and Space Astronomy, University of Colorado, Boulder, CO 80309-0389, USA
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Institut f\"ur Theoretische Physik und Astrophysik, Universit\"at Kiel, 24098 Kiel, Germany
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Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH , UK
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Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH , UK
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Institute for Astronomy (IfA), University of Vienna, T\"urkenschanzstr. 17, 1180 Vienna , Austria
}

\date{Received ; accepted }

\abstract{The core-collapse supernova SN~1987A is the only supernova in the Local Group for which we have a wealth of multiwavelength data from the pre-explosion to the present day. In this paper we present a comprehensive analysis of the X-ray emission from SN~1987A observed with \xmm\ during the period 2000--2010. We detect X-ray emission from SN~1987A in all observations with a total luminosity between 1.3--$2.5 \times 10^{35}$~erg~s$^{-1}$. We find that the X-ray spectrum is best described by a combination of two thermal components with temperatures $kT_1 = 0.31^{+0.02}_{-0.01}$~keV and $kT_2 = 0.90^{+0.07}_{-0.06}$~keV plus an additional power law component with photon index $\Gamma = 3.7^{+0.4}_{-0.3}$. We observe no significant temporal variability in either flux or spectral shape over the 10 year period covered by our observations; however we note that our data are consistent with an increase in flux over this time period at a rate $\sim 5 \times 10^{34}$ erg s$^{-1}$ yr$^{-1}$. We compare our results to those from previous X-ray observations and find that there has been no significant change in either the spectral shape or flux level since 1988 when it was first detected in X-rays with {\it Ginga}. Our results are consistent with those reported by other authors who suggest that the X-ray emission arises from either shocked circumstellar material or shocked ejecta material.}

\keywords{supernovae: individual (SN 1987A) -- ISM: supernova remnants -- ISM: individual objects (LMC N63) -- X rays: ISM }

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\section{Introduction}\label{sec:intro}


SN 1987A was discovered on February 23rd 1987 as a bright blue star in the Large Magellanic Cloud (LMC), which rapidly brightened over several days before fading away again over several months \citep[e.g.,][]{Suntzeff91}. This type II supernova event was one of only two naked eye supernovae observed since 1604; its close proximity ($d=50$ kpc) meant that it was observed across virtually all wavelengths at unprecedented detail making it one of most studied astronomical objects ever observed \citep[e.g.,][]{Bouchet91}. In particular its X-ray properties have been monitored since its discovery using both imaging and spectroscopic instruments such as {\it Ginga}, {\it ROSAT}, {\it ASCA}, {\it Chandra}, {\it XMM Newton}, and {\it Suzaku}. In this paper we present an analysis of all archival data taken between 2000--2010 using EPIC on board \xmm . This represents one third of all available data taken since 1988 when SN 1987A was first detected in X rays using {\it Ginga}.

The origin of the X rays is still not fully understood although two scenarios have been proposed; either they arise from shocked circumstellar material as a result of interaction between the reverse shock wave generated by ejecta impacting onto circumstellar material or they arise from shocked ejecta material due to interaction between different parts within the expanding ejecta itself \citep[e.g.,][]{Burrows95b}. The former scenario is supported by evidence for an asymmetric ring structure seen around SN 1987A at radio wavelengths which is thought to be due to circumstellar material ejected prior to explosion during mass loss episodes associated with pulsational pair instability episodes within its progenitor star prior to explosion \citep[e.g.,][]{Chevalier95}. This scenario has been further supported by more recent work which suggests that there may be evidence for clumping within this ring structure which could provide additional density enhancements necessary for efficient shock heating leading to enhanced levels of X ray emission \citep[e.g.,][]{Abellan09}. The latter scenario has been suggested based on evidence for non spherical structures seen at optical wavelengths which may indicate interaction between different parts within expanding ejecta itself leading to shock heating and subsequent production of high energy photons including hard X rays up to $\sim 10 - 20 $ keV energies \citep[e.g.,][]{Michael03b}. More recently this scenario has been further supported by evidence for non spherical structures seen at radio wavelengths which are thought to be due to Rayleigh Taylor instabilities resulting from interaction between different parts within expanding ejecta itself leading again to shock heating and subsequent production high energy photons including hard X rays up to $\sim 10 - 20 $ keV energies \citep[e.g.,][] {Zanardo10}.

In this paper we present an analysis of all archival data taken between 2000--2010 using EPIC on board \xmm . This represents one third ($\sim 10^4$ ks)of all available data taken since 1988 when SN 1987A was first detected in X rays using {\it Ginga}. We compare our results with those obtained previously using other instruments such as {\it ROSAT},{\it ASCA},{\it Chandra},{\it Suzaku}, etc.. Our aim here is not only study any temporal variability but also any spectral variability over this time period which may provide clues as regards origin nature origin source responsible for producing these high energy photons including hard X rays up to $\sim 10 - 20 $ keV energies .

The paper is organized as follows; Section 2 describes our observations and data reduction techniques while Section 3 presents our analysis results including both temporal and spectral variability studies . Finally Section 4 presents our conclusions regarding origin nature origin source responsible for producing these high energy photons including hard X rays up to $\sim 10 - 20 $ keV energies .

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\section{\xmm\ Observations}\label{sec:obs_reduc_techs_XMMNEWTON_observations_data_reduction_techniques}

A total number nine pointings were made towards SN 1987A using EPIC on board \xmm ; Table 1 lists details regarding each observation along with corresponding exposure times after filtering out periods affected by soft proton flares . All nine pointings were made using both MOS cameras operated in full frame mode while pn camera operated in extended full frame mode; thin filter was used throughout all nine pointings . All nine pointings were made during 2000--2010 epochs covering approximately ten year period . Figure 1 shows location each pointing relative position LMC N63 complex where SN 1987A located while Figure 2 shows light curves each pointing obtained combining MOS1/2 plus pn cameras respectively . As can seen Figure 2 there no significant variation flux level during entire ten year period covered by these nine pointings although some variations can seen during certain periods particularly during 2008 epoch where some decrease flux level can seen lasting several months before returning back original levels again . However due Poisson noise associated low count rates involved these variations can considered insignificant hence no significant temporal variations can claimed have occurred during entire ten year period covered by these nine pointings .

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