Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userHappy Birthday Swift: Ultra-long GRB141121A and its broad-band Afterglow
131
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present our extensive observational campaign on the Swift-discovered GRB141121A, al- most ten years after its launch. Our observations covers radio through X-rays, and extends for more than 30 days after discovery. The prompt phase of GRB 141121A lasted 1410 s and, at the derived redshift of z = 1.469, the isotropic energy is E{gamma},iso = 8.0x10^52 erg. Due to the long prompt duration, GRB141121A falls into the recently discovered class of UL-GRBs. Peculiar features of this burst are a flat early-time optical light curve and a radio-to-X-ray rebrightening around 3 days after the burst. The latter is followed by a steep optical-to-X-ray decay and a much shallower radio fading. We analyze GRB 141121A in the context of the standard forward-reverse shock (FS,RS) scenario and we disentangle the FS and RS contributions. Finally, we comment on the puzzling early-time (t ~3 d) behavior of GRB 141121A, and suggest that its interpretation may require a two-component jet model. Overall, our analysis confirms that the class of UL-GRBs represents our best opportunity to firmly establish the prominent emission mechanisms in action during powerful GRB explosions, and future missions (like SVOM, XTiDE, or ISS-Lobster) will provide many more of such objects.
rate research
Read More
What is driving the accelerated expansion of the universe and do we have an alternative for Einsteins cosmological constant? What is dark matter made of? Do extra dimensions of space and time exist? Is there a preferred frame in the universe? To which extent is left-handedness a preferred symmetry in nature? Whats the origin of the baryon asymmetry in the universe? These fundamental and open questions are addressed by precision experiments using ultra-cold neutrons. This year, we celebrate the 50th anniversary of their first production, followed by first pioneering experiments. Actually, ultra-cold neutrons were discovered twice in the same year, once in the eastern and once in the western world. For five decades now research projects with ultra-cold neutrons have contributed to the determination of the force constants of natures fundamental interactions, and several technological breakthroughs in precision allow to address the open questions by putting them to experimental test. To mark the event and tribute to this fabulous object, we present a birthday song for ultra-cold neutrons with acoustic resonant transitions, which are based solely on properties of ultra-cold neutrons, the inertial and gravitational mass of the neutron, Plancks constant, and the local gravity. We make use of a musical intonation system that bears no relation to basic notation and basic musical theory as applied and used elsewhere but addresses two fundamental problems of music theory, the problem of reference for the concert pitch and the problem of intonation.
The ultra-long Gamma Ray Burst GRB 111209A at redshift z=0.677, is so far the longest GRB ever observed, with rest frame prompt emission duration of ~4 hours. In order to explain the bursts exceptional longevity, a low metallicity blue supergiant progenitor has been invoked. In this work, we further investigate this peculiar burst by performing a multi-band temporal and spectral analysis of both the prompt and the afterglow emission. We use proprietary and publicly available data from Swift, Konus Wind, XMM-Newton, TAROT as well as from other ground based optical and radio telescopes. We find some peculiar properties that are possibly connected to the exceptional nature of this burst, namely: i) an unprecedented large optical delay of 410+/-50 s is measured between the peak epochs of a marked flare observed also in gamma-rays after about 2 ks from the first Swift/BAT trigger; ii) if the optical and X-ray/gamma-ray photons during the prompt emission share a common origin, as suggested by their similar temporal behavior, a certain amount of dust in the circumburst environment should be introduced, with rest frame visual dust extinction of AV=0.3-1.5 mag; iii) at the end of the X-ray steep decay phase and before the start of the X-ray afterglow, we detect the presence of a hard spectral extra power law component never revealed so far. On the contrary, the optical afterglow since the end of the prompt emission shows more common properties, with a flux power law decay with index alpha=1.6+/-0.1 and a late re-brightening feature at 1.1 day. We discuss our findings in the context of several possible interpretations given so far to the complex multi-band GRB phenomenology. We also attempt to exploit our results to further constrain the progenitor nature properties of this exceptionally long GRB, suggesting a binary channel formation for the proposed blue supergiant progenitor.
The accreting millisecond X-ray pulsar Swift J1756.9$-$2508 went into outburst in April 2018 and June 2019, 8.7 yr after the previous activity period. We investigated the temporal, timing and spectral properties of these two outbursts using data from NICER, XMM-Newton, NuSTAR, INTEGRAL, Swift and Insight-HXMT. The two outbursts exhibited similar broad-band spectra and X-ray pulse profiles. For the first time, we report the detection of the pulsed emission up to $sim100$ keV observed by Insight-HXMT during the 2018 outburst. We also found the pulsation up to $sim60$ keV observed by NICER and NuSTAR during the 2019 outburst. We performed a coherent timing analysis combining the data from two outbursts. The binary system is well described by a constant orbital period over a time span of $sim12$ years. The time-averaged broad-band spectra are well fitted by an absorbed thermal Comptonization model in a slab geometry with the electron temperature $kT_{rm e}=40$-50 keV, Thomson optical depth $tausim 1.3$, blackbody seed photon temperature $kT_{rm bb,seed}sim $0.7-0.8 keV and hydrogen column density of $N_{rm H}sim 4.2times10^{22}$ cm$^{-2}$. We searched the available data for type-I (thermonuclear) X-ray bursts, but found none, which is unsurprising given the estimated low peak accretion rate ($approx0.05$ of the Eddington rate) and generally low expected burst rates for hydrogen-poor fuel. Based on the history of four outbursts to date, we estimate the long-term average accretion rate at roughly $5times10^{-12} M_odot,{rm yr}^{-1}$ for an assumed distance of 8 kpc. The expected mass transfer rate driven by gravitational radiation in the binary implies the source can be no closer than 4 kpc.
GRB 130925A was an unusual GRB, consisting of 3 distinct episodes of high-energy emission spanning $sim$20 ks, making it a member of the proposed category of `ultra-long bursts. It was also unusual in that its late-time X-ray emission observed by Swift was very soft, and showed a strong hard-to-soft spectral evolution with time. This evolution, rarely seen in GRB afterglows, can be well modelled as the dust-scattered echo of the prompt emission, with stringent limits on the contribution from the normal afterglow (i.e. external shock) emission. We consider and reject the possibility that GRB 130925A was some form of tidal disruption event, and instead show that if the circumburst density around GRB 130925A is low, the long duration of the burst and faint external shock emission are naturally explained. Indeed, we suggest that the ultra-long GRBs as a class can be explained as those with low circumburst densities, such that the deceleration time (at which point the material ejected from the nascent black hole is decelerated by the circumburst medium) is $sim$20 ks, as opposed to a few hundred seconds for the normal long GRBs. The increased deceleration radius means that more of the ejected shells can interact before reaching the external shock, naturally explaining both the increased duration of GRB 130925A, the duration of its prompt pulses, and the fainter-than-normal afterglow.
GRB 130925A is an ultra-long GRB, and it shows clear evidences for a thermal emission in the soft X-ray data of emph{Swift}/XRT ($sim0.5$,keV), lasting till the X-ray afterglow phase. Due to the long duration of the GRB, the burst could be studied in hard X-rays with high-resolution focusing detectors (emph{NuSTAR}). The blackbody temperature, as measured by the emph{Swift}/XRT, shows a decreasing trend till the late phase (Piro et al. 2014) whereas the high-energy data reveals a significant blackbody component during the late epochs at an order of magnitude higher temperature ($sim5$,keV), as compared to the contemporaneous low energy data (Bellm et al. 2014). We resolve this apparent contradiction by demonstrating that a model with two black bodies and a power-law (2BBPL) is consistent with the data right from the late prompt emission to the afterglow phase. Both the blackbodies show a similar cooling behaviour upto the late time. We invoke a structured jet, having a fast spine and a slower sheath layer, to identify the location of these blackbodies. Independent of the physical interpretation, we propose that the 2BBPL model is a generic feature of the prompt emission of all long GRBs, and the thermal emission found in the afterglow phase of different GRBs reflects the lingering thermal component of the prompt emission with diverse time-scales. We strengthen this proposal by pointing out a close similarity between the spectral evolutions of this GRB and GRB~090618, a source with significant wide band data during the early afterglow phase.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
