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Register a new userNeutrinos from SN 1987a. A Puzzle Revisited
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Authors
Gerd Schatz
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The smallest of the four detectors which claim to have observed neutrinos from SN 1987a registered the events more than 4 h earlier than the other three ones. This claim is not usually accepted because it is difficult to understand that the other (and larger) detectors did not register any events at the same time. It is shown that microlensing of the neutrinos by a star in-between the supernova (SN) and Earth can enhance the neutrino intensity at the position of one detector by more than an order of magnitude with respect to the other detectors. Such a configuration is improbable but not impossible. Essential for this enhancement is the small source diameter, of order 100 km. So if two bursts of neutrinos were emitted by SN 1987a at a separation of about 4 h it could be explained easily that the smallest detector observed the first burst while the other ones missed it and vice versa.
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The possible detection of a compact object in the remnant of SN 1987A presents an unprecedented opportunity to follow its early evolution. The suspected detection stems from an excess of infrared emission from a dust blob near the compact objects predicted position. The infrared excess could be due to the decay of isotopes like 44Ti, accretion luminosity from a neutron star or black hole, magnetospheric emission or a wind originating from the spindown of a pulsar, or thermal emission from an embedded, cooling neutron star (NS 1987A). It is shown that the last possibility is the most plausible as the other explanations are disfavored by other observations and/or require fine-tuning of parameters. Not only are there indications the dust blob overlaps the predicted location of a kicked compact remnant, but its excess luminosity also matches the expected thermal power of a 30 year old neutron star. Furthermore, models of cooling neutron stars within the Minimal Cooling paradigm readily fit both NS 1987A and Cas A, the next-youngest known neutron star. If correct, a long heat transport timescale in the crust and a large effective stellar temperature are favored, implying relatively limited crustal n-1S0 superfluidity and an envelope with a thick layer of light elements, respectively. If the locations dont overlap, then pulsar spindown or accretion might be more likely, but the pulsars period and magnetic field or the accretion rate must be rather finely tuned. In this case, NS 1987A may have enhanced cooling and/or a heavy-element envelope.
Handed the baton from ROSAT, early observations of SN 1987A with the Chandra HETG and the XMM-Newton RGS showed broad lines with a FWHM of 10^4 km/s: the SN blast wave was continuing to shock the H II region around SN 1987A. Since then, its picturesque equatorial ring (ER) has been shocked, giving rise to a growing, dominant narrow-lined component. Even so, current HETG and RGS observations show that a broad component is still present and contributes 20% of the 0.5--2 keV flux. SN 1987As X-ray behavior can be modeled with a minimum of free parameters as the sum of two simple 1D hydrodynamic simulations: i) an on-going interaction with H II region material producing the broad emission lines and most of the 3--10 keV flux, and ii) an interaction with the dense, clumpy ER material that dominates the 0.5--2 keV flux. Toward the future, we predict a continued growth of the broad component but a drop in the 0.5--2 keV flux, once no new dense ER material is being shocked. When? Time, and new data, will tell.
Both CO and SiO have been observed at early and late phases in SN 1987A. H_2 was predicted to form at roughly the same time as these molecules, but was not detected at early epochs. Here we report the detection of NIR lines from H_2 at 2.12 mu and 2.40 mu in VLT/SINFONI spectra obtained between days 6489 and 10,120. The emission is concentrated to the core of the supernova in contrast to H-alpha and approximately coincides with the [Si I]/[Fe II] emission detected previously in the ejecta. Different excitation mechanisms and power sources of the emission are discussed. From the nearly constant H_2 luminosities we favour excitation resulting from the 44Ti decay.
Since the day of its explosion, SN 1987A (SN87A) was closely monitored with the aim to study its evolution and to detect its central compact relic. The detection of neutrinos from the supernova strongly supports the formation of a neutron star (NS). However, the constant and fruitless search for this object has led to different hypotheses on its nature. Up to date, the detection in the ALMA data of a feature somehow compatible with the emission arising from a proto Pulsar Wind Nebula (PWN) is the only hint of the existence of such elusive compact object. Here we tackle this 33-years old issue by analyzing archived observations of SN87A performed Chandra and NuSTAR in different years. We firmly detect nonthermal emission in the $10-20$ kev energy band, due to synchrotron radiation. The possible physical mechanism powering such emission is twofold: diffusive shock acceleration (DSA) or emission arising from an absorbed PWN. By relating a state-of-the-art magneto-hydrodynamic simulation of SN87A to the actual data, we reconstruct the absorption pattern of the PWN embedded in the remnant and surrounded by cold ejecta. We found that, even though the DSA scenario cannot be firmly excluded, the most likely scenario that well explains the data is the PWN emission.
We revisit the evidence for the contribution of the long-lived radioactive nuclides 44Ti, 55Fe, 56Co, 57Co, and 60Co to the UVOIR light curve of SN 1987A. We show that the V-band luminosity constitutes a roughly constant fraction of the bolometric luminosity between 900 and 1900 days, and we obtain an approximate bolometric light curve out to 4334 days by scaling the late time V-band data by a constant factor where no bolometric light curve data is available. Considering the five most relevant decay chains starting at 44Ti, 55Co, 56Ni, 57Ni, and 60Co, we perform a least squares fit to the constructed composite bolometric light curve. For the nickel isotopes, we obtain best fit values of M(56Ni) = (7.1 +- 0.3) x 10^{-2} Msun and M(57Ni) = (4.1 +- 1.8) x 10^{-3} Msun. Our best fit 44Ti mass is M(44Ti) = (0.55 +- 0.17) x 10^{-4} Msun, which is in disagreement with the much higher (3.1 +- 0.8) x 10^{-4} Msun recently derived from INTEGRAL observations. The associated uncertainties far exceed the best fit values for 55Co and 60Co and, as a result, we only give upper limits on the production masses of M(55Co) < 7.2 x 10^{-3} Msun and M(60Co) < 1.7 x 10^{-4} Msun. Furthermore, we find that the leptonic channels in the decay of 57Co (internal conversion and Auger electrons) are a significant contribution and constitute up to 15.5% of the total luminosity. Consideration of the kinetic energy of these electrons is essential in lowering our best fit nickel isotope production ratio to [57Ni/56Ni]=2.5+-1.1, which is still somewhat high but is in agreement with gamma-ray observations and model predictions.
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