arXiv:1010.1758v1 [astro-ph.HE] 8 Oct 2010 e-mail: fteCa-usrisl,teeiso rmtreodrpul older three B0656 (Vela, from near-IR emission the emissio in the the detected itself, (Sollerman to Crab- contrast wavelengths the In longer of 2009). Sollerman towards & exhi Sandberg increase pulsar, the 2003, flux of south steep knot brigh a some as a while such 2009), PWN, 2006, the of al. structures et a (Temim almost IR wel exhibit the most in PWN The spectrum a torus-like IR. its the only and in now Crab-pulsar detected been studied until have However, objects these (PWNe). of nebulae few wind pulsar neutron and rotation-powered informati responsibl from processes valuable radiation physical multiwavelength provide understood poorly can the about observations (IR) Infrared Introduction 1. nraewt aeegh(hbnve l 03 2006). 2003, al. et (Shibanov wavelength with increase esmyb epsbefrti di this for form resposible two the be distri- in energy may particles complex tems relativistic More radiating range. of same butions on the contains Crab within the 2004 break from al. emission one et The (Serafimovich 2008). al. sy X-rays a et and both Shibanov suggesting optical of the X-rays spectra between multiwavelength in tems the observed in be di break those can intensity double-knee and data from slope IR whose significantly law, and al power fer et optical single Slane a Their 2008, by 2008). al. described et al. (Williams et Shibanov IR ste 2008, the even towards an exhibited increase telescope, flux Spitzer the in with observed mid-IR 58, 3C the and B0540-69.3 (SNRs) remnants edo Send oebr8 2018 8, November srnm Astrophysics & Astronomy w on rblk pulsar Crab-like young Two infiatyseprsoei h nrrdotclta in than infrared-optical the in slope steeper significantly 3 r omnt w te usrwn eua soitdwt t with associated nebulae wind pulsar other two to common are 2 niscne,wt h pia n -a aa h resulting 70 The and 24 data. The X-ray rays. and optical the neb the with 70 of center, and fluxes 24 its infrared in the in visible compiled ag We not filaments. morphology is and source and shell The position X-rays. its in and nebula optical, wind the in than bands iepla idnbl iil nXry.Alkl counterp likely A X-rays. in visible nebula wind pulsar like 1 pia onepr obt h usradiswn euasy nebula wind its and pulsar the both to counterpart optical Conclusions. Results. Methods. Aims. Context. rpitoln eso:Nvme ,2018 8, November version: online Preprint e words. Key ff bevtroAto´mc ainlSM nttt eAstr de Instituto SPM, Astron´omico Nacional Observatorio cdmclPyia ehnlgclUiest,Khlopina University, Techonological Physical Academical Io rn eussto requests print [email protected] ff hsclTcnclIsiue oiehihsaa2,St 26, Politekhnicheskaya Institute, Technical Physical e ocnr h onepr addt aue eeaie arc examined we nature, candidate counterpart the confirm To h 22018pla idnbl ntemid-infrared the in nebula wind pulsar G292.0+1.8 The G292.0 h xeddcutratcniaei rl eetdi the in detected firmly is candidate counterpart extended The ra-adiae ae t45 ,2,ad70 and 24, 8, 4.5, at taken images Broad-band usr:gnrl–SR,plas usrwn eua,indi nebulae, wind pulsar , SNRs, – general pulsars: h oiin opooy n pcrlpoete ftede the of properties spectral and morphology, position, The + . saCsAlk uenv enn htcnan h young the contains that remnant supernova A-like Cas a is 1.8 ..Zyuzin, D.A. : µ u pe iissgetascn ra n atrspectru flatter a and break second a suggest limits upper flux m ..Zyuzin D.A. aucitn.13164man no. manuscript + W ytm soitdwith associated systems PWN ff + rne Rosrain of observations IR erence. 4 eig)so flux a show ) 14, 1 , 2 ..Danilenko A.A. , rsys- er -as mligadul-neseta ra ewe h o the between break spectral double-knee a implying X-rays, µ eeaaye n oprdwt vial pia n X-ra and optical available with compared and analyzed were m r otenbl a endtce nteoptical the in detected been has nebula the to art for e stars tmi h G292.0 the in stem ABSTRACT eper sars flat -,S.Ptrbr,142,Russia 194021, Petersburg, St. 2-8, nmı,UA,Esnd,B,Mexico BC, Ensenada, onom´ıa, UNAM, 1 nbobdmliaeeghsetu sdsrbdb power by described is spectrum multiwavelength unabsorbed bit on µ e elwt h oriae n opooyo h torus-li the of morphology and coordinates the with well ree eesug 901 Russia 194021, Petersburg, . l,wihpoal otisacnrbto rma unresol an from contribution a contains probably which ula, ly s- f- ermat 04-93ad3 8adosre naltreran three all in observed and 58 3C and B0540-69.3 remnants he ..Zharikov S.V. , n mgs hc r oiae ybih msinfo h rem the from emission bright by dominated are which images, m l t , . ia i-nrrddt bandwt h pte pc Tel Space Spitzer the with obtained data mid-infrared hival ihteVTdtce ieycniaet h pia count optical pulsar the to the candidate of likely part a ye detected last rotatio VLT obtained the all images with the optical Deep among known. energetic pulsars most powered eighth the and youngest ann h usrwsdtce nteotclrange. optical the co PWN in X-ray detected the PWN, was of pulsar part torus-like exten the inner source taining the brightest Smaller the edge-on. of only almost that axis X-rays suggest in major seen is the which counterpart with shaped elliptically coincides an didate of axis major The 2008). N Cml ta.20,Ceair20) n t spin-down its and 2005), Chevalier 2002, pulsar luminosity, al. the et of (Camilo age SNR characteristic jet al. The a et Hughes 2007). ≈ with 2002, al. et Gonzalez PWN Crab-pulsar, Park & the X-ray Safi-Harb 2003, to 2001, torus-like way al. similar a et (Hughes a powers In A. J1124-5916 Galax the Puppis PSR in and detected A be to Cas SNR after oxygen-rich third the is which pcrleeg itiuini h pia n Rso that show law G292.0 IR power the of and single counterpart optical optical-mid-IR a the the and indeed Simila in is X-rays mid-IR. distribution the in energy in that spectral source to same morphology the source of detection the report h eut r rsne n icse nScs n 4. and 3 Sects. in discussed and presented are results the sar 03.I sascae ihSRG292.0 2001, SNR al. with et (Hughes associated X-rays is and 2002) It al. 2003). et (Camilo radio the sys- Crab. these the of in seen feature break common whether single more the understand than a to tems is us break help double-knee can the systems pulsar-PWN other 90y,wihi ossetwt 7030 raeo the of age yr 2700–3700 with consistent is which yr, 2900 + . n 8 and 4.5 iul G292.0 vidual: sn pte rhvliae fteG292.0 the of images archival Spitzer Using h on S 12-96wsol eetydsoee in discovered recently only was J1124-5916 PSR young The W ytm h Rosrain r ecie nSc.2, Sect. in described are observations IR The system. PWN etdsuc lo st ofimta ti h infrared- the is it that comfirm to us allow source tected + . uenv remnant. supernova 1.8 3 E usrPRJ1451 oeigacmattorus- compact a powering J1124-5916 PSR pulsar ˙ µ n uA Shibanov Yu.A. and , ad.I sbihe n oeetne nthe in extended more and brighter is It bands. m ≈ tteln aeeghlmt hs features These limit. wavelength long the at m 1.2 + + .,PRJ1451 tr:neutron stars: – J1124-5916 PSR 1.8, × W ytmin system PWN 10 37 rss ergs − 1 akti usra h sixth the as pulsar this rank , VRI 1 VRI bands. ad Zaio tal. et (Zharikov bands + . MH11-54), (MSH 1.8 tcladX- and ptical data. y e pulsar ved +

epulsar ke c . ed we field, 1.8 asof laws escope. S 2018 ESO ges. nant + . pul- 1.8 can- er- , n- n- ar ts it y τ r 2 D.A. Zyuzin et al.: The G292.0+1.8 in the mid-IR.

2. Observations 8 µm band by elliptical isophotes, are RA≈11:24:39.129 and Dec≈-59:16:19.51. Accounting for the astrometric uncertain- + G292.0 1.8was imaged with the Spitzer telescope at several ob- ties, this is in good agreement with the X-ray position of the serving sets from March 13 to April 15 2008 using the Infrared pulsar, RA≈11:24:39.183 and Dec≈-59:16:19.41, and with the Array Camera (IRAC) and Multiband Imaging Photometer for 1 2 central position of the optical pulsar/PWN counterpart candi- Spitzer (MIPS) . The data were retrieved from the Spitzer date, RA≈11:24:39.216 and Dec≈-59:16:19.60 (Zharikov et al. archive. Various parts of the SNR were detected in all four 2008). The source ellipticity and position angle are compatible IRAC channels, although its central part, containing the pulsar, with the structure of the brightest inner part of the X-ray PWN, ff was imaged in only the second and fourth bands with e ective which has been interpreted as a Crab-like PWN torus seen al- wavelengths of 4.5 µm and 8.0 µm, respectively. We used the most edge-on (Hughes et al. 2003). IRAC post-BCD calibrated mosaic images with an effective im- The position and morphology of the detected mid-IR source age scale of 1′′. 2 per pixel and field of view (FOV) of 7.′5×7.′5. allow us to consider whether it is a true counterpart to the pul- Two separate sets of observations were obtained with the MIPS sar+PWN system. A faint jet-like structure extended south of the at the effective wavelengths of 24 µm and 70 µm to image the torus and a bright SNR filament visible N-E of the PWN in X- entire SNR. We regenerated the MIPS post-BCD calibrated mo- rays are not detected in the mid-IR. In the frames presented in saic images from respective BCD data using the MOPEX3 tool. Fig. 1, we note only one additional cross-identification, an ob- The resulting image scales are 2′′. 4 per pixelfor the first, and 4′′. 0 ject o1, showing a point-like spatial profile in X-rays but a non- for the second band with the FOV of 13.′3×12.′8 for both bands. stellar structure in the IR. This may be a background galaxy. The effective exposures were ≈3500 s per pixel for both IRAC Star-subtracted optical and mid-IR images (bottom row panels bands, ≈500 s for 24 µm, and ≈380 s for 70 µm MIPS bands. of Fig. 1) show that at the pulsar position we see the same ex- tended elliptical object in both ranges. This confirms the reality 3. Results of its optical detection in the region that is extremely crowded by background objects (Zharikov et al. 2008). Most nearby stars 3.1. Identification of the pulsar/PWN counterpart candidate contaminating the source flux in the optical becomes fainter in the IR, while the brightness of the source itself does not de- As a first step, to check the Spitzer pointing accuracy, we ap- crease, enabling its detection in the mid-IR at a higher signif- plied astrometric referencing to the IRAC images. In the IRAC icance level. As in the optical, its surface brightness distribu- FOV, eight unsaturated isolated astrometric standards from the tion reaches a peak at the pulsar position. We cannot resolve USNO-B1 catalog were selected as reference points. Their cat- any point-like object there, but the peak is probably associated alog and image positional uncertainties for both coordinates with the contribution from the pulsar. Some blurring is caused were <0′′. 2 and <0′′. 5, respectively. IRAF ccmap/cctran tasks ∼ ∼ by a lower mid-IR spatial resolution compared to the optical were used to find plate solutions. Formal rms uncertainties of one. However, the object sizes along its major axis correspond- the astrometric fit were <0′′. 2 with maximal residuals of <0′′. 5 ∼ ∼ ing to >90% of the enclosed flux are significantly larger in the for both coordinates and both IRAC bands. After astrometric ∼ IR, ≈10′′. 5, than in the optical, ≈3′′. This suggests that the source transformations the shifts between the original and transformed becomes brighter with wavelength (see below Sect. 3.2 and 3.3), images were <0′′. 4 (or less than 0.3 of the pixel scale), ensur- ∼ revealing its fainter outer regions. At 8 µm, it becomes compara- ing the almost perfect pointing accuracy of the Spitzer obser- ble in size and shapeto the torus partof the PWN seen in X-rays. vations. Combining all uncertainties, a conservative estimate Our counterpart candidate is not detected in the MIPS bands, of 1σ referencing uncertainty is ∼<0′′. 5 (or less than 0.4 of the IRAC pixel scale) in both coordinates for both bands. This is where the emission fromfilaments and the outer shell of the SNR about twice as poor as the astrometric uncertainties estimated by strongly dominates over other sources in contrast to the shorter Zharikov et al. (2008) for the deepest available Chandra/ACIS- wavelength IRAC bands. Some faint structure may be present at the pulsar position, particularly in the 24 µm image. However, I X-ray (∼<0′′. 27) and VLT/FORS2 (∼<0′′. 15) optical images of G292.0+1.8. Nevertheless, this is sufficient to identify position- the poorer spatial resolution of MIPS does not allow us to deter- ally the objects in the mid-IR, optical, and X-rays on a subarc- mine, whetherit is related to thecandidateor to afaint peninsula- second accuracy level. like part of a bright nearby filament of the remnant. The region containing the pulsar is shown in Fig. 1, where we compare the IRAC mid-IR images with the X-ray and op- 3.2. Photometry tical images obtained with Chandra/ACIS-I and VLT/FORS2 (Zharikovet al. 2008). In both IRAC bands at the pulsar po- Elliptical aperture photometry of the detected source was sition, marked by a cross, we detect a faint extended source. performed on the star-subtracted IRAC images using IRAF The FWHM of the IR point spread function varies from 2′′. 1 polyphot tasks in accordance with prescriptions and zeropoints 5 to 2′′. 5, and the extended structure of the source, which sub- given in the IRAC Observers Manual . The elliptical apertures tends up to ≈10′′. 5, is clearly resolved. In the 8 µm image, were obtained from the source surface brightness fit at 8 µm by which is less contaminated by background stars, the object has elliptical isophotes using IRAF isophot tasks. The ellipticities an elliptical shape, as can also be seen from its contours over- varied with the ellipse sizes in a range of 0.4–0.5 and the semi- ′′ laid on the X-ray and optical images4. The coordinates of the major axis of the outer isophote was found to be ∼<6 pixels (7. 2). source center, derived from the source surface brightness fit in The annulus for backgrounds was 8–23 pixels centered on the pulsar position. A typical semi-major radius, where the curves 1 see http://ssc.spitzer.caltech.edu of growth saturate, was about 5 pixels for both IRAC bands. We 2 PROGID 40583, PI P. Ghavamian reiterated the star subtraction process, varied the background re- 3 http://ssc.spitzer.caltech.edu/postbcd/mopex.html gion, and used circular apertures. The differences in the magni- 4 In both images, the contours are identical, but the internal IR con- tudes obtained were similar to the measurement statistical errors tour seen in the optical falls inside the X-ray PWN and is not visible on chosen scale levels in the X-ray image. 5 see, e.g., http://ssc.spitzer.caltech.edu/archanaly/quickphot.html D.A. Zyuzin et al.: The G292.0+1.8 pulsar wind nebula in the mid-IR. 3

Fig. 1. Top row: central ∼35′′×40′′ fragment of G292.0+1.8,containingPSR J1124-5916and its PWN as seen with the Spitzer/IRAC and Chandra/ACIS-I at 4.5 µm and 8 µm, and in 0.2–10 keV X-ray range, respectively. X-ray position of the pulsar is marked by the cross. Contours from the X-ray image are overlaid on the mid-IR images, while in X-rays the contours are from the 8 µm image. Arrows indicate the pulsar+PWN system and a backgroundobject o1 in X-rays and their mid-IR counterparts. Bottom row: zoomed fragments of the same mid-IR images showing a ∼17′′×17′′ region around the pulsar and respective I band optical image obtained with the VLT/FORS2. Background stars were subtracted. Contours of the optical pulsar+PWN counterpart candidate are overlaid on 4.5 µm image. Contours on the I image are from 8 µm, while on the 8 µm image the X-ray contours are overlaid. The images are smoothed with a Gaussian kernel of two-three pixels. The coordinates and morphology of the source seen at the pulsar position in the optical and mid-IR suggest that it is the counterpart of the X-ray pulsar+PWN system. and they were included in the resulting uncertainties. A few per- Table 1. Observed magnitudes and fluxes for the presumed in- cent of the extended source aperture corrections were insignifi- frared/optical pulsar/PWN counterpart of J1124-5916, and de- cant compared to the resulting ≈20%–30% flux error budget. reddened fluxes for the AV range of 1.86-2.10. The 3σ upper limits to the source magnitudes in the MIPS bands were estimated using the standard deviations and inher- λeff (band) Mag. log Flux log Flux a a a ent flux variations in the possible faint part of the remnant fila- observed observed de-reddened ment within the same elliptical apertures as in the IRAC bands. (µm) (mag) (µJ) (µJ) Both ways provided similar values. For 70 µm, we used a post- infrared Spitzer 70 >6.8 <3.2 <3.2 BCD filtered calibrated mosaic image generated by us with the ∼ ∼ ∼ 24 ∼>10.2 ∼<2.8 ∼<2.85 MOPEX tool. The magnitudes were converted into fluxes in +16 8.0 14.2(3) 2.13(16) 2.18(−17) physical units and the results are summarized in Table 1. Our +21 4.5 15.9(4) 1.90(21) 1.95(−22) 70 µm limit is slightly above the 5σ flux confusion limit of 1500 optical VLT µJ estimated for this MIPS band by Frayer et al. (2006). +6 0.77(I) 23.12(13) 0.13(5) 0.66(−10) +7 0.66(R) 24.12(13) -0.17(5) 0.51(−12) +7 0.55(V) 24.29(13) -0.16(5) 0.66(−13) 3.3. Multiwavelength spectrum a numbers in brackets are 1σ uncertainties referring to last significant digits quoted Using the mid-IR, optical, and X-ray data, we compiled a ten- tative multiwavelength spectrum of the pulsar/PWN system. We dereddened the observed optical/IR fluxes using a most plausible To compare the fluxes in different ranges from the same interstellar extinction range 1.86∼

70◦. An absorbed power law spectral model provided a statisti- cally acceptable fit with a photon spectral index Γ=1.85±0.02, 21 −2 absorbing column density NH =(3.4±0.1)×10 cm , and nor- malization constant C=(2.4±0.1)×10−4 photons cm−2 s−1 keV−1. The fit had χ2=1.1 per degree of freedom (dof) and the un- absorbed integral flux was 1.0×10−12 erg cm−2 s−1 in 0.3–10 keV range. The resulting Γ and NH are compatible with those of Zharikov et al. (2008), while the normalization constant and integral flux are about twice as high. This is because of a larger extraction aperture than in their work, where the aperture was chosen to fit the smaller source extent in the optical range. The optical fluxes are unchanged by the aperture increase since the likely counterpart is more compact in the optical than in the IR. The resulting unabsorbed spectrum is presented in Fig. 2. The counterpart candidate spectral energy distribution (SED) in the IR-optical range shows a steep flux increase towards the mid- IR. The fluxes in this range can be fitted by a single power- 2 Fig. 2. Tentative unabsorbed multiwavelength spectrum for the law with a spectral index αν ≈1.5 (χ ≈0.5 per dof), implying a nonthermal nature of the emission. This is expected for PWNe, innerpart of the torusregionof the G292.0+1.8pulsar/PWN sys- where synchrotron radiation from relativistic particles acceler- tem compiled from the data obtained with different instruments, ated at the pulsar wind termination shock is considered as the as indicated in the plot. Errorbars of the dereddened optical and main radiative process responsible for the continuum emission mid-IR fluxes include the AV uncertainty range shown at the top. of the nebulae. Accounting for possible contamination of the V The VLT and IRAC data are fitted by a single powerlaw, whose −α flux by O III emission from the SNR (Zharikov et al. 2008), we spectral index αν (defined by Fν ∝ ν ν ) is significantly greater excludedthis band from the fit. This leads to only a marginalim- than that for X-rays, suggesting a double knee spectral break be- provement of the fit with insignificant steepening of the spectral tween the optical and X-rays. The MIPS flux upper limits are slope within the uncertainties shown in the plot. The observed below the low frequency extension of this fit and imply a second SED cannot be produced by overlapping field stars of the same break at λ ≈20 µm. Solid lines show the best spectral fits, while brightness. Our test measurementsof nearby faint stars show that grey polygons, and dashed and dotted lines are the fit uncertain- in the latter case the spectral slope would be a positive, flat, or ties and their extensions outside the frequency ranges involved curved. in the fits. As seen from Fig. 2, the optical and mid-IR fluxes of the suggested counterpart are below the low frequency extrapolation decrease the rather large uncertainties of the IR-optical spectral of the pulsar/PWN spectrum in X-rays. This implies a double- slope and possible distinguish the pulsar from the PWN. knee spectral break between the optical and X-rays. At the same Our results increase the number of PWNe identified in the time, the flux upper limits in the MIPS bands are below the low mid-IR from three to four, and show that these objects can be frequency extrapolation of the IRAC-optical SED, suggesting a significantly brighter in the IR than in the optical, making the second break near 20 µm after which the spectrum become flat- IR range promising for the study of the PWNe. The presence of ter or goes down with the frequency decrease. These changes the double-knee breaks in the spectra between the optical and in the spectral index and breaks are similar to those observed X-rays in the three of four torus-like PWNe makes this feature for PWNe around young pulsars in SNRs 3C 58 and B0540- regular and notable. This is distinct from the Crab-PWN and has 69.3 (Serafimovich et al. 2004, Shibanov et al. 2008, Slane et al. to be taken into account in the modeling of the PWNe when 2008, Williams et al. 2008). Together with the source morphol- understanding their structure and emission nature. ogy, this is a strong evidence that the detected source is the true mid-IR and optical counterpart of the pulsar/PWN system in the Acknowledgements. We are grateful to anonymous referee for useful comments G292.0+1.8 . improving the paper. The work was partially supported by RFBR (grants 08- 02-00837a, 09-02-12080), NSh-2600.2008.2, CONACYT 48493 and PAPIIT IN101506 projects, and by the German DFG project number Ts 17/2–1. DAZ was supported by St Petersburg Goverment grant for young scientists (2.3/04- 4. Discussion 05/008). These broad-band Spitzer observations have allowed us to con- firm the pulsar/PWN counterpart nature of a faint optical neb- References ulosity detected early at the PSR J1124-5916 position with the Camilo, F., Manchester, R. N., Gaensler, B. M., et al. 2002, ApJ, 567, L71 VLT (Zharikov et al. 2008). Its similar source morphology in the Cardelli, J. A., Clayton, G. C., Mathis, J. S. 1989, ApJ, 345, 245 mid-IR, optical, and X-rays, as well as its spectral properties Chevalier, R. 2005, ApJ, 619, 839 make any alternative interpretation discussed in Zharikov et al. Flaherty, K. M., Pipher, J.L., Megeath, S.T. et al. 2007, ApJ, 663, 1069 (2008) (SNR filament, faint background spiral galaxy) very un- Frayer D.T. et al. 2006, ApJ, 647, L9 Hughes, J. P., Slane, P. O., Burrows, D. N., Garmire, G. 2001, ApJ, L153 likely. The mid-IR data have enabled us to establish the long Hughes, J. P., Slane, P. O., Park, S., et al. 2003, ApJ, 591, L139 wavelength SED of the nebula, which was very uncertain based Indebetouw, R., Mathis, J.J., Babler, B.L. et al. 2005, ApJ, 619, 931 only on the optical data, and conclude that the multiwavelength Park, S., Hughes, J.P., Slane, P.O. et al. 2007, ApJ, 670, L121 spectrum of the J1124-5916 pulsar/PWN system from the mid- Safi-Harb, S. & Gonzalez, M.E. 2002, in: ”X-rays at Sharp Focus”: Chandra / Science Symp. ASP Comf. Series Vol 262, eds. E. Schlegel and S.D. Vrtilek IR to X-rays is similar to the spectra of pulsar PWN systems in Sandberg, A., Sollerman, J. 2009, A&A, 504, 525 the SNRs B0540-69.3 and 3C 58. Forthcoming high spatial res- Serafimovich, N., Shibanov, Yu.A., Lundqvist, P., Sollerman, J. 2004, A&A, 425, olution near-IR observations of the pulsar field will allow us to 1041 D.A. Zyuzin et al.: The G292.0+1.8 pulsar wind nebula in the mid-IR. 5

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