1WGA J1713.4-3949 侵略計劃

First image of TeV-energy gamma-rays of a cosmic source: a supernova remnantHESS had just made a map of very high energy gamma-rays, of the order of TeV of the SNR RX J1713.7-3946. This is the first map in TeV gamma-rays ever done of an astronomical object.

The shock fronts of supernovae, observed in their shell-like remnants are generallybelieved to be the principal accelerators of galactic cosmic rays.

Up to now, the TeV emission of SNRs had been detected or suspected in 3 cases only.(RX J1713.7-3946, Cas A and SN1006) and with a rather large uncertainty on the positionof the emitting source.

The TeV map presented here respresents, not only one important step in the understanding of the original of galactic cosmic radiation, but demonstrates directly that shock waves in Supernova shells are indeed able to accelerate charged particles up to more than 10 TeV.

In the figure, the maps observed at different energies coincide tends to prove that very highenergy particles are indeed accelerated in the shell.

High-energy particle acceleration in the shell of a supernova remnant

RX J1713.7-3946 (situated in the Galactic plane, in the constellation Scorpius) is one of thebrighter Galactic X-ray SNRs and also a complex object interacting with molecular cloudsof different densities where TeV emission might emerge from various process. Without doubt there will be inverse Compton process, especially from low densities region(as in the eastern part) of the SNR. At the elevated densities likely to exist in the NW rim,π0-decays following proton-proton interactions, but also non-thermal Bremsstrahlung ofelectrons, could make a significant contributions.

The spatially resolved remnant has a shell morphology similar to that seen in X-rays, whichdemonstrates that very high-energy particles are accelerated there. The energy spectrum indicates efficient acceleration of charged particles to energies beyond 100 TeV, consistentwith current ideas of particle acceleration in young SNR shocks.

F. A. Aharonian et. al.

X-ray observations of the CCO in SNR G347.3-0.5J. S. Lazendic et al., ApJ., 2003

CCOs are more poorly understood objects near the centers of SNRs with detectable X-rayflux but no optical/radio counterparts nor any signs of rotation. Their spectrum are very soft,with blackbody temperatures of ~0.4keV, often requiring an additional power-law component with photon index ~4.

In this study, we address the nature of 1WGA J1713.4-3949, a compact source located atthe center of SNR G347.3-0.5 (RX J1713.7-3946). Early ROSAT observations identifiedtwo point sources within the boundaries of the SNR shell. (Pfeffermann & Aschenbach 1996)

1WGA J1714.4-3945, was determined to be ofstellar region. (Pfeffermann & Aschenbach 1996)

1WGA J1713.4-3949, located at the geometricalcenter of the SNR, no optical counterpart has beenfound within 10" of the ROSAT position, (Slane et al.

1999) and the source has correspondingly been suggested to be a associated NS.

While ASCA observations were not able to provideuseful limits to the pulsations in the X-ray band (Slane et al. 1999), radio pulsations were detected with a392ms period within a 7׳ radius region toward thissource. (PSR J1713-3945; Crawford et al. 2002)

They used FFT to search the X-ray data (Chandra, XMM & RXTE) for pulsations from 1WGA J1713.4-3949 but found no pulsation signal.The resulting timing parameters of PSR J1713-3945 are presented in Table 3. The pulsar’sdispersion measure (DM) of 337 pc cm-3 yields an estimated distance of 4.3 kpc using the revised DM-distance model of Cordes & Lazio (2002). While the distance to the radio pulsar PSR J1713-3945 is broadly consistent with SNR Distance of 6±1 kpc estimated by Slane et al. (1999), the pulsar is likely to be quite old.(τc~1.1 Myr, compared with τ<40 kyr for SNR G347.3-0.5) and doesn’t have sufficientspin-down luminosity (Ė~3.7x1033 ergs s-1) to power the observed X-ray flux from 1WGA J1713.4-3949 (Lx~6x1034 ergs s-1). PSR J1713-3945 is therefore spatially coincidentwith SNR G347.3-0.5 by chance, and there is likely no physical association between the twosystems.

The lack of radio and optical counterparts for 1WGA J1713.4-3949, the absence of X-raypulsations with the current sensitivity and time resolution, the two component spectrumand its associated luminosity are properties consistent with CCOs. (Pavlov et al 2002) Their limits on the pulsed fraction from 1WGA J1713.4-3949 are consistent with thosederived toward other CCOs (7%-15%; Pavlov et al. 2002).Accretion from a fallback disk? Accretion from a low-mass companion?Interpretations of the emission from CCOs as thermal radiation from the surface of an NS run into problems because of high surface temperatures and small emitting areas derived from the blackbody model fits.

What is the distance to the SNR G347.3-0.5? 6.3±0.4 kpc? 1kpc??

Koyama et al. (1997) compare their measurement of the column density toward G347.3-0.5with the total NH in the direction of the Galactic center to estimate a distance of 1 kpc tothe remnant. The total line-of-sight column density in the direction of G347.3-0.5 is NH=1.2x1022 cm-2

based on HI observations (Dicky & Lockman 1990) and confirmed by CO measurements. ( Bronfman et al. 1989)

The NH-value Slane et al. measure for G347.3-0.5 (~8x1021 cm-2) is a significant fractionof the total column through the Galaxy, and so the distance to the SNR must be considerablymore than 1 kpc.The nearer distance could be in agreement with the hypothesis proposed by Wang et al. (1997)

, based on historical records, that RX J1713.7-3946 is the remnant of SN that exploded in AD 393. New XMM observations (Cassam-Chenai et al. 2004b) that re-opened the whole distancequestion with new high-resolution CO mm-wave observations. (Fukui et al. 2003)

These new results suggest possible indications of interaction between the SNR shock frontand molecular gas located at 1 kpc on the NW and SW sides of the SNR.GeV γ-ray emission was detected by the EGRET instrument to the NE of the SNR (Hartman

et al. 1999). This emission was interpreted as π0 decay attributed to the interaction of CR nuclei.(accelerated at the shock in RX J1713.7-3946)At TeV γ-rays, the CANGAROO imaging Cerenkov telescope detected emission in the NWof the SNR, which was interpreted as Inverse Compton emission from accelerated electrons.(Muraishi et al. 2000) The low matter densities in the ambient medium is unfavorable for the interpretation in terms π0 decay process.

XMM-Newton observations of the SNR J1713.7-3946 and its central source(Cassam-Chenaї et al. 2004)

The X-ray bright central point source 1WGAJ 1713.4-3949 detected at the center of SNR RX J1713.7-3946 shows spectral properties very similar to those of CCOs found in SNRs (e.g., Vela junior) and which are consistent with the absorbing column density of the central diffuse X-ray emission arising from the SNR.The absorbing column density variations (0.4x1022 cm-2≤ NH ≤1.1x1022cm-2) are well reflected by the extinction in the map of integrated optical star light. The strong positive correlation between the X-ray brightness along the western rims suggests that the shock front of RX J1713.7-3946 is impacting molecular clouds there. CO and HI observations show the inferred cumulative absorbing column densities are excellent agreement with the X-ray measurements in different places of the remnant only if the SNR placed at a distance of 1.3±0.4 kpc, probably in the Sagittarius galactic arm.An excess in the CO emission found in the SW at ~1 kpc strongly suggests that molecular clouds produce the enhancement in absorption. The spectrum is steep in the central regions and flat at the presumed shock locations,particularly in the SE. However, the regions where the shock strikes molecular clouds have a steeper spectrum than those where the shock propagates into a low density medium.

XMM-Newton observations of the SNR J1713.7-3946 and its central source(Cassam-Chenaї et al. 2004)

The search for thermal emission from RX J1713.7-3946 remains unsuccessfulleading to a number density upper limit of 2x10-2 cm-3 in the ambient medium.This low density leads to lower age of SNR can be reconciled with the high densityin molecular clouds if the remnant is in radiative phase where SNR shock encountersa dense ambient medium whereas it is in the free expansion phase elsewhere.

RX J1713.7-3946’s progenitor mass is estimated to lie between 12 and 16 Mּס

based on a scenario involving the effect of stellar wind of the progenitor star.

The new observation of XMM

0207300201-- PN: 33770s/SW; MOS1: 33971s/FF; MOS2: 33976s/FF

Photons: (Photon Number) (PulseFraction) (De Jager 1994)

(keV) total backg. H_max(Freq.(Hz)) UpperLimt (2σ/3σ)

0.2~12 32461 3278 39.7 (14.895415) 6.963% / 7.767% 0.5~1.0 5386 288 43.8 (11.583325) 16.27% / 18.11% 1.0~2.0 18911 580 42.9 (51.154985) 8.413% / 9.369% 2.0~4.0 5568 645 39.5 (31.008420) 16.48% / 18.38%

(H_max : except for features "related to time resolution & <0.0003Hz")

Periodicity Search

(The pulsed fraction is estimated by CJL, 2005)

Green line is contourthat we give 40 equalspace from 0 to 3430

The black line shows the source photons in each energy;The red line shows the background photons in each energy.

This is why we search periodicity in different energy band and we only consider the spectrum fitting from 0.5-5 keV.

The EPIC MOS (left panel) and pn (right panel) energy resoultion (FWHM) as afunction of energy as present in the most recent version of the response matrices.

We consider 3 ways to rebin the channel:1. The spectra were rebinned to oversample the instrumental energy resolution by a factor of 3.2. The spectra were rebinned in order to have at least 25 counts per channel.(Before subtracting the background…)3. The spectra were rebinned in order to have at least 40 counts per channel.

Model kT (keV) R (D1 km) F(10-12 ergs cm-2 s-1) Г NH(1022 cm-2) Power-law 4.14 0.99 = 2.13/439 d.o.f

Blackbody 0.39-0.40 0.41-0.43 2.90 0.33-0.35 =1.68/439 d.o.f

Bremsstrahlung 0.90-0.93 2.95 0.64-0.66 =1.22/439 d.o.f

Blackbody 0.39-0.42 0.29-0.35 2.95 4.28-4.75 0.85-0.95 +Power-law =1.29/437 d.o.f

Blackbody 0.46-0.51 0.18-0.26 1.74 0.46-0.52 +

Blackbody 0.24-0.29 0.74-1.05 1.21 =1.19/437 d.o.f

2red

2red

2red

2red

2red

The spectra were rebinned to oversample the instrumental energy resolution by a factor of 3.

The errors are in the range Δχ2< 2.7(90% confidence level) on one parameter.

Model kT (keV) R (D1 km) F(10-12 ergs cm-2 s-1) Г NH(1022 cm-2) Power-law 2.95 4.04-4.13 0.96-0.99 = 1.44/793 d.o.f

Blackbody 0.40-0.40 0.41-0.43 2.89 0.32-0.34 =1.31/793 d.o.f

Bremsstrahlung 0.91-0.94 2.94 0.63-0.66 =1.03/793 d.o.f

Blackbody 0.38-0.41 0.29-0.36 2.95 4.06-4.51 0.81-0.91 +Power-law =1.06/791 d.o.f

Blackbody 0.48-0.54 0.15-0.23 1.59 0.45-0.51 +

Blackbody 0.25-0.30 0.71-0.96 1.35 =1.02/791 d.o.f

2red

2red

2red

2red

2red

The spectra were rebinned in order to have at least 25 counts per channel before subtracting the background.

The errors are in the range Δχ2< 2.7(90% confidence level) on one parameter.

Model kT (keV) R (D1 km) F(10-12 ergs cm-2 s-1) Г NH(1022 cm-2) Power-law 2.96 4.01-4.10 0.95-0.98 = 1.52/683 d.o.f

Blackbody 0.40-0.40 0.41-0.43 2.89 0.32-0.34 =1.38/683 d.o.f

Bremsstrahlung 0.91-0.95 2.95 0.63-0.66 =1.06/683 d.o.f

Blackbody 0.38-0.41 0.29-0.36 2.95 4.02-4.47 0.80-0.90 +Power-law =1.09/ 681d.o.f

Blackbody 0.48-0.54 0.15-0.23 1.60 0.44-0.50 +

Blackbody 0.25-0.30 0.70-0.96 1.35 =1.05/681 d.o.f

2red

2red

2red

2red

2red

The spectra are grouped so that each bin has a signal-to-noise ratio greater than 4σ.

The errors are in the range Δχ2< 2.7(90% confidence level) on one parameter.

1WGA J1713.4-3949 侵略計劃失 敗

F. A. Aharonian et. al.

Neutron starsNeutron stars

Neutron Stars (~1500)

Isolated Neutron Stars In Binary systems

Radio-quiet INS Isolated Radio Pulsars

AXPs (~6)

RQINs without γ-ray

RQINs with γ-ray

SGRs (~5)CCOs (~5)

XDINs (~7)

Others (>7)

Companion?

Radio emission ?

With γ-ray ?

With SNR ?

(Mereghetti 1998)

(Thompson 2000)

By J. L. Chiu & Lupin Lin

(Pavlov et al. 2002)

AX J1714.1-3912

(Uchiyama et al. 2003)

(Cassam-Chenaї et al. 2004)

The value of L in blackbody model is lower than predicted by standard cooling NS models for which luminosity is ~1034erg s-1 for a NS of a few thousand years (e.g. Tsurata 1998). Such alow luminosity could be explained by accelerated cooling process.Note that the temperature, radius and luminosity of the central point source 1WGA J1713.4-3949 are almost identical to what is found for the central point source in SNR RX J0852.0-4622 (also G266.2-1.2 or "Vela Junior“) adopting a distance of 1 kpc. (Becker & Aschenbach 2002; Kargaltsev et al. 2002)