Third eclipsing Black Widow PSR J1544+4937 in a Fermi source

1. Third eclipsing Black Widow PSR J1544+4937 in a Fermi source Bhaswati Bhattacharyya IUCAA SINP, 18th Oct 2012

2. People Involved Bhaswati Bhattacharyya (IUCAA) Jayanta Roy (NCRA) Paul Ray (NRL) Yashwant Gupta (NCRA)‏ Dipankar Bhattacharya (IUCAA) Michael T. Wolff (NRL) Roger Romani (Stanford) Fermi pulsar search consortium Publication (1) “Discovery of an eclipsing Black Widow PSR J1544+4937 in a Fermi source with the GMRT” Bhattacharyya & Roy et al. 2012 (in preparation) (2) “Multi –frequency study of eclipse mechanism of PSR J1544+4937” Bhattacharyya & Roy et al. 2013 (in preparation)

3. OUTLINE • Pulsar classification with P-Pdot diagram • Binary Vs Isolated MSPs : formation scenario • Black Widow pulsar : a missing link • GMRT discovery of an eclipsing BW MSP • Follow-up timing and ephemaris • Frequency dependent eclipsing; • ingress phase shift, short eclipse • Eclipse mechanism • Detection of Gamma-ray pulsation • Summary

4. 2000 known radio Pulsars in our galaxy Pulsar classification • Young • – Energetic, with • significant spin-down • noise and glitches. • Normal • – Slower, More stable, • Mostly isolated • Recycled pulsars • Faster, Most in binaries, extremely stable rotators • ->MILLISECOND PULSARS

5. Millisecond pulsars are Superb Tools for Fundamental Physics Equation of state at > nuclear densities Relativistic dynamics in binary systems Gravitational wave detection Interstellar medium Binary evolution Atomic physics (atmospheres) Solid state physics (crusts) Plasma physics (eclipses, magnetospheres)

6. Neutron Stars and Pulsars – Early History Franco Pacini 1968 • Pulsars are formed after supernovae explosion!

7. Millisecond pulsars Binary system • Millisecond pulsars are a small • population compared to the normal • pulsars, • magnetic Field ~109G • Majority of MSPs are in binary MSPs are detected in the radio, x-ray and gamma-rays • Origin of millsecond pulsars is yet • not pinned down. Leading theory : MSPs begin their life as longer period pulsar but are spun up or recycled through accretion thus millisecond pulsars are often called recycled pulsars. MSP formation

8. Binary and isolated MSPs • Majority of MSPs are naturally expected to be in binaries about 87% of MSPs are in binaries • What about Isolated MSPs? • Isolated MSPs are conceived to be formed in binary • systems where the pulsar radiation can ablate the companion ! “Black widow systems” – Missing link between Binary and isolated MSPs

9. Black Widow pulsars Black Widow spider The pulsar is destroying its own companion Eclipses seen for very large duration Very low mass companion ~ 20 Jupiter mass

10. The eclipse material extends well beyond the maximum radius at which it remain gravitationally bound to companion. • The pulsar is ablating its companion by creating significant amount of intra binary emission to obscure/block pulsar emission. The compactness of the orbit and relatively high spin down energy of the MSP can give rise to such phenomenon Eclipsing BLACK WIDOW pulsars -- Provide better understanding of evolutionary history of isolated MSPs -- Study of eclipse mechanism -- Study of the relativistic pulsar winds -- Probing pulsar magnetosphere

11. Black Widow Pulsars Before Fermi Launch Two such eclipsing BW systems in the Galactic disk reported before the launch of Fermi -- PSR B1957+20 (Fruchter et al. 1988) -- PSR J2051−0827 (Stappers et al. 1996) Black Widow Pulsars After Fermi Launch According to Ray et al. (2012) among the 43 new MSPs found in Fermi directed searches, there are at least 10 BWs (few are eclipsing). Black widow pulsars have high Edot which favors gamma-ray emission

12. Searching for millisecond pulsations with GMRT as a part of Fermi pulsar search consortium (PSC)‏ (ellaborated in Jayanta’s Talk) Low frequency facility GMRT

13. J1544+4937 : Third eclipsing black widow ! PSR J1544+4937 is in a “Black Widow” system : • Orbit is very tight (2.9hrs) • Eclipses ~ 13% of its orbit by a very low-mass companion

14. GMRT discovery of PSR J1544+4937 At 607 MHz with 61 micro second resolution Period: 2.16 ms Dispersion measure: 23.2 pc/cc Acceleration: 2.25 m/s2

15. Follow up timing Individual pulses Mean profile

16. Follow up timing of J1544+4937 Timing model Orbital velocity curve (Bhattacharyya & Nityananda 2008) Timing residual • With accurate pulsar position timing can be done with 490 days of data PSR with 2.9 hrs orbit : One of the shortest Fermi MSPs

17. Timing ephemeris

18. Frequency dependent eclipsing 607 MHz: No eclipse 244 MHz : Eclipse 322 MHz: Eclipse

19. Frequency dependent eclipsing Eclipses for large fraction of its orbit (13%) at 322 MHz Eclipses are centered around binary phase 0.24 with 22m duration According to Eggleton 1983, Roche lobe radius Opaque portion of the companion’s orbit is 0.98 Rsun, >> RL Volume occupied by the eclipsing body is well outside RL Thus not gravitationally bound to companion Indicate that pulsar is a Black Widow where the pulsar is ablating companion creating significant amount of intrabinary material obscuring pulsar emission

20. Timing residuals around eclipse phase We sampled six eclipses at 322 MHz and two eclipses at 610 MHz Top: @ 322 MHz variation of timing residual and hence electron column density around the eclipse phase Bottom: @ 607 MHz Flux fading at 607 MHz near eclipse phase Maximum delay in pulse arrival time at 607 MHz ~ 300 micro second Corresponding increase in Dispersion measure value 0.027 pc/cc Added electron density at superior conjunction ~ 8x1016 cm -2

21. Eclipse Mechanism • A number of physical mechanism explaining the phenomenon of eclipsing is • detailed in Thompson et al. (1994) • Refraction : demands a order of magnitude higher delay (~tens of ms) • than observed for PSR J1544+4937 (250 micro sec at 322 MHz) • (b) Free-free absorption : demands very low temperature or very high • Clumping, both of which is not physically possible • Pulse smearing : predicts ~374 micro sec smearing at 322 MHz • in mid eclipse phase, which is less than 1/5 th of pulse period. • (d) Scattering : no significant scattering around the eclipse boundary • (e) Induced Compton scattering : calculated optical depth <<1 • (f) Cyclotron absorption : We consider cyclotron absorption of the radio • waves by the electrons , as cause of eclipsing. • For a fixed temperature optical depth for cyclotron absorption • drops with harmonics, which may explain the lack of absorption • seen at 607 MHz. • Require further observations to better constrain the eclipse models

22. A temporal shift in eclipse ingress phase :for 2 eclipses the ingress phase is shifted to 0.16 (from 0.18) Such asymmetric increase of eclipse duration (repeatedly seen in two epochs) is very unique to this BW This may indicate that our line of sight is probing a wind zone where there is systematic outflow of eclipse material.

23. Additional short eclipses and phase changes around the eclipse boundary : observations

24. Additional short eclipses observed around eclipse boundary : observations The duration of these features ~10s−20s, Hence is not seen in Fig (generated with 42s integration). In one epoch modulations lasted longer − phase modulation of duration of 100s, followed by a short eclipse of ~ 180s, then regular emission resumes for 500s after that main eclipse starts (zoomed).

25. Additional short eclipses observed around eclipse boundary : Implication These interesting modulations are not reported for other Black widow pulsars Indicate fluctuation of plasma density around eclipsing spot. Fragmented blobs of plasma randomly oriented around eclipsing spot and obscuring radiation from pulsar can explain observed short eclipses before and after main eclipse.

26. Life span of the system The orbital decay time scale ~ 1.5 × 107 years (typical for such systems) Provides an estimate of the short life span But this can be largely contributed by which require longer monitoring Higher energy of Black Widow Pulsars For Black Widow systems measured value of is an order of magnitude higher than the other binaries, indicative of higher energy flux to ablate the companion. For PSR J1544+4937 we calculate ~ 8.4 ×1033 which is highest among other BW systems in Galactic disk

27. Gamma-ray detectability measure Considering the DM distance and ˙E of PSR J1544+4937, the gamma-ray detectability measure ~ 7.6 × 1016 erg1/2 kpc−2 s−1/2 ~ 10-2 x Vela (Similar to that of other gamma-ray detected MSPs ) MSPs Young pulsars Searched but not detected Fig. 12 of (Abdo et al. 2010)

28. Detection of Gamma-ray pulsations Gamma-ray Pulsation detected from the Fermi source by folding LAT data with accurate radio ephemeris No Optical/X-ray counter part detected

29. Summary • We report the discovery of an eclipsing Black Widow millisecond pulsar • PSR J1544+4937 in a Fermi source at the GMRT • Our discovery is the first Galactic millisecond pulsation at India. • PSR J1544+4937 is the third eclipsing Black Widow pulsar known • From regular timing campaign at the GMRT we could get phase • connected TOAs in TEMPO with 7 micro-sec timing residual. • Best achieved from the GMRT. Detection of Gamma-ray pulsations • We observe frequency dependent eclipsing for this Black widow. • We have studied eclipse characteristics of this pulsar from multi-frequency • multi epoch observations. • Orbital decay time scale ~ 1.5 × 107 years • Indicate short life span of such systems • For PSR J1544+4937 we calculate ~ 8.4 ×1033 which is highest among other BW systems in Galactic disk

30. Thank you Contact : Bhaswati Bhattachrayya IUCAA Ph: 2560 4121 Email: bhaswati@iucaa.ernet.in Website: http://www.iucaa.ernet.in/~bhaswati