Properties

Label 2.128.a_adj
Base field $\F_{2^{7}}$
Dimension $2$
$p$-rank $2$
Ordinary yes
Supersingular no
Simple yes
Geometrically simple no
Primitive no
Principally polarizable yes
Contains a Jacobian yes

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Invariants

Base field:  $\F_{2^{7}}$
Dimension:  $2$
L-polynomial:  $1 - 87 x^{2} + 16384 x^{4}$
Frobenius angles:  $\pm0.194812903431$, $\pm0.805187096569$
Angle rank:  $1$ (numerical)
Number field:  \(\Q(i, \sqrt{7})\)
Galois group:  $C_2^2$
Jacobians:  $616$
Isomorphism classes:  344

This isogeny class is simple but not geometrically simple, not primitive, ordinary, and not supersingular. It is principally polarizable and contains a Jacobian.

Newton polygon

This isogeny class is ordinary.

$p$-rank:  $2$
Slopes:  $[0, 0, 1, 1]$

Point counts

Point counts of the abelian variety

$r$ $1$ $2$ $3$ $4$ $5$
$A(\F_{q^r})$ $16298$ $265624804$ $4398050128826$ $72071123819950336$ $1180591620649602236618$

Point counts of the curve

$r$ $1$ $2$ $3$ $4$ $5$ $6$ $7$ $8$ $9$ $10$
$C(\F_{q^r})$ $129$ $16211$ $2097153$ $268485855$ $34359738369$ $4398053746547$ $562949953421313$ $72057593841690559$ $9223372036854775809$ $1180591620581793169811$

Jacobians and polarizations

This isogeny class contains the Jacobians of 616 curves (of which all are hyperelliptic), and hence is principally polarizable:

Decomposition and endomorphism algebra

All geometric endomorphisms are defined over $\F_{2^{14}}$.

Endomorphism algebra over $\F_{2^{7}}$
The endomorphism algebra of this simple isogeny class is \(\Q(i, \sqrt{7})\).
Endomorphism algebra over $\overline{\F}_{2^{7}}$
The base change of $A$ to $\F_{2^{14}}$ is 1.16384.adj 2 and its endomorphism algebra is $\mathrm{M}_{2}($\(\Q(\sqrt{-7}) \)$)$

Base change

This isogeny class is not primitive. It is a base change from the following isogeny classes over subfields of $\F_{2^{7}}$.

SubfieldPrimitive Model
$\F_{2}$2.2.a_ad

Twists

Below are some of the twists of this isogeny class.

TwistExtension degreeCommon base change
2.128.aba_qj$4$(not in LMFDB)
2.128.a_dj$4$(not in LMFDB)
2.128.ba_qj$4$(not in LMFDB)

Below is a list of all twists of this isogeny class.

TwistExtension degreeCommon base change
2.128.aba_qj$4$(not in LMFDB)
2.128.a_dj$4$(not in LMFDB)
2.128.ba_qj$4$(not in LMFDB)
2.128.an_bp$12$(not in LMFDB)
2.128.n_bp$12$(not in LMFDB)