Pulsed Detection on PSR J2021+4026 Collaborated with David Hui - - PowerPoint PPT Presentation

Pulsed Detection on PSR J2021+4026

Search for the Geminga-like pulsar Previously known Geminga-like pulsars

• i. Geminga
• ii. PSR J0007+7303

Pulsed detection of PSR J2021+4026 and its spectral features Other candidates of Geminga-like pulsars Summary

Collaborated with David Hui (CNU), Jason Wu (Max Planck), Chin-Ping Hu (NCU) and Trepl L.(FSU)

Lupin Lin (China Medical Univ.) July 9th in HKU

1st Radio-quiet γ-ray Pulsar: Geminga

Only 7 γ-ray pulsars were d e t e c t e d w i t h h i g h confidence level before 2000.

1991-2000

Many firsts of Geminga (Caraveo & Bignami 1997).!

(D.J. Thompson et al, 1999)

Pulsed Features of Geminga

(Malofeev & Malov; 1997 )

(Abdo et al., 2010)

Intrinsically or Geometircally Radio-quiet?

Before the launch of Fermi observatory, Geminga is the only one radio-quiet γ-ray pulsar (L1400<0.035 mJy kpc2=PSR J1907+0602). Two possible interpretations for a γ-ray pulsar to be radio-quiet: 1st: Geometrical: γ-ray beam is wider than the radio beam or they are in the different directions.

Outer gap model:

(Romani & Yadigaroglu 1995; Cheng & Zhang 1998)

.Radio pulsed emission is directed along magnetic dipole axis. .Particle acceleration in outer gap (where ٟB = 0) generates γ-rays .γ-ray beam is concentric with radio beam which emitted within few stellar radii from surface.

Polar-cap model:

(Radhakrishnan & Cooke 1969; Harding & Muslimov 1998)

Polar-cap model » Slot Gap model

(Arons 1983; Muslimov & Harding 2003)

Intrinsically or Geometircally Radio-quiet?

Before the launch of Fermi observatory, Geminga is the only one radio-quiet γ-ray pulsar (L1400<0.035 mJy kpc2=PSR J1907+0602). Two possible interpretations for a γ-ray pulsar to be radio-quiet: 1st: Geometrical: γ-ray beam is wider than the radio beam or they are in the different directions.

Outer gap model:

(Romani & Yadigaroglu 1995; Cheng & Zhang 1998)

.Radio pulsed emission is directed along magnetic dipole axis. .Particle acceleration in outer gap (where ٟB = 0) generates γ-rays .γ-ray beam is concentric with radio beam which emitted within few stellar radii from surface.

Polar-cap model:

(Radhakrishnan & Cooke 1969; Harding & Muslimov 1998)

Polar-cap model » Slot Gap model

(Arons 1983; Muslimov & Harding 2003)

Pair plasma µ

slot gap PFF

ΔξSG

NS surface

Intrinsically or Geometircally Radio-quiet?

Two possible interpretations for a γ-ray pulsar to be radio-quiet: 2nd: Intrinsic: radio emission is weak or silent because of unfavour spin periods and magnetic strength.

Magnificent Seven (PoPov et al., 2007)

Intrinsically or Geometircally Radio-quiet?

Two possible interpretations for a γ-ray pulsar to be radio-quiet: 2nd: Intrinsic: radio emission is weak or silent because of unfavour spin periods and magnetic strength.

Magnificent Seven (PoPov et al., 2007)

(Haberl 2007)

Characteristic age: Spin-down energy: Magnetic field: Open field line voltage:

T P/2P = 

46 3

P E 4 10 P = ×  

19

B 3.2 10 PP ×  

20 3/2 1/2

• pen

4 10 P P

−

Φ = × 

year gauss erg/s volt

More and More Radio-quiet γ-ray Pulsars

With the support of new techniques:

• 1. Weighting H-statistics (Kerr, 2011)
• 2. Sliding coherence window technique (Pletsch, 2011)

More than 30 radio- quiet γ-ray pulsars we re d i s c ove re d through high energy γ- ra y p u l s at i o n s alone.

Green beam: radio emission Pink area: γ-ray emission

Classification of Pulsars

(Morphology)+ (Wavelength)+ Edited by Yang (2010)

Black Widow Pulsars

Emission Mechanism of Geminga in X-rays and γ-rays

The most frequent problem to be questioned is that are the emitting sites/ mechanisms of X-ray and γ-ray the same for a Geminga-like pular?

• Fig. Folded light curves of Geminga

(Kargaltsev et al. 2005)

Background subtracted folded light curves of Geminga. (Caraveo et al., 2004)

Emission Mechanism of Geminga in X-rays and γ-rays

The most frequent problem to be questioned is that are the emitting sites/ mechanisms of X-ray and γ-ray the same for a Geminga-like pular?

• Fig. Folded light curves of Geminga

(Kargaltsev et al. 2005)

Background subtracted folded light curves of Geminga. (Caraveo et al., 2004)

Time-averaged spectral distribution of Geminga pulsar. (Caraveo et al., 2004) Green dashed curve: Blackbody component with Tbb=43±1 eV, covering a surface with 8.6±1 km radius. Red curve: Blackbody component with Tbb=170±30 eV, covering a surface with 40±10 m radius. Blue curve: Power-law component with photon index of 1.7±0.1.

Pulsed detection of PSR J0007+7303 in X-rays and γ-rays

How about the first radio-quiet γ-ray pulsar (PSR J0007+7303) detected by Fermi team?

• Fig. Contours of detection significance over a range
• f period and period derivative within a region around

RX J0007.0+7302 (Abdo et al.,2008).

• Fig. The Fermi LAT γ-ray source and its 95% error

region (small red circle), central PWN X-ray RX J0007.0+7302 (black cross), and error of the corresponding EGRET source 3EG J0010+7309 (blue circle) superimposed on 1 1420-MHz map of CTA 1. (Abdo et al.,2008).

Pulsed detection of PSR J0007+7303 in X-rays and γ-rays

How about the first radio-quiet γ-ray pulsar (PSR J0007+7303) detected by Fermi team?

• Fig. Contours of detection significance over a range
• f period and period derivative within a region around

RX J0007.0+7302 (Abdo et al.,2008).

• Fig. The Fermi LAT γ-ray source and its 95% error

region (small red circle), central PWN X-ray RX J0007.0+7302 (black cross), and error of the corresponding EGRET source 3EG J0010+7309 (blue circle) superimposed on 1 1420-MHz map of CTA 1. (Abdo et al.,2008).

• Fig. (Lin et al., 2010)

Left panel: Spin-frequencies of PSR J0007+7303 detected from γ-ray (Fermi; labelled by squares) and X-ray (XMM; labelled by triangle). The plus sign marks the glitch of PSR J0007+7303 with df/f=5x10-7 (Abdo et al., 2010). The circles and solid circles represent the spin frequencies detected by the Fermi data before and after the glitch, respectively. Right panel: Rayleigh test of X-ray (XMM) data around [3.114,3.218] Hz. The most significant signal corresponds to the spin frequency of PSR J0007+7303 at 3.165844 Hz.

0.2-2 keV 2-12 keV

• Fig. Pulse profiles of PSR J0007+7303

in the different energy bands (Lin et al.,

2010)

0.15-2 keV

• Fig. (Caraveo et al., 2010)

Upper panel: X-ray pulse profile of PSR J0007+7303. Gray shadow: on-pulse. Red shadow: off-pulse. Lower panel: X-ray spectrum (Black line: on-pulse; Red line:

• ff-pulse) fitted with a three component model to a account for

thermal emission (cyan symbols) of NS and non-thermal emission from pulsar (green dotted line) and PWN (blue dotted line). Cyan triangles present the thermal emission of on-pulse spectrum, while cyan squares present it of off-pulse one.

Emission mechanism of PSR J0007+7303 in X-rays and γ-rays

0.2-2 keV 2-12 keV

• Fig. Pulse profiles of PSR J0007+7303

in the different energy bands (Lin et al.,

2010)

0.1-300 GeV 0.15-2 keV

• Fig. (Caraveo et al., 2010)

Upper panel: X-ray pulse profile of PSR J0007+7303. Gray shadow: on-pulse. Red shadow: off-pulse. Lower panel: X-ray spectrum (Black line: on-pulse; Red line:

• ff-pulse) fitted with a three component model to a account for

thermal emission (cyan symbols) of NS and non-thermal emission from pulsar (green dotted line) and PWN (blue dotted line). Cyan triangles present the thermal emission of on-pulse spectrum, while cyan squares present it of off-pulse one.

Emission mechanism of PSR J0007+7303 in X-rays and γ-rays

0.2-2 keV 2-12 keV

• Fig. Pulse profiles of PSR J0007+7303

in the different energy bands (Lin et al.,

2010)

0.1-300 GeV 0.15-2 keV

• Fig. (Caraveo et al., 2010)

Upper panel: X-ray pulse profile of PSR J0007+7303. Gray shadow: on-pulse. Red shadow: off-pulse. Lower panel: X-ray spectrum (Black line: on-pulse; Red line:

• ff-pulse) fitted with a three component model to a account for

thermal emission (cyan symbols) of NS and non-thermal emission from pulsar (green dotted line) and PWN (blue dotted line). Cyan triangles present the thermal emission of on-pulse spectrum, while cyan squares present it of off-pulse one.

Emission mechanism of PSR J0007+7303 in X-rays and γ-rays

X-ray spectrum fitted with a single power-law (PL), dual component of power-law +blackbody (PL+BB) and power-law +magnetized neutron star atmosphere (PL +nsa). (Caraveo et al., 2004)

A new Geminga-like pulsar candidate

ROSAT PSPC image of γ-Cygni (G78.2+2.1), summed from 6 individual observations. North is up and east is to the left. (Brazier et al., 1996)

RX EFRET 95% error box

The EGRET and X-ray observations of the object show the steady flux, hard PL spec and high-energy cut-off that are known only among young pulsars (Merck et al. 1996). The source is at the centre of a young SNR, which shows two

• pposing arcs on its rim.

The Fγ/Fx for RX J2021.0+4026/2EG J2020+4026 is of order 6000, similar to value of Geminga.

ROSAT PSPC field around 3EG J2020+4017. The 68%, 95%, and 99% contour lines from 3EG EGRET likelihood map and the ROSAT HRI sources are

• indicated. (Becker et al., 2004)

2EG J2020+4026/3EG J2020+4017 ?? RX J2021.0+4026 ??

A new Geminga-like pulsar candidate

ROSAT PSPC image of γ-Cygni (G78.2+2.1), summed from 6 individual observations. North is up and east is to the left. (Brazier et al., 1996)

RX EFRET 95% error box

The EGRET and X-ray observations of the object show the steady flux, hard PL spec and high-energy cut-off that are known only among young pulsars (Merck et al. 1996). The source is at the centre of a young SNR, which shows two

• pposing arcs on its rim.

The Fγ/Fx for RX J2021.0+4026/2EG J2020+4026 is of order 6000, similar to value of Geminga.

ROSAT PSPC field around 3EG J2020+4017. The 68%, 95%, and 99% contour lines from 3EG EGRET likelihood map and the ROSAT HRI sources are

• indicated. (Becker et al., 2004)

2EG J2020+4026/3EG J2020+4017 ?? RX J2021.0+4026 ??

(Becker et al., 2004)

3EG J2020+4017 ?? RX J2021.0+4026 ?? 0FGL J2021.5+4026 = 2FGL J2021.5+4026 = LAT PSR J2021+4026 ?? 2XMM J202131.0+ 402645 ??

A new Geminga-like pulsar candidate

Chandra image of the 3EG J2020+4017 field. (Weisskopf et al., 2006)

Efforts to detect pulsations in EGRET data or to discover radio pulsars in the region have been unsuccessful. Pulsed detection was finally obtained using Fermi observations.

PSR J2021+4026

Frequency and frequency derivative distribution of

• pulsars. (Abdo et al., 2009)

3EG J2020+4017 ?? RX J2021.0+4026 ?? 0FGL J2021.5+4026 = 2FGL J2021.5+4026 = LAT PSR J2021+4026 ?? 2XMM J202131.0+ 402645 ??

A new Geminga-like pulsar candidate

Chandra image of the 3EG J2020+4017 field. (Weisskopf et al., 2006)

Efforts to detect pulsations in EGRET data or to discover radio pulsars in the region have been unsuccessful. Pulsed detection was finally obtained using Fermi observations.

PSR J2021+4026

Frequency and frequency derivative distribution of

• pulsars. (Abdo et al., 2009)

Folded light curve of LAT PSR J20201+4026 obtained through Fermi observations. (Abdo et al., 2009)

3EG J2020+4017 ?? RX J2021.0+4026 ?? 0FGL J2021.5+4026 = 2FGL J2021.5+4026 = LAT PSR J2021+4026 ?? 2XMM J202131.0+ 402645 ??

A new Geminga-like pulsar candidate

Chandra image of the 3EG J2020+4017 field. (Weisskopf et al., 2006)

Efforts to detect pulsations in EGRET data or to discover radio pulsars in the region have been unsuccessful. Pulsed detection was finally obtained using Fermi observations.

PSR J2021+4026

Frequency and frequency derivative distribution of

• pulsars. (Abdo et al., 2009)

Folded light curve of LAT PSR J20201+4026 obtained through Fermi observations. (Abdo et al., 2009) XMM-Newton image on 2003 Dec. 1 with MOS1/2 and PN data merged (Trepl et al., 2010).

The 8’x8’ field centered at the γ-ray position of PSR J2021+4026 which is partly covered by a Chandra

• bservation (Trepl et al., 2010).

The rotated square shows the extent of ACIS-S3 chip of the recent Chandra observation, ObsID

• 11235. The color bar shows the number of counts

detected in a pixel. (Weisskopf et al., 2011).

No X-ray pulsation can directly be detected through the previous Chandra and XMM observations. Instead of it, the X-ray counterpart can be determined by the contemporaneous ephemeris obtained from Fermi archive or the X- ray spectral behavior.

X-ray counterpart of PSR J2021+4026

The 8’x8’ field centered at the γ-ray position of PSR J2021+4026 which is partly covered by a Chandra

• bservation (Trepl et al., 2010).

The rotated square shows the extent of ACIS-S3 chip of the recent Chandra observation, ObsID

• 11235. The color bar shows the number of counts

detected in a pixel. (Weisskopf et al., 2011).

No X-ray pulsation can directly be detected through the previous Chandra and XMM observations. Instead of it, the X-ray counterpart can be determined by the contemporaneous ephemeris obtained from Fermi archive or the X- ray spectral behavior.

• Fig. Significance of pulsation detection, as

measured by the χ2 test. The data were binned into 20 bins and fit to a constant flux model. The worse the fit, the more likely the X-ray source is the γ-ray pulsar counterpart. (Weisskopf et al., 2011).

X-ray counterpart of PSR J2021+4026

Spectral behavior for the X-ray counterpart

• f PSR J2021+4026

Spectral parameters inferred from fitting the Chandra and XMM observed spectral of 2XMM J202131.0+402645. (Trep et al., 2010).

No certain X-ray emission mechanism can be determined to compare with Geminga and PSR J0007+7303 because of the limit of obtained photons. The new XMM data proposed by David Hui (FAN team) and investigated on April of 2012 is expected to solved these mysteries.

Spectral behavior for the X-ray counterpart

• f PSR J2021+4026

Spectral parameters inferred from fitting the Chandra and XMM observed spectral of 2XMM J202131.0+402645. (Trep et al., 2010). Spectral parameters inferred from the latest Chandra observation of the X-ray counterpart of PSR J2021+4026. The mass, radius and magnetic field were fixed at 1.358 M¤, 12.996 km and 1.0x1013 G. The estimate of the size for the emitting region was scaled by the distance of 1.5 kpc. (Weisskopf et al., 2011).

No certain X-ray emission mechanism can be determined to compare with Geminga and PSR J0007+7303 because of the limit of obtained photons. The new XMM data proposed by David Hui (FAN team) and investigated on April of 2012 is expected to solved these mysteries.

A New Geminga like pulsar LAT PSR J2021+4026/2XMM J202131.0+402645

• Fig. XMM/PN image around 2XMM J202131.0+402645/

PSR J2021+4026 investigated in 2012 April. Green circle: 2XMM J202131.0+402645. Green cross: X-ray counterpart of PSR J2021+4026 identified by Chandra. White circle denotes the 95% confidence error circle of 2FGL J2021.5+4026/PSR J2021+4026. Yellow eclipse: 95% error region of timing position determined by Weisskopf et al. (2011). Black circle: 95% error region of timing position determined by Ray et al. (2011).

• Fig. The periodogram of Rayleigh-test in the

frequency range of 3.76 - 3.778 Hz.

Significant X-ray pulsation can be obtained through blind search, and its uncertainty range fits to contemporaneous ephemerides derived from the previous detections of periodic signal for LAT PSR J2021+4026.

A New Geminga like pulsar LAT PSR J2021+4026/2XMM J202131.0+402645

• Fig. XMM/PN image around 2XMM J202131.0+402645/

PSR J2021+4026 investigated in 2012 April. Green circle: 2XMM J202131.0+402645. Green cross: X-ray counterpart of PSR J2021+4026 identified by Chandra. White circle denotes the 95% confidence error circle of 2FGL J2021.5+4026/PSR J2021+4026. Yellow eclipse: 95% error region of timing position determined by Weisskopf et al. (2011). Black circle: 95% error region of timing position determined by Ray et al. (2011).

• Fig. The periodogram of Rayleigh-test in the

frequency range of 3.76 - 3.778 Hz.

• Fig. Ephemerides of 2XMM J202131.0+402645/PSR

J2021+4026 detected by X-ray and γ-ray pulsations. The inset shows the zoom-in view from MJD 56010 to 56050. Each line denotes the 1st derivative of spin-frequency quoted at different literatures.

Significant X-ray pulsation can be obtained through blind search, and its uncertainty range fits to contemporaneous ephemerides derived from the previous detections of periodic signal for LAT PSR J2021+4026.

Determination of timing parameters in γ-ray band

The magnitude of the timing noise observed in PSR J2021+4026. The dotted blue curve shows the timing residuals that can be attributed solely to timing noise. The red curve us the contribution from the high-order polynomial terms, neither of which can be attributed to the spin-down of the pulsar. The green curve is the combined sunusoidal WAVE components. (Weisskopf et al., 2011).

(Lin & Hui et al., 2013)

Serious timing noise prevents the direct description of timing parameters for PSR J2021+4026 with 4-year Fermi archive. Therefore, we considered the local ephemeris.

Determination of timing parameters in γ-ray band

The magnitude of the timing noise observed in PSR J2021+4026. The dotted blue curve shows the timing residuals that can be attributed solely to timing noise. The red curve us the contribution from the high-order polynomial terms, neither of which can be attributed to the spin-down of the pulsar. The green curve is the combined sunusoidal WAVE components. (Weisskopf et al., 2011).

(Lin & Hui et al., 2013)

Serious timing noise prevents the direct description of timing parameters for PSR J2021+4026 with 4-year Fermi archive. Therefore, we considered the local ephemeris.

Determination of timing parameters in γ-ray band

The magnitude of the timing noise observed in PSR J2021+4026. The dotted blue curve shows the timing residuals that can be attributed solely to timing noise. The red curve us the contribution from the high-order polynomial terms, neither of which can be attributed to the spin-down of the pulsar. The green curve is the combined sunusoidal WAVE components. (Weisskopf et al., 2011).

(Lin & Hui et al., 2013)

Serious timing noise prevents the direct description of timing parameters for PSR J2021+4026 with 4-year Fermi archive. Therefore, we considered the local ephemeris.

• Fig. Lin & Hui et al. (2013)

Left: Pulse profiles of PSR J2021+4026 at different energy

• ranges. All the light curves were folded with the epoch zero of

MJD 56028.

According to the comparison between the X-ray and γ-ray pulsations of PSR J2021+4026:

• 1. No pulsation was detected in the soft X-ray band.

(0.15-0.7 keV)

• 2. Very marginal or No pulsation was detected in

the hard X-ray band (2-12 keV)

• 3. Pulsation can only be detected in the medium X-

ray band, which is likely attributed to a heated hot spot.

• 4. The X-ray and γ-ray pulse profiles are dissimilar,

and it indicates that the main X-ray and γ-ray pulsation originate from different emission site and mechanism.

X-ray and γ-ray pulse profiles of PSR J2021+4026

• Fig. Lin & Hui et al. (2013)

Left: Pulse profiles of PSR J2021+4026 at different energy

• ranges. All the light curves were folded with the epoch zero of

MJD 56028.

According to the comparison between the X-ray and γ-ray pulsations of PSR J2021+4026:

• 1. No pulsation was detected in the soft X-ray band.

(0.15-0.7 keV)

• 2. Very marginal or No pulsation was detected in

the hard X-ray band (2-12 keV)

• 3. Pulsation can only be detected in the medium X-

ray band, which is likely attributed to a heated hot spot.

• 4. The X-ray and γ-ray pulse profiles are dissimilar,

and it indicates that the main X-ray and γ-ray pulsation originate from different emission site and mechanism.

X-ray and γ-ray pulse profiles of PSR J2021+4026

Top: Cross-correlation of the X-ray pulse profile (0.7-2 keV) and γ-ray pulse profile (0.1-300 GeV). The coefficient attains to the max. at a phase lag of about -0.14.

• Fig. Lin & Hui et al. (2013)

X-ray Spectrum of PSR J2021+4026

The phase-averaged spectrum of PSR J2021+4026 in 0.5-10 keV. The X-ray emission

• bserved with PN (upper) and MOS1/2 (lower)

detectors are simultaneously fitted to an absorbed BB+PL model. The BB emission has a temperature of kT~0.24 keV from a emitting region with a radius of ~250 d1.5 m, and the PL component has a photon index of ~1.2.

• 1. The phase-averaged spectral fit can only

be obtained with the reasonable explanation and the acceptable fit by multi-component models.

• 2. A pure thermal scenario with two BB

components can result in a comparable goodness of fit. The hotter component (kT ~ 1.4 keV) with the radius of ~3.6d1.5 m leads to a temperature of ~ 2x107 K, which is higher than that expected from the heating by the back flow current from the outer gap (Cheng &

Zhang 1999).

• 3. The best-fit of BB+PL model and the

residuals are shown in the left figure. The PL component mainly contributes at the energies > 2 keV. But the evidence of pulsation in the hard X-ray is marginal, and it suggests a non-pulsed origin from a PWN.

• 4. The spectral result demonstrates the

thermal nature of the observed X-ray pulsation.

X-ray Spectrum of PSR J2021+4026

The phase-averaged spectrum of PSR J2021+4026 in 0.5-10 keV. The X-ray emission

• bserved with PN (upper) and MOS1/2 (lower)

detectors are simultaneously fitted to an absorbed BB+PL model. The BB emission has a temperature of kT~0.24 keV from a emitting region with a radius of ~250 d1.5 m, and the PL component has a photon index of ~1.2.

• 1. The phase-averaged spectral fit can only

be obtained with the reasonable explanation and the acceptable fit by multi-component models.

• 2. A pure thermal scenario with two BB

components can result in a comparable goodness of fit. The hotter component (kT ~ 1.4 keV) with the radius of ~3.6d1.5 m leads to a temperature of ~ 2x107 K, which is higher than that expected from the heating by the back flow current from the outer gap (Cheng &

Zhang 1999).

• 3. The best-fit of BB+PL model and the

residuals are shown in the left figure. The PL component mainly contributes at the energies > 2 keV. But the evidence of pulsation in the hard X-ray is marginal, and it suggests a non-pulsed origin from a PWN.

• 4. The spectral result demonstrates the

thermal nature of the observed X-ray pulsation.

FOV of PSR J2020+4026 in pulsed time-interval FOV of PSR J2020+4026 in unpulsed time-interval

X-ray Spectrum of PSR J2021+4026

The phase-averaged spectrum of PSR J2021+4026 in 0.5-10 keV. The X-ray emission

• bserved with PN (upper) and MOS1/2 (lower)

detectors are simultaneously fitted to an absorbed BB+PL model. The BB emission has a temperature of kT~0.24 keV from a emitting region with a radius of ~250 d1.5 m, and the PL component has a photon index of ~1.2.

• 1. The phase-averaged spectral fit can only

be obtained with the reasonable explanation and the acceptable fit by multi-component models.

• 2. A pure thermal scenario with two BB

components can result in a comparable goodness of fit. The hotter component (kT ~ 1.4 keV) with the radius of ~3.6d1.5 m leads to a temperature of ~ 2x107 K, which is higher than that expected from the heating by the back flow current from the outer gap (Cheng &

Zhang 1999).

• 3. The best-fit of BB+PL model and the

residuals are shown in the left figure. The PL component mainly contributes at the energies > 2 keV. But the evidence of pulsation in the hard X-ray is marginal, and it suggests a non-pulsed origin from a PWN.

• 4. The spectral result demonstrates the

thermal nature of the observed X-ray pulsation.

FOV of PSR J2020+4026 in pulsed time-interval FOV of PSR J2020+4026 in unpulsed time-interval

PWN of PSR J2020+4026

Hui (2013, in preparation)

X-ray pulsed spectrum of PSR J2021+4026

Hui (2013, in preparation)

• Fig. X-ray pulse profile of PSR J2021+4026. The

phase zero corresponds to MJD 56028.31153, which is the start of good-time-interval of XMM

• bservation investigated in 2012. The gray

shaded regions between the spin phases 0.6-1.0 and 1.6-2.0 mark the off-pulse phase (DC level)

• f PSRJ2021+4026. The pulsed spectrum was
• btained with the extraction of the DC level from

the blue shaded regions covering the pulsed components.

The pulsed spectrum can only obtain an acceptable fit with a single BB model, which is totally consistent with the blackbody radiation contributed in the phase-averaged spectrum. This result gives a strong evidence that the observed X-ray pulsation is resulted from a pure thermal scenario that is similar to the soft X-ray pulsation observed from two other Geminga-like pulsars (Geminga and PSR J0007+7303).

X-ray pulsed spectrum of PSR J2021+4026

The pulsed spectrum can only obtain an acceptable fit with a single BB model, which is totally consistent with the blackbody radiation contributed in the phase-averaged spectrum. This result gives a strong evidence that the observed X-ray pulsation is resulted from a pure thermal scenario that is similar to the soft X-ray pulsation observed from two other Geminga-like pulsars (Geminga and PSR J0007+7303).

The pulsed spectrum of PSR J2021+4026 in 0.5-10 keV. The X-ray pulsation observed with XMM/PN detector was fitted to an absorbed single BB model. The BB emission has a temperature of kT~0.25 keV from a emitting region with a radius of ~260 d1.5 m.

Other candidates of Geminga-like pulsars

(Abdo et al., 2009)

Other candidates can be found from the radio-quiet γ-ray pulsars.

Other candidates of Geminga-like pulsars

(Abdo et al., 2009) (Camilo et al., 2009)

Other candidates can be found from the radio-quiet γ-ray pulsars.

Other candidates of Geminga-like pulsars

(Abdo et al., 2009) (Camilo et al., 2009)

Other candidates can be found from the radio-quiet γ-ray pulsars.

Summary to our studies

The pulsed detections from the Geminga-like pulsars clearly demonstrate that the emission mechanism is different at different energy bands. The X-ray pulsations with lower temperature (~tens of eV) are originated from the surface of a NS (~ several kms in radius) and those with a little higher temperature (>100 eV) are originated from a smaller heated hot spot. Only Geminga can detect both of these two thermal components. The non-thermal (power-law) component in the spectrum can be attributed to the emission from the pulsar or the enclosing PWN. In the case of Geminga, the non-thermal pulsation can be detected in the X-rays > 2.0 keV. In the case of PSR J0007+7303, we can detect the non-thermal emission both from the pulsar and the PWN although its pulsation can not be yielded in the hard X-ray band (> 2.0 keV). In the case of PSR J2021+4026, the significant X-ray pulsation can only be obtained in 0.7-2.0 keV. The non-thermal component detected from the spectrum is mainly ascribed to PWN, and it can both be proved from the phase-resolved image and the analysis of pulsed spectrum.