Third eclipsing Black Widow
PSR J1544+4937 in a Fermi source
Bhaswati Bhattacharyya
IUCAA
SINP, 18th Oct 2012
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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)
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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
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Pulsar classification
2000 known radio
Pulsars in our galaxy
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
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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)
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Neutron Stars and Pulsars – Early History
Franco Pacini 1968
 Pulsars are formed after
supernovae explosion!
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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
MSP formation
 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.
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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
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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
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 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
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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
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Searching for millisecond pulsations with GMRT as a
part of Fermi pulsar search consortium (PSC)
(ellaborated in Jayanta’s Talk)
Low frequency facility
GMRT
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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
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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
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Follow up timing
Individual pulses
Mean profile
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Follow up timing of J1544+4937
Timing model
Orbital velocity curve
(Bhattacharyya & Nityananda 2008)

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1
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3


(
t
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t
)
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(
t

t
)
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(
t
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t
)
m
0
0
0
0
0
2
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Timing residual   m
 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
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Timing ephemeris
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Frequency dependent eclipsing
244 MHz : Eclipse
322 MHz: Eclipse
607 MHz: No eclipse
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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
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obscuring pulsar emission
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
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Eclipse Mechanism
A number of physical mechanism explaining the phenomenon of eclipsing is
detailed in Thompson et al. (1994)
(a) 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
(c) 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
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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.
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Additional short eclipses and phase changes
around the eclipse boundary : observations
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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).
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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.
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Life span of the system
The orbital decay time scale
(typical for such systems)
~ 1.5 × 107 years
Provides an estimate of the short life span
But this can be largely contributed by
monitoring
which require longer
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
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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)
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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
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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
among other BW systems in Galactic disk
~ 8.4 ×1033 which is highest
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Thank you
Contact :
Bhaswati Bhattachrayya
IUCAA
Ph: 2560 4121
Email: bhaswati@iucaa.ernet.in
Website:
http://www.iucaa.ernet.in/~bhaswati
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