**Executive Summary**
Researchers led by the Indian Institute of Astrophysics have identified the mechanism behind the Fast X-ray Transient (FXT) event EP241107a, detected on November 7, 2024. The study utilizes a multi-wavelength approach to link these mysterious flashes to the collapse of massive stars or neutron star mergers. These findings, published in the *Monthly Notices of the Royal Astronomical Society*, provide critical insights into the physics of rare "orphan afterglow" cosmic events.
**Key Points / Main Content**
**Characteristics of Fast X-ray Transients (FXTs)**
* FXTs are energetic, non-repeating flashes of X-rays resulting from violent universal processes.
* These events appear as sudden bursts of low-energy X-rays lasting from several minutes to a few hours before fading.
* Progenitors are theorized to include supernova shock breakouts, neutron star mergers, or tidal disruption events involving black holes.
**The EP241107a Observation**
* The specific event was detected on November 7, 2024, by the Einstein Probe mission, a Chinese space mission surveying the high-energy sky.
* Detailed modeling indicates the burst produced a powerful jet with kinetic energy comparable to the total energy emitted by all stars in the Milky Way over several months.
* Researchers concluded the event is likely an "orphan afterglow," representing a gamma-ray burst at the lower-energy end of the known population.
**Research Methodology and Facilities**
* A multi-wavelength approach was used to discover a radio counterpart via the Karl G. Jansky Very Large Array (USA).
* Indian ground-based facilities, including the Himalayan Chandra Telescope (HCT), the GROWTH India Telescope (GIT), and the Upgraded Giant Metrewave Radio Telescope, provided visible light monitoring and follow-up observations.
* International facilities involved include the Keck Observatory (Hawaii) and the Southern Astrophysical Research Telescope (Chile).
**Impact Analysis**
**Astronomers and the Global Scientific Community**
**Impact**
The study provides a framework for understanding the origins of FXTs and their connection to gamma-ray bursts, transforming the study of short-lived cosmic events.
**Action Required**
Researchers should utilize the multi-wavelength observation model and the findings on "orphan afterglows" to refine the classification of future transient detections.
**Indian Research Institutions (IIA, DST, IIT Bombay, NCRA)**
**Impact**
The successful lead by Indian postdoctoral fellows and the use of domestic telescopes (HCT, GIT, uGMRT) highlights the critical role of Indian infrastructure in global high-energy astrophysics.
**Action Required**
These institutions must continue to maintain and provide access to pristine observation sites like Hanle, Ladakh, for international collaborative surveys.
**International Space Missions (Einstein Probe)**
**Impact**
The detection confirms the efficacy of the Einstein Probe mission in surveying the dynamic high-energy sky and identifying rare transient events.
**Action Required**
Mission operators should continue sharing detection data with global ground-based facilities to ensure comprehensive multi-wavelength follow-up.
Key Entities Referenced
Indian Institute of Astrophysics (IIA): An autonomous institution under the Department of Science and Technology that led the study into the origins of Fast X-ray Transients (FXTs).
Einstein Probe mission: A space mission designed to survey the high-energy sky which detected the specific X-ray transient event (EP241107a) central to the research.
Department of Science and Technology (DST): The primary government department that oversees the Indian Institute of Astrophysics and facilitates major scientific research initiatives.
Indian Astronomical Observatory, Hanle, Ladakh: The high-altitude location housing the Himalayan Chandra Telescope and GROWTH India Telescope used for ground-based monitoring of the cosmic event.
Ministry of Science & Technology
Astronomers find clues to the origin of energetic
cosmic X-ray flashes
प्रव तथ: 19 JUN 2026 2:56PM by PIB Delhi
Astronomers have traced the mechanism behind a mysterious celestial non-repeating flash of X-ray called
Fast X-ray Transients (FXTs) that was detected on November 7 last year. The study of the X-ray flash
which they linked to collapse of a massive star or the merger of two neutron stars could help us better
understand the physics of these extreme events.
FXTs are energetic, non-repeating flashes of X-rays associated with violent processes in the universe.
They are a new class of transient sources in the sky, first discovered about a decade ago. These enigmatic
events appear as sudden bursts of low energy X-rays, lasting from a few minutes to several hours, before
fading rapidly from view.
Due to their brief duration, FXTs have long been challenging to study, leaving their origins uncertain.
Over the years, astronomers have proposed several possible mechanisms to explain these mysterious
flashes. Proposed progenitors of these events include supernova shock breakouts from core-collapse
supernovae, neutron stars with extreme magnetic fields rotating every few milliseconds that are formed in
the aftermath of binary neutron star mergers, and tidal disruption events involving white dwarfs and
intermediate-mass black holes.
Many FXTs are associated with high-redshift long period gamma-ray bursts (lGRBs), while others lack
any gamma-ray counterpart, suggesting low-luminosity GRBs or “orphan” afterglows.
A new study led by Deepak Eappachen and Arvind Balasubramanian, both postdoctoral fellows at the
Indian Institute of Astrophysics, an autonomous institution under the Department of Science and
Technology (DST), focuses on one such FXTs event designated EP241107a, detected on November 7,
2024 by the Einstein Probe mission. This Chinese space mission is designed to survey the dynamic high-
energy sky, and is transforming the study of short-lived cosmic events.
Using a multi-wavelength approach, the team discovered a radio counterpart to the X-ray flash using the
Karl G. Jansky Very Large Array, located in New Mexico, USA.
To augment this multi-wavelength study, the researchers also used several powerful ground-based
facilities in India. At the Indian Astronomical Observatory in Hanle, Ladakh, the Himalayan Chandra
Telescope (HCT) and the GROWTH India Telescope (GIT) took advantage of pristine skies to monitor the
event in visible light. HCT is operated by the Indian Institute of Astrophysics (IIA) and the GIT is jointly
operated by IIA and IIT Bombay. The Upgraded Giant Metrewave Radio Telescope, operated by the
National Centre for Radio Astrophysics, was also used for follow up observations. The team additionally
used the 10 metre Keck Observatory in Hawaii, along with the Southern Astrophysical Research
Telescope, a 4.1 metre optical and near infrared facility located in Chile.Fig: This image shows the detection of the counterpart (marked with arrows) to the fast X-ray transient
EP241107a detected in optical –GROWTH India Telescope (left) and in radio –Very Large Array (right).
By comparing the optical and radio observations of EP241107a with those of other extragalactic
transients, and by analysing the properties of its host galaxy, the researchers suggest that this event was
linked to a gamma-ray-burst-like explosion, caused either by the collapse of a massive star or by the
merger of two neutron stars. Detailed modelling of the afterglow indicates that the burst produced a
powerful jet with kinetic energy comparable to the total energy emitted by all the stars in the Milky Way
over several months, if assumed to be emitted equally in all directions.
The authors conclude that EP241107a most likely has a gamma-ray burst origin. EP241107a represents
one of the rarest transient events studied in detail: an explosion not directly detected in gamma rays, yet
clearly linked to a gamma-ray burst origin, sometimes referred to as an “orphan afterglow”. They explain
that this event could represent a gamma-ray burst at the lower-energy end of the known gamma-ray burst
population.
This study was published in the Monthly Notices of the Royal Astronomical Society, and is authored by
Deepak Eappachen, Arvind Balasubramanian, G. C. Anupama, D. K. Sahu and Sudhanshu Barway of the
Indian Institute of Astrophysics, and Vishwajeet Swain, V. Bhalerao, Tanishk Mohan and G. Waratkar of
the Indian Institute of Technology Bombay.
The international team also includes researchers from the California Institute of Technology, the
University of North Carolina at Chapel Hill, and the Center for Astrophysics, Harvard & Smithsonian.
Link to the paper: https://academic.oup.com/mnras/article/545/1/staf2062/8339698
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