The nature of the infrared counterpart and of the optical nebula associated with the Central Compact Object in Vela Jr.

Abstract

The X-ray source CXO J085201.4−461753 in 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 J085201.4−461753 has been possibly detected also at other wavelengths. In particular, a candidate near-infrared counterpart (H = 21.6 ±0.1) was detected by the Very Large Telescope (VLT) in addition to a 6 -wide nebula detected in Hα, interpreted as a velocitydriven bow-shock. Here, we present new near-infrared and optical VLT observations of the candidate counterpart to CXO J085201.4−461753 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 nearinfrared 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 4 offset from the SNR geometrical centre, with a 3σ upper limit of ∼ 10 mas yr −1 . This is much smaller than the expected proper motion of ∼50-100 mas yr −1 , which, in turn, is below the 3σ upper limit of ∼ 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 A and not by Hα. To summarise, we conclude that the proposed near-infrared counterpart is likely unassociated with CXO J085201.4−461753 and that the nebula is not a velocity-driven bow-shock.

A kinematic study of central compact objects and their host supernova remnants

“…Our initial list of potential targets for analysis consisted of the SNRs listed in Table 1. From this list, we excluded Puppis A, PKS 1209−51/52 (due to already precisely measured proper motion of the CCO) and Vela Jr. (due to the established lack of astrometric calibrators, Mignani et al 2019). Even though the proper motion of the CCO in Cas A has already been constrained directly (DeLaney & Satterfield 2013), we decided to include it in our target list, in order to apply our own methodology to the data.…”

“…Furthermore, their spectra can be described entirely using blackbody or NS atmosphere models with luminosities 10 33 erg s −1 , without any unambiguous evidence for nonthermal magnetospheric emission (see Becker 2009;Gotthelf et al 2013;De Luca 2017). Despite intensive searches (e.g., Mignani et al 2008Mignani et al , 2019, no point-like or diffuse counterparts to any CCO at radio, infrared, or optical wavelengths have been found with present-day instrumentation. This places tight upper limits on the presence of potential binary companions and indicates no need for additional components to explain the observed spectral energy distribution.…”

“…In contrast, for the CCO in PKS 1209−51/52, Halpern & Gotthelf (2015) measure a much smaller proper motion of (15 ± 7) mas yr −1 , which corresponds to a projected velocity below 180 km s −1 for a distance of 2 kpc. Only weak constraints can be placed on the proper motions of the CCOs in Cas A (DeLaney & Satterfield 2013) and G266.2−1.2 (Vela Jr., Mignani et al 2019), owing to a paucity of X-ray bright field sources for astrometric frame registration. Finally, very recently, Borkowski et al (2020) have shown that the CCO in G350.1−0.3 seems to exhibit only modest proper motion, contrary to expectations (see Sect.…”

X-ray spectral analysis of the neutron star in SNR 1E 0102.2−7219

“…around the NS discovered by Vogt et al (2018) may be thick enough to provide substantial extinction, though its nature and density have not yet been quantified. Such an optical feature/nebula has only been suggested around one other CCO, CXOU J085201.4-461753 in SNR G266.2-1.2/Vela Jr. (Pavlov et al 2001b; Pel- Mignani et al 2019). However, whether this optical nebula is even associated with the CCO in Vela Jr. is not certain.…”

A kinematic study of central compact objects and their host supernova remnants

“…Despite intensive searches (e.g. Mignani et al 2008Mignani et al , 2019, no point-like or diffuse counterparts to any CCO at radio, infrared or optical wavelengths have been found with present-day instrumentation. This places tight upper limits on the presence of potential binary companions and indicates no need for additional components to explain the observed spectral energy distribution.…”