On October 16, 2017, an international group of astronomers and physicists enthusiastically reported the first simultaneous detection of light and gravitational waves from the same source-a merger of two neutron stars. Now, a team that includes several University of Maryland astronomers has identified a relative relative to that historic event.
The newly described object, named GRB150101B, reported as a gamma-ray burst localized by NASA's Neil Gehrel's Swift Observatory in 2015. Follow-up observations by NASA's Chandra X-ray Observatory, the Hubble Space Telescope (HST) and the Discovery Channel Telescope (DCT) suggest that GRB150101B shares remarkable similarities with the neutron star merger, named GW170817, discovered by the Laser Interferometer Gravitational-wave Observatory (LIGO) and observed by multiple light-gathering telescopes in 2017.
A new study suggests that these two separate objects may, in fact, be directly related. The results were published on October 16, 2018 in the journal Nature Communications .
"It's a big step to go," said study lead author Eleonora Troy, an associate research scientist in the UMD Department of Astronomy with a joint appointment at NASA's Goddard Space Flight Center.
Troja and her colleagues suspected that they both GRB150101B and GW170817 were produced by the same type of event: a merger of two neutron stars. These catastrophic coalesces each generated a narrow jet, or beam, of high-energy particles. The jets each produced a short, intense gamma-ray burst (GRB) -a powerful flash that loads only a few seconds. GW170817 thus created ripples in space-time called gravitational waves, suggesting that this might be a common feature of neutron star mergers.
The apparent match between GRB150101B and GW170817 is striking: both produced on an unusually faint and short-lived gamma ray burst and both were a source of bright, blue optical light and long-lasting X-ray emission. The host galaxies are remarkably similar, based on HST and DCT observations. Both are bright elliptical galaxies with a population of a few billion years old.
"We have a case of cosmic look-alikes," said co-author Geoffrey Ryan, a postdoctoral researcher in the UMD's Department of Astronomy and a fellow of the Joint Space Science Institute.  In the cases of both GRB150101B and GW170817, the explosion was likely viewed "off -axis, "that is not directly pointing to Earth. So far, these events are the only two off-axis short GRBs that astronomers have identified.
The optical emission from GRB150101B is largely in the blue portion of the spectrum, providing an important clue that this is another kilonova, as seen in GW170817. A kilonova is a luminous flash of radioactive light that produces silver, gold, platinum and uranium.
While there are many commonalities between GRB150101B and GW170817, there are two very important differences. GRB150101B read about 1.7 billion light years away.
The second important difference is that, unlike GW170817, gravitational wave data does not exist for GRB150101B , Without this information, the team can not calculate the masses of the two objects that merged.
"Surely it's just a matter of time before another event like GW170817 wants to provide both gravitational wave data and electromagnetic imagery Alexander Kutyrev, associate research scientist at the UMD Department of Astronomy with a Joint Appointment at NASA's Goddard, said: "If the next search observation reveals a merger between a neutron star and a black hole Space Flight Center. GW170817 and GRB150101B have been detected so far additional observations in different wavelengths of light, according to the researchers. Without research detections-in particular, at longer wavelengths as X-rays or optical light-it is very difficult to determine the precise location of events that produce gamma-ray bursts.
In the case of GRB150101B, astronomers first thought that the event coincides with Swift at the center of the galaxy. The most likely explanation for such a source would be a supermassive black hole devouring gas and dust. However, follow-up observations with Chandra's galaxy
according to the researchers, even if LIGO had been operational in early 2015, it would have gravitational waves from GRB150101B because of the event's greater distance from Earth.
"Every new observation helps us to identify different parts of the puzzle." , adding gold and platinum add a shade of red, for example, "Troja added. "We've been able to identify this kilonova without gravitational wave data, so maybe in the future, we'll even be able to do so without directly observing a gamma-ray burst."
The research paper, "A luminous blue kilonova and off-axis jet from a compact binary merger at z = 0.1341, "Eleonora Troy, Geoffrey Ryan, Luigi Piro, Hendrik van Eerten, S. Bradley Cenko, Yongmin Yoon, Seong-Kook Lee, Myungshin Im, Takanori Sakamoto, Pradip Gatkine, Alexander Kutyrev and Sylvain Veilleux, which was published in the journal Nature Communications on October 16, 2018.
Neutron star merger emerge from behind sun
E. Troja et al, A luminous blue kilonova and off-axis jet from a compact binary merger at z = 0.1341, Nature Communications (2018). DOI: 10.1038 / s41467-018-06558-7