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Register a new userVLT observations of the Central Compact Object in the Vela Jr. supernova remnant
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R. P. Mignani
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X-ray observations have unveiled the existence of enigmatic point-like sources at the center of young (a few kyrs) supernova remnants. These sources, known as Central Compact Objects (CCOs), are thought to be neutron stars produced by the supernova explosion, although their X-ray phenomenology makes them markedly different from all the other young neutron stars discovered so far.The aim of this work is to search for the optical/IR counterpart of the Vela Junior CCO and to understand the nature of the associated Halpha nebula discovered by Pellizzoni et al. (2002).}{We have used deep optical (R band) and IR (J,H,Ks bands) observations recently performed by our group with the ESO VLT to obtain the first deep, high resolution images of the field with the goal of resolving the nebula structure and pinpointing a point-like source possibly associated with the neutron star.Our R-band image shows that both the nebulas flux and its structure are very similar to the Halpha ones, suggesting that the nebula spectrum is dominated by pure Halpha line emission. However, the nebula is not detected in our IR observations, whick makes it impossible to to constrain its spectrum. A faint point-like object (J>22.6, H~21.6, Ks ~ 21.4) compatible with the neutron stars Chandra X-ray position is detected in our IR images (H and Ks) but not in the optical one (R > 25.6), where it is buried by the nebula background. The nebula is most likely a bow-shock produced by the neutron star motion through the ISM or, alternatively, a photo-ionization nebula powered by UV radiation from a hot neutron star.
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We conduct a multi-wavelength morphological study of the Galactic supernova remnant RXJ0852.0-4622 (also known as Vela Jr., Vela Z and G266.2-1.2). RX J0852.0-4622 is coincident with the edge of the larger Vela supernova remnant causing confusion in the attribution of some filamentary structures to either RX J0852.0-4622 or its larger sibling. We find that the RX J0852.0-4622 radio continuum emission can be characterised by a 2-dimensional shell with a radius of 0.90+/-0.01deg (or 11.8+/-0.6pc at an assumed distance of 750pc) centred at (l,b)=(133.08+/-0.01 deg,-46.34+/-0.01deg) (or RA=8h52m19.2s, Dec=-46deg2024.0, J2000), consistent with X-ray and gamma-ray emission. Although [OIII] emission features are generally associated with the Vela SNR, one particular [OIII] emission feature, which we denote as the Vela Claw, morphologically matches a molecular clump that is thought to have been stripped by the stellar progenitor of the RX J0852.0-4622 SNR. We argue that the Vela Claw feature is possibly associated with RX J0852.0-4622. Towards the north-western edge of RX J0852.0-4622, we find a flattening of the radio spectral index towards another molecular clump also thought to be associated with RX J0852.0-4622. It is currently unclear whether this feature and the Vela Claw result from interactions between the RX J0852.0-4622 shock and the ISM.
The X-ray source CXO, J085201.4$-$461753in the few kyr-old Vela Jr. supernova remnant (G266.2-1.2) belongs to the peculiar class of isolated neutron stars dubbed Central Compact Objects (CCOs). At variance with the other CCOs, which are only detected in the X-rays, cxo has been possibly detected also at other wavelengths. In particular, a candidate near-infrared counterpart (H = 21.6 $pm$0.1) was detected by the Very Large Telescope (VLT) in addition to a 6arcsec-wide nebula detected in H$alpha$, interpreted as a velocity-driven bow-shock. Here, we present new near-infrared and optical VLT observations of the candidate counterpart to cxo and its nebula to confirm the proposed associations. Moreover, we used archival Chandra observations to measure for the first time the CXO, J085201.4$-$461753 proper motion. The comparison between the two sets of near-infrared VLT images, taken 10.56 year apart, do not show evidence of proper motion for the candidate counterpart to CXO, J085201.4$-$461753, expected from its 4arcmin offset from the SNR geometrical centre, with a $3sigma$ upper limit of $sim 10$ mas yr$^{-1}$. This is much smaller than the expected proper motion of $sim$50--100 mas yr$^{-1}$, which, in turn, is below the $3sigma$ upper limit of $sim$ 300 mas yr$^{-1}$ that we obtained with Chandra. At the same time, VLT spectroscopy resolved the nebula optical emission, which is dominated by the NII doublet at 6548 and 6584 AA and not by H$alpha$. To summarise, we conclude that the proposed near-infrared counterpart is likely unassociated with cxo and that the nebula is not a velocity-driven bow-shock.
Vela Jr. (RX J0852.0$-$4622) is one of just a few known supernova remnants (SNRs) with a resolved shell across the whole electromagnetic spectrum from radio to very-high-energy ($>100$ GeV; VHE) gamma-rays. Its proximity and large size allow for detailed spatially resolved observations of the source making Vela Jr. one of the primary sources used for the study of particle acceleration and emission mechanisms in SNRs. High-resolution X-ray observations reveal a steepening of the spectrum toward the interior of the remnant. In this study we aim for a self-consistent radiation model of Vela Jr. which at the same time would explain the broadband emission from the source and its intensity distribution. We solve the full particle transport equation combined with the high-resolution 1D hydrodynamic simulations (using Pluto code) and subsequently calculate the radiation from the remnant. The equations are solved in the test particle regime. We test two models for the magnetic field profile downstream of the shock: damped magnetic field which accounts for the damping of strong magnetic turbulence downstream, and transported magnetic field. Neither of these scenarios can fully explain the observed radial dependence of the X-ray spectrum under spherical symmetry. We show, however, that the softening of the spectrum and the X-ray intensity profile can be explained under the assumption that the emission is enhanced within a cone.
We perform a sub-threshold follow-up search for continuous nearly-monochromatic gravitational waves from the central compact objects associated with the supernova remnants Vela Jr., Cassiopeia A, and SNR G347.3$-$0.5. Across the three targets, we investigate the most promising ~ 10,000 combinations of gravitational wave frequency and frequency derivative values, based on the results from an Einstein@Home search of the LIGO O1 observing run data, dedicated to these objects. The selection threshold is set so that a signal could be confirmed using the newly released O2 run LIGO data. In order to achieve best sensitivity we perform two separate follow-up searches, on two distinct stretches of the O2 data. Only one candidate survives the first O2 follow-up investigation, associated with the central compact object in SNR G347.3-0.5, but it is not conclusively confirmed. In order to assess a possible astrophysical origin we use archival X-ray observations and search for amplitude modulations of a pulsed signal at the putative rotation frequency of the neutron star and its harmonics. This is the first extensive electromagnetic follow-up of a continuous gravitational wave candidate performed to date. No significant associated signal is identified. New X-ray observations contemporaneous with the LIGO O3 run will enable a more sensitive search for an electromagnetic counterpart. A focused gravitational wave search in O3 data based on the parameters provided here should be easily able to shed light on the nature of this outlier. Noise investigations on the LIGO instruments could also reveal the presence of a coherent contamination.
The properties of the presumably young galactic supernova remnant (SNR) RX J0852.0-4622, discovered by ROSAT, are still uncertain. The data concerning the distance to the SNR, its age, and the presence of a compact remnant remain controversial. We report the results of several XMM-Newton observations of CXOU J085201.4-461753, the central compact source in RX J0852.0-4622. The currently prefered interpretation of CXOU J085201.4-461753 being a neutron star is in line with our analysis. The Chandra candidate pulsation periods are not confirmed; actually no period was found down to a 3-sigma upper limit for any pulsed fraction. The spectrum of CXOU J085201.4-461753 is best described by either a two blackbody spectrum or a single blackbody spectrum with a high energy power law tail. The two blackbody temperatures of 4 MK and 6.6 MK along with the small size of the emitting regions with radii of 0.36 and 0.06 km invalidate the interpretation that the thermal radiation is cooling emission from the entire neutron star surface. The double blackbody model suggests emission from the neutron stars hot polar regions. No X-ray lines, including the emission feature previously claimed to be present in Chandra data, were found.
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