XMM-Newton observations of two candidate supernova remnants
1
Schmitt ,
2
Kargaltsev ,
1
Pavlov ,
3
Misanovic
B. M.
O.
G. G.
Z.
1
2
3
( Penn State University, Univeristy of Florida, Monash University)
Summary
Results (cont.)
Candidate supernova remnants G25.5+0.0 and
G23.5–0.0 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
J1837–069, we detected the recently discovered
young high-energy pulsar J1838–0655 (P =
70.5 ms, τ = 23 kyr, E = 5.5 × 1036 erg s−1 )
embedded in a PWN of 1.3' extent. The pulsar
+ PWN luminosity is L2−10 keV ≈ 5 ×
1034 erg s−1 ≈ 9 × 10−3 E at an assumed distance
of 6.6 kpc. We also detected another PWN
candidate (AX J1837.3–0652) with an extent of
2' and unabsorbed flux F2-8 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 G23.5–0.0 we detected an
extended source of a 3.2' size, which we
tentatively interpret as a PWN of the middleaged pulsar B1830–08 (P = 85.3 ms, τ = 147
kyr, E = 5.8 × 1035 erg s−1 , d = 5.67 kpc), with
the PWN luminosity L1−10 keV ≈ 4 × 1033 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 G23.50.0. We also provide detailed multiwavelength
analysis and identifications of other field
sources and discuss the possibility of
classifying each field as an SNR.
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(fX / fV) = log
fX +(mV / 2.5) + 5.37 where fX is the X-ray flux
and mV 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(fX / fV) 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 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 μm), 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.
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
χν2 = 1.27 for 56 degrees of freedom and
photon index Γ = 2.14±0.75 (Figure 3Top)
-13
 Unabsorbed X-ray flux of 9.37x10
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
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 1σ extent of HESS J1837069. 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
χν2 = 0.93 for 44 degrees of freedom
and photon index Γ = 1.10±0.27
(Figure 3 – Middle)
-12
 Unabsorbed X-ray flux of 9.62x10
erg s-1 cm-2
 No optical, infrared, or radio
counterparts found.
Source 15
 Best fit with power law model, with
χν2 = 1.05 for 41 degrees of freedom
and photon index Γ = 1.39±0.70
(Figure 3 - Bottom)
-13
 Unabsorbed X-ray flux of 7.92x10
erg s-1 cm-2
 No optical, infrared, or radio
counterparts found.
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 1σ 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 μm), 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.
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 (fX / fV) ratio and Column (5)
presents the classifications.
Conclusions
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).
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, 681:515–521,
July 2008.
T. R. Clifton and A. G. Lyne. High-radio-frequency survey for young and millisecond
pulsars. Nature, 320:43–45, March 1986.
B. M. Gaensler and S. Johnston. The case for associations between old pulsars and
supernova remnants. MNRAS, 275:L73–L75, August 1995.
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.
T. Maccacaro et al. The X-ray spectra of the extragalactic sources in the Einstein extended
medium sensitivity survey. ApJ, 326:680–690, March 1988.
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 G23.50.0 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.