Revealing nature of GRB 210205A, ZTF21aaeyldq (AT2021any) and follow-up observations with the 4K$$\times$$4K CCD imager + 3.6m DOT

Gupta, Rahul; Kumar, Amit; Castro-Tirado, A. J.; Ghosh, Ankur; Dimple,; Hu, Y.-D.; Fernández-García, E.; Caballero‐García, M. D.; Castro-Tirado, M. A.; Hedrosa, R. P.; Hermelo, I.; Vico, I.; Misra, Kuntal; Kumar, Brajesh; Aryan, Amar; Tiwari, Sugriva Nath

doi:10.1007/s12036-021-09794-4

Cited by 8 publications

(4 citation statements)

References 44 publications

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“…The goodness of fit is χ 2 /ν = 3.4 for ν = 8 degrees of freedom. The pre-break index we measure is shallower than the value of α 1 = 0.89 ± 0.03 reported by Gupta et al (2022) on the basis of GCN photometry. The post-break index we measure is shallower than the value of α 2 = 2.30 reported by Kann et al (2021b).…”

Section: Prompt Emissioncontrasting

confidence: 80%

“…The optical light curves constrain our viewing angle. For AT 2021any, the shallow (α = 1.2) index is consistent with an event viewed directly on-axis, in agreement with Gupta et al (2022). For AT 2021lfa, from the available photometry we cannot determine whether the event was initially viewed onaxis.…”

Section: Multiwavelength Properties Of the Orphan Afterglowssupporting

confidence: 69%

“…The properties of PTF11agg and AT 2020blt were presented by Cenko et al (2013) and Ho et al (2020a), respectively, and AT 2019pim will be discussed in detail in a separate paper by D. Perley et al (in preparation). Gupta et al (2022) analysed the public data of AT 2021any and concluded that its properties were consistent with being a LGRB viewed on-axis. By modeling the optical light curve of AT 2020blt, and adopting deeper limits on the accompanying γ-ray emission than Ho et al (2020a), Sarin et al (2022 argued that it was likely viewed on-axis but with an unusually low γ-ray efficiency of <2.8%.…”

Section: Multiwavelength Properties Of the Orphan Afterglowsmentioning

confidence: 99%

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Cosmological Fast Optical Transients with the Zwicky Transient Facility: A Search for Dirty Fireballs

Perley

Yao

et al. 2022

ApJ

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Dirty fireballs are a hypothesized class of relativistic massive-star explosions with an initial Lorentz factor Γinit below the Γinit ∼ 100 required to produce a long-duration gamma-ray burst (LGRB), but which could still produce optical emission resembling LGRB afterglows. Here we present the results of a search for on-axis optical afterglows using the Zwicky Transient Facility (ZTF). Our search yielded seven optical transients that resemble on-axis LGRB afterglows in terms of their red colors (g − r > 0 mag), faint host galaxies (r > 23 mag), rapid fading (dr/dt > 1 mag day−1), and in some cases X-ray and radio emission. Spectroscopy of the transient emission within a few days of discovery established cosmological distances (redshift z = 0.876 to 2.9) for six of the seven events, tripling the number of afterglows with redshift measurements discovered by optical surveys without a γ-ray trigger. A likely associated LGRB (GRB 200524A, GRB 210204A, GRB 210212B, and GRB 210610B) was identified for four events (ZTF 20abbiixp/AT 2020kym, ZTF 21aagwbjr/AT 2021buv, ZTF 21aakruew/AT 2021cwd, and ZTF 21abfmpwn/AT 2021qbd) post facto, while three (ZTF 20aajnksq/AT 2020blt, ZTF 21aaeyldq/AT 2021any, and ZTF 21aayokph/AT 2021lfa) had no detected LGRB counterpart. The simplest explanation for the three “orphan” events is that they were regular LGRBs missed by high-energy satellites owing to detector sensitivity and duty cycle, although it is possible that they were intrinsically subluminous in γ-rays or viewed slightly off-axis. We rule out a scenario in which dirty fireballs have a similar energy per solid angle to LGRBs and are an order of magnitude more common. In addition, we set the first direct constraint on the ratio of the opening angles of the material producing γ-rays and the material producing early optical afterglow emission, finding that they must be comparable.

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Section: Prompt Emissioncontrasting

confidence: 80%

Section: Multiwavelength Properties Of the Orphan Afterglowssupporting

confidence: 69%

Section: Multiwavelength Properties Of the Orphan Afterglowsmentioning

confidence: 99%

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Cosmological Fast Optical Transients with the Zwicky Transient Facility: A Search for Dirty Fireballs

Perley

Yao

et al. 2022

ApJ

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“…,Caballero-García et al (2022), andGupta et al (2022c) to create these SEDs. For GRB 201015A, the optical temporal index (a = -) follows a simple power-law decay post-optical bump and satisfies the relation α = (3p − 3)/4 in the slow-cooling regime of the ISM, which indicates that the optical emission always remains in the ν m < ν o < ν c spectral regime.…”

mentioning

confidence: 99%

Prompt Emission and Early Optical Afterglow of Very-high-energy Detected GRB 201015A and GRB 201216C: Onset of the External Forward Shock

Ror

Gupta

Jelínek

et al. 2023

ApJ

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We present a detailed prompt emission and early optical afterglow analysis of the two very-high-energy (VHE) detected bursts GRB 201015A and GRB 201216C, and their comparison with a subset of similar bursts. Time-resolved spectral analysis of multistructured GRB 201216C using the Bayesian binning algorithm revealed that during the entire duration of the burst, the low-energy spectral index (α pt) remained below the limit of the synchrotron line of death. However, statistically some of the bins supported the additional thermal component. Additionally, the evolution of spectral parameters showed that both the peak energy (E p) and α pt tracked the flux. These results were further strengthened using the values of the physical parameters obtained by synchrotron modeling of the data. Our earliest optical observations of both bursts using the F/Photometric Robotic Atmospheric Monitor Observatorio del Roque de los Muchachos and Burst Observer and Optical Transient Exploring System robotic telescopes displayed a smooth bump in their early optical light curves, consistent with the onset of the afterglow due to synchrotron emission from an external forward shock. Using the observed optical peak, we constrained the initial bulk Lorentz factors of GRB 201015A and GRB 201216C to Γ0 = 204 and Γ0 = 310, respectively. The present early optical observations are the earliest known observations constraining outflow parameters and our analysis indicate that VHE detected bursts could have a diverse range of observed luminosity within the detectable redshift range of present VHE facilities.

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Optical Transient Source AT2021lfa: A Possible “Dirty Fireball”

Ye,

Wei,

Zhu

et al. 2024

Res. Astron. Astrophys.

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AT2021lfa, also known as ZTF21aayokph, was detected by the Zwicky Transient Facility on May 4, 2021, at 05:34:48 UTC. Follow-up observations were conducted using a range of ground-based optical telescopes, as well as Swift/XRT and VLA instruments. AT2021lfa is classified as an ``orphan afterglow'' candidate due to its rapid flux decline and its reddened color ($g-r = 0.17 \pm 0.14$ mag). For optical transient source without prompt gamma-ray detection, one key point is to determine its burst time. Here we measure the burst time through fitting the initial bump feature of AT2021lfa and obtain its burst time as May 3, 2021, at 22:09:50 UTC. Using \texttt{Afterglowpy}, we model the multi-band afterglow of AT2021lfa and find that the standard model cannot reproduce the late radio observations well. Considering that the microphysical parameters $\epsilon_e$, $\epsilon_B$ (the energy fraction given to electrons and magnetic field), and $\xi_N$ (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 $\epsilon_e$, $\epsilon_B$, and $\xi_N$ and find in this case the multi-wavelength observations can be reproduced well. The 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 the radiation efficiency is less than 0.02\%, which is much smaller than that of ordinary gamma-ray bursts. It is also interesting that the fitted values of jet angle and viewing angle are very large, $\theta_c \sim$ 0.66 rad, $\theta_v \sim$ 0.53 rad, which may lead to the low Lorentz factor and radiation efficiency. When compared with GRB afterglow samples, it is evident that the onset bump timescale of AT2021lfa satisfies the empirical relationships observed in GRB samples. Additionally, the luminosity of AT2021lfa falls within the range of observations for GRB samples. Additionally, the luminosity of AT2021lfa falls within the range of observations for GRB samples; however, approximately 1 day after the burst, its luminosity exceeds that of the majority of GRB samples.

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Revealing nature of GRB 210205A, ZTF21aaeyldq (AT2021any) and follow-up observations with the 4K$$\times$$4K CCD imager + 3.6m DOT

Cited by 8 publications

References 44 publications

Cosmological Fast Optical Transients with the Zwicky Transient Facility: A Search for Dirty Fireballs

Cosmological Fast Optical Transients with the Zwicky Transient Facility: A Search for Dirty Fireballs

Prompt Emission and Early Optical Afterglow of Very-high-energy Detected GRB 201015A and GRB 201216C: Onset of the External Forward Shock

Optical Transient Source AT2021lfa: A Possible “Dirty Fireball”

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