Synchrotron Self-inverse Compton Radiation From Reverse-shock on GRB120326A

Abstract

We present multi-wavelength observations of a typical long duration GRB 120326A at $z=1.798$, including rapid observations using a submillimeter array (SMA), and a comprehensive monitoring in X-ray and optical. The SMA observation provided the fastest detection to date among seven submillimeter afterglows at 230 GHz. The prompt spectral analysis, using Swift and Suzaku yielded a spectral peak energy of $E_{\mathrm{peak}}^{\mathrm{src}}=107.8_{-15.3}^{+15.3}$ keV and equivalent isotropic energy of $E_{\mathrm{iso}}$ as $3.18_{-0.32}^{+0.40}\times 10^{52}$ erg. The temporal evolution and spectral properties in the optical were consistent with the standard forward shock synchrotron with jet collimation ($6^{\circ }.69\pm 0^{\circ }.16$). The forward shock modeling using a 2D relativistic hydrodynamic jet simulation also determined the reasonable burst explosion and the synchrotron radiation parameters for the optical afterglow. The X-ray light curve showed no apparent jet break and the temporal decay index relation between the X-ray and optical ($\alpha \mathrm{o}-{\alpha }_X=-1.45\pm 0.10$) indicated different radiation processes in the X-ray and optical. Introducing synchrotron self-inverse Compton radiation from reverse shock is a possible solution, and the detection and the slow decay of the afterglow in submillimeter supports that this is a plausible idea. The observed temporal evolution and spectral properties as well as forward shock modeling parameters, enabled to determine reasonable functions to describe the afterglow properties. Because half of events share similar properties in the X-ray and optical to the current event, GRB120326A will be a benchmarks with further rapid follow-ups, using submillimeter instruments such as SMA and ALMA.

25 pages, 7 figures, 2 tables, accepted for publication in ApJ

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• The Needle in the 100 deg2 Haystack: Uncovering Afterglows of Fermi GRBs with the Palomar Transient Factory
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• The Arcminute Microkelvin Imager Catalogue of Gamma-ray Burst afterglows at 15.7 GHz
• The nature of the late achromatic bump in GRB 120326A
• Hard X-ray Spectral Investigations of Gamma-ray Bursts, 120521C and 130606A, at High-redshift z~6
• Sub-MeV Band Observation of a Hard Burst from AXP 1E 1547.0-5408 with the Suzaku Wide-band All-sky Monitor
• ALMA and RATIR observations of GRB131030A