Abelian variety isogeny class 2.31.a_bk over $\F_{31}$

• Label: 2.31.a_bk
• Base field: $\F_{31}$
• Dimension: $2$
• $p$-rank: $2$
• Ordinary: yes
• Supersingular: no
• Simple: yes
• Geometrically simple: no
• Primitive: yes
• Principally polarizable: yes
• Contains a Jacobian: yes

Invariants

Base field:	$\F_{31}$
Dimension:	$2$
L-polynomial:	$1 + 36 x^{2} + 961 x^{4}$
Frobenius angles:	$\pm0.348599812917$, $\pm0.651400187083$
Angle rank:	$1$ (numerical)
Number field:	\(\Q(\sqrt{-2}, \sqrt{-13})\)
Galois group:	$C_2^2$
Jacobians:	$42$

This isogeny class is simple but not geometrically simple, 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

$r$	$1$	$2$	$3$	$4$	$5$
$A(\F_{q^r})$	$998$	$996004$	$887446550$	$854049525904$	$819628289498678$

Point counts of the curve

$r$	$1$	$2$	$3$	$4$	$5$	$6$	$7$	$8$	$9$	$10$
$C(\F_{q^r})$	$32$	$1034$	$29792$	$924774$	$28629152$	$887389418$	$27512614112$	$852893947774$	$26439622160672$	$819628292016554$

Jacobians and polarizations

This isogeny class is principally polarizable and contains the Jacobians of 42 curves (of which all are hyperelliptic):

• $y^2=7 x^6+28 x^5+2 x^4+25 x^3+7 x^2+11 x+6$
• $y^2=21 x^6+22 x^5+6 x^4+13 x^3+21 x^2+2 x+18$
• $y^2=16 x^6+18 x^5+7 x^4+12 x^3+27 x^2+25 x+8$
• $y^2=17 x^6+23 x^5+21 x^4+5 x^3+19 x^2+13 x+24$
• $y^2=10 x^6+15 x^5+9 x^4+9 x^3+x^2+20 x+22$
• $y^2=30 x^6+14 x^5+27 x^4+27 x^3+3 x^2+29 x+4$
• $y^2=29 x^6+18 x^5+27 x^4+7 x^3+10 x^2+6 x+23$
• $y^2=25 x^6+23 x^5+19 x^4+21 x^3+30 x^2+18 x+7$
• $y^2=7 x^6+9 x^5+6 x^4+x^3+20 x^2+16 x+4$
• $y^2=21 x^6+27 x^5+18 x^4+3 x^3+29 x^2+17 x+12$
• $y^2=24 x^6+9 x^5+5 x^4+28 x^3+16 x^2+24 x+11$
• $y^2=10 x^6+27 x^5+15 x^4+22 x^3+17 x^2+10 x+2$
• $y^2=25 x^6+18 x^5+9 x^4+27 x^2+27 x+27$
• $y^2=13 x^6+23 x^5+27 x^4+19 x^2+19 x+19$
• $y^2=14 x^6+20 x^5+29 x^3+7 x^2+18 x+4$
• $y^2=11 x^6+29 x^5+25 x^3+21 x^2+23 x+12$
• $y^2=4 x^6+24 x^5+5 x^4+6 x^3+8 x^2+15 x+19$
• $y^2=12 x^6+10 x^5+15 x^4+18 x^3+24 x^2+14 x+26$
• $y^2=18 x^6+15 x^5+18 x^4+x^3+16 x^2+11 x+28$
• $y^2=23 x^6+14 x^5+23 x^4+3 x^3+17 x^2+2 x+22$
• and

• $y^2=28 x^6+9 x^4+14 x^3+10 x^2+14 x+7$
• $y^2=22 x^6+27 x^4+11 x^3+30 x^2+11 x+21$
• $y^2=17 x^6+16 x^5+19 x^4+20 x^3+28 x^2+30 x+20$
• $y^2=20 x^6+17 x^5+26 x^4+29 x^3+22 x^2+28 x+29$
• $y^2=16 x^6+16 x^5+9 x^4+5 x^3+12 x^2+20 x+29$
• $y^2=17 x^6+17 x^5+27 x^4+15 x^3+5 x^2+29 x+25$
• $y^2=5 x^6+17 x^5+22 x^4+29 x^3+19 x^2+11 x+3$
• $y^2=15 x^6+20 x^5+4 x^4+25 x^3+26 x^2+2 x+9$
• $y^2=10 x^6+30 x^5+12 x^4+23 x^3+29 x^2+25 x+4$
• $y^2=30 x^6+28 x^5+5 x^4+7 x^3+25 x^2+13 x+12$
• $y^2=10 x^6+16 x^5+8 x^4+29 x^3+12 x^2+13 x+3$
• $y^2=30 x^6+17 x^5+24 x^4+25 x^3+5 x^2+8 x+9$
• $y^2=10 x^6+14 x^4+15 x^3+18 x^2+10$
• $y^2=30 x^6+11 x^4+14 x^3+23 x^2+30$
• $y^2=27 x^6+24 x^5+21 x^4+15 x^3+2 x^2+9 x+19$
• $y^2=19 x^6+10 x^5+x^4+14 x^3+6 x^2+27 x+26$
• $y^2=27 x^6+29 x^5+28 x^4+19 x^3+25 x^2+7 x+4$
• $y^2=19 x^6+25 x^5+22 x^4+26 x^3+13 x^2+21 x+12$
• $y^2=11 x^6+24 x^5+29 x^4+6 x^3+23 x^2+18 x+6$
• $y^2=2 x^6+10 x^5+25 x^4+18 x^3+7 x^2+23 x+18$
• $y^2=11 x^6+24 x^5+x^2+12 x+28$
• $y^2=2 x^6+10 x^5+3 x^2+5 x+22$

Decomposition and endomorphism algebra

All geometric endomorphisms are defined over $\F_{31^{2}}$.

Endomorphism algebra over $\F_{31}$

The endomorphism algebra of this simple isogeny class is \(\Q(\sqrt{-2}, \sqrt{-13})\).

Endomorphism algebra over $\overline{\F}_{31}$

The base change of $A$ to $\F_{31^{2}}$ is 1.961.bk^2 and its endomorphism algebra is $\mathrm{M}_{2}($\(\Q(\sqrt{-13}) \)$)$

Base change

This is a primitive isogeny class.

Twists

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

Twist	Extension degree	Common base change
2.31.a_abk	$4$	(not in LMFDB)
2.31.ao_du	$8$	(not in LMFDB)
2.31.o_du	$8$	(not in LMFDB)