An X-ray study of the Monoceros supernova remnant

Abstract

We present an analysis of data from both the Röntgen Satellite (ROSAT) and the Advanced Satellite for Cosmology and Astrophysics (ASCA) of the supernova remnant G18.95À1.1. We find that the X-ray emission from G18.95À1.1 is predominantly thermal, heavily absorbed with a column density around 10 22 atoms cm À2 , and can be best described by an nonequilibrium ionization (NEI) model with a temperature around 0.9 keV and an ionization timescale of 1:1 Â 10 10 cm À3 s À1. We find only marginal evidence for nonsolar abundances. Comparisons between 21 cm H i absorption data and derived parameters from our spectral analysis strongly suggest a relatively nearby remnant (a distance of about 2 kpc). Above 4 keV, we identify a small region of emission located at the tip of the central, flat-spectrum barlike feature in the radio image. We examine two possibilities for this emission region: a temperature variation within the remnant or a pulsar wind nebula (PWN). The current data do not allow us to distinguish between these possible explanations. In the scenario where this high-energy emission region corresponds to a PWN, our analysis suggests a rotational loss rate for the unseen pulsar of about 7 Â 10 35 ergs s À1 and a ratio L r /L X of about 3.6 for the entire PWN, slightly above the maximum ratio (3.4 for Vela) measured in known PWNe. Subject headings: ISM: abundances-ISM: individual (G18.95À1.1)-supernova remnants-X-rays: ISM

Discovery of a point-like very-high-energy γ-ray source in Monoceros

“…All these objects have estimated ages less than ∼2000 years, in contrast the Monoceros Loop SNR has an age of ∼3 × 10 4 years (Leahy et al 1986). This supernova remnant therefore appears to be in a different evolutionary phase (late Sedov or Radiative) compared to these known VHE sources.…”

“…Aharonian et al 2006a andKoyama et al 1997 nearby molecular clouds should produce detectable γ-ray emission (Aharonian et al 1994). For this reason the well-known Monoceros Loop SNR (G 205.5+0.5, distance ∼1.6 kpc Graham et al 1982;Leahy et al 1986), with its apparent interaction with the Rosette Nebula (a young stellar cluster/molecular cloud complex, distance 1.4 ± 0.1 kpc Hensberge et al 2000) is a prime target for observations with VHE γ-ray instruments. For the case of hadronic cosmic rays (CRs) interacting in the interstellar medium to produce pions and hence γ-rays via π 0 decay, a spatial correlation between γ-ray emission and tracers of interstellar gas is expected.…”

Observation of the Monoceros Loop SNR region with the HEGRA system of IACTs

“…These regions are located on the rim of the remnant and they coincide with the densest region of optical filaments which show a high hardness ratio (>0.3) 1 . Leahy et al (1986) found that the Monoceros SNR emitted a 0.5-3 keV X-ray flux of 1.5 × 10 −10 erg cm −2 s −1 . An observation carried out with the BeppoSAX satellite (Kaaret et al 1999) discovered a hard spectrum X-ray point source (SAX J0635+0533) within the 95% probability circle of the EGRET detection, which was later identified as a binary pulsar (Cusumano et al 2000).…”

“…Leahy et al (1985Leahy et al ( , 1986) mapped the Monoceros Loop using the E X-ray satellite and detected regions of diffuse X-ray emission. These regions are located on the rim of the remnant and they coincide with the densest region of optical filaments which show a high hardness ratio (>0.3) 1 .…”

Fermi/Lat Study of Gamma-Ray Emission in the Direction of the Monoceros Loop Supernova Remnant

“…In this paper, we adopt this distance of 1.6kpc for both objects. The age was estimated to be~3 10 years 4 based on the X-ray data and an SNR model (Leahy et al 1986). …”