COASTING EXTERNAL SHOCK IN WIND MEDIUM: AN ORIGIN FOR THE X-RAY PLATEAU DECAY COMPONENT IN<i>SWIFT</i>GAMMA-RAY BURST AFTERGLOWS

Shen, Rong-Feng; Matzner, Christopher D.

doi:10.1088/0004-637x/744/1/36

Cited by 24 publications

(31 citation statements)

References 92 publications

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“…Moreover, the optical and X‐ray emissions during the shallow‐decay phase have different temporal indices, which could be a result of the emissions of the forward and reverse shocks of a relativistic wind bubble around the central engine (Dai 2004). Recently, Shen & Matzner (2012) have proposed a new model to interpret the shallow‐decay phase in the GRB afterglows, as for GRB 090529A. This model does not require energy injection, but attributes the shallow decay to the coasting phase of the blast wave in wind medium, while the subsequent normal decay is from the standard decelerating phase of the blast wave in the same type of medium.…”

Section: Analysis and Discussionmentioning

confidence: 99%

The shallow-decay phase in both the optical and X-ray afterglows of Swift GRB 090529A: energy injection into a wind-type medium?

Xin¹,

Pozanenko²,

Канн³

et al. 2012

Monthly Notices of the Royal Astronomical Society

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The energy injection model is the usual choice for interpreting the shallow‐decay phase in Swift gamma‐ray burst (GRB) X‐ray afterglows. However, very few GRBs have simultaneous signatures of energy injection in their optical and X‐ray afterglows. Here, we report on the optical observations of GRB 090529A from 2000 s to ∼106 s after the burst, in which an achromatic decay is seen at both wavelengths. The optical light curve shows a decay from 0.37 to 0.99, with a break at ∼105 s. In the same time interval, the decay indices of the X‐ray light curve changed from 0.04 to 1.2. Comparing these values with the closure relations, the segment after 3 × 104 s is consistent with the prediction of the forward shock in an interstellar medium without any energy injection. The shallow‐decay phase between 2000 and 3 × 104 s could be a result of the external shock in a wind‐type medium with an energy injection under the condition of νo < νc < νx. However, the constraint of the spectral region is not consistent with the multiband observations. For this shallow‐decay phase, other models are also possible, such as energy injection with evolving microphysical parameters, a jet viewed off‐axis, etc.

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Section: Analysis and Discussionmentioning

confidence: 99%

The shallow-decay phase in both the optical and X-ray afterglows of Swift GRB 090529A: energy injection into a wind-type medium?

Xin¹,

Pozanenko²,

Канн³

et al. 2012

Monthly Notices of the Royal Astronomical Society

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“…The required rise could be either due to the crossing of the injection frequency ν m or due to the coasting phase before the afterglow blast wave began decelerating. In the former case, the slope of the rise α r is −0.5 (with F ν ∝ t −α r ; Sari et al 1998), and in the latter, the slope is between −3 and −2 for constant-density medium and >0.5 for a free-stellar-wind density profile (Shen & Matzner 2012).…”

Section: Notesmentioning

confidence: 98%

GRB 120422A/SN 2012bz: Bridging the gap between low- and high-luminosity gamma-ray bursts

Schulze

Malesani

Cucchiara

et al. 2014

A&A

102

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Context. At low redshift, a handful of gamma-ray bursts (GRBs) have been discovered with luminosities that are substantially lower (L iso < ∼ 10 48.5 erg s −1 ) than the average of more distant ones (L iso > ∼ 10 49.5 erg s −1 ). It has been suggested that the properties of several low-luminosity (low-L) GRBs are due to shock break-out, as opposed to the emission from ultrarelativistic jets. This has led to much debate about how the populations are connected. Aims. The burst at redshift z = 0.283 from 2012 April 22 is one of the very few examples of intermediate-L GRBs with a γ-ray luminosity of L iso ∼ 10 49.6−49.9 erg s −1 that have been detected up to now. With the robust detection of its accompanying supernova SN 2012bz, it has the potential to answer important questions on the origin of low-and high-L GRBs and the GRB-SN connection. Methods. We carried out a spectroscopy campaign using medium-and low-resolution spectrographs with 6-10-m class telescopes, which covered a time span of 37.3 days, and a multi-wavelength imaging campaign, which ranged from radio to X-ray energies over a duration of ∼270 days. Furthermore, we used a tuneable filter that is centred at Hα to map star-formation in the host and the surrounding galaxies. We used these data to extract and model the properties of different radiation components and fitted the spectral energy distribution to extract the properties of the host galaxy. Results. Modelling the light curve and spectral energy distribution from the radio to the X-rays revealed that the blast wave expanded with an initial Lorentz factor of Γ 0 ∼ 50, which is a low value in comparison to high-L GRBs, and that the afterglow had an exceptionally low peak luminosity density of < ∼ 2 × 10 30 erg s −1 Hz −1 in the sub-mm. Because of the weak afterglow component, we were able to recover the signature of a shock break-out in an event that was not a genuine low-L GRB for the first time. At 1.4 hr after the burst, the stellar envelope had a blackbody temperature of k B T ∼ 16 eV and a radius of ∼7 × 10 13 cm (both in the observer frame). The accompanying SN 2012bz reached a peak luminosity of M V = −19.7 mag, which is 0.3 mag more luminous than SN 1998bw. The synthesised nickel mass of 0.58 M , ejecta mass of 5.87 M , and kinetic energy of 4.10 × 10 52 erg were among the highest for GRB-SNe, which makes it the most luminous spectroscopically confirmed SN to date. Nebular emission lines at the GRB location were visible, which extend from the galaxy nucleus to the explosion site. The host and the explosion site had close-to-solar metallicity. The burst occurred in an isolated star-forming region with an SFR that is 1/10 of that in the galaxy's nucleus. Conclusions. While the prompt γ-ray emission points to a high-L GRB, the weak afterglow and the low Γ 0 were very atypical for such a burst. Moreover, the detection of the shock break-out signature is a new quality for high-L GRBs. So far, shock break-outs were exclusively detected for low-L GRBs, while GRB 120422A had an intermediate...

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“…The solid lines depict the median choice of parameters in both cases, varying only the viewing angle and leaving all other parameters fixed. Circles mark observed GRB data, adapted from Tang et al 2019. result in a plateau prior to the deceleration of the line of sight material (see also Shen & Matzner 2012). The reason for this is that before deceleration, the energy in the forward shock scales as E k ∝ RΓ 2 0 ∝ t. Therefore, if the X-rays are above the cooling and injection frequencies (as expected, see above), then L p ∝ E (2+p)/4 k t (2−3p)/4 ∝ t (2−p)/2 which for p ≈ 2.2 is very close to being completely flat.…”

Section: Plateaus From Materials Moving Close To the Line Of Sightmentioning

confidence: 99%

X-ray plateaus in gamma-ray bursts’ light curves from jets viewed slightly off-axis

Beniamini

Duque

Daigne

et al. 2020

Monthly Notices of the Royal Astronomical Society

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Recent work has shown, using multiple observational arguments, that cosmological GRBs are typically viewed at angles close to the cores of their jets. One of those arguments, relied on the lack of tens of days long periods of very shallow evolution that may be seen in the afterglow light-curves of GRBs viewed at large angles. Motivated by those results, we consider that GRBs only efficiently produce γ-rays within a narrow region around the core. This results in plateaus in the X-ray light-curve that would be seen by a large fraction of observers and would last between 10 2 −10 5 s. These plateaus naturally reproduce the observed distributions of time-scales and luminosities as well as the inter-correlations between plateau duration, plateau luminosity and γ-ray energy. An advantage of this interpretation is that it involves no late time energy injection which would be both challenging from the point of view of the central engine and, as we show here, less natural given the observed correlations between plateau and prompt properties.

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COASTING EXTERNAL SHOCK IN WIND MEDIUM: AN ORIGIN FOR THE X-RAY PLATEAU DECAY COMPONENT INSWIFTGAMMA-RAY BURST AFTERGLOWS

Cited by 24 publications

References 92 publications

The shallow-decay phase in both the optical and X-ray afterglows of Swift GRB 090529A: energy injection into a wind-type medium?

The shallow-decay phase in both the optical and X-ray afterglows of Swift GRB 090529A: energy injection into a wind-type medium?

GRB 120422A/SN 2012bz: Bridging the gap between low- and high-luminosity gamma-ray bursts

X-ray plateaus in gamma-ray bursts’ light curves from jets viewed slightly off-axis

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