Astronomers Find Most Luminous "Cow" to Shine in X-Rays

Artwork comparing a normal supernova to a Cow-like supernova
Credit: Bill Saxton, NRAO/AUI/NSF

The location of AT2020mrf is seen here in images from the eROSITA X-ray telescope. The right panel shows the detection of a new source between July 21 and July 24, 2020. The left panel shows that the source was not there six months earlier. Credit: Pavel Medvedev, SRG/eROSITA

Yuhan Yao
Credit: Yuhan Yao/Caltech

Shri Kulkarni
Credit: Caltech

Results narrow in on what powers new class of supernovae

 

Another member of the new "Cow" class of supernova explosions has been discovered—the brightest one seen in X-rays to date. The new event, dubbed AT2020mrf, is only the fifth found so far belonging to the Cow class of supernovae. The group is named after the first supernova found in this class, AT2018cow, whose randomly generated name just happened to spell the word "cow."

 

What lies behind these unusual stellar explosions? New evidence points to either active black holes or neutron stars.When a massive star explodes, it leaves behind either a black hole or a dead stellar remnant called a neutron star. Typically, these stellar remnants are relatively inactive and shrouded by material ejected in the explosion. But according to Yuhan Yao (MS '20), a graduate student at Caltech, Cow-like events have at their cores very active, and mostly exposed, compact objects that emit high-energy X-ray emission. Yao presented the new findings virtually at the 239th meeting of the American Astronomical Society."We can see down into the heart of these explosions to directly witness the birth of black holes and neutron stars," she says, noting the supernovae are not cloaked by material.

The first Cow event, AT2018cow, shocked astronomers when it was discovered in 2018: the stellar explosion was 10 times brighter in visible light than typical supernovae and faded more quickly. It also gave off a large amount of highly variable X-rays, leading astronomers to believe that they were directly witnessing the birth of a black hole or neutron star for the first time.

Another distinguishing factor of Cows is that they throw off heaps of mass before they explode, and this mass gets illuminated later, after the explosion. When the stars blow up, they generate shock waves that are thought to plow through the pre-existing material, causing them to glow in radio and millimeter-wavelength light.

AT2020mrf is the first to be found initially in X-rays rather than optical light. Yao and her colleagues spotted the event in July 2020 using X-ray data from the Russian--German Spektrum-Roentgen-Gamma (SRG) telescope. They checked observations taken in optical light by the Zwicky Transient Facility (ZTF), which operates from Caltech's Palomar Observatory, and found that ZTF had also spotted the event.

The SRG data revealed that this explosion initially shined with 20 times more X-ray light than the original Cow event. Data captured one year later by NASA's Chandra X-Ray Observatory showed that the explosion was not only still sizzling but shining with 200 times more X-ray light than that detected from the original Cow event over a similar timeframe.

"When I saw the Chandra data, I didn't believe the analysis at first," Yao says. "I reran the analysis several times. This is the brightest Cow supernova seen to date in X-rays.

" Astronomers say that a "central engine" within the supernova debris must be powering the intense, ongoing X-ray radiation. 

"The large amount of energy release and the fast X-ray variability seen in AT2020mrf provide strong evidence that the nature of the central engine is either a very active black hole or a rapidly spinning neutron star called a magnetar," Yao says. "In Cow-like events, we still don't know why the central engine is so active, but it probably has something to do with the type of the progenitor star being different from normal explosions."

Because this event did not look exactly like the other four Cow-like events, Yao says this new class of supernovae is more diverse than originally thought. "Finding more members of this class will help us narrow in on the source of their power," she says.

The study, titled "The X-ray and Radio Loud Fast Blue Optical Transient AT2020mrf: Implications for an Emerging Class of Engine-Driven Massive Star Explosions," has been submitted to The Astrophysical Journal. Other authors include Yao's advisor Shri Kulkarni, the George Ellery Hale Professor of Astronomy and Planetary Science at Caltech; Anna Ho (MS '17, PhD '20) and David Khatami of UC Berkeley; Pavel Medvedev, Sergey Sazonov, Marat Gilfanov, Georgii Khorunzhev, and Rashid Sunyaev of Space Research Institute at the Russian Academy of Sciences; Nayana A.J. of the Indian Institute of Astrophysics; Daniel Perley of Liverpool John Moores University in England; and Poonam Chandra of the National Centre for Radio Astrophysics in India. Sazonov is also affiliated with the Moscow Institute of Physics and Technology, and Gilfanov and Sunyaev are affiliated with the Max Planck Institute for Astrophysics.

Written by Whitney Clavin
 

Contact:

Whitney Clavin
(626) 395‑1944
wclavin@caltech.edu

Source: Caltech - California Institute of Technology/News

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Super-bright stellar explosion is likely a dying star giving birth to a black hole or neutron star

An artist’s impression of the mysterious burst AT2018cow.
Credits:Credit: National Astronomical Observatory of Japan

The discovery, based on an unusual event dubbed “the Cow,” may offer astronomers a new way to spot infant compact objects.

In June of 2018, telescopes around the world picked up a brilliant blue flash from the spiral arm of a galaxy 200 million light years away. The powerful burst appeared at first to be a supernova, though it was much faster and far brighter than any stellar explosion scientists had yet seen. The signal, procedurally labeled AT2018cow, has since been dubbed simply “the Cow,” and astronomers have catalogued it as a fast blue optical transient, or FBOT — a bright, short-lived event of unknown origin.

Now an MIT-led team has found strong evidence for the signal’s source. In addition to a bright optical flash, the scientists detected a strobe-like pulse of high-energy X-rays. They traced hundreds of millions of such X-ray pulses back to the Cow, and found the pulses occurred like clockwork, every 4.4 milliseconds, over a span of 60 days.

Based on the frequency of the pulses, the team calculated that the X-rays must have come from an object measuring no more than 1,000 kilometers wide, with a mass smaller than 800 suns. By astrophysical standards, such an object would be considered compact, much like a small black hole or a neutron star.

Their findings, published today in the journal Nature Astronomy, strongly suggest that AT2018cow was likely a product of a dying star that, in collapsing, gave birth to a compact object in the form of a black hole or neutron star. The newborn object continued to devour surrounding material, eating the star from the inside — a process that released an enormous burst of energy.

“We have likely discovered the birth of a compact object in a supernova,” says lead author Dheeraj “DJ” Pasham, a research scientist in MIT’s Kavli Institute for Astrophysics and Space Research. “This happens in normal supernovae, but we haven’t seen it before because it’s such a messy process. We think this new evidence opens possibilities for finding baby black holes or baby neutron stars.”

Video explaining the new discovery from AT2018cow

“The core of the Cow”

AT2018cow is one of many “astronomical transients” discovered in 2018. The “cow” in its name is a random coincidence of the astronomical naming process (for instance, “aaa” refers to the very first astronomical transient discovered in 2018). The signal is among a few dozen known FBOTs, and it is one of only a few such signals that have been observed in real-time. Its powerful flash — up to 100 times brighter than a typical supernova — was detected by a survey in Hawaii, which immediately sent out alerts to observatories around the world.

“It was exciting because loads of data started piling up,” Pasham says. “The amount of energy was orders of magnitude more than the typical core collapse supernova. And the question was, what could produce this additional source of energy?”

Astronomers have proposed various scenarios to explain the super-bright signal. For instance, it could have been a product of a black hole born in a supernova. Or it could have resulted from a middle-weight black hole stripping away material from a passing star. However, the data collected by optical telescopes haven’t resolved the source of the signal in any definitive way. Pasham wondered whether an answer could be found in X-ray data.

“This signal was close and also bright in X-rays, which is what got my attention,” Pasham says. “To me, the first thing that comes to mind is, some really energetic phenomenon is going on to generate X-rays. So, I wanted to test out the idea that there is a black hole or compact object at the core of the Cow.”

Finding a pulse

The team looked to X-ray data collected by NASA’s Neutron Star Interior Composition Explorer (NICER), an X-ray-monitoring telescope aboard the International Space Station. NICER started observing the Cow about five days after its initial detection by optical telescopes, monitoring the signal over the next 60 days. This data was recorded in a publicly available archive, which Pasham and his colleagues downloaded and analyzed.

The team looked through the data to identify X-ray signals emanating near AT2018cow, and confirmed that the emissions were not from other sources such as instrument noise or cosmic background phenomena. They focused on the X-rays and found that the Cow appeared to be giving off bursts at a frequency of 225 hertz, or once every 4.4 milliseconds.

Pasham seized on this pulse, recognizing that its frequency could be used to directly calculate the size of whatever was pulsing. In this case, the size of the pulsing object cannot be larger than the distance that the speed of light can cover in 4.4 milliseconds. By this reasoning, he calculated that the size of the object must be no larger than 1.3x108 centimeters, or roughly 1,000 kilometers wide.

“The only thing that can be that small is a compact object — either a neutron star or black hole,” Pasham says.

The team further calculated that, based on the energy emitted by AT2018cow, it must amount to no more than 800 solar masses.

“This rules out the idea that the signal is from an intermediate black hole,” Pasham says.

Apart from pinning down the source for this particular signal, Pasham says the study demonstrates that X-ray analyses of FBOTs and other ultrabright phenomena could be a new tool for studying infant black holes.

“Whenever there’s a new phenomenon, there’s excitement that it could tell something new about the universe,” Pasham says. “For FBOTs, we have shown we can study their pulsations in detail, in a way that’s not possible in the optical. So, this is a new way to understand these newborn compact objects.”

This research was supported, in part, by NASA.

Jennifer Chu | MIT News Office

Source: Massachusetts Institute of Technology (MIT)/News

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Astronomers Discover New Class of Cosmic Explosions

Artist's conception illustrates the differences in phenomena resulting from an "ordinary" core-collapse supernova explosion, an explosion creating a gamma-ray burst, and one creating a Fast Blue Optical Transient. Details in text. Credit: Bill Saxton, NRAO/AUI/NSF.  Hi-Res File

Artist's conception illustrates the phenomena that make up the new class of cosmic explosions called Fast Blue Optical Transients. Credit: Bill Saxton, NRAO/AUI/NSF.  Hi-Res File

Astronomers have found two objects that, added to a strange object discovered in 2018, constitute a new class of cosmic explosions. The new type of explosion shares some characteristics with supernova explosions of massive stars and with the explosions that generate gamma-ray bursts (GRBs), but still has distinctive differences from each.

The saga began in June of 2018 when astronomers saw a cosmic blast with surprising characteristics and behavior. The object, dubbed AT2018cow (“The Cow”), drew worldwide attention from scientists and was studied extensively. While it shared some characteristics with supernova explosions, it differed in important aspects, particularly its unusual initial brightness and how rapidly it brightened and faded in just a few days.

In the meantime, two additional blasts — one from 2016 and one from 2018 — also showed unusual characteristics and were being observed and analyzed. The two new explosions are called CSS161010 (short for CRTS CSS161010 J045834-081803), in a galaxy about 500 million light-years from Earth, and ZTF18abvkwla (“The Koala”), in a galaxy about 3.4 billion light-years distant. Both were discovered by automated sky surveys (Catalina Real-time Transient Survey, All-Sky Automated Survey for Supernovae, and Zwicky Transient Facility) using visible-light telescopes to scan large areas of sky nightly.

Two teams of astronomers followed up those discoveries by observing the objects with the National Science Foundation’s Karl G. Jansky Very Large Array (VLA). Both teams also used the Giant Metrewave Radio Telescope in India and the team studying CSS161010 used NASA’s Chandra X-ray Observatory. Both objects gave the observers surprises.

Anna Ho, of Caltech, lead author of the study on ZTF18abvkwla, immediately noted that the object’s radio emission was as bright as that from a gamma-ray burst. “When I reduced the data, I thought I had made a mistake,” she said.

Deanne Coppejans, of Northwestern University, led the study on CSS161010, which found that the object had launched an “unexpected” amount of material into interstellar space at more than half the speed of light. Her Northwestern co-author Raffaella Margutti, said, “It took almost two years to figure out what we were looking at just because it was so unusual.”

In both cases, the follow-up observations indicated that the objects shared features in common with AT2018cow. The scientists concluded that these events, called Fast Blue Optical Transients (FBOTs), represent, along with AT2018cow, a type of stellar explosion significantly different from others. The scientists reported their findings in papers in the Astrophysical Journal and the Astrophysical Journal Letters.

FBOTs probably begin, the astronomers said, the same way as certain supernovae and gamma-ray bursts — when a star much more massive than the Sun explodes at the end of its “normal” atomic fusion-powered life. The differences show up in the aftermath of the initial explosion.

In the “ordinary” supernova of this type, called a core-collapse supernova, the explosion sends a spherical blast wave of material into interstellar space. If, in addition to this, a rotating disk of material briefly forms around the neutron star or black hole left after the explosion and propels narrow jets of material at nearly the speed of light outward in opposite directions, these jets can produce narrow beams of gamma rays, causing a gamma-ray burst.

The rotating disk, called an accretion disk, and the jets it produces, are called an “engine” by astronomers.

FBOTs, the astronomers concluded, also have such an engine. In their case, unlike in gamma-ray bursts, it is enshrouded by thick material. That material probably was shed by the star just before it exploded, and may have been pulled from it by a binary companion.

When the thick material near the star is struck by the blast wave, it causes the bright visible-light burst soon after the explosion that initially made these objects appear so unusual. That bright burst also is why astronomers call these blasts “fast blue optical transients.” This is one of the characteristics that distinguished them from ordinary supernovae.

As the blastwave from the explosion collides with the material around the star as it travels outwards, it produces radio emission. This very bright emission was the important clue that proved that the explosion was powered by an engine.

The shroud of dense material “means that the progenitor star is different from those leading to gamma-ray bursts,” Ho said. The astronomers said that in the Cow and in CSS161010, the dense material included hydrogen, something never seen in in gamma-ray bursts.

Using the W.M. Keck Observatory, the astronomers found that both CSS 161010 and ZTF18abvkwla, like the Cow, are in small, dwarf galaxies. Coppejans said that the dwarf galaxy properties “might allow some very rare evolutionary paths of stars” that lead to these distinctive explosions.

Although a common element of the FBOTs is that all three have a ‘central engine,’ the astronomers caution that the engine also could be the result of stars being shredded by black holes, though they consider supernova-type explosions to be the more likely candidate.

“Observations of more FBOTs and their environments will answer this question,” Margutti said.

To do that, the scientists say they will need to use telescopes covering a wide range of wavelengths, as they have done with the first three objects. “While FBOTs have proven rarer and harder to find than some of us were hoping, in the radio band they’re also much more luminous than we’d guessed, allowing us to provide quite comprehensive data even on events that are far away,” said Daniel Perley, of the Liverpool John Moores University.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc. The study of CSS161010 was partially supported by the Heising-Simons Foundation, NASA, and the National Science Foundation.

Source: National Radio Astronomy Observatory (NRAO)/News

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Media Contact:

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Coppejans et al. 2020, ApJL, 895, L23
DOI: 10.3847/2041-8213/ab8cc

Ho et al. 2020, ApJ, 895, 49
DOI:10.3847/1538-4357/ab8bcf

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The cosmic cow explained - radio signals point to an explosion and a newborn magnetar

Artist's impression of the cosmic cow

Credit: Shanghai Astronomical Observatory, China

Observations using 21 telescopes of the European VLBI Network (EVN) have revealed that a cosmic explosion, called AT2018cow most likely formed a neutron star with an extremely powerful magnetic field - known as a magnetar. The high-resolution radio images produced in this new study show physical properties of the stellar remnant that make alternative explanations less likely, say scientists.

Among short-lived sky phenomena, AT2018cow (The Cow) is an astronomical event like no other. First detected in 2018, it received its memorable name by chance according to alphabetical protocol to classify such events. However, it was not just its name that makes it memorable. AT2018cow was identified in a relatively nearby galaxy (about 200 million light years away). Its proximity, exceptionally brief brightness and unusually high temperature led to widespread attention upon discovery.

Originally discovered with optical telescopes, follow up observations were conducted across wavelengths from X-ray to radio. These observations indicated that there is a ‘central engine' which powered the event. This resulted in theories that the mysterious source could be a supernova - a star whose central core collapsed - or a Tidal Disruption Event (TDE), where a white dwarf star is being ripped apart as it approaches a massive black hole.

In the current study, an international team was led by Prashanth Mohan, astronomer at the Shanghai Astronomical Observatory, China.

"Both these theories suggested that the observed central engine would produce relativistic jets - a high energy expulsion of material. These jets, when aligned with our line of sight, would appear much brighter as ionised matter is accelerated close to the speed of light, and could be responsible for the exceptional brightness of the event. With a network of radio telescopes, we decided to test whether that was the case", explains Tao An.

The team monitored the radio afterglow to search for a relativistic jet from the Cow. They conducted five observations over the course of a year, using a total of 21 telescopes from the European VLBI Network (EVN). The high-resolution radio imaging provided by the EVN, led the team to a surprising conclusion: there was no sign of a relativistic jet.

"These most detailed images in the radio regime do not show any relativistic motion or expansion during this time period. That argues against a jet in the Cow, at least later in its evolution. Instead it seems that the Cow was intrinsically bright and originated from a star exploding as a supernova", says Jun Yang, astronomer at Onsala Space Observatory, Chalmers University of Technology in Sweden.

Further, the astronomers' observations reveal physical conditions that can only be explained by the presence of a neutron star with extremely strong magnetic fields (a magnetar), which was born in the explosion. "We see signs that material from the explosion expanded into a dense, magnetized environment. The way the radio signals faded is just what we might expect if the Cow's "central engine" is a magnetar which formed from the collapse of a star's core" says Prashanth Mohan.

Such characteristics point to another intriguing possibility, the scientists suggest. Interaction of a magnetar with its strongly magnetized environment around it might also produce short enigmatic phenomena known as Fast Radio Bursts (FRBs).

"The EVN is the most sensitive standalone VLBI network in the world that has delivered cutting edge results in the field of transient science. It has by now provided the most accurate localizations of two FRBs. There is an intriguing possibility that there may be a link between FRBs and other type of transient sources (like the event that produced 2018ATcow), but this requires further studies", concludes Zsolt Paragi from the Joint Institute for VLBI ERIC (JIVE).

Source: Joint Institute for VLBI ERIC (JIVE)

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Publication link

Prashanth Mohan, Tao An, and Jun Yang. The Nearby Luminous Transient AT2018cow: A Magnetar Formed in a Subrelativistically Expanding Nonjetted Explosion. 2020, ApJL, 888, 24 https://iopscience.iop.org/article/10.3847/2041-8213/ab64d1

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Contact

Assist. Prof. Prashanth Mohan - lead author
Shanghai Astronomical Observatory, China
Email: pmohan@shao.ac.cn

Prof. Tao An - author
Shanghai Astronomical Observatory, China
Email: antao@shao.ac.cn

Dr. Jun Yang - author
Onsala Space Observatory, Sweden
Email: jun.yang@chalmers.se

Zsolt Paragi - EVN contact
The Joint Institute for VLBI ERIC (JIVE), the Netherlands
Email: paragi@jive.eu
Phone: +31 521 596 536

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Additional information

Observations were conducted with the European Very Long Baseline Interferometry Network (EVN). The EVN is the most sensitive Very Long Baseline Interferometry (VLBI) array in the world, which allows researchers to conduct unique, high-resolution, radio astronomical observations of cosmic radio sources. Data from the EVN is processed at the Joint Institute for VLBI ERIC (JIVE) - an international research infrastructure based in the Netherlands, which also provides support, conducts leading research and forwards technical development in the field of radio astronomy.

A total of 21 antennas from the EVN were involved in these observations: 300 m Arecibo, (USA), 32 m Badary (Russia), 32 m Cambridge (UK), 25 m Defford (UK), 100 m Effelsberg (Germany) 26 m Hartebeesthoek (South Africa), 32 m Irbene (Latvia), 16 m Irbene (Latvia), 76 m Lovell (UK), 40 m Kunming (China), 25 m Knockin (UK), 25 m Medicina (Italy), 25 m Onsala (Sweden), 64 m Sardinia (Italy), 32 m Svetloe (Russia), 65 m Tianma (China), 32 m Torun (Poland), 26 m Urumqi (China), 25 m Westerbork (Netherlands), 40 m Yebes (Spain), 32 m Zelenchukskaya (Russia).

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Astronomers Study Mysterious New Type of Cosmic Blast

ALMA and VLA images of AT2018cow at left; visible-light image of outburst in its host galaxy at right. Images not to same scale. Images of the blast itself do not indicate its size, but are the result of its brightness and the characteristics of the telescopes. Credit: Sophia Dagnello, NRAO/AUI/NSF; R. Margutti, W.M. Keck Observatory; Ho, et al. Hi-res image

Artist's conception of a cosmic blast with a "central engine," such as that suggested for AT2018cow. Black hole at center is pulling in material that forms a rapidly-rotating disk that radiates prolific amounts of energy and propels superfast jets of material from its poles. Jet encounters material surrounding the blast. Credit: Bill Saxton, NRAO/AUI/NSF. Hi-res image

Intensely studied event's characteristics are unprecedented

When astronomers discovered a cosmic explosion in a galaxy nearly 200 million light-years from Earth last June 16, they soon realized it was something different. While still debating the details, scientists now believe they may have gotten their first glimpse of the birth of a powerful phenomenon seen throughout the Universe.

The explosion was discovered by the ATLAS all-sky survey system in Hawaii, and immediately got the attention of astronomers. First, it was unusually bright for a supernova explosion — a common source of such outbursts. In addition, it brightened, then faded, much faster than expected.

Half a year later, “despite being one of the most intensely studied cosmic events in history, watched by astronomers all over the world, we still don’t know what it is,” said Anna Ho, of Caltech, who led a team using the Atacama Large Millimeter/submillimeter Array (ALMA), in Chile, among other telescopes. The object, dubbed AT2018cow, “heralds a new class” of energetic cosmic blasts, Ho added.

The explosion’s unusual characteristics “were enough to get everybody excited,” said Raffaella Margutti, of Northwestern University, who led a team that used telescopes ranging from gamma rays to radio waves, including the National Science Foundation’s Karl G. Jansky Very Large Array (VLA), to study the object. “In addition, AT2018cow’s distance of 200 million light-years, is nearby, by astronomical standards,” making it an excellent target for study, Margutti said.

Astronomers are presenting their findings about the object at the American Astronomical Society’s meeting in Seattle, Washington.

After watching the object and measuring its changing characteristics with a worldwide collection of ground-based and orbiting telescopes, scientists still are not sure exactly what it is, but they have two leading explanations. It may be, they suspect, either a very unusual supernova, or the shredding of a star that passed too close to a massive black hole, called a Tidal Disruption Event (TDE). Researchers are quick to point out, however, that the object’s characteristics don’t match previously-seen examples of either one.

“If it is a supernova, then it is unlike any supernova we have ever seen,” Ho said. The object’s range of colors, or spectrum, she said, “doesn’t look like a supernova at all.” In addition, it was brighter in millimeter waves — those seen by ALMA — than any other supernova.

It also differs from previously-seen Tidal Disruption Events.

“It’s off-center in its host galaxy,” Deanne Coppejans, of Northwestern University, said, meaning it can’t be a star shredded by the supermassive black hole at the galaxy’s center. “If it’s a TDE, then we need an intermediate mass black hole to do the shredding, and those are expected to form in stellar clusters,” Kate Alexander, an Einstein Fellow at Northwestern, added. The problem with that, she pointed out, is that AT2018cow appears to be inside a high-density interstellar medium, which “is difficult to reconcile with the density of gas in stellar clusters.”

Most of the researchers agree that AT2018cow’s behavior requires a central source of ongoing energy unlike those of other supernova explosions. The best candidate, they said, is a black hole that is drawing material from its surroundings. The inflowing material forms a rotating disk around the black hole and that disk radiates prolific amounts of energy. This is the type of “central engine” that powers quasars and radio galaxies throughout the Universe as well as smaller examples such as microquasars.

When a star much more massive than the Sun ceases thermonuclear fusion and collapses of its own gravity, producing a “normal” supernova explosion, no such central engine is produced. However, in the extreme cases called hypernovas, which produce gamma ray bursts, such a central engine produces the superfast jets of material that generate the gamma rays. That engine, however is very short-lived, lasting only a matter of seconds.

If such a central engine powered AT2018cow, it lasted for weeks, making this event distinct from the collapse-induced explosions of supernovas and the more-energetic such explosions that produce gamma ray bursts. In the case of a TDE, the “engine” would come to life as the black hole drew in material from the star shredded by its gravitational pull.

Alternatively, the “engine” resulting from a supernova explosion might be a rapidly-rotating neutron star with an extremely powerful magnetic field — a magnetar.

“We know from theory that black holes and neutron stars form when a star dies, but we’ve never seen them right after they are born. Never,” Margutti said.

“This is very exciting, since it would be the first time that astronomers have witnessed the birth of a central engine,” Ho said.

However, because of AT2018cow’s strange behavior, the verdict still is unclear, the scientists said. The central energy source could be a powerful shock wave hitting a dense shell of material at the object’s core. Either the strange supernova or the TDE explanation still is viable, Ho’s team said.

The astronomers look forward to more work on AT2018cow and to more objects like it.

“During the first few weeks, this object was very bright at millimeter wavelengths, so that means that, with ALMA now available, we may be able to find and study others,” Ho said. “The peak strength of the radio emission starts at ALMA wavelengths, and only moved to VLA wavelengths after a few weeks,” she added.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Southern Observatory (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the Ministry of Science and Technology (MOST) in Taiwan and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

Media Contact:

Dave Finley, Public Information Officer
(575) 835-7302
dfinley@nrao.edu

Source: National Radio Astronomy Observatory (NRAO)/News

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