: Burgess et al., GCN 14583) triggered Konus-Wind at T0=3D84544.491s UT (23:29:04.491)
The light curve shows multiple partly overlapped peaks from ~T0-15 s to ~T0+105s. The emission is seen up to 12 MeV.
A possible hard precursor is seen in the 360-1400 keV light curve at ~T0-50s, but its attribution to GRB 130504C is yet unclear.
The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB130504_T84544/
As observed by Konus-Wind, the burst had a fluence of (2.0 =B1 0.1)x10-4 erg/cm2, and a 64-ms peak flux, measured from T0+21.440s, of (2.6 =B1 0.2)x10-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range).
The time-integrated spectrum (measured from T0 to T0+105.216 s) is best fit in the 20 keV - 15 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha =3D -1.32 =B1 0.04, the high energy photon index beta =3D -2.15 =B1 0.1, the peak energy Ep =3D 452 =B1 49 keV, chi2 =3D 110/97 dof.
The spectrum at the maximum count rate (measured from T0+21.248 to T0+23.296 s) is best fit in the 20 keV - 15 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha =3D -0.74 =B1 0.12, the high energy photon index beta =3D -1.93 =B1 0.06, the peak energy Ep =3D 251 =B1 38 keV, chi2 =3D 61/66 dof.
All the quoted results are preliminary.
GCN Circular #14588
P. D'Avanzo, A. Melandri (INAF-OAB), P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team:
We have analysed 7.7 ks of XRT data for the Fermi-LAT-detected burst: GRB 130504C, from 65.6 ks to 93.3 ks after the Fermi-LAT trigger. The data are entirely in Photon Counting (PC) mode. The X-ray source reported by D'Avanzo et al. (GCN Circ. 14584) displays behaviour consistent with fading. We propose it as the X-ray afterglow of GRB 130504C.
The refined XRT position is RA, Dec = 91.63038, +3.8339 which is equivalent to:
```
RA (J2000): 06 06 31.29
Dec(J2000): +03 50 02.0
```
with an uncertainty of 3.6 arcsec (radius, 90% confidence).
The light curve can be modelled with a power-law decay with a decay index of alpha=1.3 (+/-1.0).
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.8 (+/-0.3). The best-fitting absorption column is 5.1 (+2.0, -1.6) x 10^21 cm^-2, in excess of the Galactic value of 2.5 x 10^21 cm^-2 (Kalberla et al. 2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 5.0 x 10^-11 (7.9 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Total column:             5.1 (+2.0, -1.6) x 10^21 cm^-2
Galactic foreground: 2.5 x 10^21 cm^-2
Excess significance: 2.7 sigma
Photon index:             1.8 (+/-0.3)
```
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00020267.
This circular is an official product of the Swift-XRT team.
GCN Circular #14601
T. Yasuda, M. Tashiro, Y. Terada, Y. Ishida, H. Ueno, S. Sugimoto (Saitama U.), M. Ohno, K. Takaki, T. Kawano, R. Nakamura, S. Furui, Y. Fukazawa (Hiroshima U.), M. Yamauchi, N. Ohmori, M. Akiyama (Univ. of Miyazaki), K. Yamaoka (Nagoya U.), S. Sugita (Ehime U.), Y. E. Nakagawa, M. Kokubun, T. Takahashi (ISAS/JAXA), W. Iwakiri (RIKEN), Y. Hanabata (ICRR), Y. Urata (NCU), K. Nakazawa, K. Makishima (Univ. of Tokyo) on behalf of the Suzaku WAM team, report:
The bright, long GRB 130504C (GCN 14574; Fermi-LAT detection : Kocevski et al.) triggered the Suzaku Wide-band All-sky Monitor (WAM) which covers an energy range of 50 keV - 5 MeV at 23:29:00.540 UT (=T0).
The observed light curve shows a multi-peaked structure starting at T0-9 s, ending at T0+110 s with a duration (T90) of about 67 seconds. The fluence in 100 - 1000 keV was 9.11 (+0.14/-0.51) x10^-5 erg/cm^2. The 1-s peak flux measured from T0+ 27 s was 15.9 (+0.3/-4.0) photons/cm^2/s in the same energy range.
Preliminary result shows that the time-averaged spectrum from T0-9 s to T0+110 s is well fitted by a GRB Band model as follows. the low-energy photon index alpha: -1.59 (+0.17/-0.12), the high-energy photon index beta: -2.43 (+0.17/-0.33), and the peak energy Epeak: 845 (+227/-159) keV (chi^2/d.o.f = 77.0/50).
Due to the brightness of this burst, a 1% systematic error was added for low energy channels. All the quoted errors are at statistical 90% confidence level.
The light curves for this burst are available at: http://www.astro.isas.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/trig/grb_table.html
GCN Circular #14603
P. D'Avanzo (INAF-OAB), A.Y. Lien (NASA-GSFC), P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team:
We have analysed 12.3 ks of XRT data for the Fermi-LAT-detected burst GRB 130504C (Kocevski et al. GCn Circ 14574), from 65.6 ks to 278.7 ks after the Fermi-LAT trigger. The data are entirely in Photon Counting (PC) mode. The X-ray source reported by D'Avanzo et al. (GCN Circ. 14584, 14588) displays a fading behaviour.
The overall light curve can be modelled with a power-law decay with a decay index of alpha=1.39 (+0.32, -0.25).
We confirm it as the X-ray afterglow of GRB 130504C.
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00020267.

Back to JG's homepage

Jochen Greiner, last update: 08-May-2013 [Disclaimer]