Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 2610.02889

Study of the Ultra-Long GRB 220627A: Exploring a Possible Blue Supergiant Collapsar Origin

Ayush Garg·Amit Shukla·Dorottya Szécsi·G. C. Anupama
View original source ↗Read source document ↗Export metadata ↓

Abstract

Ultra-long gamma-ray bursts (ul-GRBs) challenge standard collapsar models because their extreme durations require central engines active for $\sim10^{3}-10^{4}$ s. While the prompt spectral evolution of typical GRBs is difficult to resolve due to their short durations, ul-GRBs provide a unique opportunity to study spectral evolution on extended timescales. We present a time-resolved spectroscopic study of GRB 220627A, one of the most luminous ul-GRBs known ($E_{\rm iso}\sim10^{54}$ erg, $T_{90}>1000$ s), consisting of two bright emission episodes separated by $\sim600$ s quiescent interval. Using a novel HOP algorithm-based segmentation method, we identify optimal time intervals for time-resolved spectroscopy. A Comptonized power-law (CPL) model well describes the prompt emission ($\sim 10$ keV-40 MeV) across all timescales. Fermi-GBM spectroscopy reveals a transition from a hard, slow-cooling synchrotron spectrum ($α_{\rm I}=-0.70$) during episode-I to a softer, fast-cooling synchrotron spectrum ($α_{\rm II}=-1.29$) during episode-II. This evolution closely resembles that of the magnetar-candidate GRB 091024A, highlighting a potential progenitor degeneracy based solely on spectral evolution. However, the extreme isotropic-equivalent energy exceeds the maximum energy available from magnetar spin-down, strongly favouring a blue supergiant (BSG) collapsar origin. The prolonged activity and multi-episode structure are naturally explained by sustained accretion through an extended stellar envelope. Our results demonstrate that ul-GRBs can display magnetar-like spectral evolution while being powered by BSG collapsars. GRB 220627A highlights the need for combining time-resolved spectroscopy with energetic constraints to distinguish between progenitor scenarios and understand the physical origin of ul-GRBs.

Explore related subjects

astro-ph.HE

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Ayush Garg, Amit Shukla, Dorottya Szécsi, G. C. Anupama. 2026-10-02. Study of the Ultra-Long GRB 220627A: Exploring a Possible Blue Supergiant Collapsar Origin. https://arxiv.org/abs/2610.02889

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Limit on high energy neutrino emission from Abell 119 using IceCube 10-year muon track data

We carry out a search for high energy muon neutrino emission from the galaxy cluster Abell 119, motivated by a recent tentative detection of GeV gamma-ray emission from this cluster using the Fermi-LAT telescope, which hinted at a hadronic origin. For this purpose, we used the 10-year muon track data from 2008-2018, provided by the IceCube Collaboration and implement the unbinned maximum likelihood method. We do not find any statistically significant excess and the observed value of the test statistic is consistent with a null result. We then obtain upper limits (at 90\% confidence level) on the differential muon neutrino energy flux from this cluster, whose value is equal to $1.2 \times 10^{-9}~\mathrm{GeV}~\mathrm{cm}^{-2}~\mathrm{s}^{-1}$ at a pivot energy of 100 TeV, after assuming a neutrino spectral index of 2.0. The neutrino flux expected under the hadronic interpretation is, however, approximately an order of magnitude smaller than our flux limit, and hence the hadronic model cannot be ruled out based on our upper limit. Among the next generation neutrino detectors, IceCube-Gen2 and TRIDENT neutrino detector should be able to confirm or rule out a hadronic origin for the gamma-ray emission in Abell 119 with 10 years of exposure.

astro-ph.HE↗
arXiv2026

Granular mass perturbations on the pulsar - supermassive black hole system

Discovery and timing observations of a radio pulsar orbiting around Sagittarius A*, the supermassive black hole (SMBH) in our Galactic Centre (GC), will provide unprecedented opportunities of studying the SMBH spacetime, testing gravity theories, and probing the astrophysical environment in the GC. However, unknown mass distributions might cause timing residuals that are much larger than the timing precision. With extensive numerical simulations, for the first time we find that the perturbations caused by a granular cusp of stellar-mass black holes in the GC lead to post-fit timing residuals of 10-100 s--contrary to traditional wisdom--even for a pulsar in a tight orbit with an orbital period $P_b=0.5\,{\rm yr}$. Such a large timing residual can lead to significant measurement bias or even prevent construction of a phase-connected timing solution for the full orbit. We revisit the idea of extracting SMBH parameters only with data around periastron where the perturbation is small. Under the realistic phase-disconnected assumption, we point out that it is vital to consider the frame-dragging effect in the light propagation, which breaks parameter degeneracy and leads to an order of magnitude improvement for the measurement precision of the SMBH spin.

astro-ph.HE↗
arXiv2026

Spectral study of the outburst decay of the accreting millisecond X-ray pulsar SRGA J144459.2-604207

We study the spectra of the accreting X-ray millisecond pulsar SRGA J144459.2-604207 during the 2024 outburst using the Neutron star Interior Composition Explorer (NICER) and Swift observations. The spectra during the outburst decay, reflares, and quiescent state are explored using the absorbed Comptonized model. We find that the spectra during the quiescent state can also be explained using the absorbed power-law and absorbed blackbody model. The spectral evolution of the source is explored as the outburst decays into quiescence. We study the long-term quiescent X-ray activity of the source spanning roughly 45 years and find that the long-term quiescent luminosity may be explained using the deep crustal heating model. We also find that the coronal activity of the companion star alone cannot power the quiescent X-ray luminosity of the source. We place the source on the radio-X-ray luminosity plane and compare its position with other sources. We estimate the propeller luminosity of the source and find that it is smaller than the estimated luminosity during reflares and the quiescent state during the 2024 outburst. Several reflares are detected during the outburst decay, one of which is near-simultaneous with the detection of an ultrafast outflow and radio emission. We explore plausible mechanisms that may power outflow, radio emission and associated jet formation in this accreting binary.

astro-ph.HE↗