Tarraneh Eftekhari
The advent of wide-field optical surveys has led to the discovery of superluminous supernovae (SLSNe), a new class of stellar explosions that are 10-100 times more luminous than ordinary supernovae. Despite a growing sample of hydrogen-poor SLSNe, the mechanisms powering these particular events remain an ongoing debate. Radio observations provide a unique opportunity to probe the underlying energy sources which are otherwise obscured in the optical/UV regime. Here we present a large radio and millimeter survey of SLSNe and long gamma-ray bursts (LGRBs), which are theorized to share similar progenitors, to search for compact radio nebulae from magnetars and fast radio bursts (FRBs). The discovery and localization of the repeating fast radio burst FRB 121102 to a dwarf host galaxy has prompted theories suggesting that FRBs are produced by young magnetars born in SLSNe and or LGRBs. Thus, the detection of an FRB from one of these sources would immediately implicate magnetars as the underlying progenitors, and confirm a link between FRBs, SLSNe, and LGRBs. Our survey led to the detection of radio emission from the position of the nearby SLSN PTF10hgi, which represents the first such detection, and is consistent with a model of a central engine driven nebula. We use the remainder of our sample to place limits on central engines from these sources.
Long-duration gamma-ray bursts (LGRBs) are among the most violent explosions in the universe, releasing gamma-ray radiation following the core-collapse of massive stars.
The sources of energy that produce the observed emission from both events are not well understood. However, a number of similarities suggest that they may share a common origin.
Both SLSNe and LGRBs exhibit a preference for faint, low-metallicity dwarf galaxies. Figure 1 shows optical images of 2 SLSN and 2 LGRB host galaxies. They are all similar in that they are small and irregular in shape.
Both show similar features in their spectra.
Increasing evidence that SLSNe and LGRBs are powered by magnetars.
Magnetars are highly magnetized neutron stars, which are the dense cores left behind after a massive star explodes in a supernova.
Radio and millimeter observations can be used to detect clear signatures of magnetar engines.
More evidence emerged in favor of a possible connection between SLSNe, LGRBs, and magnetars with the discovery of the repeating fast radio burst FRB121102, which was localized to a dwarf galaxy. Fast radio bursts are bright bursts of radio emission lasting only fractions of a second.
In addition to the host identification, the source was associated with a source of radio emission. This has prompted theories suggesting that FRBs are produced by young magnetars born in SLSN and/or LGRB explosions.
Figure 3 shows an optical image of the host galaxy of FRB121102 which looks very similar to the SLSN and LGRB hosts shown on slide 1.
Figure 4 shows a radio image of FRB121102 which has a small bright source of radio emission.
Figure 5 shows the original FRB. It is a single spike of intensity, relative to a baseline of noise.
We conducted a large radio and millimeter survey of SLSNe and LGRBs to search for evidence of magnetars.
We detected radio emission from the location of the SLSN PTF10hgi and found that the observations were fully consistent with a central engine.
Figure 6 shows a radio and optical image of ptf10hgi side by side. The radio image shows a point source of emission, while the optical image shows emission from the galaxy which is diffuse and extended.
We find that the same model used to describe the FRB 121102 persistent radio source can explain the observed data for PTF10hgi. We also find that a relativistic jet can explain the emission. In both cases, this points to a central engine.
Figure 7 shows light curve models for PTF10hgi. There is 1 curve corresponding to a model for a relativistic jet, and 2 curves showing the models at 6 and 100 ghz for a nebula. Each of the models run through the 6 GHz data point for PTF10hgi.
The remainder of sources are not detected. Figure 8 consists of a grid of 5 x 5 panels, where each panel shows the light curve model for a magnetar nebula compared to our data points. Most of the data points are above the models, although a small handful lie below.
Our search for FRBs from these sources has not yet led to any detections. Based on what we know from other FRB sources, but continued observations to search for FRBs directly from these sources are needed. Such a connection would immediately implicate magnetars as the progenitors of SLSNe and LGRBs and confirm a connection with FRBs.