Deep optical observations of the central X-ray source in the Puppis A supernova remnant

Abstract

Context. X-ray observations revealed a group of radio-silent isolated neutron stars (INSs) at the centre of young supernova remnants (SNRs), dubbed central compact objects or CCOs, with properties different from those of classical rotation-powered pulsars. In at least three cases, evidence points towards CCOs being low-magnetized INSs, born with slow rotation periods, and possibly accreting from a debris disc of material formed out of the supernova event. Understanding the origin of the diversity of the CCOs can shed light on supernova explosion and neutron star formation models. Optical/infrared (IR) observations are crucial to test different CCO interpretations. Aims. The aim of our work is to perform a deep optical investigation of the CCO RX J0822.0−4300 in the Puppis A SNR, one of the most poorly understood in the CCO family. Methods. By using as a reference the Chandra X-ray coordinates of RX J0822.0−4300 we performed deep optical observations in the B, V and I bands with the Very Large Telescope (VLT). Results. We found no candidate optical counterpart within 3σ of the computed Chandra X-ray position down to 5σ limits of B ∼ 27.2, V ∼ 26.9, and I ∼ 25.6, the deepest obtained in the optical band for this source. Conclusions. These limits confirm the non-detection of a companion brighter than an M 5 dwarf. At the same time, they do not constrain optical emission from the neutron star surface, while emission from the magnetosphere would require a spectral break in the optical/IR.

SPITZEROBSERVATIONS OF DUST DESTRUCTION IN THE PUPPIS A SUPERNOVA REMNANT

“…X-ray observations have revealed a neutron star, RXJ0822− 4300, associated with the Puppis A SNR (e.g., Petre et al 1996;Winkler & Petre 2007;Gotthelf & Halpern 2009). However, this object has not been detected at optical wavelengths or in deep 4.5 and 8 μm observations with IRAC (Wang et al 2007;Mignani et al 2009). Likewise, in our shallow MIPS observations, there is no detection of any associated emission at 24, 70, or 160 μm.…”

Optical, ultraviolet, and infrared observations of isolated neutron stars

“…For the CCO in PKS 1209−51, the originally proposed nIR identification with a low-mass M-star (Pavlov et al 2004) was ruled out by an improved astrometry analysis (Mignani et al 2007b;Wang et al 2007b) and by the upper limit on the proper motion of the proposed candidate counterpart (De Luca et al 2009). No viable candidate counterpart was found for the CCOs in Cas A (Fesen et al 2006), Kesteven 79 (Gotthelf et al 2005), G347.3−0.5 (Mignani et al 2008c), Puppis A (Wang et al 2007b;Mignani et al 2009d). For all of them, the derived optical/nIR upper limits enable to rule out the presence of a binary companion other than a very low mass star (M5 type or later), although they do not exclude the presence of a debris disc as well, like in the case of the magnetars.…”

HST and VLT observations of the neutron star 1E 1207.4–5209

“…Of course, in both cases the conclusion about the non-association of source Z with 1E 1207.4−5209 would not change. Thus, 1E 1207.4−5209 remains, as yet, unidentified in the optical/IR, as all the other CCOs observed so far (Fesen et al 2006;De Luca et al 2008;Mignani et al 2008Mignani et al , 2009a, with the only possible exception of the source in the Vela Jr. SNR (Mignani et al 2007b). The upper limits to the optical/IR flux presented here are the deepest available so far for a member of the CCO class and correspond to an (unabsorbed) optical-to-X-ray flux ratio F 814W /F 0.3−3 keV ∼ 5 × 10 −6 .…”