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 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 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 Multiwavelength observations of GRB afterglows

2011 ◽  
Vol 7 (S279) ◽  
pp. 58-66
Author(s):  
Alberto J. Castro-Tirado
Keyword(s):  
Gamma Ray ◽  
Early Time ◽  
Global Networks ◽  
Gamma Ray Burst ◽  
French Alps ◽  
Physical Mechanisms ◽  
Forward Shock ◽  
Robotic Telescopes ◽  
Emission Phase ◽  
Multiwavelength Observations

AbstractMultiwavelength observations of gamma-ray burst afterglows are presented, in particular those in the optical and millimetre wavelengths. I will focus on the observations mostly carried out at Spanish ground-based observatories (mainly the 10.4m GTC) and at the Plateau de Bure Interferometer in the French Alps. The importance of global networks of robotic telescopes (like BOOTES, established worldwide) for early time observations in order to put constraints on the physical mechanisms of the GRB early time emission phase is also discussed. The overall observational efforts provide additional clues for a better understanding of the reverse and forward shock. Finally I will report on the Lomonosov/UFFO-p capabilities taking into account its launch in 2012.

scholarly journals A multiwavelength analysis of a collection of short-duration GRBs observed between 2012 and 2015

2019 ◽  
Vol 485 (4) ◽  
pp. 5294-5318 ◽  
Author(s):  
S B Pandey ◽  
Y Hu ◽  
Ao J Castro-Tirado ◽  
A S Pozanenko ◽  
R Sánchez-Ramírez ◽  
...  
Keyword(s):  
Short Duration ◽  
Gamma Ray ◽  
High Energy ◽  
Photometric Data ◽  
Host Galaxy ◽  
Late Time ◽  
Time Data ◽  
Emission Data ◽  
Temporal Decay ◽  
Prompt Emission

Abstract We investigate the prompt emission and the afterglow properties of short-duration gamma-ray burst (sGRB) 130603B and another eight sGRB events during 2012–2015, observed by several multiwavelength facilities including the Gran Canarias Telescope 10.4 m telescope. Prompt emission high energy data of the events were obtained by INTEGRAL-SPI-ACS, Swift-BAT, and Fermi-GBM satellites. The prompt emission data by INTEGRAL in the energy range of 0.1–10 MeV for sGRB 130603B, sGRB 140606A, sGRB 140930B, sGRB 141212A, and sGRB 151228A do not show any signature of the extended emission or precursor activity and their spectral and temporal properties are similar to those seen in case of other short bursts. For sGRB 130603B, our new afterglow photometric data constrain the pre-jet-break temporal decay due to denser temporal coverage. For sGRB 130603B, the afterglow light curve, containing both our new and previously published photometric data is broadly consistent with the ISM afterglow model. Modeling of the host galaxies of sGRB 130603B and sGRB 141212A using the LePHARE software supports a scenario in which the environment of the burst is undergoing moderate star formation activity. From the inclusion of our late-time data for eight other sGRBs we are able to: place tight constraints on the non-detection of the afterglow, host galaxy, or any underlying ‘kilonova’ emission. Our late-time afterglow observations of the sGRB 170817A/GW170817 are also discussed and compared with the sub-set of sGRBs.

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 Rapid-response radio observations of short GRB 181123B with the Australia Telescope Compact Array

2021 ◽  
Author(s):  
G E Anderson ◽  
M E Bell ◽  
J Stevens ◽  
M D Aksulu ◽  
J C A Miller-Jones ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Early Time ◽  
Rapid Response ◽  
Radio Flux ◽  
Radio Observations ◽  
Forward Shock ◽  
Radio Band ◽  
Short Grbs ◽  
Compact Array

Abstract We introduce the Australia Telescope Compact Array (ATCA) rapid-response mode by presenting the first successful trigger on the short-duration gamma-ray burst (GRB) 181123B. Early-time radio observations of short GRBs may provide vital insights into the radio afterglow properties of Advanced LIGO- and Virgo-detected gravitational wave events, which will in turn inform follow-up strategies to search for counterparts within their large positional uncertainties. The ATCA was on target within 12.6 hr post-burst, when the source had risen above the horizon. While no radio afterglow was detected during the 8.3 hr observation, we obtained force-fitted flux densities of 7 ± 12 and 15 ± 11μJy at 5.5 and 9 GHz, respectively. Afterglow modelling of GRB 181123B showed that the addition of the ATCA force-fitted radio flux densities to the Swift X-ray Telescope detections provided more stringent constraints on the fraction of thermal energy in the electrons (log $\epsilon _e = -0.75^{+0.39}_{-0.40}$ rather than log $\epsilon _e = -1.13^{+0.82}_{-1.2}$ derived without the inclusion of the ATCA values), which is consistent with the range of typical εe derived from GRB afterglow modelling. This allowed us to predict that the forward shock may have peaked in the radio band ∼10 days post-burst, producing detectable radio emission ≳ 3 − 4 days post-burst. Overall, we demonstrate the potential for extremely rapid radio follow-up of transients and the importance of triggered radio observations for constraining GRB blast wave properties, regardless of whether there is a detection, via the inclusion of force-fitted radio flux densities in afterglow modelling efforts.

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 The strange case of SN 2011ja and its host

2013 ◽  
Vol 9 (S296) ◽  
pp. 342-343
Author(s):  
Sayan Chakraborti ◽  
Alak Ray ◽  
Randall Smith ◽  
Stuart Ryder ◽  
Naveen Yadav ◽  
...  
Keyword(s):  
Compton Scattering ◽  
Power Law ◽  
Density Profile ◽  
Thermal Plasma ◽  
Host Galaxy ◽  
Reverse Shock ◽  
X Ray ◽  
Inverse Compton Scattering ◽  
Inverse Compton ◽  
Forward Shock

AbstractSN 2001ja was observed twice in three months using the Chandra X-Ray Observatory. The X-ray flux could be due to interaction with the circumstellar medium, perhaps dominated by the reverse shock heated thermal plasma, or from inverse Compton scattering at the forward shock. In both cases, for a steady wind-like circumstellar density profile, the X-ray flux is expected to fall off as a power law or faster. But the flux from the position of SN 2011ja, increased by a factor of three between these observations. In this presentation, we investigated possible reasons, including contamination from other astrophysical sources such as a X-Ray Binary, within the Chandra's resolution, in the host galaxy using our observations, modelling and pre-explosion Chandra/XMM data.

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