Summary Candidate supernova remnants G25.5+0.0 and G23.5–0.0 were observed by XMM-Newton in the...
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- Summary Candidate supernova remnants G25.5+0.0 and G23.50.0 were observed by XMM-Newton in the course of a snap-shot survey of plerionic and composite SNRs. In the field of G25.5+0.0, which contains the extended TeV source HESS J1837069, we detected the recently discovered young high-energy pulsar J18380655 (P = 70.5 ms, = 23 kyr, E = 5.5 10 36 erg s 1 ) embedded in a PWN of 1.3' extent. The pulsar + PWN luminosity is L 210 keV 5 10 34 erg s 1 9 10 3 E at an assumed distance of 6.6 kpc. We also detected another PWN candidate (AX J1837.30652) with an extent of 2' and unabsorbed flux F 2-8 keV 9 10 13 erg cm 2 s 1. A portion of this field was analyzed in a recent investigation using Chandra by Gotthelf & Halpern (2008). In the field of G23.50.0 we detected an extended source of a 3.2' size, which we tentatively interpret as a PWN of the middle- aged pulsar B183008 (P = 85.3 ms, = 147 kyr, E = 5.8 10 35 erg s 1, d = 5.67 kpc), with the PWN luminosity L 110 keV 4 10 33 erg s 1 6 10 3 E. Studies by Clifton & Lyne (1986) and Gaensler & Johnston (1995) sought to find an association between PSR B1830-08 and W41, however our analysis appears to establish a relation between PSR B1830-08 and G23.5- 0.0. We also provide detailed multiwavelength analysis and identifications of other field sources and discuss the possibility of classifying each field as an SNR. Results Analysis of the G23.5-0.0 field revealed several point sources and one diffuse source. The diffuse X-ray source (Source 8) was found to be positionally coincident with PSR B1830-08. The positional relation between Source 8 and PSR B1830-08, apparent in Figure 1, is of particular interest. Spectral and multiwavelength analysis provided the following information. Source 8 Best fit with power law model, with 2 = 1.27 for 56 degrees of freedom and photon index = 2.140.75 (Figure 3- Top) Unabsorbed X-ray flux of 9.37x10 -13 erg s -1 cm -2 No optical, infrared, or radio counterparts found in catalogs. Possible diffuse radio counterpart found in New GPS 20 cm radio image Conclusions The analysis of Source 1 and Source 15 in field G25.5+0.0 agreed with the results presented by Gotthelf & Halpern (2008). We conclude Source 1 is a counterpart to PSR J1838-0655 and it cannot be ruled out that this source is associated with HESS J1837-069. We also find that Source 15 is a counterpart to AX J1837.3-0652. Our results support the hypothesis that AX J1837.3-0652 is a second PWN in G25.5+0.0. Results from the analysis of Source 8 in G23.5- 0.0 tentatively suggest this source is the PWN of PSR B1830-08. The majority of sources were only classifiable using multiwavelength data. X-ray sources with no optical or infrared counterparts (section 3 in Table 1) were mostly identified as AGN. We note these sources will have the least accurate results but cannot be repudiated as possible pulsar candidates. We considered X-ray sources with optical and infrared counterparts (section 4 in Table 1) unlikely pulsar/PWN candidates. The nomogram results coupled with intrinsic color analysis classified the majority of sources as stars and AGN, and the accuracy of the combined methods is sufficient to discount these sources as pulsars or PWN. Fields G23.5-0.0 and G25.5+0.0 were observed as candidate supernova remnants, however it is unlikely that either field is a SNR. Our images do not reveal shell structures in radio or X-rays and we do not observe X-ray filaments. In G25.5+0.0 we do not observe any extended emission beyond the detected sources. A region of diffuse emission surrounding PSR B1830-08 in G23.5-0.0 could possibly be an SNR, but considering the age of the pulsar it is doubtful. B. M. Schmitt 1, O. Kargaltsev 2, G. G. Pavlov 1, Z. Misanovic 3 ( 1 Penn State University, 2 Univeristy of Florida, 3 Monash University) References E. V. Gotthelf and J. P. Halpern. Discovery of a Young, Energetic 70.5 ms Pulsar Associated with the TeV Gamma-Ray Source HESS J1837-069. ApJ, 681:515521, July 2008. T. R. Clifton and A. G. Lyne. High-radio-frequency survey for young and millisecond pulsars. Nature, 320:4345, March 1986. B. M. Gaensler and S. Johnston. The case for associations between old pulsars and supernova remnants. MNRAS, 275:L73L75, August 1995. T. Maccacaro et al. The X-ray spectra of the extragalactic sources in the Einstein extended medium sensitivity survey. ApJ, 326:680690, March 1988. Figure 1. Left PN, MOS1, and MOS2 combined X-ray image (0.2 12 keV) of G23.5-0.0 field. Green numbered regions denote sources identified by the XMM SAS task emldetect. Center PN, MOS1, and MOS2 combined X-ray image smoothed to emphasize diffuse emission Diffuse X-ray emission from Source 8, a possible PWN of PSR 1830-08, is discernible in this image. White circular region marks PSR B1830-08. Right Multiwavelength true-color image of G23.5-0.0 field. Blue denotes X-ray emission, red denotes infrared emission (Spitzer 8.0 m), and green denotes radio emission (New GPS 20 cm - 1.4 GHz). The bright radio and infrared emission on the left border of the image is due to the SNR shell of G23.3-0.3, a nearby remnant. A faint area of diffuse radio emission appears to be correlated to the diffuse X-ray emission of Source 8. XMM-Newton observations of two candidate supernova remnants Results (cont.) We attempted to classify reliably detected sources using multiwavelength data via the HEASARC Browse service. With these data we classified our sources with an X-ray Flux vs. Visual Magnitude nomogram (Maccacaro et al. 1988). The procedure estimates log(f X / f V ) = log f X +(m V / 2.5) + 5.37 where f X is the X-ray flux and m V is the apparent magnitude in the V band. This method is restricted by several sources of error, and the classifications are considered estimates. A number of X-ray sources were found to have no optical counterparts in the V band, however, we found a lower limit on log(f X / f V ) by using the GSC II V-band limiting magnitude (19.5). The results of the procedure can be found in Table 1 where we attempted to classify sources with optical and NIR (2MASS) counterparts based on their color. Figure 5 also shows X-ray fluxes vs. NIR magnitudes for the sources from Table 1. Figure 2. Left PN, MOS1, and MOS2 combined X-ray image (0.2 12 keV) of G25.5+0.0 field. Green numbered regions denote sources identified by the XMM SAS task emldetect. Yellow elliptical region identifies the 1 extent of HESS J1837-069 in the field. Center PN, MOS1, and MOS2 combined X-ray image smoothed to emphasize diffuse emission. Diffuse X-ray emission from Source 15 is easily discernible in this image. The diffuse emission of Sources 1 and 6 are also seen. The white circular region marks the position of PSR J1838-0655 and the white diamond region marks the position AX 1837.3-0652 (a potential PWN). Right Multiwavelength true-color image of G25.5+0.0 field. Blue denotes X-ray emission, red denotes infrared emission (Spitzer 8.0 m), and green denotes radio emission (New GPS 20 cm - 1.4 GHz). Sources 1 and 15 do not appear to have any diffuse or point infrared/radio counterparts. Source 6 has bright, point infrared and radio counterparts as well as diffuse components. A similar analysis of the G25.5+0.0 field revealed many point sources and three diffuse sources, two with resolvable point sources and one without (see Figure 2). Source 1 appears positionally coincident with PSR J1838-0655 and falls within the 1 extent of HESS J1837- 069. Source 15 positionally coincides with the presumed PWN, AX J1837.3-0652. Source 6 is likely a counterpart to star forming region 25.38-0.19. Diffuse radio and infrared components are seen in Figure 2. The positional coincidences between Source 1 & PSR J1838-0655 and Source 15 & AX J1837.3-0652 are of particular interest. Spectral and multiwavelength analysis produced the following information. Source 1 Best fit with power law model, with 2 = 0.93 for 44 degrees of freedom and photon index = 1.100.27 (Figure 3 Middle) Unabsorbed X-ray flux of 9.62x10 -12 erg s -1 cm -2 No optical, infrared, or radio counterparts found. Source 15 Best fit with power law model, with 2 = 1.05 for 41 degrees of freedom and photon index = 1.390.70 (Figure 3 - Bottom) Unabsorbed X-ray flux of 7.92x10 -13 erg s -1 cm -2 No optical, infrared, or radio counterparts found. Figure 4. Infrared (J) Magnitude vs. X-ray flux plot. Legend details the X-ray source classifications based on X-ray flux and visual appearance. The sources aligned along the Y axis were found not to have an near-infrared counterpart leading to a magnitude bound of 17.1 (the limiting J magnitude of the 2MASS catalog). Table 1. The table is divided into sections regarding properties of the sources. The first section includes bright, diffuse X-ray sources with a resolvable point source and no counterparts. The second section includes bright, solely diffuse sources with no counterparts. The third section lists X-ray sources without counterparts. The fourth section includes all sources with optical or near-IR counterparts. The ratios of the first three sections are all lower limits. Column (1) lists the field. Column (2) lists the Source ID for the X-ray source. Column (3) lists the X-ray flux, Column (4) lists the log (f X / f V ) ratio and Column (5) presents the classifications. Figure 3. Xspec generated spectra of the three pulsar/PWN candidates in G23.5-0.0 and G25.5+0.0. Each spectra was best fit using a power law model convolved with a photoelectric absorption model. The fit results are detailed in the Results section.