Astronomy and Astrophysics – Astrophysics
Scientific paper
Mar 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002phrvd..65f4009m&link_type=abstract
Physical Review D, vol. 65, Issue 6, id. 064009
Astronomy and Astrophysics
Astrophysics
12
Wave Generation And Sources, Black Holes, Gamma-Ray Sources, Gamma-Ray Bursts
Scientific paper
The unusual features of supernova (SN) 1998bw and its apparent association with the gamma-ray burst (GRB) event GRB980425 were highlighted by Kulkarni et al. At its peak SN 1998bw was anomalously superluminous in radio wavelengths with an inferred fluence Eradio>=1049 erg [S. Kulkarni et al., Nature (London) 395, 663 (1998)], while the apparent expansion velocity of its ejecta (~10-5Msolar) suggests a shock wave moving relativistically (Vexp~2c). The unique properties of SN 1998bw strengthen the case for it being linked with GRB980425. I present a consistent, novel mechanism to explain the peculiar event SN 1998bw and similar phenomena in GRBs: Conversion of powerful, high frequency (~2 kHz) gravitational waves (GWs) into electromagnetic waves [M. Johnston, R. Ruffini, and F. Zerilli, Phys. Rev. Lett. 31, 1317 (1973)] might have taken place during SN 1998bw. Yet, conversion of GRB photons into GWs, as advanced by Johnston, Ruffini, and Zerilli [Phys. Lett. 49B, 185 (1974)], may also occur. These processes can produce GRBs depleted in γ rays but enhanced in x rays, for instance, or even more plausibly induce dark GRBs, those with no optical afterglow. The class of GWs needed to drive the calorimetric changes of these gamma-ray bursts may be generated by (a) the nonaxisymmetric dynamics of a torus surrounding the hypernova (or failed supernova) magnetized stellar-mass black hole (BH) remnant, as in van Putten's mechanism for driving long GRBs powered by the BH spin energy [Phys. Rev. Lett. 87, 091101 (2001)], or in the van Putten and Ostriker mechanism to account for the bimodal distribution in duration in GRBs [Astrophys. J. Lett. 552, L32 (2001)], where the torus magnetohydrodynamics may be dominated by either hyperaccretion onto a slowly spinning BH or suspended accretion onto a fast rotating BH, or (b) the just formed black hole with electromagnetic structure as in the GRB central engine mechanism of Ruffini et al. [Astrophys. J. Lett. 555, L107 (2001); 555, L113 (2001)], provided the issue concerning the origin of the black hole charge can be suitably clarified. In both of these mechanisms the total energy radiated as GWs is about ΔEGW~1053 erg×(M/10Msolar), which for the conversion efficiency estimated here turns out to be enough to explain the superluminous radio wavelength emission from SN 1998bw. Thus, I argue this process could have induced the enhancement in the radio luminosity of SN 1998bw as evidenced in its light curve [Fig. 2, in S. Kulkarni et al., Nature (London) 395, 663 (1998)] and optical light curves of GRB980326 [J. Bloom et al., Nature (London) 401, 453 (1998)] and GRB990712 [G. Björnsson et al., Astrophys. J. Lett. 552, L121 (2001)]. Moreover, GW-driven plasma density perturbations moving at the speed of light may up- (or down-) convert fireball photons, which could cause further substantial modifications of the gamma-ray burst or supernova calorimetry.
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