Prompt emission analysis of luminous GRB 210619B observed with {it Fermi} and ASIM: a transition between thermal to non-thermal outflow?. (arXiv:2205.07790v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Caballero_Garcia_M/0/1/0/all/0/1">M.D. Caballero-García</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gupta_R/0/1/0/all/0/1">Rahul Gupta</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pandey_S/0/1/0/all/0/1">S. B. Pandey</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Oates_S/0/1/0/all/0/1">S. R. Oates</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Marisaldi_M/0/1/0/all/0/1">M. Marisaldi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hu_Y/0/1/0/all/0/1">Y.-D. Hu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Castro_Tirado_A/0/1/0/all/0/1">A. J. Castro-Tirado</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sanchez_Ramirez_R/0/1/0/all/0/1">R. Sánchez-Ramírez</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Connell_P/0/1/0/all/0/1">P. H. Connell</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Christiansen_F/0/1/0/all/0/1">F. Christiansen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ror_A/0/1/0/all/0/1">A. Kumar Ror</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Aryan_A/0/1/0/all/0/1">A. Aryan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bai_J/0/1/0/all/0/1">J.-M. Bai</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Castro_Tirado_M/0/1/0/all/0/1">M. A. Castro-Tirado</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fan_Y/0/1/0/all/0/1">Y.-F. Fan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fernandez_Garcia_E/0/1/0/all/0/1">E. Fernández-García</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kumar_A/0/1/0/all/0/1">A. Kumar</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lindanger_A/0/1/0/all/0/1">A. Lindanger</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mezentsev_A/0/1/0/all/0/1">A. Mezentsev</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Navarro_Gonzalez_J/0/1/0/all/0/1">J. Navarro-González</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Neubert_T/0/1/0/all/0/1">T. Neubert</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ostgaard_N/0/1/0/all/0/1">N. Østgaard</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Perez_Garcia_I/0/1/0/all/0/1">I. Pérez-García</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Reglero_V/0/1/0/all/0/1">V. Reglero</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sarria_D/0/1/0/all/0/1">D. Sarria</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sun_T/0/1/0/all/0/1">T. R. Sun</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Xiong_D/0/1/0/all/0/1">D.-R. Xiong</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Yang_J/0/1/0/all/0/1">J. Yang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Yang_Y/0/1/0/all/0/1">Y.-H. Yang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zhang_B/0/1/0/all/0/1">B.-B. Zhang</a>
We report detailed prompt emission observations and analysis of the very
bright and long GRB 210619B, detected by the Atmosphere-Space Interactions
Monitor (ASIM) installed on the International Space Station ({it ISS}) and the
Gamma-ray Burst Monitor (GBM) on-board the Fermi mission. Our main goal is to
understand the radiation mechanisms and jet composition of GRB 210619B. With a
measured redshift of $z$ = 1.937 we find that GRB 210619B falls within the 10
most luminous bursts observed by Fermi so far. The energy-resolved prompt
emission light curve of GRB 210619B exhibits an extremely bright hard emission
pulse followed by softer/longer emission pulses. The low-energy photon indices
($alpha_{rm pt}$) values obtained using the time-resolved spectral analysis
of the burst reveal a transition between the thermal (during harder pulse) to
non-thermal (during softer pulse) outflow. We examine the correlation between
spectral parameters and find that both peak energy and $alpha_{rm pt}$
exhibit the flux tracking pattern. The late time broadband photometric dataset
can be explained within the framework of the external forward shock model with
$nu_m$ $< nu_c$ $< nu_{x}$ (where $nu_m$, $nu_c$, and $nu_{x}$ are the
synchrotron peak, cooling-break, and X-ray frequencies, respectively) spectral
regime supporting a rarely observed hard electron energy index ($p<$ 2). We
find moderate values of host extinction of E(B-V) = 0.14 $pm$ 0.01 for the
Small Magellanic Cloud (SMC) extinction law. In addition, we also report
late-time optical observations with the 10.4,m GTC placing deep upper limits
for the host galaxy (located at $z$=1.937), favouring a faint, dwarf host for
the burst.
We report detailed prompt emission observations and analysis of the very
bright and long GRB 210619B, detected by the Atmosphere-Space Interactions
Monitor (ASIM) installed on the International Space Station ({it ISS}) and the
Gamma-ray Burst Monitor (GBM) on-board the Fermi mission. Our main goal is to
understand the radiation mechanisms and jet composition of GRB 210619B. With a
measured redshift of $z$ = 1.937 we find that GRB 210619B falls within the 10
most luminous bursts observed by Fermi so far. The energy-resolved prompt
emission light curve of GRB 210619B exhibits an extremely bright hard emission
pulse followed by softer/longer emission pulses. The low-energy photon indices
($alpha_{rm pt}$) values obtained using the time-resolved spectral analysis
of the burst reveal a transition between the thermal (during harder pulse) to
non-thermal (during softer pulse) outflow. We examine the correlation between
spectral parameters and find that both peak energy and $alpha_{rm pt}$
exhibit the flux tracking pattern. The late time broadband photometric dataset
can be explained within the framework of the external forward shock model with
$nu_m$ $< nu_c$ $< nu_{x}$ (where $nu_m$, $nu_c$, and $nu_{x}$ are the
synchrotron peak, cooling-break, and X-ray frequencies, respectively) spectral
regime supporting a rarely observed hard electron energy index ($p<$ 2). We
find moderate values of host extinction of E(B-V) = 0.14 $pm$ 0.01 for the
Small Magellanic Cloud (SMC) extinction law. In addition, we also report
late-time optical observations with the 10.4,m GTC placing deep upper limits
for the host galaxy (located at $z$=1.937), favouring a faint, dwarf host for
the burst.
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