Observations counsel GRB origin for quick X-ray transient detected by Einstein Probe

Astronomers have performed multiwavelength observations of a just lately detected quick X-ray transient designated EP241107a. Outcomes of the observational marketing campaign, published November 4 on the arXiv preprint server, shed extra gentle on the character of this transient, suggesting a gamma-ray burst origin.

Typically, quick X-ray transients (FXTs) are bursts in gentle X-rays lasting from a couple of hundred seconds to a number of hours. They’re very troublesome to detect as a result of they happen at unpredictable places and instances and their exercise may be very transient. Furthermore, their nature remains to be puzzling. Nonetheless, astronomers making an attempt to clarify their origin take note of a number of eventualities; as an illustration, stellar flares, supernova shock breakouts, and lengthy gamma-ray bursts (GRBs).

A mysterious transient

EP241107a is an FXT detected on November 7, 2024 with the Broad-field X-ray Telescope (WXT) onboard the Einstein Probe (EP)—a Chinese language area telescope launched into area in January 2024. The transient has an optical counterpart, which was recognized within the I_c-band at a magnitude of 17.85.

On condition that the character and properties of EP241107a stay unsure, a group of astronomers led by Deepak Eappachen of the Indian Institute of Astrophysics in Bengaluru, India, determined to examine this transient with the usage of ground-based telescopes, together with the GROWTH-India Telescope (GIT) and Himalayan Chandra Telescope (HCT).

“We use our multiwavelength observations of the transient counterpart, together with publicly obtainable information, mixed with our afterglow and host modeling, to derive constraints on the character of EP241107a,” the researchers wrote.

Constraining FXT properties

Initially, the observations detected a radio counterpart of EP241107a at 10 GHz and 6 GHz, with flux densities of about 232 and 207 𝜇Jy, respectively. The spectroscopic redshift of the transient was decided to be 0.457.

EP241107a had an X-ray luminosity of about 3.4 quindecillion erg/s (within the 0.5-4 keV band) when detected with EP. Subsequently, its X-ray luminosity was increased when in comparison with the expected X-ray luminosities of typical supernova shock breakout (SN SBO).

The examine discovered that roughly 60 minutes post-detection, an X-ray afterglow with a luminosity of 0.012 quindecillion erg/s was detected within the 0.5–10 keV band. This X-ray counterpart declined quickly.

When it got here to the host galaxy of EP241107a, the observations discovered that it has a stellar mass of about two billion photo voltaic plenty and its star formation fee was estimated to be at a stage of 0.6 photo voltaic plenty per 12 months.

Gamma-ray burst origin

Summing up the outcomes, the astronomers in contrast the optical and radio observations of EP241107a and its host galaxy properties with different extragalactic transients. The comparability factors to a gamma-ray burst (GRB) origin of this transient.

“We in contrast the radio and optical gentle curves of EP241107a with these of different transients and located that EP241107a is in step with the parameter area occupied by GRB afterglows,” the astronomers concluded.

Nonetheless, the authors of the paper famous that the absence of gamma-ray emission, the inferred on-axis viewing geometry and the energetics derived from afterglow modeling all collectively counsel that EP241107a is an intrinsically faint GRB.

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