Probing into emission mechanisms of GRB 190530A using time-resolved spectra and polarization studies: Synchrotron Origin?

Abstract

Multi-pulsed GRB 190530A, detected by the GBM and LAT onboard Fermi, is the sixth most fluent GBM burst detected so far. This paper presents the timing, spectral, and polarimetric analysis of the prompt emission observed using AstroSat and Fermi to provide insight into the prompt emission radiation mechanisms. The time-integrated spectrum shows conclusive proof of two breaks due to peak energy and a second lower energy break. Time-integrated (55.43 ± 21.30 %) as well as time-resolved polarization measurements, made by the Cadmium Zinc Telluride Imager (CZTI) onboard AstroSat, show a hint of high degree of polarization. The presence of a hint of high degree of polarization and the values of low energy spectral index (αpt) do not run over the synchrotron limit for the first two pulses, supporting the synchrotron origin in an ordered magnetic field. However, during the third pulse, αpt exceeds the synchrotron line of death in few bins, and a thermal signature along with the synchrotron component in the time-resolved spectra is observed. Furthermore, we also report the earliest optical observations constraining afterglow polarization using the MASTER (P < 1.3 %) and the redshift measurement (z= 0.9386) obtained with the 10.4m GTC telescopes. The broadband afterglow can be described with a forward shock model for an ISM-like medium with a wide jet opening angle. We determine a circumburst density of n0 ∼ 7.41, kinetic energy EK ∼ 7.24 × 1054 erg, and radiated γ-ray energy Eγ, iso ∼ 6.05 × 1054 erg, respectively.

Multi-wavelength study of the luminous GRB 210619B observed with Fermi and ASIM

“…Figure 14 (bottom panel) shows the distribution of time-resolved peak energy as a function of 𝛼 pt of GRB 210619B along with a large sample of GRBs. Furthermore, we also compared the spectral parameters of GRB 210619B with those bursts (GRB 131231A, GRB 140102A, GRB 190530A, and others) having "Double-tracking" evolution pattern of 𝐸 p and 𝛼 pt Gupta et al 2021Gupta et al , 2022. We noticed that some bursts are consistent with the non-thermal thin shell synchrotron emission model, however, some of them required a hybrid non-thermal synchrotron plus thermal photospheric emission.…”

“…According to the classical fireball model, initially, the jetted outflow is optically thick, and due to expansion, the flow becomes transparent at a certain point (also known as photospheric radius, r ph ), and thermal radiation emitted towards the observer, results as a subdominant/dominant part of the entire observed prompt gamma-ray spectra (Beloborodov & Mészáros 2017). Moreover, some spectra show a few additional features, such as a sub-GeV spectral cut-off (Vianello et al 2018;Chand et al 2020), a low energy break in the spectrum (Ravasio et al 2019;Gupta et al 2022), and multiple components (Tak et al 2019). Thus, it is challenging to explain the radiation physics of GRBs using a single model (different spectral components are associated with different emissions originated at different regions).…”

“…More recently, Li et al (2021) performed the time-resolved spectral analysis of multi-pulsed GRBs observed by Fermi GBM and found that the typical pattern of the pulses becomes softer with time, mostly with 𝛼 pt becoming smaller, suggesting a transition from the photosphere to synchrotron emission. For some bright bursts, some authors Gupta et al 2021Gupta et al , 2022 examined the evolution pattern of spectral parameters and noticed that 𝐸 p and 𝛼 pt both show a flux tracking ("double-tracking") behavior.…”

The long-active afterglow of GRB 210204A: Detection of the most delayed flares in a Gamma-Ray Burst

“…We utilised the deviance information criterion (DIC; Spiegelhalter et al 2002) to find the best fit model. A more detailed methodology for GBM data analysis is discussed in Gupta et al (2021bGupta et al ( , 2022.…”

Tale of GRB 171010A/SN 2017htp and GRB 171205A/SN 2017iuk: Magnetar origin?

“…GRB 171010A was discovered by the Fermi Large Area Telescope (LAT; Atwood et al 2009) and Gamma-ray Burst Monitor (GBM; Meegan et al 2009) on 2017-10-10 UT 19:00:50.58 (JD = 2458037.292;Omodei et al 2017;Poolakkil & Meegan 2017) at = 04 ℎ 26 19 .46 and = −10 • 27 ′ 45 ′′ .9 (J2000). We obtained the Fermi GBM data of GRB 171010A from the Fermi GBM Burst Catalog 2 and performed the temporal and spectral data analysis following the methodology presented in Gupta et al (2022);Caballero-García et al (2022). For the temporal analysis of the GBM data, we have used RMFIT software and utilized the two brightest sodium iodide detectors (NaI-8 and NaI-b) and the brightest bismuth germanate detector (BGO-1).…”