Relativistic Jets Powering the Early Bumps in Superluminous Supernovae

Concetti Chiave

A relativistic jet launched by a central engine, such as a magnetar or accreting black hole, can successfully break through the expanding supernova ejecta and power bright ultraviolet/optical emission lasting several days after the explosion, matching the observed "bumps" in the light curves of many superluminous supernovae.

Sintesi

The authors investigate whether the early emission phase observed as "bumps" in the light curves of some superluminous supernovae (SLSNe) can be powered by a collimated jet from the same central engine responsible for the bulk of the SLSN emission at later times.

Using 3D relativistic hydrodynamic simulations, the authors find that a jet with properties (luminosity Lj ≈ 10^45.5 erg/s, duration teng ≈ 10 days) compatible with those needed to power SLSNe can successfully break through the expanding supernova ejecta. The interaction of the jet and its shocked cocoon with the ejecta near the breakout radius generates bright ultraviolet/optical emission lasting for about a week, reaching a peak luminosity ≳ 10^44 erg/s.

The luminosity and temperature of this cocoon emission match those observed in the early bumps of SLSN light curves, weeks prior to the optical maximum. The authors suggest that confirmation of jet breakout signatures, such as days-long internal X-ray emission, large photosphere velocities (v/c ≳ 0.1), or radio afterglow detection, would provide strong evidence for central engines powering SLSNe.

Statistiche

The jet has a luminosity of Lj ≈ 3 × 10^45 erg/s and a duration of teng ≈ 10.3 days.
The ejecta mass is Mej ≈ 20 M⊙ with a front velocity of vej ≈ 10,000 km/s.
The jet breaks out of the ejecta after tb ≈ 5.5 days.

Citazioni

"The luminosity and temperature of the cocoon emission match those observed in the early bumps of SLSN light curves, weeks prior to the optical maximum."
"Confirmation of jet breakout signatures, such as days-long internal X-ray emission, large photosphere velocities (v/c ≳ 0.1), or radio afterglow detection, would provide strong evidence for central engines powering SLSNe."

Approfondimenti chiave tratti da

Late Jets, Early Sparks: Illuminating the Premaximum Bumps in Superluminous Supernovae

by Ore Gottlieb... alle arxiv.org 10-01-2024

https://arxiv.org/pdf/2407.20348.pdf

Domande più approfondite

How would the properties of the early emission, such as its luminosity and duration, change if the jet power or opening angle were different from the values assumed in this study?

If the jet power (Lj) or opening angle (θj) were altered from the values assumed in this study, the properties of the early emission in superluminous supernovae (SLSNe) would be significantly affected.

Jet Power (Lj):

Increased Jet Power: If the jet power were increased, the luminosity of the early emission would likely rise correspondingly. A higher Lj would lead to a more energetic jet-cocoon interaction, resulting in a greater amount of thermal energy being released as radiation. This could enhance the peak luminosity of the early bumps observed in SLSN light curves, potentially exceeding the typical range of (10^{43} - 10^{45} , \text{erg s}^{-1}).
Decreased Jet Power: Conversely, if Lj were reduced, the luminosity of the early emission would decrease, possibly leading to less pronounced early bumps. The duration of the emission might also be affected; a lower power could result in a shorter duration of observable emission, as the energy deposited into the cocoon would be insufficient to sustain prolonged radiation.

Opening Angle (θj):

Wider Opening Angle: A wider opening angle would allow the jet to interact with a larger volume of the surrounding ejecta, potentially increasing the luminosity of the early emission due to a greater area for energy deposition. However, this could also lead to a dilution of the emitted radiation, as the energy would be spread over a larger area, possibly resulting in a lower peak luminosity.
Narrower Opening Angle: A narrower opening angle would concentrate the jet's energy into a smaller region, potentially leading to a more intense but shorter-lived emission. This could result in a sharper, more pronounced early bump in the light curve, but with a rapid decline as the energy is quickly radiated away.

In summary, variations in jet power and opening angle would directly influence the luminosity and duration of the early emission in SLSNe, with higher power generally leading to brighter and longer-lasting emissions, while changes in the opening angle would affect the spatial distribution and intensity of the emitted radiation.

What alternative mechanisms, besides a relativistic jet, could potentially explain the observed early bumps in SLSN light curves, and how could they be distinguished observationally?

Several alternative mechanisms could account for the observed early bumps in SLSN light curves, aside from the proposed relativistic jet model:

Shock Interaction with Circumstellar Medium (CSM):

Mechanism: This scenario posits that the fast-moving supernova ejecta collide with a dense CSM, which could have been expelled by the progenitor star prior to the explosion. The interaction generates shock waves that heat the surrounding material, leading to enhanced luminosity.
Distinguishing Observations: Observationally, this could be differentiated from jet-driven emission by looking for signatures of CSM interaction, such as specific spectral features indicative of shock heating or the presence of broad emission lines. Additionally, the light curve shape might differ, with a more gradual rise and fall compared to the sharper features expected from jet breakout.

Delayed Shock Breakout:

Mechanism: A delayed shock breakout could occur if the energy from the central engine is released in a spherical manner, creating a shock wave that breaks out of the ejecta after a delay. This could lead to a similar early bump in luminosity.
Distinguishing Observations: This mechanism could be identified by the temporal correlation between the shock breakout and the main explosion, as well as the spectral characteristics of the emitted light. If the early emission is isotropic and not collimated, it would suggest a spherical breakout rather than a jet.

Magnetar Activity:

Mechanism: A rapidly spinning magnetar could inject energy into the ejecta, heating it and causing early emission. The energy released from the magnetar's spin-down could lead to observable luminosity.
Distinguishing Observations: The signature of magnetar activity could be identified through the detection of high-energy gamma-ray or X-ray emissions, as well as specific light curve features that correlate with the magnetar's spin-down timescale. The presence of a persistent X-ray source could also indicate magnetar activity.

In conclusion, while relativistic jets provide a compelling explanation for early bumps in SLSN light curves, alternative mechanisms such as shock interactions with CSM, delayed shock breakout, and magnetar activity could also account for these observations. Distinguishing between these scenarios would rely on detailed spectral analysis and light curve modeling.

Given the uncertainties in the jet properties and their interaction with the supernova ejecta, what other observable signatures might arise that could provide additional insights into the central engine powering SLSNe?

The uncertainties surrounding jet properties and their interactions with supernova ejecta present opportunities for various observable signatures that could yield insights into the central engine powering superluminous supernovae (SLSNe):

X-ray Emission:

Signature: If the jet successfully breaks out of the ejecta, it may produce internal X-ray emission detectable by observatories. This emission could arise from the interaction of the jet with the surrounding material, leading to high-energy photons.
Implications: Detection of X-ray emission, particularly for on-axis observers, would provide strong evidence for the presence of a relativistic jet and its interaction with the ejecta.

Radio Afterglow:

Signature: As the jet interacts with the circumstellar medium (CSM), it could produce a radio afterglow detectable at later times. This emission would arise from synchrotron radiation generated by relativistic electrons accelerated in the shock front.
Implications: The presence of a radio afterglow would indicate ongoing jet activity and could help constrain the jet's energy and structure. Observations of the radio light curve could also provide insights into the density and structure of the CSM.

Spectroscopic Signatures:

Signature: Spectroscopy of the early emission could reveal Doppler-broadened lines indicative of high-velocity ejecta. The presence of broad emission lines could suggest energetic processes associated with a central engine.
Implications: Analyzing the spectral features could help distinguish between different powering mechanisms, such as jet-driven versus CSM interaction, based on the observed line profiles and shifts.

Polarization Measurements:

Signature: The emission from a relativistic jet may exhibit polarization due to the ordered magnetic fields within the jet. Measuring the degree and angle of polarization could provide insights into the jet's structure and dynamics.
Implications: Polarization measurements could help confirm the presence of a jet and provide information about its orientation and the magnetic field configuration, offering additional constraints on the central engine model.

Temporal Variability:

Signature: Monitoring the light curves for rapid variability could indicate the presence of a central engine that is not only powerful but also capable of modulating its output.
Implications: Such variability could suggest a more complex engine mechanism, potentially involving interactions between different components (e.g., a magnetar and a jet) or changes in the surrounding environment.

In summary, various observable signatures, including X-ray emissions, radio afterglows, spectroscopic features, polarization measurements, and temporal variability, could provide valuable insights into the central engine powering SLSNe. These observations would enhance our understanding of the mechanisms behind these extraordinary cosmic events.