AA(School
of Astronomy and Space Science, Nanjing University, Nanjing 210093,
China; Key Laboratory of Modern Astronomy and Astrophysics (Nanjing
University), Ministry of Education, Nanjing 210093, China), AB(School of
Astronomy and Space Science, Nanjing University, Nanjing 210093, China;
Key Laboratory of Modern Astronomy and Astrophysics (Nanjing
University), Ministry of Education, Nanjing 210093, China)
Publication:
Nature Physics, Volume 9, Issue 8, pp. 465-467 (2013).
X-ray flares detected in nearly half of gamma-ray-burst (GRB) afterglows
are one of the most intriguing phenomena in high-energy astrophysics.
All of the observations indicate that the central engines of bursts,
after the gamma-ray emission has ended, still have long periods of
activity, during which energetic explosions eject relativistic
materials, leading to late-time X-ray emission. It is thus expected that
X-ray flares provide important clues as to the nature of the central
engines of GRBs, and more importantly, unveil the physical mechanism of
the flares themselves, which has so far remained mysterious. Here we
report statistical results of X-ray flares of GRBs with known redshifts,
and show that X-ray flares and solar flares share three statistical
properties: power-law frequency distributions for energies, durations
and waiting times. All of the distributions can be well understood
within the physical framework of a self-organized criticality (SOC)
system. The statistical properties of X-ray flares of GRBs are similar
to solar flares, and thus both can be attributed to a SOC process. Both
types of flares may be driven by a magnetic reconnection process, but
X-ray flares of GRBs are produced in ultra-strongly magnetized
millisecond pulsars or long-term hyperaccreting disks around
stellar-mass black holes.
Palmer, D. M.;
Barthelmy, S.; Gehrels, N.; Kippen, R. M.; Cayton, T.; Kouveliotou, C.;
Eichler, D.; Wijers, R. A. M. J.; Woods, P. M.; Granot, J.; and 18 coauthors
A giant γ-ray flare from the magnetar SGR 1806 - 20
Kouveliotou, C.;
Fishman, G. J.; Meegan, C. A.; Paciesas, W. S.; van Paradijs, J.;
Norris, J. P.; Preece, R. D.; Briggs, M. S.; Horack, J. M.;
Pendleton, G. N.; Green, D. A.
The rarity of soft γ-ray repeaters deduced from reactivation of SGR1806 - 20
AA(Department of Astronomy, University of Arizona, 933 N. Cherry Avenue, Tucson, AZ 85721, USA), AB(Sabancı University, Faculty of Engineering and Natural Sciences, Orhanlı- Tuzla, İstanbul 34956, Turkey), AC(Department of Astronomy, University of Arizona, 933 N. Cherry Avenue, Tucson, AZ 85721, USA)
Publication:
Monthly Notices of the Royal Astronomical Society, Volume 418, Issue 4, pp. 2773-2778. (MNRAS Homepage)
The observed upper bound on the spin-down rate of the otherwise typical soft gamma-ray repeater SGR 0418+5729 has challenged the interpretation of this source as a neutron star with ultrastrong magnetic fields. Current limits imply a dipole magnetic field strength of less than 7.5 × 1012G, which is significantly smaller than that of a typical SGR. Independent of the properties inferred from X-ray timing, the X-ray spectra of neutron stars allow a measurement of their magnetic field strengths because they are distorted from pure blackbodies due to the presence of a magnetic field in a radiative equilibrium atmosphere. In this paper, we model high signal-to-noise ratio XMM-Newton spectra of SGR 0418+5729 to place constraints on the strength of the magnetic field at the surface of the neutron star. Our analysis shows that neutron star atmosphere models with moderate magnetic field strengths (1012-13G) cannot fit the X-ray spectra, whereas models with stronger magnetic fields are able to account for the observations. We find that the strength of the magnetic field at the surface is 1.0 × 1014G. This value, although lower than all of the other SGRs analysed to date, is still high enough to generate the observed X-ray bursts from the source. In connection to the spin-down limits, it also implies a significantly non-dipolar structure of the magnetic field. We discuss the results of our spectral modelling and compare them with other SGRs.
Astrophysics - High Energy Astrophysical Phenomena, General Relativity and Quantum Cosmology
Comment:
8 pages, 3 figures. For a repository of data used in the publication, go to: https://dcc.ligo.org/cgi-bin/DocDB/ShowDocument?docid=15166. Also see the announcement for this paper on ligo.org at: http://www.ligo.org/science/Publication-GRB051103/index.php
We present the results of a LIGO search for gravitational waves (GWs) associated with GRB 051103, a short-duration hard-spectrum gamma-ray burst (GRB) whose electromagnetically determined sky position is coincident with the spiral galaxy M81, which is 3.6 Mpc from Earth. Possible progenitors for short-hard GRBs include compact object mergers and soft gamma repeater (SGR) giant flares. A merger progenitor would produce a characteristic GW signal that should be detectable at the distance of M81, while GW emission from an SGR is not expected to be detectable at that distance. We found no evidence of a GW signal associated with GRB 051103. Assuming weakly beamed gamma-ray emission with a jet semi-angle of 30 deg we exclude a binary neutron star merger in M81 as the progenitor with a confidence of 98%. Neutron star-black hole mergers are excluded with > 99% confidence. If the event occurred in M81 our findings support the the hypothesis that GRB 051103 was due to an SGR giant flare, making it the most distant extragalactic magnetar observed to date.
