HST-UV observations of PSR J1023+0038

Juan V. Hernández Santisteban

8th Bonn Workshop Formation and Evolution of Neutron Stars

Bonn, 30 November 2015

C. Knigge, J. Hessels, A. Archibald, R. Breton, D. Altamirano, J. Greiner, J. Matthews, J. Patterson

Juan V. Hernández Santisteban!30 November 2015 8th Bonn Workshop: Different Flavours of MSPs and their Connections 2

• The Accretion disk peaks in the UV !

• Significant Outflow. Winds? !• Propeller state?

Why?

How?• HST: 3 NUV + 5 FUV orbits • Time-tag mode

NUV: 125µs, FUV: 32ms

PSR J1023+0038The Astrophysical Journal, 785:131 (8pp), 2014 April 20 Takata et al.

10-13

10-12

10-11

10-10

102 104 106 108 1010

Flu

x (e

rg c

m-2

s-1

)

Energy (eV)

Before June 2013

Star

Shock

Outer Gap

PW (Not seen here)

10-13

10-12

10-11

10-10

102 104 106 108 1010

Flu

x (e

rg c

m-2

s-1

)

Energy (eV)

After June 2013

Star+Disk

Shock

Outer Gap

PW

Figure 3. Multi-wavelength spectra before (left) and after (right) late June 2013. The dashed, dotted, and dashed-dotted line represent the calculated spectra ofthe emissions from the shock, outer gap (see Wang et al. 2010), and cold relativistic pulsar wind, respectively. For the shock emissions, we assume a distance ofRs ∼ 8 × 1010 cm and a power law index of p = 1.6 before late June 2013 and Rs ∼ 5 × 1010 cm and p = 2.2 after late June 2013, respectively. In the left panel,the stellar (G5V) spectrum (thick-curve line) and X-ray data (thick-double-dotted line) are taken from Wang et al. (2009) and Tam et al. (2010), respectively. The fluxpredicted by inverse Compton process of the cold relativistic pulsar wind before late June 2013 is of the order of ∼10−13 erg cm−2 s−1, and its spectrum is not seen inthe figure.

observations that no radio pulsation has been detected below5 GHz during the accretion active state. In this scenario, therotation-powered MSP is still active. While detecting the pulsa-tion can be difficult, radio imaging can still be used to check theaforementioned scenario as such a technique is not hampered bythe complicated environment. Also, as the local charge densitycan possibly be increased by the aforementioned processes, ifthe observed frequency is below the local plasma density, thiscan lead to a nondetection, even with imaging. In view of this,a high-frequency radio imaging observation is encouraged toconfirm/refute this alternative scenario.

4. DISCUSSION

We performed a multi-wavelength study of the MSP binaryJ1023 using UV/optical, X-ray, and gamma-ray data duringits accretion active state starting in late 2013 June. Not onlyare there significant UV/optical and X-ray enhancements, thegamma-rays have increased by a factor of ∼10. We suggestthat there is a newly formed accretion disk associated withUV emission, and the enhanced gamma-rays are produced viainverse Compton scattering between the UV emission fromthe disk and pulsar wind. At the same time, some fraction ofthe pulsar wind is stopped by the intrabinary shock, resultingin an increase in X-ray radiation. The accretion disk hasbeen evaporated because of the gamma-rays from the pulsarmagnetosphere, smearing out the pulsed radio emission eventhough the rotation-powered MSP is still active.

As Figure 1 indicates, the gamma-ray emission has brightenedby a factor of 10 on a timescale of several days. In the inverseCompton scenario discussed in Section 3, the brighteningtimescale seen by Fermi corresponds to a migration timescaleof the disk down to r ∼ 108–9 cm, where the inverse Comptonscattering process is more efficient with a shorter mean freepath than the process occurring at the outer part of the disk,R ∼ 1010–11 cm. If one assumes a standard disk model, one cansee that the migration timescale of the disk from R ∼ 1010 cmto R ∼ 108–9 cm is of the order of several to 10 days; that is,τmi ∼ R/vR ∼ 9α

−4/50.1 M

−3/1016 R

3/410 days, where vR is the radial

velocity of the disk and R10 = (R/1010 cm).

Because UV/optical emissions are originated from the ac-cretion disk, their variability timescale τUV/opt ∼ 100 s maycorrespond to the Keplerian motion at the emission region. Thestandard disk model implies that UV/optical emissions withthe observed luminosity level are mainly from the axial dis-tance R ∼ 109–10 cm, corresponding to an orbital period of∼160(R/5 × 109)3/2 s, which is consistent with the observedtimescale.

In the X-ray energy bands, the origin of the timescaleτX ∼ 50–100 s of the observed variability is more speculativewith the shock emission model discussed in Section 3. Butone may consider that the observed variability is caused byeither perturbation of shock front due to clumpy stellar wind orwind speed variation (vw ∼ 108 cm s−1), or sound propagation(cs ∼ 108 cm s−1) in the shock front (Rs ∼ 5×1010 cm). A moredetailed consideration will be required to identify the origin ofthe X-ray variability.

J.T. and K.S.C. are supported by a GRF grant from theHK Government under HKU7009 11P. A.K.H.K. is sup-ported by the National Science Council of the Republicof China (Taiwan) through grants NSC100-2628-M-007-002-MY3, NSC100-2923-M-007-001-MY3, and NSC101-2119-M-008-007-MY3. P.H.T. is supported by the National Sci-ence Council of the Republic of China (Taiwan) throughgrant NSC101-2112-M-007-022-MY3. C.Y.H. is supported bythe National Research Foundation of Korea through grant2011-0023383.

REFERENCES

Alpar, M. A., Cheng, A. F., Ruderman, M. A., & Shaham, J. 1982, Natur,300, 728

Archibald, A. M., Kaspi, V. M., Bogdanov, S., et al. 2010, ApJ, 722, 88Archibald, A. M., Kaspi, V. M., Hessels, J. W. T., et al. 2013, ApJ, submitted

(arXiv:1311.5161)Archibald, A. M., Stairs, I. H., Ransom, S. M., et al. 2009, Sci, 324, 1411Becker, R. H., White, R. L., & Helfand, D. J. 1995, ApJ, 450, 559Blumenthal, G. R., & Gould, R. J. 1970, RvMP, 42, 237Bogdanov, S., Archibald, A. M., Hessels, J. W. T., et al. 2011, ApJ, 742, 97Bond, H. E., White, R. L., Becker, R. H., & O’Brien, M. S. 2002, PASP,

114, 1359

7

The Astrophysical Journal, 785:131 (8pp), 2014 April 20 Takata et al.

10-13

10-12

10-11

10-10

102 104 106 108 1010

Flu

x (e

rg c

m-2

s-1

)

Energy (eV)

Before June 2013

Star

Shock

Outer Gap

PW (Not seen here)

10-13

10-12

10-11

10-10

102 104 106 108 1010

Flu

x (e

rg c

m-2

s-1

)

Energy (eV)

After June 2013

Star+Disk

Shock

Outer Gap

PW

Figure 3. Multi-wavelength spectra before (left) and after (right) late June 2013. The dashed, dotted, and dashed-dotted line represent the calculated spectra ofthe emissions from the shock, outer gap (see Wang et al. 2010), and cold relativistic pulsar wind, respectively. For the shock emissions, we assume a distance ofRs ∼ 8 × 1010 cm and a power law index of p = 1.6 before late June 2013 and Rs ∼ 5 × 1010 cm and p = 2.2 after late June 2013, respectively. In the left panel,the stellar (G5V) spectrum (thick-curve line) and X-ray data (thick-double-dotted line) are taken from Wang et al. (2009) and Tam et al. (2010), respectively. The fluxpredicted by inverse Compton process of the cold relativistic pulsar wind before late June 2013 is of the order of ∼10−13 erg cm−2 s−1, and its spectrum is not seen inthe figure.

observations that no radio pulsation has been detected below5 GHz during the accretion active state. In this scenario, therotation-powered MSP is still active. While detecting the pulsa-tion can be difficult, radio imaging can still be used to check theaforementioned scenario as such a technique is not hampered bythe complicated environment. Also, as the local charge densitycan possibly be increased by the aforementioned processes, ifthe observed frequency is below the local plasma density, thiscan lead to a nondetection, even with imaging. In view of this,a high-frequency radio imaging observation is encouraged toconfirm/refute this alternative scenario.

4. DISCUSSION

We performed a multi-wavelength study of the MSP binaryJ1023 using UV/optical, X-ray, and gamma-ray data duringits accretion active state starting in late 2013 June. Not onlyare there significant UV/optical and X-ray enhancements, thegamma-rays have increased by a factor of ∼10. We suggestthat there is a newly formed accretion disk associated withUV emission, and the enhanced gamma-rays are produced viainverse Compton scattering between the UV emission fromthe disk and pulsar wind. At the same time, some fraction ofthe pulsar wind is stopped by the intrabinary shock, resultingin an increase in X-ray radiation. The accretion disk hasbeen evaporated because of the gamma-rays from the pulsarmagnetosphere, smearing out the pulsed radio emission eventhough the rotation-powered MSP is still active.

As Figure 1 indicates, the gamma-ray emission has brightenedby a factor of 10 on a timescale of several days. In the inverseCompton scenario discussed in Section 3, the brighteningtimescale seen by Fermi corresponds to a migration timescaleof the disk down to r ∼ 108–9 cm, where the inverse Comptonscattering process is more efficient with a shorter mean freepath than the process occurring at the outer part of the disk,R ∼ 1010–11 cm. If one assumes a standard disk model, one cansee that the migration timescale of the disk from R ∼ 1010 cmto R ∼ 108–9 cm is of the order of several to 10 days; that is,τmi ∼ R/vR ∼ 9α

−4/50.1 M

−3/1016 R

3/410 days, where vR is the radial

velocity of the disk and R10 = (R/1010 cm).

Because UV/optical emissions are originated from the ac-cretion disk, their variability timescale τUV/opt ∼ 100 s maycorrespond to the Keplerian motion at the emission region. Thestandard disk model implies that UV/optical emissions withthe observed luminosity level are mainly from the axial dis-tance R ∼ 109–10 cm, corresponding to an orbital period of∼160(R/5 × 109)3/2 s, which is consistent with the observedtimescale.

In the X-ray energy bands, the origin of the timescaleτX ∼ 50–100 s of the observed variability is more speculativewith the shock emission model discussed in Section 3. Butone may consider that the observed variability is caused byeither perturbation of shock front due to clumpy stellar wind orwind speed variation (vw ∼ 108 cm s−1), or sound propagation(cs ∼ 108 cm s−1) in the shock front (Rs ∼ 5×1010 cm). A moredetailed consideration will be required to identify the origin ofthe X-ray variability.

J.T. and K.S.C. are supported by a GRF grant from theHK Government under HKU7009 11P. A.K.H.K. is sup-ported by the National Science Council of the Republicof China (Taiwan) through grants NSC100-2628-M-007-002-MY3, NSC100-2923-M-007-001-MY3, and NSC101-2119-M-008-007-MY3. P.H.T. is supported by the National Sci-ence Council of the Republic of China (Taiwan) throughgrant NSC101-2112-M-007-022-MY3. C.Y.H. is supported bythe National Research Foundation of Korea through grant2011-0023383.

REFERENCES

Alpar, M. A., Cheng, A. F., Ruderman, M. A., & Shaham, J. 1982, Natur,300, 728

Archibald, A. M., Kaspi, V. M., Bogdanov, S., et al. 2010, ApJ, 722, 88Archibald, A. M., Kaspi, V. M., Hessels, J. W. T., et al. 2013, ApJ, submitted

(arXiv:1311.5161)Archibald, A. M., Stairs, I. H., Ransom, S. M., et al. 2009, Sci, 324, 1411Becker, R. H., White, R. L., & Helfand, D. J. 1995, ApJ, 450, 559Blumenthal, G. R., & Gould, R. J. 1970, RvMP, 42, 237Bogdanov, S., Archibald, A. M., Hessels, J. W. T., et al. 2011, ApJ, 742, 97Bond, H. E., White, R. L., Becker, R. H., & O’Brien, M. S. 2002, PASP,

114, 1359

7

Takata et al. 2014

Juan V. Hernández Santisteban!30 November 2015 8th Bonn Workshop: Different Flavours of MSPs and their Connections

pulsations are thought to be due to return current heating of themagnetic poles (Archibald et al. 2010) rather than heating bychanneled accretion.

Examination of the combined XMM-Newton light curvesrevealed three distinct luminosity modes9 (Figures 3, 4, and 5),all of which are present during the LMXB state. Similarbehavior is seen from PSR J1023+0038 at the higher energies

observed with NuSTAR (Tendulkar et al. 2014), as well asduring the LMXB states of the two other known transitionalRMSPs: PSR J1824−2452I and XSS J12270−4859 (deMartino et al. 2013; Linares 2014; Linares et al. 2014). Inthe 0.3–10 keV photon energy range, our XMM-Newtonobservations show a steady “low” mode with luminosity

5 10 erg s32 1_ q � , a steady “high” mode with luminosity3 10 erg s33 1_ q � , and occasional, more erratic “flares” during

which the luminosity typically exceeds 5 10 erg s33 1q � , andreaches as high as 3 10 erg s34 1q � . The three modes havesimilar hard power-law spectra (photon index 1.7_ ; Tendulkaret al. 2014). The low, high, and flare modes occupy roughly20%, 80%, and 1%–2% of the data, respectively, in both the2013 November and 2014 June data sets. Switching betweenthe low and high modes appears to occur within 10–30 s, whilethe flares have a more complex structure. The low and highmode durations are typically tens of seconds up to tens ofminutes long, and the distribution of their durations follows apower law (Tendulkar et al. 2014). No obvious periodicity orother discernible regular pattern is present. Moreover, theluminosity in low/high mode appears to be nearly constant andequal in both the 2013 November and 2014 June observations.The majority of the photons were collected during the high

mode, where we find that the 0.3–10 keV X-rays are pulsedwith a rms pulsed fraction of 8.13(14)% (count rate0.311(5) s 1� ; see also Figure 6). In the low mode we detectno significant pulsations, and set a 95% confidence upper limiton the pulsed fraction of 2.4% (count rate 0.016 s 1� ). Thisimplies that if any pulsations are present in the low mode, theymust form a substantially smaller luminosity fraction (andmuch smaller absolute luminosity) in the low mode than theydo in the high mode. Pulsations are also not detected during theflares, with a 95% upper limit on the pulsed fraction of 1.4%(count rate 0.15 s 1� ): if any pulsations are present during the

Figure 4. Distribution of fluxes in the 2013 November and 2014 Juneobservations. All pn and MOS photons from both observations were combinedto form an exposure-corrected light curve with 10 s time bins, and histogramsof the resulting count rates are plotted. Horizontal error bars show thehorizontal smearing due to Poisson noise in the light curve bins. Vertical dottedlines show the cuts we chose between low, high, and flare modes.

Figure 3. Short section of the combined XMM-Newton light-curve, showing the low (green), high (black), and flare (red) modes. Times at which the mode isindeterminate are marked in gray, and times excluded from pulsation searching because of background flaring are marked in yellow. See Figure 4 for how thethresholds were set, and Figure 7 for the whole light curve.

9 The PSR J1023+0038 system has been observed to switch between RMSPand LMXB states. To describe the different X-ray luminosities observed duringthe LMXB state, we use the term mode, that is, low, high and flare mode.

4

The Astrophysical Journal, 807:62 (9pp), 2015 July 1 Archibald et al.

3

LightcurvesMode Switching?

10s bins

Variability of lines and continuum are correlated

Bogdanov et al. 2014, Archibald et al. 2015

Juan V. Hernández Santisteban!30 November 2015 8th Bonn Workshop: Different Flavours of MSPs and their Connections 4

Lightcurves

No coherent pulsations nor QPOs

Juan V. Hernández Santisteban!30 November 2015 8th Bonn Workshop: Different Flavours of MSPs and their Connections 5

FUV

FWHM ~4000 km/s

Juan V. Hernández Santisteban!30 November 2015 8th Bonn Workshop: Different Flavours of MSPs and their Connections 6

Fe II in emission (observed in QSOs, Veestergard & Wilkes, 2001)

NUV

Juan V. Hernández Santisteban!30 November 2015 8th Bonn Workshop: Different Flavours of MSPs and their Connections 7

X-Shooter spectra courtesy of C. Bassa

Truncated disc?Rin~100 RLC

Juan V. Hernández Santisteban!30 November 2015 8th Bonn Workshop: Different Flavours of MSPs and their Connections 8

AE Aqr - A Benchmark for Magnetic Propeller

Wynn et al. 1996 • Correlated multi-wavelength flaring !!!!!!!!!!• Single Peak lines, no evidence for

accretion disc !• >99% of material is ejected from the

system !

• Flares likely due to collisions of ejected blobsPearson et al. 2003

Pearson et al. 2003Welsh et al. 1998

Juan V. Hernández Santisteban!30 November 2015 8th Bonn Workshop: Different Flavours of MSPs and their Connections 9

AE Aqr analogue?

Similar Outflow?!in AE Aqr its being launched at ~1010 cm

Eracleous et al. 1996

Juan V. Hernández Santisteban!30 November 2015 8th Bonn Workshop: Different Flavours of MSPs and their Connections 10

Conclusions

• Rich and complex UV spectra !

• UV to NIR SED well described by donor + S-S disc !

• Disc is truncated at ~100 RLC !

• Similarities between outflows in AE Aqr and PSR J1023

Rosseta Stone for tMSP?

Juan V. Hernández Santisteban!30 November 2015 8th Bonn Workshop: Different Flavours of MSPs and their Connections 11

Juan V. Hernández Santisteban!30 November 2015 8th Bonn Workshop: Different Flavours of MSPs and their Connections 12

Juan V. Hernández Santisteban!30 November 2015 8th Bonn Workshop: Different Flavours of MSPs and their Connections 13

Juan V. Hernández Santisteban!30 November 2015 8th Bonn Workshop: Different Flavours of MSPs and their Connections 14

No coherent pulsations nor QPOs

Juan V. Hernández Santisteban!30 November 2015 8th Bonn Workshop: Different Flavours of MSPs and their Connections 15