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Optical Transient Source AT2021lfa:A Possible“Dirty Fireball”

Research in Astronomy and Astrophysics 2024年第4期24卷 124-133页

作者： Xue-Mei Ye Da-Ming Wei Yi-Ming Zhu Zhi-Ping Jin Key Laboratory of Dark Matter and Space Astronomy Purple Mountain ObservatoryChinese Academy of SciencesNanjing 210023China School of Astronomy and Space Science University of Science and Technology of ChinaHefei 230026China National Astronomical Observatories/Nanjing Institute of Astronomical Optics&Technology Chinese Academy of SciencesNanjing 210042China CAS Key Laboratory of Astronomical Optics&Technology Nanjing Institute of Astronomical Optics&TechnologyNanjing 210042China

AT2021lfa,also known as ZTF21aayokph,was detected by the Zwicky Transient Facility on 2021 May 4,a 05:34:48 ***-up observations were conducted using a range of ground-based optical telescopes,as wel as Swift/XRT and VLA ***2021lfa is classified as an“orphan afterglow”candidate due to its rapid flux decline and its reddened color(g-r=0.17±0.14 mag).For an optical transient source without promp gamma-ray detection,one key point is to determine its burst *** we measure the burst time through fitting the initial bump feature of AT2021lfa and obtain its burst time as 2021 May 3,at 22:09:50 *** afterglowpy,we model the multi-band afterglow of AT2021lfa and find that the standard model canno reproduce the late radio observations *** that the microphysical parameters ε_(e),ε_(B)(the energy fraction given to electrons and magnetic field),andξN(the fraction of accelerated electrons)may vary with time we then model the afterglow of AT2021lfa taking into account the temporal evolution of the physical parameters ε_(e),ε^(B),and ξ_(N) and find in this case the multi-wavelength observations can be reproduced *** initial Lorentz factor of AT2021lfa can be estimated from the peak time of the early afterglow,which yields a value of about 18 suggesting that AT2021lfa should be classified as a“dirty fireball.”From the upper limit for the prompt emission energy of AT2021lfa,we obtain that the radiation efficiency is less than 0.02%,which is much smaller than that of ordinary gamma-ray bursts(GRBs).It is also interesting that the fitted values of jet angle and viewing angle are very large,θ_(c)~0.66 rad,θ_(v)~0.53 rad,which may lead to the low Lorentz factor and radiation *** compared with GRB afterglow samples,it is evident that the onset bump timescale of AT2021lfa satisfies the empirical relationships observed in GRB ***,the luminosity of AT2021lfa falls within the range of observations for GRB samples;howeve

关键词： gamma-rays:ism methods:numerical radiation mechanisms:non-thermal

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On the Jet Structures of GRB 050820A and GRB 070125

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Research in Astronomy and Astrophysics 2022年第8期22卷 249-257页

作者： Xin-Yu Li Hao-Ning He Da-Ming Wei Key Laboratory of Dark Matter and Space Astronomy Purple Mountain ObservatoryChinese Academy of SciencesNanjing 210033China School of Astronomy and Space Science University of Science and Technology of ChinaHefei 230026China

We present the broadband numerical modeling of afterglows for two remarkably bright long gamma-ray bursts(GRBs),GRB 050820 A and GRB 070125,with a wide range of observations from the radio band to the X-ray *** our work,we fit light curves and constrain physical parameters using a standard forward shock model from the afterglowpy Python package,considering different jet structures and the jet lateral *** GRB 050820 A,the constrained jet is close to a top-hat jet with an extremely small half opening angle of about 0.015 rad,and the circumburst matter density is as small as 10^(-7)cm^(-3),which suggests that this peculiar long GRB might originate from metal-poor stars with low mass-loss *** explain the late time optical light curves of GRB 070125,the effects of the lateral expansion and the participation factor of electrons that are accelerated by the shock have to be taken into *** constrained results for GRB 070125 show that the jet is also close to a top-hat jet with a half opening angle of about 0.1 rad,the viewing angle is about 0.05 rad,the circumburst density is about 10 cm^(-3),and the participation factor is about *** jet energy of the two bursts is required to be~1051–1052 erg,which can be produced by a millisecond magnetar or a hyper-accreting black hole.

关键词： methods:numerical ism:jets and outflows gamma-rays:ism gamma-rays:general

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