scholarly journals MAGNETOHYDRODYNAMIC EFFECTS IN RELATIVISTIC EJECTA

2010 ◽  
Vol 19 (06) ◽  
pp. 991-996
Author(s):  
YOSUKE MIZUNO ◽  
BING ZHANG ◽  
BRUNO GIACOMAZZO ◽  
KEN-ICHI NISHIKAWA ◽  
PHILIP E. HARDEE ◽  
...  
Keyword(s):  
Rarefaction Wave ◽  
Gamma Ray ◽  
Flux Ratio ◽  
Lorentz Factor ◽  
Magnetic Pressure ◽  
Initial Value ◽  
Reverse Shock ◽  
Thermal Pressure ◽  
Wave Regime ◽  
Forward Shock

We study the problem of deceleration of an arbitrarily magnetized relativistic ejecta in a static unmagnetized medium and its connection to the physics of gamma-ray bursts (GRBs). By computing exact solutions of the Riemann problem describing this scenario, we find that with the same initial Lorentz factor, the reverse shock becomes progressively weaker with increasing magnetization parameter σ (the Poynting-to-kinetic flux ratio). The reverse shock becomes a rarefaction wave when σ exceeds a critical value defined by the balance between magnetic pressure in the ejecta and thermal pressure in the forward shock. In the rarefaction wave regime, the rarefied region is accelerated to a Lorentz factor that is significantly larger than the initial value due to the strong magnetic pressure in the ejecta. We discuss the implications for models of GRBs.

scholarly journals Diverse Features of the Multiwavelength Afterglows of Gamma-Ray Bursts: Natural or Special?

2016 ◽  
Vol 2016 ◽  
pp. 1-10 ◽  
Author(s):  
J. J. Geng ◽  
Y. F. Huang
Keyword(s):  
Black Holes ◽  
Numerical Method ◽  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Shock Model ◽  
Reverse Shock ◽  
X Ray ◽  
Electron Positron ◽  
Forward Shock ◽  
Electron Positron Pair

The detection of optical rebrightenings and X-ray plateaus in the afterglows of gamma-ray bursts (GRBs) challenges the generic external shock model. Recently, we have developed a numerical method to calculate the dynamics of the system consisting of a forward shock and a reverse shock. Here, we briefly review the applications of this method in the afterglow theory. By relating these diverse features to the central engines of GRBs, we find that the steep optical rebrightenings would be caused by the fall-back accretion of black holes, while the shallow optical rebrightenings are the consequence of the injection of the electron-positron-pair wind from the central magnetar. These studies provide useful ways to probe the characteristics of GRB central engines.

scholarly journals The Bright Optical Flash and Afterglow from the Gamma-Ray Burst GRB 130427A

Science ◽  
2013 ◽  
Vol 343 (6166) ◽  
pp. 38-41 ◽  
Author(s):  
W. T. Vestrand ◽  
J. A. Wren ◽  
A. Panaitescu ◽  
P. R. Wozniak ◽  
H. Davis ◽  
...  
Keyword(s):  
Gamma Rays ◽  
Gamma Ray ◽  
Massive Stars ◽  
Close Correlation ◽  
Optical Observations ◽  
X Rays ◽  
Reverse Shock ◽  
Gamma Ray Burst ◽  
Forward Shock ◽  
Gamma Ray Emission

The optical light generated simultaneously with x-rays and gamma rays during a gamma-ray burst (GRB) provides clues about the nature of the explosions that occur as massive stars collapse. We report on the bright optical flash and fading afterglow from powerful burst GRB 130427A. The optical and >100–megaelectron volt (MeV) gamma-ray flux show a close correlation during the first 7000 seconds, which is best explained by reverse shock emission cogenerated in the relativistic burst ejecta as it collides with surrounding material. At later times, optical observations show the emergence of emission generated by a forward shock traversing the circumburst environment. The link between optical afterglow and >100-MeV emission suggests that nearby early peaked afterglows will be the best candidates for studying gamma-ray emission at energies ranging from gigaelectron volts to teraelectron volts.

scholarly journals A New Era of Submillimeter GRB Afterglow Follow-Ups with the Greenland Telescope

2015 ◽  
Vol 2015 ◽  
pp. 1-12 ◽  
Author(s):  
Yuji Urata ◽  
Kuiyun Huang ◽  
Keiichi Asada ◽  
Hiroyuki Hirashita ◽  
Makoto Inoue ◽  
...  
Keyword(s):  
First Generation ◽  
Gamma Ray ◽  
High Redshift ◽  
Greenland Ice Sheet ◽  
Theoretical Models ◽  
Reverse Shock ◽  
New Era ◽  
Forward Shock

Planned rapid submillimeter (submm) gamma-ray-bursts (GRBs) follow-up observations conducted using the Greenland Telescope (GLT) are presented. The GLT is a 12-m submm telescope to be located at the top of the Greenland ice sheet, where the high altitude and dry weather porvide excellent conditions for observations at submm wavelengths. With its combination of wavelength window and rapid responding system, the GLT will explore new insights on GRBs. Summarizing the current achievements of submm GRB follow-ups, we identify the following three scientific goals regarding GRBs: (1) systematic detection of bright submm emissions originating from reverse shock (RS) in the early afterglow phase, (2) characterization of forward shock and RS emissions by capturing their peak flux and frequencies and performing continuous monitoring, and (3) detections of GRBs at a high redshift as a result of the explosion of first generation stars through systematic rapid follow-ups. The light curves and spectra calculated by available theoretical models clearly show that the GLT could play a crucial role in these studies.

scholarly journals Reverse shocks in the relativistic outflows of gravitational wave-detected neutron star binary mergers

2019 ◽  
Vol 489 (2) ◽  
pp. 1820-1827 ◽  
Author(s):  
Gavin P Lamb ◽  
Shiho Kobayashi
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Gravitational Wave ◽  
Strong Magnetic Field ◽  
Gamma Ray ◽  
Reverse Shock ◽  
Central Engine ◽  
Forward Shock ◽  
Binary Mergers ◽  
Star Binary

ABSTRACT The afterglows to gamma-ray bursts (GRBs) are due to synchrotron emission from shocks generated as an ultrarelativistic outflow decelerates. A forward and a reverse shock will form, however, where emission from the forward shock is well studied as a potential counterpart to gravitational wave-detected neutron star mergers the reverse shock has been neglected. Here, we show how the reverse shock contributes to the afterglow from an off-axis and structured outflow. The off-axis reverse shock will appear as a brightening feature in the rising afterglow at radio frequencies. For bursts at ∼100 Mpc, the system should be inclined ≲20° for the reverse shock to be observable at ∼0.1–10 d post-merger. For structured outflows, enhancement of the reverse shock emission by a strong magnetic field within the outflow is required for the emission to dominate the afterglow at early times. Early radio photometry of the afterglow could reveal the presence of a strong magnetic field associated with the central engine.

scholarly journals Linking extended and plateau emissions of short gamma-ray bursts

2020 ◽  
Vol 493 (1) ◽  
pp. 783-791 ◽  
Author(s):  
Tatsuya Matsumoto ◽  
Shigeo S Kimura ◽  
Kohta Murase ◽  
Peter Mészáros
Keyword(s):  
Gamma Ray ◽  
Lorentz Factor ◽  
Gamma Ray Bursts ◽  
Radiation Efficiency ◽  
High Radiation ◽  
Average Value ◽  
Forward Shock ◽  
Compactness Arguments ◽  
Prompt Emission ◽  
Extended Emission

ABSTRACT Some short gamma-ray bursts (SGRBs) show a longer lasting emission phase, called extended emission (EE) lasting ${\sim}10^{2\!-\!3}\, \rm s$, as well as a plateau emission (PE) lasting ${\sim}10^{4\!-\!5}\, \rm s$. Although a long-lasting activity of the central engines is a promising explanation for powering both emissions, their physical origin and their emission mechanisms are still uncertain. In this work, we study the properties of the EEs and their connection with the PEs. First, we constrain the minimal Lorentz factor Γ of the outflows powering EEs, using compactness arguments and find that the outflows should be relativistic, Γ ≳ 10. We propose a consistent scenario for the PEs, where the outflow eventually catches up with the jet responsible for the prompt emission, injecting energy into the forward shock formed by the prior jet, which naturally results in a PE. We also derive the radiation efficiency of EEs and the Lorentz factor of the outflow within our scenario for 10 well-observed SGRBs accompanied by both EE and PE. The efficiency has an average value of ${\sim}3\, {{\ \rm per\ cent}}$ but shows a broad distribution ranging from ∼0.01 to ${\sim}100{{\ \rm per\ cent}}$. The Lorentz factor is ∼20–30, consistent with the compactness arguments. These results suggest that EEs are produced by a slower outflow via more inefficient emission than the faster outflow that causes the prompt emission with a high radiation efficiency.

scholarly journals Coherence scale of magnetic fields generated in early time forward shocks of Gamma Ray Bursts

2021 ◽  
Author(s):  
N Jordana-Mitjans ◽  
C G Mundell ◽  
R J Smith ◽  
C Guidorzi ◽  
M Marongiu ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Early Time ◽  
Host Galaxy ◽  
Optical Polarization ◽  
Reverse Shock ◽  
Intrinsic Polarization ◽  
Temporal Decay ◽  
Forward Shock ◽  
Current Sample ◽  
Low Degrees

Abstract We report the earliest-ever detection of optical polarization from a GRB forward shock (GRB 141220A), measured 129.5 − 204.3 s after the burst using the multi-colour RINGO3 optical polarimeter on the 2-m fully autonomous robotic Liverpool Telescope. The temporal decay gradient of the optical light curves from 86 s to ∼2200 s post-burst is typical of classical forward shocks with α = 1.091 ± 0.008. The low optical polarization $P_{BV} = 2.8 _{- 1.6} ^{+ 2.0} \, \%$ (2σ) at mean time ∼168 s post-burst is compatible with being induced by the host galaxy dust (AV, HG = 0.71 ± 0.15 mag), leaving low polarization intrinsic to the GRB emission itself —as theoretically predicted for forward shocks and consistent with previous detections of low degrees of optical polarization in GRB afterglows observed hours to days after the burst. The current sample of early-time polarization data from forward shocks suggests polarization from (a) the Galactic and host galaxy dust properties (i.e. $P \sim 1\%-3\%$), (b) contribution from a polarized reverse shock (GRB deceleration time, jet magnetization) or (c) forward shock intrinsic polarization (i.e. $P \le 2\%$), which depends on the magnetic field coherence length scale and the size of the observable emitting region (burst energetics, circumburst density).

scholarly journals Radio afterglows of very high-energy gamma-ray bursts 190829A and 180720B

2020 ◽  
Vol 496 (3) ◽  
pp. 3326-3335 ◽  
Author(s):  
L Rhodes ◽  
A J van der Horst ◽  
R Fender ◽  
I M Monageng ◽  
G E Anderson ◽  
...  
Keyword(s):  
Gamma Ray ◽  
High Energy ◽  
The Other ◽  
Host Galaxy ◽  
Reverse Shock ◽  
Forward Shock ◽  
Very High Energy ◽  
Energy Gamma ◽  
Stereoscopic System ◽  
Very High

ABSTRACT We present high-cadence multifrequency radio observations of the long gamma-ray burst (GRB) 190829A, which was detected at photon energies above 100 GeV by the High Energy Stereoscopic System (H.E.S.S.). Observations with the Meer Karoo Array Telescope (MeerKAT, 1.3 GHz) and Arcminute Microkelvin Imager – Large Array (AMI-LA, 15.5 GHz) began one day post-burst and lasted nearly 200 d. We used complementary data from Swift X-Ray Telescope (XRT), which ran to 100 d post-burst. We detected a likely forward shock component with both MeerKAT and XRT up to over 100 d post-burst. Conversely, the AMI-LA light curve appears to be dominated by reverse shock emission until around 70 d post-burst when the afterglow flux drops below the level of the host galaxy. We also present previously unpublished observations of the other H.E.S.S.-detected GRB, GRB 180720B from AMI-LA, which shows likely forward shock emission that fades in less than 10 d. We present a comparison between the radio emission from the three GRBs with detected very high energy (VHE) gamma-ray emission and a sensitivity-limited radio afterglow sample. GRB 190829A has the lowest isotropic radio luminosity of any GRB in our sample, but the distribution of luminosities is otherwise consistent, as expected, with the VHE GRBs being drawn from the same parent distribution as the other radio-detected long GRBs.

scholarly journals An early peak in the radio light curve of short-duration gamma-ray burst 200826A

2021 ◽  
Vol 503 (2) ◽  
pp. 2966-2972
Author(s):  
Lauren Rhodes ◽  
Rob Fender ◽  
David R A Williams ◽  
Kunal Mooley
Keyword(s):  
Light Curve ◽  
Short Duration ◽  
Gamma Ray ◽  
Lorentz Factor ◽  
Opening Angle ◽  
Absorption Frequency ◽  
Gamma Ray Burst ◽  
Early Peak ◽  
Forward Shock ◽  
Radio Band

ABSTRACT We present the results of radio observations from the eMERLIN telescope combined with X-ray data from Swift for the short-duration gamma-ray burst (GRB) 200826A, located at a redshift of 0.71. The radio light curve shows evidence of a sharp rise, a peak around 4–5 d post-burst, followed by a relatively steep decline. We provide two possible interpretations based on the time at which the light curve reached its peak. (1) If the light curve peaks earlier, the peak is produced by the synchrotron self-absorption frequency moving through the radio band, resulting from the forward shock propagating into a wind medium and (2) if the light curve peaks later, the turnover in the light curve is caused by a jet break. In the former case we find a minimum equipartition energy of ∼3 × 1047 erg and bulk Lorentz factor of ∼5, while in the latter case we estimate the jet opening angle of ∼9–16°. Due to the lack of data, it is impossible to determine which is the correct interpretation, however due to its relative simplicity and consistency with other multiwavelength observations which hint at the possibility that GRB 200826A is in fact a long GRB, we prefer the scenario one over scenario two.

scholarly journals Formation of transient high-β plasmas in a magnetized, weakly collisional regime

2021 ◽  
Vol 87 (1) ◽  
Author(s):  
T. Byvank ◽  
D. A. Endrizzi ◽  
C. B. Forest ◽  
S. J. Langendorf ◽  
K. J. McCollam ◽  
...  
Keyword(s):  
Experimental Data ◽  
Magnetic Flux ◽  
Plasma Physics ◽  
System Size ◽  
Magnetic Pressure ◽  
Magnetized Plasma ◽  
Inertial Fusion ◽  
Thermal Pressure ◽  
Astrophysical Objects ◽  
Collisional Regime

We present experimental data providing evidence for the formation of transient ( ${\sim }20\ \mathrm {\mu }\textrm {s}$ ) plasmas that are simultaneously weakly magnetized (i.e. Hall magnetization parameter $\omega \tau > 1$ ) and dominated by thermal pressure (i.e. ratio of thermal-to-magnetic pressure $\beta > 1$ ). Particle collisional mean free paths are an appreciable fraction of the overall system size. These plasmas are formed via the head-on merging of two plasmas launched by magnetized coaxial guns. The ratio $\lambda _{\textrm {gun}}=\mu _0 I_{\textrm {gun}}/\psi _{\textrm {gun}}$ of gun current $I_{\textrm {gun}}$ to applied magnetic flux $\psi _{\textrm {gun}}$ is an experimental knob for exploring the parameter space of $\beta$ and $\omega \tau$ . These experiments were conducted on the Big Red Ball at the Wisconsin Plasma Physics Laboratory. The transient formation of such plasmas can potentially open up new regimes for the laboratory study of weakly collisional, magnetized, high- $\beta$ plasma physics; processes relevant to astrophysical objects and phenomena; and novel magnetized plasma targets for magneto-inertial fusion.

scholarly journals An Accreting Stellar Binary Model for Active Periodic Fast Radio Bursts

2021 ◽  
Vol 922 (2) ◽  
pp. 98
Author(s):  
Can-Min Deng ◽  
Shu-Qing Zhong ◽  
Zi-Gao Dai
Keyword(s):  
Compact Object ◽  
Radio Bursts ◽  
Reverse Shock ◽  
X Ray ◽  
Highly Active ◽  
Surrounding Environment ◽  
Binary Model ◽  
Forward Shock ◽  
Long Lifetime

Abstract In this work, we propose an accreting stellar binary model for understanding the active periodic fast radio bursts (FRBs). The system consists of a stellar compact object (CO) and a donor star (DS) companion in an eccentric orbit, where the DS fills its own Roche lobe near the periastron. The CO accretes the material from the DS and then drives relativistic magnetic blobs. The interaction between the magnetic blobs and the stellar wind of the DS produces a pair of shocks. We find that both the reverse shock and the forward shock are likely to produce FRBs via the synchrotron maser mechanism. We show that this system can in principle sufficiently produce highly active FRBs with a long lifetime, and also can naturally explain the periodicity and the duty cycle of the activity that appeared in FRBs 180916 and 121102. The radio nebula excited by the long-term injection of magnetic blobs into the surrounding environment may account for the associated persistent radio source. In addiction, we discuss the possible multiwavelength counterparts of FRB 180916 in the context of this model. Finally, we encourage the search for FRBs in ultraluminous X-ray sources.

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