1WGA J 侵略計劃

First image of TeV-energy gamma-rays of a cosmic source: a supernova remnant HESS had just made a map of very high energy gamma-rays, of the order of TeV of the SNR RX J 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 generally believed 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 J , Cas A and SN1006) and with a rather large uncertainty on the position of 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 high energy particles are indeed accelerated in the shell.

High-energy particle acceleration in the shell of a supernova remnant RX J (situated in the Galactic plane, in the constellation Scorpius) is one of the brighter Galactic X-ray SNRs and also a complex object interacting with molecular clouds of 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, π 0 -decays following proton-proton interactions, but also non-thermal Bremsstrahlung of electrons, could make a significant contributions. The spatially resolved remnant has a shell morphology similar to that seen in X-rays, which demonstrates that very high-energy particles are accelerated there. The energy spectrum indicates efficient acceleration of charged particles to energies beyond 100 TeV, consistent with current ideas of particle acceleration in young SNR shocks. F. A. Aharonian et. al.

X-ray observations of the CCO in SNR G J. S. Lazendic et al., ApJ., 2003 CCOs are more poorly understood objects near the centers of SNRs with detectable X-ray flux 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 J , a compact source located at the center of SNR G (RX J ). Early ROSAT observations identified two point sources within the boundaries of the SNR shell. (Pfeffermann & Aschenbach 1996) 1WGA J , was determined to be of stellar region. (Pfeffermann & Aschenbach 1996) 1WGA J , located at the geometrical center of the SNR, no optical counterpart has been found 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 provide useful limits to the pulsations in the X-ray band (Slane et al. 1999), radio pulsations were detected with a 392ms period within a 7 ׳ radius region toward this source. (PSR J ; Crawford et al )

They used FFT to search the X-ray data (Chandra, XMM & RXTE) for pulsations from 1WGA J but found no pulsation signal. The resulting timing parameters of PSR J are presented in Table 3. The pulsar’s dispersion 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 J is broadly consistent with SNR Distance of 6±1 kpc estimated by Slane et al. (1999), the pulsar is likely to be quite old. (τ c ~1.1 Myr, compared with τ<40 kyr for SNR G ) and doesn’t have sufficient spin-down luminosity (Ė~3.7x10 33 ergs s -1 ) to power the observed X-ray flux from 1WGA J (L x ~6x10 34 ergs s -1 ). PSR J is therefore spatially coincident with SNR G by chance, and there is likely no physical association between the two systems.

The lack of radio and optical counterparts for 1WGA J , the absence of X-ray pulsations with the current sensitivity and time resolution, the two component spectrum and its associated luminosity are properties consistent with CCOs. (Pavlov et al 2002) Their limits on the pulsed fraction from 1WGA J are consistent with those derived toward other CCOs (7%-15%; Pavlov et al ). 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 G ? 6.3±0.4 kpc? 1kpc??

Koyama et al. (1997) compare their measurement of the column density toward G with the total N H in the direction of the Galactic center to estimate a distance of 1 kpc to the remnant. The total line-of-sight column density in the direction of G is N H =1.2x10 22 cm -2 based on HI observations (Dicky & Lockman 1990) and confirmed by CO measurements. ( Bronfman et al. 1989) The N H -value Slane et al. measure for G (~8x10 21 cm -2 ) is a significant fraction of the total column through the Galaxy, and so the distance to the SNR must be considerably more 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 J is the remnant of SN that exploded in AD 393. New XMM observations (Cassam-Chenai et al. 2004b) that re-opened the whole distance question with new high-resolution CO mm-wave observations. (Fukui et al. 2003) These new results suggest possible indications of interaction between the SNR shock front and 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 π 0 decay attributed to the interaction of CR nuclei. (accelerated at the shock in RX J ) At TeV γ-rays, the CANGAROO imaging Cerenkov telescope detected emission in the NW of 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 π 0 decay process.

XMM-Newton observations of the SNR J and its central source (Cassam-Chenaї et al. 2004) The X-ray bright central point source 1WGAJ detected at the center of SNR RX J 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 (0.4x10 22 cm -2 ≤ N H ≤1.1x10 22 cm -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 J 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 J and its central source (Cassam-Chenaї et al. 2004) The search for thermal emission from RX J remains unsuccessful leading 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 density in molecular clouds if the remnant is in radiative phase where SNR shock encounters a dense ambient medium whereas it is in the free expansion phase elsewhere. RX J ’s progenitor mass is estimated to lie between 12 and 16 M סּ based on a scenario involving the effect of stellar wind of the progenitor star.

The new observation of XMM 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~ ( ) 6.963% / 7.767% 0.5~ ( ) 16.27% / 18.11% 1.0~ ( ) 8.413% / 9.369% 2.0~ ( ) 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 contour that we give 40 equal space 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 keV.

The EPIC MOS (left panel) and pn (right panel) energy resoultion (FWHM) as a function 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 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 (D 1 km) F( ergs cm -2 s -1 ) Г N H (10 22 cm -2 ) Power-law = 2.13/439 d.o.f Blackbody =1.68/439 d.o.f Bremsstrahlung =1.22/439 d.o.f Blackbody Power-law =1.29/437 d.o.f Blackbody Blackbody =1.19/437 d.o.f The spectra were rebinned to oversample the instrumental energy resolution by a factor of 3. The errors are in the range Δχ 2 < 2.7(90% confidence level) on one parameter.

Model kT (keV) R (D 1 km) F( ergs cm -2 s -1 ) Г N H (10 22 cm -2 ) Power-law = 1.44/793 d.o.f Blackbody =1.31/793 d.o.f Bremsstrahlung =1.03/793 d.o.f Blackbody Power-law =1.06/791 d.o.f Blackbody Blackbody =1.02/791 d.o.f The spectra were rebinned in order to have at least 25 counts per channel before subtracting the background. The errors are in the range Δχ 2 < 2.7(90% confidence level) on one parameter.

Model kT (keV) R (D 1 km) F( ergs cm -2 s -1 ) Г N H (10 22 cm -2 ) Power-law = 1.52/683 d.o.f Blackbody =1.38/683 d.o.f Bremsstrahlung =1.06/683 d.o.f Blackbody Power-law =1.09/ 681d.o.f Blackbody Blackbody =1.05/681 d.o.f The spectra are grouped so that each bin has a signal-to-noise ratio greater than 4σ. The errors are in the range Δχ 2 < 2.7(90% confidence level) on one parameter.

1WGA J 侵略計劃 失 敗

F. A. Aharonian et. al.

Neutron stars Neutron stars (Mereghetti 1998) (Thompson 2000) By J. L. Chiu & Lupin Lin (Pavlov et al. 2002)

AX J (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 ~10 34 erg s for a NS of a few thousand years (e.g. Tsurata 1998). Such a low luminosity could be explained by accelerated cooling process. Note that the temperature, radius and luminosity of the central point source 1WGA J are almost identical to what is found for the central point source in SNR RX J (also G or "Vela Junior“) adopting a distance of 1 kpc. (Becker & Aschenbach 2002; Kargaltsev et al. 2002)